fix(codex): preserve transcript sync across mode switches

cli/src/codex/utils/codexSessionScanner.test.ts

@@ -59,6 +59,27 @@ describe('codexSessionScanner', () => {
         expect(events[0]?.type).toBe('event_msg');
     });
 
+    it('flushes an appended tail without waiting for the watcher', async () => {
+        await writeFile(
+            transcriptPath,
+            JSON.stringify({ type: 'session_meta', payload: { id: 'session-flush' } }) + '\n'
+        );
+
+        scanner = await createCodexSessionScanner({
+            transcriptPath,
+            onEvent: (event) => events.push(event)
+        });
+
+        await appendFile(
+            transcriptPath,
+            JSON.stringify({ type: 'event_msg', payload: { type: 'agent_message', message: 'final tail' } }) + '\n'
+        );
+        await scanner.flush();
+
+        expect(events).toHaveLength(1);
+        expect(events[0]?.payload).toEqual({ type: 'agent_message', message: 'final tail' });
+    });
+
     it('reads exactly the requested transcript byte range', async () => {
         const initial = 'existing transcript\n';
         const appended = 'new event\n';

cli/src/codex/utils/codexSessionScanner.ts

@@ -11,6 +11,7 @@ interface CodexSessionScannerOptions {
 }
 
 export interface CodexSessionScanner {
+    flush: () => Promise<void>;
     cleanup: () => Promise<void>;
     setTranscriptPath: (transcriptPath: string) => Promise<void>;
 }
@@ -20,6 +21,9 @@ export async function createCodexSessionScanner(opts: CodexSessionScannerOptions
     await scanner.start();
 
     return {
+        flush: async () => {
+            await scanner.flush();
+        },
         cleanup: async () => {
             await scanner.cleanup();
         },