diff --git a/gateway/session.py b/gateway/session.py
index 3ba5b10c48..be74201c9f 100644
--- a/gateway/session.py
+++ b/gateway/session.py
@@ -3875,6 +3875,19 @@ class SessionStore:
         db = self._db
         if db is None or not hasattr(db, "rebuild_fts"):
             return False
+        # Guard against the same WAL split-brain risk as the automatic
+        # rebuild paths: skip when a foreign process holds state.db or
+        # its WAL sidecars open.
+        if hasattr(db, "_foreign_state_db_holders"):
+            foreign_holders = db._foreign_state_db_holders()
+            if foreign_holders:
+                logger.warning(
+                    "Skipping Session DB FTS rebuild while foreign processes "
+                    "hold the database or WAL sidecars (%s); canonical "
+                    "transcript writes remain available.",
+                    foreign_holders,
+                )
+                return False
         try:
             rebuilt = db.rebuild_fts()
         except Exception as exc:
diff --git a/hermes_state.py b/hermes_state.py
index a7d706e296..c795815164 100644
--- a/hermes_state.py
+++ b/hermes_state.py
@@ -4286,6 +4286,12 @@ class SessionDB(SessionSearchMixin, SessionSchemaMixin, SessionPortabilityMixin)
             return False
         if not self._is_fts_write_corruption_error(exc):
             return False
+        # Set the one-shot flag before the foreign-holder check: even when
+        # the rebuild is skipped, the fail-open path that follows persists
+        # the FTS_STALE_KEY marker so the next process startup will retry
+        # via _recover_stale_fts (which has its own holder guard). Setting
+        # the flag here also avoids re-running the expensive psutil scan on
+        # every subsequent corrupted write through this instance.
         self._fts_runtime_rebuild_attempted = True
         foreign_holders = self._foreign_state_db_holders()
         if foreign_holders: