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.

app/rag/archive_upload.py

@@ -18,6 +18,13 @@ The guarantees (phase 49 locked decisions):
   unpack directory, and device/FIFO members — and counting every
   extracted byte against a cap (zip-bomb guard). Any failure removes the
   partial ``target_dir`` so no half-unpacked tree survives.
+* :func:`unpack_archive` also restores each regular file's member mtime
+  (the zip DOS ``date_time`` or the tar ``mtime``) — phase 106, D2:
+  uploaded archives keep their file dates, which the importer reads as
+  the document creation date. Directories, symlinks, and hardlinks are
+  untouched; the cap and every safety check above are unchanged (the
+  ``utime`` sits after a successful ``_write_capped``, so a failed
+  unpack still removes the partial tree).
 * :func:`swap_in` makes ``new_dir`` become ``final_dir`` with **no
   missing window**: the previous folder is renamed to a unique
   same-filesystem ``.old-`` sibling first, the new folder is renamed
@@ -33,6 +40,7 @@ import stat
 import tarfile
 import uuid
 import zipfile
+from datetime import UTC, datetime
 from pathlib import Path, PurePosixPath
 from typing import IO
 
@@ -183,6 +191,16 @@ def _unpack_zip(archive: Path, target: Path, max_extract_bytes: int) -> None:
             else:
                 with zf.open(member) as src:
                     _write_capped(src, dest, max_extract_bytes, total)
+                # Phase 106 (D2): restore the member's DOS mtime — a
+                # tz-agnostic epoch value, UTC-rendered exactly like an
+                # mtime — so uploaded archives keep their file dates.
+                # Regular files only; an OSError here still removes the
+                # partial tree in unpack_archive like any write failure.
+                # ``ns=`` takes INTEGER nanoseconds (a float seconds
+                # value raises TypeError), so convert explicitly.
+                mtime = datetime(*member.date_time, tzinfo=UTC).timestamp()
+                mtime_ns = int(mtime * 1_000_000_000)
+                os.utime(dest, ns=(mtime_ns, mtime_ns))
 
 
 def _unpack_tar(archive: Path, target: Path, max_extract_bytes: int) -> None:
@@ -206,6 +224,14 @@ def _unpack_tar(archive: Path, target: Path, max_extract_bytes: int) -> None:
                 if src is None:
                     raise ArchiveUploadError("corrupt archive member")
                 _write_capped(src, dest, max_extract_bytes, total)
+                # Phase 106 (D2): restore the member's mtime (epoch
+                # seconds — a tz-agnostic value) so uploaded archives
+                # keep their file dates. Regular files only; an OSError
+                # here still removes the partial tree in unpack_archive.
+                # ``ns=`` takes INTEGER nanoseconds (a float seconds
+                # value raises TypeError), so convert explicitly.
+                mtime_ns = int(member.mtime * 1_000_000_000)
+                os.utime(dest, ns=(mtime_ns, mtime_ns))
             else:  # char/block device, FIFO
                 raise ArchiveUploadError(
                     "tar archives with device or FIFO members are not allowed"