fix(evidence): lock GC and preflight search ownership

harness/tht/corpus/pipeline.py

@@ -124,6 +124,10 @@ class CorpusPipeline:
         return protected
 
     def gc(self, *, workspace_root: Path, dry_run: bool = False) -> dict:
+        with self.store.writer_lock():
+            return self._gc(workspace_root=workspace_root, dry_run=dry_run)
+
+    def _gc(self, *, workspace_root: Path, dry_run: bool = False) -> dict:
         self._assert_workspace_binding()
         published = self.store.published_generations()
         list_vectors = getattr(self.vector_store, "list_evidence_generations", None)

harness/tht/corpus/store.py

@@ -10,6 +10,7 @@ import stat
 import shutil
 import uuid
 import hashlib
+import threading
 from datetime import UTC, datetime
 from pathlib import Path
 from contextlib import contextmanager
@@ -49,6 +50,7 @@ class CorpusStore:
         self.active_path = self.root / "ACTIVE"
         self._replace = os.replace
         self._fsync_directory = self._sync_root
+        self._lock_state = threading.local()
         self._ensure_root()
 
     def _ensure_root(self) -> None:
@@ -61,6 +63,14 @@ class CorpusStore:
 
     @contextmanager
     def writer_lock(self):
+        depth = getattr(self._lock_state, "depth", 0)
+        if depth:
+            self._lock_state.depth = depth + 1
+            try:
+                yield
+            finally:
+                self._lock_state.depth -= 1
+            return
         lock_path = self.root / ".writer.lock"
         fd = os.open(lock_path, os.O_RDWR | os.O_CREAT | os.O_NOFOLLOW | os.O_CLOEXEC, 0o600)
         try:
@@ -68,8 +78,10 @@ class CorpusStore:
             if not stat.S_ISREG(info.st_mode) or info.st_uid != os.getuid() or info.st_nlink != 1:
                 raise UnsafeCorpusPath("corpus writer lock is unsafe")
             fcntl.flock(fd, fcntl.LOCK_EX)
+            self._lock_state.depth = 1
             yield
         finally:
+            self._lock_state.depth = 0
             fcntl.flock(fd, fcntl.LOCK_UN)
             os.close(fd)