fix(ws): handle response stream errors on failed WS upgrade

[pi0]

Summary

• Add res.on("error", onOutgoingError) before res.pipe(socket) in both ws-incoming.ts (ProxyServer) and ws.ts (proxyUpgrade) to catch upstream response stream errors during failed WebSocket upgrades
• Guard against writing to already-destroyed sockets with !socket.destroyed && socket.writable checks
• Separate the settled rejection logic from the writable guard in proxyUpgrade so the promise always rejects on non-upgrade responses

Fixes the crash described in upstream http-party/node-http-proxy#1439: when the target returns a non-upgrade HTTP response (e.g., 502) and the connection resets mid-body, the unhandled error event on the response stream crashes the process.

Test plan

• Added regression test in test/ws.test.ts — proxyUpgrade with upstream that destroys socket mid-response
• Added regression test in test/http-proxy.test.ts — ProxyServer.ws() with same scenario
• Added test/ws-destroyed-socket.test.ts — tests for writing to destroyed sockets before upstream responds
• Full test suite passes (2520 tests, 0 failures)

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ℹ️ Review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro

Run ID: 32c18bcb-1db0-40bb-a544-a5bb12901ca0

📥 Commits

Reviewing files that changed from the base of the PR and between b7075ab and 23cafec.

📒 Files selected for processing (5)

• src/middleware/ws-incoming.ts
• src/ws.ts
• test/http-proxy.test.ts
• test/ws-destroyed-socket.test.ts
• test/ws.test.ts

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch fix/ws-upgrade-socket-error

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 96.12%. Comparing base (b7075ab) to head (23cafec).
⚠️ Report is 2 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #116   +/-   ##
=======================================
  Coverage   96.11%   96.12%           
=======================================
  Files           8        8           
  Lines         644      645    +1     
  Branches      244      243    -1     
=======================================
+ Hits          619      620    +1     
  Misses         24       24           
  Partials        1        1           

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