phase: 106_document_dates

Everything is verified green. Final report:

**Phase 106 — Document dates (final verification pass; all 10 tasks already complete)**

- Verified all phase artifacts: alembic `0020` (dev DB at `0020`), `doc_dates.py`, git `file_commit_dates`, importer `doc_dates_by_root`/`dates_updated`, both entry-point wirings, date APIs + tree `created_at`/`updated_at`, LLM surfaces (prompt block, `read` line 2, appended `ls` field), `apply_recency_boost` in `retrieve()`, UI columns/badge, admin editor, mock-LLM regex — all present and correct; no defects found, no fixes needed.
- `uv run pytest --cov=app --cov-report=term-missing` → **2299 passed, TOTAL 99%** (>90% ✓)
- `uv run pytest tests/e2e/test_document_dates.py -v --no-cov` → **6/6 passed** in isolation (DB up)
- 12 regression E2E suites (retrieval_quality, whole_document_context, agent_document_tools, ls_tree_drilldown, read_truncation_cap, kb_tree, kb_tree_nav, document_viewer, edit_summaries, import_documents, sync_button, hidden_folders_toggle, smoke) → **all green in isolation**
- `uv run ruff check .` → clean; `uv run pyright` → **0 errors, 0 warnings**

**Completion criteria:** 1) non-null `created_at` + 0020 upgrade/downgrade on dev DB ✓ (real-Alembic integration tests) 2) sync refresh/older/manual-persists/content-reset/no sources_meta bump ✓ 3) zip/tar mtime + future→today ✓ 4) LLM date surfaces + cross-check ✓ 5) UI Created/Updated/badge positions ✓ 6) admin editor set+revert round-trip ✓ 7) old-correct-beats-new-similar (defaults & boost-off) + near-tie + `BOR_RECENCY_BOOST=0` byte-identical ✓ 8) full gate ✓ 9) commit/phase-move — left to harness per instructions.

- **Notable:** recency default tuned 0.001 → **0.0007** (task 07 step 5 explicitly permits; measured margins recorded in `test_recency_boost.py` docstring).
- **Next pending phase:** none — `todo/` holds only this phase.

tests/unit/test_config.py

@@ -37,6 +37,10 @@ def test_defaults_match_locked_decisions(monkeypatch: pytest.MonkeyPatch) -> Non
     assert s.hybrid_lexical_candidates >= 1
     assert s.rrf_k >= 1
     assert s.top_n_docs >= 1
+    # Phase 106, D6: the recency boost is ON by default (0.0007 — the
+    # fine-line-tuned value, task 07) with a 365-day decay timescale.
+    assert s.recency_boost == 0.0007
+    assert s.recency_half_life_days == 365
     # Owner instruction 2026-08-22: answers may run up to 32 768 tokens.
     assert s.max_output_tokens == 32_768
     # Phase 17: the model's thinking streams by default (kill-switch off).
@@ -235,6 +239,47 @@ def test_read_max_chars_rejects_negative(monkeypatch: pytest.MonkeyPatch) -> Non
         _settings()
 
 
+def test_recency_boost_default_and_env_override(
+    monkeypatch: pytest.MonkeyPatch,
+) -> None:
+    """Phase 106, D6: the recency boost on the RRF-fused score is ON by
+    default (0.0007 — the fine-line-tuned value, task 07; ``0`` is the
+    byte-identical kill switch) with a 365-day decay timescale; both
+    env-tunable so the owner re-tunes live."""
+    monkeypatch.delenv("BOR_RECENCY_BOOST", raising=False)
+    monkeypatch.delenv("BOR_RECENCY_HALF_LIFE_DAYS", raising=False)
+    s = _settings()
+    assert s.recency_boost == 0.0007
+    assert s.recency_half_life_days == 365
+    monkeypatch.setenv("BOR_RECENCY_BOOST", "0")
+    monkeypatch.setenv("BOR_RECENCY_HALF_LIFE_DAYS", "90")
+    s = _settings()
+    assert s.recency_boost == 0.0
+    assert s.recency_half_life_days == 90
+    monkeypatch.setenv("BOR_RECENCY_BOOST", "0.002")
+    assert _settings().recency_boost == 0.002
+
+
+def test_recency_boost_rejects_negative(monkeypatch: pytest.MonkeyPatch) -> None:
+    """``0`` is the kill switch — a NEGATIVE boost would demote fresh
+    documents (the exact opposite of D6), so the validator fails loudly
+    at startup naming the field (the ``agent_max_rounds`` pattern)."""
+    monkeypatch.setenv("BOR_RECENCY_BOOST", "-0.001")
+    with pytest.raises(ValidationError, match="recency_boost"):
+        _settings()
+
+
+def test_recency_half_life_rejects_non_positive(
+    monkeypatch: pytest.MonkeyPatch,
+) -> None:
+    """A ``0``/negative decay timescale would divide the exponent by
+    zero — the validator fails loudly at startup naming the field."""
+    for bad in ("0", "-365"):
+        monkeypatch.setenv("BOR_RECENCY_HALF_LIFE_DAYS", bad)
+        with pytest.raises(ValidationError, match="recency_half_life_days"):
+            _settings()
+
+
 def test_stream_thinking_default_true_and_env_parse(monkeypatch: pytest.MonkeyPatch) -> None:
     """Phase 17 kill-switch (``BOR_STREAM_THINKING``): on by default,
     ``0``/``false`` turn the ``thinking`` SSE frames off."""