## Summary
- publish optimistic provider-neutral goal snapshots for submitted and
steered goal commands
- advertise and implement `set`, using steering for an active turn and
an ordinary prompt while idle
- suppress stale old-goal runtime updates while replacement/clear is
pending and roll back failed commands
- keep cancellation turn-scoped and orphan-account pending steers so
stale results cannot settle the next prompt
- reject unsupported pause/resume controls without host-side fallbacks
## Validation
- `npm test -- --run` (702 passed, 20 skipped)
- `npm run check`
- `npm run build`
- regression coverage for idle/active set and clear, stale runtime
updates, command failure rollback, cancellation, and stale steer
isolation
## Summary
- advertise a provider-neutral goal extension in
`InitializeResponse._meta.goal`
- map Claude SDK `active_goal` messages to
`session_info_update._meta.goal`
- expose the shared `_session/goal` control method with the truthfully
supported `clear` action
- document the extension as a candidate shape for a future first-class
ACP goal API
## Architecture
A goal is persistent **session state**, not the lifecycle of one
`session/prompt` request. `goal.status === "active"` says that the
objective may drive more work; it does not say that a prompt is
executing now.
This keeps two independent axes:
1. **Goal state** is published asynchronously as session metadata and
may survive multiple prompt turns.
2. **Prompt activity** follows the backend's actual running/quiescent
boundaries. While a turn runs, clients use advertised steering or prompt
queueing. Once the backend is quiescent, an ordinary `session/prompt` is
valid even if the goal remains active.
The metadata is deliberately provider-neutral:
```json
{
"_meta": {
"goal": {
"version": 1,
"controlMethod": "_session/goal",
"actions": ["clear"]
}
}
}
```
State is emitted as `session_info_update._meta.goal`; `null` clears it.
The common snapshot vocabulary supports `objective`, common statuses,
timestamps in Unix milliseconds, budgets/usage, iteration count, and a
continuation reason. Each implementation emits only fields it actually
knows. This shape is intentionally close to a future typed ACP
capability/update so promotion out of `_meta` would not require a
provider-specific migration.
Control actions are capability-negotiated. The shared vocabulary
reserves `set`, `pause`, `resume`, and `clear`, but an agent advertises
only the subset it can implement with correct semantics.
## Claude mapping
The Claude runtime already emits internal `active_goal` messages,
although that message is not currently included in the public
`SDKMessage` union. The adapter handles it before the exhaustive switch:
- `condition` → `objective`
- `iterations` → `iterations`
- `set_at` → `createdAt`
- `last_reason` → `lastReason`
- `value: null` → `goal: null`
Provider bookkeeping such as `tokens_at_start` is intentionally not
exposed. Goal updates do not settle, extend, or otherwise mutate ACP
prompt lifecycle. Claude's existing Stop hook remains authoritative for
whether the backend itself continues working.
Only `clear` is advertised for out-of-band control. It submits `/goal
clear` through the existing session prompt queue, preserving the
adapter's established ordering and turn ownership. Setting a goal
remains available through `/goal <condition>` but is not advertised as a
control action because it starts the long-running Stop-hook workflow.
The companion Codex implementation is agentclientprotocol/codex-acp#371.
## Verification
- `npm run test:run` — 692 passed, 20 skipped
- `npm run build`
- `npm run check`
