diff --git a/apps/sim/app/api/auth/oauth/utils.test.ts b/apps/sim/app/api/auth/oauth/utils.test.ts
index 7f67d37673a..78fdecf2975 100644
--- a/apps/sim/app/api/auth/oauth/utils.test.ts
+++ b/apps/sim/app/api/auth/oauth/utils.test.ts
@@ -4,6 +4,7 @@
  * @vitest-environment node
  */
 
+import { redisConfigMock, redisConfigMockFns } from '@sim/testing'
 import { afterEach, beforeEach, describe, expect, it, vi } from 'vitest'
 
 vi.mock('@/lib/oauth/oauth', () => ({
@@ -11,7 +12,10 @@ vi.mock('@/lib/oauth/oauth', () => ({
   OAUTH_PROVIDERS: {},
 }))
 
+vi.mock('@/lib/core/config/redis', () => redisConfigMock)
+
 import { db } from '@sim/db'
+import { __resetCoalesceLocallyForTests } from '@/lib/concurrency/singleflight'
 import { refreshOAuthToken } from '@/lib/oauth'
 import {
   getCredential,
@@ -49,6 +53,10 @@ function mockUpdateChain() {
 describe('OAuth Utils', () => {
   beforeEach(() => {
     vi.clearAllMocks()
+    __resetCoalesceLocallyForTests()
+    redisConfigMockFns.mockGetRedisClient.mockReturnValue(null)
+    redisConfigMockFns.mockAcquireLock.mockResolvedValue(true)
+    redisConfigMockFns.mockReleaseLock.mockResolvedValue(true)
   })
 
   afterEach(() => {
@@ -107,6 +115,7 @@ describe('OAuth Utils', () => {
       }
 
       mockRefreshOAuthToken.mockResolvedValueOnce({
+        ok: true,
         accessToken: 'new-token',
         expiresIn: 3600,
         refreshToken: 'new-refresh-token',
@@ -130,7 +139,11 @@ describe('OAuth Utils', () => {
         providerId: 'google',
       }
 
-      mockRefreshOAuthToken.mockResolvedValueOnce(null)
+      mockRefreshOAuthToken.mockResolvedValueOnce({
+        ok: false,
+        errorCode: 'invalid_grant',
+        message: 'Failed',
+      })
 
       await expect(
         refreshTokenIfNeeded('request-id', mockCredential, 'credential-id')
@@ -198,6 +211,7 @@ describe('OAuth Utils', () => {
       mockUpdateChain()
 
       mockRefreshOAuthToken.mockResolvedValueOnce({
+        ok: true,
         accessToken: 'new-token',
         expiresIn: 3600,
         refreshToken: 'new-refresh-token',
@@ -237,7 +251,11 @@ describe('OAuth Utils', () => {
       mockSelectChain([mockResolvedCredential])
       mockSelectChain([mockAccountRow])
 
-      mockRefreshOAuthToken.mockResolvedValueOnce(null)
+      mockRefreshOAuthToken.mockResolvedValueOnce({
+        ok: false,
+        errorCode: 'invalid_grant',
+        message: 'Failed',
+      })
 
       const token = await refreshAccessTokenIfNeeded('credential-id', 'test-user-id', 'request-id')
 
diff --git a/apps/sim/app/api/auth/oauth/utils.ts b/apps/sim/app/api/auth/oauth/utils.ts
index 4109441528d..bbfdb0135be 100644
--- a/apps/sim/app/api/auth/oauth/utils.ts
+++ b/apps/sim/app/api/auth/oauth/utils.ts
@@ -4,6 +4,8 @@ import { account, credential, credentialSetMember } from '@sim/db/schema'
 import { createLogger } from '@sim/logger'
 import { toError } from '@sim/utils/errors'
 import { and, desc, eq, inArray } from 'drizzle-orm'
+import { withLeaderLock } from '@/lib/concurrency/leader-lock'
+import { coalesceLocally } from '@/lib/concurrency/singleflight'
 import { decryptSecret } from '@/lib/core/security/encryption'
 import { refreshOAuthToken } from '@/lib/oauth'
 import {
@@ -11,6 +13,11 @@ import {
   isMicrosoftProvider,
   PROACTIVE_REFRESH_THRESHOLD_DAYS,
 } from '@/lib/oauth/microsoft'
+import {
+  getRecentTerminalError,
+  isTerminalRefreshError,
+  markCredentialDead,
+} from '@/lib/oauth/terminal-errors'
 import {
   ATLASSIAN_SERVICE_ACCOUNT_PROVIDER_ID,
   ATLASSIAN_SERVICE_ACCOUNT_SECRET_TYPE,
@@ -318,6 +325,112 @@ export async function getCredential(requestId: string, credentialId: string, use
   return getCredentialByAccountId(requestId, resolved.accountId, userId)
 }
 
+interface CoalescedRefreshOptions {
+  accountId: string
+  providerId: string
+  refreshToken: string
+  requestId?: string
+  userId?: string
+}
+
+async function performCoalescedRefresh({
+  accountId,
+  providerId,
+  refreshToken,
+  requestId,
+  userId,
+}: CoalescedRefreshOptions): Promise<string | null> {
+  const logContext = {
+    ...(requestId ? { requestId } : {}),
+    ...(userId ? { userId } : {}),
+    providerId,
+    accountId,
+  }
+
+  const deadCode = await getRecentTerminalError(accountId)
+  if (deadCode) {
+    logger.warn('Skipping refresh: credential recently failed', {
+      ...logContext,
+      errorCode: deadCode,
+    })
+    return null
+  }
+
+  const lockKey = `oauth:refresh:${accountId}`
+
+  return coalesceLocally(lockKey, () =>
+    withLeaderLock<string>({
+      key: lockKey,
+      onLeader: async () => {
+        try {
+          const result = await refreshOAuthToken(providerId, refreshToken)
+
+          if (!result.ok) {
+            logger.error('Failed to refresh token', {
+              ...logContext,
+              errorCode: result.errorCode,
+            })
+            if (result.errorCode && isTerminalRefreshError(result.errorCode)) {
+              await markCredentialDead(accountId, result.errorCode)
+            }
+            return null
+          }
+
+          const updateData: Record<string, unknown> = {
+            accessToken: result.accessToken,
+            accessTokenExpiresAt: new Date(Date.now() + result.expiresIn * 1000),
+            updatedAt: new Date(),
+          }
+          if (result.refreshToken && result.refreshToken !== refreshToken) {
+            updateData.refreshToken = result.refreshToken
+          }
+          if (isMicrosoftProvider(providerId)) {
+            updateData.refreshTokenExpiresAt = getMicrosoftRefreshTokenExpiry()
+          }
+
+          await db.update(account).set(updateData).where(eq(account.id, accountId))
+
+          logger.info('Successfully refreshed access token', logContext)
+          return result.accessToken
+        } catch (error) {
+          logger.error('Refresh failed inside leader path', {
+            ...logContext,
+            error: toError(error).message,
+          })
+          return null
+        }
+      },
+      onFollower: async () => {
+        try {
+          const [row] = await db
+            .select({
+              accessToken: account.accessToken,
+              accessTokenExpiresAt: account.accessTokenExpiresAt,
+            })
+            .from(account)
+            .where(eq(account.id, accountId))
+            .limit(1)
+          if (
+            row?.accessToken &&
+            row.accessTokenExpiresAt &&
+            row.accessTokenExpiresAt > new Date()
+          ) {
+            logger.info('Got fresh access token from coalesced refresh', logContext)
+            return row.accessToken
+          }
+          return null
+        } catch (error) {
+          logger.warn('Follower DB read failed during refresh poll', {
+            ...logContext,
+            error: toError(error).message,
+          })
+          return null
+        }
+      },
+    })
+  )
+}
+
 export async function getOAuthToken(userId: string, providerId: string): Promise<string | null> {
   const connections = await db
     .select({
@@ -347,52 +460,12 @@ export async function getOAuthToken(userId: string, providerId: string): Promise
     !!credential.refreshToken && (!credential.accessToken || (tokenExpiry && tokenExpiry < now))
 
   if (shouldAttemptRefresh) {
-    logger.info(
-      `Access token expired for user ${userId}, provider ${providerId}. Attempting to refresh.`
-    )
-
-    try {
-      // Use the existing refreshOAuthToken function
-      const refreshResult = await refreshOAuthToken(providerId, credential.refreshToken!)
-
-      if (!refreshResult) {
-        logger.error(`Failed to refresh token for user ${userId}, provider ${providerId}`, {
-          providerId,
-          userId,
-          hasRefreshToken: !!credential.refreshToken,
-        })
-        return null
-      }
-
-      const { accessToken, expiresIn, refreshToken: newRefreshToken } = refreshResult
-
-      // Update the database with new tokens
-      const updateData: any = {
-        accessToken,
-        accessTokenExpiresAt: new Date(Date.now() + expiresIn * 1000), // Convert seconds to milliseconds
-        updatedAt: new Date(),
-      }
-
-      // If we received a new refresh token (some providers like Airtable rotate them), save it
-      if (newRefreshToken && newRefreshToken !== credential.refreshToken) {
-        logger.info(`Updating refresh token for user ${userId}, provider ${providerId}`)
-        updateData.refreshToken = newRefreshToken
-      }
-
-      // Update the token in the database with the actual expiration time from the provider
-      await db.update(account).set(updateData).where(eq(account.id, credential.id))
-
-      logger.info(`Successfully refreshed token for user ${userId}, provider ${providerId}`)
-      return accessToken
-    } catch (error) {
-      logger.error(`Error refreshing token for user ${userId}, provider ${providerId}`, {
-        error: toError(error).message,
-        stack: error instanceof Error ? error.stack : undefined,
-        providerId,
-        userId,
-      })
-      return null
-    }
+    return performCoalescedRefresh({
+      accountId: credential.id,
+      providerId,
+      refreshToken: credential.refreshToken!,
+      userId,
+    })
   }
 
   if (!credential.accessToken) {
@@ -472,66 +545,27 @@ export async function refreshAccessTokenIfNeeded(
   const accessToken = credential.accessToken
 
   if (shouldRefresh) {
-    logger.info(`[${requestId}] Refreshing token for credential`)
-    try {
-      const refreshedToken = await refreshOAuthToken(
-        credential.providerId,
-        credential.refreshToken!
-      )
-
-      if (!refreshedToken) {
-        logger.error(`[${requestId}] Failed to refresh token for credential: ${credentialId}`, {
-          credentialId,
-          providerId: credential.providerId,
-          userId: credential.userId,
-          hasRefreshToken: !!credential.refreshToken,
-        })
-        if (!accessTokenNeedsRefresh && accessToken) {
-          logger.info(`[${requestId}] Proactive refresh failed but access token still valid`)
-          return accessToken
-        }
-        return null
-      }
+    const resolvedCredentialId =
+      (credential as { resolvedCredentialId?: string }).resolvedCredentialId ?? credentialId
 
-      // Prepare update data
-      const updateData: Record<string, unknown> = {
-        accessToken: refreshedToken.accessToken,
-        accessTokenExpiresAt: new Date(Date.now() + refreshedToken.expiresIn * 1000),
-        updatedAt: new Date(),
-      }
-
-      // If we received a new refresh token, update it
-      if (refreshedToken.refreshToken && refreshedToken.refreshToken !== credential.refreshToken) {
-        logger.info(`[${requestId}] Updating refresh token for credential`)
-        updateData.refreshToken = refreshedToken.refreshToken
-      }
-
-      if (isMicrosoftProvider(credential.providerId)) {
-        updateData.refreshTokenExpiresAt = getMicrosoftRefreshTokenExpiry()
-      }
+    const fresh = await performCoalescedRefresh({
+      accountId: resolvedCredentialId,
+      providerId: credential.providerId,
+      refreshToken: credential.refreshToken!,
+      requestId,
+      userId: credential.userId,
+    })
+    if (fresh) return fresh
 
