fix(coding-agent): clear label timestamp cache on new sessions

closes #6354

packages/coding-agent/CHANGELOG.md

@@ -17,6 +17,7 @@
 - Fixed custom session entries appended during assistant streaming to render before the live assistant message, matching persisted session order.
 - Fixed oversized bash tool timeouts to fail with a clear validation error instead of being clamped to an immediate timeout ([#6181](https://github.com/earendil-works/pi/issues/6181)).
 - Fixed the edit tool schema to allow model-invented extra replacement fields instead of rejecting otherwise valid edits ([#6278](https://github.com/earendil-works/pi/issues/6278)).
+- Fixed new session resets to clear cached label timestamps ([#6354](https://github.com/earendil-works/pi/issues/6354)).
 
 ### Removed
 

packages/coding-agent/src/core/session-manager.ts

@@ -864,6 +864,7 @@ export class SessionManager {
 		this.fileEntries = [header];
 		this.byId.clear();
 		this.labelsById.clear();
+		this.labelTimestampsById.clear();
 		this.leafId = null;
 		this.flushed = false;