diff --git a/src/main/codex-accounts/legacy-shared-auth-migration.test.ts b/src/main/codex-accounts/legacy-shared-auth-migration.test.ts
index f77e9c390a3..d7274c3e227 100644
--- a/src/main/codex-accounts/legacy-shared-auth-migration.test.ts
+++ b/src/main/codex-accounts/legacy-shared-auth-migration.test.ts
@@ -142,6 +142,93 @@ describe('legacy shared Codex auth migration', () => {
   })
 })
 
+describe('legacy shared Codex MCP credentials migration (#8440)', () => {
+  it('carries the shared MCP .credentials.json into the identity-proven home with 0600 perms', () => {
+    const stale = createAuth('one@example.com', 'acct-1', 'stale', 1_000)
+    const fresh = createAuth('one@example.com', 'acct-1', 'fresh', 2_000)
+    const account = fixture.createAccount('account-1', 'acct-1', stale)
+    fixture.writeSharedAuth(fresh)
+    const mcpStore = JSON.stringify({ MCP_OAUTH: { 'server-a': { access_token: 'tok-a' } } })
+    fixture.writeSharedCredentials(mcpStore)
+
+    fixture.migrate([account], account.id)
+
+    const credentialsPath = fixture.accountCredentialsPath(account)
+    expect(readFileSync(credentialsPath, 'utf-8')).toBe(mcpStore)
+    if (process.platform !== 'win32') {
+      expect(statSync(credentialsPath).mode & 0o777).toBe(0o600)
+    }
+    expect(fixture.marker()).toMatchObject({ outcome: 'migrated', accountId: account.id })
+  })
+
+  it('carries the shared MCP store even when auth.json is already current', () => {
+    const fresh = createAuth('one@example.com', 'acct-1', 'fresh', 2_000)
+    const account = fixture.createAccount('account-1', 'acct-1', fresh)
+    fixture.writeSharedAuth(fresh)
+    const mcpStore = JSON.stringify({ MCP_OAUTH: { 'server-a': { access_token: 'tok-a' } } })
+    fixture.writeSharedCredentials(mcpStore)
+
+    fixture.migrate([account], account.id)
+
+    expect(readFileSync(fixture.accountCredentialsPath(account), 'utf-8')).toBe(mcpStore)
+    expect(fixture.marker()).toMatchObject({ outcome: 'already-current' })
+  })
+
+  it('is a no-op when the shared mirror has no MCP .credentials.json', () => {
+    const stale = createAuth('one@example.com', 'acct-1', 'stale', 1_000)
+    const fresh = createAuth('one@example.com', 'acct-1', 'fresh', 2_000)
+    const account = fixture.createAccount('account-1', 'acct-1', stale)
+    fixture.writeSharedAuth(fresh)
+
+    fixture.migrate([account], account.id)
+
+    expect(existsSync(fixture.accountCredentialsPath(account))).toBe(false)
+    expect(fixture.marker()).toMatchObject({ outcome: 'migrated' })
+  })
+
+  it('never clobbers a newer per-account .credentials.json', () => {
+    const stale = createAuth('one@example.com', 'acct-1', 'stale', 1_000)
+    const fresh = createAuth('one@example.com', 'acct-1', 'fresh', 2_000)
+    const account = fixture.createAccount('account-1', 'acct-1', stale)
+    fixture.writeSharedAuth(fresh)
+    fixture.writeSharedCredentials(
+      JSON.stringify({ MCP_OAUTH: { 'server-a': { access_token: 'shared-stale' } } })
+    )
+    const perAccountStore = JSON.stringify({
+      MCP_OAUTH: { 'server-a': { access_token: 'per-account-fresh' } }
+    })
+    writeFileSync(fixture.accountCredentialsPath(account), perAccountStore, 'utf-8')
+
+    fixture.migrate([account], account.id)
+
+    expect(readFileSync(fixture.accountCredentialsPath(account), 'utf-8')).toBe(perAccountStore)
+  })
+
+  it('never leaks the shared MCP store to a non-matching account', () => {
+    const account1 = fixture.createAccount(
+      'account-1',
+      'acct-duplicate',
+      createAuth('same@example.com', 'acct-duplicate', 'one', 1_000)
+    )
+    const account2 = fixture.createAccount(
+      'account-2',
+      'acct-duplicate',
+      createAuth('same@example.com', 'acct-duplicate', 'two', 1_000)
+    )
+    fixture.writeSharedAuth(createAuth('same@example.com', 'acct-duplicate', 'shared', 2_000))
+    fixture.writeSharedCredentials(
+      JSON.stringify({ MCP_OAUTH: { 'server-a': { access_token: 'tok-a' } } })
+    )
+
+    // Ambiguous identity: neither account is a unique match, so nothing is carried.
+    fixture.migrate([account1, account2], account1.id)
+
+    expect(existsSync(fixture.accountCredentialsPath(account1))).toBe(false)
+    expect(existsSync(fixture.accountCredentialsPath(account2))).toBe(false)
+    expect(existsSync(fixture.markerPath)).toBe(false)
+  })
+})
+
 function createFixture() {
   const root = mkdtempSync(join(tmpdir(), 'orca-codex-auth-migration-'))
   const managedAccountsRoot = join(root, 'codex-accounts')
@@ -175,6 +262,12 @@ function createFixture() {
     writeSharedAuth(auth: string) {
       writeFileSync(join(sharedRuntimeHome, 'auth.json'), auth, 'utf-8')
     },
+    writeSharedCredentials(credentials: string) {
+      writeFileSync(join(sharedRuntimeHome, '.credentials.json'), credentials, 'utf-8')
+    },
+    accountCredentialsPath(account: CodexManagedAccount) {
+      return join(account.managedHomePath, '.credentials.json')
+    },
     migrate(hostAccounts: readonly CodexManagedAccount[], activeHostAccountId: string | null) {
       migrateLegacySharedAuthToPerAccountHome({
         activeHostAccountId,
diff --git a/src/main/codex-accounts/legacy-shared-auth-migration.ts b/src/main/codex-accounts/legacy-shared-auth-migration.ts
index 7a697e10a5e..d3a9f247ac4 100644
--- a/src/main/codex-accounts/legacy-shared-auth-migration.ts
+++ b/src/main/codex-accounts/legacy-shared-auth-migration.ts
@@ -20,6 +20,7 @@ type TrustedAccountAuth = {
   account: CodexManagedAccount
   authContents: string | null
   authPath: string
+  homePath: string
 }
 
