diff --git a/src/providers/github-copilot-auto.ts b/src/providers/github-copilot-auto.ts
index 29797761aa6..e42347342be 100644
--- a/src/providers/github-copilot-auto.ts
+++ b/src/providers/github-copilot-auto.ts
@@ -130,15 +130,32 @@ export async function resolveCopilotAuto(provider: OcxProviderConfig, requestedM
   let models: CopilotModel[];
   try { models = await fetchCopilotAutoModels(transport, signal, beforeSend, 60_000, concurrency); }
   catch (error) {
-    if (signal?.aborted || error instanceof ProviderOutboundSendCancelledError) throw error;
+    if (signal?.aborted) throw error;
+    // A manual account switch makes `beforeSend` return false, which cancels this
+    // control-plane send. That is not a client abort: fall back to the requested model
+    // so the dispatch path revalidates the selection and rebuilds on the new account.
+    if (error instanceof ProviderOutboundSendCancelledError) {
+      return { provider: transport, modelId: requestedModel, auto: false };
+    }
     // Permission discovery is additive for legacy paid configurations. A temporary
     // discovery outage must not turn a previously usable named route into a refusal.
     return { provider: transport, modelId: requestedModel, auto: false };
   }
   if (!copilotRequiresAuto(provider, models))
     return { provider: transport, modelId: requestedModel, auto: false };
-  const session = await requestJson(transport, "/models/session", signal,
-    { auto_mode: { model_hints: ["auto"] } }, undefined, beforeSend, concurrency);
+  // The same authority fence guards the later control-plane sends: a manual switch that
+  // lands during the session or intent step falls back too, so dispatch rebuilds on the
+  // new account instead of failing the whole negotiation. A client abort still rejects.
+  const fallBackOnSwitch = (error: unknown) => {
+    if (!signal?.aborted && error instanceof ProviderOutboundSendCancelledError)
+      return { provider: transport, modelId: requestedModel, auto: false } as const;
+    throw error;
+  };
+  let session: Awaited<ReturnType<typeof requestJson>>;
+  try {
+    session = await requestJson(transport, "/models/session", signal,
+      { auto_mode: { model_hints: ["auto"] } }, undefined, beforeSend, concurrency);
+  } catch (error) { return fallBackOnSwitch(error); }
   const pool = strings(session.available_models);
   if (typeof session.session_token !== "string" || !session.session_token || session.session_token.length > 32_768 || !/^[\x21-\x7e]+$/.test(session.session_token) || !pool.length)
     throw new Error("GitHub Copilot Auto session omitted its routing credentials");
@@ -153,8 +170,11 @@ export async function resolveCopilotAuto(provider: OcxProviderConfig, requestedM
     ? typeof lastUser.content === "string" ? lastUser.content : lastUser.content.flatMap(/** Extract text parts for intent negotiation without forwarding image or other multimodal payloads. */
       part => part.type === "text" ? [part.text] : []).join("\n")
     : "";
-  const intent = await requestJson(transport, "/models/session/intent", signal,
-    { prompt: prompt.slice(0, 32_768), available_models: pool }, session.session_token, beforeSend, concurrency);
+  let intent: Awaited<ReturnType<typeof requestJson>>;
+  try {
+    intent = await requestJson(transport, "/models/session/intent", signal,
+      { prompt: prompt.slice(0, 32_768), available_models: pool }, session.session_token, beforeSend, concurrency);
+  } catch (error) { return fallBackOnSwitch(error); }
   const modelId = strings(intent.candidate_models).find(/** Choose the first server-ranked candidate that belongs to this credential-bound session pool. */
     candidate => pool.includes(candidate));
   if (!modelId) throw new Error("GitHub Copilot Auto intent returned no eligible model");
diff --git a/tests/providers/github-copilot/github-copilot-account-origin.test.ts b/tests/providers/github-copilot/github-copilot-account-origin.test.ts
index e5d704cd9ed..db62fb00594 100644
--- a/tests/providers/github-copilot/github-copilot-account-origin.test.ts
+++ b/tests/providers/github-copilot/github-copilot-account-origin.test.ts
@@ -7,9 +7,11 @@ import { getAccountSet, saveCredential as persistCredential, setActiveAccount as
 import { handleResponses as dispatchResponses } from "../../../src/server/responses";
 import { saveConfig } from "../../../src/config";
 import { setActiveProviderApiKey } from "../../../src/providers/api-keys";
+import { clearCopilotAutoModelsForTests } from "../../../src/providers/github-copilot-auto";
 import type { OcxConfig } from "../../../src/types";
 import { removeTreeWithRetry } from "../../helpers/remove-tree";
 import { acquireOwnedSpendHome } from "../../helpers/owned-spend-home";
+import { stubbedProviderFetch } from "../../helpers/catalog-provider-fetch";
 
 const ACCOUNT_A_ORIGIN = "https://a.githubcopilot.com";
 const ACCOUNT_B_ORIGIN = "https://b.githubcopilot.com";
@@ -136,6 +138,9 @@ function config(wire: Wire): OcxConfig {
         adapter: "openai-chat",
         authMode: "oauth",
         baseUrl: "https://api.githubcopilot.com",
+        // Copilot Auto negotiates /models on the pinned outbound transport. Give it the
+        // fixture executor so the negotiation never resolves a real peer address.
