[Bug]: Mistral Vibe provider added through ACP fails to Sign In

Before submitting

I searched existing issues and did not find a duplicate.
I included enough detail to reproduce or investigate the problem.

Area

apps/server

Steps to reproduce

Add Mistral Vibe ACP provider
Get to the Sign In step.
Press Sign-In button

Expected behavior

Probably browser pop up to log in? Not sure what should happen. But it should just work™️

Actual behavior

After pressing Sign-In, it just shows "Starting sign-in…", and nothing ever happens. Provider is not usable at all.

Impact

Blocks work completely

Version or commit

fed41fa (T3-Code-0.0.46-nightly.20261003.2623-x86_64.AppImage)

Environment

ArchLinux, AppImage, KDE Plasma

Logs or stack traces

{
  "type": "effect-span",
  "name": "RpcClient.authenticate",
  "traceId": "5aad801bc48e845f73fde51b80109949",
  "spanId": "f3930e92419a4289",
  "parentSpanId": "22a8598b3cc2c258",
  "sampled": true,
  "kind": "internal",
  "startTimeUnixNano": "1791019393562301642",
  "endTimeUnixNano": "1791019437157042074",
  "durationMs": 43594.740432,
  "attributes": {
    
  },
  "events": [
    
  ],
  "links": [
    
  ],
  "exit": {
    "_tag": "Failure",
    "cause": "Error: Browser sign-in status could not be retrieved.\n    at ProviderAuthService.start (file:///tmp/.mount_T3-Cod5XHvcM/resources/app.asar/apps/server/dist/binCli-CCV0Rnbz.mjs:248078:108)\n    at ProviderAuthService.start (definition) (file:///tmp/.mount_T3-Cod5XHvcM/resources/app.asar/apps/server/dist/binCli-CCV0Rnbz.mjs:100193:10)\n    at ws.rpc.provider.auth.start (file:///tmp/.mount_T3-Cod5XHvcM/resources/app.asar/apps/server/dist/binCli-CCV0Rnbz.mjs:237142:104)"
  }
}

Screenshots, recordings, or supporting files

No response

Workaround

No response

@gamelaster

Note

Grok responding on behalf of Julius.

Triage

Thanks for the report and the trace, @gamelaster!

The trace shows sign-in getting through to Mistral Vibe and failing on Vibe's side. RpcClient.authenticate, which is the ACP authenticate call, ran for about 44 seconds and then failed with Browser sign-in status could not be retrieved. That message comes from Vibe's browser sign-in status check (POLL_FAILED in Vibe's vibe/setup/auth/http_browser_sign_in_gateway.py), and it happens after the sign-in has already been created. It isn't the "could not open a browser" error or the "sign-in timed out" error. The T3 auth code involved hasn't changed on current main.

Why the button stays on "Starting sign-in…"

T3 doesn't tell Vibe that it can handle browser sign-in itself (Vibe's browser-auth-delegated capability), so Vibe only offers its blocking browser-auth method. T3 calls authenticate and waits while Vibe opens a browser on its own and polls console.mistral.ai. No sign-in URL ever comes back to the settings screen. When the poll fails, the row should switch to "The ACP agent could not complete sign-in.", but the actual Vibe reason only shows up in the trace.

Workarounds for now

Set MISTRAL_API_KEY in this provider's environment variables. T3 passes that environment through to vibe-acp.
Or sign in through the Vibe CLI so the key is saved under ~/.vibe, then refresh the provider. If CLI sign-in fails the same way, the problem is Vibe's status check rather than the T3 button.

What would help next (please redact any secrets)

The output of vibe --version and vibe-acp --version
Whether a browser window opened at all
The lines in ~/.vibe/logs/vibe.logs around "Browser sign-in", which should include the HTTP error this message hides
Whether CLI sign-in works on the same machine

A maintainer will decide on the fix direction.

Answers:

vibe 2.25.8, vibe-acp 2.25.8
no browser window opened at all
~/.vibe/logs/vibe.logs is empty
yes, it works good. I am already logged in

Manually setting MISTRAL_API_KEY is indeed working workaround.

Since this is a bug in Mistral itself, I think this link might be helpful to others who run into this problem as well. There's also another workaround described in the issue on the mistral issues-project page.

mistralai/mistral-vibe#941

Yea i found that mistral vibe has a lot of stuff that deviates from the spec...

fix(provider-acp-registry): advertise browser-auth-delegated for Mist…

Note

🤖 Claude Opus 5.5 responding on behalf of Theo

Thanks for the report. This fault is outside T3 Code, so we cannot fix it here. Please report it to the project that owns that tool. If you find a fault in T3 Code itself, please open a new issue with steps to reproduce it.

login over t3code works now with vibe 3.0.3

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[Bug]: Mistral Vibe provider added through ACP fails to Sign In #15118

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[Bug]: Mistral Vibe provider added through ACP fails to Sign In #15118

Description

Before submitting

Area

Steps to reproduce

Expected behavior

Actual behavior

Impact

Version or commit

Environment

Logs or stack traces

Screenshots, recordings, or supporting files

Workaround

Activity

juliusmarminge commented on Oct 3, 2026

Triage

gamelaster commented on Oct 3, 2026

alimuratgymn commented on Oct 8, 2026

juliusmarminge commented on Oct 8, 2026

t3dotgg commented on Oct 21, 2026

alimuratgymn commented on Oct 30, 2026

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