diff --git a/mempalace/convo_miner.py b/mempalace/convo_miner.py
index 663f1a0..63b46f0 100644
--- a/mempalace/convo_miner.py
+++ b/mempalace/convo_miner.py
@@ -16,7 +16,13 @@ from datetime import datetime
 from collections import defaultdict
 
 from .normalize import normalize
-from .palace import NORMALIZE_VERSION, SKIP_DIRS, file_already_mined, get_collection
+from .palace import (
+    NORMALIZE_VERSION,
+    SKIP_DIRS,
+    file_already_mined,
+    get_collection,
+    mine_lock,
+)
 
 
 # File types that might contain conversations
@@ -273,50 +279,60 @@ 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.
+def _file_chunks_locked(collection, source_file, chunks, wing, room, agent, extract_mode):
+    """Lock the source file, purge stale drawers, and upsert fresh chunks.
 
-    Returns (drawers_added, room_counts_delta).
+    Combines the per-file serialization that prevents concurrent agents from
+    duplicating work (via mine_lock) with the normalize-version rebuild
+    contract (purge-before-insert so pre-v2 drawers don't survive).
+
+    Returns (drawers_added, room_counts_delta, skipped).
     """
-    # 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]}"
+    with mine_lock(source_file):
+        # Re-check after lock — another agent may have just finished this file
+        # at the current schema. A stale-version hit here returns False, so we
+        # still fall through to the purge+rebuild path below.
+        if file_already_mined(collection, source_file):
+            return 0, room_counts_delta, True
+
+        # Purge stale drawers first. When the normalize schema bumps,
+        # file_already_mined() returned False for pre-v2 drawers — clean
+        # them out so the source doesn't end up with mixed old/new drawers.
         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
+            collection.delete(where={"source_file": source_file})
+        except Exception:
+            pass
+
+        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, False
 
 
 def mine_convos(
@@ -422,10 +438,14 @@ def mine_convos(
         if extract_mode != "general":
             room_counts[room] += 1
 
-        # Purge stale drawers + file fresh chunks.
-        drawers_added, room_delta = _file_convo_chunks(
+        # Lock + purge stale + file fresh chunks. Lock serializes concurrent
+        # agents; purge removes pre-v2 drawers so the schema bump applies.
+        drawers_added, room_delta, skipped = _file_chunks_locked(
             collection, source_file, chunks, wing, room, agent, extract_mode
         )
+        if skipped:
+            files_skipped += 1
+            continue
         for r, n in room_delta.items():
             room_counts[r] += n
 
diff --git a/mempalace/miner.py b/mempalace/miner.py
index 49e0d25..522b33a 100644
--- a/mempalace/miner.py
+++ b/mempalace/miner.py
@@ -15,7 +15,13 @@ from pathlib import Path
 from datetime import datetime
 from collections import defaultdict
 
-from .palace import NORMALIZE_VERSION, SKIP_DIRS, file_already_mined, get_collection
+from .palace import (
+    NORMALIZE_VERSION,
+    SKIP_DIRS,
+    file_already_mined,
+    get_collection,
+    mine_lock,
+)
 
 READABLE_EXTENSIONS = {
     ".txt",
@@ -435,29 +441,37 @@ def process_file(
         print(f"    [DRY RUN] {filepath.name} → room:{room} ({len(chunks)} drawers)")
         return len(chunks), 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
-    # with chromadb 0.6.3) into a clean delete+insert, bypassing the update
-    # path entirely.
-    try:
-        collection.delete(where={"source_file": source_file})
-    except Exception:
-        pass
+    # 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
 
-    drawers_added = 0
-    for chunk in chunks:
-        added = add_drawer(
-            collection=collection,
-            wing=wing,
-            room=room,
-            content=chunk["content"],
-            source_file=source_file,
-            chunk_index=chunk["chunk_index"],
-            agent=agent,
-        )
-        if added:
-            drawers_added += 1
+        # 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
+        # with chromadb 0.6.3) into a clean delete+insert, bypassing the update
+        # path entirely.
+        try:
+            collection.delete(where={"source_file": source_file})
+        except Exception:
+            pass
+
+        drawers_added = 0
+        for chunk in chunks:
+            added = add_drawer(
+                collection=collection,
+                wing=wing,
+                room=room,
+                content=chunk["content"],
+                source_file=source_file,
+                chunk_index=chunk["chunk_index"],
+                agent=agent,
+            )
+            if added:
+                drawers_added += 1
 
     return drawers_added, room
 
diff --git a/mempalace/palace.py b/mempalace/palace.py
index 9cfb55e..bb7916e 100644
--- a/mempalace/palace.py
+++ b/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
@@ -60,6 +62,45 @@ 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.
 
diff --git a/mempalace/version.py b/mempalace/version.py
index 1eb21a2..45176bc 100644
--- a/mempalace/version.py
+++ b/mempalace/version.py
@@ -1,3 +1,3 @@
 """Single source of truth for the MemPalace package version."""
 
-__version__ = "3.1.0"
+__version__ = "3.2.0"