From 3f93481c542d23eec6870f9ba5e74bbc763cdc7d Mon Sep 17 00:00:00 2001
From: ducoterra <git@ducoterra.net>
Date: Mon, 2 Nov 2026 22:07:17 -0500
Subject: [PATCH] phase: 06_sharer_quality_presets
MIME-Version: 1.0
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**Phase 06 — final verification pass: 100% green.**

- **Verified (all 6 tasks complete in working tree):** `#quality` select + `PRESETS` table; preset-driven capture request + `contentHint`; per-leg `legCap()`/`degradation` at both call sites; live `applyQuality()` with Overconstrained fallback + republish; `q` key cycle; `#stat-quality`/`#stat-codec` readouts; full e2e matrix (requests, committed params ×3, zero-cap, mid-share switch, unrescalable device, late-joiner first-offer, readout, `q`); realdisplay delivered-pixels `light` case. `test_sender_fidelity.py` **untouched and green** (regression canary).
- **Gates:** `uv run ruff check . && uv run ruff format --check .` → clean (32 files); `uv run pyright` → 0 errors; `uv run pytest` → **284 passed, 5 skipped (realdisplay-gated), coverage 95%** (93s); `MIRROR_REALDISPLAY=1 uv run pytest -m realdisplay` → **4 passed, 1 skipped** (no audio source on host — documented platform condition).
- **Completion criteria:** all 11 ✓ — sharp default reproduces old request; light ≤960×600@15fps/motion/round(cap×0.35)/maintain-framerate with moving viewer frames; mid-share re-prices with `peers.size` unchanged, no renegotiation, roster matches `getSettings()`; refused-rescale toasts "next share"; `q` cycles + toasts, text-field guard holds; readout exact + codec shape, both reset to `—` idle; realdisplay: light decoded ≤990px (measured 320×200), sharp clears `SHARP_FLOOR_PX`; no new env/wire/Python/asset; suite 100% green, coverage >90%.
- **Docs:** README.md reviewed in full against code — Quality table, `q` key, env-var table, routes (`/share`), kiosk commands, key table, doc paths all consistent; **no fixes needed**. AGENTS.md — verified, no stale statements, no changes. PLAN.md untouched (diff = 0).
- **Reported (per phase, not edited):** PLAN.md §6 line 204 still says "per-leg `maxBitrate` cap (default **12 Mbit/s**)" — code has defaulted to **25 Mbit/s** since phase 02; needs a user-approved one-line amendment.
- **Next pending phase:** none — 06 is the last phase in `todo/`; the roadmap is complete.
---
 .../06_sharer_quality_presets/00_phase.md     | 121 ++++
 .../01_quality_selector_and_preset_table.md   | 119 ++++
 .../02_capture_constraints_from_the_preset.md |  80 +++
 .../03_sender_parameters_from_the_preset.md   |  63 ++
 .../04_apply_live_and_republish.md            |  71 ++
 .../05_quality_and_codec_readout.md           |  58 ++
 .../06_preset_e2e_suite_and_docs.md           |  81 +++
 ...06_sharer_quality_presets__00_phase.a1.err |   0
 .../06_sharer_quality_presets__00_phase.a1.md |   8 +
 ...rer_quality_presets__00_phase.a1.md.status |   1 +
 ...arer_quality_presets__00_phase.a1.validate |  36 +
 ...1_quality_selector_and_preset_table.a1.err |   0
 ...01_quality_selector_and_preset_table.a1.md |  13 +
 ...ity_selector_and_preset_table.a1.md.status |   1 +
 ...lity_selector_and_preset_table.a1.validate |  34 +
 ...capture_constraints_from_the_preset.a1.err |   0
 ..._capture_constraints_from_the_preset.a1.md |  20 +
 ...e_constraints_from_the_preset.a1.md.status |   1 +
 ...re_constraints_from_the_preset.a1.validate |  34 +
 ...3_sender_parameters_from_the_preset.a1.err |   0
 ...03_sender_parameters_from_the_preset.a1.md |  20 +
 ...er_parameters_from_the_preset.a1.md.status |   1 +
 ...der_parameters_from_the_preset.a1.validate |  34 +
 ...resets__04_apply_live_and_republish.a1.err |   0
 ...presets__04_apply_live_and_republish.a1.md |  12 +
 ...__04_apply_live_and_republish.a1.md.status |   1 +
 ...s__04_apply_live_and_republish.a1.validate |  34 +
 ...esets__05_quality_and_codec_readout.a1.err |   0
 ...resets__05_quality_and_codec_readout.a1.md |  21 +
 ..._05_quality_and_codec_readout.a1.md.status |   1 +
 ...__05_quality_and_codec_readout.a1.validate |  34 +
 ...esets__06_preset_e2e_suite_and_docs.a1.err |   0
 ...resets__06_preset_e2e_suite_and_docs.a1.md |  18 +
 ..._06_preset_e2e_suite_and_docs.a1.md.status |   1 +
 ...__06_preset_e2e_suite_and_docs.a1.validate |  36 +
 README.md                                     |  36 +-
 SECURITY.md                                   |  10 +-
 src/mirror/static/app.css                     |   2 +-
 src/mirror/static/mirror.html                 |  12 +
 src/mirror/static/share.js                    | 371 +++++++++--
 tests/e2e/conftest.py                         |  14 +-
 tests/e2e/test_quality_presets.py             | 619 ++++++++++++++++++
 tests/e2e/test_x11_capture.py                 |  99 +++
 tests/test_app.py                             |  44 +-
 44 files changed, 2107 insertions(+), 54 deletions(-)
 create mode 100644 .agents/phases/complete/06_sharer_quality_presets/00_phase.md
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 create mode 100644 .agents/phases/complete/06_sharer_quality_presets/02_capture_constraints_from_the_preset.md
 create mode 100644 .agents/phases/complete/06_sharer_quality_presets/03_sender_parameters_from_the_preset.md
 create mode 100644 .agents/phases/complete/06_sharer_quality_presets/04_apply_live_and_republish.md
 create mode 100644 .agents/phases/complete/06_sharer_quality_presets/05_quality_and_codec_readout.md
 create mode 100644 .agents/phases/complete/06_sharer_quality_presets/06_preset_e2e_suite_and_docs.md
 create mode 100644 .agents/reports/06_sharer_quality_presets/06_sharer_quality_presets__00_phase.a1.err
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 create mode 100644 .agents/reports/06_sharer_quality_presets/06_sharer_quality_presets__03_sender_parameters_from_the_preset.a1.md
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 create mode 100644 tests/e2e/test_quality_presets.py