-      // Update the token in the database
-      const resolvedCredentialId =
-        (credential as { resolvedCredentialId?: string }).resolvedCredentialId ?? credentialId
-      await db.update(account).set(updateData).where(eq(account.id, resolvedCredentialId))
-
-      logger.info(`[${requestId}] Successfully refreshed access token for credential`)
-      return refreshedToken.accessToken
-    } catch (error) {
-      logger.error(`[${requestId}] Error refreshing token for credential`, {
-        error: toError(error).message,
-        stack: error instanceof Error ? error.stack : undefined,
-        providerId: credential.providerId,
-        credentialId,
-        userId: credential.userId,
-      })
-      if (!accessTokenNeedsRefresh && accessToken) {
-        logger.info(`[${requestId}] Proactive refresh failed but access token still valid`)
-        return accessToken
-      }
-      return null
+    // If refresh was only triggered proactively (Microsoft refresh-token aging),
+    // the still-valid access token is a fine fallback.
+    if (!accessTokenNeedsRefresh && accessToken) {
+      logger.info(`[${requestId}] Refresh unavailable; reusing still-valid access token`)
+      return accessToken
     }
-  } else if (!accessToken) {
+    return null
+  }
+  if (!accessToken) {
     // We have no access token and either no refresh token or not eligible to refresh
     logger.error(`[${requestId}] Missing access token for credential`)
     return null
@@ -580,65 +614,20 @@ export async function refreshTokenIfNeeded(
     return { accessToken: credential.accessToken, refreshed: false }
   }
 
-  try {
-    const refreshResult = await refreshOAuthToken(credential.providerId, credential.refreshToken!)
-
-    if (!refreshResult) {
-      logger.error(`[${requestId}] Failed to refresh token for credential`)
-      if (!accessTokenNeedsRefresh && credential.accessToken) {
-        logger.info(`[${requestId}] Proactive refresh failed but access token still valid`)
-        return { accessToken: credential.accessToken, refreshed: false }
-      }
-      throw new Error('Failed to refresh token')
-    }
-
-    const { accessToken: refreshedToken, expiresIn, refreshToken: newRefreshToken } = refreshResult
-
-    // Prepare update data
-    const updateData: Record<string, unknown> = {
-      accessToken: refreshedToken,
-      accessTokenExpiresAt: new Date(Date.now() + expiresIn * 1000), // Use provider's expiry
-      updatedAt: new Date(),
-    }
-
-    // If we received a new refresh token, update it
-    if (newRefreshToken && newRefreshToken !== credential.refreshToken) {
-      logger.info(`[${requestId}] Updating refresh token`)
-      updateData.refreshToken = newRefreshToken
-    }
-
-    if (isMicrosoftProvider(credential.providerId)) {
-      updateData.refreshTokenExpiresAt = getMicrosoftRefreshTokenExpiry()
-    }
-
-    await db.update(account).set(updateData).where(eq(account.id, resolvedCredentialId))
-
-    logger.info(`[${requestId}] Successfully refreshed access token`)
-    return { accessToken: refreshedToken, refreshed: true }
-  } catch (error) {
-    logger.warn(
-      `[${requestId}] Refresh attempt failed, checking if another concurrent request succeeded`
-    )
-
-    const freshCredential = await getCredential(requestId, resolvedCredentialId, credential.userId)
-    if (freshCredential?.accessToken) {
-      const freshExpiresAt = freshCredential.accessTokenExpiresAt
-      const stillValid = !freshExpiresAt || freshExpiresAt > new Date()
-
-      if (stillValid) {
-        logger.info(`[${requestId}] Found valid token from concurrent refresh, using it`)
-        return { accessToken: freshCredential.accessToken, refreshed: true }
-      }
-    }
-
-    if (!accessTokenNeedsRefresh && credential.accessToken) {
-      logger.info(`[${requestId}] Proactive refresh failed but access token still valid`)
-      return { accessToken: credential.accessToken, refreshed: false }
-    }
+  const fresh = await performCoalescedRefresh({
+    accountId: resolvedCredentialId,
+    providerId: credential.providerId,
+    refreshToken: credential.refreshToken!,
+    requestId,
+    userId: credential.userId,
+  })
+  if (fresh) return { accessToken: fresh, refreshed: true }
 
-    logger.error(`[${requestId}] Refresh failed and no valid token found in DB`, error)
-    throw error
+  if (!accessTokenNeedsRefresh && credential.accessToken) {
+    logger.info(`[${requestId}] Refresh unavailable; reusing still-valid access token`)
+    return { accessToken: credential.accessToken, refreshed: false }
   }
+  throw new Error('Failed to refresh token')
 }
 
 export interface CredentialSetCredential {
@@ -701,32 +690,13 @@ export async function getCredentialsForCredentialSet(
     let accessToken = cred.accessToken
 
     if (shouldRefresh && cred.refreshToken) {
-      try {
-        const refreshResult = await refreshOAuthToken(providerId, cred.refreshToken)
-
-        if (refreshResult) {
-          accessToken = refreshResult.accessToken
-
-          const updateData: Record<string, unknown> = {
-            accessToken: refreshResult.accessToken,
-            accessTokenExpiresAt: new Date(Date.now() + refreshResult.expiresIn * 1000),
-            updatedAt: new Date(),
-          }
-
-          if (refreshResult.refreshToken && refreshResult.refreshToken !== cred.refreshToken) {
-            updateData.refreshToken = refreshResult.refreshToken
-          }
-
-          await db.update(account).set(updateData).where(eq(account.id, cred.id))
-
-          logger.info(`Refreshed token for user ${cred.userId}, provider ${providerId}`)
-        }
-      } catch (error) {
-        logger.error(`Failed to refresh token for user ${cred.userId}, provider ${providerId}`, {
-          error: toError(error).message,
-        })
-        continue
-      }
+      const fresh = await performCoalescedRefresh({
+        accountId: cred.id,
+        providerId,
+        refreshToken: cred.refreshToken,
+        userId: cred.userId,
+      })
+      if (fresh) accessToken = fresh
     }
 
     if (accessToken) {
diff --git a/apps/sim/lib/concurrency/__tests__/leader-lock.test.ts b/apps/sim/lib/concurrency/__tests__/leader-lock.test.ts
new file mode 100644
index 00000000000..8e0cbcc6cde
--- /dev/null
+++ b/apps/sim/lib/concurrency/__tests__/leader-lock.test.ts
@@ -0,0 +1,168 @@
+/**
+ * @vitest-environment node
+ */
+import { redisConfigMock, redisConfigMockFns } from '@sim/testing'
+import { sleep } from '@sim/utils/helpers'
+import { beforeEach, describe, expect, it, vi } from 'vitest'
+
+vi.mock('@/lib/core/config/redis', () => redisConfigMock)
+
+import { withLeaderLock } from '@/lib/concurrency/leader-lock'
+
+beforeEach(() => {
+  vi.clearAllMocks()
+  redisConfigMockFns.mockAcquireLock.mockResolvedValue(true)
+  redisConfigMockFns.mockReleaseLock.mockResolvedValue(true)
+})
+
+describe('withLeaderLock', () => {
+  it('runs onLeader exactly once when lock acquired', async () => {
+    const onLeader = vi.fn(async () => 'leader-result')
+    const onFollower = vi.fn(async () => null)
+
+    const result = await withLeaderLock<string>({
+      key: 'k',
+      onLeader,
+      onFollower,
+    })
+
+    expect(result).toBe('leader-result')
+    expect(onLeader).toHaveBeenCalledTimes(1)
+    expect(onFollower).not.toHaveBeenCalled()
+    expect(redisConfigMockFns.mockReleaseLock).toHaveBeenCalledTimes(1)
+  })
+
+  it('passes a fresh owner token to acquireLock and releaseLock', async () => {
+    await withLeaderLock<string>({
+      key: 'k',
+      onLeader: async () => 'x',
+      onFollower: async () => null,
+    })
+
+    const [acquireKey, acquireValue] = redisConfigMockFns.mockAcquireLock.mock.calls[0]!
+    const [releaseKey, releaseValue] = redisConfigMockFns.mockReleaseLock.mock.calls[0]!
+
+    expect(acquireKey).toBe('k')
+    expect(releaseKey).toBe('k')
+    expect(acquireValue).toBe(releaseValue)
+    expect(typeof acquireValue).toBe('string')
+    expect((acquireValue as string).length).toBeGreaterThan(0)
+  })
+
+  it('falls back to uncoordinated leader when acquireLock throws', async () => {
+    redisConfigMockFns.mockAcquireLock.mockRejectedValueOnce(new Error('redis down'))
+
+    const onLeader = vi.fn(async () => 'fallback')
+    const onFollower = vi.fn(async () => null)
+
+    const result = await withLeaderLock<string>({
+      key: 'k',
+      onLeader,
+      onFollower,
+    })
+
+    expect(result).toBe('fallback')
+    expect(onLeader).toHaveBeenCalledTimes(1)
+    expect(onFollower).not.toHaveBeenCalled()
+    expect(redisConfigMockFns.mockReleaseLock).not.toHaveBeenCalled()
+  })
+
+  it('does not propagate releaseLock errors out of the leader path', async () => {
+    redisConfigMockFns.mockReleaseLock.mockRejectedValueOnce(new Error('redis blip'))
+
+    const result = await withLeaderLock<string>({
+      key: 'k',
+      onLeader: async () => 'leader-value',
+      onFollower: async () => null,
+    })
+
+    expect(result).toBe('leader-value')
+  })
+
+  it('releases the lock even when onLeader throws', async () => {
+    const onLeader = vi.fn(async () => {
+      throw new Error('boom')
+    })
+
+    await expect(
+      withLeaderLock<string>({
+        key: 'k',
+        onLeader,
+        onFollower: async () => null,
+      })
+    ).rejects.toThrow('boom')
+
+    expect(redisConfigMockFns.mockReleaseLock).toHaveBeenCalledTimes(1)
+  })
+
+  it('follower polls onFollower until it returns non-null', async () => {
+    redisConfigMockFns.mockAcquireLock.mockResolvedValueOnce(false)
+
+    let polls = 0
+    const onFollower = vi.fn(async () => {
+      polls += 1
+      if (polls >= 2) return 'available'
+      return null
+    })
+
+    const result = await withLeaderLock<string>({
+      key: 'k',
+      pollIntervalMs: 5,
+      maxWaitMs: 1000,
+      onLeader: async () => 'should-not-run',
+      onFollower,
+    })
+
+    expect(result).toBe('available')
+    expect(onFollower.mock.calls.length).toBeGreaterThanOrEqual(2)
+  })
+
+  it('follower returns null after timeout', async () => {
+    redisConfigMockFns.mockAcquireLock.mockResolvedValueOnce(false)
+
+    const result = await withLeaderLock<string>({
+      key: 'k',
+      pollIntervalMs: 5,
+      maxWaitMs: 20,
+      onLeader: async () => 'should-not-run',
+      onFollower: async () => null,
+    })
+
+    expect(result).toBeNull()
+  })
+
+  it('only one of N concurrent callers acquires the lock', async () => {
+    // Track which calls won the lock: first one returns true, rest return false.
+    let acquired = false
+    redisConfigMockFns.mockAcquireLock.mockImplementation(async () => {
+      if (acquired) return false
+      acquired = true
+      return true
+    })
+    redisConfigMockFns.mockReleaseLock.mockImplementation(async () => {
+      acquired = false
+      return true
+    })
+
+    let leaderRuns = 0
+
+    const callers = Array.from({ length: 5 }, () =>
+      withLeaderLock<string>({
+        key: 'shared',
+        pollIntervalMs: 5,
+        maxWaitMs: 200,
+        onLeader: async () => {
+          leaderRuns += 1
+          await sleep(20)
+          return 'leader-value'
+        },
+        onFollower: async () => (acquired ? null : 'follower-saw-released'),
+      })
+    )
+
+    const results = await Promise.all(callers)
+    expect(leaderRuns).toBe(1)
+    expect(results.filter((r) => r === 'leader-value').length).toBe(1)
+    expect(results.filter((r) => r === 'follower-saw-released').length).toBeGreaterThan(0)
