fix(grok): surface per-model reasoning effort in the composer

[ahmed-besic]

What Changed

Grok already advertises per-model reasoning effort menus over ACP (models.availableModels[]._meta.reasoningEfforts), but T3 published every Grok model with empty capabilities and never applied a selected effort. The composer therefore had no Reasoning control for Grok, unlike Claude/Codex.

This maps each model's advertised menu into optionDescriptors (reasoningEffort), passes _meta.reasoningEffort through session/set_model on session start and each turn (including mid-thread effort-only changes), and wires the same selection into Grok text generation.

Why

Grok Build supports Low/Medium/High (and other per-model menus for custom models). Without reading _meta and applying effort on session/set_model, T3 always ran at the CLI default and users could not change it from the UI.

Related open work: #5160 takes a spawn-flag approach and blocks mid-thread changes. This PR is narrower: discovery + apply via the existing ACP session/set_model _meta path, which Grok applies in place without restarting the process.

UI Changes

Uses the existing Traits picker — no new UI components. Once Grok ACP discovery succeeds, models with reasoningEfforts show a Reasoning select; models with different menus keep their own options.

• Before: Grok models have no Reasoning control in the composer traits menu.
• After: Grok models that advertise effort menus show Reasoning, and the selected value is applied on the next send (same thread is fine for effort-only changes).

Live-verified against grok agent stdio and the T3 web UI over Tailscale.

Validation

• vp test run src/provider/acp/GrokAcpSupport.test.ts src/provider/Layers/GrokProvider.test.ts — 17 passed
• Live ACP probe: session/set_model with _meta.reasoningEffort applies the override
• Manual web UI check: Reasoning control appears for discovered Grok models and updates per model

Checklist

• This PR is small and focused
• I explained what changed and why
• I included before/after screenshots for any UI changes (happy to add if needed — behavior uses the existing traits control)
• A video is not applicable (no animation/timing change)

Made by Grok Build via the Grok Build harness while working on T3 Code.

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Note

Medium Risk
Touches Grok ACP model selection and session/set_model request shaping, so incorrect _meta handling could misconfigure runtime effort. Scope is limited to the Grok provider path and covered by unit tests.

Overview
Grok models that advertise reasoningEfforts in ACP _meta now expose a Reasoning select in the composer, and the chosen effort is applied on send.

Discovery maps each model's _meta.reasoningEfforts into optionDescriptors instead of empty capabilities. applyGrokAcpModelSelection now accepts selections and calls session/set_model with _meta.reasoningEffort even for effort-only changes (no model switch). The same selection is wired through session start, turns, and Grok text generation.

^{Reviewed by Cursor Bugbot for commit c8d471b. Bugbot is set up for automated code reviews on this repo. Configure here.}

Note

Surface per-model reasoning effort selection in the Grok composer

• Adds buildGrokCapabilitiesFromModelMeta in GrokProvider.ts to parse _meta.reasoningEfforts from model metadata into a select option descriptor, replacing the previous EMPTY_CAPABILITIES fallback.
• Extends applyGrokAcpModelSelection in GrokAcpSupport.ts to accept selections and call setSessionModel when a reasoningEffort selection is present, even if the model ID is unchanged.
• Updates AcpSessionRuntime.setSessionModel to accept and forward an optional options._meta payload so reasoning effort reaches the ACP set_model request.
• Propagates modelSelection.options through GrokAdapter.ts and GrokTextGeneration.ts to ensure selections apply during both session setup and text generation.

^{Macroscope summarized c8d471b.}

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[macroscopeapp]

Approvability

Verdict: Needs human review

This PR introduces new user-facing functionality (per-model reasoning effort selection in the composer), propagating new _meta configuration through multiple provider layers. New features that add user-facing behavior warrant human review.

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[ahmed-besic]

Additional fixes at #5405, #5409, #5412