Clean up session tracking on session_end to prevent unbounded map growth

gateway_start only fires on full process restart. Without cleanup,
sessionIds and workspaceDirsBySessionKey grow indefinitely across
/new and /reset cycles. session_end now deletes entries for the
completed session key.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

openclaw/src/index.ts

@@ -61,6 +61,12 @@ interface AfterCompactionEvent {
   compactedCount: number;
 }
 
+interface SessionEndEvent {
+  sessionId: string;
+  messageCount: number;
+  durationMs?: number;
+}
+
 interface EventContext {
   sessionKey?: string;
   workspaceDir?: string;
@@ -93,6 +99,7 @@ interface OpenClawPluginApi {
       ((event: "tool_result_persist", callback: EventCallback<ToolResultPersistEvent>) => void) &
       ((event: "agent_end", callback: EventCallback<AgentEndEvent>) => void) &
       ((event: "session_start", callback: EventCallback<SessionStartEvent>) => void) &
+      ((event: "session_end", callback: EventCallback<SessionEndEvent>) => void) &
       ((event: "after_compaction", callback: EventCallback<AfterCompactionEvent>) => void) &
       ((event: "gateway_start", callback: EventCallback<Record<string, never>>) => void);
   runtime: {
@@ -528,6 +535,15 @@ export default function claudeMemPlugin(api: OpenClawPluginApi): void {
     }, api.logger);
   });
 
+  // ------------------------------------------------------------------
+  // Event: session_end — clean up session tracking to prevent unbounded growth
+  // ------------------------------------------------------------------
+  api.on("session_end", async (_event, ctx) => {
+    const key = ctx.sessionKey || "default";
+    sessionIds.delete(key);
+    workspaceDirsBySessionKey.delete(key);
+  });
+
   // ------------------------------------------------------------------
   // Event: gateway_start — clear session tracking for fresh start
   // ------------------------------------------------------------------