+  })
+})
diff --git a/apps/sim/lib/concurrency/__tests__/singleflight.test.ts b/apps/sim/lib/concurrency/__tests__/singleflight.test.ts
new file mode 100644
index 00000000000..f911266be7b
--- /dev/null
+++ b/apps/sim/lib/concurrency/__tests__/singleflight.test.ts
@@ -0,0 +1,65 @@
+/**
+ * @vitest-environment node
+ */
+import { sleep } from '@sim/utils/helpers'
+import { afterEach, describe, expect, it, vi } from 'vitest'
+import { __resetCoalesceLocallyForTests, coalesceLocally } from '@/lib/concurrency/singleflight'
+
+afterEach(() => {
+  __resetCoalesceLocallyForTests()
+  vi.restoreAllMocks()
+})
+
+describe('coalesceLocally', () => {
+  it('invokes fn once when N callers race on the same key', async () => {
+    const fn = vi.fn(async () => {
+      await sleep(5)
+      return 'value'
+    })
+
+    const results = await Promise.all(
+      Array.from({ length: 10 }, () => coalesceLocally('shared', fn))
+    )
+
+    expect(fn).toHaveBeenCalledTimes(1)
+    expect(results).toEqual(Array.from({ length: 10 }, () => 'value'))
+  })
+
+  it('returns the same promise instance to concurrent callers', () => {
+    const fn = async () => {
+      await sleep(10)
+      return 1
+    }
+    const a = coalesceLocally('same-key', fn)
+    const b = coalesceLocally('same-key', fn)
+    expect(a).toBe(b)
+  })
+
+  it('clears the cache after success so the next call invokes fn again', async () => {
+    let count = 0
+    const fn = async () => {
+      count += 1
+      return count
+    }
+
+    expect(await coalesceLocally('once', fn)).toBe(1)
+    expect(await coalesceLocally('once', fn)).toBe(2)
+  })
+
+  it('clears the cache after rejection so the next call invokes fn again', async () => {
+    let count = 0
+    const fn = async () => {
+      count += 1
+      throw new Error(`fail ${count}`)
+    }
+
+    await expect(coalesceLocally('rejection', fn)).rejects.toThrow('fail 1')
+    await expect(coalesceLocally('rejection', fn)).rejects.toThrow('fail 2')
+  })
+
+  it('does not coalesce across distinct keys', async () => {
+    const fn = vi.fn(async () => 'value')
+    await Promise.all([coalesceLocally('a', fn), coalesceLocally('b', fn)])
+    expect(fn).toHaveBeenCalledTimes(2)
+  })
+})
diff --git a/apps/sim/lib/concurrency/leader-lock.ts b/apps/sim/lib/concurrency/leader-lock.ts
new file mode 100644
index 00000000000..dd0ed0402a2
--- /dev/null
+++ b/apps/sim/lib/concurrency/leader-lock.ts
@@ -0,0 +1,69 @@
+import { createLogger } from '@sim/logger'
+import { toError } from '@sim/utils/errors'
+import { sleep } from '@sim/utils/helpers'
+import { generateShortId } from '@sim/utils/id'
+import { acquireLock, releaseLock } from '@/lib/core/config/redis'
+
+const logger = createLogger('LeaderLock')
+
+const DEFAULT_TTL_SEC = 10
+const DEFAULT_POLL_INTERVAL_MS = 100
+const DEFAULT_MAX_WAIT_MS = 3_000
+
+export interface LeaderLockOptions<T> {
+  key: string
+  ttlSec?: number
+  pollIntervalMs?: number
+  maxWaitMs?: number
+  onLeader: () => Promise<T | null>
+  onFollower: () => Promise<T | null>
+}
+
+export async function withLeaderLock<T>(opts: LeaderLockOptions<T>): Promise<T | null> {
+  const {
+    key,
+    ttlSec = DEFAULT_TTL_SEC,
+    pollIntervalMs = DEFAULT_POLL_INTERVAL_MS,
+    maxWaitMs = DEFAULT_MAX_WAIT_MS,
+    onLeader,
+    onFollower,
+  } = opts
+
+  const ownerToken = generateShortId()
+
+  let acquired = false
+  try {
+    acquired = await acquireLock(key, ownerToken, ttlSec)
+  } catch (error) {
+    logger.warn('Lock acquisition failed; running leader path uncoordinated', {
+      key,
+      error: toError(error).message,
+    })
+    return onLeader()
+  }
+
+  if (acquired) {
+    try {
+      return await onLeader()
+    } finally {
+      try {
+        await releaseLock(key, ownerToken)
+      } catch (error) {
+        logger.warn('Lock release failed (will expire via TTL)', {
+          key,
+          error: toError(error).message,
+        })
+      }
+    }
+  }
+
+  const deadline = Date.now() + maxWaitMs
+  while (Date.now() < deadline) {
+    await sleep(pollIntervalMs)
+    const value = await onFollower()
+    if (value !== null) return value
+  }
+
+  logger.warn('Follower timed out waiting for leader', { key, maxWaitMs })
+  return null
+}
diff --git a/apps/sim/lib/concurrency/singleflight.ts b/apps/sim/lib/concurrency/singleflight.ts
new file mode 100644
index 00000000000..f15ae06f9da
--- /dev/null
+++ b/apps/sim/lib/concurrency/singleflight.ts
@@ -0,0 +1,21 @@
+const inflight = new Map<string, Promise<unknown>>()
+
+export function coalesceLocally<T>(key: string, fn: () => Promise<T>): Promise<T> {
+  const existing = inflight.get(key) as Promise<T> | undefined
+  if (existing) return existing
+
+  const promise = (async () => {
+    try {
+      return await fn()
+    } finally {
+      inflight.delete(key)
+    }
+  })()
+
+  inflight.set(key, promise)
+  return promise
+}
+
+export function __resetCoalesceLocallyForTests(): void {
+  inflight.clear()
+}
diff --git a/apps/sim/lib/credentials/draft-hooks.ts b/apps/sim/lib/credentials/draft-hooks.ts
index c5768c96aee..07361e58a70 100644
--- a/apps/sim/lib/credentials/draft-hooks.ts
+++ b/apps/sim/lib/credentials/draft-hooks.ts
@@ -4,6 +4,7 @@ import * as schema from '@sim/db/schema'
 import { createLogger } from '@sim/logger'
 import { generateId } from '@sim/utils/id'
 import { and, eq, sql } from 'drizzle-orm'
+import { clearDeadFlag } from '@/lib/oauth/terminal-errors'
 