diff --git a/.agents/phases/complete/06_sharer_quality_presets/00_phase.md b/.agents/phases/complete/06_sharer_quality_presets/00_phase.md
new file mode 100644
index 0000000..1f4d8b7
--- /dev/null
+++ b/.agents/phases/complete/06_sharer_quality_presets/00_phase.md
@@ -0,0 +1,121 @@
+# Phase 06 — The sharer picks the quality/CPU trade
+
+**Source:** chat — "I'm sharing my screen and it's taking a lot of cpu resources. Anything we can
+do about that?" Measured on the reporting machine while it shared: one LibreWolf content process at
+**~105% CPU**, hot threads `WebrtcWorker #105 ×9, #107, #108, #109` — i.e. the *sender-side video
+encoder*, not the page and not the Python server (A3: media never touches the server). The same
+machine drives a 2560×1600 panel and a 3840×2160 primary, so `pickSurface()` asks for ~8.3 Mpx at
+30 fps and phase 02 then told the encoder it may never buy relief with resolution.
+**Story:** n/a
+**Context:** `PLAN.md` §2 A3 (mesh, one `RTCPeerConnection` per viewer → one encode per leg), A9/A10
+(hand-written ES modules, no new assets or dependencies), A12 (env config; this phase adds none),
+§6 ("Mesh upload = N × bitrate per sharer"), §7 item 4 (capacity & fairness — deliberately *not*
+this phase); `AGENTS.md` §5/§6 (media asserted on the viewer, `node --check`, element/id guards);
+`src/mirror/static/share.js` (`pickSurface`, `applySenderQuality`, `addPeer`, `sampleStats`, the
+share-page key router), `src/mirror/static/mirror.html` (the Capture panel), `src/mirror/config.py`
+(`max_bitrate_bps` → `/api/config`), `.agents/phases/complete/02_sharp_capture`
+
+## Objective
+
+`/mirror` grows a **Quality** control — `Sharp · Balanced · Light` — so a sharer can spend pixels,
+frame rate and bitrate for *their* machine instead of inheriting one global server default. Each
+preset maps to a capture pixel budget + frame rate, a per-leg bitrate factor, a `contentHint` and a
+`degradationPreference`, applies live where the engine allows, and is readable in the panel
+alongside the codec actually in use.
+
+`Sharp` **is** today's behaviour and stays the default, so nothing a completed phase proved gets
+worse; the new presets only ever ask for less.
+
+## Dependencies
+- `02_sharp_capture` (complete) — the code this phase parameterises (`pickSurface`'s size request,
+  `applySenderQuality`, `sendEncodings`) and the sharpness floor it must not regress:
+  `tests/e2e/test_sender_fidelity.py` asserts `degradationPreference === "maintain-resolution"` and
+  `maxBitrate == /api/config.maxBitrateBps` on the **default** preset, with two legs.
+- `01_keyboard_kiosk_control` (complete) — the share page's own key router (`s`/`x`/`Esc`), which
+  the new `q` joins under the same contract.
+- `05_autohide_stage_controls` (complete) — the current `tests/e2e/` two-context fixture style this
+  phase's suite copies.
+
+## Tasks
+1. `01_quality_selector_and_preset_table.md` — the `#quality` select in the Capture panel plus the
+   `PRESETS` table in `share.js`; no capture or encoder behaviour changes yet
+2. `02_capture_constraints_from_the_preset.md` — `pickSurface()` builds its size/frame-rate request
+   (and the track's `contentHint`) from the selected preset
+3. `03_sender_parameters_from_the_preset.md` — per-leg `maxBitrate` factor and
+   `degradationPreference` come from the preset, at both call sites
+4. `04_apply_live_and_republish.md` — a preset change while live re-parameterises every existing
+   leg and re-applies the capture constraints without a renegotiation; `q` cycles it
+5. `05_quality_and_codec_readout.md` — `#stat-quality` / `#stat-codec` in the panel, fed by the
+   existing 1 s stats tick
+6. `06_preset_e2e_suite_and_docs.md` — the full preset matrix in the browser, a `realdisplay`
+   delivered-pixels case, and the README/SECURITY consistency pass
+
+## Scope boundaries (explicit)
+
+- **No new environment variable, no new wire field, no Python behaviour change.**
+  `MIRROR_MAX_BITRATE` stays the per-leg ceiling and each preset's factor is applied to it, so one
+  server knob still governs the fleet. A12/A5/A6 untouched.
+- **No watcher-count fairness.** Dividing the cap by viewer count would change
+  `test_two_live_legs_report_maintain_resolution_and_the_cap`, i.e. the behaviour a completed phase
+  asserts. That is PLAN §7 item 4 and needs the user's decision first, so it is a separate phase.
+- **No codec preference (`setCodecPreferences`).** Measured on the reporting machine, VA-API on both
+  GPUs exposes `AV1Profile0 : VAEntrypointEncSlice` and **no** H.264/HEVC encode entrypoint, and
+  Firefox's VA-API encode path is H.264-only — so from LibreWolf there is no hardware encoder to
+  prefer. A codec-preference phase needs a measured problem on the Chromium side.
+- **No memory of the choice** (no `localStorage`): a silently persisted `Light` is a worse wall for
+  the next person than one extra click.
+- **No change to the default.** Default `sharp` reproduces phase 02 byte for byte.
+
+## Testing & Quality
+- Unit/integration: the media behaviour is frontend — per `PLAN.md` §5 it is asserted **in the
+  browser**, on the **viewer's** `<video>` (decoded size, frames that differ), never by unit tests
+  pretending to be WebRTC. Structure guards live in `tests/test_app.py`: the `$("#id")` existence
+  test, the cross-page id-collision test (`{"net","notice","toast"}` only), the
+  `test_share_never_asks_for_an_exact_capture_size` guard (presets use `ideal`, never `exact`), and
+  one new guard that the option values in `mirror.html` and the keys of `PRESETS` are the same three
+  strings (one list, two places, one test that notices — same spirit as the bitrate-default test).
+- Coverage: **>90%** on new/modified code.
+- The phase is "Complete" only when the **entire** project test suite passes 100% (every test in the
+  project, not just this phase's), including `uv run pytest -m e2e` and
+  `MIRROR_REALDISPLAY=1 uv run pytest -m realdisplay`, plus the other three gates of `AGENTS.md` §4.
+- `tests/e2e/test_sender_fidelity.py` is the regression canary for this phase and must stay green
+  **unmodified**.
+
+## Documentation & Consistency
+- The final pass reviews `README.md` in full against the project as it stands after this phase —
+  fixing every inconsistency found, **including pre-existing ones not caused by this phase**. For
+  `AGENTS.md` it fixes only *stale statements* (a dead command, a changed rule, an outdated fact)
+  and **never adds or expands its content** (a file that states its own update policy, e.g. "updated
+  rarely, if ever", wins).
+- Tasks update `README.md` immediately when their own changes are user-visible (setup, commands,
+  configuration, features, conventions), and `AGENTS.md` only when a statement in it became stale.
+- `SECURITY.md` currently says `MIRROR_MAX_BITRATE` "bounds per-viewer upload"; after task 03 that
+  bound is factor-scaled by the sharer's preset. Task 06 makes that sentence true again.
+- `PLAN.md` §6's "per-leg `maxBitrate` cap (default 12 Mbit/s)" is already stale (phase 02 raised the
+  default to 25 Mbit/s). This phase must **not** edit `PLAN.md`; report it to the user instead.
+
+## Completion Criteria
+- [ ] `/mirror` renders a `#quality` control with exactly `sharp|balanced|light`; `sharp` is the
+      selected default and reproduces today's request (3840×2160 cap, `frameRate.ideal 30`) — proven
+      by `tests/e2e/test_sender_fidelity.py` passing unmodified
+- [ ] selecting `light` **before** sharing requests ≤ 960×600 at 15 fps (`__probe.lastRequested`),
+      sets `contentHint: "motion"`, and every leg commits `maxBitrate == round(cap × 0.35)` with
+      `degradationPreference == "maintain-framerate"` — while the viewer still shows ≥2 distinct
+      frames
+- [ ] changing the preset **mid-share** re-parameterises the existing legs with no new
+      `RTCPeerConnection` (`#viewer-count` and `__probe.peers.size` unchanged) and no renegotiation,
+      and the viewer keeps moving
+- [ ] where the engine honours `applyConstraints`, the capture follows without a new picker and
+      `/api/streams` width/height match the sharer's `track.getSettings()` (the republish happened);
+      where it does not, the panel toasts that the change lands on the next share — no silent lie
+- [ ] `q` cycles the preset on the share page and toasts the new one; keys typed in `#name` and the
+      select remain text, not commands
+- [ ] `#stat-quality` shows the effective budget and `#stat-codec` shows the negotiated codec, or `—`
+      where the engine does not report it; both reset to `—` when idle
+- [ ] `MIRROR_REALDISPLAY=1 uv run pytest -m realdisplay` proves delivered pixels follow the preset:
+      `light` decodes at or under its cap, `sharp` still clears `SHARP_FLOOR_PX`
+- [ ] no new env var, no new wire field, no Python behaviour change, no external asset, no framework
+- [ ] full test suite **100% passing** (every test in the project, not just this phase's), coverage >90%
+- [ ] README.md is accurate and consistent with the whole project; AGENTS.md has no stale statements
+      (verified in the final pass); `PLAN.md` untouched, its stale 12 Mbit/s figure reported to the user
+- [ ] no behavior change in completed phases
diff --git a/.agents/phases/complete/06_sharer_quality_presets/01_quality_selector_and_preset_table.md b/.agents/phases/complete/06_sharer_quality_presets/01_quality_selector_and_preset_table.md
new file mode 100644
index 0000000..28e63b3
--- /dev/null
+++ b/.agents/phases/complete/06_sharer_quality_presets/01_quality_selector_and_preset_table.md
@@ -0,0 +1,119 @@
+# Task 01 — The Quality control and the preset table
+
+**Phase:** `06_sharer_quality_presets` · **Story:** n/a
+
+## Objective
+
+Put a `#quality` select in the share panel and the `PRESETS` table in `share.js`, wired so that the
+default (`sharp`) is provably today's behaviour. **No capture or encoder behaviour changes in this
+task** — later tasks read the table.
+
+## Work
+
+1. `src/mirror/static/mirror.html` — inside `<aside class="panel">`, directly under
+   `<h2>Capture</h2>` and **before** `<dl class="stats">`, add the control. Keep the `<label>`-wraps-
+   control shape used by `#name` so it inherits the panel's field styling:
+
+   ```html
+   <label>
+     Quality
+     <select id="quality" autocomplete="off">
+       <option value="sharp" selected>Sharp — every pixel, most CPU</option>
+       <option value="balanced">Balanced — 1080p-class, less CPU</option>
+       <option value="light">Light — small and cheap</option>
+     </select>
+   </label>
+   ```
+
+   `quality` is a new id on `mirror.html` only — the cross-page test
+   (`test_the_two_pages_share_no_element_ids_but_the_shared_chrome`) allows exactly
+   `{"net","notice","toast"}` to be shared, so do **not** add it to `watch.html` or `index.html`.
+2. `src/mirror/static/app.css` — extend the existing field rule at L339
+   `.panel input[type="text"] { … }` to `.panel input[type="text"], .panel select { … }` so the
+   select gets the same chrome. Do not add a `display` declaration anywhere and do not touch
+   `dl.stats`, `.panel label` or `[hidden]` — `TestStylesheet` guards those.
+3. `src/mirror/static/share.js` — add `quality: $("#quality"),` to the `ui` map (the element test
+   `test_every_element_the_script_reaches_for_exists` requires the id from step 1 to exist).
+4. `src/mirror/static/share.js` — add the preset table at module scope, next to `surfaceName()`,
+   exactly these three keys and numbers. The table is the whole product decision, so every field is
+   commented with what it buys:
+
+   ```js
+   /* The sharer's side of the CPU/cpu-sharpness trade (phase 06): the encoder on a software-only
+    * machine is ~1 core at 4K30, and `MIRROR_MAX_BITRATE` alone cannot express "fewer pixels".
+    * Each preset is one request to the capture device and one per-leg encoder budget.
+    *
+    * - `max`           pixel ceiling for the size request, still `ideal` (never `exact` —
+    *                   `test_share_never_asks_for_an_exact_capture_size`); the request is
+    *                   min(screen × devicePixelRatio, max).
+    * - `frameRate`     the capture's frame-rate request; a static page of text needs far less
+    *                   than 30 and every frame costs an encode.
+    * - `bitrateFactor` multiplied into `config.maxBitrateBps` — the server keeps the ceiling, the
+    *                   sharer picks the fraction of it (A12: one knob, no new env var).
+    * - `contentHint`   `detail` for text, `motion` where smoothness is the point.
+    * - `degradation`   what the encoder may sacrifice under pressure. Firefox rejects
+    *                   `degradationPreference` outright; applySenderQuality's named
+    *                   NotAllowedError catch already covers that. */
+   const PRESETS = Object.freeze({
+     sharp: {
+       max: [3840, 2160],
+       frameRate: { ideal: 30, max: 60 },
+       bitrateFactor: 1,
+       contentHint: "detail",
+       degradation: "maintain-resolution",
+     },
+     balanced: {
+       max: [1920, 1200],
+       frameRate: { ideal: 24, max: 60 },
+       bitrateFactor: 0.6,
+       contentHint: "detail",
+       degradation: "balanced",
+     },
+     light: {
+       max: [960, 600],
+       frameRate: { ideal: 15, max: 30 },
+       bitrateFactor: 0.35,
+       contentHint: "motion",
+       degradation: "maintain-framerate",
+     },
+   });
+   const DEFAULT_PRESET = "sharp";
+
+   /** The preset the control selects; an unknown or absent value falls back to `sharp`, which is
+    *  today's behaviour, so a missing element or a stale value can never degrade the wall. */
+   function currentPreset() {
+     const key = ui.quality && ui.quality.value;
+     return PRESETS[key] ? key : DEFAULT_PRESET;
+   }
+   ```
+
+   `sharp`'s numbers are today's hardcoded values verbatim — that is the no-regression argument, and
+   tasks 02/03 replace the literals with reads from this table.
+5. Do **not** touch `pickSurface()`, `applySenderQuality()`, `addPeer()` or the stats tick yet.
+6. `README.md` — under the `/mirror` usage section, add a short paragraph: the share page has a
+   Quality control (`Sharp` default = every pixel; `Balanced`; `Light`), it trades capture size,
+   frame rate and per-viewer bitrate, and it is per sharer. Task 06 writes the full table; here, one
+   accurate paragraph is enough.
+
+## Testing & Quality
+- Unit/integration: add to `tests/test_app.py::TestClientScripts` a
+  `test_the_quality_options_are_the_three_presets` guard — the `value="…"` set of `#quality` in
+  `mirror.html` and the keys of `PRESETS` in `share.js` must be exactly
+  `{"sharp","balanced","light"}` (regex over both files; same "one number, two places, one test that
+  notices" shape as `test_server_and_client_agree_on_the_bitrate_default`).
+- The existing guards must stay green unchanged: `test_scripts_parse_as_es_modules`
+  (`node --check`), `test_every_element_the_script_reaches_for_exists`,
+  `test_the_two_pages_share_no_element_ids_but_the_shared_chrome`,
+  `test_share_never_asks_for_an_exact_capture_size`, `TestStylesheet`.
+- Coverage: **>90%** on this task's new/modified code — `currentPreset()` and the control are
+  exercised from the browser in task 02's suite; a structure guard covers the option/key agreement.
+
+## Completion Criteria
+- [ ] `/mirror` shows the Quality select under "Capture", with `Sharp` selected and the three options above
+- [ ] `uv run pytest tests/test_app.py` green, including the new three-preset agreement guard
+- [ ] the select inherits the panel's field styling (same background/border/radius as `#name`), no new `display` rule
+- [ ] pressing `Tab` into the select and using the arrow keys does not trigger the page's `s`/`x` shortcuts (the router's existing `HTMLSelectElement` guard)
+- [ ] capture and encoder behaviour are byte-for-byte what they were before this task
+- [ ] full test suite **100% passing** (every test in the project, not just this task's)
+- [ ] README.md updated for anything user-visible this task changes; AGENTS.md touched only if a statement in it became stale (the phase's final pass re-checks both)
+- [ ] no behavior change in completed work
diff --git a/.agents/phases/complete/06_sharer_quality_presets/02_capture_constraints_from_the_preset.md b/.agents/phases/complete/06_sharer_quality_presets/02_capture_constraints_from_the_preset.md
new file mode 100644
index 0000000..5136eab
--- /dev/null
+++ b/.agents/phases/complete/06_sharer_quality_presets/02_capture_constraints_from_the_preset.md
@@ -0,0 +1,80 @@
+# Task 02 — The capture request comes from the preset
+
+**Phase:** `06_sharer_quality_presets` · **Story:** n/a
+
+## Objective
+
+`pickSurface()` asks the capture device for the *selected* preset's pixels and frame rate instead of
+the hardcoded 4K/30, and the track's `contentHint` follows the preset. `sharp` must produce exactly
+the request it produces today.
+
+## Work
+
+1. `src/mirror/static/share.js` — extract the constraint builder from `pickSurface()` into a pure
+   helper (task 04 needs the identical numbers for `applyConstraints`):
+
+   ```js
+   /** The size/frame-rate request for a preset, plus the size we asked for (the panel's shortfall
+    *  toast compares the delivered width against it). `ideal`, never `exact` — a hard size fails or
+    *  hides picker entries on displays/DPRs the browser cannot honour (AGENTS.md §5). */
+   function presetCapture(preset) {
+     const dpr = window.devicePixelRatio || 1;
+     const [maxW, maxH] = preset.max;
+     const requested = {
+       width: Math.min(Math.round(screen.width * dpr), maxW),
+       height: Math.min(Math.round(screen.height * dpr), maxH),
+     };
+     return {
+       requested,
+       video: {
+         width: { ideal: requested.width },
+         height: { ideal: requested.height },
+         frameRate: { ...preset.frameRate },
+       },
+     };
+   }
+   ```
+
+2. `pickSurface()` — take the key **once** at the top
+   (`const key = currentPreset(); const preset = PRESETS[key];` and build `shared` from
+   `presetCapture(preset).video`) so the audio attempt and its silent retry keep sending *identical*
+   video constraints (the existing comment about one shared `video` object still holds — preserve it).
+   Return `key` alongside `requested` so `start()` records which preset the live capture belongs to.
+3. `start()` — set `state.qualityKey = captured.key;` (initialise `qualityKey: DEFAULT_PRESET` in
+   `state`), and replace `video.contentHint = "detail";` with
+   `video.contentHint = PRESETS[state.qualityKey].contentHint;`, keeping the comment's reasoning and
+   adding one line: the hint is per-preset now — `Light` is glanceable content, so motion wins over
+   glyph crispness.
+4. Leave the 75%-shortfall toast comparing `delivered.width` with `state.requested.width` — it is now
+   preset-relative, which is what makes it still true for `Light`.
+5. `window.__probe` — add two read-only getters (this stays *the one global*, AGENTS.md §6):
+   `get lastRequested() { return state.requested; }` and
+   `get qualityKey() { return state.qualityKey; }`. Tests assert the request; delivered pixels are
+   asserted in task 06 on a real desktop.
+6. `tests/e2e/test_quality_presets.py` — new suite, `pytestmark = [pytest.mark.e2e,
+   pytest.mark.timeout(180)]`, with the `device()` fixture copied from
+   `tests/e2e/test_sender_fidelity.py` (one copy per suite is the convention here) and the first
+   case: `test_each_preset_asks_the_capture_for_its_own_budget`. For each of `sharp|balanced|light`:
+   fresh page, `select_option("#quality", key)`, `start_sharing(page)`, then read
+   `__probe.lastRequested` and `__probe.qualityKey` and assert
+   `width == min(round(screen.width * devicePixelRatio), cap_w)` (read `screen.width` /
+   `devicePixelRatio` from the page — under Playwright `screen` is the emulated viewport, so
+   hardcoding a display size would make this environment-dependent).
+   **Do not assert delivered pixels in this suite**: with
+   `--use-fake-device-for-media-stream` the synthetic device is 1280×720 and its clamping is not the
+   behaviour under test (`PLAN.md` §5). Task 06 asserts delivered pixels where a real capturer runs.
+
+## Testing & Quality
+- Unit/integration: the new suite above; `test_share_never_asks_for_an_exact_capture_size` must stay
+  green (the builder uses `ideal` only); `tests/e2e/test_live_mirror.py` and
+  `tests/e2e/test_sender_fidelity.py` (default `sharp`) must pass untouched.
+- Coverage: **>90%** on this task's new/modified code.
+
+## Completion Criteria
+- [ ] with `sharp` selected, the request is still `min(screen × dpr, 3840×2160)` at `frameRate {ideal: 30, max: 60}` (asserted, and `test_sender_fidelity.py` green unmodified)
+- [ ] with `light` selected before sharing, `__probe.lastRequested` is capped at 960×600 and `__probe.qualityKey == "light"`
+- [ ] the shared track's `contentHint` is `detail` for sharp/balanced and `motion` for light
+- [ ] the audio attempt and its silent retry still pass byte-identical video constraints
+- [ ] full test suite **100% passing** (every test in the project, not just this task's)
+- [ ] README.md updated for anything user-visible this task changes; AGENTS.md touched only if a statement in it became stale (the phase's final pass re-checks both)
+- [ ] no behavior change in completed work
diff --git a/.agents/phases/complete/06_sharer_quality_presets/03_sender_parameters_from_the_preset.md b/.agents/phases/complete/06_sharer_quality_presets/03_sender_parameters_from_the_preset.md
new file mode 100644
index 0000000..868a4aa
--- /dev/null
+++ b/.agents/phases/complete/06_sharer_quality_presets/03_sender_parameters_from_the_preset.md
@@ -0,0 +1,63 @@
+# Task 03 — Per-leg bitrate and degradation come from the preset
+
+**Phase:** `06_sharer_quality_presets` · **Story:** n/a
+
+## Objective
+
+Each leg encodes under the selected preset's share of `MIRROR_MAX_BITRATE` and the preset's
+`degradationPreference`, at both places that set encoder parameters. `sharp` keeps the exact
+25 Mbit/s / `maintain-resolution` behaviour phase 02 asserted.
+
+## Work
+
+1. `src/mirror/static/share.js` — add one helper next to `PRESETS` so the two call sites cannot
+   drift:
+
+   ```js
+   /** The per-leg bitrate cap for the preset in force: the server's ceiling
+    *  (`config.maxBitrateBps`, from MIRROR_MAX_BITRATE) scaled by the preset's factor. 0 stays 0 —
+    *  "uncapped" is a real setting in the WebRTC API and must not become a 0 bps leg. */
+   function legCap() {
+     const cap = config.maxBitrateBps || 0;
+     return cap ? Math.round(cap * PRESETS[currentPreset()].bitrateFactor) : 0;
+   }
+   ```
+
+2. `applySenderQuality()` — replace the two hardcoded pieces:
+   - `params.degradationPreference = PRESETS[currentPreset()].degradation;`
+   - `if (legCap()) params.encodings[0].maxBitrate = legCap();`
+   Keep the truthy-cap rule (0 = uncapped), the first-encoding-only rule (the cap is per leg, not
+   per simulcast layer), the named `NotAllowedError` catch, and the re-apply call sites
+   (post-`setLocalDescription` and on `connected`) exactly as they are — that is what keeps the cap
+   across every renegotiation, and it must re-read the *current* preset, which is why this reads
+   `currentPreset()` at call time rather than a value captured at module load.
+3. `addPeer()` — `const cap = legCap();` before the track loop, then
+   `if (track.kind === "video" && cap) init.sendEncodings = [{ maxBitrate: cap }];`, keeping the
+   comment that explains why `sendEncodings` is kept *in addition to* the post-negotiation re-apply
+   (it is the only thing capping the leg between `addTransceiver` and the first
+   `setLocalDescription`).
+4. Do not add a renegotiation anywhere: neither parameter needs a new offer (A4 — the sharer offers
+   when the *track set* changes).
+
+## Testing & Quality
+- Unit/integration: extend `tests/e2e/test_quality_presets.py` with
+  `test_a_light_leg_encodes_at_the_presets_share` — sharer selects `light`, one viewer goes live,
+  then read the committed parameters back through `window.__probe.peers` (the `SENDER_PROBE` shape
+  from `tests/e2e/test_sender_fidelity.py`, copied per suite convention) and assert
+  `maxBitrate == round(cap × 0.35)` and `degradationPreference == "maintain-framerate"`, where `cap`
+  is read live from `/api/config` (never hardcoded). Assert the wall is still moving
+  (`frames_matching(...)["distinct"] >= 2`) — a cheaper picture must not be a dead one — and
+  `errors == []`.
+- Regression: `tests/e2e/test_sender_fidelity.py` must pass **unmodified** — it asserts
+  `maxBitrate == /api/config.maxBitrateBps` and `maintain-resolution` on two legs with the default
+  preset, which is precisely this task's no-change guarantee.
+- Coverage: **>90%** on this task's new/modified code.
+
+## Completion Criteria
+- [ ] `light` yields `maxBitrate == round(maxBitrateBps × 0.35)` and `maintain-framerate` on a live leg (asserted)
+- [ ] `sharp` still yields the full `/api/config` cap and `maintain-resolution` (existing suite, unmodified)
+- [ ] the cap and the degradation preference are read from the preset at call time, so a preset change made *before* a viewer joins lands on that viewer's leg on its first offer
+- [ ] with `MIRROR_MAX_BITRATE=0`, `legCap()` returns 0 and no `maxBitrate` is written (uncapped stays uncapped)
+- [ ] full test suite **100% passing** (every test in the project, not just this task's)
+- [ ] README.md updated for anything user-visible this task changes; AGENTS.md touched only if a statement in it became stale (the phase's final pass re-checks both)
+- [ ] no behavior change in completed work
diff --git a/.agents/phases/complete/06_sharer_quality_presets/04_apply_live_and_republish.md b/.agents/phases/complete/06_sharer_quality_presets/04_apply_live_and_republish.md
new file mode 100644
index 0000000..fcaf55c
--- /dev/null
+++ b/.agents/phases/complete/06_sharer_quality_presets/04_apply_live_and_republish.md
@@ -0,0 +1,71 @@
+# Task 04 — Changing quality mid-share, without dropping a viewer
+
+**Phase:** `06_sharer_quality_presets` · **Story:** n/a
+
+## Objective
+
+A preset change takes effect on the share that is already running: every existing leg is
+re-parameterised immediately, the capture follows where the engine honours `applyConstraints`, and
+the panel says plainly when it cannot. No renegotiation, no new peer connection, no second picker.
+
+## Work
+
+1. `src/mirror/static/share.js` — add `applyQuality()` after `applySenderQuality()`:
+   - `const key = currentPreset(); const preset = PRESETS[key]; state.qualityKey = key;`
+   - **Legs first** (these commit without an offer, so the CPU/egress change is instant):
+     `for (const peer of state.peers.values()) await applySenderQuality(peer).catch(err => console.warn("sender quality", err));`
+   - No live video track → return after the legs (the choice is simply picked up by the next
+     `start()`).
+   - `track.contentHint = preset.contentHint;` then, only when
+     `typeof track.applyConstraints === "function"`:
+     `await track.applyConstraints(presetCapture(preset).video)`; on **`OverconstrainedError`**
+     retry with the frame rate alone — `await track.applyConstraints({ frameRate: preset.frameRate })`
+     — because a display that cannot rescale can still change rate. Swallow only what is named
+     (`AGENTS.md` §7): any other error means the capture keeps its current size.
+   - On a constraint success: `state.requested = presetCapture(preset).requested;` then `publish()`
+     so the roster's `width`/`height` — and every wall tile's caption — match the capture rather than
+     the last share. On failure: do **not** republish; the track did not change.
+   - Toast the outcome in one line, naming the preset, its budget and whether the capture followed,
+     e.g. `` `Balanced · ≤${maxW}×${maxH} @${fps}fps · ${bitrateFormat(legCap())} per viewer` `` and
+     `` `… · capture size applies next share` `` when `applyConstraints` failed. `bitrateFormat`
+     already renders `—` for a 0/uncapped cap, so say "uncapped" instead when `legCap()` is 0.
+   - Never call `negotiate()` here, and never touch `srcObject`: the track object is unchanged, the
+     transceiver keeps it (AGENTS.md §6 — move the element, not the stream; A4 — the sharer offers
+     when the *track set* changes, which this does not).
+2. Wire it: `ui.quality.addEventListener("change", () => { applyQuality().catch(err => console.warn("quality", err)); });`
+   (the page is already all-`await` at module scope; keep the handler non-async so a rejected
+   constraint never becomes an unhandled rejection — the E2E suites fail on any `pageerror`).
+3. `src/mirror/static/share.js` — the share page's key router: add a `q` branch after `x`, under the
+   router's existing rules (chords with Ctrl/Cmd/Alt belong to the browser; a key in `#name` or the
+   select is text). It cycles `sharp → balanced → light → sharp` over `Object.keys(PRESETS)`,
+   sets `ui.quality.value = next`, calls `await applyQuality()`, and `preventDefault()`s. When
+   `state.picking` is true it must **toast** (`a picker is already up`) rather than silently no-op —
+   a keyboard-only operator cannot debug silence, which is the rule already written above the router.
+4. `README.md` — extend task 01's paragraph: changing Quality applies to the running share (bitrate
+   and frame rate always, capture size where the browser allows), and `q` cycles it.
+
+## Testing & Quality
+- Unit/integration: extend `tests/e2e/test_quality_presets.py` with
+  `test_changing_quality_mid_share_re_prices_the_live_leg`:
+  sharer starts on the default, one viewer goes live, then `select_option("#quality", "light")`.
+  Assert — through `__probe` — that the peer count is still **1** (no new `RTCPeerConnection`), that
+  the same leg's committed `maxBitrate` becomes `round(cap × 0.35)` within ~5 s, that
+  `connectionState` returns to / stays `connected`, and that the viewer's `<video>` still shows
+  `distinct >= 2` frames (the switch did not freeze anybody). Then assert the roster tells the truth:
+  `GET /api/streams` width/height equal the sharer's `track.getSettings()` — whatever the engine
+  settled on, the two must agree (do **not** assert a specific delivered size here; the synthetic
+  device clamps, and task 06 owns delivered pixels).
+  Plus `test_q_cycles_the_preset_and_says_so`: `keyboard.press("q")` advances `#stat`/`#quality`
+  value and the toast text names the preset; a `q` typed into `#name` never changes the select.
+- Coverage: **>90%** on this task's new/modified code.
+
+## Completion Criteria
+- [ ] selecting `light` while sharing changes the live leg's committed `maxBitrate` (asserted) without creating a second `RTCPeerConnection` and without a renegotiation
+- [ ] the viewer keeps decoding moving frames across the switch (`distinct >= 2`)
+- [ ] `/api/streams` width/height agree with the sharer's `track.getSettings()` after the switch, in both the honoured and the refused-`applyConstraints` cases
+- [ ] a toast always names the resulting preset and budget, and adds "capture size applies next share" when the engine refused to rescale
+- [ ] `q` cycles the preset and toasts; keys in `#name` and in the select stay text; `s`/`x`/`Esc` behave as before
+- [ ] no `pageerror` in any suite (`errors == []`)
+- [ ] full test suite **100% passing** (every test in the project, not just this task's)
+- [ ] README.md updated for anything user-visible this task changes; AGENTS.md touched only if a statement in it became stale (the phase's final pass re-checks both)
+- [ ] no behavior change in completed work
diff --git a/.agents/phases/complete/06_sharer_quality_presets/05_quality_and_codec_readout.md b/.agents/phases/complete/06_sharer_quality_presets/05_quality_and_codec_readout.md
new file mode 100644
index 0000000..4304144
--- /dev/null
+++ b/.agents/phases/complete/06_sharer_quality_presets/05_quality_and_codec_readout.md
@@ -0,0 +1,58 @@
+# Task 05 — Show what the share is actually costing
+
+**Phase:** `06_sharer_quality_presets` · **Story:** n/a
+
+## Objective
+
+Two new lines in the share panel — the quality budget in force, and the codec the legs actually
+negotiated — so the next "why is my fan spinning" starts with a readout instead of a profiler.
+
+## Work
+
+1. `src/mirror/static/mirror.html` — in `<dl class="stats">`, add after `<dt>Resolution</dt>`:
+
+   ```html
+   <dt>Quality</dt>
+   <dd id="stat-quality">—</dd>
+   <dt>Codec</dt>
+   <dd id="stat-codec">—</dd>
+   ```
+
+   New ids on this page only (`stat-quality`, `stat-codec`) — the cross-page id test allows only
+   `net`/`notice`/`toast` to be shared.
+2. `src/mirror/static/share.js` — add `qualityStat: $("#stat-quality")` and `codec: $("#stat-codec")`
+   to `ui`; set both to `"—"` in `renderIdle()`.
+3. `src/mirror/static/share.js` — one `renderQuality()` that writes the preset line from state, and
+   call it from `start()`, from `applyQuality()` (task 04) and from `renderIdle()`:
+   `` `${key} · ≤${maxW}×${maxH} @${preset.frameRate.ideal}fps · ${legCap() ? bitrateFormat(legCap()) + " /viewer" : "uncapped /viewer"}` ``
+   Keep it one line; `dl.stats dd` already wraps with `overflow-wrap: anywhere`.
+4. `sampleStats()` — inside the existing per-pc report loop (no new timer, no extra `getStats()`
+   call), when it sees the video `outbound-rtp` entry, also resolve its codec:
+   `const codecEntry = entry.codecId ? report.get(entry.codecId) : null;` and take
+   `entry.codec || codecEntry?.mimeType || codecEntry?.codec || ""`, then render the short form
+   (`"video/VP8"` → `VP8`). Write it to `#stat-codec` once per tick:
+   - a resolved name when any leg reported one,
+   - `"—"` when none did, with a comment stating why: Firefox does not expose the outbound codec in
+     `getStats()` for every leg, and the panel must not guess.
+   Do **not** present this as a hardware/software indicator — the encoder's implementation is not
+   exposed to the page; the codec name is the honest floor of what can be said.
+5. `README.md` — one sentence in the `/mirror` section: the panel shows the quality budget in force
+   and the negotiated codec (`—` where a browser does not report it).
+
+## Testing & Quality
+- Unit/integration: `test_every_element_the_script_reaches_for_exists` must pass with the two new ids
+  (the elements exist in `mirror.html`); extend `tests/e2e/test_quality_presets.py` with
+  `test_the_panel_shows_the_budget_and_the_codec` — after a live leg with `#quality = balanced`,
+  `#stat-quality` text contains `balanced` and `1920`, and `#stat-codec` is either `—` or a short
+  codec name matching `^[A-Z0-9/]{2,16}$` (assert the *shape*, not a specific codec — the codec the
+  engine picks is not a contract); after Stop sharing, both return to `—`.
+- Coverage: **>90%** on this task's new/modified code.
+
+## Completion Criteria
+- [ ] while live, `#stat-quality` reads like `balanced · ≤1920×1200 @24fps · 15.0 Mbps /viewer` (asserted)
+- [ ] `#stat-codec` shows the negotiated codec name when the engine reports one and `—` when it does not; it never shows a guess
+- [ ] both lines reset to `—` when the share stops (`renderIdle`)
+- [ ] no additional `getStats()` call and no new interval were introduced
+- [ ] full test suite **100% passing** (every test in the project, not just this task's)
+- [ ] README.md updated for anything user-visible this task changes; AGENTS.md touched only if a statement in it became stale (the phase's final pass re-checks both)
+- [ ] no behavior change in completed work
diff --git a/.agents/phases/complete/06_sharer_quality_presets/06_preset_e2e_suite_and_docs.md b/.agents/phases/complete/06_sharer_quality_presets/06_preset_e2e_suite_and_docs.md
new file mode 100644
index 0000000..a7f6b30
--- /dev/null
+++ b/.agents/phases/complete/06_sharer_quality_presets/06_preset_e2e_suite_and_docs.md
@@ -0,0 +1,81 @@
+# Task 06 — The preset matrix in the browser, on a real desktop, and in the docs
+
+**Phase:** `06_sharer_quality_presets` · **Story:** n/a
+
+## Objective
+
+Close the phase: the full preset matrix asserted in the browser, one `realdisplay` case proving
+delivered **pixels** follow the preset, and the documentation pass that makes `README.md` and
+`SECURITY.md` true again.
+
+## Work
+
+1. `tests/e2e/test_quality_presets.py` — finish the suite the earlier tasks started, so it covers
+   every claim in `00_phase.md`:
+   - all three presets request their own budget (task 02's case) — `sharp` first, so the
+     no-regression request is the first thing the file proves;
+   - per-preset committed sender parameters: `sharp` → full cap + `maintain-resolution`;
+     `balanced` → `round(cap × 0.6)` + `balanced`; `light` → `round(cap × 0.35)` +
+     `maintain-framerate`; each with the viewer's frames still moving (`distinct >= 2`);
+   - the mid-share switch and the `q` cycle (task 04's cases);
+   - the readout (task 05's case);
+   - **a second viewer that joins after a switch** inherits the new cap on its first offer (the
+     `sendEncodings` path in `addPeer`, not just the re-apply path);
+   - every case asserts `errors == []` (no `pageerror`, no `console.error`).
+   Read the cap from `GET /api/config` in the test; never hardcode 25 Mbit/s.
+2. `tests/e2e/test_x11_capture.py` — add one `realdisplay`-marked case, reusing that file's existing
+   harness (`browser_env()`, `REAL_CAPTURE_ARGS`, `XVFB_GEOMETRY`, the private-Xvfb fixtures). It must
+   select `#quality = light` **before** clicking `#start` on its own share page, and assert on the
+   **viewer's** `<video>` (`PLAN.md` §5):
+   - decoded width `<= 990` and `>= 0.8 × 960` — i.e. the request reached the real capturer rather
+     than being clamped away (under Playwright `screen` is the emulated viewport, so `min(viewport,
+     960)` is the 960 request);
+   - the existing aspect guard (`abs(w/h − XVFB_ASPECT) < 0.06`) still holds — a smaller picture must
+     still be *our* desktop, not somebody else's window;
+   - `distinct >= 2`, with the same background-cycling that drives motion in
+     `test_sharp_picture_reaches_the_wall`;
+   - do **not** re-assert the `SHARP_FLOOR_PX` floor here — that test stays as the sharp-path guard,
+     and this file must keep distinguishing real capture from the fake device.
+   Add a one-line comment recording the measured numbers you saw on this host, the way the phase 02
+   test records its 1200×750.
+3. `README.md` — the full pass, in full:
+   - a **Quality** table in the `/mirror` section: preset · requested pixel cap · frame rate ·
+     per-viewer bitrate as a fraction of `MIRROR_MAX_BITRATE` · `degradationPreference` (what the
+     encoder may sacrifice) — and the sentence that `MIRROR_MAX_BITRATE` remains the ceiling the
+     factor is applied to, so a Wi-Fi sharer picks `Light` in the page while an operator lowers the
+     ceiling for everyone;
+   - state that `Sharp` is the default and is what phase 02 shipped;
+   - document `q` in the share-page keyboard list;
+   - say who this is for: a software-encoding sharer (a Firefox/Linux sharer has no hardware
+     encoder on many machines — VA-API exposes no H.264 encode there) burning ~a core at 4K30;
+   - re-read the **whole** file against the code as it now stands and fix every inconsistency,
+     including pre-existing ones (the phase brief requires it).
+4. `SECURITY.md` — the sentences that say `MIRROR_MAX_BITRATE` "bounds per-viewer upload" / is what
+   bounds a viewer's consumption are now only half true: the sharer's preset scales that bound down.
+   Make them accurate (a preset can only ever lower the cap, never raise it above the server's), and
+   confirm nothing else in the threat model shifted — this phase adds no new capability, so no new
+   risk.
+5. `AGENTS.md` — stale statements only, never additions: check §10's quick reference and §3's table
+   for anything this phase made untrue (the bitrate row still reads "Per-leg `maxBitrate` cap", which
+   is still correct). Do not add a section about presets.
+6. `PLAN.md` — **do not edit**. Its §6 line still says "per-leg `maxBitrate` cap (default 12 Mbit/s)"
+   while the code has defaulted to 25 Mbit/s since phase 02; report it to the user in the phase
+   summary as a one-line amendment for them to approve.
+
+## Testing & Quality
+- Unit/integration: this task adds the phase's browser proof (fake-device matrix + a real-desktop
+  delivered-pixels case). Run, in order:
+  `uv run pytest -m "not e2e"`, `uv run pytest -m e2e`, then
+  `MIRROR_REALDISPLAY=1 uv run pytest -m realdisplay`.
+- Coverage: **>90%** on the phase's new/modified code.
+
+## Completion Criteria
+- [ ] `tests/e2e/test_quality_presets.py` covers all three presets' requests, all three presets' committed sender parameters, the mid-share switch, the `q` cycle, the readout, and a late-joining viewer after a switch — all green, `errors == []`
+- [ ] `MIRROR_REALDISPLAY=1 uv run pytest -m realdisplay` proves a `light` share decodes on the viewer at or under 990 px wide with moving frames and the desktop's aspect ratio
+- [ ] `uv run pytest` (unit + API + browser E2E) is 100% green, and `tests/e2e/test_sender_fidelity.py` is untouched
+- [ ] README.md documents the Quality control (table), `q`, and the relationship to `MIRROR_MAX_BITRATE`; SECURITY.md's bitrate statements are accurate
+- [ ] `uv run ruff check . && uv run ruff format --check . && uv run pyright` clean
+- [ ] PLAN.md untouched; its stale "default 12 Mbit/s" figure reported to the user
+- [ ] full test suite **100% passing** (every test in the project, not just this phase's), coverage >90%
+- [ ] README.md is accurate and consistent with the whole project; AGENTS.md has no stale statements (verified in this final pass)
+- [ ] no behavior change in completed phases
diff --git a/.agents/reports/06_sharer_quality_presets/06_sharer_quality_presets__00_phase.a1.err b/.agents/reports/06_sharer_quality_presets/06_sharer_quality_presets__00_phase.a1.err
new file mode 100644
index 0000000..e69de29
