feat(normalize): auto-rebuild stale drawers via NORMALIZE_VERSION schema gate

Without this, the strip_noise improvement only helps new mines. Every
user who had already mined Claude Code JSONL sessions would keep their
noise-polluted drawers forever, because convo_miner's file_already_mined
skip short-circuits before re-processing.

Adds a versioned schema gate so upgrades propagate silently:

- palace.NORMALIZE_VERSION=2 — bumped when the normalization pipeline
  changes shape (this PR's strip_noise is the v1→v2 bump).
- file_already_mined now returns False if the stored normalize_version
  is missing or less than current, triggering a rebuild on next mine.
- Both miners stamp drawers with the current normalize_version.
- convo_miner now purges stale drawers before inserting fresh chunks
  (mirrors miner.py's existing delete+insert), extracted into
  _file_convo_chunks helper to keep mine_convos under ruff's C901 limit.

User experience: upgrade mempalace, run `mempalace mine` as usual, old
noisy drawers get silently replaced with clean ones. No erase needed,
no "you need to rebuild" changelog footgun.

Tests:
- test_file_already_mined_returns_false_for_stale_normalize_version —
  pins the version gate contract for missing/v1/current.
- test_add_drawer_stamps_normalize_version — fresh project-miner drawers
  carry the field.
- test_mine_convos_rebuilds_stale_drawers_after_schema_bump — end-to-end
  proof that a pre-v2 palace gets silently cleaned on next mine, with
  orphan drawers purged and NOT skipped.

Existing test_file_already_mined_check_mtime updated to include the
new field; all other tests unaffected.

mempalace/convo_miner.py

@@ -16,7 +16,7 @@ from datetime import datetime
 from collections import defaultdict
 
 from .normalize import normalize
-from .palace import SKIP_DIRS, get_collection, file_already_mined
+from .palace import NORMALIZE_VERSION, SKIP_DIRS, file_already_mined, get_collection
 
 
 # File types that might contain conversations
@@ -51,6 +51,7 @@ def _register_file(collection, source_file: str, wing: str, agent: str):
                 "added_by": agent,
                 "filed_at": datetime.now().isoformat(),
                 "ingest_mode": "registry",
+                "normalize_version": NORMALIZE_VERSION,
             }
         ],
     )
@@ -272,6 +273,52 @@ def scan_convos(convo_dir: str) -> list:
 # =============================================================================
 
 
+def _file_convo_chunks(collection, source_file, chunks, wing, room, agent, extract_mode):
+    """Purge stale drawers for ``source_file`` then upsert fresh chunks.
+
+    Returns (drawers_added, room_counts_delta).
+    """
+    # Purge stale drawers first. When the normalize schema bumps,
+    # file_already_mined() returns False for pre-v2 drawers and we land
+    # here — clean them out so the source doesn't end up with a mix of
+    # old-noise and new-clean drawers.
+    try:
+        collection.delete(where={"source_file": source_file})
+    except Exception:
+        pass
+
+    room_counts_delta: dict = defaultdict(int)
+    drawers_added = 0
+    for chunk in chunks:
+        chunk_room = chunk.get("memory_type", room) if extract_mode == "general" else room
+        if extract_mode == "general":
+            room_counts_delta[chunk_room] += 1
+        drawer_id = f"drawer_{wing}_{chunk_room}_{hashlib.sha256((source_file + str(chunk['chunk_index'])).encode()).hexdigest()[:24]}"
+        try:
+            collection.upsert(
+                documents=[chunk["content"]],
+                ids=[drawer_id],
+                metadatas=[
+                    {
+                        "wing": wing,
+                        "room": chunk_room,
+                        "source_file": source_file,
+                        "chunk_index": chunk["chunk_index"],
+                        "added_by": agent,
+                        "filed_at": datetime.now().isoformat(),
+                        "ingest_mode": "convos",
+                        "extract_mode": extract_mode,
+                        "normalize_version": NORMALIZE_VERSION,
+                    }
+                ],
+            )
+            drawers_added += 1
+        except Exception as e:
+            if "already exists" not in str(e).lower():
+                raise
+    return drawers_added, room_counts_delta
+
+
 def mine_convos(
     convo_dir: str,
     palace_path: str,
@@ -375,34 +422,12 @@ def mine_convos(
         if extract_mode != "general":
             room_counts[room] += 1
 
-        # File each chunk
-        drawers_added = 0
-        for chunk in chunks:
-            chunk_room = chunk.get("memory_type", room) if extract_mode == "general" else room
-            if extract_mode == "general":
-                room_counts[chunk_room] += 1
-            drawer_id = f"drawer_{wing}_{chunk_room}_{hashlib.sha256((source_file + str(chunk['chunk_index'])).encode()).hexdigest()[:24]}"
-            try:
-                collection.upsert(
-                    documents=[chunk["content"]],
-                    ids=[drawer_id],
-                    metadatas=[
-                        {
-                            "wing": wing,
-                            "room": chunk_room,
-                            "source_file": source_file,
-                            "chunk_index": chunk["chunk_index"],
-                            "added_by": agent,
-                            "filed_at": datetime.now().isoformat(),
-                            "ingest_mode": "convos",
-                            "extract_mode": extract_mode,
-                        }
-                    ],
-                )
-                drawers_added += 1
-            except Exception as e:
-                if "already exists" not in str(e).lower():
-                    raise
+        # Purge stale drawers + file fresh chunks.
+        drawers_added, room_delta = _file_convo_chunks(
+            collection, source_file, chunks, wing, room, agent, extract_mode
+        )
+        for r, n in room_delta.items():
+            room_counts[r] += n
 
         total_drawers += drawers_added
         print(f"  ✓ [{i:4}/{len(files)}] {filepath.name[:50]:50} +{drawers_added}")