diff --git a/src/servers/sidecar/claude/state.ts b/src/servers/sidecar/claude/state.ts
index b55e63ec..59dfd5fc 100644
--- a/src/servers/sidecar/claude/state.ts
+++ b/src/servers/sidecar/claude/state.ts
@@ -71,14 +71,34 @@ export function updateState(patch: Partial<PersistedState>): void {
   scheduleSave();
 }
 
+/**
+ * Both of these write through instead of debouncing.
+ *
+ * This map is the only thing that lets a conversation be reattached with `--resume` after the agent
+ * sidecar dies, so it is precisely the state that must not be in a 30s window when the process is
+ * killed rather than asked to stop — `flushAndSave` on SIGTERM covers a `pm2 restart`, but not a
+ * crash or a SIGKILL, which is the case the resume path exists for. Losing it silently starts the
+ * next turn as a fresh Claude session and orphans the transcript on disk.
+ *
+ * There is nothing to debounce: `onSessionId` fires on every message but with the same id, so the
+ * equality guard collapses it to one write per session, and clearing happens once.
+ */
 export function setClaudeSession(sessionKey: string, sessionId: string): void {
+  if (currentState.claudeSessions[sessionKey] === sessionId) return;
   currentState.claudeSessions[sessionKey] = sessionId;
-  scheduleSave();
+  writeThrough();
 }
 
 export function clearClaudeSession(sessionKey: string): void {
+  if (!(sessionKey in currentState.claudeSessions)) return;
   delete currentState.claudeSessions[sessionKey];
-  scheduleSave();
+  writeThrough();
+}
+
+function writeThrough(): void {
+  void flushAndSave().catch((err) => {
+    console.error('[claude-state] save failed:', err instanceof Error ? err.message : err);
+  });
 }
 
 export function getClaudeSession(sessionKey: string): string | undefined {