diff --git a/apps/sim/app/api/mcp/oauth/start/route.test.ts b/apps/sim/app/api/mcp/oauth/start/route.test.ts
index 68dd96b2bf3..555e2d2fa4d 100644
--- a/apps/sim/app/api/mcp/oauth/start/route.test.ts
+++ b/apps/sim/app/api/mcp/oauth/start/route.test.ts
@@ -162,6 +162,23 @@ describe('MCP OAuth start route', () => {
     expect(body.error).not.toContain('ECONNREFUSED')
     expect(body.error).not.toContain('internal-db-host')
   })
+
+  it('returns an actionable 4xx when the server does not support dynamic client registration', async () => {
+    mcpOauthMockFns.mockMcpAuthGuarded.mockRejectedValueOnce(
+      new Error('Incompatible auth server: does not support dynamic client registration')
+    )
+    const request = new NextRequest(
+      'http://localhost:3000/api/mcp/oauth/start?workspaceId=workspace-1&serverId=server-1'
+    )
+
+    const response = await GET(request)
+    const body = await response.json()
+
+    expect(response.status).toBe(422)
+    expect(body.error).toBe(
+      "This server doesn't support OAuth client registration. Configure a token instead."
+    )
+  })
 })
 
 describe('surfaceOauthError', () => {
diff --git a/apps/sim/app/api/mcp/oauth/start/route.ts b/apps/sim/app/api/mcp/oauth/start/route.ts
index edb17a0f1c9..4354257a1e0 100644
--- a/apps/sim/app/api/mcp/oauth/start/route.ts
+++ b/apps/sim/app/api/mcp/oauth/start/route.ts
@@ -2,7 +2,7 @@ import { OAuthError, ServerError } from '@modelcontextprotocol/sdk/server/auth/e
 import { db } from '@sim/db'
 import { mcpServers } from '@sim/db/schema'
 import { createLogger } from '@sim/logger'
-import { toError } from '@sim/utils/errors'
+import { getErrorMessage, toError } from '@sim/utils/errors'
 import { and, eq, isNull } from 'drizzle-orm'
 import type { NextRequest } from 'next/server'
 import { NextResponse } from 'next/server'
@@ -25,6 +25,14 @@ import { createMcpErrorResponse } from '@/lib/mcp/utils'
 const logger = createLogger('McpOauthStartAPI')
 const OAUTH_START_TTL_MS = 10 * 60 * 1000
 const MAX_SURFACED_ERROR_LENGTH = 250
+const DCR_UNSUPPORTED_MESSAGE =
+  "This server doesn't support OAuth client registration. Configure a token instead."
+
+function isDynamicClientRegistrationUnsupported(error: unknown): boolean {
+  return getErrorMessage(error, '')
+    .toLowerCase()
+    .includes('does not support dynamic client registration')
+}
 
 export function surfaceOauthError(error: unknown): string {
   // Spec-compliant OAuth servers throw typed subclasses with clean RFC 6749 fields.
@@ -148,6 +156,9 @@ export const GET = withRouteHandler(
             authorizationUrl: e.authorizationUrl,
           })
         }
+        if (isDynamicClientRegistrationUnsupported(e)) {
+          return createMcpErrorResponse(toError(e), DCR_UNSUPPORTED_MESSAGE, 422)
+        }
         throw e
       }
     } catch (error) {
diff --git a/apps/sim/app/workspace/[workspaceId]/settings/components/mcp/mcp.tsx b/apps/sim/app/workspace/[workspaceId]/settings/components/mcp/mcp.tsx
index c2769a36e54..92f3fc7f60a 100644
--- a/apps/sim/app/workspace/[workspaceId]/settings/components/mcp/mcp.tsx
+++ b/apps/sim/app/workspace/[workspaceId]/settings/components/mcp/mcp.tsx
@@ -85,7 +85,12 @@ function ServerListItem({
   onViewDetails,
 }: ServerListItemProps) {
   const transportLabel = formatTransportLabel(server.transport || 'http')
-  const toolsLabel = getServerToolsLabel(tools, server.connectionStatus, server.lastError)
+  const toolsLabel = getServerToolsLabel(
+    tools,
+    server.connectionStatus,
+    server.lastError,
+    server.authType
+  )
   const hasConnectionIssue =
     server.connectionStatus === 'error' || server.connectionStatus === 'disconnected'
 
@@ -380,6 +385,8 @@ export function MCP() {
     const refreshAction = getRefreshActionState({
       mutationStatus: isCurrentRefresh ? refreshServerMutation.status : 'idle',
       connectionStatus: isCurrentRefresh ? refreshServerMutation.data?.status : undefined,
+      authType: server.authType,
+      error: isCurrentRefresh ? refreshServerMutation.data?.error : undefined,
       workflowsUpdated: isCurrentRefresh ? refreshServerMutation.data?.workflowsUpdated : undefined,
     })
 
