ducoterra
2e79430ac7
The internal deployment exists (deployments repo, `mirror/`: quadlet, nginx edge, certbot, route53, VM SOP), so the docs that said "the real fix is HTTPS" were describing a future that has arrived from a different direction — TLS terminates in nginx on the service VM, not in this process, and there is no `--https` flag here. SECURITY.md's trust model said "trusted: anyone who can open a TCP connection". With an allow list in production that sentence was simply no longer true, so the table now names the address space, and a new section says what the list is and what it is not: one wall (network/nginx) and one belt (the app, for the path that bypasses nginx at 127.0.0.1:8080), plus the thing neither can do — once two browsers are in the room their media never asks the server again, and it can never tell you *who*, only *where from*. Saying "defence in depth" about that would have been the dishonest version. PLAN.md gains A19 (TLS + admission in production, LOCKED) and A18 becomes deprioritised rather than deleted — standalone `mirror serve --https` is still worth having for offline/ad-hoc use, it just stopped being the thing blocking cross-device sharing, and candidate phase 1 is now share-page resilience. AGENTS.md gains the two rules most likely to be broken by a well-meaning edit: trust XFF only from a trusted proxy, and change the nginx and app lists in the same commit. LLM-Generated: true
146 lines
8.2 KiB
Markdown
146 lines
8.2 KiB
Markdown
# mirror — Agent Operating Rules
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**Read `.agents/PLAN.md` before touching anything here.** It holds the locked
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architectural decisions; this file holds the rules for working inside them.
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`mirror` is browser-only screen mirroring for a local network: `/mirror` shares a
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window/screen/tab via the OS-native picker, `/watch` shows every live mirror and
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lets anyone take one fullscreen. Media flows peer-to-peer over WebRTC; the server
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is a roster and a signaling relay. Linux is the reference platform.
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---
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## 1. The order of reading
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1. `.agents/PLAN.md` — architecture, locked anchors, verification ladder.
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2. `README.md` — the user-facing contract.
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3. `SECURITY.md` — why there is no authentication, and what that costs.
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4. `src/mirror/registry.py` — the whole policy lives here. Read it before
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changing behavior; it is short and it is the product.
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## 2. Phased execution
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```
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.agents/
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├── PLAN.md ← locked design (do not edit without an explicit decision)
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└── phases/
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├── todo/ ← pending phases: NN_name/00_phase.md + NN_task.md
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└── complete/ ← finished phases, read-only history
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```
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* New work enters through the **`phase-authoring` skill**, never as a direct
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implementation of a vague request.
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* Phases run through the **`phased-execution` skill**.
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* Never edit anything in `phases/complete/`. Ask before editing `phases/todo/`.
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* Never edit `PLAN.md` unless the user explicitly authorises a change to a locked
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decision, and record the reason in the same change.
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* A phase is not done until every gate in §4 passes.
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*(The roadmap is intentionally empty at the prototype stage: a working prototype
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came first, and the candidate phase list is §7 of `PLAN.md`.)*
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## 3. Locked decisions that are easy to break by accident
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| Rule | Why it exists |
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|---|---|
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| **No external assets.** No CDN, remote font, remote icon, `@import`, or analytics | LAN/offline correctness. `tests/test_app.py::TestClientScripts::test_nothing_is_loaded_from_a_cdn` fails the build if you add one |
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| **No framework, no bundler** in `src/mirror/static/` | Two pages and one WebSocket. `node --check` is the entire frontend toolchain |
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| **Media never passes through the server** | The server relays JSON only. Anything that puts frames in the Python process violates A3 |
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| **`Registry` stays pure** — no sockets, no FastAPI, no `await` | It returns `list[Envelope]`. Transport lives in `Hub`. This is why the policy has 100%-ish unit coverage |
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| **camelCase on the wire, snake_case in Python**, via `alias_generator=to_camel` | A silently-dropped `displaySurface` was a real bug we shipped. Any new multi-word field needs an alias test |
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| **No authentication** (A11) — but the **address is the access control** (A19) | Product brief: no accounts. What decides who gets in is `MIRROR_ALLOW_CIDRS` (`src/mirror/access.py`), enforced in the HTTP middleware *and* before the socket accepts. If you think it needs auth, that is a `PLAN.md` discussion first — and see `SECURITY.md` |
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| **Trust `X-Forwarded-For` only from `MIRROR_TRUSTED_PROXIES`, left-most value only** | Otherwise a browser writes its own pass. The deployment's nginx must *overwrite* the header (`$remote_addr`, never `$proxy_add_x_forwarded_for`) — and the nginx `allow`/`deny` list and `MIRROR_ALLOW_CIDRS` change in the same commit |
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| **`/healthz` stays exempt from the address gate** | The podman `HealthCmd` probes it from loopback, which the production list otherwise excludes — an exempt probe is why the container is not permanently unhealthy |
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| **No STUN/TURN by default** | A LAN tool must not announce internal addresses to a third party |
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| **Teardown is broadcast to every viewer**, not just subscribers | Tiles are drawn on `stream_added`; a non-subscribed viewer still has a stale tile to clear |
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| **Keep both `<video>` elements `muted playsinline`** | Autoplay policy on iOS/Safari otherwise blocks the wall entirely |
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## 4. Gates — run all four before calling anything done
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```bash
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uv run ruff check . && uv run ruff format --check .
