phase: 88_mobile_chat_hamburger_boot

All completion criteria verified green. Final state confirmed: phase stays in `todo/` per A4 (owner device gate), task files in `complete/`, no `app/` changes, no commits made (harness commits).

## Phase 88 — final verification pass report

**Verified (all 6 tasks already complete):** `touch-action: manipulation` on mobile `#nav-toggle`; `#view-chat.chat-booted` double-rAF sticky handover (CSS gate + app.js boot IIFE); `body.nav-menu-open` marker in `setNavMenu` + ≤640px `visibility: hidden` rule; router boot contract (`wasMounted && !opts.boot` + `boot: true`); new unit module (10 pins) + 4-test real-touch E2E story.

**Test / lint / coverage:**
- `uv run pytest --cov=app --cov-report=term-missing` → 1741 passed, **99%** on `app/` (>90% ✓)
- `tests/e2e/test_mobile_chat_hamburger_boot.py` 4/4, `test_mobile_hamburger_nav.py` 8/8, `test_pinned_composer.py` 4/4, `test_smoke.py` 3/3 — each in isolation, `--no-cov` ✓
- `uv run ruff check .` clean; `uv run pyright` 0 errors ✓

**Completion criteria:** (1) 360px cold-boot touch-action + sticky handover + tap-opens-menu-with-cluster-hidden (E2E 1–2) ✓; (2) boot fires no `bor:view-refresh`, re-show fires exactly one, `/sources.html` regression (E2E 3–4) ✓; (3) full gate green ✓; (4) diff limited to 4 assets + 2 new tests + phase files, 0 changes in `app/` ✓; (5) commit deferred to harness per executor rules ✓; (6) owner device re-verification **pending** (A4 — gates the archive; no Owner report recorded yet).

**Deviations (both documented in-tree):** unit pins updated in `test_frontend_router.py`/`test_hamburger_nav.py` (their exact-text pins collided with the mandated new guard/marker text — without them the suite goes red); `boot: true` count pinned at 1 not 2 (codebase has one boot call site, no `history.state` branch — verified against git HEAD).

**Next pending phase:** none in `todo/` — pipeline awaits the owner's on-device report (archive, or `?dbg=nav` instrumentation follow-up if the menu is still dead).

frontend/assets/styles.css

@@ -1263,6 +1263,19 @@ details.thinking .thinking-text ul { margin: 0 0 0.5rem; }
   position: sticky;
   bottom: env(safe-area-inset-bottom, 0);
 }
+/* Phase 88: pre-boot, the composer cluster is NOT sticky. The sticky
+   promotion (a compositor layer) is deferred out of the first layout
+   commit — on real Android, the cluster's sticky layer born at first
+   commit was eating the hamburger's click (owner bug report
+   2026-09-08; the client-side switch into chat — same layer, born on
+   a settled page — always worked). app.js adds .chat-booted two
+   frames after boot settles; no-JS keeps the cluster static, which in
+   the only no-JS state (empty, 100dvh document) sits exactly where
+   the pin would. */
+#view-chat:not(.chat-booted) .chat-bottom,
+#view-chat:not(.chat-booted) .composer {
+  position: static;
+}
 .composer {
   display: flex;
   align-items: flex-end;
@@ -3550,6 +3563,9 @@ details.thinking .thinking-text ul { margin: 0 0 0.5rem; }
     border: 0;
     border-radius: var(--radius-sm);
     cursor: pointer;
+    touch-action: manipulation; /* Phase 88: standard dead-mobile-button fix — the
+      toggle's taps must not wait on the double-tap-zoom/pinch disambiguation
+      (owner bug report 2026-09-08: dead hamburger on chat-page cold boots). */
   }
   .nav-toggle:hover { background: var(--brand-soft); color: var(--brand-ink); }
   /* The icon is sized (an unsized inline SVG would default to 300px
@@ -3588,6 +3604,15 @@ details.thinking .thinking-text ul { margin: 0 0 0.5rem; }
     pointer-events: auto;
     transition: opacity 180ms ease, transform 180ms ease, visibility 0s;
   }
+  /* Phase 88: while the mobile menu is open, the chat's sticky bottom
+     cluster is hidden — it is the other positioned/layered element on
+     the page and must not compete for taps with the open menu (it also
+     overlaps the menu's lower rows on short viewports — menu y58→417
+     vs cluster top y395 at 390×600). visibility (not display): layout
+     is preserved, so closing never reflows the chat column. */
+  body.nav-menu-open .chat-bottom {
+    visibility: hidden;
+  }
   /* Menu rows: comfortable ≥44px targets (0.75rem × 2 + the 1rem line)
      and readable text — replaces the old .nav-link pill squeeze. */
   .app-nav .nav-link { padding: 0.75rem 1.25rem; font-size: 1rem; }