fix(grok): surface context window usage in the composer

[ahmed-besic]

What Changed

Grok already reports session context fill and model window size over ACP, but T3 never turned that into the composer context meter that Codex already shows.

This maps:

• ACP sessionUpdate: "usage_update" (used / size) when present
• Grok's current path: session/update _meta.totalTokens while streaming, plus availableModels[]._meta.totalContextTokens for the window size
• Prompt response _meta.totalTokens / _meta.usage as a reliable end-of-turn snapshot

Those become thread.token-usage.updated → context-window.updated, which the existing ContextWindowMeter already renders. No new UI components.

Cursor gets a no-op case for the shared TokenUsageUpdated parse event so the ACP union stays exhaustive; wiring makeAcpTokenUsageUpdatedEvent there is the same one-liner once verified against a real Cursor ACP install.

Why

Codex threads show a context ring (used / max / %). Grok threads showed nothing, even though grok agent stdio already streams fill (_meta.totalTokens) and advertises per-model windows (totalContextTokens, e.g. 500k / 200k / 128k). Without the adapter mapping, the meter never got a snapshot.

Live probe against grok 0.2.118: Grok does not emit standard ACP usage_update yet, so this PR supports that path for when it lands and uses the _meta sources that work today.

UI Changes

Uses the existing context window meter in the composer.

• Before: Grok threads have no context size / fill indicator.
• After: After the first usage-bearing update (stream meta or prompt result), Grok shows the same ring + used/max tooltip as Codex.

Validation

• vp test run src/provider/acp/AcpRuntimeModel.test.ts src/provider/acp/AcpCoreRuntimeEvents.test.ts src/provider/acp/GrokAcpSupport.test.ts — 23 passed
• vp test run src/provider/Layers/GrokAdapter.test.ts — 20 passed
• Live ACP probe (grok agent stdio): confirmed _meta.totalTokens on session/update, totalContextTokens on models, and prompt _meta.usage; no usage_update from this CLI version yet
• Meter math from live numbers: e.g. 19,267 / 500,000 ≈ 3.9% used

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 after a UI smoke against a Grok thread)
• 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

Low Risk
Provider-adapter and event-mapping changes with broad test coverage; no auth or persistence changes, and Cursor behavior is unchanged (no-op).

Overview
Wires Grok ACP session data into the existing composer context meter by emitting thread.token-usage.updated runtime events (same path Codex already uses).

ACP parsing now materializes TokenUsageUpdated from standard usage_update (used / size) and, when that is absent, from session/update _meta.totalTokens (Grok’s current streaming signal). A shared makeAcpTokenUsageUpdatedEvent builds the canonical runtime payload.

Grok adapter caches per-model windows from availableModels[]._meta.totalContextTokens, enriches snapshots with maxTokens and compactsAutomatically, and forwards usage on stream updates (including between turns when activeTurnId is cleared) plus an end-of-turn snapshot from prompt _meta. Cursor adds an exhaustive no-op TokenUsageUpdated branch until the same path is verified live.

Web labels the grok provider in context-window display helpers.

^{Reviewed by Cursor Bugbot for commit e7f3b2e. Bugbot is set up for automated code reviews on this repo. Configure here.}

Note

Surface context window usage in the Grok provider composer

• Adds thread.token-usage.updated event emission to the Grok adapter, fired both during streaming (via ACP session/update notifications) and at the end of each prompt turn from prompt response metadata.
• Introduces helpers in GrokAcpSupport.ts to extract context window sizes from model metadata, build a modelId→window map, and enrich usage snapshots with maxTokens and compactsAutomatically.
• Extends AcpRuntimeModel.ts to parse usage_update ACP notifications and _meta fields into TokenUsageUpdated events.
• Adds makeAcpTokenUsageUpdatedEvent factory in AcpCoreRuntimeEvents.ts for consistent construction of token-usage runtime events across ACP providers.
• Maps the grok provider string to 'Grok' in contextWindow.ts for correct UI display.

^{Macroscope summarized e7f3b2e.}

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[macroscopeapp]

Approvability

Verdict: Needs human review

This PR introduces new user-facing functionality (context window usage meter in the composer) with ~650 lines of new code, new event types, and new state management. Despite the 'fix' label, this is a feature addition that warrants human review.

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