phase: 122_image_documents

**Phase 122 (image documents) — final verification pass: all green. No code changes were needed; defects found: none.**

**Verified (implementation already complete in working tree, reviewed end-to-end):**
- Toggle (`BOR_IMAGES`/`BOR_IMAGE_EXTENSIONS`/`BOR_IMAGE_DIR`, off by default) + `GET /api/config` `images` flag
- Ingest: bytes digest, `image_dir` persistent copy, `content = summary = vision description` (chat-model call; only text embedded), fail-soft skip + `images_failed` counter
- Serve/display: `/api/documents/{id}/image` route (404 matrix), viewer `<img>` + description, Sources 48px lazy thumbnails, chat inline source figure (alt = summary), agent `read` marker
- Prune guard: images-off syncs never prune `is_image` docs

**Test / lint / coverage (exact commands & outcomes):**
- `uv run pytest` → exit 0 (green; note: pytest 9.1.1 `-q` omits the final count line in output — exit code authoritative)
- `uv run pytest --cov=app --cov-report=term-missing` → **2715 passed, exit 0, TOTAL 99%** (>90% gate)
- `uv run ruff check . && uv run pyright` → "All checks passed!" / "0 errors, 0 warnings, 0 informations"
- `uv run pytest tests/e2e/test_image_documents.py -v --no-cov` → **4 passed, exit 0** (isolation)

**Completion criteria:** (1) images=true → described/embedded/displayed docs: ✅ (E2E + integration) · (2) images=false byte-identical + image docs survive sync: ✅ (E2E negative app + unit/integration) · (3) viewer + chat rendering with alt text; failed description skips + logs, sync completes: ✅ · (4) test/lint/coverage gates: ✅ · (5) commit + phase move: deferred to harness per this pass's rules (working tree left uncommitted).

**Notable deviation (pre-existing, documented in code):** image route uses `require_user` (phase-79 posture, same gate as the document content endpoint) rather than the phase text's "public" parenthetical — matches the endpoint it mirrors.

**Next pending phase:** `123_chat_image_questions`.

app/rag/agent.py

@@ -427,6 +427,18 @@ READ_TRUNCATION_NOTICE = (
     "document."
 )
 
+#: The image-document marker (phase 122, task 05): the line prefixed to
+#: the vision DESCRIPTION a ``read`` of a standalone-image document
+#: returns — the model must reason about what it is reading (the text
+#: below is a description GENERATED from the image, not the image's
+#: own words). It sits on the result's THIRD line: the ``Document …``
+#: header and the phase-106 date line stay byte-identical (the E2E
+#: mock's ``_READ_RESULT_PREFIX`` header contract), and a NON-image
+#: doc's result carries no marker at all (byte-identical to pre-122).
+IMAGE_DOC_MARKER = (
+    "Image document — the text below is a description generated from the image:"
+)
+
 #: The no-source ``ls`` refusal with the teaching parenthetical
 #: appended (phase 72): used when a stripped scope has no ``/`` and
 #: matches no registered source (the incident's ``ls(path='.')``). The
@@ -1270,6 +1282,12 @@ def _execute_tool(
             return _no_document_refusal(db, arg)
         holder.read_docs.append(doc)
         holder.tool_calls += 1
+        # Phase 122 (task 05): an image document's content IS the vision
+        # description — the marker line (a third line between the
+        # byte-identical header/date lines and the text) tells the model
+        # what it is reading. A text doc's ``marker`` is "" — the result
+        # stays byte-identical to pre-122.
+        marker = f"{IMAGE_DOC_MARKER}\n" if doc.is_image else ""
         cap = settings.read_max_chars
         if len(doc.content) > cap:
             # Phase 95 (owner permission 2026-09-10, ``TODO.md`` L5): the
@@ -1293,17 +1311,20 @@ def _execute_tool(
             return (
                 f"Document {doc.source}/{doc.path}:\n"
                 f"date: {doc.created_at:%Y-%m-%d}\n"
+                f"{marker}"
                 f"{doc.content[:cap]}\n"
                 f"{TRUNCATION_MARKER}\n"
                 f"{READ_TRUNCATION_NOTICE.format(shown=cap, total=len(doc.content))}"
             )
         # At or under the cap: the pre-phase-95 result plus the
         # phase-106 D5 date line (first line byte-identical — the
-        # mock's header contract; no marker, no notice, no holder
-        # entry, no ToolResultPiece).
+        # mock's header contract; no truncation marker, no notice, no
+        # holder entry, no ToolResultPiece) — and, phase 122, the
+        # image-document marker line for image docs only.
         return (
             f"Document {doc.source}/{doc.path}:\n"
             f"date: {doc.created_at:%Y-%m-%d}\n"
+            f"{marker}"
             f"{doc.content}"
         )
     if call.name == "grep":