fix(tui): update model display during fallback (#82296)

* fix(tui): update fallback model display

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

* Refresh checks after proof update

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

* chore: refresh CI after main repairs

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

---------

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

src/tui/tui-event-handlers.test.ts

@@ -213,6 +213,82 @@ describe("tui-event-handlers: handleAgentEvent", () => {
     expect(tui.requestRender).toHaveBeenCalledTimes(1);
   });
 
+  it("updates the displayed model from fallback lifecycle steps", () => {
+    const { state, tui, handleAgentEvent } = createHandlersHarness({
+      state: {
+        activeChatRunId: "run-fallback",
+        sessionInfo: {
+          verboseLevel: "on",
+          modelProvider: "llamaforge",
+          model: "qwen/qwen3.5-9b",
+        },
+      },
+    });
+
+    handleAgentEvent({
+      runId: "run-fallback",
+      stream: "lifecycle",
+      data: {
+        phase: "fallback_step",
+        fallbackStepFinalOutcome: "next_fallback",
+        fallbackStepFromModel: "openai-codex/gpt-5.5",
+        fallbackStepToModel: "openrouter/meta-llama/llama-3.1-70b",
+      },
+    });
+
+    expect(state.sessionInfo.modelProvider).toBe("openrouter");
+    expect(state.sessionInfo.model).toBe("meta-llama/llama-3.1-70b");
+    expect(tui.requestRender).toHaveBeenCalled();
+  });
+
+  it("accepts fallback model updates for the pending run before chat registration", () => {
+    const { state, tui, handleAgentEvent } = createHandlersHarness({
+      state: {
+        activeChatRunId: null,
+        pendingChatRunId: "run-pending",
+        sessionInfo: {
+          verboseLevel: "on",
+          modelProvider: "llamaforge",
+          model: "qwen/qwen3.5-9b",
+        },
+      },
+    });
+
+    handleAgentEvent({
+      runId: "run-pending",
+      stream: "lifecycle",
+      data: {
+        phase: "fallback_step",
+        fallbackStepFinalOutcome: "succeeded",
+        fallbackStepFromModel: "openrouter/meta-llama/llama-3.1-70b",
+        fallbackStepToModel: "nvidia/deepseek-ai/deepseek-v3.2",
+      },
+    });
+
+    expect(state.sessionInfo.modelProvider).toBe("nvidia");
+    expect(state.sessionInfo.model).toBe("deepseek-ai/deepseek-v3.2");
+    expect(tui.requestRender).toHaveBeenCalled();
+  });
+
+  it("ignores fallback model updates for unrelated runs", () => {
+    const { state, tui, handleAgentEvent } = createHandlersHarness({
+      state: {
+        activeChatRunId: "run-active",
+        sessionInfo: { verboseLevel: "on", modelProvider: "openai", model: "gpt-5.5" },
+      },
+    });
+
+    handleAgentEvent({
+      runId: "run-other",
+      stream: "lifecycle",
+      data: { phase: "fallback_step", fallbackStepToModel: "openrouter/other-model" },
+    });
+
+    expect(state.sessionInfo.modelProvider).toBe("openai");
+    expect(state.sessionInfo.model).toBe("gpt-5.5");
+    expect(tui.requestRender).not.toHaveBeenCalled();
+  });
+
   it("captures runId from chat events when activeChatRunId is unset", () => {
     const { state, chatLog, handleChatEvent, handleAgentEvent } = createHandlersHarness({
       state: { activeChatRunId: null },

src/tui/tui-event-handlers.ts

@@ -191,6 +191,36 @@ export function createEventHandlers(context: EventHandlerContext) {
       : "auth or provider access failed for the current provider. Run /auth to refresh credentials; if you already re-authed, switch models/providers because this account may still be blocked for inference.";
   };
 
+  const parseProviderModelRef = (
+    modelRef: unknown,
+  ): { provider: string; model: string } | undefined => {
+    if (typeof modelRef !== "string") {
+      return undefined;
+    }
+    const trimmed = modelRef.trim();
+    const separator = trimmed.indexOf("/");
+    if (separator <= 0 || separator >= trimmed.length - 1) {
+      return undefined;
+    }
+    const provider = trimmed.slice(0, separator).trim();
+    const model = trimmed.slice(separator + 1).trim();
+    return provider && model ? { provider, model } : undefined;
+  };
+
+  const applyFallbackStepModelUpdate = (evt: AgentEvent): boolean => {
+    const data = evt.data ?? {};
+    if (evt.stream !== "lifecycle" || asString(data.phase, "") !== "fallback_step") {
+      return false;
+    }
+    const target = parseProviderModelRef(data.fallbackStepToModel);
+    if (!target) {
+      return false;
+    }
+    state.sessionInfo.modelProvider = target.provider;
+    state.sessionInfo.model = target.model;
+    return true;
+  };
+
   const noteSessionRun = (runId: string) => {
     sessionRuns.set(runId, Date.now());
     pruneRunMap(sessionRuns);
@@ -471,7 +501,16 @@ export function createEventHandlers(context: EventHandlerContext) {
     // active chat run id, not the session id. Tool results can arrive after the chat
     // final event, so accept finalized runs for tool updates.
     const isActiveRun = evt.runId === state.activeChatRunId;
-    const isKnownRun = isActiveRun || sessionRuns.has(evt.runId) || finalizedRuns.has(evt.runId);
+    const isPendingRun = evt.runId === state.pendingChatRunId;
+    const isSessionRun = sessionRuns.has(evt.runId);
+    if ((isActiveRun || isPendingRun || isSessionRun) && applyFallbackStepModelUpdate(evt)) {
+      if (isActiveRun) {
+        armStreamingWatchdog(evt.runId);
+      }
+      tui.requestRender();
+      return;
+    }
+    const isKnownRun = isActiveRun || isSessionRun || finalizedRuns.has(evt.runId);
     if (!isKnownRun) {
       return;
     }