@@ -427,7 +434,12 @@ export function MCP() {
               <div className='flex flex-col gap-2'>
                 <span className='text-[var(--text-muted)] text-caption'>Status</span>
                 <p className='text-[var(--text-error)] text-sm'>
-                  {getServerToolsLabel([], server.connectionStatus, server.lastError)}
+                  {getServerToolsLabel(
+                    [],
+                    server.connectionStatus,
+                    server.lastError,
+                    server.authType
+                  )}
                 </p>
               </div>
             )}
diff --git a/apps/sim/app/workspace/[workspaceId]/settings/components/mcp/refresh-action-state.test.ts b/apps/sim/app/workspace/[workspaceId]/settings/components/mcp/refresh-action-state.test.ts
index a9eeb89513e..2ac09d8b300 100644
--- a/apps/sim/app/workspace/[workspaceId]/settings/components/mcp/refresh-action-state.test.ts
+++ b/apps/sim/app/workspace/[workspaceId]/settings/components/mcp/refresh-action-state.test.ts
@@ -31,6 +31,37 @@ describe('getRefreshActionState', () => {
     })
   })
 
+  it('shows Authorization required when an OAuth refresh finishes disconnected', () => {
+    expect(
+      getRefreshActionState({
+        mutationStatus: 'success',
+        connectionStatus: 'disconnected',
+        authType: 'oauth',
+        workflowsUpdated: 0,
+      })
+    ).toEqual({
+      text: 'Authorization required',
+      textTone: 'error',
+      disabled: false,
+    })
+  })
+
+  it('keeps Failed when a disconnected OAuth refresh has a concrete error', () => {
+    expect(
+      getRefreshActionState({
+        mutationStatus: 'success',
+        connectionStatus: 'disconnected',
+        authType: 'oauth',
+        error: 'The MCP server took too long to respond and timed out',
+        workflowsUpdated: 0,
+      })
+    ).toEqual({
+      text: 'Failed',
+      textTone: 'error',
+      disabled: false,
+    })
+  })
+
   it('preserves successful refresh feedback', () => {
     expect(
       getRefreshActionState({
diff --git a/apps/sim/app/workspace/[workspaceId]/settings/components/mcp/refresh-action-state.ts b/apps/sim/app/workspace/[workspaceId]/settings/components/mcp/refresh-action-state.ts
index 28a6869921e..7f37d47d9d4 100644
--- a/apps/sim/app/workspace/[workspaceId]/settings/components/mcp/refresh-action-state.ts
+++ b/apps/sim/app/workspace/[workspaceId]/settings/components/mcp/refresh-action-state.ts
@@ -1,10 +1,12 @@
 import type { MutationStatus } from '@tanstack/react-query'
-import type { RefreshMcpServerResult } from '@/lib/api/contracts/mcp'
+import type { McpServer, RefreshMcpServerResult } from '@/lib/api/contracts/mcp'
 import type { SettingsAction } from '@/app/workspace/[workspaceId]/settings/components/settings-header/settings-header'
 
 interface RefreshActionStateInput {
   mutationStatus: MutationStatus
   connectionStatus?: RefreshMcpServerResult['status']
+  authType?: McpServer['authType']
+  error?: RefreshMcpServerResult['error']
   workflowsUpdated?: number
 }
 
@@ -13,12 +15,23 @@ type RefreshActionState = Pick<SettingsAction, 'text' | 'textTone' | 'disabled'>
 export function getRefreshActionState({
   mutationStatus,
   connectionStatus,
+  authType,
+  error,
   workflowsUpdated,
 }: RefreshActionStateInput): RefreshActionState {
   if (mutationStatus === 'pending') {
     return { text: 'Refreshing...', textTone: undefined, disabled: true }
   }
 
+  if (
+    mutationStatus === 'success' &&
+    connectionStatus === 'disconnected' &&
+    authType === 'oauth' &&
+    !error?.trim()
+  ) {
+    return { text: 'Authorization required', textTone: 'error', disabled: false }
+  }
+
   if (
     mutationStatus === 'error' ||
     (mutationStatus === 'success' && connectionStatus !== 'connected')
diff --git a/apps/sim/app/workspace/[workspaceId]/settings/components/mcp/server-tools-label.test.ts b/apps/sim/app/workspace/[workspaceId]/settings/components/mcp/server-tools-label.test.ts
index e65dadf68e4..373ae480af4 100644
--- a/apps/sim/app/workspace/[workspaceId]/settings/components/mcp/server-tools-label.test.ts
+++ b/apps/sim/app/workspace/[workspaceId]/settings/components/mcp/server-tools-label.test.ts
@@ -12,12 +12,20 @@ describe('getServerToolsLabel', () => {
     expect(getServerToolsLabel([], 'error', null)).toBe('Unable to connect')
   })
 
