phase: 153_document_viewer_context

That last `--co` (collect-only) run was my probe mistake — it shows 34% because no tests execute under collect-only. The valid coverage run was the real gate command executed earlier: `uv run pytest --cov=app --cov-report=term-missing` → **TOTAL 99%** (exit 0, all 3544 tests executed). All gates are verified.

## Phase 153 — final verification pass report

**Verified (all tasks 01–04 complete in `complete/`):**
- Modal `fullPageUrl(source, path, back = null)` + `openDocumentModal(…, back = null)` with module-level `currentBack`; 5 chat call sites pass `"/"`, sources.js call site unchanged (byte-identical Sources path); `documentUrl` comment now true
- Copy-path control (shared `renderDocument` core, icon+text, text = accessible name) on both surfaces; per-page clipboard helpers with the fallback-field + status-line contract; `#doc-copy-announcer` live region; styles + 44px touch floor
- Unit pins: `&back=%2F` / no-`back` byte-identity, `currentBack` single-writer guard, copy strings byte-pinned, phase-13 regression pins untouched

**Test / lint / coverage results:**
- `uv run pytest` → **3544 passed**, 0 failed (full unit + integration)
- `uv run pytest --cov=app --cov-report=term-missing` → **TOTAL 99%** (>90% gate)
- `uv run pytest tests/e2e/test_document_viewer_context.py -v --no-cov` → **8 passed** in 47.33s, in isolation (DB up, mock LLM)
- `uv run ruff check . && uv run pyright` → clean (0 errors/warnings)

**Completion criteria:** all met — (1) chat→modal→Full page: `href="/"` + "Chat"; Sources→modal→Full page: `href="/sources.html"` + "Sources" with `back=` asserted absent; (2) no-`back` URLs byte-identical to pre-phase; (3) Copy path: "Path copied." on success (clipboard readback), prefilled select-on-focus fallback field + "Path ready — copy it from the field." on rejected clipboard, both surfaces parameterized; (4) copied string exactly `docs/homelab/kubernetes.md`; (5) full suite green, E2E isolated green, lint clean, coverage 99%; (6) commit by harness.

**Documentation:** README.md reviewed in full — phase-153 feature already named in the Chat section; routes, env reference, workflows, deployment all consistent — no changes needed. AGENTS.md reviewed in full — rules, gates, and quick-reference commands verified against the repo (incl. `test_smoke.py`, `.env.example`, gitignore entries) — consistent, no changes needed.

**Notable:** pytest 9.1.1 quirk — a doubled `-q` (pyproject `addopts` + explicit `-q`) swallows the final "N passed" summary line while still exiting 0; the plain `uv run pytest` gate command prints it. No defects found in prior work.

**Next pending phase:** `154_sync_status_freshness`.

.agents/phases/todo/158_thinking_timeline/01_schema_segments.md

@@ -0,0 +1,69 @@
+# Task 01 — the validated `ChatMessage.segments` field (server)
+
+**Phase:** `158_thinking_timeline` · **Story:** n/a
+
+## Objective
+Saved-chat writes accept the new optional `segments` array (a discriminated
+`thinking`/`tool` union with phase-83-style caps), omit it when absent so
+pre-phase records round-trip byte-identically, and reject malformed values at
+the `extra="forbid"` boundary.
+
+## Work
+1. `app/schemas.py`:
+   - `ChatThinkingSegment` (a `BaseModel`, beside `ToolCall`): `kind:
+     Literal["thinking"]`, `text: str = Field(min_length=1, max_length=32_000)`
+     (`HistoryTurn`'s cap, phase 83 — docstring cross-reference).
+   - `ChatToolSegment` (a `BaseModel`): `kind: Literal["tool"]` + the EXACT
+     `ToolCall` field set (name / argument / offset / limit / path / truncated /
+     chars_shown / chars_total with their existing types and caps — mirror, do
+     not weaken; docstring cross-references `ToolCall` as the shape source).
+   - `ChatSegment = Annotated[Union[ChatThinkingSegment, ChatToolSegment],
+     Field(discriminator="kind")]`.
+   - `ChatMessage.segments: list[ChatSegment] | None = Field(default=None,
+     max_length=50)` — with the phase-83 voice comment (the cap sizing: far
+     past any realistic turn — the round cap is 10 → ≤ 20 entries; 50 matches
+     the `tools` cap).
+   - The EXISTING wrap serializer (`_drop_image_when_absent`) gains the
+     omission rule: after the two image pops, `if self.segments is None:
+     data.pop("segments", None)` — ABSENT, never `null` (the phase-50
+     round-trip contract; the phase-122 `SourceRef.image_url` omission
+     precedent, the phase-113 lesson applied up front: the field EXISTS so
+     the boundary does NOT 422 the done-time auto-save carrying it).
+   - The `ChatMessage` docstring gains the phase-158 paragraph (the shape,
+     the omission rule, the `extra="forbid"` boundary) in the established
+     voice; `HistoryTurn` and everything in `app/rag/` is UNTOUCHED (the
+     history wire stays `{who, text, thinking}`).
+2. NO migration, NO router change (`app/api/chats.py` validates through
+   `ChatMessage` — `m.model_dump()` + `ChatMessage.model_validate(m)` already
+   carry the new field end to end, including the public shared read
+   `SharedChatOut.messages`).
+
+## Testing & Quality
+- Integration (extend `tests/integration/test_chats_api.py` — the file already
+  pins the brain-record contract, phase 83/113/120/123/124):
+  - a record WITH `segments` (one `thinking` entry + two `tool` entries
+    carrying every additive field: `offset/limit`, `path`,
+    `truncated/chars_shown/chars_total`) is accepted by `POST /api/chats` and
+    round-trips through `GET` (the shape preserved, entry order preserved);
+  - `segments` with 51 entries → 422; a thinking-segment `text` of 32 001
+    chars → 422; a segment with `kind: "bogus"` → 422; a record with a stray
+    top-level key (e.g. `"foo": 1`) still → 422 (the `extra="forbid"`
+    boundary intact);
+  - a record WITHOUT `segments` (a pre-phase brain record, the full phase-113
+    shape) round-trips with the key ABSENT from the served JSON (never
+    `null` — the byte-identity pin, the phase-50 contract);
+  - the shared read path (the public read endpoint's `messages`) carries the
+    segments of a saved record with them (the public shape, the phase-51
+    contract).
+- Coverage: **>90%** on this task's new/modified code (the schema code is
+  exercised by the integration tests).
+
+## Completion Criteria
+- [ ] the three models + the field + the serializer rule land exactly as
+      designed (a source check)
+- [ ] the new integration tests are green; the EXISTING
+      `test_chats_api.py` tests stay green unchanged
+- [ ] `uv run pytest tests/integration -q` green; `uv run ruff check . && uv
+      run pyright` clean
+- [ ] no change in `app/rag/`, no migration, no router change (a `git diff
+      --stat` scoped check)