diff --git a/extensions/openai/openai-codex-cli-auth.test.ts b/extensions/openai/openai-codex-cli-auth.test.ts
index 097ec9194ed..2c528ff5f86 100644
--- a/extensions/openai/openai-codex-cli-auth.test.ts
+++ b/extensions/openai/openai-codex-cli-auth.test.ts
@@ -233,6 +233,7 @@ describe("readOpenAICodexCliOAuthProfile", () => {
             access: "expired-local-access",
             refresh: "expired-local-refresh",
             expires: Date.now() - 60_000,
+            accountId: "acct_123",
           },
         },
       },
@@ -249,6 +250,43 @@ describe("readOpenAICodexCliOAuthProfile", () => {
     });
   });
 
+  it("refuses cli bootstrap when the stored default profile is expired but identity mismatches", () => {
+    const accessToken = buildJwt({
+      exp: Math.floor(Date.now() / 1000) + 600,
+      "https://api.openai.com/profile": {
+        email: "codex@example.com",
+      },
+    });
+    vi.spyOn(fs, "readFileSync").mockReturnValue(
+      JSON.stringify({
+        auth_mode: "chatgpt",
+        tokens: {
+          access_token: accessToken,
+          refresh_token: "refresh-token",
+          account_id: "acct_123",
+        },
+      }),
+    );
+
+    const parsed = readOpenAICodexCliOAuthProfile({
+      store: {
+        version: 1,
+        profiles: {
+          [OPENAI_CODEX_DEFAULT_PROFILE_ID]: {
+            type: "oauth",
+            provider: "openai-codex",
+            access: "expired-local-access",
+            refresh: "expired-local-refresh",
+            expires: Date.now() - 60_000,
+            accountId: "acct_local",
+          },
+        },
+      },
+    });
+
+    expect(parsed).toBeNull();
+  });
+
   it("allows the runtime-only Codex CLI profile when the stored default already matches", () => {
     const accessToken = buildJwt({
       exp: Math.floor(Date.now() / 1000) + 600,
diff --git a/extensions/openai/openai-codex-cli-auth.ts b/extensions/openai/openai-codex-cli-auth.ts
index 9b24a1cf471..f847ac18a40 100644
--- a/extensions/openai/openai-codex-cli-auth.ts
+++ b/extensions/openai/openai-codex-cli-auth.ts
@@ -89,29 +89,30 @@ function normalizeAuthEmailToken(value: string | undefined): string | undefined
   return normalizeAuthIdentityToken(value)?.toLowerCase();
 }
 
-// Keep this overwrite guard aligned with the canonical OAuth identity-copy rule
-// in src/agents/auth-profiles/oauth.ts without widening the plugin SDK surface.
-function isSafeToReplaceStoredIdentity(
-  existing: Pick<OAuthCredential, "accountId" | "email">,
-  incoming: Pick<OAuthCredential, "accountId" | "email">,
+function hasIdentityContinuity(
+  existing: Pick<OAuthCredential, "accountId" | "email"> | undefined,
+  incoming: OAuthCredential,
 ): boolean {
+  if (!existing) {
+    return true;
+  }
+  if (oauthCredentialMatches(existing as OAuthCredential, incoming)) {
+    return true;
+  }
+
   const existingAccountId = normalizeAuthIdentityToken(existing.accountId);
   const incomingAccountId = normalizeAuthIdentityToken(incoming.accountId);
-  const existingEmail = normalizeAuthEmailToken(existing.email);
-  const incomingEmail = normalizeAuthEmailToken(incoming.email);
-
   if (existingAccountId !== undefined && incomingAccountId !== undefined) {
     return existingAccountId === incomingAccountId;
   }
+
+  const existingEmail = normalizeAuthEmailToken(existing.email);
+  const incomingEmail = normalizeAuthEmailToken(incoming.email);
   if (existingEmail !== undefined && incomingEmail !== undefined) {
     return existingEmail === incomingEmail;
   }
 
