Remove dead session wall-clock plumbing

The status bar no longer shows a session timer, so drop useSessionClock,
its tests, and the unread sessionStartedAt prop/state chain.

Author: TheGreatAxios

src/tui/app.tsx

@@ -178,9 +178,6 @@ export type AppProps = {
   // Emits "scrollUp"/"scrollDown" for mouse-wheel events, which are stripped
   // from stdin before they reach useInput (see createFilteredStdin).
   mouseEvents?: EventEmitter;
-  // Wall-clock ms timestamp the session started. Drives the whole-session timer
-  // in the status bar; reset on /new.
-  sessionStartedAt?: number;
   // Inspectable child sessions for the Agents strip and enter-session UI.
   subAgentSessions?: SubAgentSessionStore;
   /** Goal mode operator surface. */
@@ -266,7 +263,6 @@ export function App({
   globallyOnboarded = false,
   globalOnboardingPath,
   mouseEvents,
-  sessionStartedAt: sessionStartedAtProp,
   subAgentSessions,
   goalApi,
   telemetryNotice,
@@ -651,8 +647,6 @@ export function App({
   const copyTargetList = copyModeOpen ? copyTargetsRef.current : [];
 
   const [, forceRender] = useState(0);
-  // Whole-session timer for the status bar. Held in state so /new can zero it.
-  const [sessionStartedAt, setSessionStartedAt] = useState(sessionStartedAtProp ?? Date.now());
 
   const {
     sendMessage,
@@ -693,7 +687,6 @@ export function App({
     promptXaiRelogin,
     setExpandedTools,
     setInputValue,
-    setSessionStartedAt,
     setEnteredSessionId,
     setAgentsNavOpen,
     setAgentsNavIndex,

src/tui/hooks/use-message-pipeline.ts

@@ -44,7 +44,6 @@ export type UseMessagePipelineArgs = {
   promptXaiRelogin: (name: string) => void;
   setExpandedTools: Dispatch<SetStateAction<ReadonlySet<string>>>;
   setInputValue: Dispatch<SetStateAction<string>>;
-  setSessionStartedAt: Dispatch<SetStateAction<number>>;
   setEnteredSessionId: Dispatch<SetStateAction<string | null>>;
   setAgentsNavOpen: Dispatch<SetStateAction<boolean>>;
   setAgentsNavIndex: Dispatch<SetStateAction<number>>;
@@ -98,7 +97,6 @@ export function useMessagePipeline({
   promptXaiRelogin,
   setExpandedTools,
   setInputValue,
-  setSessionStartedAt,
   setEnteredSessionId,
   setAgentsNavOpen,
   setAgentsNavIndex,
@@ -226,7 +224,6 @@ export function useMessagePipeline({
     lastSentMessageRef.current = "";
     quotaAutoRetryFiredRef.current = true;
     setInputValue("");
-    setSessionStartedAt(Date.now());
     setEnteredSessionId(null);
     setAgentsNavOpen(false);
     setAgentsNavIndex(0);

src/tui/hooks/use-session-clock.ts

@@ -1466,7 +1466,6 @@ export async function runTUI(initialConfig: Config): Promise<number> {
       activePlugins={activePlugins}
       initialWorkflowStatus={workflowController.status()}
       mouseEvents={mouseEvents}
-      sessionStartedAt={startedAt}
       subAgentSessions={subAgentSessions}
       goalApi={{
         get: () => goalGovernor.get(),