feat(core): enhance startup profiling with cross-process timing and UI milestones

packages/cli/src/gemini.tsx

@@ -328,6 +328,22 @@ export async function startInteractiveUI(
 export async function main() {
   const cliStartupHandle = startupProfiler.start('cli_startup');
 
+  const parentStartTime = process.env['GEMINI_CLI_PARENT_START_TIME'];
+  if (parentStartTime) {
+    const startAbsMs = parseInt(parentStartTime, 10);
+    // Record how long the parent process(es) took before this child started.
+    startupProfiler.recordPhase(
+      'parent_process_duration',
+      startAbsMs,
+      performance.timeOrigin,
+    );
+    // Measure overall time from the very first process start
+    startupProfiler.start('overall_startup', {}, startAbsMs);
+    // Measure time from this child process launch
+    startupProfiler.start('child_process_to_ui_visible');
+    startupProfiler.start('child_process_to_typing_ready');
+  }
+
   // Listen for admin controls from parent process (IPC) in non-sandbox mode. In
   // sandbox mode, we re-fetch the admin controls from the server once we enter
   // the sandbox.

packages/cli/src/ui/AppContainer.tsx

@@ -429,7 +429,6 @@ export const AppContainer = (props: AppContainerProps) => {
         await config.initialize();
       }
       setConfigInitialized(true);
-      startupProfiler.flush(config);
 
       const sessionStartSource = resumedSessionData
         ? SessionStartSource.Resume
@@ -2578,6 +2577,23 @@ Logging in with Google... Restarting Gemini CLI to continue.
     ],
   );
 
+  const hasFlushedStartupRef = useRef(false);
+  useEffect(() => {
+    if (
+      authState === AuthState.Authenticated &&
+      !hasFlushedStartupRef.current
+    ) {
+      startupProfiler.endPhase('child_process_to_typing_ready');
+      startupProfiler.endPhase('overall_startup');
+      startupProfiler.flush(config);
+      hasFlushedStartupRef.current = true;
+    }
+  }, [authState, config]);
+
+  useLayoutEffect(() => {
+    startupProfiler.endPhase('child_process_to_ui_visible');
+  }, []);
+
   if (authState === AuthState.AwaitingGoogleLoginRestart) {
     return (
       <LoginWithGoogleRestartDialog

packages/cli/src/utils/relaunch.ts

@@ -55,7 +55,15 @@ export async function relaunchAppInChildProcess(
       ...additionalScriptArgs,
       ...scriptArgs,
     ];
-    const newEnv = { ...process.env, GEMINI_CLI_NO_RELAUNCH: 'true' };
+
+    const parentStartTime =
+      process.env['GEMINI_CLI_PARENT_START_TIME'] || Date.now().toString();
+
+    const newEnv = {
+      ...process.env,
+      GEMINI_CLI_NO_RELAUNCH: 'true',
+      GEMINI_CLI_PARENT_START_TIME: parentStartTime,
+    };
 
     // The parent process should not be reading from stdin while the child is running.
     process.stdin.pause();