-  it('shows a disconnected state when OAuth was not completed', () => {
-    expect(getServerToolsLabel([], 'disconnected', null)).toBe('Not Connected')
+  it('shows that OAuth authorization is required when OAuth was not completed', () => {
+    expect(getServerToolsLabel([], 'disconnected', null, 'oauth')).toBe(
+      'OAuth authorization required'
+    )
+  })
+
+  it('keeps the generic disconnected state for non-OAuth servers', () => {
+    expect(getServerToolsLabel([], 'disconnected', null, 'headers')).toBe('Not Connected')
   })
 
   it('shows the persisted error for disconnected connections', () => {
-    expect(getServerToolsLabel([], 'disconnected', 'Request timed out')).toBe('Request timed out')
+    expect(getServerToolsLabel([], 'disconnected', 'Request timed out', 'oauth')).toBe(
+      'Request timed out'
+    )
   })
 
   it('continues showing discovered tools for healthy connections', () => {
diff --git a/apps/sim/app/workspace/[workspaceId]/settings/components/mcp/server-tools-label.ts b/apps/sim/app/workspace/[workspaceId]/settings/components/mcp/server-tools-label.ts
index f9d8d4896af..495cea5f9ff 100644
--- a/apps/sim/app/workspace/[workspaceId]/settings/components/mcp/server-tools-label.ts
+++ b/apps/sim/app/workspace/[workspaceId]/settings/components/mcp/server-tools-label.ts
@@ -7,14 +7,17 @@ interface NamedTool {
 export function getServerToolsLabel(
   tools: NamedTool[],
   connectionStatus?: McpServer['connectionStatus'],
-  lastError?: McpServer['lastError']
+  lastError?: McpServer['lastError'],
+  authType?: McpServer['authType']
 ): string {
   if (connectionStatus === 'error') {
     return lastError?.trim() || 'Unable to connect'
   }
 
   if (connectionStatus === 'disconnected') {
-    return lastError?.trim() || 'Not Connected'
+    return (
+      lastError?.trim() || (authType === 'oauth' ? 'OAuth authorization required' : 'Not Connected')
+    )
   }
 
   const count = tools.length
diff --git a/apps/sim/lib/core/security/input-validation.server.ts b/apps/sim/lib/core/security/input-validation.server.ts
index 7f81039622c..e3074a2accd 100644
--- a/apps/sim/lib/core/security/input-validation.server.ts
+++ b/apps/sim/lib/core/security/input-validation.server.ts
@@ -433,9 +433,21 @@ export function createPinnedLookup(resolvedIP: string): LookupFunction {
  *
  * The `Agent` is captured for the lifetime of the returned function, so repeated
  * calls (e.g. a provider tool loop) reuse its keep-alive connections.
+ *
+ * `allowH2` opts the pinned Agent into HTTP/2 (ALPN-negotiated, h1.1 fallback).
+ * It defaults to `false` to leave existing consumers unchanged. Enabling it does
+ * not weaken pinning: the pinned `connect.lookup` forces every connection on the
+ * Agent to `resolvedIP` regardless of authority, so h2 connection coalescing can
+ * never reach an address other than the validated one.
  */
-export function createPinnedFetch(resolvedIP: string): typeof fetch {
-  const dispatcher = new Agent({ connect: { lookup: createPinnedLookup(resolvedIP) } })
+export function createPinnedFetch(
+  resolvedIP: string,
+  options?: { allowH2?: boolean }
+): typeof fetch {
+  const dispatcher = new Agent({
+    allowH2: options?.allowH2 ?? false,
+    connect: { lookup: createPinnedLookup(resolvedIP) },
+  })
 
   const pinned = async (input: RequestInfo | URL, init?: RequestInit): Promise<Response> => {
     // double-cast-allowed: DOM RequestInfo/URL and undici fetch input types differ but are structurally compatible at runtime (Node's global fetch IS undici)
diff --git a/apps/sim/lib/core/security/pinned-fetch.server.test.ts b/apps/sim/lib/core/security/pinned-fetch.server.test.ts
index e07d0d412dd..0ecfa22cb9e 100644
--- a/apps/sim/lib/core/security/pinned-fetch.server.test.ts
+++ b/apps/sim/lib/core/security/pinned-fetch.server.test.ts
@@ -55,6 +55,18 @@ describe('createPinnedFetch', () => {
     expect(resolved).toEqual({ address: '203.0.113.10', family: 4 })
   })
 
