diag(mcp): per-request phase logging on the streamable-HTTP transport

[waleedlatif1]

Summary

• Adds per-request phase logging to the pinned MCP transport fetch (createPinnedMcpFetch), mirroring the OAuth guarded-fetch instrumentation that isolated the /oauth/start body stall.
• Logs each transport request (host + method), the response headers with TTFB, and failures.
• Why: the logs prove our client's first connect to these servers consistently hangs to the 30s client timeout while a normal client's initialize returns in ~120 ms — but we haven't isolated where it stalls. This logging shows whether the first connect hangs before response headers (connect/request phase) or after (the SDK's stream/body read) — the data needed to root-cause it before touching the single-IP-pin SSRF control.

Type of Change

• Diagnostic (temporary logging; no behavior change)

Testing

Type-check + biome clean. No behavior change — wraps the existing pinned fetch with logging only.

Checklist

• Code follows project style guidelines
• Self-reviewed my changes
• Tests added/updated and passing
• No new warnings introduced
• I confirm that I have read and agree to the terms outlined in the Contributor License Agreement (CLA)

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1 Skipped Deployment

Project	Deployment	Actions	Updated (UTC)
docs	Skipped		Jul 21, 2026 9:49pm

[cursor]

PR Summary

Low Risk
Logging-only wrapper around existing fetch; no timeout, pinning, or response handling changes.

Overview
Adds diagnostic instrumentation around the pinned fetch returned by createPinnedMcpFetch, following the same phase-logging pattern already used on OAuth guarded fetches.

Each transport call now logs request start (host + method), response headers (status + TTFB), or a failure (elapsed ms and error metadata) via a new McpTransportFetch logger. The underlying pinned fetch and close behavior are unchanged—only a wrapper that rethrows errors after logging.

The intent is to tell whether first initialize hangs before response headers (connect/request) or after (SDK stream/body read), without changing SSRF pinning or transport semantics.

^{Reviewed by Cursor Bugbot for commit a12bac5. Configure here.}

[greptile-apps]

Greptile Summary

This PR adds phase logging to the pinned MCP transport fetch. The main changes are:

• Logs each transport request with its host and method.
• Logs response status and time to first byte.
• Logs structured error details before rethrowing failures.

Confidence Score: 5/5

This looks safe to merge.

• The updated failure log captures the error name and nested cause code for expected transport failures.
• The wrapper preserves the original response, rejection, and dispatcher cleanup behavior.
• No blocking issues were found in the changed code.

Important Files Changed

Filename	Overview
apps/sim/lib/mcp/pinned-fetch.ts	Wraps the pinned fetch with request, response-header, timing, and structured failure logs while preserving response and error propagation.

_{Reviews (2): Last reviewed commit: "diag(mcp): include error name/code in tr..." | Re-trigger Greptile}

[waleedlatif1]

@greptile

[waleedlatif1]

@cursor review

[cursor]

✅ Bugbot reviewed your changes and found no new issues!

Comment @cursor review or bugbot run to trigger another review on this PR

^{Reviewed by Cursor Bugbot for commit a12bac5. Configure here.}