-  const existingHasIdentity = existingAccountId !== undefined || existingEmail !== undefined;
-  if (existingHasIdentity) {
-    return false;
-  }
-  return true;
+  return false;
 }
 
 export function readOpenAICodexCliOAuthProfile(params: {
@@ -152,17 +153,13 @@ export function readOpenAICodexCliOAuthProfile(params: {
     });
     return null;
   }
-  if (
-    existingOAuth &&
-    hasUsableOAuthCredential(existingOAuth) &&
-    !oauthCredentialMatches(existingOAuth, credential)
-  ) {
+  if (!hasIdentityContinuity(existingOAuth, credential)) {
     return null;
   }
   if (
     existingOAuth &&
-    !oauthCredentialMatches(existingOAuth, credential) &&
-    !isSafeToReplaceStoredIdentity(existingOAuth, credential)
+    hasUsableOAuthCredential(existingOAuth) &&
+    !oauthCredentialMatches(existingOAuth, credential)
   ) {
     return null;
   }
diff --git a/src/agents/auth-health.test.ts b/src/agents/auth-health.test.ts
index c40d7f9cf6e..1f7dbb1a6ff 100644
--- a/src/agents/auth-health.test.ts
+++ b/src/agents/auth-health.test.ts
@@ -127,6 +127,7 @@ describe("buildAuthHealthSummary", () => {
           access: "expired-access",
           refresh: "expired-refresh",
           expires: now - 10_000,
+          accountId: "acct-cli",
         },
       },
     };
diff --git a/src/agents/auth-profiles.external-cli-sync.test.ts b/src/agents/auth-profiles.external-cli-sync.test.ts
index 4b46f002c8e..ae8461b4fcc 100644
--- a/src/agents/auth-profiles.external-cli-sync.test.ts
+++ b/src/agents/auth-profiles.external-cli-sync.test.ts
@@ -154,6 +154,7 @@ describe("external cli oauth resolution", () => {
         access: "fresh-cli-access",
         refresh: "fresh-cli-refresh",
         expires: Date.now() + 5 * 24 * 60 * 60_000,
+        accountId: "acct-123",
       });
 
       expect(
@@ -174,6 +175,7 @@ describe("external cli oauth resolution", () => {
             access: "expired-local-access",
             refresh: "expired-local-refresh",
             expires: Date.now() - 60_000,
+            accountId: "acct-123",
           }),
           imported,
         }),
@@ -255,6 +257,7 @@ describe("external cli oauth resolution", () => {
         access: "codex-fresh-access",
         refresh: "codex-fresh-refresh",
         expires: Date.now() + 5 * 24 * 60 * 60_000,
+        accountId: "acct-codex",
       }),
     );
     mocks.readMiniMaxCliCredentialsCached.mockReturnValue(
@@ -263,6 +266,7 @@ describe("external cli oauth resolution", () => {
         access: "minimax-fresh-access",
         refresh: "minimax-fresh-refresh",
         expires: Date.now() + 5 * 24 * 60 * 60_000,
+        email: "minimax@example.com",
       }),
     );
 
@@ -274,12 +278,14 @@ describe("external cli oauth resolution", () => {
           access: "codex-stale-access",
           refresh: "codex-stale-refresh",
           expires: Date.now() - 5_000,
+          accountId: "acct-codex",
         }),
         [MINIMAX_CLI_PROFILE_ID]: makeOAuthCredential({
           provider: "minimax-portal",
           access: "minimax-stale-access",
           refresh: "minimax-stale-refresh",
           expires: Date.now() - 5_000,
+          email: "minimax@example.com",
         }),
       },
     });
diff --git a/src/agents/auth-profiles/external-cli-sync.ts b/src/agents/auth-profiles/external-cli-sync.ts
index ab1104eb7cd..4a30e22a953 100644
--- a/src/agents/auth-profiles/external-cli-sync.ts
+++ b/src/agents/auth-profiles/external-cli-sync.ts
@@ -11,6 +11,7 @@ import { log } from "./constants.js";
 import {
   areOAuthCredentialsEquivalent,
   hasUsableOAuthCredential,
+  isSafeToOverwriteStoredOAuthIdentity,
   shouldBootstrapFromExternalCliCredential,
   shouldReplaceStoredOAuthCredential,
 } from "./oauth-manager.js";
@@ -19,6 +20,7 @@ import type { AuthProfileStore, OAuthCredential } from "./types.js";
 export {
   areOAuthCredentialsEquivalent,
   hasUsableOAuthCredential,
+  isSafeToOverwriteStoredOAuthIdentity,
   shouldBootstrapFromExternalCliCredential,
   shouldReplaceStoredOAuthCredential,
 } from "./oauth-manager.js";
@@ -147,6 +149,17 @@ export function resolveExternalCliAuthProfiles(
       });
       continue;
     }
+    if (
+      existingOAuth &&
+      !isSafeToOverwriteStoredOAuthIdentity(existingOAuth, creds) &&
+      !areOAuthCredentialsEquivalent(existingOAuth, creds)
+    ) {
+      log.warn("refused external cli oauth bootstrap: identity mismatch or missing binding", {
+        profileId: providerConfig.profileId,
+        provider: providerConfig.provider,
+      });
+      continue;
+    }
     if (
       !shouldBootstrapFromExternalCliCredential({
         existing: existingOAuth,
diff --git a/src/agents/auth-profiles/external-oauth.test.ts b/src/agents/auth-profiles/external-oauth.test.ts
index af4de0d251b..6f88462099e 100644
--- a/src/agents/auth-profiles/external-oauth.test.ts
+++ b/src/agents/auth-profiles/external-oauth.test.ts
@@ -130,6 +130,8 @@ describe("auth external oauth helpers", () => {
         access: "fresh-cli-access-token",
         refresh: "fresh-cli-refresh-token",
         expires: createUsableOAuthExpiry(),
+        accountId: "acct-cli",
+        expires: createUsableOAuthExpiry(),
       }),
     );
 