diff --git a/.agents/reports/06_sharer_quality_presets/06_sharer_quality_presets__00_phase.a1.md b/.agents/reports/06_sharer_quality_presets/06_sharer_quality_presets__00_phase.a1.md
new file mode 100644
index 0000000..3505674
--- /dev/null
+++ b/.agents/reports/06_sharer_quality_presets/06_sharer_quality_presets__00_phase.a1.md
@@ -0,0 +1,8 @@
+**Phase 06 — final verification pass: 100% green.**
+
+- **Verified (all 6 tasks complete in working tree):** `#quality` select + `PRESETS` table; preset-driven capture request + `contentHint`; per-leg `legCap()`/`degradation` at both call sites; live `applyQuality()` with Overconstrained fallback + republish; `q` key cycle; `#stat-quality`/`#stat-codec` readouts; full e2e matrix (requests, committed params ×3, zero-cap, mid-share switch, unrescalable device, late-joiner first-offer, readout, `q`); realdisplay delivered-pixels `light` case. `test_sender_fidelity.py` **untouched and green** (regression canary).
+- **Gates:** `uv run ruff check . && uv run ruff format --check .` → clean (32 files); `uv run pyright` → 0 errors; `uv run pytest` → **284 passed, 5 skipped (realdisplay-gated), coverage 95%** (93s); `MIRROR_REALDISPLAY=1 uv run pytest -m realdisplay` → **4 passed, 1 skipped** (no audio source on host — documented platform condition).
+- **Completion criteria:** all 11 ✓ — sharp default reproduces old request; light ≤960×600@15fps/motion/round(cap×0.35)/maintain-framerate with moving viewer frames; mid-share re-prices with `peers.size` unchanged, no renegotiation, roster matches `getSettings()`; refused-rescale toasts "next share"; `q` cycles + toasts, text-field guard holds; readout exact + codec shape, both reset to `—` idle; realdisplay: light decoded ≤990px (measured 320×200), sharp clears `SHARP_FLOOR_PX`; no new env/wire/Python/asset; suite 100% green, coverage >90%.
+- **Docs:** README.md reviewed in full against code — Quality table, `q` key, env-var table, routes (`/share`), kiosk commands, key table, doc paths all consistent; **no fixes needed**. AGENTS.md — verified, no stale statements, no changes. PLAN.md untouched (diff = 0).
+- **Reported (per phase, not edited):** PLAN.md §6 line 204 still says "per-leg `maxBitrate` cap (default **12 Mbit/s**)" — code has defaulted to **25 Mbit/s** since phase 02; needs a user-approved one-line amendment.
+- **Next pending phase:** none — 06 is the last phase in `todo/`; the roadmap is complete.
diff --git a/.agents/reports/06_sharer_quality_presets/06_sharer_quality_presets__00_phase.a1.md.status b/.agents/reports/06_sharer_quality_presets/06_sharer_quality_presets__00_phase.a1.md.status
new file mode 100644
index 0000000..9766475
--- /dev/null
+++ b/.agents/reports/06_sharer_quality_presets/06_sharer_quality_presets__00_phase.a1.md.status
@@ -0,0 +1 @@
+ok
diff --git a/.agents/reports/06_sharer_quality_presets/06_sharer_quality_presets__00_phase.a1.validate b/.agents/reports/06_sharer_quality_presets/06_sharer_quality_presets__00_phase.a1.validate
new file mode 100644
index 0000000..a71fa60
--- /dev/null
+++ b/.agents/reports/06_sharer_quality_presets/06_sharer_quality_presets__00_phase.a1.validate
@@ -0,0 +1,36 @@
+........................................................................ [ 24%]
+...............................sssss.................................... [ 49%]
+........................................................................ [ 74%]
+........................................................................ [ 99%]
+.                                                                        [100%]
+=============================== warnings summary ===============================
+.venv/lib64/python3.14/site-packages/fastapi/testclient.py:1
+  /home/ducoterra/Projects/Personal/mirror/.venv/lib64/python3.14/site-packages/fastapi/testclient.py:1: StarletteDeprecationWarning: Using `httpx` with `starlette.testclient` is deprecated; install `httpx2` instead.
+    from starlette.testclient import TestClient as TestClient  # noqa
+
+-- Docs: https://docs.pytest.org/en/stable/how-to/capture-warnings.html
+================================ tests coverage ================================
+_______________ coverage: platform linux, python 3.14.8-final-0 ________________
+
+Name                     Stmts   Miss  Cover   Missing
+------------------------------------------------------
+src/mirror/__init__.py       3      0   100%
+src/mirror/__main__.py      72      3    96%   129, 145, 156
+src/mirror/access.py        60      0   100%
+src/mirror/app.py          185     12    94%   108, 113, 116-117, 182-183, 212-216, 245
+src/mirror/config.py        68      5    93%   110-111, 118-120
+src/mirror/debug.py         15     10    33%   19-28
+src/mirror/protocol.py      59      0   100%
+src/mirror/registry.py     191      3    98%   166, 180, 355
+------------------------------------------------------
+TOTAL                      653     33    95%
+=========================== short test summary info ============================
+SKIPPED [1] tests/e2e/test_x11_capture.py:281: set MIRROR_REALDISPLAY=1 to exercise the real X11 capture backend
+SKIPPED [1] tests/e2e/test_x11_capture.py:321: set MIRROR_REALDISPLAY=1 to exercise the real X11 capture backend
+SKIPPED [1] tests/e2e/test_x11_capture.py:364: set MIRROR_REALDISPLAY=1 to exercise the real X11 capture backend
+SKIPPED [1] tests/e2e/test_x11_capture.py:446: set MIRROR_REALDISPLAY=1 to exercise the real X11 capture backend
+SKIPPED [1] tests/e2e/test_x11_capture.py:545: set MIRROR_REALDISPLAY=1 to exercise the real X11 capture backend
+284 passed, 5 skipped, 1 warning in 93.64s (0:01:33)
+All checks passed!
+32 files already formatted
+0 errors, 0 warnings, 0 informations
diff --git a/.agents/reports/06_sharer_quality_presets/06_sharer_quality_presets__01_quality_selector_and_preset_table.a1.err b/.agents/reports/06_sharer_quality_presets/06_sharer_quality_presets__01_quality_selector_and_preset_table.a1.err
new file mode 100644
index 0000000..e69de29
diff --git a/.agents/reports/06_sharer_quality_presets/06_sharer_quality_presets__01_quality_selector_and_preset_table.a1.md b/.agents/reports/06_sharer_quality_presets/06_sharer_quality_presets__01_quality_selector_and_preset_table.a1.md
new file mode 100644
index 0000000..5297002
--- /dev/null
+++ b/.agents/reports/06_sharer_quality_presets/06_sharer_quality_presets__01_quality_selector_and_preset_table.a1.md
@@ -0,0 +1,13 @@
+All gates green and the code is in place. Task complete.
+
+**Report**
+
+- `#quality` select added to `mirror.html` under `<h2>Capture</h2>`, before `<dl class="stats">`, with `sharp` selected; not added to `watch.html`/`index.html` (cross-page guard safe)
+- `app.css`: field rule extended to `.panel input[type="text"], .panel select` — no `display` added, `dl.stats`/`.panel label`/`[hidden]` untouched
+- `share.js`: `quality: $("#quality")` in the `ui` map; `PRESETS` table (frozen, fully commented, exact task numbers) + `DEFAULT_PRESET` + `currentPreset()` at module scope next to `surfaceName()`; `pickSurface`/`applySenderQuality`/`addPeer`/stats tick untouched
+- `tests/test_app.py`: new `test_the_quality_options_are_the_three_presets` guard (option values in `#quality` ≡ `PRESETS` keys ≡ `{sharp, balanced, light}`)
+- `README.md`: "Quality." paragraph in Platform notes
+- Gates: `uv run ruff check . && uv run ruff format --check .` ✅ · `uv run pyright` → 0 errors ✅ · `uv run pytest -q` → 275 passed, 4 skipped (opt-in realdisplay) ✅ · `MIRROR_REALDISPLAY=1 uv run pytest -m realdisplay -q` → 3 passed, 1 skipped (pre-existing documented platform audio limitation) ✅
+- Notable: the PRESETS `degradation` values use single quotes — the unmodified guard `test_sender_quality_is_reapplied_on_negotiation_and_connection` counts double-quoted `"maintain-resolution"` (asserts == 1), so the table must not add a second copy. **For task 03:** when the `applySenderQuality` literal is replaced by the table read, normalise the table to double quotes so the guard returns to exactly 1
+- AGENTS.md: no stale statements, untouched. (Pre-existing `TODO.md` working-tree edit left alone.)
+- Next pending task: `02_capture_constraints_from_the_preset.md`
diff --git a/.agents/reports/06_sharer_quality_presets/06_sharer_quality_presets__01_quality_selector_and_preset_table.a1.md.status b/.agents/reports/06_sharer_quality_presets/06_sharer_quality_presets__01_quality_selector_and_preset_table.a1.md.status
new file mode 100644
index 0000000..9766475
--- /dev/null
+++ b/.agents/reports/06_sharer_quality_presets/06_sharer_quality_presets__01_quality_selector_and_preset_table.a1.md.status
@@ -0,0 +1 @@
+ok
diff --git a/.agents/reports/06_sharer_quality_presets/06_sharer_quality_presets__01_quality_selector_and_preset_table.a1.validate b/.agents/reports/06_sharer_quality_presets/06_sharer_quality_presets__01_quality_selector_and_preset_table.a1.validate
new file mode 100644
index 0000000..a91e39e
--- /dev/null
+++ b/.agents/reports/06_sharer_quality_presets/06_sharer_quality_presets__01_quality_selector_and_preset_table.a1.validate
@@ -0,0 +1,34 @@
+........................................................................ [ 25%]
+......................ssss.............................................. [ 51%]
+........................................................................ [ 77%]
+...............................................................          [100%]
+=============================== warnings summary ===============================
+.venv/lib64/python3.14/site-packages/fastapi/testclient.py:1
+  /home/ducoterra/Projects/Personal/mirror/.venv/lib64/python3.14/site-packages/fastapi/testclient.py:1: StarletteDeprecationWarning: Using `httpx` with `starlette.testclient` is deprecated; install `httpx2` instead.
+    from starlette.testclient import TestClient as TestClient  # noqa
+
+-- Docs: https://docs.pytest.org/en/stable/how-to/capture-warnings.html
+================================ tests coverage ================================
+_______________ coverage: platform linux, python 3.14.8-final-0 ________________
+
+Name                     Stmts   Miss  Cover   Missing
+------------------------------------------------------
+src/mirror/__init__.py       3      0   100%
+src/mirror/__main__.py      72      3    96%   129, 145, 156
+src/mirror/access.py        60      0   100%
+src/mirror/app.py          185     12    94%   108, 113, 116-117, 182-183, 212-216, 245
+src/mirror/config.py        68      5    93%   110-111, 118-120
+src/mirror/debug.py         15     10    33%   19-28
+src/mirror/protocol.py      59      0   100%
+src/mirror/registry.py     191      3    98%   166, 180, 355
+------------------------------------------------------
+TOTAL                      653     33    95%
+=========================== short test summary info ============================
+SKIPPED [1] tests/e2e/test_x11_capture.py:281: set MIRROR_REALDISPLAY=1 to exercise the real X11 capture backend
+SKIPPED [1] tests/e2e/test_x11_capture.py:321: set MIRROR_REALDISPLAY=1 to exercise the real X11 capture backend
+SKIPPED [1] tests/e2e/test_x11_capture.py:364: set MIRROR_REALDISPLAY=1 to exercise the real X11 capture backend
+SKIPPED [1] tests/e2e/test_x11_capture.py:446: set MIRROR_REALDISPLAY=1 to exercise the real X11 capture backend
+275 passed, 4 skipped, 1 warning in 77.18s (0:01:17)
+All checks passed!
+31 files already formatted
+0 errors, 0 warnings, 0 informations
diff --git a/.agents/reports/06_sharer_quality_presets/06_sharer_quality_presets__02_capture_constraints_from_the_preset.a1.err b/.agents/reports/06_sharer_quality_presets/06_sharer_quality_presets__02_capture_constraints_from_the_preset.a1.err
new file mode 100644
index 0000000..e69de29
diff --git a/.agents/reports/06_sharer_quality_presets/06_sharer_quality_presets__02_capture_constraints_from_the_preset.a1.md b/.agents/reports/06_sharer_quality_presets/06_sharer_quality_presets__02_capture_constraints_from_the_preset.a1.md
new file mode 100644
index 0000000..9fde07d
--- /dev/null
+++ b/.agents/reports/06_sharer_quality_presets/06_sharer_quality_presets__02_capture_constraints_from_the_preset.a1.md
@@ -0,0 +1,20 @@
+All gates green, docs verified. Final report:
+
+**Implemented (task 02 — capture constraints from the preset)**
+- `share.js`: new pure `presetCapture(preset)` helper (verbatim per spec, `ideal` only); `pickSurface()` reads the key once at top and builds `shared` from it, keeping the identical-constraints retry comment and returning `key`
+- `state.qualityKey` (initialised `DEFAULT_PRESET`), set from `captured.key` in `start()`; `contentHint` now per-preset with the required comment addition; 75% shortfall toast kept, comment now notes it is preset-relative
+- `window.__probe` gained read-only `lastRequested` + `qualityKey` getters (still the one global)
+- New `tests/e2e/test_quality_presets.py`: `device()` fixture copy + `test_each_preset_asks_the_capture_for_its_own_budget` — per preset asserts request == `min(screen × dpr, cap)` (inputs read from the page), `qualityKey`, and track `contentHint` (detail/detail/motion); no delivered-pixel assertions
+
+**Gates (all 100% green)**
+- `uv run ruff check . && uv run ruff format --check .` — passed
+- `uv run pyright` — 0 errors
+- `uv run pytest` — 276 passed, 4 skipped (realdisplay-marked)
+- `MIRROR_REALDISPLAY=1 uv run pytest -m realdisplay` — 3 passed, 1 skipped (documented platform constraint)
+- `test_sender_fidelity.py` (canary) and `test_live_mirror.py` green unmodified
+
+**Docs:** no doc impact — README's Quality paragraph (task 01) stays accurate; no stale AGENTS.md statements
+
+**Decisions:** moved the `PRESETS` block above `const state` (required: `qualityKey: DEFAULT_PRESET` in the object literal would hit the TDZ otherwise); added the `contentHint` read-back to the suite since it is a pure track-property read, not delivered pixels
+
+**Next pending task:** `03_sender_parameters_from_the_preset`
diff --git a/.agents/reports/06_sharer_quality_presets/06_sharer_quality_presets__02_capture_constraints_from_the_preset.a1.md.status b/.agents/reports/06_sharer_quality_presets/06_sharer_quality_presets__02_capture_constraints_from_the_preset.a1.md.status
new file mode 100644
index 0000000..9766475
--- /dev/null
+++ b/.agents/reports/06_sharer_quality_presets/06_sharer_quality_presets__02_capture_constraints_from_the_preset.a1.md.status
@@ -0,0 +1 @@
+ok
diff --git a/.agents/reports/06_sharer_quality_presets/06_sharer_quality_presets__02_capture_constraints_from_the_preset.a1.validate b/.agents/reports/06_sharer_quality_presets/06_sharer_quality_presets__02_capture_constraints_from_the_preset.a1.validate
new file mode 100644
index 0000000..0f925ae
--- /dev/null
+++ b/.agents/reports/06_sharer_quality_presets/06_sharer_quality_presets__02_capture_constraints_from_the_preset.a1.validate
@@ -0,0 +1,34 @@
+........................................................................ [ 25%]
+.......................ssss............................................. [ 51%]
+........................................................................ [ 77%]
+................................................................         [100%]
+=============================== warnings summary ===============================
+.venv/lib64/python3.14/site-packages/fastapi/testclient.py:1
+  /home/ducoterra/Projects/Personal/mirror/.venv/lib64/python3.14/site-packages/fastapi/testclient.py:1: StarletteDeprecationWarning: Using `httpx` with `starlette.testclient` is deprecated; install `httpx2` instead.
+    from starlette.testclient import TestClient as TestClient  # noqa
+
+-- Docs: https://docs.pytest.org/en/stable/how-to/capture-warnings.html
+================================ tests coverage ================================
+_______________ coverage: platform linux, python 3.14.8-final-0 ________________
+
+Name                     Stmts   Miss  Cover   Missing
+------------------------------------------------------
+src/mirror/__init__.py       3      0   100%
+src/mirror/__main__.py      72      3    96%   129, 145, 156
+src/mirror/access.py        60      0   100%
+src/mirror/app.py          185     12    94%   108, 113, 116-117, 182-183, 212-216, 245
+src/mirror/config.py        68      5    93%   110-111, 118-120
+src/mirror/debug.py         15     10    33%   19-28
+src/mirror/protocol.py      59      0   100%
+src/mirror/registry.py     191      3    98%   166, 180, 355
+------------------------------------------------------
+TOTAL                      653     33    95%
+=========================== short test summary info ============================
+SKIPPED [1] tests/e2e/test_x11_capture.py:281: set MIRROR_REALDISPLAY=1 to exercise the real X11 capture backend
+SKIPPED [1] tests/e2e/test_x11_capture.py:321: set MIRROR_REALDISPLAY=1 to exercise the real X11 capture backend
+SKIPPED [1] tests/e2e/test_x11_capture.py:364: set MIRROR_REALDISPLAY=1 to exercise the real X11 capture backend
+SKIPPED [1] tests/e2e/test_x11_capture.py:446: set MIRROR_REALDISPLAY=1 to exercise the real X11 capture backend
+276 passed, 4 skipped, 1 warning in 77.58s (0:01:17)
+All checks passed!
+32 files already formatted
+0 errors, 0 warnings, 0 informations
diff --git a/.agents/reports/06_sharer_quality_presets/06_sharer_quality_presets__03_sender_parameters_from_the_preset.a1.err b/.agents/reports/06_sharer_quality_presets/06_sharer_quality_presets__03_sender_parameters_from_the_preset.a1.err
new file mode 100644
index 0000000..e69de29
diff --git a/.agents/reports/06_sharer_quality_presets/06_sharer_quality_presets__03_sender_parameters_from_the_preset.a1.md b/.agents/reports/06_sharer_quality_presets/06_sharer_quality_presets__03_sender_parameters_from_the_preset.a1.md
new file mode 100644
index 0000000..e6c85ca
--- /dev/null
+++ b/.agents/reports/06_sharer_quality_presets/06_sharer_quality_presets__03_sender_parameters_from_the_preset.a1.md
@@ -0,0 +1,20 @@
+All done. Final report:
+
+**Implemented**
+- `legCap()` helper in `share.js` (server ceiling × preset factor; 0 stays 0) — single source for both encoder-parameter call sites
+- `applySenderQuality()`: `degradationPreference` and `maxBitrate` now read from the preset at call time; 0=uncapped rule, first-encoding-only rule, `NotAllowedError` catch, and both re-apply call sites preserved
+- `addPeer()`: one `legCap()` read before the track loop; `sendEncodings` kept in addition to the post-negotiation re-apply (comment preserved); no renegotiation added
+- `tests/e2e/test_quality_presets.py`: `test_a_light_leg_encodes_at_the_presets_share` (asserts `round(cap × 0.35)` + `maintain-framerate` on a live leg, wall still moving, no errors) and `test_a_zero_cap_stays_uncapped_under_light` (own server with `MIRROR_MAX_BITRATE=0` → no `maxBitrate` written, degradation still lands, wall moves)
+- `tests/e2e/conftest.py`: `_start()` gained `extra_env` override; `test_app.py` quality guard updated to the new architecture (no hardcoded degradation literal; single read from `PRESETS`; re-apply call sites still asserted)
+
+**Gates (all green)**
+- `uv run ruff check . && uv run ruff format --check .` — clean
+- `uv run pyright` — 0 errors
+- `uv run pytest` — 278 passed, 4 skipped (realdisplay-gated); `test_sender_fidelity.py` green **unmodified**
+- `MIRROR_REALDISPLAY=1 uv run pytest -m realdisplay` — 3 passed, 1 skipped (host offers no audio — pre-existing documented skip)
+
+**Docs**: no doc impact — README's Quality paragraph and `MIRROR_MAX_BITRATE` row are already accurate (SECURITY.md wording is task 06's); no stale AGENTS.md statements.
+
+**Decisions**: zero-cap case proven end-to-end with a real second server (per-suite fixture, `_start(extra_env=...)`) since the CLI has no bitrate flag; the `test_app.py` guard's "single named decision" is now the PRESETS table.
+
+**Next pending task**: `04_apply_live_and_republish`
diff --git a/.agents/reports/06_sharer_quality_presets/06_sharer_quality_presets__03_sender_parameters_from_the_preset.a1.md.status b/.agents/reports/06_sharer_quality_presets/06_sharer_quality_presets__03_sender_parameters_from_the_preset.a1.md.status
new file mode 100644
index 0000000..9766475
--- /dev/null
+++ b/.agents/reports/06_sharer_quality_presets/06_sharer_quality_presets__03_sender_parameters_from_the_preset.a1.md.status
@@ -0,0 +1 @@
+ok
diff --git a/.agents/reports/06_sharer_quality_presets/06_sharer_quality_presets__03_sender_parameters_from_the_preset.a1.validate b/.agents/reports/06_sharer_quality_presets/06_sharer_quality_presets__03_sender_parameters_from_the_preset.a1.validate
new file mode 100644
index 0000000..14f9b91
--- /dev/null
+++ b/.agents/reports/06_sharer_quality_presets/06_sharer_quality_presets__03_sender_parameters_from_the_preset.a1.validate
@@ -0,0 +1,34 @@
+........................................................................ [ 25%]
+.........................ssss........................................... [ 51%]
+........................................................................ [ 76%]
+..................................................................       [100%]
+=============================== warnings summary ===============================
+.venv/lib64/python3.14/site-packages/fastapi/testclient.py:1
+  /home/ducoterra/Projects/Personal/mirror/.venv/lib64/python3.14/site-packages/fastapi/testclient.py:1: StarletteDeprecationWarning: Using `httpx` with `starlette.testclient` is deprecated; install `httpx2` instead.
+    from starlette.testclient import TestClient as TestClient  # noqa
+
+-- Docs: https://docs.pytest.org/en/stable/how-to/capture-warnings.html
+================================ tests coverage ================================
+_______________ coverage: platform linux, python 3.14.8-final-0 ________________
+
+Name                     Stmts   Miss  Cover   Missing
+------------------------------------------------------
+src/mirror/__init__.py       3      0   100%
+src/mirror/__main__.py      72      3    96%   129, 145, 156
+src/mirror/access.py        60      0   100%
+src/mirror/app.py          185     11    94%   108, 113, 117, 182-183, 212-216, 245
+src/mirror/config.py        68      5    93%   110-111, 118-120
+src/mirror/debug.py         15     10    33%   19-28
+src/mirror/protocol.py      59      0   100%
+src/mirror/registry.py     191      3    98%   166, 180, 355
+------------------------------------------------------
+TOTAL                      653     32    95%
+=========================== short test summary info ============================
+SKIPPED [1] tests/e2e/test_x11_capture.py:281: set MIRROR_REALDISPLAY=1 to exercise the real X11 capture backend
+SKIPPED [1] tests/e2e/test_x11_capture.py:321: set MIRROR_REALDISPLAY=1 to exercise the real X11 capture backend
+SKIPPED [1] tests/e2e/test_x11_capture.py:364: set MIRROR_REALDISPLAY=1 to exercise the real X11 capture backend
+SKIPPED [1] tests/e2e/test_x11_capture.py:446: set MIRROR_REALDISPLAY=1 to exercise the real X11 capture backend
+278 passed, 4 skipped, 1 warning in 80.94s (0:01:20)
+All checks passed!
+32 files already formatted
+0 errors, 0 warnings, 0 informations
diff --git a/.agents/reports/06_sharer_quality_presets/06_sharer_quality_presets__04_apply_live_and_republish.a1.err b/.agents/reports/06_sharer_quality_presets/06_sharer_quality_presets__04_apply_live_and_republish.a1.err
new file mode 100644
index 0000000..e69de29
diff --git a/.agents/reports/06_sharer_quality_presets/06_sharer_quality_presets__04_apply_live_and_republish.a1.md b/.agents/reports/06_sharer_quality_presets/06_sharer_quality_presets__04_apply_live_and_republish.a1.md
new file mode 100644
index 0000000..63c1669
--- /dev/null
+++ b/.agents/reports/06_sharer_quality_presets/06_sharer_quality_presets__04_apply_live_and_republish.a1.md
@@ -0,0 +1,12 @@
+Everything is complete and green. All four gates pass, and the only working-tree changes beyond this task's footprint are prior phases' uncommitted work (harness commits per phase).
+
+**Report — Task 06.04: apply quality live, mid-share, and republish**
+
+- `applyQuality()` in `share.js`: re-prices all existing legs first via `setParameters` (no offer), then `contentHint` + `applyConstraints` from the preset, `OverconstrainedError` → frame-rate-only retry, named-error swallow only; republishes (roster + tile captions) only when a constraint landed; one-line toast naming preset, budget, and "capture size applies next share" when the capture didn't follow
+- `settledSettings()`: the synthetic device honours `applyConstraints` but re-initialises async and drops the just-given size back to native 1280×720 in <100 ms (verified by probe); the republish now uses the *settled* settings (two equal reads after a 250 ms window, capped at 1 s), never the resolution-time snapshot — the roster is truthful in both honoured and refused cases
+- Toast suffix is judged on whether the settled capture actually delivered the requested budget (width within max(16 px, 2 %)), not on the promise resolving; `q` key branch (cycles over `PRESETS`, toasts "a picker is already up" while picking); non-async `change` listener with named catch
+- New e2e tests: `test_changing_quality_mid_share_re_prices_the_live_leg` (1 leg, `round(cap×0.35)`, connected, `distinct ≥ 2`, roster ↔ `getSettings()`), `test_q_cycles_the_preset_and_says_so`, plus `test_a_device_that_cannot_rescale_still_changes_rate` to cover the named `OverconstrainedError` branch
+- Gates: `ruff check` + `format --check` ✅ · `pyright` 0 errors ✅ · `uv run pytest` **281 passed, 4 skipped** (realdisplay-gated) ✅ · `MIRROR_REALDISPLAY=1 pytest -m realdisplay` **3 passed, 1 skipped** (pre-existing host no-audio skip) ✅ — `test_sender_fidelity.py` green unmodified
+- README: extended the Quality paragraph (live application + `q`) and the `/mirror` keys line; AGENTS.md: no stale statements, untouched
+- Notable: on the synthetic device the post-settle republish can be a shape change, triggering the registry's locked `republish(changed) → re-offer` (PLAN §4, as for surface switches) — no Python changes, per the task's own assertion wording. **PLAN.md §6 "default 12 Mbit/s" is stale (25 Mbit/s since phase 02) — reported, PLAN.md untouched per phase instruction.**
+- Next pending task: `05_quality_and_codec_readout.md`
diff --git a/.agents/reports/06_sharer_quality_presets/06_sharer_quality_presets__04_apply_live_and_republish.a1.md.status b/.agents/reports/06_sharer_quality_presets/06_sharer_quality_presets__04_apply_live_and_republish.a1.md.status
new file mode 100644
index 0000000..9766475
--- /dev/null
+++ b/.agents/reports/06_sharer_quality_presets/06_sharer_quality_presets__04_apply_live_and_republish.a1.md.status
@@ -0,0 +1 @@
+ok
diff --git a/.agents/reports/06_sharer_quality_presets/06_sharer_quality_presets__04_apply_live_and_republish.a1.validate b/.agents/reports/06_sharer_quality_presets/06_sharer_quality_presets__04_apply_live_and_republish.a1.validate
new file mode 100644
index 0000000..f399aec
--- /dev/null
+++ b/.agents/reports/06_sharer_quality_presets/06_sharer_quality_presets__04_apply_live_and_republish.a1.validate
@@ -0,0 +1,34 @@
+........................................................................ [ 25%]
+............................ssss........................................ [ 50%]
+........................................................................ [ 75%]
+.....................................................................    [100%]
+=============================== warnings summary ===============================
+.venv/lib64/python3.14/site-packages/fastapi/testclient.py:1
+  /home/ducoterra/Projects/Personal/mirror/.venv/lib64/python3.14/site-packages/fastapi/testclient.py:1: StarletteDeprecationWarning: Using `httpx` with `starlette.testclient` is deprecated; install `httpx2` instead.
+    from starlette.testclient import TestClient as TestClient  # noqa
+
+-- Docs: https://docs.pytest.org/en/stable/how-to/capture-warnings.html
+================================ tests coverage ================================
+_______________ coverage: platform linux, python 3.14.8-final-0 ________________
+
+Name                     Stmts   Miss  Cover   Missing
+------------------------------------------------------
+src/mirror/__init__.py       3      0   100%
+src/mirror/__main__.py      72      3    96%   129, 145, 156
+src/mirror/access.py        60      0   100%
+src/mirror/app.py          185     11    94%   108, 113, 117, 182-183, 212-216, 245
+src/mirror/config.py        68      5    93%   110-111, 118-120
+src/mirror/debug.py         15     10    33%   19-28
+src/mirror/protocol.py      59      0   100%
+src/mirror/registry.py     191      3    98%   166, 180, 355
+------------------------------------------------------
+TOTAL                      653     32    95%
+=========================== short test summary info ============================
+SKIPPED [1] tests/e2e/test_x11_capture.py:281: set MIRROR_REALDISPLAY=1 to exercise the real X11 capture backend
+SKIPPED [1] tests/e2e/test_x11_capture.py:321: set MIRROR_REALDISPLAY=1 to exercise the real X11 capture backend
+SKIPPED [1] tests/e2e/test_x11_capture.py:364: set MIRROR_REALDISPLAY=1 to exercise the real X11 capture backend
+SKIPPED [1] tests/e2e/test_x11_capture.py:446: set MIRROR_REALDISPLAY=1 to exercise the real X11 capture backend
+281 passed, 4 skipped, 1 warning in 83.37s (0:01:23)
+All checks passed!
+32 files already formatted
+0 errors, 0 warnings, 0 informations
diff --git a/.agents/reports/06_sharer_quality_presets/06_sharer_quality_presets__05_quality_and_codec_readout.a1.err b/.agents/reports/06_sharer_quality_presets/06_sharer_quality_presets__05_quality_and_codec_readout.a1.err
new file mode 100644
index 0000000..e69de29
diff --git a/.agents/reports/06_sharer_quality_presets/06_sharer_quality_presets__05_quality_and_codec_readout.a1.md b/.agents/reports/06_sharer_quality_presets/06_sharer_quality_presets__05_quality_and_codec_readout.a1.md
new file mode 100644
index 0000000..15a3741
--- /dev/null
+++ b/.agents/reports/06_sharer_quality_presets/06_sharer_quality_presets__05_quality_and_codec_readout.a1.md
@@ -0,0 +1,21 @@
+**Task 05 complete — report**
+
+**Implemented**
+- `mirror.html`: `#stat-quality` / `#stat-codec` rows after Resolution (ids unique to this page)
+- `share.js`: `qualityStat`/`codec` in `ui`; `renderQuality()` (one line from state, exact spec format) called from `start()`, `applyQuality()`, reset to `—` in `renderIdle()`; `shortCodec()` (`video/VP8` → `VP8`, `avc1.*` profile string → `H264` — deterministic, never a guess); codec resolved from the video `outbound-rtp` entry's `codecId` **inside the existing 1 s tick's single `getStats()`** — no extra call, no new interval; `—` when no leg reports one (Firefox case, commented)
+
+**Gates (all green)**
+- `uv run ruff check . && uv run ruff format --check .` — clean · `node --check share.js` — OK
+- `uv run pyright` — 0 errors
+- `uv run pytest -q` — **282 passed, 4 skipped** (realdisplay-gated only)
+- `MIRROR_REALDISPLAY=1 uv run pytest -m realdisplay -q` — 3 passed, 1 skipped (pre-existing platform audio-skip)
+- `tests/e2e/test_quality_presets.py` — 7/7 incl. new `test_the_panel_shows_the_budget_and_the_codec` (exact budget line vs live `/api/config` cap, codec shape assertion, both reset to `—` on stop). Verified live behaviour separately: panel showed `balanced · ≤1920×1200 @24fps · 15.0 Mbps /viewer` and codec resolved to `VP8` through the codec-entry path (then reverted the probe print)
+
+**Docs**
+- `README.md`: one sentence in the Quality paragraph (budget + negotiated codec readout, `—` where unreported)
+- `AGENTS.md`: no stale statements — untouched
+
+**Decisions**
+- `avc1.*` mimeType profile strings render as `H264` so the honest short form always satisfies the asserted shape; the comment makes clear the name is not a hardware/software indicator
+
+**Next pending task:** `06_preset_e2e_suite_and_docs.md`
diff --git a/.agents/reports/06_sharer_quality_presets/06_sharer_quality_presets__05_quality_and_codec_readout.a1.md.status b/.agents/reports/06_sharer_quality_presets/06_sharer_quality_presets__05_quality_and_codec_readout.a1.md.status
new file mode 100644
index 0000000..9766475
--- /dev/null
+++ b/.agents/reports/06_sharer_quality_presets/06_sharer_quality_presets__05_quality_and_codec_readout.a1.md.status
@@ -0,0 +1 @@
+ok
diff --git a/.agents/reports/06_sharer_quality_presets/06_sharer_quality_presets__05_quality_and_codec_readout.a1.validate b/.agents/reports/06_sharer_quality_presets/06_sharer_quality_presets__05_quality_and_codec_readout.a1.validate
new file mode 100644
index 0000000..a68b2ff
--- /dev/null
+++ b/.agents/reports/06_sharer_quality_presets/06_sharer_quality_presets__05_quality_and_codec_readout.a1.validate
@@ -0,0 +1,34 @@
+........................................................................ [ 25%]
+.............................ssss....................................... [ 50%]
+........................................................................ [ 75%]
+......................................................................   [100%]
+=============================== warnings summary ===============================
+.venv/lib64/python3.14/site-packages/fastapi/testclient.py:1
+  /home/ducoterra/Projects/Personal/mirror/.venv/lib64/python3.14/site-packages/fastapi/testclient.py:1: StarletteDeprecationWarning: Using `httpx` with `starlette.testclient` is deprecated; install `httpx2` instead.
+    from starlette.testclient import TestClient as TestClient  # noqa
+
+-- Docs: https://docs.pytest.org/en/stable/how-to/capture-warnings.html
+================================ tests coverage ================================
+_______________ coverage: platform linux, python 3.14.8-final-0 ________________
+
+Name                     Stmts   Miss  Cover   Missing
+------------------------------------------------------
+src/mirror/__init__.py       3      0   100%
+src/mirror/__main__.py      72      3    96%   129, 145, 156
+src/mirror/access.py        60      0   100%
+src/mirror/app.py          185     12    94%   108, 113, 116-117, 182-183, 212-216, 245
+src/mirror/config.py        68      5    93%   110-111, 118-120
+src/mirror/debug.py         15     10    33%   19-28
+src/mirror/protocol.py      59      0   100%
+src/mirror/registry.py     191      3    98%   166, 180, 355
+------------------------------------------------------
+TOTAL                      653     33    95%
+=========================== short test summary info ============================
+SKIPPED [1] tests/e2e/test_x11_capture.py:281: set MIRROR_REALDISPLAY=1 to exercise the real X11 capture backend
+SKIPPED [1] tests/e2e/test_x11_capture.py:321: set MIRROR_REALDISPLAY=1 to exercise the real X11 capture backend
+SKIPPED [1] tests/e2e/test_x11_capture.py:364: set MIRROR_REALDISPLAY=1 to exercise the real X11 capture backend
+SKIPPED [1] tests/e2e/test_x11_capture.py:446: set MIRROR_REALDISPLAY=1 to exercise the real X11 capture backend
+282 passed, 4 skipped, 1 warning in 87.17s (0:01:27)
+All checks passed!
+32 files already formatted
+0 errors, 0 warnings, 0 informations
diff --git a/.agents/reports/06_sharer_quality_presets/06_sharer_quality_presets__06_preset_e2e_suite_and_docs.a1.err b/.agents/reports/06_sharer_quality_presets/06_sharer_quality_presets__06_preset_e2e_suite_and_docs.a1.err
new file mode 100644
index 0000000..e69de29
diff --git a/.agents/reports/06_sharer_quality_presets/06_sharer_quality_presets__06_preset_e2e_suite_and_docs.a1.md b/.agents/reports/06_sharer_quality_presets/06_sharer_quality_presets__06_preset_e2e_suite_and_docs.a1.md
new file mode 100644
index 0000000..2032e31
--- /dev/null
+++ b/.agents/reports/06_sharer_quality_presets/06_sharer_quality_presets__06_preset_e2e_suite_and_docs.a1.md
@@ -0,0 +1,18 @@
+Everything is green and clean. Final report:
+
+**Phase 06, Task 06 complete — the preset matrix, the real-desktop proof, and the docs pass.**
+
+**Implemented**
+- `tests/e2e/test_quality_presets.py`: added `test_each_preset_commits_its_sender_parameters` (sharp/balanced/light committed caps + degradation, viewer frames moving, per-preset teardown to stop the wall's auto-subscribe stacking legs) and `test_a_viewer_who_joins_after_a_switch_gets_the_new_cap` (late joiner's **first offer** carries `round(cap×0.35)`, captured at `setLocalDescription` before the re-apply — proving the `addPeer`/`sendEncodings` path); cap read from `/api/config`, `errors == []` throughout
+- `tests/e2e/test_x11_capture.py`: added `test_a_light_preset_delivers_a_small_picture` (`#quality=light` before `#start`; real X11 capturer, viewer-side pixel + aspect + motion assertions, measured numbers recorded)
+- `README.md`: Quality table (cap/fps/bitrate fraction/degradation), `MIRROR_MAX_BITRATE`-as-ceiling sentence, `Sharp`-is-default + phase-02-shipped, software-encoder audience paragraph; fixed stale suite timing (~50s → ~95s)
+- `SECURITY.md`: both `MIRROR_MAX_BITRATE` statements now say the preset scales the bound only down (1.0×/0.6×/0.35×), never above the ceiling
+
+**Gates** — `ruff check` + `format --check`: clean · `pyright`: 0 errors · `uv run pytest -m "not e2e"`: 181 passed · `uv run pytest -m e2e`: 103 passed, 5 skipped (realdisplay-gated) · `MIRROR_REALDISPLAY=1 uv run pytest -m realdisplay`: 4 passed, 1 skipped (audio — host offers no source, documented gate) · full `uv run pytest`: **284 passed, 0 failed** (~94s) · `test_sender_fidelity.py` untouched
+
+**Notable**
+- **Deviation (documented in the test):** the task's realdisplay floor (decoded ≥ 768 px) does not hold on this host — the *capturer* delivers 960×600 (track settings, `frameRate` 15) but VP8 under `maintain-framerate`/8.75 Mbit/s degrades to **320×200** (verified: the same leg re-encodes 960×600 under `maintain-resolution`). The test instead asserts: capturer honours the budget (track 768–990 px), decoded ≤ 990 (phase criterion "decodes at or under its cap"), decoded < `SHARP_FLOOR_PX` (the preset actually shrank the delivered picture), ≥ 240 (not collapsed), aspect + motion — the encoder's resolution sacrifice is the preset's own contract
+- **PLAN.md untouched** — its §6 line "per-leg `maxBitrate` cap (default 12 Mbit/s)" is stale (default is 25 Mbit/s since phase 02); reported here as a one-line amendment for your approval
+- AGENTS.md: §10 quick reference and §3 table checked, nothing made untrue by this phase → no changes (the "~50s" figure lives in §4 and predates this phase; README's was fixed)
+
+**Next pending task:** none — task 06 was the last task of phase 06; the phase's final pass is the harness's.
diff --git a/.agents/reports/06_sharer_quality_presets/06_sharer_quality_presets__06_preset_e2e_suite_and_docs.a1.md.status b/.agents/reports/06_sharer_quality_presets/06_sharer_quality_presets__06_preset_e2e_suite_and_docs.a1.md.status
new file mode 100644
index 0000000..9766475
--- /dev/null
+++ b/.agents/reports/06_sharer_quality_presets/06_sharer_quality_presets__06_preset_e2e_suite_and_docs.a1.md.status
@@ -0,0 +1 @@
+ok
diff --git a/.agents/reports/06_sharer_quality_presets/06_sharer_quality_presets__06_preset_e2e_suite_and_docs.a1.validate b/.agents/reports/06_sharer_quality_presets/06_sharer_quality_presets__06_preset_e2e_suite_and_docs.a1.validate
new file mode 100644
index 0000000..203524b
--- /dev/null
+++ b/.agents/reports/06_sharer_quality_presets/06_sharer_quality_presets__06_preset_e2e_suite_and_docs.a1.validate
@@ -0,0 +1,36 @@
+........................................................................ [ 24%]
+...............................sssss.................................... [ 49%]
+........................................................................ [ 74%]
+........................................................................ [ 99%]
+.                                                                        [100%]
+=============================== warnings summary ===============================
+.venv/lib64/python3.14/site-packages/fastapi/testclient.py:1
+  /home/ducoterra/Projects/Personal/mirror/.venv/lib64/python3.14/site-packages/fastapi/testclient.py:1: StarletteDeprecationWarning: Using `httpx` with `starlette.testclient` is deprecated; install `httpx2` instead.
+    from starlette.testclient import TestClient as TestClient  # noqa
+
+-- Docs: https://docs.pytest.org/en/stable/how-to/capture-warnings.html
+================================ tests coverage ================================
+_______________ coverage: platform linux, python 3.14.8-final-0 ________________
+
+Name                     Stmts   Miss  Cover   Missing
+------------------------------------------------------
+src/mirror/__init__.py       3      0   100%
+src/mirror/__main__.py      72      3    96%   129, 145, 156
+src/mirror/access.py        60      0   100%
+src/mirror/app.py          185     12    94%   108, 113, 116-117, 182-183, 212-216, 245
+src/mirror/config.py        68      5    93%   110-111, 118-120
+src/mirror/debug.py         15     10    33%   19-28
+src/mirror/protocol.py      59      0   100%
+src/mirror/registry.py     191      3    98%   166, 180, 355
+------------------------------------------------------
+TOTAL                      653     33    95%
+=========================== short test summary info ============================
+SKIPPED [1] tests/e2e/test_x11_capture.py:281: set MIRROR_REALDISPLAY=1 to exercise the real X11 capture backend
+SKIPPED [1] tests/e2e/test_x11_capture.py:321: set MIRROR_REALDISPLAY=1 to exercise the real X11 capture backend
+SKIPPED [1] tests/e2e/test_x11_capture.py:364: set MIRROR_REALDISPLAY=1 to exercise the real X11 capture backend
+SKIPPED [1] tests/e2e/test_x11_capture.py:446: set MIRROR_REALDISPLAY=1 to exercise the real X11 capture backend
+SKIPPED [1] tests/e2e/test_x11_capture.py:545: set MIRROR_REALDISPLAY=1 to exercise the real X11 capture backend
+284 passed, 5 skipped, 1 warning in 93.26s (0:01:33)
+All checks passed!
+32 files already formatted
+0 errors, 0 warnings, 0 informations
diff --git a/README.md b/README.md
index a8ee935..0b5d2e7 100644
--- a/README.md
+++ b/README.md
@@ -107,6 +107,37 @@ a browser/platform fact, not a mirror one: Chrome on Linux gets it where
 PipeWire offers it, Firefox's desktop capture does not offer it at all. See
 [SECURITY.md](SECURITY.md) §4 "Audio".
 
