fix(mcp): pinned fetch dispatches through global fetch so Response passes instanceof checks

[waleedlatif1]

Summary

• Fixes the "Invalid OAuth error response: SyntaxError: JSON Parse error: Unexpected identifier "object". Raw body: [object Response]" toast shown when authorizing an MCP server whose OAuth error response body isn't a clean spec-compliant JSON object
• Root cause: createPinnedFetch (used for DNS-pinned SSRF-guarded MCP OAuth requests) called a separately-imported undici package's fetch, returning a Response from that module's own copy of the Response class — a distinct constructor reference from Node's global Response, even though Node's global fetch is itself undici-backed
• The MCP SDK's OAuth error parser does input instanceof Response ? await input.text() : input to decide whether to read the response body. Against the separately-imported undici Response, this check fails, so the raw Response object itself gets treated as the body text — stringifying to the literal "[object Response]" in the error message, which then also fails a JSON.parse attempt
• Fix: dispatch through the global fetch instead (passing the same undici Agent as its dispatcher option — Node's fetch forwards this to undici at runtime), so the returned Response is the same class reference every consumer's instanceof Response check expects
• Verified directly with a standalone repro script: instanceof Response is false via the old undici-imported fetch and true via the global fetch with a dispatcher — confirmed the exact bug and the fix

Type of Change

• Bug fix

Testing

• Standalone repro script against real undici/global fetch confirmed both the bug and the fix
• Updated pinned-fetch.server.test.ts to mock the global fetch instead of undici's now-unused fetch export (the old mock target was silently unused, so those assertions were hitting real network calls)
• All existing tests touching createPinnedFetch pass (21/21), plus provider tests that consume it (25/25)
• bun run check:api-validation passes (this change removes 3 double-casts, adds 0)

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 12, 2026 4:34am

[cursor]

PR Summary

Low Risk
Small change in the SSRF-pinned fetch path with the same Agent/dispatcher semantics; tests were updated to match and reduce accidental real-network calls.

Overview
createPinnedFetch still pins outbound connections with the same undici Agent and DNS lookup, but it now calls global fetch with dispatcher in the init instead of undici's separately imported fetch.

That fixes MCP OAuth (and any SDK that does input instanceof Response) treating error bodies as the literal "[object Response]" when the pinned client returned a Response from a different module copy of the class. IP pinning behavior is unchanged; only which fetch/Response constructor is used.

Tests stub global fetch instead of mocking an unused undici fetch export, so assertions no longer hit the real network.

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[cursor]

Cursor Bugbot has reviewed your changes using default effort and found 1 potential issue.

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[cursor]

Pinned fetch broken under Bun

High Severity

createPinnedFetch now calls the global fetch with an undici Agent as dispatcher. Production starts via Bun (CMD ["bun", "apps/sim/bootstrap.js"]), and Bun’s fetch is known not to honor undici Agent connect options such as custom lookup. The prior undici-imported fetch did apply that pinning. DNS-rebinding SSRF guards for MCP OAuth and Azure provider traffic can therefore fail open while instanceof Response checks pass. Unit tests run under @vitest-environment node, so they do not catch this runtime gap.

 

^{Reviewed by Cursor Bugbot for commit 1ad1ccd. Configure here.}

[greptile-apps]

Greptile Summary

This PR fixes MCP pinned fetch responses by routing through the platform fetch path. The main changes are:

• createPinnedFetch now calls global fetch with the pinned undici dispatcher.
• The separate undici.fetch import and related type casts were removed.
• The pinned fetch tests now stub global fetch instead of the unused undici fetch export.

Confidence Score: 5/5

This looks safe to merge.

• No blocking issues found in the changed code.
• The server package targets Node, where the global fetch path can use the undici dispatcher.
• The updated tests now mock the fetch binding that createPinnedFetch actually calls.

Important Files Changed

Filename	Overview
apps/sim/lib/core/security/input-validation.server.ts	Routes pinned requests through global fetch while preserving the pinned undici dispatcher.
apps/sim/lib/core/security/pinned-fetch.server.test.ts	Updates the test mock to target the global fetch path used by the changed implementation.

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