phase: 109_turn_progress_loader

All gates green. Final report:

**Phase 109 — final verification pass (all 3 tasks were already complete; no re-implementation needed)**

- Verified D15 (thinking-handler re-open `block.open = true` after `ensureThinkingBlock`; delta keeps closing; "never reopens" narrative removed; restore path still collapses) and D16 (single static `#turn-loader` in composer row, `aria-hidden`, sole `turnLoader.hidden = !inFlight` write in `setUiState`; CSS reuses `typing` keyframes + reduced-motion override after the main rule + provenance; global `[hidden]` guard intact; mock `TURN_PROGRESS_TRIGGER` repro marker; `app/` untouched — pure UI phase).
- Unit pins: `tests/unit/test_frontend_turn_loader.py` (9 tests) — green via full run.
- `uv run pytest tests/e2e/test_turn_progress_loader.py -v --no-cov` → **3 passed** (isolation, DB up): loader visible send→tool-gap→final-thinking, hidden after done; re-opened scratchpad carries `marker-thought-42`/`marker-final-thought-42`; `#send-status` carries state text, back to empty idle; reduced-motion context stills dots (computed `animation-name: none`) with loader still visible.
- Regressions in isolation: `test_thinking_display` 5 passed, `test_stop_generation` 3 passed, `test_big_read_progress` 4 passed, `test_loading_feedback` 5 passed.
- `uv run pytest` → **2314 passed**; `uv run pytest --cov=app --cov-report=term-missing` → **TOTAL 99%** (>90%); `uv run ruff check .` clean; `uv run pyright` → 0 errors, 0 warnings.
- All terminal paths (done→idle L2554, stream error→error L2543, timeout→error L2247) funnel through `setUiState` — never-stale by construction.
- No defects found; no code changes made in this pass. Commit + phase-dir move left to the harness per pipeline rules (working tree carries all changes).
- Next pending phase: `108_history_wire_check` (still in `todo/`; out of scope here).

frontend/index.html

@@ -295,6 +295,18 @@
             <span class="btn-label" id="send-label">Send</span>
             <span class="visually-hidden" aria-live="polite" id="send-status"></span>
           </button>
+          <!-- Phase 109 (TODO.md L3, D16): the persistent in-turn loader —
+               ONE static element in the composer's status row, the
+               visible companion of the #send-status line. It is
+               DECORATIVE (aria-hidden): #send-status stays the sole a11y
+               announcer, so the state's meaning never moves (the L1791
+               house pattern). Hidden by default (idle on load); app.js's
+               setUiState is the SOLE writer of its hidden attribute —
+               shown iff the turn is in flight, hidden by construction in
+               every terminal state (PLAN §7.4 never-stale, no
+               per-handler cleanup). Never constructed in JS: the
+               createElement/textContent house rule. -->
+          <div id="turn-loader" class="turn-loader" aria-hidden="true" hidden></div>
         </form>
       </div>
     </div>