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uv run pyright # must be 0 errors
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uv run pytest # unit + API + browser E2E (~20s)
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MIRROR_REALDISPLAY=1 uv run pytest -m realdisplay # Linux-native X11 capture
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```
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Coverage is ~94%; the media path is covered by browser assertions, not by unit
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tests pretending to be WebRTC.
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## 5. Browser testing rules
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Non-negotiable, all learned the hard way (full notes in `PLAN.md` §5):
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* Launch with **`channel="chromium"`**. The headless shell has no media stack —
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`navigator.mediaDevices` does not exist there.
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* Serve pages over **`http://127.0.0.1:<port>`**. On `about:blank` or a plain
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LAN IP, `mediaDevices` is undefined and the test proves nothing.
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* Deterministic capture: `--use-fake-ui-for-media-stream
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--use-fake-device-for-media-stream` → a real, *moving* 1280×720 monitor stream.
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* Real capture (the `realdisplay` suite): private **Xvfb**, headed Chromium,
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`--auto-select-desktop-capture-source="Entire screen"`, `--ozone-platform=x11`,
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and **never** `--use-fake-ui-for-media-stream` (it approves the request without
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selecting a source and the capturer dies with `NotReadableError`).
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* **Strip `WAYLAND_DISPLAY` and `DBUS_SESSION_BUS_ADDRESS`** from any headed
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browser env (`tests/e2e/test_x11_capture.py::browser_env`). Otherwise the
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portal captures the developer's actual desktop and pops a permission dialog on
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their real screen.
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* Assert media on the **viewer's** `<video>` — decoded size and *frames that
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differ*. The sharer's preview proves nothing crossed the wire.
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* Two browser **processes**, not two contexts, when a test means "two machines".
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## 6. JavaScript rules
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* Plain ES modules loaded with `<script type="module">`. No globals beyond
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`window.__probe` in test scaffolding.
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* Every element a script looks up (`$("#id")`) must exist in its page — enforced
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by `test_every_element_the_script_reaches_for_exists`.
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* Element ids must not collide **across** pages (one shared stylesheet):
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`test_the_two_pages_share_no_element_ids_but_the_shared_chrome`. The only
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allowed shared ids are `net`, `notice`, `toast`.
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* WebRTC: the **sharer always offers, the viewer always answers**. Queue ICE
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candidates until `remoteDescription` exists; serialise offers per peer to avoid
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glare. Reuse `net.js` rather than duplicating socket logic.
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* Never move a `<video>` element's `srcObject` to "switch views" — move the
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element (that is how `/watch` staging works) so the peer connection survives.
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## 7. Python rules
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* `from __future__ import annotations`, full type hints, Google-style docstrings
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on public functions.
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* Starlette ≥1.10 raises **`WebSocketDisconnected`** (a `RuntimeError`) when the
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app has already closed a socket, and `WebSocketDisconnect` when the peer does.
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Catch both; read a socket you closed and you will crash the connection handler.
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* Registry errors are `RegistryError(code, message, fatal)`; `fatal` means the
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socket closes after the error frame is delivered. New error codes get a test.
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* No bare `except:`; swallow only what you can name, and say why in a comment.
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## 8. What to do when something behaves mysteriously
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Reproduce at the lowest layer that can fail:
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1. `curl -s localhost:8055/api/streams | python -m json.tool` — server truth.
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2. `websocat ws://localhost:8055/ws` — speak the protocol by hand (see PLAN §3).
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3. `uv run pytest tests/test_registry.py` — is the policy wrong, or the wiring?
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4. Only then reach for a browser, and print `pageerror`/`console` from the first
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line of the test.
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## 9. Commits
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* Conventional Commits (`feat:`, `fix:`, `test:`, `docs:`, `chore:`).
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* Always `--no-gpg-sign`, always append the trailer `LLM-Generated: true`
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(the `git-commit` skill does this).
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* Never commit `.env`, keys, or `.agents/phase-sessions/`.
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## 10. Quick reference
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| I want to… | Do |
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| Run it | `uv run mirror serve` → `:8055` |
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| Share / watch | `/mirror` · `/watch` |
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| Debug with an editor | `DEBUGPY=1 uv run mirror serve` (port 5678) |
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| Server truth about mirrors | `GET /api/streams` |
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| What the browser may know | `GET /api/config` |
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| Everything fast, no browser | `uv run pytest -m "not e2e"` |
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| Only the real-desktop test | `MIRROR_REALDISPLAY=1 uv run pytest -m realdisplay` |
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