fix(gsd): handle session_switch event so /resume restores GSD state (#2587)

The GSD extension only listened for session_start, not session_switch.
When /resume switched to a previous session, GSD's write-gate, loop guard,
discussion flow, service tier, and tool API keys were never re-initialized,
leaving GSD in stale state from the prior session.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/resources/extensions/gsd/bootstrap/register-hooks.ts

@@ -69,6 +69,14 @@ export function registerHooks(pi: ExtensionAPI): void {
     }
   });
 
+  pi.on("session_switch", async (_event, ctx) => {
+    resetWriteGateState();
+    resetToolCallLoopGuard();
+    clearDiscussionFlowState();
+    await syncServiceTierStatus(ctx);
+    loadToolApiKeys();
+  });
+
   pi.on("before_agent_start", async (event, ctx: ExtensionContext) => {
     return buildBeforeAgentStartResult(event, ctx);
   });

src/resources/extensions/gsd/extension-manifest.json

@@ -12,7 +12,7 @@
       "gsd_requirement_update", "gsd_milestone_generate_id"
     ],
     "commands": ["gsd", "kill", "worktree", "exit"],
-    "hooks": ["session_start"],
+    "hooks": ["session_start", "session_switch"],
     "shortcuts": ["Ctrl+Alt+G"]
   }
 }