+  it('defaults allowH2 to false so existing consumers are unchanged', () => {
+    createPinnedFetch('203.0.113.10')
+    const opts = capturedAgentOptions[0] as { allowH2?: boolean }
+    expect(opts.allowH2).toBe(false)
+  })
+
+  it('opts the Agent into HTTP/2 when allowH2 is requested', () => {
+    createPinnedFetch('203.0.113.10', { allowH2: true })
+    const opts = capturedAgentOptions[0] as { allowH2?: boolean }
+    expect(opts.allowH2).toBe(true)
+  })
+
   it('uses IPv6 family when the validated IP is IPv6', async () => {
     createPinnedFetch('2606:4700:4700::1111')
     const { connect } = capturedAgentOptions[0] as { connect: { lookup: PinnedLookup } }
diff --git a/apps/sim/lib/mcp/client.test.ts b/apps/sim/lib/mcp/client.test.ts
index c568f425d61..198a67e5c4c 100644
--- a/apps/sim/lib/mcp/client.test.ts
+++ b/apps/sim/lib/mcp/client.test.ts
@@ -1,6 +1,7 @@
 /**
  * @vitest-environment node
  */
+import { UnauthorizedError } from '@modelcontextprotocol/sdk/client/auth.js'
 import { beforeEach, describe, expect, it, vi } from 'vitest'
 
 const { mockLogger, mockSdkConnect, mockSdkListTools } = vi.hoisted(() => ({
@@ -265,6 +266,55 @@ describe('McpClient notification handler', () => {
     expect(JSON.stringify(mockLogger.error.mock.calls)).not.toContain(secret)
   })
 
+  it('does not misclassify rejected static headers as an OAuth authorization flow', async () => {
+    mockSdkConnect.mockRejectedValueOnce(new UnauthorizedError('Static token rejected'))
+    const client = new McpClient({
+      config: {
+        ...createConfig(),
+        authType: 'headers',
+        headers: { Authorization: 'Bearer rejected-static-token' },
+      },
+      securityPolicy: { requireConsent: false, auditLevel: 'basic' },
+    })
+
+    await expect(client.connect()).rejects.toBeInstanceOf(UnauthorizedError)
+
+    expect(mockLogger.error).toHaveBeenCalledWith(
+      expect.stringContaining('Failed to connect'),
+      expect.objectContaining({ outcome: 'unauthorized' })
+    )
+    expect(client.getStatus().lastError).toBe('Authentication failed')
+  })
+
+  it('logs tools/list failures without echoed credentials or session identifiers', async () => {
+    const secret = 'opaque-tools-list-credential'
+    mockSdkListTools.mockRejectedValueOnce(new Error(`Upstream rejected ${secret}`))
+    const client = new McpClient({
+      config: {
+        ...createConfig(),
+        authType: 'headers',
+        headers: { 'X-Custom-Credential': secret },
+      },
+      securityPolicy: { requireConsent: false, auditLevel: 'basic' },
+    })
+
+    await client.connect()
+    await expect(client.listTools()).rejects.toThrow(secret)
+
+    expect(mockLogger.error).toHaveBeenCalledWith(
+      expect.stringContaining('Failed to list tools'),
+      expect.objectContaining({
+        phase: 'tools/list',
+        serverId: 'server-1',
+        sessionIdPresent: true,
+        error: expect.objectContaining({ name: 'Error' }),
+      })
+    )
+    const logged = JSON.stringify(mockLogger.error.mock.calls)
+    expect(logged).not.toContain(secret)
+    expect(logged).not.toContain('test-session')
+  })
+
   it('passes configured headers for OAuth transports as well as header auth transports', () => {
     const authProvider = {} as unknown as NonNullable<McpClientOptions['authProvider']>
     new McpClient({
diff --git a/apps/sim/lib/mcp/client.ts b/apps/sim/lib/mcp/client.ts
index 50a90355c14..bc3d32c6dde 100644
--- a/apps/sim/lib/mcp/client.ts
+++ b/apps/sim/lib/mcp/client.ts
@@ -9,11 +9,11 @@ import {
   ToolListChangedNotificationSchema,
 } from '@modelcontextprotocol/sdk/types.js'
 import { createLogger } from '@sim/logger'
-import { describeError, getErrorMessage } from '@sim/utils/errors'
+import { getErrorMessage } from '@sim/utils/errors'
 import { getMaxExecutionTimeout } from '@/lib/core/execution-limits'
-import { createPinnedFetch } from '@/lib/core/security/input-validation.server'
-import { sanitizeForLogging } from '@/lib/core/security/redaction'
+import { getMcpSafeErrorDiagnostics } from '@/lib/mcp/error-diagnostics'
 import { McpOauthRedirectRequired } from '@/lib/mcp/oauth'
+import { createPinnedMcpFetch } from '@/lib/mcp/pinned-fetch'
 import {
   type McpClientOptions,
   McpConnectionError,
@@ -43,10 +43,16 @@ type ConnectionOutcome =
   | 'cancelled'
   | 'error'
 
