fix: add file-level locking to prevent multi-agent duplicate drawers

Root cause: when multiple agents mine simultaneously, both pass
file_already_mined() check, both delete+insert the same file's
drawers, creating duplicates or losing data.

Fix: mine_lock() in palace.py — cross-platform file lock (fcntl on
Unix, msvcrt on Windows). Both miner.py and convo_miner.py now lock
per-file during the delete+insert cycle and re-check after acquiring
the lock.

Tested:
- Lock acquires and releases correctly
- Second agent blocks until first releases (0.25s wait)
- 33/33 existing tests pass
- Cross-platform: fcntl (macOS/Linux), msvcrt (Windows)

Based on v3.2.0 tag.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

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 SKIP_DIRS, get_collection, file_already_mined, mine_lock
 
 
 # File types that might contain conversations
@@ -375,34 +375,40 @@ def mine_convos(
         if extract_mode != "general":
             room_counts[room] += 1
 
-        # File each chunk
+        # File each chunk — lock to prevent concurrent agents duplicating
         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
+        with mine_lock(source_file):
+            # Re-check after lock — another agent may have just finished this file
+            if file_already_mined(collection, source_file):
+                files_skipped += 1
+                continue
+
+            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
 
         total_drawers += drawers_added
         print(f"  ✓ [{i:4}/{len(files)}] {filepath.name[:50]:50} +{drawers_added}")