@@ -139,6 +141,7 @@ describe("auth external oauth helpers", () => {
           access: "stale-store-access-token",
           refresh: "stale-store-refresh-token",
           expires: Date.now() - 60_000,
+          accountId: "acct-cli",
         }),
       }),
     );
diff --git a/src/agents/auth-profiles/oauth-manager.test.ts b/src/agents/auth-profiles/oauth-manager.test.ts
new file mode 100644
index 00000000000..71a3fbdd746
--- /dev/null
+++ b/src/agents/auth-profiles/oauth-manager.test.ts
@@ -0,0 +1,71 @@
+import { describe, expect, it } from "vitest";
+import { isSafeToOverwriteStoredOAuthIdentity, OAuthManagerRefreshError } from "./oauth-manager.js";
+import type { AuthProfileStore, OAuthCredential } from "./types.js";
+
+function createCredential(overrides: Partial<OAuthCredential> = {}): OAuthCredential {
+  return {
+    type: "oauth",
+    provider: "openai-codex",
+    access: "access-token",
+    refresh: "refresh-token",
+    expires: Date.now() + 60_000,
+    ...overrides,
+  };
+}
+
+describe("isSafeToOverwriteStoredOAuthIdentity", () => {
+  it("accepts matching account identities", () => {
+    expect(
+      isSafeToOverwriteStoredOAuthIdentity(
+        createCredential({ accountId: "acct-123" }),
+        createCredential({ access: "rotated-access", accountId: "acct-123" }),
+      ),
+    ).toBe(true);
+  });
+
+  it("refuses overwriting an existing identity-less credential with a different token", () => {
+    expect(
+      isSafeToOverwriteStoredOAuthIdentity(
+        createCredential({}),
+        createCredential({ access: "rotated-access", accountId: "acct-123" }),
+      ),
+    ).toBe(false);
+  });
+
+  it("refuses non-overlapping identity evidence", () => {
+    expect(
+      isSafeToOverwriteStoredOAuthIdentity(
+        createCredential({ accountId: "acct-123" }),
+        createCredential({ access: "rotated-access", email: "user@example.com" }),
+      ),
+    ).toBe(false);
+  });
+});
+
+describe("OAuthManagerRefreshError", () => {
+  it("serializes without leaking credential or store secrets", () => {
+    const refreshedStore: AuthProfileStore = {
+      version: 1,
+      profiles: {
+        "openai-codex:default": createCredential({
+          access: "store-access",
+          refresh: "store-refresh",
+        }),
+      },
+    };
+    const error = new OAuthManagerRefreshError({
+      credential: createCredential({ access: "error-access", refresh: "error-refresh" }),
+      profileId: "openai-codex:default",
+      refreshedStore,
+      cause: new Error("boom"),
+    });
+
+    const serialized = JSON.stringify(error);
+    expect(serialized).toContain("openai-codex");
+    expect(serialized).toContain("openai-codex:default");
+    expect(serialized).not.toContain("error-access");
+    expect(serialized).not.toContain("error-refresh");
+    expect(serialized).not.toContain("store-access");
+    expect(serialized).not.toContain("store-refresh");
+  });
+});
diff --git a/src/agents/auth-profiles/oauth-manager.ts b/src/agents/auth-profiles/oauth-manager.ts
index 3d5d4bab611..9456709a582 100644
--- a/src/agents/auth-profiles/oauth-manager.ts
+++ b/src/agents/auth-profiles/oauth-manager.ts
@@ -36,10 +36,10 @@ export type ResolvedOAuthAccess = {
 };
 
