feat(server): ACP sessionUpdate parity for Grok clients

[EnzoTironi]

Recovery: New PR after head fork EnzoTironi/t3code was deleted (auto-closed #5422). Same branch tip. #5424/#5425 stay closed (absorbed into Grok native).

Original: #5422

What Changed

Shared ACP session/update parsing so live Grok (and other ACP clients) map into typed runtime events instead of being dropped:

• agent_thought_chunk → reasoning stream (streamKind: reasoning_text)
• usage_update → thread.token-usage.updated via makeAcpTokenUsageEvent
• available_commands_update, config_option_update, session_info_update, user_message_chunk
• UnknownSessionUpdate fallback for forward compatibility
• session/set_model optional _meta pass-through (needed by Grok effort)
• acp-mock-agent toggles for Grok-shaped session behavior

Fixes #5417

Why

Live grok agent stdio already emits these update kinds. Without shared parser coverage, each provider adapter drops them or casts ad hoc. Putting the model in AcpRuntimeModel / AcpCoreRuntimeEvents keeps orchestration pure.

UI Changes

None (server/shared ACP only).

Checklist

• This PR is small and focused (~+379 / 6 files)
• I explained what changed and why
• UI screenshots N/A
• Video N/A

Test plan

• AcpRuntimeModel / AcpCoreRuntimeEvents unit tests
• Live Grok 0.2.x initialize/session on macOS

Model: grok-4.5 (Grok Build)

---

Note

Medium Risk
Touches core ACP event parsing and Cursor runtime event emission for token usage and streaming; behavior changes for live ACP sessions but scope is server-only with unit test coverage.

Overview
Extends shared ACP session/update handling so Grok-shaped agents no longer drop common update kinds. parseSessionUpdateEvent now emits typed events for reasoning chunks (agent_thought_chunk → ContentDelta with streamKind: reasoning_text), token usage, slash commands, live config options, session title/metadata, and user echo chunks, with an UnknownSessionUpdate fallback for forward compatibility.

Adds makeAcpTokenUsageEvent and optional streamKind on makeAcpContentDeltaEvent so adapters can publish thread.token-usage.updated and distinguish assistant vs reasoning text. CursorAdapter wires UsageUpdated through that helper and forwards streamKind / rawPayload on content deltas.

AcpSessionRuntime now returns authenticateResult from startup, passes optional _meta on session/set_model, and refreshes configOptionsRef when config_option_update arrives so config validation stays current. The acp-mock-agent gains Grok-like toggles (/compact, session info, usage on prompt result, init commands, non-numeric JSON-RPC id).

^{Reviewed by Cursor Bugbot for commit 6fbe75f. Bugbot is set up for automated code reviews on this repo. Configure here.}

Note

Add ACP sessionUpdate parity for Grok clients with token usage, thought chunks, and session info events

• Extends AcpRuntimeModel.ts to parse additional ACP session update types: agent_thought_chunk, user_message_chunk, usage_update, available_commands_update, config_option_update, and session_info_update, plus an UnknownSessionUpdate fallback.
• Adds makeAcpTokenUsageEvent factory in AcpCoreRuntimeEvents.ts to produce thread.token-usage.updated runtime events; makeAcpContentDeltaEvent now accepts an optional streamKind to distinguish assistant_text from reasoning_text.
• Wires UsageUpdated and ContentDelta (with streamKind/rawPayload) through the CursorAdapter so token usage and stream kind reach the event stream.
• Updates AcpSessionRuntime.ts to return authenticateResult from start(), keep configOptionsRef in sync on live updates, and forward optional _meta in setSessionModel.
• Extends the mock agent script acp-mock-agent.ts to simulate /compact commands, session_info_update notifications, skills-reload responses, and token usage fields in prompt responses.

^{Macroscope summarized 6fbe75f.}

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[macroscopeapp]

Approvability

Verdict: Needs human review

This PR introduces a new feature adding multiple new session update event types (usage, commands, config, session info, thought chunks) with parsing logic and runtime integration across several layers. The scope and new capability introduced warrant human review.

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[cursor]

Cursor Bugbot has reviewed your changes using high effort and found 1 potential issue.

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