test(auto-reply): accelerate fallback coverage (#107316)

src/auto-reply/reply/agent-runner-auth-profile.ts

@@ -41,3 +41,33 @@ export function resolveRunAuthProfile(
     workspaceDir: run.workspaceDir,
   });
 }
+
+/** Applies an auto-fallback probe's pinned auth to its fallback candidate. */
+export function resolveFallbackCandidateRun(
+  run: FollowupRun["run"],
+  provider: string,
+  model: string,
+): FollowupRun["run"] {
+  const probe = run.autoFallbackPrimaryProbe;
+  const isPrimaryProbeCandidate = probe && provider === probe.provider && model === probe.model;
+  if (
+    !probe ||
+    provider !== probe.fallbackProvider ||
+    isPrimaryProbeCandidate ||
+    !probe.fallbackAuthProfileId
+  ) {
+    return run;
+  }
+  const candidateRun: FollowupRun["run"] = {
+    ...run,
+    provider,
+    model,
+    authProfileId: probe.fallbackAuthProfileId,
+  };
+  if (probe.fallbackAuthProfileIdSource) {
+    candidateRun.authProfileIdSource = probe.fallbackAuthProfileIdSource;
+  } else {
+    delete candidateRun.authProfileIdSource;
+  }
+  return candidateRun;
+}

src/auto-reply/reply/agent-runner-execution.test.ts

@@ -27,6 +27,7 @@ import { getReplyPayloadMetadata } from "../reply-payload.js";
 import type { TemplateContext } from "../templating.js";
 import { SILENT_REPLY_TOKEN } from "../tokens.js";
 import type { GetReplyOptions, ReplyPayload } from "../types.js";
+import { resolveFallbackCandidateRun } from "./agent-runner-auth-profile.js";
 import {
   buildEmptyInteractiveReplyPayload,
   buildKnownAgentRunFailureReplyPayload,
@@ -2081,7 +2082,7 @@ describe("runAgentTurnWithFallback", () => {
     expect(rechecked.hasAutoFallbackProvenance).toBeUndefined();
   });
 
-  it("keeps fallback auth available when a primary probe falls back", async () => {
+  it("keeps fallback auth available when a primary probe falls back", () => {
     const probe = {
       provider: "anthropic",
       model: "claude-sonnet-4-6",
@@ -2096,21 +2097,7 @@ describe("runAgentTurnWithFallback", () => {
     followupRun.run.authProfileId = "anthropic:primary";
     followupRun.run.authProfileIdSource = "auto";
     followupRun.run.autoFallbackPrimaryProbe = probe;
-    state.runWithModelFallbackMock.mockImplementationOnce(async (params: FallbackRunnerParams) => ({
-      result: await params.run("google", "gemini-3-pro"),
-      provider: "google",
-      model: "gemini-3-pro",
-      attempts: [{ provider: "anthropic", model: "claude-sonnet-4-6", error: "rate limit" }],
-    }));
-    state.runEmbeddedAgentMock.mockResolvedValueOnce({
-      payloads: [{ text: "fallback" }],
-      meta: {},
-    });
-
-    const runAgentTurnWithFallback = await getRunAgentTurnWithFallback();
-    await runAgentTurnWithFallback(createMinimalRunAgentTurnParams({ followupRun }));
-
-    expectMockCallArgFields(state.runEmbeddedAgentMock, 0, "embedded run", {
+    expect(resolveFallbackCandidateRun(followupRun.run, "google", "gemini-3-pro")).toMatchObject({
       provider: "google",
       model: "gemini-3-pro",
       authProfileId: "google:fallback",

src/auto-reply/reply/agent-runner-execution.ts

@@ -121,7 +121,7 @@ import {
   resolveAgentLifecycleTerminalMetadata,
   type AgentLifecycleTerminalBackstop,
 } from "./agent-lifecycle-terminal.js";
-import { resolveRunAuthProfile } from "./agent-runner-auth-profile.js";
+import { resolveFallbackCandidateRun, resolveRunAuthProfile } from "./agent-runner-auth-profile.js";
 import {
   clearDroppedCliSessionBinding,
   createCliReasoningStreamBridge,
@@ -1490,30 +1490,6 @@ async function runAgentTurnWithFallbackInternal(
   const preserveUserFacingSessionState = shouldPreserveUserFacingSessionStateForInputProvenance(
     effectiveRun.inputProvenance,
   );
-  const resolveRunForFallbackCandidate = (provider: string, model: string): FollowupRun["run"] => {
-    const probe = effectiveRun.autoFallbackPrimaryProbe;
-    const isPrimaryProbeCandidate = probe && provider === probe.provider && model === probe.model;
-    if (
-      probe &&
-      provider === probe.fallbackProvider &&
-      !isPrimaryProbeCandidate &&
-      probe.fallbackAuthProfileId
-    ) {
-      const candidateRun: FollowupRun["run"] = {
-        ...effectiveRun,
-        provider,
-        model,
-        authProfileId: probe.fallbackAuthProfileId,
-      };
-      if (probe.fallbackAuthProfileIdSource) {
-        candidateRun.authProfileIdSource = probe.fallbackAuthProfileIdSource;
-      } else {
-        delete candidateRun.authProfileIdSource;
-      }
-      return candidateRun;
-    }
-    return effectiveRun;
-  };
   let liveModelSwitchRuntimeEntry:
     | Pick<SessionEntry, "agentHarnessId" | "agentRuntimeOverride" | "modelSelectionLocked">
     | undefined;
@@ -1945,7 +1921,7 @@ async function runAgentTurnWithFallbackInternal(
               queuedUserMessagePersistedAcrossFallback;
             const suppressAssistantErrorPersistenceForCandidate =
               assistantErrorPersistedAcrossFallback;
-            const candidateRun = resolveRunForFallbackCandidate(provider, model);
+            const candidateRun = resolveFallbackCandidateRun(effectiveRun, provider, model);
             const candidateThinkLevel = resolveCandidateThinkingLevel({
               cfg: runtimeConfig,
               provider,

src/auto-reply/reply/followup-runner.test.ts

@@ -6752,7 +6752,10 @@ describe("createFollowupRunner messaging delivery and dedupe", () => {
         onAgentEvent?: (evt: { stream: string; data: Record<string, unknown> }) => Promise<void>;
       }) => {
         await args.onAgentEvent?.({ stream: "compaction", data: { phase: "start" } });
-        return { payloads: [], meta: {} };
+        return {
+          payloads: [{ text: DELIVERY_NO_REPLY_RUNTIME_CONTRACT.silentText }],
+          meta: {},
+        };
       },
     );
     const runner = createFollowupRunner({