Grok driver sends invalid modelId to Grok's ACP — `session/set_model` fails with `unknown model id`

[NixBit404]

Description

When a user selects the Grok provider in T3 and sends a message, the session start fails with Error: Invalid params at decodeJsonError. The actual error from Grok's ACP is unknown model id.

Steps to reproduce

1. Install Grok Build CLI: curl -fsSL https://x.ai/cli/install.sh | bash
2. Add Grok to T3's ~/.t3/userdata/settings.json:

   {
     "providerInstances": {
       "grok": {
         "driver": "grok",
         "enabled": true,
         "config": {
           "enabled": true,
           "binaryPath": "grok",
           "customModels": []
         }
       }
     }
   }

3. Open T3 chat, set provider to Grok, send a message

Expected behavior

Grok responds with chat output.

Actual behavior

T3 shows Error: Invalid params at decodeJsonError (file:///.../apps/server/dist/bin.mjs:90812:59).

Root cause

T3's MODEL_SLUG_ALIASES_BY_PROVIDER map (line 988 of apps/server/dist/bin.mjs) has no entry for [GROK_DRIVER_KIND]. The driver falls back to the hardcoded "grok-build" slug, but Grok's ACP only accepts grok-4.6 and grok-4.5.

Verified via direct ACP probe against grok agent stdio:

modelId sent	Grok response
"grok-build"	❌ error: unknown model id
"grok-4.6"	✅ Success
"grok-4.5"	✅ Success
"grok-4", "grok-3", "grok-2"	❌ unknown model id
"grok-build-plan"	❌ unknown model id (this is the agentType in metadata, not a modelId)

Suggested fix

Add an alias entry to MODEL_SLUG_ALIASES_BY_PROVIDER:

[GROK_DRIVER_KIND]: {
    "grok-build": "grok-4.6"  // or "grok-4.5" — both are valid
}

Workaround (for users)

Add customModels: ["grok-4.6"] to the Grok provider config in settings.json. Then pick "grok-4.6" in the SPA model picker. The default "Grok Build" option still fails.

Environment

• T3 macOS app v0.0.33
• Grok Build CLI v1.0.5
• macOS 26.6.2
• Server URL: http://127.0.0.1:3773