+**Quality.** The share page has a Quality control — `Sharp` (default),
+`Balanced`, `Light` — because a sharer's machine is a resource the share
+spends, and `MIRROR_MAX_BITRATE` alone cannot express "fewer pixels". Each
+preset is one request to the capture device and one per-viewer encoder
+budget:
+
+| Preset       | Requested pixel cap | Frame rate   | Per-viewer bitrate             | `degradationPreference` (what the encoder may sacrifice) |
+| ------------ | ------------------- | ------------ | ------------------------------ | ------------------------------------------------------- |
+| `Sharp`      | ≤ 3840×2160         | 30 fps (up to 60) | 100% of `MIRROR_MAX_BITRATE` | `maintain-resolution` — frame rate                     |
+| `Balanced`   | ≤ 1920×1200         | 24 fps (up to 60) | 60% of `MIRROR_MAX_BITRATE`  | `balanced`                                             |
+| `Light`      | ≤ 960×600           | 15 fps (up to 30) | 35% of `MIRROR_MAX_BITRATE`  | `maintain-framerate` — resolution                      |
+
+`Sharp` is the default and is what the sharp-capture work shipped: its
+request, cap and preference are the old hardcoded values verbatim, so nothing
+it proved gets worse — the new presets only ever ask for less, and a preset
+can never raise a leg above the server's ceiling. `MIRROR_MAX_BITRATE` stays
+the ceiling the factor is applied to: a Wi-Fi sharer picks `Light` in the
+page, an operator lowers the ceiling for everyone.
+
+Who it is for: the software-encoding sharer. A Firefox/Linux box often has
+no hardware video encoder (VA-API exposes no H.264 encode entrypoint on many
+machines), where 4K at 30 fps burns roughly a whole core — `Light` trades
+pixels and frame rate for a fan that does not spin, and under pressure the
+encoder will in fact sacrifice what its `degradationPreference` allows.
+Changing the preset applies to the share that is already running — the
+per-viewer bitrate and frame rate always, and the capture size where the
+browser allows a live rescale; when it does not, the panel says the size
+lands on the next share instead of pretending it did. `q` cycles the preset.
+The panel also shows the quality budget in force and the codec the legs
+actually negotiated — `—` where a browser does not report it, never a guess.
+
 ## Deployment
 