 export class OAuthManagerRefreshError extends Error {
-  readonly credential: OAuthCredential;
   readonly profileId: string;
   readonly provider: string;
-  readonly refreshedStore: AuthProfileStore;
+  readonly #refreshedStore: AuthProfileStore;
+  readonly #credential: OAuthCredential;
 
   constructor(params: {
     credential: OAuthCredential;
@@ -52,10 +52,27 @@ export class OAuthManagerRefreshError extends Error {
       { cause: params.cause },
     );
     this.name = "OAuthManagerRefreshError";
-    this.credential = params.credential;
+    this.#credential = params.credential;
     this.profileId = params.profileId;
     this.provider = params.credential.provider;
-    this.refreshedStore = params.refreshedStore;
+    this.#refreshedStore = params.refreshedStore;
+  }
+
+  getRefreshedStore(): AuthProfileStore {
+    return this.#refreshedStore;
+  }
+
+  getCredential(): OAuthCredential {
+    return this.#credential;
+  }
+
+  toJSON(): { name: string; message: string; profileId: string; provider: string } {
+    return {
+      name: this.name,
+      message: this.message,
+      profileId: this.profileId,
+      provider: this.provider,
+    };
   }
 }
 
@@ -122,6 +139,60 @@ export function hasUsableOAuthCredential(
   return resolveTokenExpiryState(credential.expires, now) === "valid";
 }
 