 type CompletedOutcome = 'already-current' | 'migrated' | 'no-shared-auth' | 'not-newer'
@@ -62,6 +63,14 @@ export function migrateLegacySharedAuthToPerAccountHome({
   if (match.authContents === null) {
     return
   }
+
+  // Why: Codex file-mode MCP OAuth tokens live in $CODEX_HOME/.credentials.json
+  // (issue #8440), keyed by MCP server URL with no account identity of their
+  // own. The uniquely-matched auth.json is the only proof this shared mirror is
+  // the active account's, so carry its co-located MCP store into the same
+  // per-account home or those servers silently need re-auth after upgrade.
+  migrateSharedMcpCredentials(sharedRuntimeHome, match.homePath)
+
   if (match.authContents === sharedAuthContents) {
     writeCompletedMarker(markerPath, 'already-current', match.account.id)
     return
@@ -93,7 +102,30 @@ function readTrustedAccountAuth(
     expectedAccountId: account.id
   })
   const authPath = join(trustedHome, 'auth.json')
-  return { account, authContents: readRegularFile(authPath), authPath }
+  return {
+    account,
+    authContents: readRegularFile(authPath),
+    authPath,
+    homePath: trustedHome
+  }
+}
+
+// Why: MCP OAuth tokens have no identity claim to match on, so we only ever
+// write the shared store into the one identity-proven account's home, and never
+// clobber a newer .credentials.json that account authed in its own home going
+// forward. Absent source is a plain no-op.
+function migrateSharedMcpCredentials(sharedRuntimeHome: string, perAccountHome: string): void {
+  const sharedCredentials = readRegularFile(join(sharedRuntimeHome, '.credentials.json'))
+  if (sharedCredentials === null) {
+    return
+  }
+  const perAccountCredentialsPath = join(perAccountHome, '.credentials.json')
+  if (regularFileState(perAccountCredentialsPath) === 'present') {
+    return
+  }
+  // Why: atomic 0600 write mirrors auth.json so a crash cannot leave a partial
+  // MCP store or widen permissions on sensitive tokens.
+  writeFileAtomically(perAccountCredentialsPath, sharedCredentials, { mode: 0o600 })
 }
 
 function readRegularFile(filePath: string): string | null {