phase: 104_chip_sizing_question_cap

All completion criteria verified. Final report:

**Phase 104 — final verification pass: all green**
- Verified (no code changes needed): single-line ellipsized `.suggestion-chip` CSS + deleted `.maybe-try` override, `renderChips` full-text `title` + `aria-label`-when-clipped, `maxlength="4000"` + `#char-count` counter + `handleSend` over-cap guard, unit pins file, schemas boundary pins, dedicated E2E suite.
- E2E (isolation): `uv run pytest tests/e2e/test_chip_sizing_question_cap.py -v --no-cov` → **6 passed**; regressions: `test_suggestion_chips.py` 8 passed, `test_pinned_composer.py` 4 passed, `test_responsive_polish.py` 7 passed, `test_chat_history.py` 5 passed.
- `uv run pytest` → **2102 passed**; `--cov=app` → **99%** (>90%); `uv run ruff check . && uv run pyright` → clean, 0 errors.
- Criteria: chip E2E (single-line, clipped, title+aria-label full text) ✅; paste caps at exactly 4,000, send streams, counter hides ✅; programmatic 5,000-char fill → banner, no turn, text kept ✅; 4,000/4,001 boundary pinned + HTML maxlength == JS constant cross-file pin ✅.
- Diff scope: `frontend/`, new unit file, `tests/unit/test_schemas.py`, new E2E file, phase files — **no `app/` diff, no migration, no `shared.js` diff**.
- Deviations: 4 regression test files touched — 2 genuine DOM-pin conflicts from the new `#char-count` child (explicitly anticipated by the overview) + 3 documented **pre-existing E2E flake fixes** (smooth-scroll race, tab-walk heuristic, 10 ms timeout), each verified pre-existing on the pre-phase-104 tree.
- No commit made (harness commits per the execution protocol override).
- Next pending phase: `98_sync_summary_visibility`.

frontend/index.html

@@ -252,6 +252,15 @@
           </button>
         </div>
 
+        <!-- Phase 104 (owner 2026-09-12): the question-length counter —
+             hidden until 80% of the 4,000-char cap (app.js
+             updateCharCount); the .is-max state uses the --err-* family
+             PLUS a copy change (B3: text + color, never color alone). NOT
+             a live region: per-keystroke feedback is decorative — the
+             over-cap failure path announces through the error banner
+             (role=alert). -->
+        <p class="char-count" id="char-count" hidden></p>
+
           <!-- Composer (phase 48, 2026-08-29, TODO.md L3): one button, two
                roles — #send-btn reads "Send" when idle and morphs into the
                enabled "Stop" control (.is-stop, rose treatment) while a turn
@@ -270,12 +279,16 @@
                precedent as the tuning form's noValidate). -->
         <form class="composer" id="composer" novalidate>
           <label class="visually-hidden" for="message-input">Ask Brain of Reese a question</label>
+          <!-- maxlength=4000 mirrors ChatRequest.message max_length=4000
+               (app/schemas.py) — the server 422s beyond; the #char-count
+               line makes the cap visible (app.js updateCharCount). -->
           <textarea
             id="message-input"
             name="message"
             rows="1"
             placeholder="Ask me anything…"
             autocomplete="off"
+            maxlength="4000"
           ></textarea>
           <button type="submit" class="send-btn" id="send-btn">
             <span class="spinner" aria-hidden="true" hidden></span>