refactor(acp): reduce bridge to automation protocol

packages/ui/user-approval/README.md

@@ -4,11 +4,11 @@ Channel-neutral one-shot approval seam. `ctx.approval.request(req)` returns `all
 
 Each request must belong to an open agent turn. The service appends a paired `approval/asked` and `approval/decided` audit record, while the model sees only the resulting logged tool outcome. An aborted request resolves `cancelled`; an audit append that fails before commit rejects rather than returning an unlogged decision.
 
-Answerers are `approval/request` waterfall listeners. Return an outcome to answer for an owned agent or call `next()` to delegate. Agent-scoped listeners receive only that agent's requests; compose one terminal answerer per deployment because sibling listener order is not a policy priority mechanism. The ACP bridge is the shipped human answerer.
+Answerers are `approval/request` waterfall listeners. Return an outcome to answer for an owned agent or call `next()` to delegate. Agent-scoped listeners receive only that agent's requests; compose one terminal answerer per deployment because sibling listener order is not a policy priority mechanism. The ACP automation bridge supplies one-shot machine decisions for sessions it owns.
 
 `ApprovalPolicy` is `'ask'` or `'never'`. The effective value is the last `approval/policy` event, falling back to config; `setApprovalPolicy()` is the write path. `'never'` rejects before interactive dispatch and is the only policy stated in the prompt. Switches produce at most one coalesced notice, attributed to the user when the override follows the last `request/header` and to operator/config otherwise.
 
-The tools pipeline routes `ask` decisions through this seam and fails closed when it is absent; the sandboxed bash tool also uses it for escalated retries. The ACP bridge is the shipped human answerer for calls it owns. Audit events remain log-only, so the model sees only the asking consumer's result. See the [approval-seam Agent Note](../../../.agents/notes/implemented/feature/2026-07-06-approval-seam.md) and [sandbox Agent Note](../../../.agents/notes/implemented/feature/2026-07-06-sandbox.md).
+The tools pipeline routes `ask` decisions through this seam and fails closed when it is absent; the sandboxed bash tool also uses it for escalated retries. The ACP automation bridge answers calls for its own agents through the client's machine policy. Audit events remain log-only, so the model sees only the asking consumer's result. See the [approval-seam Agent Note](../../../.agents/notes/implemented/feature/2026-07-06-approval-seam.md) and [sandbox Agent Note](../../../.agents/notes/implemented/feature/2026-07-06-sandbox.md).
 
 ## Model Experience
 
@@ -57,5 +57,5 @@ Append-only; newly visible content follows the reusable request prefix and does
 
 - **Requests are valid only inside an open turn** — an idle or between-turn caller throws before auditing; a durable out-of-turn approval workflow is deferred.
 - **Only one-shot grants exist** — the outcome vocabulary has `allowed-once` but no `allow-always`, remembered rule, revocation, or grant store; session policy is only `ask` / `never`.
-- **The request carries no tool arguments** — a UI must correlate `callId` with an already rendered tool call, and a call-less request cannot be presented by the shipped ACP answerer.
+- **The request carries no tool arguments** — an answerer sees the tool name, reason, and optional call id; the ACP machine channel requires a call id and delegates requests without one.
 - **No built-in answerer** — headless or incompletely composed deployments resolve `unavailable` and fail closed; the service itself never prompts a human.