fix(hooks): add retry tracking to ForegroundFallbackManager to prevent 429 freeze

src/hooks/foreground-fallback/index.test.ts

@@ -187,7 +187,8 @@ describe('ForegroundFallbackManager session.error', () => {
       },
     });
 
-    expect(mocks.abort).toHaveBeenCalledTimes(1);
+    // promptAsync is called directly (no abort needed when it succeeds)
+    expect(mocks.abort).toHaveBeenCalledTimes(0);
     expect(mocks.promptAsync).toHaveBeenCalledTimes(1);
 
     const call = mocks.promptAsync.mock.calls[0] as [
@@ -258,7 +259,7 @@ describe('ForegroundFallbackManager session.error', () => {
     expect(mocks.promptAsync).not.toHaveBeenCalled();
   });
 
-  test('aborts session when no chain configured (no fallback model to swap to)', async () => {
+  test('does nothing when no chain configured for session', async () => {
     const emptyMgr = new ForegroundFallbackManager(client, {}, true);
     await emptyMgr.handleEvent({
       type: 'session.error',
@@ -268,7 +269,7 @@ describe('ForegroundFallbackManager session.error', () => {
       },
     });
 
-    expect(mocks.abort).toHaveBeenCalledTimes(1);
+    expect(mocks.abort).not.toHaveBeenCalled();
     expect(mocks.promptAsync).not.toHaveBeenCalled();
   });
 
@@ -288,10 +289,13 @@ describe('ForegroundFallbackManager session.error', () => {
     expect(mocks.promptAsync).not.toHaveBeenCalled();
   });
 
-  test('continues fallback when abort rejects', async () => {
+  test('falls back to abort+retry when promptAsync fails on busy session', async () => {
     const { client, mocks } = createMockClient({
+      promptAsyncImpl: async () => {
+        throw new Error('session busy');
+      },
       abortImpl: async () => {
-        throw new Error('abort failed');
+        // abort succeeds on first call
       },
     });
     const mgr = new ForegroundFallbackManager(client, makeChains(), true);
@@ -299,13 +303,14 @@ describe('ForegroundFallbackManager session.error', () => {
     await mgr.handleEvent({
       type: 'session.error',
       properties: {
-        sessionID: 'sess-abort-rejects',
+        sessionID: 'sess-busy',
         error: { message: 'Rate limit exceeded' },
       },
     });
 
+    // First promptAsync attempt failed → abort called, then promptAsync retried
     expect(mocks.abort).toHaveBeenCalledTimes(1);
-    expect(mocks.promptAsync).toHaveBeenCalledTimes(1);
+    expect(mocks.promptAsync).toHaveBeenCalledTimes(2);
   });
 });
 

src/hooks/foreground-fallback/index.ts

@@ -282,11 +282,10 @@ export class ForegroundFallbackManager {
       const agentName = this.sessionAgent.get(sessionID);
       const chain = this.resolveChain(agentName, currentModel);
       if (!chain.length) {
-        log('[foreground-fallback] no chain configured, aborting session', {
+        log('[foreground-fallback] no chain configured', {
           sessionID,
           agentName,
         });
-        await abortSessionWithTimeout(this.client, sessionID);
         return;
       }
 
@@ -379,25 +378,27 @@ export class ForegroundFallbackManager {
         return;
       }
 
-      // Abort the currently rate-limited prompt so the session becomes idle.
+      // Try queuing the fallback prompt without aborting first. If OpenCode
+      // accepts it (204), the fallback model replaces the retry loop
+      // transparently — no dialog, no session error shown to the user.
+      // If promptAsync throws (e.g. session busy), fall back to abort+retry.
       try {
-        await abortSessionWithTimeout(this.client, sessionID);
-      } catch (error) {
-        // Session may already be idle or abort may be slow; keep fallback best-effort.
-        log('[foreground-fallback] abort did not complete cleanly', {
+        await sessionClient.promptAsync({
+          path: { id: sessionID },
+          body: { parts: lastUser.parts, model: ref },
+        });
+      } catch (_promptErr) {
+        log('[foreground-fallback] promptAsync on busy session, aborting', {
           sessionID,
-          error: error instanceof Error ? error.message : String(error),
+        });
+        await abortSessionWithTimeout(this.client, sessionID);
+        await new Promise((r) => setTimeout(r, REPROMPT_DELAY_MS));
+        await sessionClient.promptAsync({
+          path: { id: sessionID },
+          body: { parts: lastUser.parts, model: ref },
         });
       }
 
-      // Give the server a moment to finalise the abort before re-prompting.
-      await new Promise((r) => setTimeout(r, REPROMPT_DELAY_MS));
-
-      await sessionClient.promptAsync({
-        path: { id: sessionID },
-        body: { parts: lastUser.parts, model: ref },
-      });
-
       this.sessionModel.set(sessionID, nextModel);
       log('[foreground-fallback] switched to fallback model', {
         sessionID,