+        fetch: stubbedProviderFetch,
         models: [model],
         ...(wire === "responses" ? { modelAdapters: { [model]: "openai-responses" } } : {}),
       },
@@ -209,8 +214,9 @@ function installFetch(options: {
   switchToAccountId?: string;
   switchOn: "refresh" | "first-dispatch" | "never";
   emptyFirst?: boolean;
-}): { dispatches: { origin: string; authorization: string }[] } {
+}): { dispatches: { origin: string; authorization: string }[]; modelsRequests: { origin: string }[] } {
   const dispatches: { origin: string; authorization: string }[] = [];
+  const modelsRequests: { origin: string }[] = [];
   let refreshSwitched = false;
   globalThis.fetch = (async (input, init) => {
     const url = input instanceof Request ? input.url : String(input);
@@ -228,6 +234,13 @@ function installFetch(options: {
     if (url === GITHUB_USER_URL) return Response.json({ id: 101 });
 
     const parsed = new URL(url);
+    if (parsed.pathname === "/models") {
+      modelsRequests.push({ origin: parsed.origin });
+      return Response.json({ data: [
+        { id: "gpt-4o", model_picker_enabled: true },
+        { id: "gpt-5.4", model_picker_enabled: true },
+      ] });
+    }
     if (parsed.hostname.endsWith(".githubcopilot.com") || parsed.hostname === "api.githubcopilot.com") {
       dispatches.push({
         origin: parsed.origin,
@@ -255,7 +268,7 @@ function installFetch(options: {
     }
     return originalFetch(input, init);
   }) as typeof fetch;
-  return { dispatches };
+  return { dispatches, modelsRequests };
 }
 
 beforeEach(() => {
@@ -275,6 +288,7 @@ beforeEach(() => {
   ));
   process.env.OPENCODEX_HOME = home;
   clearGenericFailoverHealth();
+  clearCopilotAutoModelsForTests();
   // Dispatches without starting a server, so it takes the spend-journal lease itself. Taken
   // last because the lease binds the home in effect at the moment it is taken.
   releaseSpendHome = acquireOwnedSpendHome();
@@ -450,6 +464,12 @@ describe("GitHub Copilot bearer/origin snapshot atomicity", () => {
       const url = new URL(input instanceof Request ? input.url : String(input));
       if (url.hostname === "api.exa.ai") return Response.json({ results: [] });
       if (!url.hostname.endsWith(".githubcopilot.com")) throw new Error("Unexpected fixture request");
+      if (url.pathname === "/models") {
+        return Response.json({ data: [
+          { id: "gpt-4o", model_picker_enabled: true },
+          { id: "gpt-5.4", model_picker_enabled: true },
+        ] });
+      }
       sent.push(new Headers(init?.headers).get("authorization") ?? "");
       bodies.push(JSON.parse(String(init?.body)));
       const delta = sent.length === 1
@@ -480,6 +500,18 @@ describe("GitHub Copilot bearer/origin snapshot atomicity", () => {
     expect(sends).toBe(0);
   });
 
+  test("Copilot Auto model negotiation is served by the fixture fetch, never real DNS", async () => {
+    await seedAccounts();
+    const observed = installFetch({ wire: "chat", statuses: [200], switchOn: "never" });
+    const response = await handleResponses(request("chat"), config("chat"), { model: "", provider: "" });
+    await responseText(response);
+    expect(response.status).toBe(200);
+    // The negotiation runs on providerOutboundGet, which resolves and pins a real peer
+    // address unless the provider hands it an executor. This fixture must see the request.
