phase: 185_sync_defer_content_fast_path

All gates green. Report:

**Implemented / verified (phase 185)**
- `_doc_row_stmt` is the ONE deferral helper for all four fast-path row loads; only `Document.content` is deferred, no `raiseload`/`noload` (LOCKED A1/A2) — pinned by `tests/unit/test_importer_defer_content.py`.
- `tests/integration/test_import_fast_path_columns.py` (5), `tests/e2e/test_fast_path_deferred_content.py` (3, isolation) green; added 2 constraint pins to `test_import_session_retention.py` (summary-NULL backfill survives the cadence; both prune guards cost the same statement budget).
- **Fixed 6 pre-existing E2E failures** (all reproduce at HEAD with this phase's importer reverted): stale pins from phase 168 `Settings` nav link (`test_nav_rename_sources`), phase 182 `verbatim.js` script count (`test_steering`), phase 175 `/api/chats?limit=…` pagination breaking `endswith` counting (`test_navbar_refresh`), phase-167 lazy-drill race in the breadcrumb read (`test_modal_back_button`), nav-length tab budget (`test_suggestion_chips`).
- **Fixed a genuine flake** in `test_source_chip_quality` (passed/failed across identical runs): `ORDER BY embedding <=> q` is not a total order, so equal-cosine fixtures get a different RRF rank each run. Pinned it as an explicit tie-group (`_assert_ranked` / `_assert_related_pair`) instead of an exact order.

**Tests / lint (all 100% green)**
- `uv run pytest --cov=app --cov-report=term-missing` → **4519 passed**, `app/rag/importer.py` **99%**, `TOTAL` **99%** (>90%).
- `uv run ruff check .` → All checks passed; `uv run pyright` → 0 errors.
- Full E2E sweep, one pytest process per file (the README's sanctioned loop) → **167/167 files OK, 0 FAIL** (re-run after the fixes).

**Completion criteria**: helper shared by 4 loads ✅ · column-list + 1-SELECT + backfill pins ✅ · `test_importer_unchanged_fast_path.py` 24 passed, zero expectation edits ✅ · full suite + coverage + lint/types ✅ · phase E2E in isolation ✅ · docs accurate ✅ · commit left to the harness (no git commands run).

**Documentation**: README + AGENTS.md already carry the phase-185 rule; full pass found and fixed no doc inconsistencies (env vars: all 85 `Settings` fields documented in `.env.example` + README, no ghosts; every `app/… tests/… scripts/…` path referenced in both files exists).

**Deviations**: (1) the ranking non-determinism behind the chip-quality flake is real in `app/rag/retriever.py` — a SQL tie-break would cost pgvector index usage, so I kept the fix test-side; a follow-up phase should make vector-candidate ranking a total order. (2) Two tracked E2E screenshots were regenerated by the sweep (artifacts, left modified).

**Next pending phase**: `186_git_log_streaming_dates`.

tests/e2e/test_source_chip_quality.py

@@ -114,6 +114,46 @@ def _ask(page: Page, message: str) -> None:
     page.click("#send-btn")
 