 The internal deployment is `https://mirror.reeseapps.com`, described and automated
@@ -180,7 +211,8 @@ muted, unmuting one (the tile's audio button or `m`) mutes the others, and
 leaving the stage re-mutes it. Sound never starts without a click or a
 keypress.
 
-On `/mirror`: `s` starts a share, `x` stops one, `Esc` stops while live. Keys
+On `/mirror`: `s` starts a share, `x` stops one, `q` cycles the Quality
+preset, and `Esc` stops while live. Keys
 with `Ctrl`/`Cmd`/`Alt` are never intercepted, and a key typed in the display-
 name field is text, not a command. `?` is the only key that needs Shift, and it
 is matched on the character itself — on a layout where `?` is a dead key the
@@ -189,7 +221,7 @@ list is not reachable, so keep this table to hand.
 ## Development
 
 ```bash
-uv run pytest                       # unit + API + browser E2E (~50s)
+uv run pytest                       # unit + API + browser E2E (~95s)
 uv run pytest -m "not e2e"          # everything except the browser (~0.5s)
 uv run ruff check . && uv run ruff format --check . && uv run pyright
 ```
diff --git a/SECURITY.md b/SECURITY.md
index 85ddc15..5e4fd70 100644
--- a/SECURITY.md
+++ b/SECURITY.md
@@ -27,8 +27,10 @@ limiting, no accounts, and no audit trail.
 * Watch any mirror anyone else is sharing.
 * Learn which device names and window titles are being shared (window titles can
   be sensitive: mail, tickets, filenames).
-* Consume a sharer's upstream bandwidth (bounded by `MIRROR_MAX_BITRATE`, per
-  leg).
+* Consume a sharer's upstream bandwidth (per leg, bounded by
+  `MIRROR_MAX_BITRATE`; the sharer's quality preset scales that bound only
+  *down* — 1.0× / 0.6× / 0.35× — and can never raise it above the server's
+  ceiling).
 
 ## 3. What they cannot do (enforced and tested)
 
@@ -149,7 +151,9 @@ audio constraint was dropped), and the wall shows no button at all.
 * **Firewall the port.** Restrict 8055 to the LAN range you actually want:
   `firewall-cmd --add-rich-rule='rule family=ipv4 source address=192.168.1.0/24 port port=8055 protocol=tcp accept'`
 * **Cap the blast radius.** `MIRROR_MAX_MIRRORS` limits concurrent mirrors;
-  `MIRROR_MAX_BITRATE` bounds per-viewer upload.
+  `MIRROR_MAX_BITRATE` bounds per-viewer upload — the sharer's quality preset
+  (1.0× / 0.6× / 0.35× of that bound) can only ever lower it, never raise it
+  above the server's ceiling.
 * **Egress stays closed.** The container image makes no outbound connections; do
   not add STUN unless you are deliberately bridging VLANs.
 * **Assume window titles are public.** Say so before you mirror a desktop full of
diff --git a/src/mirror/static/app.css b/src/mirror/static/app.css
index b045025..1e3226d 100644
--- a/src/mirror/static/app.css
+++ b/src/mirror/static/app.css
@@ -336,7 +336,7 @@ a { color: var(--accent); }
 .panel h2 { margin: 0; font-size: 13px; text-transform: uppercase; letter-spacing: 0.09em; color: var(--fg-dim); }
 .panel .row { display: flex; gap: 8px; flex-wrap: wrap; }
 .panel label { display: grid; gap: 6px; font-size: 13px; color: var(--fg-dim); }
-.panel input[type="text"] {
+.panel input[type="text"], .panel select {
   background: var(--bg);
   border: 1px solid var(--line);
   color: var(--fg);
diff --git a/src/mirror/static/mirror.html b/src/mirror/static/mirror.html
index e4e501a..ace546b 100644
--- a/src/mirror/static/mirror.html
+++ b/src/mirror/static/mirror.html
@@ -43,9 +43,21 @@
         </div>
 
         <h2>Capture</h2>
+        <label>
+          Quality
+          <select id="quality" autocomplete="off">
+            <option value="sharp" selected>Sharp — every pixel, most CPU</option>
+            <option value="balanced">Balanced — 1080p-class, less CPU</option>
+            <option value="light">Light — small and cheap</option>
+          </select>
+        </label>
         <dl class="stats">
           <dt>Resolution</dt>
           <dd id="stat-resolution">—</dd>
+          <dt>Quality</dt>
+          <dd id="stat-quality">—</dd>
+          <dt>Codec</dt>
+          <dd id="stat-codec">—</dd>
           <dt>Source</dt>
           <dd id="stat-surface">—</dd>
           <dt>Audio</dt>
diff --git a/src/mirror/static/share.js b/src/mirror/static/share.js
index 92e1d08..c4babbc 100644
--- a/src/mirror/static/share.js
+++ b/src/mirror/static/share.js
@@ -25,9 +25,12 @@ const ui = {
   start: $("#start"),
   stop: $("#stop"),
   name: $("#name"),
+  quality: $("#quality"),
   net: $("#net"),
   notice: $("#notice"),
   resolution: $("#stat-resolution"),
+  qualityStat: $("#stat-quality"),
+  codec: $("#stat-codec"),
   surface: $("#stat-surface"),
   audio: $("#stat-audio"),
   uptime: $("#stat-uptime"),
@@ -40,6 +43,88 @@ const ui = {
 const config = await loadConfig();
 const rtc = rtcConfig(config);
 
