[Bug]: Grok (ACP) ignores selected reasoning effort: reasoningEffort is never mapped to Grok's reasoning_effort option #15251

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

1. Enable the Grok provider (Grok CLI 1.0.46, grok agent stdio, ACP protocolVersion 1).
2. Start a Grok thread (or a delegated Grok task) with model grok-4.6 and reasoning effort Low.
3. Send any prompt.
4. Check Grok's own session journal (~/.grok/sessions/<cwd>/<session>/chat_history.jsonl).

Expected behavior

Grok runs the turn at the selected effort (low).

Actual behavior

Grok runs at its default xhigh. The run's modelSelection is correct ({"id":"reasoningEffort","value":"low"}), but the value never reaches the ACP session.

Root cause, as far as I can see in the server bundle:

1. On session/new, Grok advertises effort as a config option with a different id:
   {"id":"reasoning_effort","category":"thought_level","type":"select","currentValue":"xhigh","options":["xhigh","high","medium","low"]}.
   session/set_config_option {configId:"reasoning_effort", value:"low"} works (the response shows currentValue:"low").
2. The generic ACP configureSession applies modelSelection.options only by exact id. reasoningEffort ≠ reasoning_effort, so it logs "ACP session does not expose requested configuration option(s)" and sets nothing.
3. The Grok flavor's applyModelSelection calls applyGrokAcpModelSelection without requestedReasoningEffort / currentReasoningEffort. Only the text-generation path passes them. The provider event log shows session/set_model with two fields (sessionId, modelId) and no _meta.reasoningEffort.

Impact

• Major degradation or frequent failure

Every Grok turn and delegated Grok task ignores the chosen effort. This costs latency and quota, and orchestration that relies on cheap low-effort Grok workers gets xhigh runs.

Version or commit

0.0.46-nightly.20261003.2623

Environment

macOS (Apple Silicon), T3 Code Nightly desktop app, Grok CLI 1.0.46 (stable).

Logs or stack traces

provider event log (delegated Grok task): method "session/set_model", status "started", request {"valueType":"object","fieldCount":2}
modelSelection of the same run: {"instanceId":"grok","model":"grok-4.6","options":[{"id":"reasoningEffort","value":"low"}]}

Workaround

A local patch that resolves an option by category when the exact id is missing (reasoningEffort → the select option with category thought_level), then calls setConfigOption with the found option's own id. Another possible fix: pass requestedReasoningEffort and currentReasoningEffort from the Grok flavor's applyModelSelection, as the text-generation path already does.