chore(mcp): remove temporary HTTP diagnostics (#5795)

Reverts the temporary McpHttpDiag instrumentation from #5782 now that it has
served its purpose: it confirmed the OAuth fetch fix (#5789) makes the flow reach
and complete the token exchange, and it isolated a separate, pre-existing
transport-initialize stall (Gauge returns 200 + session then no body for 30s,
reproducible only from the staging egress — not from a fresh IP, and not with the
SDK/h2/pinning/tee in isolation).

- Delete apps/sim/lib/mcp/http-diagnostics.ts.
- Restore client.ts transport fetch to `...(pinned ? { fetch: pinned.fetch } : {})`.
- Restore oauth/auth.ts fetchFn to the plain SSRF-guarded default.
- Drop the diagnostic-specific test assertion.

Removes the body tee() from the transport hot path so the streamable-HTTP
connection runs clean while the transport stall is investigated separately.

Author: waleedlatif1

apps/sim/lib/mcp/client.test.ts

@@ -381,9 +381,6 @@ describe('McpClient notification handler', () => {
       {
         authProvider,
         requestInit: { headers: { 'X-Sim-Via': 'workflow' } },
-        // The transport fetch is always wrapped for diagnostics (a no-op passthrough
-        // under test); it defaults to globalThis.fetch when the server isn't pinned.
-        fetch: expect.any(Function),
       }
     )
   })

apps/sim/lib/mcp/client.ts

@@ -12,7 +12,6 @@ import { createLogger } from '@sim/logger'
 import { getErrorMessage } from '@sim/utils/errors'
 import { getMaxExecutionTimeout } from '@/lib/core/execution-limits'
 import { getMcpSafeErrorDiagnostics } from '@/lib/mcp/error-diagnostics'
-import { withMcpHttpDiagnostics } from '@/lib/mcp/http-diagnostics'
 import { McpOauthRedirectRequired } from '@/lib/mcp/oauth'
 import { createPinnedMcpFetch } from '@/lib/mcp/pinned-fetch'
 import {
@@ -102,9 +101,7 @@ export class McpClient {
     this.transport = new StreamableHTTPClientTransport(new URL(this.config.url), {
       authProvider: useOauth ? this.authProvider : undefined,
       requestInit: { headers: this.config.headers },
-      // Wrap whether pinned or not (SDK's default is globalThis.fetch, so passing it is
-      // behavior-neutral) so the diagnostic also covers unpinned/allowlisted servers.
-      fetch: withMcpHttpDiagnostics(pinned?.fetch ?? globalThis.fetch, 'transport'),
+      ...(pinned ? { fetch: pinned.fetch } : {}),
     })
 
     this.client = new Client(

apps/sim/lib/mcp/http-diagnostics.ts

@@ -1,5 +1,4 @@
 import { auth, type OAuthClientProvider } from '@modelcontextprotocol/sdk/client/auth.js'
-import { withMcpHttpDiagnostics } from '@/lib/mcp/http-diagnostics'
 import { createSsrfGuardedMcpFetch } from '@/lib/mcp/pinned-fetch'
 
 type McpAuthOptions = Parameters<typeof auth>[1]
@@ -18,6 +17,6 @@ export function mcpAuthGuarded(
 ): ReturnType<typeof auth> {
   return auth(provider, {
     ...options,
-    fetchFn: withMcpHttpDiagnostics(options.fetchFn ?? createSsrfGuardedMcpFetch(), 'oauth'),
+    fetchFn: options.fetchFn ?? createSsrfGuardedMcpFetch(),
   })
 }