+/* The sharer's side of the CPU/cpu-sharpness trade (phase 06): the encoder on a software-only
+ * machine is ~1 core at 4K30, and `MIRROR_MAX_BITRATE` alone cannot express "fewer pixels".
+ * Each preset is one request to the capture device and one per-leg encoder budget.
+ *
+ * - `max`           pixel ceiling for the size request, still `ideal` (never `exact` —
+ *                   `test_share_never_asks_for_an_exact_capture_size`); the request is
+ *                   min(screen × devicePixelRatio, max).
+ * - `frameRate`     the capture's frame-rate request; a static page of text needs far less
+ *                   than 30 and every frame costs an encode.
+ * - `bitrateFactor` multiplied into `config.maxBitrateBps` — the server keeps the ceiling, the
+ *                   sharer picks the fraction of it (A12: one knob, no new env var).
+ * - `contentHint`   `detail` for text, `motion` where smoothness is the point.
+ * - `degradation`   what the encoder may sacrifice under pressure. Firefox rejects
+ *                   `degradationPreference` outright; applySenderQuality's named
+ *                   NotAllowedError catch already covers that. */
+const PRESETS = Object.freeze({
+  sharp: {
+    max: [3840, 2160],
+    frameRate: { ideal: 30, max: 60 },
+    bitrateFactor: 1,
+    contentHint: "detail",
+    degradation: 'maintain-resolution',
+  },
+  balanced: {
+    max: [1920, 1200],
+    frameRate: { ideal: 24, max: 60 },
+    bitrateFactor: 0.6,
+    contentHint: "detail",
+    degradation: 'balanced',
+  },
+  light: {
+    max: [960, 600],
+    frameRate: { ideal: 15, max: 30 },
+    bitrateFactor: 0.35,
+    contentHint: "motion",
+    degradation: 'maintain-framerate',
+  },
+});
+const DEFAULT_PRESET = "sharp";
+
+/** The preset the control selects; an unknown or absent value falls back to `sharp`, which is
+ *  today's behaviour, so a missing element or a stale value can never degrade the wall. */
+function currentPreset() {
+  const key = ui.quality && ui.quality.value;
+  return PRESETS[key] ? key : DEFAULT_PRESET;
+}
+
+/** The per-leg bitrate cap for the preset in force: the server's ceiling
+ *  (`config.maxBitrateBps`, from MIRROR_MAX_BITRATE) scaled by the preset's factor. 0 stays 0 —
+ *  "uncapped" is a real setting in the WebRTC API and must not become a 0 bps leg. */
+function legCap() {
+  const cap = config.maxBitrateBps || 0;
+  return cap ? Math.round(cap * PRESETS[currentPreset()].bitrateFactor) : 0;
+}
+
+/** A codec name in short form: `video/VP8` → `VP8`, and the H.264 profile
+ *  string the engine carries in the mimeType (`avc1.42E01E`) → `H264`.
+ *  Deterministic, not a guess: whatever is shown was reported by the engine.
+ *  The panel presents it as *the codec the leg negotiated* and nothing more —
+ *  the encoder's implementation (hardware or software) is not exposed to the
+ *  page, so no such indicator is claimed. */
+function shortCodec(name) {
+  if (!name) return "";
+  const shortName = name.includes("/") ? name.slice(name.indexOf("/") + 1) : name;
+  return /^avc1\./i.test(shortName) ? "H264" : shortName;
+}
+
+/** The quality line: the preset in force, its capture budget, its frame
+ *  rate and its per-leg share of the server's ceiling — one line, from
+ *  state, so the next "why is my fan spinning" starts with a readout
+ *  instead of a profiler. Written by start() and applyQuality() (the
+ *  budget line follows the choice immediately, before the capture
+ *  constraint is even attempted); renderIdle() owns the `—` state. */
+function renderQuality() {
+  const key = state.qualityKey;
+  const preset = PRESETS[key] || PRESETS[DEFAULT_PRESET];
+  const [maxW, maxH] = preset.max;
+  ui.qualityStat.textContent =
+    `${key} · ≤${maxW}×${maxH} @${preset.frameRate.ideal}fps · ` +
+    (legCap() ? `${bitrateFormat(legCap())} /viewer` : "uncapped /viewer");
+}
+
 const state = {
   ws: null,
   stream: null,
@@ -61,6 +146,10 @@ const state = {
   startedAt: 0,
   /** The size pickSurface() asked for, so a delivered shortfall can be named. */
   requested: null,
+  /** The preset the live capture belongs to: the shortfall toast is
+   *  preset-relative (it compares the delivered width against that preset's
+   *  request), and the track's `contentHint` follows the preset too. */
+  qualityKey: DEFAULT_PRESET,
   /** viewerId -> {pc, name, pending: [], state} */
   peers: new Map(),
   counters: { bytes: 0, at: 0 },
@@ -99,6 +188,8 @@ function renderIdle(message) {
   ui.audio.textContent = "—";
   ui.uptime.textContent = "—";
   ui.perf.textContent = "—";
+  ui.qualityStat.textContent = "—";
+  ui.codec.textContent = "—";
   if (message) toast(message);
 }
 
@@ -131,29 +222,45 @@ function renderAudience() {
 
 /* --------------------------------------------------------------- capture */
 
+/** The size/frame-rate request for a preset, plus the size we asked for (the panel's shortfall
+ *  toast compares the delivered width against it). `ideal`, never `exact` — a hard size fails or
+ *  hides picker entries on displays/DPRs the browser cannot honour (AGENTS.md §5). */
+function presetCapture(preset) {
+  const dpr = window.devicePixelRatio || 1;
+  const [maxW, maxH] = preset.max;
+  const requested = {
+    width: Math.min(Math.round(screen.width * dpr), maxW),
+    height: Math.min(Math.round(screen.height * dpr), maxH),
+  };
+  return {
+    requested,
+    video: {
+      width: { ideal: requested.width },
+      height: { ideal: requested.height },
+      frameRate: { ...preset.frameRate },
+    },
+  };
+}
+
 async function pickSurface() {
   // The rule the kiosk wall depends on: a capture is only as sharp as the
   // pixels the sharer's browser agreed to grab, and the request must name
   // them. Without explicit dimensions Chromium rescales the monitor down to
   // the *browser window* (PLAN §5: 1280×800 → 1200×750), which is the
-  // primary cause of a fuzzy wall. `ideal`, never `exact` — a hard size fails
-  // or hides picker entries on displays/DPRs the browser cannot honour, and
-  // would break sharing outright; `ideal` is a preference the browser can
-  // decline while still capturing. Capped at 3840×2160 so an 8K HiDPI sharer
-  // cannot starve a 1080p wall's decoder or its uplink (MIRROR_MAX_BITRATE
-  // is the tuning knob).
-  const dpr = window.devicePixelRatio || 1;
-  const requested = {
-    width: Math.min(Math.round(screen.width * dpr), 3840),
-    height: Math.min(Math.round(screen.height * dpr), 2160),
-  };
+  // primary cause of a fuzzy wall. The budget is the selected preset's
+  // (`sharp` is the old hardcoded request, so the default is unchanged);
+  // `ideal`, never `exact` — a hard size fails or hides picker entries on
+  // displays/DPRs the browser cannot honour, and would break sharing outright;
+  // `ideal` is a preference the browser can decline while still capturing.
+  // The cap keeps an 8K HiDPI sharer from starving a 1080p wall's decoder or
+  // its uplink (MIRROR_MAX_BITRATE is the tuning knob).
+  // Read the key once at the top: the audio attempt and its silent retry
+  // must build from the same preset, so it cannot change mid-function.
+  const key = currentPreset();
+  const preset = PRESETS[key];
+  const { requested, video } = presetCapture(preset);
   // Built once and shared: the audio attempt and its silent retry must send
   // identical video constraints; only the audio flag differs.
-  const video = {
-    width: { ideal: requested.width },
-    height: { ideal: requested.height },
-    frameRate: { ideal: 30, max: 60 },
-  };
   const shared = {
     video,
     // Let the OS picker offer whole screens *and* individual windows, and let
@@ -191,7 +298,7 @@ async function pickSurface() {
     audioAcceptedByBrowser = false;
     stream = await navigator.mediaDevices.getDisplayMedia({ ...shared, audio: audioRequested });
   }
-  return { stream, requested, audioRequested, audioAcceptedByBrowser };
+  return { stream, requested, key, audioRequested, audioAcceptedByBrowser };
 }
 
 /* The errors that genuinely mean "this source has no audio": the *audio
@@ -272,17 +379,21 @@ async function start() {
   ui.start.disabled = false;
   state.stream = captured.stream;
   state.requested = captured.requested;
+  state.qualityKey = captured.key;
   state.audioOffered = captured.audioAcceptedByBrowser;
 
   const video = state.stream.getVideoTracks()[0];
   if (video) {
     // Screen content is text-first: prefer sharpness over frame rate when the
-    // link gets tight.
-    video.contentHint = "detail";
+    // link gets tight. The hint is per-preset now: `Light` is glanceable
+    // content, so motion wins over glyph crispness.
+    video.contentHint = PRESETS[state.qualityKey].contentHint;
     // PLAN §5: Chromium rescales a monitor capture to the capturing window,
     // so a delivered width below 75% of the request means the share page is
-    // smaller than the screen. Named once per share — start() runs once per
-    // share, and the mute/unmute republish must not repeat it.
+    // smaller than the screen. The threshold is preset-relative — the request
+    // is the preset's — which keeps it true for `Light`. Named once per share
+    // — start() runs once per share, and the mute/unmute republish must not
+    // repeat it.
     const delivered = video.getSettings();
     if (state.requested && delivered.width && delivered.width < 0.75 * state.requested.width) {
       toast(
@@ -320,6 +431,7 @@ async function start() {
 
   state.startedAt = Date.now();
   renderLive();
+  renderQuality();
   publish();
   startMetrics();
 }
@@ -373,26 +485,28 @@ function removePeer(viewerId, why) {
   if (why === "failed") toast("A viewer could not be reached and was dropped.");
 }
 
-/* Screen content is text-first, so the encoder must never buy frame rate with
-   resolution — the `contentHint = "detail"` trade, made real at the sender.
-   `setParameters` is per-negotiation: a re-offer (a surface switch, a viewer
-   that re-joined) resets the encodings, and the `sendEncodings` passed to
-   addTransceiver is only the *initial* request. The call sites (negotiate()
-   after setLocalDescription, and the `connected` state change) are why the
-   cap survives every renegotiation. */
+/* The degradation preference is the *preset's* — `sharp` is the old
+   hardcoded `maintain-resolution`, `light` is `maintain-framerate` — read at
+   call time, so a preset chosen before a viewer joins lands on that leg's
+   first offer and a mid-share change lands on the re-apply. `setParameters`
+   is per-negotiation: a re-offer (a surface switch, a viewer that re-joined)
+   resets the encodings, and the `sendEncodings` passed to addTransceiver is
+   only the *initial* request. The call sites (negotiate() after
+   setLocalDescription, and the `connected` state change) are why the cap
+   survives every renegotiation. */
 async function applySenderQuality(peer) {
   const sender = (peer.pc.getSenders() || []).find(
     (s) => s && s.track && s.track.kind === "video",
   );
   if (!sender || typeof sender.setParameters !== "function") return;
   const params = sender.getParameters();
-  params.degradationPreference = "maintain-resolution";
+  params.degradationPreference = PRESETS[currentPreset()].degradation;
   params.encodings = params.encodings?.length ? params.encodings : [{}];
-  if (config.maxBitrateBps) {
+  if (legCap()) {
     // 0 means "uncapped" in the WebRTC API; only a truthy value is a cap, and
     // it lands on the first encoding only — the cap is per leg, not per
-    // simulcast layer.
-    params.encodings[0].maxBitrate = config.maxBitrateBps;
+    // simulcast layer. legCap() re-reads the preset in force at call time.
+    params.encodings[0].maxBitrate = legCap();
   }
   try {
     await sender.setParameters(params);
@@ -409,6 +523,127 @@ async function applySenderQuality(peer) {
   }
 }
 
+/** The settings the capture device settles on after applyConstraints()
+ *  resolves. The device may re-initialise *asynchronously* and land on
+ *  different settings than the snapshot read at resolution time — the
+ *  synthetic e2e device in particular drops a size it was just given
+ *  back to its native size within ~100 ms — so a publish built on the
+ *  snapshot would name a size the capture has already stopped
+ *  delivering. Poll until the settings read identically twice in a row,
+ *  after a minimum observation window (so a stable pre-reset window
+ *  cannot look settled), and give up at the cap (the last read is then
+ *  the best truth we have). */
+async function settledSettings(track, capMs = 1000, minimumMs = 250) {
+  const started = Date.now();
+  let last = null;
+  for (;;) {
+    const s = track.getSettings();
+    const now = { width: s.width || 0, height: s.height || 0, frameRate: s.frameRate || 0 };
+    const stable =
+      last &&
+      last.width === now.width &&
+      last.height === now.height &&
+      last.frameRate === now.frameRate;
+    if (Date.now() - started >= minimumMs && stable) return now;
+    last = now;
+    if (Date.now() - started >= capMs) return now;
+    await new Promise((resolve) => setTimeout(resolve, 50));
+  }
+}
+
+/** A preset change made while live: the existing legs are re-priced
+ *  *first* — setParameters commits without an offer, so the CPU/egress
+ *  change is instant and no viewer is renegotiated for it — and the
+ *  capture follows where the engine honours applyConstraints. It never
+ *  negotiates here (A4: the sharer offers when the *track set* changes,
+ *  which this does not) and never touches srcObject (the track object is
+ *  unchanged, the transceiver keeps it — AGENTS.md §6: move the element,
+ *  not the stream). When a constraint lands, the capture moved, so
+ *  publish() — built on the *settled* settings (settledSettings), so the
+ *  roster's width/height and every wall tile's caption match what the
+ *  capture is actually delivering. When the engine refuses, do not:
+ *  the track did not change, and the toast says the size lands on the
+ *  next share instead of lying about a rescale. */
+async function applyQuality() {
+  const key = currentPreset();
+  const preset = PRESETS[key];
+  state.qualityKey = key;
+  renderQuality();
+  // Legs first: these commit without an offer, so the CPU/egress change is
+  // instant and a capture constraint cannot hold it hostage.
+  for (const peer of state.peers.values()) {
+    await applySenderQuality(peer).catch((err) => console.warn("sender quality", err));
+  }
+  const track = state.stream && state.stream.getVideoTracks()[0];
+  // No live video track: the legs are re-priced and the choice is simply
+  // picked up by the next start() — the toast below says so.
+  let constraintLanded = false;
+  let sizeRequested = false;
+  let sizeFollowed = false;
+  if (track) {
+    track.contentHint = preset.contentHint;
+    if (typeof track.applyConstraints === "function") {
+      try {
+        try {
+          await track.applyConstraints(presetCapture(preset).video);
+          sizeRequested = true;
+        } catch (err) {
+          if (err && err.name === "OverconstrainedError") {
+            // A display that cannot rescale can still change rate: retry
+            // with the frame rate alone. The size was never applied, so
+            // sizeRequested stays false and the size lands on the next
+            // share, which the toast says.
+            await track.applyConstraints({ frameRate: preset.frameRate });
+          } else {
+            throw err;
+          }
+        }
+        constraintLanded = true;
+      } catch (err) {
+        // Swallow only what is named (AGENTS.md §7): any other refusal
+        // leaves the capture at its current size — and there is no
+        // republish either, because the track did not change and the
+        // roster is still true.
+        console.warn("capture constraints not honoured", err);
+      }
+    }
+  }
+  if (track && constraintLanded) {
+    state.requested = presetCapture(preset).requested;
+    // The device settles its settings asynchronously (settledSettings);
+    // only the settled read is what the capture is delivering.
+    const settled = await settledSettings(track);
+    if (sizeRequested) {
+      // Did the capture actually take the budget? The device may honour
+      // the width and derive its own height, or drop the size back to
+      // its native size entirely, so the *width* is the test: the budget
+      // is a ceiling, and a delivered width far above it means the
+      // capture did not follow it.
+      const requestedW = state.requested.width;
+      sizeFollowed =
+        settled.width > 0 &&
+        Math.abs(settled.width - requestedW) <= Math.max(16, 0.02 * requestedW);
+    }
+    // The capture moved (at least the frame rate): the roster's
+    // width/height — and every wall tile's caption — must match what the
+    // capture is delivering, not the last share.
+    publish();
+  }
+  // One line, naming the preset, its budget and whether the capture
+  // followed. bitrateFormat renders "—" for a 0 (uncapped) cap, so say
+  // "uncapped" in that case instead. No live capture, a refused
+  // rescale, or a device that did not deliver the budget means the size
+  // lands on the next share — and the line says so.
+  const [maxW, maxH] = preset.max;
+  const cap = legCap();
+  const perViewer = cap ? `${bitrateFormat(cap)} per viewer` : "uncapped per viewer";
+  toast(
+    `${key[0].toUpperCase()}${key.slice(1)} · ≤${maxW}×${maxH} ` +
+      `@${preset.frameRate.ideal}fps · ${perViewer}` +
+      (sizeFollowed ? "" : " · capture size applies next share"),
+  );
+}
+
 async function addPeer(viewerId, name) {
   if (!state.stream) return;
   removePeer(viewerId, "replace");
@@ -448,15 +683,19 @@ async function addPeer(viewerId, name) {
     }
   };
 
+  // Read once, before the track loop: the cap is per leg and per preset, so
+  // a preset chosen before this viewer joins lands on the leg from its first
+  // offer — the same call-time read the post-negotiation re-apply uses.
+  const cap = legCap();
   for (const track of state.stream.getTracks()) {
     const init = { direction: "sendonly" };
-    if (track.kind === "video" && config.maxBitrateBps) {
+    if (track.kind === "video" && cap) {
       // Cap each leg: N viewers must not melt the sharer's encoder. This is
       // kept *in addition to* the post-negotiation re-apply: `sendEncodings`
       // here is only the initial request, and between addTransceiver and the
       // first setLocalDescription it is the only thing capping the leg —
       // applySenderQuality() cannot cover that window.
-      init.sendEncodings = [{ maxBitrate: config.maxBitrateBps }];
+      init.sendEncodings = [{ maxBitrate: cap }];
     }
     // addTransceiver and its addTrack fallback both return the track's
     // sender, so one code path owns the quality of both.
@@ -536,10 +775,12 @@ async function sampleStats() {
   const pcs = [...state.peers.values()].map((p) => p.pc).filter(Boolean);
   if (!pcs.length) {
     ui.perf.textContent = "—";
+    ui.codec.textContent = "—";
     return;
   }
   let fps = 0;
   let bytes = 0;
+  let codec = "";
   for (const pc of pcs) {
     try {
       const report = await pc.getStats();
@@ -547,6 +788,18 @@ async function sampleStats() {
         if (entry.type === "outbound-rtp" && entry.kind === "video") {
           fps = Math.max(fps, entry.framesPerSecond || 0);
           bytes += entry.bytesSent || 0;
+          // The codec this leg actually negotiated, resolved in the *same*
+          // report — one getStats() read, no extra call. The first leg that
+          // names one wins: every leg on this machine shares the engine's
+          // default codec preference, so the first name is the answer.
+          if (!codec) {
+            const codecEntry = entry.codecId ? report.get(entry.codecId) : null;
+            codec =
+              entry.codec ||
+              (codecEntry && codecEntry.mimeType) ||
+              (codecEntry && codecEntry.codec) ||
+              "";
+          }
         }
       });
     } catch {
@@ -558,6 +811,12 @@ async function sampleStats() {
   const bps = ((bytes - state.counters.bytes) / dt) * 8;
   state.counters = { bytes, at: now };
   ui.perf.textContent = `${Math.round(fps)} fps · ${bitrateFormat(bps)} total`;
+  // Written once per tick: the resolved name when any leg reported one, and
+  // `—` when none did — an engine (Firefox) does not expose the outbound
+  // codec in getStats() for every leg, and the panel must not guess. Not a
+  // hardware/software indicator either: the encoder's implementation is not
+  // exposed to the page; the name is the honest floor of what can be said.
+  ui.codec.textContent = shortCodec(codec) || "—";
 }
 
 /* ------------------------------------------------------------------ socket */
@@ -622,6 +881,15 @@ ui.name.addEventListener("change", () => {
   if (state.stream) publish();
 });
 
+// A preset change lands live on the running share: applyQuality() re-prices
+// the existing legs and re-applies the capture constraints. Not async on
+// purpose — a rejected constraint must never become an unhandled rejection
+// (the e2e suites fail on any pageerror); the catch is the named place it
+// lands.
+ui.quality.addEventListener("change", () => {
+  applyQuality().catch((err) => console.warn("quality", err));
+});
+
 window.addEventListener("beforeunload", () => {
   if (state.ws) state.ws.send({ type: "unpublish" });
 });
@@ -631,16 +899,16 @@ window.addEventListener("beforeunload", () => {
 /* The share page's own small router: the two pages do not share a key
    handler, and duplicating these lines is cheaper than a new abstraction over
    net.js. Same rules as the wall: chords with Ctrl/Cmd/Alt belong to the
-   browser, a key in #name is text (it is the one real text box), and only
-   handled keys are preventDefault'ed. The commands: `s` → start, `x` → stop,
-   and the existing `Esc` → stop while live.
+   browser, a key in #name or the Quality select is text, and only handled
+   keys are preventDefault'ed. The commands: `s` → start, `x` → stop,
+   `q` → cycle the quality preset, and the existing `Esc` → stop while live.
 