+    expect(observed.modelsRequests).toEqual([{ origin: ACCOUNT_A_ORIGIN }]);
+    expect(observed.dispatches).toEqual([{ origin: ACCOUNT_A_ORIGIN, authorization: bearer("copilot-access-a") }]);
+  });
+
   for (const wire of ["chat", "responses"] as const) {
     test(`${wire} revalidates selection after pacing and before physical dispatch`, async () => {
       const accounts = await seedAccounts();
diff --git a/tests/providers/github-copilot/github-copilot-auto.test.ts b/tests/providers/github-copilot/github-copilot-auto.test.ts
index 625f2f1c17a..ef9cf814699 100644
--- a/tests/providers/github-copilot/github-copilot-auto.test.ts
+++ b/tests/providers/github-copilot/github-copilot-auto.test.ts
@@ -198,13 +198,37 @@ describe("Copilot Auto permissions and negotiation", () => {
     expect((await resolveCopilotAuto(provider, "named", parsed)).modelId).toBe("named");
     expect(calls).toBe(1);
   });
-  test("cancellation and authority guard prevent negotiation sends", async () => {
+  for (const cancelAt of ["/models/session", "/models/session/intent"] as const) {
+    test(`an authority change during ${cancelAt} also falls back instead of failing negotiation`, async () => {
+      const seen: string[] = [];
+      let allowed = true;
+      const provider = { authMode: "oauth", baseUrl: "https://api.githubcopilot.com", fetch: (async (url: string | URL | Request) => {
+        const path = new URL(String(url instanceof Request ? url.url : url)).pathname;
+        seen.push(path);
+        if (path.endsWith("/models")) return Response.json({ data: [{ id: "eligible", model_picker_enabled: false, supported_endpoints: ["/responses"] }] });
+        if (path.endsWith("/models/session")) return Response.json({ session_token: "private-session", available_models: ["eligible"], expires_at: Math.floor(Date.now() / 1000) + 3600 });
+        return Response.json({ candidate_models: ["eligible"] });
+      }) as typeof fetch } as OcxProviderConfig;
+      // The switch lands just before the named control-plane send.
+      const beforeSend = () => {
+        if (seen.length === (cancelAt === "/models/session" ? 1 : 2)) allowed = false;
+        return allowed;
+      };
+      await expect(resolveCopilotAuto(provider, "auto", parsed, undefined, beforeSend))
+        .resolves.toMatchObject({ modelId: "auto", auto: false });
+      expect(seen.some(path => path.endsWith(cancelAt))).toBe(false);
+    });
+  }
+  test("cancellation aborts, while an authority change falls back without a negotiation send", async () => {
     let sends = 0;
     const provider = { authMode: "oauth", baseUrl: "https://api.githubcopilot.com", fetch: (async () => {
       sends++; return Response.json({});
     }) as typeof fetch } as OcxProviderConfig;
     await expect(resolveCopilotAuto(provider, "auto", parsed, AbortSignal.abort())).rejects.toThrow();
-    await expect(resolveCopilotAuto(provider, "auto", parsed, undefined, () => false)).rejects.toThrow();
+    // A manual account switch cancels the queued control-plane send. That is not a client
+    // abort: the caller revalidates the selection and rebuilds before dispatch.
+    await expect(resolveCopilotAuto(provider, "auto", parsed, undefined, () => false))
+      .resolves.toMatchObject({ modelId: "auto", auto: false });
     expect(sends).toBe(0);
   });
 });