+function normalizeAuthIdentityToken(value: string | undefined): string | undefined {
+  const trimmed = value?.trim();
+  return trimmed ? trimmed : undefined;
+}
+
+function normalizeAuthEmailToken(value: string | undefined): string | undefined {
+  return normalizeAuthIdentityToken(value)?.toLowerCase();
+}
+
+function hasOAuthIdentity(credential: Pick<OAuthCredential, "accountId" | "email">): boolean {
+  return (
+    normalizeAuthIdentityToken(credential.accountId) !== undefined ||
+    normalizeAuthEmailToken(credential.email) !== undefined
+  );
+}
+
+function hasMatchingOAuthIdentity(
+  existing: Pick<OAuthCredential, "accountId" | "email">,
+  incoming: Pick<OAuthCredential, "accountId" | "email">,
+): boolean {
+  const existingAccountId = normalizeAuthIdentityToken(existing.accountId);
+  const incomingAccountId = normalizeAuthIdentityToken(incoming.accountId);
+  if (existingAccountId !== undefined && incomingAccountId !== undefined) {
+    return existingAccountId === incomingAccountId;
+  }
+
+  const existingEmail = normalizeAuthEmailToken(existing.email);
+  const incomingEmail = normalizeAuthEmailToken(incoming.email);
+  if (existingEmail !== undefined && incomingEmail !== undefined) {
+    return existingEmail === incomingEmail;
+  }
+
+  return false;
+}
+
+export function isSafeToOverwriteStoredOAuthIdentity(
+  existing: OAuthCredential | undefined,
+  incoming: OAuthCredential,
+): boolean {
+  if (!existing || existing.type !== "oauth") {
+    return true;
+  }
+  if (existing.provider !== incoming.provider) {
+    return false;
+  }
+  if (areOAuthCredentialsEquivalent(existing, incoming)) {
+    return true;
+  }
+  if (!hasOAuthIdentity(existing)) {
+    return false;
+  }
+  return hasMatchingOAuthIdentity(existing, incoming);
+}
+
 export function shouldBootstrapFromExternalCliCredential(params: {
   existing: OAuthCredential | undefined;
   imported: OAuthCredential;
@@ -224,6 +295,13 @@ export function resolveEffectiveOAuthCredential(params: {
     });
     return params.credential;
   }
+  if (!isSafeToOverwriteStoredOAuthIdentity(params.credential, imported)) {
+    log.warn("refused external oauth bootstrap credential: identity mismatch or missing binding", {
+      profileId: params.profileId,
+      provider: params.credential.provider,
+    });
+    return params.credential;
+  }
   const shouldBootstrap = shouldBootstrapFromExternalCliCredential({
     existing: params.credential,
     imported,
@@ -322,7 +400,7 @@ export function createOAuthManager(adapter: OAuthManagerAdapter) {
           if (existing && existing.provider !== params.refreshed.provider) {
             return false;
           }
-          if (existing && !adapter.isSafeToCopyOAuthIdentity(existing, params.refreshed)) {
+          if (existing && !isSafeToOverwriteStoredOAuthIdentity(existing, params.refreshed)) {
             log.warn("refused to mirror OAuth credential: identity mismatch or regression", {
               profileId: params.profileId,
             });
@@ -423,18 +501,33 @@ export function createOAuthManager(adapter: OAuthManagerAdapter) {
           credential: cred,
         });
         if (externallyManaged) {
-          if (
-            shouldReplaceStoredOAuthCredential(cred, externallyManaged) &&
-            !areOAuthCredentialsEquivalent(cred, externallyManaged)
-          ) {
-            store.profiles[params.profileId] = externallyManaged;
-            saveAuthProfileStore(store, params.agentDir);
-          }
-          if (hasUsableOAuthCredential(externallyManaged)) {
-            return {
-              apiKey: await adapter.buildApiKey(externallyManaged.provider, externallyManaged),
-              credential: externallyManaged,
-            };
+          if (externallyManaged.provider !== cred.provider) {
+            log.warn("refused external oauth bootstrap credential: provider mismatch", {
+              profileId: params.profileId,
+              provider: cred.provider,
+            });
+          } else if (!isSafeToOverwriteStoredOAuthIdentity(cred, externallyManaged)) {
+            log.warn(
+              "refused external oauth bootstrap credential: identity mismatch or missing binding",
+              {
+                profileId: params.profileId,
+                provider: cred.provider,
+              },
+            );
+          } else {
+            if (
+              shouldReplaceStoredOAuthCredential(cred, externallyManaged) &&
+              !areOAuthCredentialsEquivalent(cred, externallyManaged)
+            ) {
+              store.profiles[params.profileId] = { ...externallyManaged };
+              saveAuthProfileStore(store, params.agentDir);
+            }
+            if (hasUsableOAuthCredential(externallyManaged)) {
+              return {
+                apiKey: await adapter.buildApiKey(externallyManaged.provider, externallyManaged),
+                credential: externallyManaged,
+              };
+            }
           }
         }
 
diff --git a/src/agents/auth-profiles/oauth.mirror-refresh.test.ts b/src/agents/auth-profiles/oauth.mirror-refresh.test.ts
index b89ad72582c..911c6e90007 100644
--- a/src/agents/auth-profiles/oauth.mirror-refresh.test.ts
+++ b/src/agents/auth-profiles/oauth.mirror-refresh.test.ts
@@ -652,11 +652,10 @@ describe("resolveApiKeyForProfile OAuth refresh mirror-to-main (#26322)", () =>
     });
   });
 
-  it("mirrors an identity-carrying refresh into a main store that has no identity (upgrade)", async () => {
-    // The Codex P1 scenario: main holds a pre-capture OAuth record (no
-    // accountId), the fresh sub-agent refresh response carries accountId.
-    // Mirror must accept so subsequent peers can adopt from main instead
-    // of hitting refresh_token_reused.
+  it("refuses to mirror into a main store that lacks identity binding", async () => {
+    // Authoritative main-store overwrites now require a positive identity
+    // match. A pre-capture main credential must not be replaced by a
+    // sub-agent refresh from an arbitrary account.
     const profileId = "openai-codex:default";
     const provider = "openai-codex";
     const freshExpiry = Date.now() + 60 * 60 * 1000;
@@ -704,13 +703,14 @@ describe("resolveApiKeyForProfile OAuth refresh mirror-to-main (#26322)", () =>
     });
     expect(result?.apiKey).toBe("sub-refreshed-access");
 