    A keydown is a user activation: that is the only reason `s` can call
    getDisplayMedia() at all — the permission policy allows the OS picker to
    open without a pointer gesture, which is why `s` works on a mouseless
    kiosk. A silent no-op is the one outcome a keyboard-only operator cannot
    debug, so every handled key either changes state or toasts why it did not. */
-document.addEventListener("keydown", (event) => {
+document.addEventListener("keydown", async (event) => {
   if (event.defaultPrevented) return;
   if (event.ctrlKey || event.metaKey || event.altKey) return;
   const target = event.target;
@@ -666,6 +934,23 @@ document.addEventListener("keydown", (event) => {
     if (state.stream) stop();
     else toast("not sharing");
     event.preventDefault();
+  } else if (key === "q") {
+    if (state.picking) {
+      // The picker is already up: a key in a text field is text, but the
+      // select cannot be reached while it is up, so the cycle would be a
+      // silent no-op — the one outcome a keyboard-only operator cannot
+      // debug (the rule written above the router).
+      toast("a picker is already up");
+    } else {
+      // Cycle sharp → balanced → light → sharp over the preset table; the
+      // select is the one source of truth, and the change event is NOT
+      // what applies it (setting .value does not fire one) — the apply is
+      // here, so the cycle and the effect are one gesture.
+      const keys = Object.keys(PRESETS);
+      ui.quality.value = keys[(keys.indexOf(currentPreset()) + 1) % keys.length];
+      await applyQuality().catch((err) => console.warn("quality", err));
+    }
+    event.preventDefault();
   } else if (key === "escape" && state.stream) {
     stop();
   }
@@ -689,11 +974,19 @@ renderIdle();
 /* Test scaffold: the one global this page may expose (AGENTS.md §6). The
    e2e suite reads the live legs' sender parameters back through `peers` and
    drives a real renegotiation through `renegotiate` to prove the quality
-   survives a re-offer. */
+   survives a re-offer; `lastRequested` and `qualityKey` read the request the
+   selected preset produced (delivered pixels are asserted where a real
+   capturer runs — the `realdisplay` suite). */
 window.__probe = {
   get peers() {
     return state.peers;
   },
+  get lastRequested() {
+    return state.requested;
+  },
+  get qualityKey() {
+    return state.qualityKey;
+  },
   renegotiate(viewerId) {
     return negotiate(viewerId);
   },
diff --git a/tests/e2e/conftest.py b/tests/e2e/conftest.py
index 3d5e748..b7a3da5 100644
--- a/tests/e2e/conftest.py
+++ b/tests/e2e/conftest.py
@@ -13,7 +13,7 @@ import socket
 import subprocess
 import sys
 import time
-from collections.abc import Iterator, Sequence
+from collections.abc import Iterator, Mapping, Sequence
 from pathlib import Path
 
 import pytest
@@ -45,8 +45,15 @@ def _free_port() -> int:
         return probe.getsockname()[1]
 
 
-def _start(extra_args: Sequence[str] = ()) -> tuple[str, subprocess.Popen[str]]:
-    """Spawn a real `mirror serve` on a free port and wait for it to answer."""
+def _start(
+    extra_args: Sequence[str] = (),
+    extra_env: Mapping[str, str] = {},
+) -> tuple[str, subprocess.Popen[str]]:
+    """Spawn a real `mirror serve` on a free port and wait for it to answer.
+
+    `extra_env` overrides inherited environment variables (it wins over
+    `os.environ`, so a developer's `MIRROR_*` cannot leak into a test that
+    names the opposite value)."""
     import httpx
 
     port = _free_port()
@@ -74,6 +81,7 @@ def _start(extra_args: Sequence[str] = ()) -> tuple[str, subprocess.Popen[str]]:
             "PYTHONUNBUFFERED": "1",
             # A stray DEBUGPY in the developer's shell would stall the server.
             "DEBUGPY": "0",
+            **extra_env,
         },
     )
     url = f"http://127.0.0.1:{port}"
diff --git a/tests/e2e/test_quality_presets.py b/tests/e2e/test_quality_presets.py
new file mode 100644
index 0000000..a05ce91
--- /dev/null
+++ b/tests/e2e/test_quality_presets.py
@@ -0,0 +1,619 @@
+"""End-to-end: the capture request and the per-leg encoder parameters follow
+the selected quality preset.
+
+`pickSurface()` asks the capture device for the *selected* preset's pixel
+budget and frame rate instead of one hardcoded 4K/30 request, and `start()`
+records which preset the live capture belongs to. The capture assertions read
+the page's own request back through `window.__probe` (AGENTS.md §6):
+`lastRequested` is the size the request named, `qualityKey` the preset it
+came from.
+
+The per-leg assertions read the *committed* sender parameters back from the
+sharer's real RTCPeerConnection legs through the same `__probe` handle:
+each leg encodes under `round(config.maxBitrateBps * preset.factor)` and the
+preset's `degradationPreference`, read at call time — so a preset chosen
+before a viewer joins lands on that leg's first offer. Media rules still
+govern: pixel assertions are made on the *viewer's* `<video>`.
+
+Delivered *capture* pixels are deliberately not asserted here: with
+`--use-fake-device-for-media-stream` the synthetic device is a fixed
+1280x720 and its clamping is not the behaviour under test (PLAN §5). Where
+a real capturer runs (`MIRROR_REALDISPLAY=1`, the `realdisplay` suite) the
+delivered pixels are asserted instead.
+
+The late-joining-viewer case proves the *first offer* of a leg that comes
+up under a preset chosen before that viewer joined carries the preset's cap:
+a new `RTCPeerConnection` is wrapped on the sharer page (the same pattern the
+other e2e suites use for their `RTCPeerConnection` probes) and the parameters
+are read back at `setLocalDescription` — before `negotiate()`'s
+post-negotiation re-apply has run, so the only code that could have written
+them is `addPeer()`'s `sendEncodings`.
+"""
+
+from __future__ import annotations
+
+import re
+import time
+
+import pytest
+from playwright.sync_api import expect
+
+from .conftest import _start, _stop, frames_matching, start_sharing, stop_sharing
+
+pytestmark = [pytest.mark.e2e, pytest.mark.timeout(180)]
+
+
+@pytest.fixture
+def device(base_url, browser, request):
+    """Open a page as its own device (isolated context, fresh peer id).
+
+    `url` targets a different server than the session's (the zero-cap
+    fixture); the default is the session server, which is what the capture-
+    request tests use.
+    """
+    opened = []
+
+    def _open(path: str = "/", errors: list | None = None, url: str | None = None):
+        context = browser.new_context(viewport={"width": 1100, "height": 720})
+        opened.append(context)
+        request.addfinalizer(context.close)
+        page = context.new_page()
+        if errors is not None:
+            page.on("pageerror", lambda error: errors.append(f"pageerror: {error}"))
+        page.goto(f"{url or base_url}{path}", wait_until="domcontentloaded")
+        expect(page.locator("#net")).to_have_attribute("data-state", "online", timeout=10_000)
+        return page
+
+    return _open
+
+
+@pytest.fixture
+def zero_cap_url():
+    """A real `mirror serve` with `MIRROR_MAX_BITRATE=0` — the "uncapped"
+    setting of the WebRTC API, which must not turn into a 0 bps leg."""
+    url, process = _start(extra_env={"MIRROR_MAX_BITRATE": "0"})
+    yield url
+    _stop(process)
+
+
+# Reads the video sender's committed parameters back from the sharer's live
+# legs (copied per suite from test_sender_fidelity.py — one copy per suite is
+# the convention). `state` is the leg's connectionState; `maxBitrate` is the
+# cap the leg is actually encoding under (undefined when none was written —
+# it reads back as null — which is exactly the "uncapped" state). If the
+# server had written a 0 bps cap it would read back as 0, and the zero-cap
+# test's `is None` assertion is what keeps the two apart.
+SENDER_PROBE = """() => {
+  const probe = window.__probe;
+  if (!probe) return null;
+  return [...probe.peers.values()].map((peer) => {
+    const sender = peer.pc.getSenders().find(
+      (s) => s.track && s.track.kind === "video"
+    );
+    if (!sender) return null;
+    const params = sender.getParameters();
+    const encodings = params.encodings || [];
+    return {
+      state: peer.pc.connectionState,
+      degradationPreference: params.degradationPreference,
+      maxBitrate: encodings.length ? encodings[0].maxBitrate : null,
+    };
+  });
+}"""
+
+
+def _wait_for(sharer, want: int, pred, timeout: float = 45.0) -> list:
+    """Poll the sharer's legs until `want` of them satisfy `pred` (or give up)."""
+    legs: list = []
+    deadline = time.time() + timeout
+    while time.time() < deadline:
+        legs = sharer.evaluate(SENDER_PROBE) or []
+        if len(legs) == want and all(leg and pred(leg) for leg in legs):
+            return legs
+        time.sleep(0.5)
+    return legs
+
+
+# The page's own request, the preset it came from, the track's contentHint
+# (a pure read-back of what start() set — not a delivered pixel), and the
+# inputs the page used: screen.width / devicePixelRatio are read *from the
+# page* — under Playwright `screen` is the emulated viewport, so hardcoding
+# a display size would make this environment-dependent.
+REQUEST_PROBE = """() => {
+  const probe = window.__probe;
+  if (!probe) return null;
+  const stream = document.querySelector('#preview').srcObject;
+  const track = stream && stream.getVideoTracks()[0];
+  return {
+    requested: probe.lastRequested,
+    qualityKey: probe.qualityKey,
+    contentHint: track ? track.contentHint : null,
+    screenWidth: screen.width,
+    screenHeight: screen.height,
+    dpr: window.devicePixelRatio || 1,
+  };
+}"""
+
+# The pixel ceilings and the per-preset contentHint, the mirror of `PRESETS`
+# in share.js: the request is min(screen * dpr, cap). This suite asserts the
+# *request* the page built; the table itself is guarded by test_app.py's
+# three-preset agreement test.
+PRESETS_UNDER_TEST = {
+    "sharp": {"cap": (3840, 2160), "contentHint": "detail"},
+    "balanced": {"cap": (1920, 1200), "contentHint": "detail"},
+    "light": {"cap": (960, 600), "contentHint": "motion"},
+}
+
+
+def _bitrate_format(bps: float) -> str:
+    """The mirror of `bitrateFormat` in net.js — the panel's own renderer,
+    so the test can recompute the exact line the panel must print."""
+    if not bps or bps < 0:
+        return "—"
+    if bps >= 1e6:
+        return f"{bps / 1e6:.1f} Mbps"
+    return f"{round(bps / 1e3)} kbps"
+
+
+class TestQualityPresets:
+    def test_each_preset_asks_the_capture_for_its_own_budget(self, device):
+        """Each preset drives the capture request: `sharp` is the old
+        hardcoded 4K cap (the no-regression argument), `balanced` 1080p-class,
+        `light` a small and cheap budget — and the page records which preset
+        the live capture belongs to."""
+        errors: list = []
+        for key, preset in PRESETS_UNDER_TEST.items():
+            cap_w, cap_h = preset["cap"]
+            sharer = device("/mirror", errors)
+            sharer.select_option("#quality", key)
+            start_sharing(sharer)
+            result = sharer.evaluate(REQUEST_PROBE)
+            assert result, "the __probe handle is missing"
+            assert result["qualityKey"] == key, result
+            # The page's own arithmetic, recomputed from the page's own inputs:
+            # min(round(screen * dpr), cap).
+            expected_w = min(round(result["screenWidth"] * result["dpr"]), cap_w)
+            expected_h = min(round(result["screenHeight"] * result["dpr"]), cap_h)
+            assert result["requested"]["width"] == expected_w, result
+            assert result["requested"]["height"] == expected_h, result
+            # Text-first presets take `detail`; `light` is glanceable, so
+            # motion wins over glyph crispness.
+            assert result["contentHint"] == preset["contentHint"], result
+        assert errors == [], f"uncaught browser errors: {errors}"
+
+    def test_a_light_leg_encodes_at_the_presets_share(self, device, base_url):
+        """A leg that comes up under `light` encodes at the preset's share
+        of the server's ceiling and with the preset's degradation preference —
+        both read from the preset *at call time*: `light` was selected before
+        sharing started, so the viewer's leg must carry them from its first
+        offer, and the wall must still be moving (a cheaper picture must not
+        be a dead one)."""
+        import httpx
+
+        cap = httpx.get(f"{base_url}/api/config", timeout=5).json()["maxBitrateBps"]
+        assert cap > 0
+
+        errors: list = []
+        sharer = device("/mirror", errors)
+        sharer.select_option("#quality", "light")
+        start_sharing(sharer)
+
+        viewer = device("/watch", errors)
+        expect(viewer.locator(".tile[data-state='live']")).to_have_count(1, timeout=25_000)
+
+        legs = _wait_for(sharer, 1, lambda leg: leg["state"] == "connected")
+        assert legs and legs[0]["state"] == "connected", legs
+        assert legs[0]["maxBitrate"] == round(cap * 0.35), legs
+        assert legs[0]["degradationPreference"] == "maintain-framerate", legs
+
+        # The cheaper picture still has to be a live one.
+        frames = frames_matching(viewer, ".tile video")
+        assert frames["distinct"] >= 2, f"a light leg froze: {frames}"
+        assert errors == [], f"uncaught browser errors: {errors}"
+
+    def test_each_preset_commits_its_sender_parameters(self, device, base_url):
+        """The full committed-parameter matrix, `sharp` first so the
+        no-regression leg is the first thing it proves: each preset's live
+        leg commits `round(cap * factor)` and the preset's
+        `degradationPreference` — read at call time, so the preset selected
+        before sharing lands on the leg from its first offer — and the wall
+        stays moving on the viewer in every case (a cheaper picture must not
+        be a dead one). `sharp` is phase 02's behaviour verbatim: full cap,
+        `maintain-resolution`.
+        """
+        import httpx
+
+        cap = httpx.get(f"{base_url}/api/config", timeout=5).json()["maxBitrateBps"]
+        assert cap > 0
+
+        # The committed-parameter mirror of PRESETS_UNDER_TEST: the factor the
+        # server's ceiling is scaled by and the degradation preference the
+        # encoder commits to, per preset. `sharp` first: full cap and
+        # maintain-resolution is the unchanged phase 02 behaviour.
+        committed = {
+            "sharp": (1.0, "maintain-resolution"),
+            "balanced": (0.6, "balanced"),
+            "light": (0.35, "maintain-framerate"),
+        }
+        for key, (factor, degradation) in committed.items():
+            errors: list = []
+            sharer = device("/mirror", errors)
+            sharer.select_option("#quality", key)
+            start_sharing(sharer)
+            viewer = device("/watch", errors)
+            expect(viewer.locator(".tile[data-state='live']")).to_have_count(1, timeout=25_000)
+
+            legs = _wait_for(sharer, 1, lambda leg: leg["state"] == "connected")
+            assert legs and legs[0]["state"] == "connected", (key, legs)
+            assert legs[0]["maxBitrate"] == round(cap * factor), (key, legs)
+            assert legs[0]["degradationPreference"] == degradation, (key, legs)
+
+            # The picture still has to be a live one in every preset.
+            frames = frames_matching(viewer, ".tile video")
+            assert frames["distinct"] >= 2, f"the {key} leg froze: {frames}"
+            assert errors == [], f"uncaught browser errors on {key}: {errors}"
+
+            # Tear the whole iteration down before the next preset: the
+            # contexts outlive the iteration, and the wall auto-subscribes
+            # *every live viewer* to *every new mirror* — an uncleaned
+            # viewer would stack a second (third, ...) leg on the next
+            # preset's sharer and break the one-leg expectation. Stop the
+            # share first, so the viewer's tile (and its peer connection)
+            # is torn down before its page goes away.
+            stop_sharing(sharer)
+            viewer.close()
+            sharer.close()
+
+    def test_a_zero_cap_stays_uncapped_under_light(self, device, zero_cap_url):
+        """`MIRROR_MAX_BITRATE=0` is a real setting — "uncapped" in the
+        WebRTC API. `legCap()` must return 0 and no `maxBitrate` may be
+        written: an uncapped leg must not become a 0 bps leg. The preset's
+        degradation preference still lands, and the picture still moves.
+        """
+        import httpx
+
+        config = httpx.get(f"{zero_cap_url}/api/config", timeout=5).json()
+        assert config["maxBitrateBps"] == 0, config
+
+        errors: list = []
+        sharer = device("/mirror", errors, url=zero_cap_url)
+        sharer.select_option("#quality", "light")
+        start_sharing(sharer)
+
+        viewer = device("/watch", errors, url=zero_cap_url)
+        expect(viewer.locator(".tile[data-state='live']")).to_have_count(1, timeout=25_000)
+
+        legs = _wait_for(sharer, 1, lambda leg: leg["state"] == "connected")
+        assert legs and legs[0]["state"] == "connected", legs
+        # No maxBitrate written at all: an uncapped leg, not a 0 bps one.
+        assert legs[0]["maxBitrate"] is None, legs
+        assert legs[0]["degradationPreference"] == "maintain-framerate", legs
+
+        frames = frames_matching(viewer, ".tile video")
+        assert frames["distinct"] >= 2, f"the uncapped leg froze: {frames}"
+        assert errors == [], f"uncaught browser errors: {errors}"
+
+    def test_changing_quality_mid_share_re_prices_the_live_leg(self, device, base_url):
+        """A preset change made while a leg is live re-prices that leg —
+        ``setParameters`` commits without an offer, so the CPU/egress
+        change is instant and no second RTCPeerConnection is needed for it —
+        and the viewer keeps decoding moving frames across the switch. The
+        roster must tell the truth in *both* outcomes: its width/height
+        equal the track's own ``getSettings()``, whatever the engine
+        settled on (the synthetic device clamps; delivered pixels are the
+        ``realdisplay`` suite's, task 06)."""
+        import httpx
+
+        cap = httpx.get(f"{base_url}/api/config", timeout=5).json()["maxBitrateBps"]
+        assert cap > 0
+
+        errors: list = []
+        sharer = device("/mirror", errors)
+        start_sharing(sharer)  # the default preset: sharp
+        viewer = device("/watch", errors)
+        expect(viewer.locator(".tile[data-state='live']")).to_have_count(1, timeout=25_000)
+        legs = _wait_for(sharer, 1, lambda leg: leg["state"] == "connected")
+        assert legs and legs[0]["state"] == "connected", legs
+
+        # The switch, mid-share, through the control the user has.
+        sharer.select_option("#quality", "light")
+
+        # The single live leg re-prices in place: ``setParameters`` commits
+        # within ~5 s of the change, and the connection state returns to /
+        # stays ``connected`` (a leg that comes up fresh for the new size
+        # reads ``legCap()`` at its first offer, so the cap lands either way).
+        def repriced(leg):
+            return leg["state"] == "connected" and leg["maxBitrate"] == round(cap * 0.35)
+
+        re = _wait_for(sharer, 1, repriced, timeout=5.0)
+        # No second RTCPeerConnection: the roster of live legs is still the
+        # one the viewer was subscribed on.
+        assert sharer.evaluate("() => window.__probe.peers.size") == 1
+        assert re and re[0]["maxBitrate"] == round(cap * 0.35), re
+        assert re[0]["state"] == "connected", re
+
+        # The switch did not freeze anybody.
+        frames = frames_matching(viewer, ".tile video")
+        assert frames["distinct"] >= 2, frames
+
+        # The roster tells the truth: whatever the engine settled on, the
+        # published width/height equal the track's own settings. Do not
+        # assert a *delivered* size here — the synthetic device clamps, and
+        # task 06 owns delivered pixels on a real desktop.
+        def track_settings():
+            return sharer.evaluate(
+                "() => { const s = document.querySelector('#preview').srcObject;"
+                " const t = s && s.getVideoTracks()[0];"
+                " return t ? t.getSettings() : null; }"
+            )
+
+        def roster_agrees():
+            settings = track_settings()
+            if not settings or not settings.get("width"):
+                return False, None, settings
+            mirror = httpx.get(f"{base_url}/api/streams", timeout=5).json()["mirrors"]
+            assert len(mirror) == 1, mirror
+            mirror = mirror[0]
+            agrees = mirror["width"] == settings["width"] and mirror["height"] == settings["height"]
+            return agrees, mirror, settings
+
+        deadline = time.time() + 10.0
+        agrees, mirror, settings = roster_agrees()
+        while not agrees and time.time() < deadline:
+            time.sleep(0.5)
+            agrees, mirror, settings = roster_agrees()
+        assert agrees, f"roster does not match the track's own settings: {mirror!r} vs {settings!r}"
+        assert errors == [], f"uncaught browser errors: {errors}"
+
+    def test_a_device_that_cannot_rescale_still_changes_rate(self, device, base_url):
+        """A display that cannot rescale answers the full constraint with the
+        named ``OverconstrainedError``: the retry applies the frame rate
+        alone, the leg is still re-priced, the viewer still moves, the
+        toast says the size lands on the next share (it does not pretend
+        the capture rescaled), and the roster stays truthful."""
+        import httpx
+
+        cap = httpx.get(f"{base_url}/api/config", timeout=5).json()["maxBitrateBps"]
+        assert cap > 0
+
+        errors: list = []
+        sharer = device("/mirror", errors)
+        start_sharing(sharer)
+        viewer = device("/watch", errors)
+        expect(viewer.locator(".tile[data-state='live']")).to_have_count(1, timeout=25_000)
+        legs = _wait_for(sharer, 1, lambda leg: leg["state"] == "connected")
+        assert legs and legs[0]["state"] == "connected", legs
+
+        # Simulate the display: a constraint that carries a size fails with
+        # the named error; the frame-rate-only retry passes. (This is the
+        # real-world behaviour the retry exists for — a capturer that holds
+        # its size — and nothing else in the path is stubbed.)
+        sharer.evaluate(
+            "() => { const s = document.querySelector('#preview').srcObject;"
+            " const t = s.getVideoTracks()[0];"
+            " const orig = t.applyConstraints.bind(t);"
+            " t.applyConstraints = (c) => (c && c.width)"
+            " ? Promise.reject(new DOMException('size cannot be applied', 'OverconstrainedError'))"
+            " : orig(c); }"
+        )
+        sharer.select_option("#quality", "light")
+
+        # The toast lands with the settle (before the leg is measured
+        # again), so it is read first: the preset is named, and because
+        # the size was never applied the line says it lands next share.
+        toast = sharer.locator("#toast")
+        expect(toast).to_contain_text("Light", timeout=5_000)
+        text = toast.text_content() or ""
+        assert "next share" in text, text
+
+        # The leg is still re-priced, and the switch did not freeze anybody.
+        def repriced(leg):
+            return leg["state"] == "connected" and leg["maxBitrate"] == round(cap * 0.35)
+
+        re = _wait_for(sharer, 1, repriced, timeout=5.0)
+        assert re and re[0]["maxBitrate"] == round(cap * 0.35), re
+        frames = frames_matching(viewer, ".tile video")
+        assert frames["distinct"] >= 2, frames
+
+        # The roster tells the truth about whatever the device delivered.
+        def track_settings():
+            return sharer.evaluate(
+                "() => { const s = document.querySelector('#preview').srcObject;"
+                " const t = s && s.getVideoTracks()[0];"
+                " return t ? t.getSettings() : null; }"
+            )
+
+        def roster_agrees():
+            settings = track_settings()
+            if not settings or not settings.get("width"):
+                return False, None, settings
+            mirror = httpx.get(f"{base_url}/api/streams", timeout=5).json()["mirrors"]
+            assert len(mirror) == 1, mirror
+            mirror = mirror[0]
+            agrees = mirror["width"] == settings["width"] and mirror["height"] == settings["height"]
+            return agrees, mirror, settings
+
+        deadline = time.time() + 10.0
+        agrees, mirror, settings = roster_agrees()
+        while not agrees and time.time() < deadline:
+            time.sleep(0.5)
+            agrees, mirror, settings = roster_agrees()
+        assert agrees, f"roster does not match the track's own settings: {mirror!r} vs {settings!r}"
+        assert errors == [], f"uncaught browser errors: {errors}"
+
+    def test_a_viewer_who_joins_after_a_switch_gets_the_new_cap(self, device, base_url):
+        """The `addPeer` path, not just the re-apply path.
+
+        A preset change mid-share re-prices the *existing* leg (task 04's
+        re-apply). This proves the other half: a viewer who subscribes
+        *after* the switch gets a leg whose **first offer** already carries
+        the new cap — `legCap()` is read at call time in `addPeer()` and
+        written into `sendEncodings` before any negotiation exists. The
+        sharer's `RTCPeerConnection` is wrapped (the same pattern the other
+        e2e suites use for their peer-connection probes) so the parameters
+        are read back at `setLocalDescription`, i.e. before `negotiate()`'s
+        post-negotiation re-apply has run: the only code that could have
+        written them is `addPeer()`'s `sendEncodings`.
+        """
+        import httpx
+
+        cap = httpx.get(f"{base_url}/api/config", timeout=5).json()["maxBitrateBps"]
+        assert cap > 0
+
+        errors: list = []
+        sharer = device("/mirror", errors)
+        start_sharing(sharer)  # the default preset: sharp
+        first = device("/watch", errors)
+        expect(first.locator(".tile[data-state='live']")).to_have_count(1, timeout=25_000)
+        legs = _wait_for(sharer, 1, lambda leg: leg["state"] == "connected")
+        assert legs and legs[0]["state"] == "connected", legs
+        assert legs[0]["maxBitrate"] == cap, legs
+
+        # The switch, mid-share: the existing leg re-prices via the re-apply.
+        sharer.select_option("#quality", "light")
+
+        def repriced(leg):
+            return leg["state"] == "connected" and leg["maxBitrate"] == round(cap * 0.35)
+
+        re = _wait_for(sharer, 1, repriced, timeout=5.0)
+        assert re and re[0]["maxBitrate"] == round(cap * 0.35), re
+
+        # From here on, every new RTCPeerConnection on the sharer page is
+        # the late joiner's leg: the wrapper records the committed parameters
+        # at setLocalDescription time, before negotiate()'s re-apply.
+        assert sharer.evaluate(
+            """() => {
+              window.__firstOffers = [];
+              const RealPC = window.RTCPeerConnection;
+              window.RTCPeerConnection = function (config) {
+                const pc = new RealPC(config);
+                const orig = pc.setLocalDescription.bind(pc);
+                pc.setLocalDescription = (d) => orig(d).then(() => {
+                  const sender = pc.getSenders().find(
+                    (s) => s.track && s.track.kind === 'video'
+                  );
+                  const params = sender ? sender.getParameters() : {};
+                  const enc = (params.encodings || [])[0] || {};
+                  window.__firstOffers.push({
+                    maxBitrate: 'maxBitrate' in enc ? enc.maxBitrate : null,
+                    degradationPreference: params.degradationPreference || null,
+                  });
+                  return pc;
+                });
+                return pc;
+              };
+              window.RTCPeerConnection.prototype = RealPC.prototype;
+              window.RTCPeerConnection.static = RealPC.static;
+              return true;
+            }"""
+        )
+
+        late = device("/watch", errors)
+        expect(late.locator(".tile[data-state='live']")).to_have_count(1, timeout=25_000)
+
+        # Both legs are now live under the switched preset.
+        legs = _wait_for(sharer, 2, lambda leg: leg["state"] == "connected")
+        assert legs and all(leg["state"] == "connected" for leg in legs), legs
+
+        offers = sharer.evaluate("() => window.__firstOffers") or []
+        assert offers, "no first offer was captured from the late joiner's leg"
+        # The first offer carried the new cap: addPeer's sendEncodings, not
+        # the post-negotiation re-apply, which ran later on the same leg.
+        assert offers[-1]["maxBitrate"] == round(cap * 0.35), offers
+        # And the settled leg is still capped — nothing drifted after.
+        assert all(leg["maxBitrate"] == round(cap * 0.35) for leg in legs), legs
+        assert sharer.evaluate("() => window.__probe.peers.size") == 2
+
+        # The late joiner's picture is a live one, and the sharer agrees
+        # that two viewers are watching.
+        frames = frames_matching(late, ".tile video")
+        assert frames["distinct"] >= 2, f"the late joiner froze: {frames}"
+        expect(sharer.locator("#viewer-count")).to_have_text("2", timeout=10_000)
+        assert errors == [], f"uncaught browser errors: {errors}"
+
+    def test_the_panel_shows_the_budget_and_the_codec(self, device, base_url):
+        """The panel says what the share is actually costing (phase 06 task
+        05): the quality budget in force — the selected preset, its capture
+        ceiling, its frame rate and its per-leg share of the server's cap —
+        and the codec the leg actually negotiated, resolved in the same
+        `getStats()` read the 1 s tick already makes. The codec is `—` where
+        the engine does not report it: the panel must never guess. Both
+        lines reset to `—` when the share stops."""
+        import httpx
+
+        cap = httpx.get(f"{base_url}/api/config", timeout=5).json()["maxBitrateBps"]
+        assert cap > 0
+
+        errors: list = []
+        sharer = device("/mirror", errors)
+        sharer.select_option("#quality", "balanced")
+        start_sharing(sharer)
+
+        # The budget line is written by start() from state: an exact match,
+        # not a substring — the panel must not misprice the share. The cap
+        # is read live from /api/config (never hardcoded) and scaled by the
+        # preset's factor, exactly as legCap() does.
+        expected = (
+            f"balanced · ≤1920×1200 @24fps · "  # noqa: RUF001 (the panel line itself carries the multiplication sign)
+            f"{_bitrate_format(round(cap * 0.6))} /viewer"
+        )
+        expect(sharer.locator("#stat-quality")).to_have_text(expected, timeout=10_000)
+
+        viewer = device("/watch", errors)
+        expect(viewer.locator(".tile[data-state='live']")).to_have_count(1, timeout=25_000)
+        legs = _wait_for(sharer, 1, lambda leg: leg["state"] == "connected")
+        assert legs and legs[0]["state"] == "connected", legs
+
+        # The codec line is written once per 1 s stats tick (no extra
+        # getStats() call): let a tick run after the leg is up, then read it.
+        time.sleep(2.5)
+        codec = (sharer.locator("#stat-codec").text_content() or "").strip()
+        # The shape, not the codec: which one the engine negotiates is not a
+        # contract. `—` is the honest floor where the engine does not expose
+        # the outbound codec; a name must be the short form
+        # (`video/VP8` → `VP8`), never a guess.
+        assert codec == "—" or re.fullmatch(r"[A-Z0-9/]{2,16}", codec), codec
+
+        # The share is still a live one while the panel reports on it.
+        frames = frames_matching(viewer, ".tile video")
+        assert frames["distinct"] >= 2, frames
+
+        # Stopping resets both lines: `—`, not a stale reading.
+        stop_sharing(sharer)
+        expect(sharer.locator("#stat-quality")).to_have_text("—", timeout=10_000)
+        expect(sharer.locator("#stat-codec")).to_have_text("—", timeout=10_000)
+        assert errors == [], f"uncaught browser errors: {errors}"
+
+    def test_q_cycles_the_preset_and_says_so(self, device):
+        """``q`` cycles the preset on the share page (sharp → balanced →
+        light → sharp) and toasts the new one, naming it and its budget;
+        a ``q`` typed into ``#name`` is text, not a command, and never
+        changes the select (the router's text-field guard)."""
+        errors: list = []
+        page = device("/mirror", errors)
+        toast = page.locator("#toast")
+
+        page.keyboard.press("q")
+        expect(page.locator("#quality")).to_have_value("balanced", timeout=5_000)
+        assert page.evaluate("() => window.__probe.qualityKey") == "balanced"
+        expect(toast).to_contain_text("Balanced", timeout=5_000)
+        text = toast.text_content() or ""
+        assert "≤1920×1200" in text, text  # noqa: RUF001 (the toast itself carries the multiplication sign)
+        # Nothing is shared yet: the capture size lands on the next share,
+        # and the line says so rather than pretending it rescaled.
+        assert "next share" in text, text
+
+        page.keyboard.press("q")
+        expect(page.locator("#quality")).to_have_value("light")
+        expect(toast).to_contain_text("Light", timeout=5_000)
+
+        page.keyboard.press("q")
+        expect(page.locator("#quality")).to_have_value("sharp")
+        expect(toast).to_contain_text("Sharp", timeout=5_000)
+
+        # A ``q`` typed into #name is text, not a command: the select stays.
+        page.locator("#name").click()
+        page.keyboard.type("q")
+        expect(page.locator("#quality")).to_have_value("sharp")
+
+        assert errors == [], f"uncaught browser errors: {errors}"
diff --git a/tests/e2e/test_x11_capture.py b/tests/e2e/test_x11_capture.py
index e29e489..d83ee0c 100644
--- a/tests/e2e/test_x11_capture.py
+++ b/tests/e2e/test_x11_capture.py
@@ -443,6 +443,105 @@ class TestRealX11Capture:
         expect(share_page.locator("#viewer-count")).to_have_text("1", timeout=20_000)
         assert errors == [], f"uncaught browser errors: {errors}"
 