-function classifyConnectionOutcome(error: unknown): ConnectionOutcome {
-  if (error instanceof McpOauthRedirectRequired || error instanceof UnauthorizedError) {
+function classifyConnectionOutcome(
+  error: unknown,
+  authType: McpServerConfig['authType']
+): ConnectionOutcome {
+  if (error instanceof McpOauthRedirectRequired) {
     return 'authorization_required'
   }
+  if (error instanceof UnauthorizedError) {
+    return authType === 'oauth' ? 'authorization_required' : 'unauthorized'
+  }
   const message = getErrorMessage(error, '').toLowerCase()
   if (message.includes('connection attempt cancelled')) return 'cancelled'
   if (message.includes('timeout') || message.includes('timed out')) return 'timeout'
@@ -92,7 +98,7 @@ export class McpClient {
     this.transport = new StreamableHTTPClientTransport(new URL(this.config.url), {
       authProvider: useOauth ? this.authProvider : undefined,
       requestInit: { headers: this.config.headers },
-      ...(resolvedIP ? { fetch: createPinnedFetch(resolvedIP) } : {}),
+      ...(resolvedIP ? { fetch: createPinnedMcpFetch(resolvedIP) } : {}),
     })
 
     this.client = new Client(
@@ -109,7 +115,9 @@ export class McpClient {
     this.client.onerror = (error) => {
       logger.warn(`MCP transport error for ${this.config.name}`, {
         serverId: this.config.id,
-        error: sanitizeForLogging(getErrorMessage(error, 'Unknown transport error'), 200),
+        phase: 'transport',
+        sessionIdPresent: Boolean(this.transport.sessionId),
+        error: getMcpSafeErrorDiagnostics(error),
       })
     }
   }
@@ -178,25 +186,21 @@ export class McpClient {
     } catch (error) {
       this.isConnected = false
       const errorMessage = getErrorMessage(error, 'Unknown error')
-      const describedError = describeError(error)
-      const outcome = classifyConnectionOutcome(error)
+      const outcome = classifyConnectionOutcome(error, this.config.authType)
       logger.error(`Failed to connect to MCP server ${this.config.name}`, {
         ...diagnostics,
         durationMs: Date.now() - startedAt,
-        error: {
-          name: sanitizeForLogging(describedError.name, 100),
-          code: describedError.code ? sanitizeForLogging(describedError.code, 100) : undefined,
-          errno: describedError.errno ? sanitizeForLogging(describedError.errno, 100) : undefined,
-          syscall: describedError.syscall
-            ? sanitizeForLogging(describedError.syscall, 100)
-            : undefined,
-        },
+        error: getMcpSafeErrorDiagnostics(error),
         outcome,
       })
       if (outcome === 'authorization_required') {
         this.connectionStatus.lastError = undefined
         throw error
       }
+      if (error instanceof UnauthorizedError) {
+        this.connectionStatus.lastError = 'Authentication failed'
+        throw error
+      }
       this.connectionStatus.lastError = errorMessage
       throw new McpConnectionError(errorMessage, this.config.name)
     }
@@ -236,6 +240,7 @@ export class McpClient {
       MCP_CLIENT_CONSTANTS.LIST_TOOLS_MAX_TOTAL_TIMEOUT_MS
     )
     const maxTotalTimeoutMs = MCP_CLIENT_CONSTANTS.LIST_TOOLS_MAX_TOTAL_TIMEOUT_MS
+    const startedAt = Date.now()
 