-    // Main must have accepted the mirror, with the identity marker added.
+    // Main must remain unchanged because there was no positive identity
+    // binding to authorize the overwrite.
     const mainRaw = JSON.parse(
       await fs.readFile(path.join(mainAgentDir, "auth-profiles.json"), "utf8"),
     ) as AuthProfileStore;
     expect(mainRaw.profiles[profileId]).toMatchObject({
-      access: "sub-refreshed-access",
-      accountId: "acct-sub",
+      access: "main-pre-capture-access",
+      refresh: "main-pre-capture-refresh",
     });
   });
 
diff --git a/src/agents/auth-profiles/oauth.openai-codex-refresh-fallback.test.ts b/src/agents/auth-profiles/oauth.openai-codex-refresh-fallback.test.ts
index a9e74088480..d2679cd82e8 100644
--- a/src/agents/auth-profiles/oauth.openai-codex-refresh-fallback.test.ts
+++ b/src/agents/auth-profiles/oauth.openai-codex-refresh-fallback.test.ts
@@ -271,6 +271,7 @@ describe("resolveApiKeyForProfile openai-codex refresh fallback", () => {
             access: "expired-access-token",
             refresh: "expired-refresh-token",
             expires: Date.now() - 60_000,
+            accountId: "acct-cli",
           },
         },
       },
@@ -313,6 +314,7 @@ describe("resolveApiKeyForProfile openai-codex refresh fallback", () => {
             access: "expired-access-token",
             refresh: "expired-refresh-token",
             expires: Date.now() - 60_000,
+            accountId: "acct-cli",
           },
         },
       },
@@ -470,6 +472,56 @@ describe("resolveApiKeyForProfile openai-codex refresh fallback", () => {
     expect(refreshProviderOAuthCredentialWithPluginMock).not.toHaveBeenCalled();
   });
 
+  it("refuses mismatched imported Codex CLI credentials when the stored default is expired", async () => {
+    const profileId = "openai-codex:default";
+    saveAuthProfileStore(
+      {
+        version: 1,
+        profiles: {
+          [profileId]: {
+            type: "oauth",
+            provider: "openai-codex",
+            access: "expired-access-token",
+            refresh: "expired-refresh-token",
+            expires: Date.now() - 60_000,
+            accountId: "acct-local",
+          },
+        },
+      },
+      agentDir,
+    );
+    readCodexCliCredentialsCachedMock.mockReturnValueOnce({
+      type: "oauth",
+      provider: "openai-codex",
+      access: "fresh-cli-access-token",
+      refresh: "fresh-cli-refresh-token",
+      expires: Date.now() + 86_400_000,
+      accountId: "acct-cli",
+    });
+    refreshProviderOAuthCredentialWithPluginMock.mockResolvedValueOnce({
+      type: "oauth",
+      provider: "openai-codex",
+      access: "rotated-local-access-token",
+      refresh: "rotated-local-refresh-token",
+      expires: Date.now() + 86_400_000,
+      accountId: "acct-local",
+    });
+
+    await expect(
+      resolveApiKeyForProfile({
+        store: ensureAuthProfileStore(agentDir),
+        profileId,
+        agentDir,
+      }),
+    ).resolves.toEqual({
+      apiKey: "rotated-local-access-token",
+      provider: "openai-codex",
+      email: undefined,
+    });
+
+    expect(refreshProviderOAuthCredentialWithPluginMock).toHaveBeenCalledTimes(1);
+  });
+
   it("keeps the canonical refresh token when imported Codex CLI state is stale", async () => {
     const profileId = "openai-codex:default";
     saveAuthProfileStore(
diff --git a/src/agents/auth-profiles/oauth.ts b/src/agents/auth-profiles/oauth.ts
index 9bc170c84d6..a0191ede27b 100644
--- a/src/agents/auth-profiles/oauth.ts
+++ b/src/agents/auth-profiles/oauth.ts
@@ -469,7 +469,7 @@ export async function resolveApiKeyForProfile(
   } catch (error) {
     const refreshedStore =
       error instanceof OAuthManagerRefreshError
-        ? error.refreshedStore
+        ? error.getRefreshedStore()
         : loadAuthProfileStoreForSecretsRuntime(params.agentDir);
     const fallbackProfileId = suggestOAuthProfileIdForLegacyDefault({
       cfg,