feat(grok): add /compact slash command and compaction feedback

[ahmed-besic]

What Changed

Grok Build already has a first-class /compact [context] command to manually compress conversation history. T3 could technically send that text as a prompt (Grok ACP treats /compact as the compact command), but:

1. The command never appeared in the composer / menu for Grok (unlike Claude provider slash commands)
2. When compaction finished, Grok emitted _x.ai/session_notification with auto_compact_completed and T3 ignored it — so the turn looked empty with no success feedback

This PR:

• Advertises /compact on the Grok provider snapshot as a provider slash command (Grok-only; optional note for what to preserve)
• Handles x.ai/session_notification / _x.ai/session_notification for auto_compact_completed
• Emits thread.state.changed { state: "compacted" }, which the existing ingestion path turns into the Context compacted work-log row (same UI as Claude/Codex compaction)

Why

Grok 4.5’s context window is large (500k tokens), but model quality typically degrades well before that — often around the ~200k range in long agent threads. Auto-compact only kicks in near the window limit, so long productive Grok threads in T3 can get “soft-bad” (worse tool use, more drift) without an obvious way to reclaim context mid-session.

Grok Build already ships manual /compact for this reason. T3 should expose the same control so users can compact proactively instead of only when auto-compact finally runs (or when quality has already slipped). Showing Context compacted makes the action trustworthy — without it, sending /compact looks like a no-op.

Wire format (Grok 0.2.118 ACP): there is no working dedicated compact RPC in this version; manual compact is session/prompt with text /compact…, then auto_compact_completed on the session notification channel.

UI Changes

• Before: Grok / menu has no compact entry; sending /compact may run but leaves no visible feedback.
• After: /compact appears under Grok provider commands; successful compact shows the existing Context compacted work-log entry (with token before/after in event detail).

No new UI components — reuses provider slash commands + context-compaction activity.

Validation

• vp test apps/server/src/provider/acp/XAiAcpExtension.test.ts apps/server/src/provider/Layers/GrokProvider.test.ts apps/server/src/provider/Layers/GrokAdapter.test.ts — 38 passed
• Live ACP probe: session/prompt /compact emits _x.ai/session_notification auto_compact_completed
• Manual T3 web (feat/grok-compact-slash): Grok menu shows compact; after send, Context compacted appears in the work log

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)
• 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
Additive Grok ACP extension handling and provider metadata; no auth, billing, or shared ingestion logic changes beyond wiring an existing compacted state event.

Overview
Exposes Grok’s manual /compact flow in T3 and turns Grok’s compaction completion signal into the same Context compacted work-log feedback other providers already get.

The Grok provider snapshot now advertises a compact slash command (optional hint for what to preserve) on every probe path so it shows up in the composer / menu. On the wire, GrokAdapter listens for x.ai/session_notification / _x.ai/session_notification, parses auto_compact_completed via new XAiSessionNotification / extractXAiAutoCompactCompleted helpers, and emits thread.state.changed with state: "compacted" plus token before/after (and optional summary preview)—reusing existing ingestion for the work log. The ACP mock agent simulates /compact prompts by emitting that notification; adapter and extension tests cover the mapping.

^{Reviewed by Cursor Bugbot for commit c3b7351. Bugbot is set up for automated code reviews on this repo. Configure here.}

Note

Add /compact slash command and compaction feedback to Grok provider

• Adds a compact slash command to the Grok provider's snapshot metadata so clients can surface it in the UI.
• Extends GrokAdapter to handle x.ai/session_notification and _x.ai/session_notification ACP events, translating auto_compact_completed notifications into thread.state.changed events with a compacted payload including tokensBefore, tokensAfter, and optional summaryPreview.
• Adds XAiAcpExtension with schema validation and an extractXAiAutoCompactCompleted utility to parse and normalize compaction notification payloads.
• Updates the ACP mock agent to emit a session notification when a prompt starts with /compact, enabling end-to-end integration testing.

^{Macroscope summarized c3b7351.}

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[macroscopeapp]

Approvability

Verdict: Needs human review

This PR introduces a new user-facing feature (the /compact slash command and compaction feedback UI). New features adding user-facing capabilities warrant human review regardless of how well-scoped they are.

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