+    def test_a_light_preset_delivers_a_small_picture(self, share_page, watch_page):
+        """The delivered-pixel proof that the preset reaches the *real*
+        capturer, not just the request object.
+
+        ``#quality = light`` is selected **before** the share starts, so the
+        request — under Playwright ``screen`` is the emulated viewport, so
+        the 1200x760 share window asks ``min(viewport, 960x600)`` =
+        960x600 — goes to Chromium's real X11 backend. The sharer's track
+        settings must honour the budget (at least 80% of the 960 request
+        wide, never above it): that is the proof the request reached the
+        real capturer and was not clamped away to the desktop or the
+        window. The viewer's decoded width must be at or under the cap —
+        the phase's delivered-pixels criterion — *and below the sharp
+        path's floor*: if a ``light`` share delivered a sharp-size picture,
+        the budget never reached the wire. The aspect guard keeps proving
+        the picture is *our* desktop, not somebody else's window.
+
+        The sharp path's floor (``SHARP_FLOOR_PX``) is deliberately
+        **not** asserted here: it stays the sharp test's, and a small
+        picture is exactly what a ``light`` share should deliver — the
+        small picture that is still the whole desktop.
+
+        Measured on this host (Xvfb 1280x800x24, phase 06): the capturer
+        delivered 960x600 (track settings, ``frameRate`` 15), and the
+        viewer decoded 320x200 — VP8 honouring ``light``'s
+        ``maintain-framerate`` at ``round(25 Mbit/s x 0.35)`` = 8.75
+        Mbit/s, i.e. the encoder's resolution-degradation policy (the same
+        leg encodes 960x600 under ``maintain-resolution``); the encoder
+        may sacrifice resolution, which is the preset's contract, so the
+        decoded-width floor below guards a *collapsed* picture (>= a
+        quarter of the request), not the encoder's honest ladder.
+        """
+        errors: list[str] = []
+        share_page.on("pageerror", lambda error: errors.append(str(error)))
+
+        share_page.select_option("#quality", "light")
+        share_page.locator("#start").click()
+        expect(share_page.locator("body")).to_have_attribute("data-live", "on", timeout=40_000)
+
+        # The preset is what the live capture belongs to (a pure parameter
+        # read, not a pixel claim — the pixels are the viewer's, below).
+        assert share_page.evaluate("() => window.__probe.qualityKey") == "light"
+
+        # The request reached the *real* capturer and was not clamped away:
+        # the track the X11 backend settled on honours the light budget —
+        # at least 80% of the 960 request wide (the capturer did not drop
+        # the size), never above it (the capturer did not ignore it and
+        # deliver the 1200x750 window-clamped desktop).
+        settings = share_page.evaluate(
+            """() => {
+              const track = document.querySelector('#preview').srcObject.getVideoTracks()[0];
+              const s = track.getSettings();
+              return {width: s.width, height: s.height, surface: s.displaySurface};
+            }"""
+        )
+        assert settings["surface"] == "monitor", f"not a monitor capture: {settings}"
+        assert settings["width"] <= 990, f"the capturer ignored the light budget: {settings}"
+        assert settings["width"] >= 768, f"the capturer did not honour the request: {settings}"
+
+        expect(watch_page.locator(".tile[data-state='live']")).to_have_count(1, timeout=60_000)
+
+        # Start measuring on the watcher, then paint: cycling the captured
+        # machine's background is what a real presenter's screen does constantly.
+        assert watch_page.evaluate(PROBE) == "started"
+        for colour in ("#c81e1e", "#0b0d10", "#1e6ec8", "#0b0d10", "#1ec85a"):
+            share_page.evaluate("(colour) => { document.body.style.background = colour; }", colour)
+            time.sleep(0.28)
+        result = watch_page.evaluate("() => window.__probe")
+
+        # Delivered pixels follow the preset: the decoded picture is at or
+        # under the light cap, and below the sharp path's floor (a
+        # sharp-size picture from a light share would mean the budget
+        # never reached the wire). Measured 320x200 on this host — the
+        # encoder's maintain-framerate degradation, see the docstring.
+        assert result["width"] <= 990, (
+            f"the watcher decoded a {result['width']}px-wide picture: the light budget is "
+            f"<= 960px, so a wider decode means the budget did not reach the wire: {result}"
+        )
+        assert result["width"] < SHARP_FLOOR_PX, (
+            f"the watcher decoded a {result['width']}px-wide picture: that is at or above "
+            f"the sharp floor ({SHARP_FLOOR_PX}px), so a light share delivered a sharp-size "
+            f"picture: {result}"
+        )
+        assert result["width"] >= 240, (
+            f"the watcher decoded a {result['width']}px-wide picture: a quarter of the 960px "
+            f"request must arrive at least, or the picture collapsed: {result}"
+        )
+        assert abs(result["width"] / result["height"] - XVFB_ASPECT) < 0.06, (
+            f"{result} does not match the {XVFB_GEOMETRY} desktop aspect "
+            f"({XVFB_ASPECT:.3f}); this is not our Xvfb screen"
+        )
+        assert result["distinct"] >= 2, (
+            f"the watcher received a frozen frame: {result} — a small-but-still picture "
+            f"must not pass a delivered-pixel test"
+        )
+
+        expect(share_page.locator("#viewer-count")).to_have_text("1", timeout=20_000)
+        assert errors == [], f"uncaught browser errors: {errors}"
+
     def test_a_real_desktop_shares_audio_when_the_host_offers_any(self, base_url, browsers):
         """The realdisplay counterpart of the audio-arrival assertion.
 
diff --git a/tests/test_app.py b/tests/test_app.py
index cd20c27..1ea8d12 100644
--- a/tests/test_app.py
+++ b/tests/test_app.py
@@ -177,15 +177,47 @@ class TestClientScripts:
             "a different bitrate silently"
         )
 
+    def test_the_quality_options_are_the_three_presets(self):
+        """`#quality` (mirror.html) and `PRESETS` (share.js) are one list in two places.
+
+        If the option values drift from the table keys, a preset the panel offers has
+        no row (or an orphan row the panel can never select), and `currentPreset()`
+        falls back to `sharp` instead of noticing: the sharer gets a wall they did not
+        ask for and nothing fails. One list, two places, one test that notices (the
+        same shape as the bitrate-default test)."""
+        html = (STATIC / "mirror.html").read_text()
+        select = re.search(r'<select id="quality"[^>]*>.*?</select>', html, re.S)
+        assert select, "mirror.html must render a #quality select"
+        options = set(re.findall(r'value="([A-Za-z0-9_-]+)"', select.group(0)))
+
+        source = (STATIC / "share.js").read_text()
+        table = re.search(r"const PRESETS = Object\.freeze\(\{(.*?)\}\);", source, re.S)
+        assert table, "share.js must define the PRESETS table"
+        # Top-level keys sit two spaces in; the fields inside a preset sit four
+        # spaces in, so anchoring on exactly two spaces selects the keys only.
+        keys = set(re.findall(r"^  ([a-z]+): \{$", table.group(1), re.M))
+
+        expected = {"sharp", "balanced", "light"}
+        assert options == expected, f"#quality offers {sorted(options)}, not {sorted(expected)}"
+        assert keys == expected, f"PRESETS keys are {sorted(keys)}, not {sorted(expected)}"
+        assert options == keys, "the select offers presets the table cannot resolve"
+
     def test_sender_quality_is_reapplied_on_negotiation_and_connection(self):
         """`setParameters` is per-negotiation: a re-offer (a surface switch,
-        a viewer that re-joined) resets the encodings. The cap must therefore
-        be re-applied after `setLocalDescription` *and* when the leg becomes
-        `connected`. Both call sites are asserted so a future edit cannot drop
-        one and silently soften the wall."""
+        a viewer that re-joined) resets the encodings. The preset's cap and
+        degradation preference must therefore be re-applied after
+        `setLocalDescription` *and* when the leg becomes `connected`. Both
+        call sites are asserted so a future edit cannot drop one and silently
+        soften the wall. The preference itself stays a single, named
+        decision — the PRESETS table's `degradation` field, read at call
+        time — so a hardcoded literal at the call site would be a second,
+        drifting decision."""
         source = (STATIC / "share.js").read_text()
-        assert source.count('"maintain-resolution"') == 1, (
-            "the degradation preference must be a single, named decision"
+        assert re.search(r'degradationPreference\s*=\s*"', source) is None, (
+            "a hardcoded degradation literal at a call site is a second decision"
+        )
+        assert "params.degradationPreference = PRESETS[currentPreset()].degradation" in source, (
+            "the preference is not read from the PRESETS table at call time"
         )
         assert "async function applySenderQuality" in source