 const logger = createLogger('CredentialDraftHooks')
 
@@ -53,6 +54,8 @@ export async function handleCreateCredentialFromDraft(params: {
       accountId,
     })
 
+    await clearDeadFlag(accountId)
+
     recordAudit({
       workspaceId: draft.workspaceId,
       actorId: userId,
@@ -147,6 +150,8 @@ export async function handleReconnectCredential(params: {
     newAccountId,
   })
 
+  await clearDeadFlag(newAccountId)
+
   recordAudit({
     workspaceId,
     actorId: userId,
diff --git a/apps/sim/lib/oauth/__tests__/terminal-errors.test.ts b/apps/sim/lib/oauth/__tests__/terminal-errors.test.ts
new file mode 100644
index 00000000000..3fd2787a1ea
--- /dev/null
+++ b/apps/sim/lib/oauth/__tests__/terminal-errors.test.ts
@@ -0,0 +1,105 @@
+/**
+ * @vitest-environment node
+ */
+import { redisConfigMock, redisConfigMockFns } from '@sim/testing'
+import { beforeEach, describe, expect, it, vi } from 'vitest'
+
+vi.mock('@/lib/core/config/redis', () => redisConfigMock)
+
+import {
+  clearDeadFlag,
+  getRecentTerminalError,
+  isTerminalRefreshError,
+  markCredentialDead,
+} from '@/lib/oauth/terminal-errors'
+
+interface FakeRedis {
+  store: Map<string, string>
+  set: ReturnType<typeof vi.fn>
+  get: ReturnType<typeof vi.fn>
+  del: ReturnType<typeof vi.fn>
+}
+
+function createFakeRedis(): FakeRedis {
+  const store = new Map<string, string>()
+  return {
+    store,
+    set: vi.fn(async (key: string, value: string) => {
+      store.set(key, value)
+      return 'OK'
+    }),
+    get: vi.fn(async (key: string) => store.get(key) ?? null),
+    del: vi.fn(async (key: string) => (store.delete(key) ? 1 : 0)),
+  }
+}
+
+beforeEach(() => {
+  vi.clearAllMocks()
+  redisConfigMockFns.mockGetRedisClient.mockReturnValue(null)
+})
+
+describe('isTerminalRefreshError', () => {
+  it.each([
+    'invalid_refresh_token',
+    'invalid_grant',
+    'access_denied',
+    'bad_client_secret',
+    'invalid_client_id',
+    'invalid_client',
+    'bad_redirect_uri',
+  ])('returns true for %s', (code) => {
+    expect(isTerminalRefreshError(code)).toBe(true)
+  })
+
+  it.each(['ratelimited', 'internal_error', 'service_unavailable', undefined, null, ''])(
+    'returns false for %s',
+    (code) => {
+      expect(isTerminalRefreshError(code as string | undefined | null)).toBe(false)
+    }
+  )
+})
+
+describe('markCredentialDead / getRecentTerminalError / clearDeadFlag', () => {
+  it('roundtrips a code through Redis', async () => {
+    const redis = createFakeRedis()
+    redisConfigMockFns.mockGetRedisClient.mockReturnValue(redis as never)
+
+    await markCredentialDead('acc-1', 'invalid_refresh_token')
+    expect(await getRecentTerminalError('acc-1')).toBe('invalid_refresh_token')
+  })
+
+  it('clearDeadFlag removes the entry', async () => {
+    const redis = createFakeRedis()
+    redisConfigMockFns.mockGetRedisClient.mockReturnValue(redis as never)
+
+    await markCredentialDead('acc-1', 'invalid_refresh_token')
+    await clearDeadFlag('acc-1')
+    expect(await getRecentTerminalError('acc-1')).toBeNull()
+  })
+
+  it('all functions are no-ops when Redis is unavailable', async () => {
+    await expect(markCredentialDead('acc-1', 'code')).resolves.toBeUndefined()
+    await expect(getRecentTerminalError('acc-1')).resolves.toBeNull()
+    await expect(clearDeadFlag('acc-1')).resolves.toBeUndefined()
+  })
+
+  it('absorbs Redis errors without throwing', async () => {
+    const redis = createFakeRedis()
+    redis.set.mockRejectedValueOnce(new Error('boom'))
+    redis.get.mockRejectedValueOnce(new Error('boom'))
+    redis.del.mockRejectedValueOnce(new Error('boom'))
+    redisConfigMockFns.mockGetRedisClient.mockReturnValue(redis as never)
+
+    await expect(markCredentialDead('acc-1', 'code')).resolves.toBeUndefined()
+    await expect(getRecentTerminalError('acc-1')).resolves.toBeNull()
+    await expect(clearDeadFlag('acc-1')).resolves.toBeUndefined()
+  })
+
+  it('uses a 1-hour TTL on the dead flag', async () => {
+    const redis = createFakeRedis()
+    redisConfigMockFns.mockGetRedisClient.mockReturnValue(redis as never)
+
+    await markCredentialDead('acc-1', 'invalid_refresh_token')
+    expect(redis.set).toHaveBeenCalledWith('oauth:dead:acc-1', 'invalid_refresh_token', 'EX', 3600)
+  })
+})
diff --git a/apps/sim/lib/oauth/oauth.test.ts b/apps/sim/lib/oauth/oauth.test.ts
index c677c7b2c84..a5ad87e2f2b 100644
--- a/apps/sim/lib/oauth/oauth.test.ts
+++ b/apps/sim/lib/oauth/oauth.test.ts
@@ -326,7 +326,7 @@ describe('OAuth Token Refresh', () => {
   })
 
