Declarative Copilot fails on devtunnel API call: The request was canceled due to the configured HttpClient.Timeout of 20 seconds elapsing

[andreyselitsky]

Describe the bug
Intermittent DevTunnel Timeout When Debugging Declarative Plugin with API Locally

When starting a debugging session (F5) for the Declarative Copilot with API plugin, initial requests often experience a timeout error:

"The request was canceled due to the configured HttpClient.Timeout of 20 seconds elapsing."

This timeout error generally occurs during the first few attempts, then gradually resolves as the DevTunnel stabilizes. Directly accessing the API via localhost (proxied through DevTunnel) works smoothly, so it seems the issue is specific to DevTunnel initialization delays. This behavior slows down the debugging process, impacting the development experience.

To Reproduce
Steps to reproduce the behavior:

1. Go to Declarative Copilot with API sample (e.g., func repairs).
2. Hit F5 to start Debugging in Chrome.
3. Open your Copilot and request repairs.
4. See error (enable Dev info in chat): "The request was canceled due to the configured HttpClient.Timeout of 20 seconds elapsing."
5. The issue generally resolves after a few retries as DevTunnel performance improves.

Expected behavior
Ideally, DevTunnel should respond promptly from the start, without delays or timeouts.

VS Code Extension Information (please complete the following information):

• OS: macOS Sonoma
• Version: 14.5 (23F79)

CLI Information (please complete the following information):

• TTK v5.10.0

Additional context
There also appears to be occasional caching of the previous DevTunnel URL between reruns, leading to API call failures with a 404 error.

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[lijie-lee]

Hi @andreyselitsky, thanks for your reaching out. I'll try to repoduce this issue and get back.

[lijie-lee]

Hi @andreyselitsky, I've tried to reproduce this issue by the steps you provided. It works well by my side.

Actually, we're upgrading the devtunnel used by TTK. You could have a try when the new release version is available.

Anyway, for now, there are two solutions may help you to walkaround:

1. Use other tunnel alternatives choose your own tunnel solution
2. Setup devtunnel by devtunnel cli by yourself and set the devtunnel session url to "OPENAPI_SERVER_URL" in the env file. (refer to Persistent Dev-Tunnel URLs Configuration for detail)