Codex VS Code extension intermittently aborts Responses streaming (Bad Request, response.failed) even for simple prompts #15840

What version of the IDE extension are you using?

26.324.21329

What subscription do you have?

Azure Provider

Which IDE are you using?

VS Code

What platform is your computer?

Edition Windows 11 Pro Version 22H2 Installed on ‎4/‎23/‎2024 OS build 22621.4317 Serial number 5CG408345R Experience Windows Feature Experience Pack 1000.22700.1041.0

What issue are you seeing?

When using the Codex VS Code extension with the Responses API, requests intermittently fail with “Bad Request” and streaming errors such as:

stream disconnected before completion: response.failed event received

This can happen even for very simple prompts like “hi”, especially on the first message of a new chat.
The same Responses API request (same model, same key, same prompt) works reliably in Postman, which suggests the issue is specific to the Codex extension’s request / streaming handling rather than the backend API.

What steps can reproduce the bug?

1. Open a new chat in Codex.
2. Send a simple prompt:
   hi
3. Codex UI immediately shows “Bad Request”.
4. No response text is streamed.
5. Provider logs show the request marked as stream completion failed.
6. Sending the same prompt again (hi) sometimes succeeds, sometimes fails again.
7. During longer conversations, similar failures can also appear mid‑chat with:
   stream disconnected before completion: response.failed event received

What is the expected behavior?

• Simple prompts (e.g. “hi”) should never fail
• First message in a new chat should stream reliably
• Extension should not abort valid Responses streams
• Errors in optional/internal features should not cause request failure

Additional information

Observed Extension Logs (First Request Failure)

When the first request fails, the VS Code extension logs consistently show the following error:

Error fetching
errorMessage="local-environments is not supported in the extension"
errorName=Error
...
url=vscode://codex/local-environments

This error appears before the response fails.

Note: Warnings such as
Received broadcast but no handler is configured
can be seen both in successful and failed runs, so they may be incidental rather than the direct cause.

Provider / Backend Observations

From Azure / APIM logs:

• Failed requests are marked with:
  • isStreamCompletion = Failed
  • completion_tokens = 0
• No partial completion is recorded.
• The request itself is accepted (no request validation error).

Control Test (Important)

✅ Postman (Same Request)

• Same Responses API
• Same model
• Same API key
• Same prompt (hi)

Result:

• ✅ Always succeeds
• ✅ Response returned normally
• ✅ No streaming failure

❌ Codex VS Code Extension

Result:

• ❌ Intermittent “Bad Request”
• ❌ response.failed
• ❌ No completion tokens
• ❌ Unreliable streaming behavior