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
@@ -375,8 +375,14 @@ 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
+        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":

mempalace/miner.py

@@ -15,7 +15,7 @@ from pathlib import Path
 from datetime import datetime
 from collections import defaultdict
 
-from .palace import SKIP_DIRS, get_collection, file_already_mined
+from .palace import SKIP_DIRS, get_collection, file_already_mined, mine_lock
 
 READABLE_EXTENSIONS = {
     ".txt",
@@ -434,6 +434,14 @@ def process_file(
         print(f"    [DRY RUN] {filepath.name} → room:{room} ({len(chunks)} drawers)")
         return len(chunks), room
 
+    # Lock this file so concurrent agents don't interleave delete+insert.
+    # Without the lock, two agents can both pass file_already_mined(),
+    # both delete, and both insert — creating duplicates or losing data.
+    with mine_lock(source_file):
+        # Re-check after acquiring lock — another agent may have just finished
+        if file_already_mined(collection, source_file, check_mtime=True):
+            return 0, room
+
         # Purge stale drawers for this file before re-inserting the fresh chunks.
         # Converts modified-file re-mines from upsert-over-existing-IDs (which hits
         # hnswlib's thread-unsafe updatePoint path and can segfault on macOS ARM

mempalace/palace.py

@@ -4,6 +4,8 @@ palace.py — Shared palace operations.
 Consolidates collection access patterns used by both miners and the MCP server.
 """
 
+import contextlib
+import hashlib
 import os
 
 from .backends.chroma import ChromaBackend
@@ -50,6 +52,41 @@ def get_collection(
     )
 
 
+@contextlib.contextmanager
+def mine_lock(source_file: str):
+    """Cross-platform file lock for mine operations.
+
+    Prevents multiple agents from mining the same file simultaneously,
+    which causes duplicate drawers when the delete+insert cycle interleaves.
+    """
+    lock_dir = os.path.join(os.path.expanduser("~"), ".mempalace", "locks")
+    os.makedirs(lock_dir, exist_ok=True)
+    lock_path = os.path.join(
+        lock_dir, hashlib.sha256(source_file.encode()).hexdigest()[:16] + ".lock"
+    )
+
+    lf = open(lock_path, "w")
+    try:
+        if os.name == "nt":
+            import msvcrt
+            msvcrt.locking(lf.fileno(), msvcrt.LK_LOCK, 1)
+        else:
+            import fcntl
+            fcntl.flock(lf, fcntl.LOCK_EX)
+        yield
+    finally:
+        try:
+            if os.name == "nt":
+                import msvcrt
+                msvcrt.locking(lf.fileno(), msvcrt.LK_UNLCK, 1)
+            else:
+                import fcntl
+                fcntl.flock(lf, fcntl.LOCK_UN)
+        except Exception:
+            pass
+        lf.close()
+
+
 def file_already_mined(collection, source_file: str, check_mtime: bool = False) -> bool:
     """Check if a file has already been filed in the palace.