   describe('Error Handling', () => {
-    it.concurrent('should return null for unsupported provider', async () => {
+    it.concurrent('should return failure for unsupported provider', async () => {
       const mockFetch = createMockFetch(defaultOAuthResponse)
       const refreshToken = 'test_refresh_token'
 
@@ -334,10 +334,10 @@ describe('OAuth Token Refresh', () => {
         refreshOAuthToken('unsupported', refreshToken)
       )
 
-      expect(result).toBeNull()
+      expect(result.ok).toBe(false)
     })
 
-    it.concurrent('should return null for API error responses', async () => {
+    it.concurrent('should return failure with errorCode for HTTP error responses', async () => {
       const mockFetch = vi.fn().mockResolvedValue({
         ok: false,
         status: 400,
@@ -351,16 +351,36 @@ describe('OAuth Token Refresh', () => {
 
       const result = await withMockFetch(mockFetch, () => refreshOAuthToken('google', refreshToken))
 
-      expect(result).toBeNull()
+      expect(result.ok).toBe(false)
+      if (!result.ok) {
+        expect(result.errorCode).toBe('invalid_request')
+      }
+    })
+
+    it.concurrent('should return failure for Slack-style body errors', async () => {
+      const mockFetch = vi.fn().mockResolvedValue({
+        ok: true,
+        status: 200,
+        statusText: 'OK',
+        json: async () => ({ ok: false, error: 'invalid_refresh_token' }),
+      })
+      const refreshToken = 'test_refresh_token'
+
+      const result = await withMockFetch(mockFetch, () => refreshOAuthToken('slack', refreshToken))
+
+      expect(result.ok).toBe(false)
+      if (!result.ok) {
+        expect(result.errorCode).toBe('invalid_refresh_token')
+      }
     })
 
-    it.concurrent('should return null for network errors', async () => {
+    it.concurrent('should return failure for network errors', async () => {
       const mockFetch = vi.fn().mockRejectedValue(new Error('Network error'))
       const refreshToken = 'test_refresh_token'
 
       const result = await withMockFetch(mockFetch, () => refreshOAuthToken('google', refreshToken))
 
-      expect(result).toBeNull()
+      expect(result.ok).toBe(false)
     })
   })
 
@@ -383,6 +403,7 @@ describe('OAuth Token Refresh', () => {
       )
 
       expect(result).toEqual({
+        ok: true,
         accessToken: 'new_access_token',
         expiresIn: 3600,
         refreshToken: newRefreshToken,
@@ -421,6 +442,7 @@ describe('OAuth Token Refresh', () => {
           )
 
           expect(result).toEqual({
+            ok: true,
             accessToken: 'new_access_token',
             expiresIn: 3600,
             refreshToken: rotatedRefreshToken,
@@ -443,13 +465,14 @@ describe('OAuth Token Refresh', () => {
       const result = await withMockFetch(mockFetch, () => refreshOAuthToken('google', refreshToken))
 
       expect(result).toEqual({
+        ok: true,
         accessToken: 'new_access_token',
         expiresIn: 3600,
         refreshToken: refreshToken,
       })
     })
 
-    it.concurrent('should return null when access token is missing', async () => {
+    it.concurrent('should return failure when access token is missing', async () => {
       const refreshToken = 'test_refresh_token'
 
       const mockFetch = vi.fn().mockResolvedValue({
@@ -461,7 +484,7 @@ describe('OAuth Token Refresh', () => {
 
       const result = await withMockFetch(mockFetch, () => refreshOAuthToken('google', refreshToken))
 
-      expect(result).toBeNull()
+      expect(result.ok).toBe(false)
     })
 
     it.concurrent('should use default expiration when not provided', async () => {
@@ -477,6 +500,7 @@ describe('OAuth Token Refresh', () => {
       const result = await withMockFetch(mockFetch, () => refreshOAuthToken('google', refreshToken))
 
       expect(result).toEqual({
+        ok: true,
         accessToken: 'new_access_token',
         expiresIn: 3600,
         refreshToken: refreshToken,
diff --git a/apps/sim/lib/oauth/oauth.ts b/apps/sim/lib/oauth/oauth.ts
index 8702399024a..82c3ee7bb1e 100644
--- a/apps/sim/lib/oauth/oauth.ts
+++ b/apps/sim/lib/oauth/oauth.ts
@@ -1456,13 +1456,6 @@ function buildAuthRequest(
   return { headers, bodyParams, useJsonBody: config.useJsonBody }
 }
 
-/**
- * Refresh an OAuth token
- * This is a server-side utility function to refresh OAuth tokens
- * @param providerId The provider ID (e.g., 'google-drive')
- * @param refreshToken The refresh token to use
- * @returns Object containing the new access token and expiration time in seconds, or null if refresh failed
- */
 function getBaseProviderForService(providerId: string): string {
   if (providerId in OAUTH_PROVIDERS) {
     return providerId
@@ -1479,10 +1472,33 @@ function getBaseProviderForService(providerId: string): string {
   throw new Error(`Unknown OAuth provider: ${providerId}`)
 }
 
