fix: prevent stale codex processing banner

Codex can finish a turn and clear the composer banner while delayed status
checks or parent processing state still believe the session is running.
That leaves a stale path that can re-open the banner after the response
is already complete.

This was visible with Codex responses that render a delayed remote image.
The image load/reflow gives late session-status handling a chance to
reassert processing. A simple text-only prompt did not create the same
render window.

Reproduces with Codex using:

Reply with exactly the following Markdown, no code fence, no explanation:

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![scroll reflow test](https://picsum.photos/seed/pr788-scroll/1600/1400)

BOTTOM_SENTINEL_PR_788

Did not reproduce with: hi

The fix marks Codex terminal turns complete before status probes can
report them active, ignores stale processing status after a terminal
event, and only restores local loading when a session newly enters
processing.

server/openai-codex.js

@@ -279,6 +279,16 @@ export async function queryCodex(command, options = {}, ws) {
         startedAt: new Date().toISOString()
       });
     };
+    const markSessionFinished = (id) => {
+      if (!id) {
+        return;
+      }
+
+      const session = activeCodexSessions.get(id);
+      if (session && session.status !== 'aborted') {
+        session.status = 'completed';
+      }
+    };
 
     // Existing sessions can be tracked immediately; new sessions are tracked after thread.started.
     if (capturedSessionId) {
@@ -324,6 +334,10 @@ export async function queryCodex(command, options = {}, ws) {
         continue;
       }
 
+      if (event.type === 'turn.completed' || event.type === 'turn.failed') {
+        markSessionFinished(capturedSessionId || sessionId);
+      }
+
       const transformed = transformCodexEvent(event);
 
       // Normalize the transformed event into NormalizedMessage(s) via adapter
@@ -354,6 +368,8 @@ export async function queryCodex(command, options = {}, ws) {
 
     // Send completion event
     if (!terminalFailure) {
+      markSessionFinished(capturedSessionId || sessionId);
+
       sendMessage(ws, createNormalizedMessage({
         kind: 'complete',
         actualSessionId: capturedSessionId || thread.id || sessionId || null,