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`.

tests/unit/test_schemas.py

@@ -15,6 +15,7 @@ from pydantic import ValidationError
 
 from app.schemas import (
     ChatMessage,
+    ChatRequest,
     SavedChatCreate,
     SavedChatUpdate,
     SourceRef,
@@ -34,6 +35,7 @@ TITLE_CAP = 500  # documents.title String(500)
 NAME_CAP = 100  # ToolCall.name
 ARGUMENT_CAP = 2000  # ToolCall.argument
 MESSAGES_CAP = 200  # SavedChatCreate/Update.messages
+QUESTION_CAP = 4_000  # ChatRequest.message — the cap the composer mirrors (phase 104)
 
 
 def _source_ref() -> dict:
@@ -174,6 +176,30 @@ def test_chat_message_tools_one_over_cap_rejects() -> None:
     _failed_loc(exc.value, "tools")
 
 
+# ---------------------------------------------------------------------------
+# ChatRequest.message (the 4,000-char question cap — phase 104, A3)
+# ---------------------------------------------------------------------------
+
+
+def test_chat_request_message_at_cap_validates() -> None:
+    """EXACTLY 4,000 chars passes — the cap admits "a code example of a
+    few dozen lines" (owner A3) and the composer's maxlength + counter
+    mirror this exact boundary (the 4,000/4,000 E2E submit must not
+    422)."""
+    req = ChatRequest.model_validate({"message": "a" * QUESTION_CAP})
+    assert len(req.message) == QUESTION_CAP
+
+
+def test_chat_request_message_one_over_cap_rejects() -> None:
+    """4,001 chars is the 422 the UI now prevents blind: the server cap
+    stays the backstop (pre-existing, untouched — this phase only pins
+    it at the boundary, phase-83 pattern), naming ``message`` in the
+    error loc."""
+    with pytest.raises(ValidationError) as exc:
+        ChatRequest.model_validate({"message": "a" * (QUESTION_CAP + 1)})
+    _failed_loc(exc.value, "message")
+
+
 # ---------------------------------------------------------------------------
 # SourceRef (documents column-length mirrors)
 # ---------------------------------------------------------------------------