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/e2e/test_responsive_polish.py

@@ -130,8 +130,24 @@ def _assert_no_doc_overflow(page: Page, label: str) -> None:
 
 
 def _tab_outline_walk(page: Page, max_tabs: int = 60) -> list[dict[str, str]]:
-    """Real keyboard Tab walk; returns each focused element's outline."""
-    first_key: str | None = None
+    """Real keyboard Tab walk; returns each focused element's outline.
+
+    The walk covers a FULL focus cycle (it starts wherever Chromium
+    resumes after the skip-link check — mid-document, right after
+    #main — and ends when focus wraps back to the FIRST element it
+    visited). The wrap is detected by TRUE element identity: each
+    newly focused element is stamped with a unique ``data-tabwalk-id``
+    and the cycle ends when a STAMPED element is focused again.
+    Phase 104 (task 04, 2026-09-12): the pre-104 heuristic keyed on
+    the first 24 chars of the element's text — two chips sharing that
+    prefix (e.g. the two identical "How is my Kubernetes cluster set
+    up? write a long answer" opener chips left in ``saved_chats`` by
+    test_pinned_composer.py, which runs suites in sequence on the
+    shared e2e DB) collided and cut the walk short at two entries,
+    flaking ``len(seen) >= 3``. Verified pre-existing on the
+    pre-phase-104 tree (the mid-document Tab start is Chromium
+    behavior, not a phase-104 change)."""
+    first_id: str | None = None
     seen: list[dict[str, str]] = []
     for _ in range(max_tabs):
         page.keyboard.press("Tab")
@@ -142,7 +158,13 @@ def _tab_outline_walk(page: Page, max_tabs: int = 60) -> list[dict[str, str]]:
                 const cls = String(el.className).split(" ")[0];
                 const label = (el.getAttribute("aria-label")
                     || el.textContent || "").trim().slice(0, 24);
+                let id = el.getAttribute("data-tabwalk-id");
+                if (!id) {
+                    id = "tw" + ((window.__twSeq = (window.__twSeq || 0) + 1));
+                    el.setAttribute("data-tabwalk-id", id);
+                }
                 return {
+                    id: id,
                     key: el.tagName + "#" + (el.id || "") + "." + cls + ":" + label,
                     outline_style: cs.outlineStyle,
                     outline_width: cs.outlineWidth,
@@ -151,11 +173,11 @@ def _tab_outline_walk(page: Page, max_tabs: int = 60) -> list[dict[str, str]]:
         )
         if info["key"].startswith("BODY"):
             continue  # focus has not entered the document yet
-        if first_key is None:
-            first_key = info["key"]
+        if first_id is None:
+            first_id = info["id"]
         seen.append(info)
-        if len(seen) > 1 and info["key"] == first_key:
-            break  # wrapped back to the first focusable
+        if len(seen) > 1 and info["id"] == first_id:
+            break  # wrapped back to the first focusable (same ELEMENT)
     return seen