[benbrandt]

Summary

• Return initial availableCommands in ACP v2 session/new, session/resume (omitted/null/full replay), and session/fork responses instead of sending an initial commands notification.
• Reuse the existing command builder and a shared v2 input converter. Preserve AIR command-action and skill-path metadata, and leave v1 behavior unchanged.
• List skills once per setup using that session's cwd and additional directories, including forks. Seed change detection from the response; subsequent command changes still use replacement notifications.
• Keep initial discovery best-effort: setup succeeds without availableCommands if discovery fails. Preserve newer command snapshots when overlapping reads finish out of order, and reject stale setup when the session closes or is replaced during discovery.
• Document the v2 client contract and update lifecycle snapshots/fixtures.

System prompts and standard subagent support remain separate work packages; the current AIR subagent contract is untouched.

Validation

• npm run typecheck — passed, including examples.
• npm test — 1,821 passed, 36 skipped.
• npm run build — passed.
• npm run test:integration — 5 passed against real Codex app-server with a local mock model. V2 coverage verifies initial commands on new, all resume modes, and fork, with no redundant initial command notifications.
• Focused wire tests cover AIR/non-AIR metadata, fork-specific skill discovery, unchanged and changed command lists, discovery failure/recovery, overlapping reads, and closure during discovery.
• Live-model smoke test via npm run codex-test — passed.
• git diff --check — passed.

The full live-model E2E suite was not run.

Specification checked at agent-client-protocol@4034a8cbc99bc48fd4579f70a3407b07907e0eb6, notably docs/protocol/v2/slash-commands.mdx and the unstable v2 setup response schemas.