fix(server): alias Grok's product-name model slug to a valid ACP modelId

[Exotic209093]

Summary

Fixes #7791. Selecting the Grok provider and sending a message fails immediately with Error: Invalid params at decodeJsonError — the underlying ACP error is unknown model id. Grok's ACP session/set_model only accepts grok-4.6 and grok-4.5 as modelIds. T3 sends "grok-build" (the Grok Build CLI's own product name, not a model id) as the default, and Grok's ACP rejects it outright.

Verified directly against a live ACP probe (per the issue): "grok-build" → unknown model id; "grok-4.6"/"grok-4.5" → success.

Fix

Added a MODEL_SLUG_ALIASES_BY_PROVIDER entry for the Grok driver — the same mechanism Claude and Codex already use for their own display/legacy slugs (e.g. Claude's opus → claude-opus-5) — so normalizeModelSlug/resolveGrokAcpBaseModelId resolve "grok-build" to "grok-4.6" before it ever reaches the wire. DEFAULT_MODEL_BY_PROVIDER's display slug is untouched, matching how the other providers' aliasing works.

Also updated apps/server/scripts/acp-mock-agent.ts's mock Grok ACP model list, which previously accepted the never-actually-valid "grok-build" — that mock now mirrors the real Grok ACP's behavior ("grok-4.6" valid, "grok-build" not), which is what let this bug slip past the existing test suite.

Test plan

• Added a regression test in packages/shared/src/model.test.ts asserting normalizeModelSlug("grok-build", grok) resolves to "grok-4.6".
• Updated the existing resolveGrokAcpBaseModelId test to assert the default (and explicit "grok-build") now resolve to "grok-4.6" instead of passing through verbatim.
• vp test run packages/shared/src/model.test.ts apps/server/src/provider/acp/GrokAcpSupport.test.ts — passed.
• Full Grok test suite (GrokAdapter.test.ts, GrokProvider.test.ts, GrokTextGeneration.test.ts, AcpRuntimeModel.test.ts) run under Linux (these spawn real subprocesses, which needs a POSIX environment) — 56 passed, 0 failed, after updating the mock agent's model list.
• Confirmed Cursor's tests are unaffected: Cursor uses its own dedicated cursor/list_available_models RPC, not the generic ACP session-model mechanism the mock's model list change touches.
• vp run --filter t3 typecheck — clean.
• vp lint on changed files — clean.

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Note

Low Risk
Small model-id alias plus mock-agent alignment; no auth or data-path changes. Display default remains grok-build.

Overview
Fixes Grok ACP session/set_model failing with unknown model id when the default product slug grok-build is sent on the wire.

Adds a Grok entry in MODEL_SLUG_ALIASES_BY_PROVIDER so normalizeModelSlug / resolveGrokAcpBaseModelId map grok-build → grok-4.6 (the id Grok ACP actually accepts). Display default is unchanged.

The ACP mock agent now lists grok-4.6 instead of grok-build, matching real Grok ACP so this cannot slip past tests again.

^{Reviewed by Cursor Bugbot for commit 8e90ce6. Configure here.}

Note

Alias Grok's grok-build product slug to valid ACP modelId grok-4.6

Adds a grok-build → grok-4.6 entry to MODEL_SLUG_ALIASES_BY_PROVIDER in model.ts because grok-build is a CLI product name, not a valid ACP modelId (ACP only accepts grok-4.6 and grok-4.5). Updates the mock ACP agent in acp-mock-agent.ts and the resolveGrokAcpBaseModelId tests in GrokAcpSupport.test.ts to use grok-4.6 as the default and fallback modelId instead of grok-build. Also adds a normalization test case in model.test.ts.

^{Macroscope summarized 8e90ce6.}

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[macroscopeapp]

Approvability

Verdict: Approved at 8e90ce6

Macroscope's review found this PR approvable — Straightforward bug fix that adds a model slug alias to convert 'grok-build' to a valid Grok ACP model ID ('grok-4.6'). The change follows existing alias patterns, is well-documented, and includes appropriate test coverage.

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