     try {
       const result: ListToolsResult = await this.client.listTools(undefined, {
@@ -265,7 +270,15 @@ export class McpClient {
         serverName: this.config.name,
       }))
     } catch (error) {
-      logger.error(`Failed to list tools from server ${this.config.name}:`, error)
+      logger.error(`Failed to list tools from server ${this.config.name}`, {
+        serverId: this.config.id,
+        phase: 'tools/list',
+        durationMs: Date.now() - startedAt,
+        idleTimeoutMs,
+        maxTotalTimeoutMs,
+        sessionIdPresent: Boolean(this.transport.sessionId),
+        error: getMcpSafeErrorDiagnostics(error),
+      })
       throw error
     }
   }
diff --git a/apps/sim/lib/mcp/error-diagnostics.test.ts b/apps/sim/lib/mcp/error-diagnostics.test.ts
new file mode 100644
index 00000000000..2badd603c05
--- /dev/null
+++ b/apps/sim/lib/mcp/error-diagnostics.test.ts
@@ -0,0 +1,39 @@
+/**
+ * @vitest-environment node
+ */
+
+import { describe, expect, it } from 'vitest'
+import { getMcpSafeErrorDiagnostics } from './error-diagnostics'
+
+describe('getMcpSafeErrorDiagnostics', () => {
+  it('redacts and truncates structural fields without emitting message text', () => {
+    const secret = 'sk-abcdefghijklmnopqrstuvwxyz1234567890'
+    const error = Object.assign(new Error(`message contains ${secret}`), {
+      name: `Bearer ${secret}`,
+      code: `code-${'c'.repeat(200)}`,
+      errno: `api_key: "${secret}"`,
+      syscall: `Bearer ${secret}`,
+      sessionId: secret,
+    })
+
+    const diagnostics = getMcpSafeErrorDiagnostics(error)
+
+    expect(diagnostics).toEqual({
+      name: expect.any(String),
+      code: expect.any(String),
+      errno: expect.any(String),
+      syscall: expect.any(String),
+    })
+    expect(diagnostics).not.toHaveProperty('message')
+    expect(diagnostics).not.toHaveProperty('causeChain')
+    expect(diagnostics).not.toHaveProperty('sessionId')
+    for (const value of Object.values(diagnostics)) {
+      expect(value).not.toContain(secret)
+      expect(value?.length).toBeLessThanOrEqual(100)
+    }
+    expect(diagnostics.name).toContain('[REDACTED]')
+    expect(diagnostics.errno).toContain('[REDACTED]')
+    expect(diagnostics.syscall).toContain('[REDACTED]')
+    expect(diagnostics.code).toHaveLength(100)
+  })
+})
diff --git a/apps/sim/lib/mcp/error-diagnostics.ts b/apps/sim/lib/mcp/error-diagnostics.ts
new file mode 100644
index 00000000000..ce3b6bac7b4
--- /dev/null
+++ b/apps/sim/lib/mcp/error-diagnostics.ts
@@ -0,0 +1,25 @@
+import { describeError } from '@sim/utils/errors'
+import { sanitizeForLogging } from '@/lib/core/security/redaction'
+
+const MAX_DIAGNOSTIC_FIELD_LENGTH = 100
+
+export interface McpSafeErrorDiagnostics {
+  name: string
+  code: string | undefined
+  errno: string | undefined
+  syscall: string | undefined
+}
+
+/** Returns bounded structural error fields without messages, causes, or session identifiers. */
+export function getMcpSafeErrorDiagnostics(error: unknown): McpSafeErrorDiagnostics {
+  const described = describeError(error)
+  const sanitizeOptional = (value: string | undefined) =>
+    value === undefined ? undefined : sanitizeForLogging(value, MAX_DIAGNOSTIC_FIELD_LENGTH)
+
+  return {
+    name: sanitizeForLogging(described.name, MAX_DIAGNOSTIC_FIELD_LENGTH),
+    code: sanitizeOptional(described.code),
+    errno: sanitizeOptional(described.errno),
+    syscall: sanitizeOptional(described.syscall),
+  }
+}
diff --git a/apps/sim/lib/mcp/oauth/probe.test.ts b/apps/sim/lib/mcp/oauth/probe.test.ts
index d691f1178c7..ff5d96525a7 100644
--- a/apps/sim/lib/mcp/oauth/probe.test.ts
+++ b/apps/sim/lib/mcp/oauth/probe.test.ts
@@ -15,10 +15,8 @@ const { mockCreatePinnedFetch, mockCreateSsrfGuardedMcpFetch, mockPinnedFetch, m
     }
   })
 
-vi.mock('@/lib/core/security/input-validation.server', () => ({
-  createPinnedFetch: mockCreatePinnedFetch,
-}))
 vi.mock('@/lib/mcp/pinned-fetch', () => ({
+  createPinnedMcpFetch: mockCreatePinnedFetch,
   createSsrfGuardedMcpFetch: mockCreateSsrfGuardedMcpFetch,
 }))
 
diff --git a/apps/sim/lib/mcp/oauth/probe.ts b/apps/sim/lib/mcp/oauth/probe.ts
index 4343f27870a..431480ae0f6 100644
--- a/apps/sim/lib/mcp/oauth/probe.ts
+++ b/apps/sim/lib/mcp/oauth/probe.ts
@@ -1,9 +1,8 @@
 import { extractWWWAuthenticateParams } from '@modelcontextprotocol/sdk/client/auth.js'
 import type { FetchLike } from '@modelcontextprotocol/sdk/shared/transport.js'
 import { createLogger } from '@sim/logger'
-import { createPinnedFetch } from '@/lib/core/security/input-validation.server'
 import { isLoopbackHostname } from '@/lib/core/utils/urls'
-import { createSsrfGuardedMcpFetch } from '@/lib/mcp/pinned-fetch'
+import { createPinnedMcpFetch, createSsrfGuardedMcpFetch } from '@/lib/mcp/pinned-fetch'
 import type { McpAuthType } from '@/lib/mcp/types'
 
 const logger = createLogger('McpOauthProbe')
@@ -34,7 +33,7 @@ export async function detectMcpAuthType(
   }
 
