fix(core,cli): resolve TOCTOU, concurrency, and performance regressions in plan resolution

packages/cli/src/ui/AppContainer.tsx

@@ -1340,11 +1340,6 @@ Logging in with Google... Restarting Gemini CLI to continue.
         }
       }
 
-      const parsedCommand = parseSlashCommand(
-        submittedValue,
-        slashCommands ?? [],
-      );
-
       const isSlash = isSlashCommand(submittedValue.trim());
       const isIdle = streamingState === StreamingState.Idle;
       const isAgentRunning =
@@ -1352,6 +1347,10 @@ Logging in with Google... Restarting Gemini CLI to continue.
         isToolExecuting(pendingHistoryItems);
 
       if (isSlash && isAgentRunning) {
+        const parsedCommand = parseSlashCommand(
+          submittedValue,
+          slashCommands ?? [],
+        );
         const commandToExecute = parsedCommand.commandToExecute;
         if (commandToExecute?.isSafeConcurrent) {
           void handleSlashCommand(submittedValue);

packages/cli/src/ui/hooks/slashCommandProcessor.test.tsx

@@ -1130,18 +1130,19 @@ describe('useSlashCommandProcessor', () => {
       });
       expect(spySetContext).toHaveBeenLastCalledWith('extB');
 
-      // 3. Run /plan (Default)
+      // 3. Run /help (Concurrent global command)
+      spySetContext.mockClear();
+      await act(async () => {
+        await hook.current.handleSlashCommand('/help');
+      });
+      // A concurrent command should NOT modify the active extension context
+      expect(spySetContext).not.toHaveBeenCalled();
+
+      // 4. Run /plan (Default)
       await act(async () => {
         await hook.current.handleSlashCommand('/plan my task');
       });
       expect(spySetContext).toHaveBeenLastCalledWith(undefined);
-
-      // 4. Run /clear (Global)
-      await act(async () => {
-        await hook.current.handleSlashCommand('/help');
-      });
-      // Context should still be undefined
-      expect(spySetContext).toHaveBeenLastCalledWith(undefined);
     });
   });
 });

packages/cli/src/ui/hooks/slashCommandProcessor.ts

@@ -371,7 +371,7 @@ export const useSlashCommandProcessor = (
         extensionContext,
       } = parseSlashCommand(trimmed, commands);
 
-      if (config) {
+      if (config && commandToExecute && !commandToExecute.isSafeConcurrent) {
         if (extensionContext) {
           if (config.hasExtensionPlanDir(extensionContext)) {
             config.setActiveExtensionContext(extensionContext);