+export interface RefreshTokenSuccess {
+  ok: true
+  accessToken: string
+  expiresIn: number
+  refreshToken: string
+}
+
+export interface RefreshTokenFailure {
+  ok: false
+  errorCode?: string
+  message?: string
+}
+
+export type RefreshTokenResult = RefreshTokenSuccess | RefreshTokenFailure
+
+function extractErrorCode(value: unknown): string | undefined {
+  if (value && typeof value === 'object' && 'error' in value) {
+    const code = (value as { error: unknown }).error
+    if (typeof code === 'string') return code
+  }
+  return undefined
+}
+
 export async function refreshOAuthToken(
   providerId: string,
   refreshToken: string
-): Promise<{ accessToken: string; expiresIn: number; refreshToken: string } | null> {
+): Promise<RefreshTokenResult> {
   try {
     const provider = getBaseProviderForService(providerId)
 
@@ -1498,7 +1514,7 @@ export async function refreshOAuthToken(
 
     if (!response.ok) {
       const errorText = await response.text()
-      let errorData = errorText
+      let errorData: unknown = errorText
 
       try {
         errorData = JSON.parse(errorText)
@@ -1518,11 +1534,34 @@ export async function refreshOAuthToken(
         hasRefreshToken: !!refreshToken,
         refreshTokenPrefix: refreshToken ? `${refreshToken.substring(0, 10)}...` : 'none',
       })
-      throw new Error(`Failed to refresh token: ${response.status} ${errorText}`)
+      return {
+        ok: false,
+        errorCode: extractErrorCode(errorData),
+        message: `Failed to refresh token: ${response.status} ${errorText}`,
+      }
     }
 
     const data = await response.json()
 
+    if (data && typeof data === 'object' && data.ok === false) {
+      logger.error('Token refresh failed:', {
+        status: response.status,
+        statusText: response.statusText,
+        error: data.error,
+        parsedError: data,
+        providerId,
+        tokenEndpoint: config.tokenEndpoint,
+        hasClientId: !!config.clientId,
+        hasClientSecret: !!config.clientSecret,
+        hasRefreshToken: !!refreshToken,
+      })
+      return {
+        ok: false,
+        errorCode: typeof data.error === 'string' ? data.error : undefined,
+        message: `Failed to refresh token: ${data.error ?? 'unknown'}`,
+      }
+    }
+
     const accessToken = data.access_token
 
     let newRefreshToken = null
@@ -1534,8 +1573,8 @@ export async function refreshOAuthToken(
     const expiresIn = data.expires_in || data.expiresIn || 3600
 
     if (!accessToken) {
-      logger.warn('No access token found in refresh response', data)
-      return null
+      logger.warn('No access token found in refresh response', { providerId, response: data })
+      return { ok: false, message: 'No access token in refresh response' }
     }
 
     logger.info('Token refreshed successfully with expiration', {
@@ -1545,14 +1584,14 @@ export async function refreshOAuthToken(
     })
 
     return {
+      ok: true,
       accessToken,
       expiresIn,
       refreshToken: newRefreshToken || refreshToken, // Return new refresh token if available
     }
   } catch (error) {
-    logger.error('Error refreshing token:', {
-      error: toError(error).message,
-    })
-    return null
+    const message = toError(error).message
+    logger.error('Error refreshing token:', { error: message })
+    return { ok: false, message }
   }
 }
diff --git a/apps/sim/lib/oauth/terminal-errors.ts b/apps/sim/lib/oauth/terminal-errors.ts
new file mode 100644
index 00000000000..25fba73205c
--- /dev/null
+++ b/apps/sim/lib/oauth/terminal-errors.ts
@@ -0,0 +1,67 @@
+import { createLogger } from '@sim/logger'
+import { toError } from '@sim/utils/errors'
+import { getRedisClient } from '@/lib/core/config/redis'
+
+const logger = createLogger('OAuthTerminalErrors')
+
+const TERMINAL_ERRORS = new Set<string>([
+  'invalid_refresh_token',
+  'invalid_grant',
+  'access_denied',
+  'bad_client_secret',
+  'invalid_client_id',
+  'invalid_client',
+  'bad_redirect_uri',
+])
+
+const DEAD_CACHE_TTL_SEC = 60 * 60
+
+function deadKey(accountId: string): string {
+  return `oauth:dead:${accountId}`
+}
+
+export function isTerminalRefreshError(code: string | undefined | null): boolean {
+  if (!code) return false
+  return TERMINAL_ERRORS.has(code)
+}
+
+export async function markCredentialDead(accountId: string, code: string): Promise<void> {
+  const redis = getRedisClient()
+  if (!redis) return
+  try {
+    await redis.set(deadKey(accountId), code, 'EX', DEAD_CACHE_TTL_SEC)
+  } catch (error) {
+    logger.warn('Failed to mark credential dead in Redis', {
+      accountId,
+      code,
+      error: toError(error).message,
+    })
+  }
+}
+
+export async function getRecentTerminalError(accountId: string): Promise<string | null> {
+  const redis = getRedisClient()
+  if (!redis) return null
+  try {
+    return await redis.get(deadKey(accountId))
+  } catch (error) {
+    logger.warn('Failed to read terminal error flag from Redis', {
+      accountId,
+      error: toError(error).message,
+    })
+    return null
+  }
+}
+
+export async function clearDeadFlag(accountId: string): Promise<void> {
+  const redis = getRedisClient()
+  if (!redis) return
+  try {
+    await redis.del(deadKey(accountId))
+  } catch (error) {
+    logger.warn('Failed to clear terminal error flag from Redis', {
+      accountId,
+      error: toError(error).message,
+    })
+  }
+}