 
+def _assert_ranked(recorded: str, groups: list[list[str]]) -> None:
+    """Compare a ``query_log.sources`` string against an expected rank list
+    whose trailing entries are TIE-GROUPS (order-free sets).
+
+    WHY the groups exist: the E2E mock embedder builds real token-overlap
+    vectors, so several tiny fixture documents end up on EXACTLY the same
+    fused score. ``fuse`` then sorts by ``(-score, -cosine, path,
+    position)``… but that only orders chunks whose SCORES differ; between
+    two documents tied in both lists the vector rank itself comes out of
+    ``ORDER BY embedding <=> q``, which is not a total order, so Postgres
+    (a parallel seq scan handing its partial sorts back) may return the
+    tied pair the other way round between two runs of the SAME fixture.
+    That was this suite's flake. The rank of every block, and the exact
+    SET inside it, are still pinned — what the story pins is that the
+    record carries the FULL retrieval (LOCKED A3), not the luck of a tie.
+    """
+    docs = [d.strip() for d in recorded.split(",")]
+    expected = [d for group in groups for d in group]
+    assert len(docs) == len(expected), f"recorded {docs}, expected {expected}"
+    at = 0
+    for group in groups:
+        window = docs[at : at + len(group)]
+        assert sorted(window) == sorted(group), (
+            f"rank block {at + 1}..{at + len(group)}: got {window}, "
+            f"expected the set {sorted(group)}"
+        )
+        at += len(group)
+
+
+def _assert_related_pair(links: object, titles: set[str]) -> None:
+    """The two related-doc links carry EXACTLY these two documents, in
+    either order (the same tie the record pins as a group — see
+    :func:`_assert_ranked`)."""
+    found = {
+        links.nth(i).get_attribute("title")  # pyright: ignore[reportAttributeAccessIssue]
+        for i in range(2)
+    }
+    assert found == titles, f"related pair is {found}, expected {titles}"
+
+
 def test_single_source_question_shows_exactly_one_citation_chip(
     page: Page, app_url: str, mock_llm: int, db_ready: None
 ) -> None:
@@ -179,15 +219,18 @@ def test_single_source_question_shows_exactly_one_citation_chip(
     # (best eff 0.016277) now out-ranks ``kubernetes.md`` (0.016036);
     # re-pinned against the post-phase walk (the record's CONTENT —
     # suggested + related + read, deduped — is LOCKED A3, untouched).
-    assert row_log.sources == (
-        "docs/homelab/ssh/ssh_aliases.txt, "
-        "docs/homelab/container_gitlab/gitlab-compose.yaml, "
-        "docs/homelab/scripts/uptime_probe.py, "
-        "docs/homelab/backups.md, "
-        "docs/homelab/kubernetes.md, "
-        "docs/homelab/quadlet/compose.container, "
-        "docs/homelab/networking/static-dns.json"
-    ), row_log.sources
+    _assert_ranked(
+        row_log.sources,
+        [
+            ["docs/homelab/ssh/ssh_aliases.txt"],
+            ["docs/homelab/container_gitlab/gitlab-compose.yaml"],
+            ["docs/homelab/scripts/uptime_probe.py"],
+            # The tied pair this record used to pin in an arbitrary order.
+            ["docs/homelab/backups.md", "docs/homelab/kubernetes.md"],
+            ["docs/homelab/quadlet/compose.container"],
+            ["docs/homelab/networking/static-dns.json"],
+        ],
+    )
 
 
 def test_deflected_question_shows_zero_citation_chips(
@@ -225,8 +268,9 @@ def test_deflected_question_shows_zero_citation_chips(
     # record, but a deflected turn cites nothing, so they never render
     # as chips.
     expect(links).to_have_count(2)
-    expect(links.nth(0)).to_contain_text("backups.md")
-    expect(links.nth(1)).to_contain_text("kubernetes.md")
+    # The pair, as a SET: the two are tied in the fused score (see
+    # :func:`_assert_ranked`), so only their presence is a contract.
+    _assert_related_pair(links, {"docs/homelab/backups.md", "docs/homelab/kubernetes.md"})
 
     # ZERO citation chips under the bubble — the weak hits are scored
     # docs, not citations (the phase-112/113 contract on the wire).
@@ -243,12 +287,16 @@ def test_deflected_question_shows_zero_citation_chips(
     assert row_log.deflected is True
     assert 0.0 < row_log.top_score < get_settings().relevance_threshold
     assert row_log.fts_hits == 0
-    assert row_log.sources == (
-        "docs/deployments/new-service.md, "
-        "docs/homelab/ssh/ssh_aliases.txt, "
-        "docs/homelab/quadlet/lan.network, "
-        "docs/homelab/scripts/uptime_probe.py, "
-        "docs/homelab/quadlet/compose.container, "
-        "docs/homelab/backups.md, "
-        "docs/homelab/kubernetes.md"
-    ), row_log.sources
+    _assert_ranked(
+        row_log.sources,
+        [
+            ["docs/deployments/new-service.md"],
+            ["docs/homelab/ssh/ssh_aliases.txt"],
+            ["docs/homelab/quadlet/lan.network"],
+            ["docs/homelab/scripts/uptime_probe.py"],
+            ["docs/homelab/quadlet/compose.container"],
+            # The related row IS this pair, and the row's order is the same
+            # tie — pinned as a set below (``_assert_related_pair``).
+            ["docs/homelab/backups.md", "docs/homelab/kubernetes.md"],
+        ],
+    )