fix(mcp): settle the /mcp auth wait when bearer auth writes the response

[yulin0629]

Problem

app.all("/mcp") waits for bearerAuth like this:

await new Promise<void>((resolve, reject) => {
  bearerAuth(req, res, (error?: unknown) => { if (error) reject(error); else resolve(); });
});

The SDK's requireBearerAuth middleware only calls next() on success. On 401/403/400 it writes the response itself and returns without calling next, so the Promise above never settles. Every rejected request leaves the handler continuation, req and res reachable for the lifetime of the process. Clients see a normal 401, so nothing looks wrong; the daemon just grows a little on each bad token, which matters once /mcp is on a public hostname.

Fix

Also resolve when the response finishes or closes, so a request that the middleware rejects releases its handler. Behaviour on success is unchanged (res.headersSent short-circuit still applies).

Verification

• tsc --noEmit clean
• src/server-oauth.test.ts and src/server.test.ts pass (23/23)

Found while running a fork of DevSpace with a static bearer path in front of the same middleware; the bug itself is independent of that change.

Summary by CodeRabbit

• Bug Fixes
  • Improved request handling so authentication processing completes when a response finishes or closes, preventing requests from remaining pending.

[chatgpt-codex-connector]

Codex Review Summary

This comment shows the latest Codex review activity on this pull request.

Review	Status	Commit	Review trigger
📝 Code Review	✅ Completed 2026-09-15T06:59:54.798925Z	7705cb5	PR opened

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No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Repository UI

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Plan: Advanced

Run ID: 03491764-79e6-4d4b-b29e-b782d5fcfcea

📥 Commits

Reviewing files that changed from the base of the PR and between 3ee2b1e and 7705cb5.

📒 Files selected for processing (1)

• src/server.ts

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📝 Walkthrough

Walkthrough

The /mcp route now resolves the bearer-auth wrapper promise when the response emits finish or close, in addition to the bearer-auth callback.

Changes

MCP response lifecycle

Layer / File(s)	Summary
Response event resolution src/server.ts	The /mcp route adds one-time finish and close listeners that resolve the bearer-auth wrapper promise.

Priority: ⬇️ Low

Estimated code review effort: 1 (Trivial) | ~5 minutes

Change: Bug fix · Severity of issue fixed: Low

Suggested reviewers: waishnav

Merge Risk: ⚪ Minimal · up to 0ecfe

The change is narrowly scoped, and reported compilation and server tests pass without an established merge-blocking failure.

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 0.00% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 1 functions across 1 files.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly identifies the MCP authentication fix and describes the response-settlement behavior changed in the pull request.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

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• Create PR with unit tests

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_{A rabbit watched the response flow
finish and close now signal “go”
The auth promise no longer waits
It hops past unfinished states
And lands where completion grows}

_{Comment @coderabbitai help to get the list of available commands.}

[Copilot]

🟡 Changes recommended

The response-close path can continue to the MCP handler before bearer authentication has completed.

Get a fresh assessment by requesting another Copilot review.

Pull request overview

Updates /mcp bearer-auth handling so rejected requests do not leave the authentication wait pending.

Changes:

• Settles the auth wait on response finish or close.
• Preserves successful-auth and headersSent behavior.

File summaries

File	Description
src/server.ts	Adds response lifecycle listeners around bearer authentication; the close path requires a guard before continuation.

Review details

• Files reviewed: 1/1 changed files
• Comments generated: 1
• Review effort level: Lite

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[yulin0629]

Closes #354.

[greptile-apps]

Greptile Summary

The /mcp bearer-authentication wait now completes when authentication middleware ends a request with a 401, 403, or 400 response without calling next(). The surrounding MCP server and OAuth behavior remains covered by passing focused tests.

Confidence Score: 5/5

Safe to merge: the affected bearer-authentication lifecycle completes correctly while preserving denied-request responses.

No actionable findings remain. Runtime coverage exercised invalid-token, insufficient-scope, and malformed-request denial paths, and the focused MCP server and OAuth tests passed.

Files Needing Attention: None.

T-Rex Logs

What T-Rex did

• Exercised the /mcp bearer-auth wait with real terminating 401, 403, and 400 middleware responses.
• Observed that the updated behavior preserved the same denial responses and settled every continuation.
• Ran the before/after runtime scripts and the focused test suite, which completed with 23 passing tests.
• Validated that after lifecycle listeners are present, 401 (invalid_token), 403 (insufficient_scope), and 400 (invalid_request) responses produce continuationSettled: true; without them, the status remains false.
• Cross-checked the before/after artifacts and test outputs to confirm the changes were exercised and results captured in the provided logs.

_{Ran code and verified through T-Rex}

_{Reviews (1): Last reviewed commit: 7705cb5 | Re-trigger Greptile}

[Waishnav]

Thanks for catching the unresolved auth wait — that part is real. I don’t think we should fix it by resolving on finish/close, though.

requireBearerAuth is already Express middleware, so the simpler and safer fix is to compose it directly:

app.all("/mcp", bearerAuth, async (req, res) => {
  // existing MCP route logic
});

That removes the manual Promise entirely. It also avoids the close race where the route can resume before token verification has completed.

I also wasn’t able to reproduce the claimed permanent per-request memory leak: the pending continuation becomes unreachable and the request objects were collectible after GC. So I’d describe the bug as incorrect/unnecessary async control flow rather than a confirmed process-lifetime leak.

Could you rework this PR around native Express middleware composition instead?