phase: 123_chat_image_questions

All gates green. Verification complete.

**Phase 123 — final verification pass (all 4 tasks already in `complete/`)**

- Verified the full implementation is in the working tree: `app/api/chat_images.py` (upload/serve pair), `ChatRequest.image`/`ChatMessage.image` (path-validated, omitted-when-None), toggle-off + stale-file hinted error frames, `build_user_content` multimodal build at both sites (chat.py deflected branch + `run_agent`), config-gated composer attach/preview/upload-then-send, restore + shared rendering, CSP `img-src 'self' data:` carve-out, mock-LLM capture buffer.
- `uv run pytest` → **2796 passed**, exit 0 (unit + integration).
- `uv run pytest --cov=app --cov-report=term-missing` → **TOTAL 99%** (29/4615 missed; phase-123 modules 99–100%).
- `uv run pytest tests/e2e/test_chat_image_questions.py -v --no-cov` → **5 passed** in isolation.
- `uv run ruff check . && uv run pyright` → clean (0 errors).

**Completion criteria:** (1) attach→send→multimodal text+image to the model, bubble/reload/shared all render it, saved chat stores the PATH with `"base64" not in json.dumps(stored)` — **verified** (E2E tests 1–4 + integration round-trip); (2) `BOR_IMAGES=false` — control hidden, exact hinted error frame, zero model calls / no query_log row — **verified** (E2E test 5 + integration); (3) text-only byte-identical (`content` stays a plain `str`) — **verified** (unit + integration); (4) all gates green — **verified**; (5) commit + phase move — left to the harness per pipeline rules (no `git add`/`commit` run).

No defects found; no live-infrastructure changes (repo + local dev DB only). **Next pending phase: none** — 123 is the last phase in `todo/`.

app/rag/summarizer.py

@@ -117,6 +117,18 @@ IMAGE_MIMES: dict[str, str] = {
 IMAGE_FALLBACK_MIME = "application/octet-stream"
 
 
+def image_data_url(data: bytes, mime: str) -> str:
+    """One image's bytes as a data URL for a multimodal message (phase
+    122; factored for phase 123, task 01).
+
+    ``data:<mime>;base64,<ascii>`` — the OpenAI-compatible ``image_url``
+    payload's ``url``. ONE helper, both call sites: :func:`describe_image`
+    (document-image descriptions) and the chat question-image path
+    (``app.api.chat``'s multimodal user message, phase 123).
+    """
+    return f"data:{mime};base64,{base64.b64encode(data).decode('ascii')}"
+
+
 class SummaryLLM(Protocol):
     """The one-shot chat surface the summarizer needs.
 
@@ -223,7 +235,7 @@ async def describe_image(
     the doc is skipped, counted in ``images_failed``, and the sync
     continues (LOCKED A3).
     """
-    data_url = f"data:{mime};base64,{base64.b64encode(data).decode('ascii')}"
+    data_url = image_data_url(data, mime)
     messages: list[dict[str, Any]] = [
         {
             "role": "user",