   const probeFetch: FetchLike = resolvedIP
-    ? createPinnedFetch(resolvedIP)
+    ? createPinnedMcpFetch(resolvedIP)
     : createSsrfGuardedMcpFetch()
 
   const controller = new AbortController()
diff --git a/apps/sim/lib/mcp/orchestration/server-lifecycle.test.ts b/apps/sim/lib/mcp/orchestration/server-lifecycle.test.ts
new file mode 100644
index 00000000000..1bfee2875a7
--- /dev/null
+++ b/apps/sim/lib/mcp/orchestration/server-lifecycle.test.ts
@@ -0,0 +1,98 @@
+/**
+ * @vitest-environment node
+ */
+import {
+  auditMock,
+  dbChainMock,
+  dbChainMockFns,
+  drizzleOrmMock,
+  encryptionMock,
+  loggerMock,
+  posthogServerMock,
+  resetDbChainMock,
+  schemaMock,
+} from '@sim/testing'
+import { beforeEach, describe, expect, it, vi } from 'vitest'
+
+const { mockClearCache, mockOauthCredsChanged } = vi.hoisted(() => ({
+  mockClearCache: vi.fn(),
+  mockOauthCredsChanged: vi.fn(),
+}))
+
+vi.mock('@sim/audit', () => auditMock)
+vi.mock('@sim/db', () => ({
+  ...dbChainMock,
+  mcpServers: schemaMock.mcpServers,
+}))
+vi.mock('@sim/db/schema', () => ({
+  mcpServerOauth: schemaMock.mcpServerOauth,
+}))
+vi.mock('@sim/logger', () => loggerMock)
+vi.mock('@sim/utils/id', () => ({ generateId: vi.fn() }))
+vi.mock('drizzle-orm', () => drizzleOrmMock)
+vi.mock('@/lib/core/security/encryption', () => encryptionMock)
+vi.mock('@/lib/mcp/domain-check', () => ({
+  McpDnsResolutionError: class extends Error {},
+  McpDomainNotAllowedError: class extends Error {},
+  McpSsrfError: class extends Error {},
+  validateMcpDomain: vi.fn(),
+  validateMcpServerSsrf: vi.fn(),
+}))
+vi.mock('@/lib/mcp/oauth', () => ({
+  detectMcpAuthType: vi.fn(),
+  oauthCredsChanged: mockOauthCredsChanged,
+  revokeMcpOauthTokens: vi.fn(),
+}))
+vi.mock('@/lib/mcp/service', () => ({
+  mcpService: { clearCache: mockClearCache },
+}))
+vi.mock('@/lib/mcp/utils', () => ({ generateMcpServerId: vi.fn() }))
+vi.mock('@/lib/posthog/server', () => posthogServerMock)
+
+import { performUpdateMcpServer } from '@/lib/mcp/orchestration/server-lifecycle'
+
+describe('MCP server lifecycle orchestration', () => {
+  beforeEach(() => {
+    vi.clearAllMocks()
+    resetDbChainMock()
+    mockOauthCredsChanged.mockResolvedValue(false)
+  })
+
+  it('clears the workspace cache when an OAuth client ID implicitly changes the auth type', async () => {
+    dbChainMockFns.limit.mockResolvedValueOnce([
+      {
+        url: 'https://example.com/mcp',
+        authType: 'headers',
+        oauthClientId: 'client-1',
+        oauthClientSecret: null,
+      },
+    ])
+    dbChainMockFns.returning.mockResolvedValueOnce([
+      {
+        id: 'server-1',
+        workspaceId: 'workspace-1',
+        name: 'Example',
+        transport: 'streamable-http',
+        url: 'https://example.com/mcp',
+        authType: 'oauth',
+      },
+    ])
+
+    const result = await performUpdateMcpServer({
+      workspaceId: 'workspace-1',
+      userId: 'user-1',
+      serverId: 'server-1',
+      oauthClientId: 'client-1',
+      oauthClientIdProvided: true,
+    })
+
+    expect(result.success).toBe(true)
+    expect(dbChainMockFns.set).toHaveBeenCalledWith(expect.objectContaining({ authType: 'oauth' }))
+    // Flipping to OAuth must reset the server to disconnected — it hasn't
+    // completed an auth flow, so it can't remain 'connected'.
+    expect(dbChainMockFns.set).toHaveBeenCalledWith(
+      expect.objectContaining({ connectionStatus: 'disconnected', lastConnected: null })
+    )
+    expect(mockClearCache).toHaveBeenCalledWith('workspace-1')
+  })
+})
diff --git a/apps/sim/lib/mcp/orchestration/server-lifecycle.ts b/apps/sim/lib/mcp/orchestration/server-lifecycle.ts
index d8d2d73115a..56a5c96c0f2 100644
--- a/apps/sim/lib/mcp/orchestration/server-lifecycle.ts
+++ b/apps/sim/lib/mcp/orchestration/server-lifecycle.ts
@@ -351,7 +351,11 @@ export async function performUpdateMcpServer(
     })
     const shouldClearOauth = urlChanged || credsChanged
     const resolvedAuthType = (updateData.authType ?? currentServer.authType) as McpAuthType
-    if (shouldClearOauth && resolvedAuthType === 'oauth') {
+    const authTypeChanged = resolvedAuthType !== currentServer.authType
+    // Switching a server to OAuth (via creds/URL change or a plain authType flip)
+    // must reset it to disconnected: an OAuth server has not completed its auth
+    // flow, so it can't legitimately remain 'connected' (matches the create path).
+    if ((shouldClearOauth || authTypeChanged) && resolvedAuthType === 'oauth') {
       updateData.connectionStatus = 'disconnected'
       updateData.lastConnected = null
     }
@@ -384,6 +388,8 @@ export async function performUpdateMcpServer(
     const shouldClearCache =
       urlChanged ||
       credsChanged ||
+      params.transport !== undefined ||
+      authTypeChanged ||
       params.enabled !== undefined ||
       params.headers !== undefined ||
       params.timeout !== undefined ||
diff --git a/apps/sim/lib/mcp/pinned-fetch.test.ts b/apps/sim/lib/mcp/pinned-fetch.test.ts
index 64354ee708b..3dc7701d6a7 100644
--- a/apps/sim/lib/mcp/pinned-fetch.test.ts
+++ b/apps/sim/lib/mcp/pinned-fetch.test.ts
@@ -31,7 +31,7 @@ describe('createSsrfGuardedMcpFetch', () => {
     await fetchLike('https://attacker.example/revoke', { method: 'POST' })
 
     expect(mockValidateMcpServerSsrf).toHaveBeenCalledWith('https://attacker.example/revoke')
-    expect(mockCreatePinnedFetch).toHaveBeenCalledWith('203.0.113.10')
+    expect(mockCreatePinnedFetch).toHaveBeenCalledWith('203.0.113.10', { allowH2: true })
     expect(sentinelFetch).toHaveBeenCalledWith('https://attacker.example/revoke', {
       method: 'POST',
     })
@@ -54,7 +54,7 @@ describe('createSsrfGuardedMcpFetch', () => {
     await fetchLike(new URL('https://attacker.example/discover'))
 
     expect(mockValidateMcpServerSsrf).toHaveBeenCalledWith('https://attacker.example/discover')
-    expect(mockCreatePinnedFetch).toHaveBeenCalledWith('203.0.113.10')
+    expect(mockCreatePinnedFetch).toHaveBeenCalledWith('203.0.113.10', { allowH2: true })
   })
 
   it('falls back to global fetch when validation returns no IP', async () => {
diff --git a/apps/sim/lib/mcp/pinned-fetch.ts b/apps/sim/lib/mcp/pinned-fetch.ts
index 3184a0da7a9..4188d348cac 100644
--- a/apps/sim/lib/mcp/pinned-fetch.ts
+++ b/apps/sim/lib/mcp/pinned-fetch.ts
@@ -2,6 +2,18 @@ import type { FetchLike } from '@modelcontextprotocol/sdk/shared/transport.js'
 import { createPinnedFetch } from '@/lib/core/security/input-validation.server'
 import { validateMcpServerSsrf } from '@/lib/mcp/domain-check'
 
+/**
+ * Pinned fetch for all MCP traffic. MCP servers are commonly deployed behind
+ * HTTP/2 fronts (CDNs, cloud LBs), and undici's Agent is h1.1-only unless opted
+ * into h2 via ALPN — so every MCP connection enables it. This is the single
+ * source of the "MCP implies h2" decision; the base `createPinnedFetch` keeps
+ * its h1.1 default for non-MCP consumers. Pinning is unaffected: the pinned
+ * lookup forces the socket to `resolvedIP` regardless of negotiated protocol.
+ */
+export function createPinnedMcpFetch(resolvedIP: string): typeof fetch {
+  return createPinnedFetch(resolvedIP, { allowH2: true })
+}
+
 /**
  * Builds a `FetchLike` that validates every outbound request URL against the
  * MCP SSRF policy before issuing it, then pins the connection to the resolved
@@ -25,7 +37,7 @@ export function createSsrfGuardedMcpFetch(): FetchLike {
   return (async (url, init) => {
     const target = typeof url === 'string' ? url : url.href
     const resolvedIP = await validateMcpServerSsrf(target)
-    const pinnedFetch: FetchLike = resolvedIP ? createPinnedFetch(resolvedIP) : globalThis.fetch
+    const pinnedFetch: FetchLike = resolvedIP ? createPinnedMcpFetch(resolvedIP) : globalThis.fetch
     return pinnedFetch(url, init)
   }) satisfies FetchLike
 }