feat(example): sandbox-acp-agent — the live composition; RFCs to implemented

The three-entry cordis.yml (dsh-sandbox-local + dsh-bash-sandbox at a
read-only default + dsh-approval) served over ACP: the first live approval
composition. Recorded snapshot scenarios pin the wire end to end —
config-options advertisement, the mode-switching arc as the suite pinned
header (both switches, the prompt-section delta, one changed-by-the-user
notice per knob, a confined write landing under the switched mode), and
both escalation branches over scripted permissionAnswers (a grant runs
confined under workspace-write; a rejection executes nothing and pins the
fail-closed text). The with-key escalation e2e drives a real model +
real runner + the real bridge answerer, world-verified; ci.yml snapshot
lane and e2e.yml install bubblewrap so the confined replays actually
execute.

Both RFCs move to implemented/ (Decision/Consequences form, deferred
phases tracked in their own sections), with every cross-reference flipped.

packages/ui/acp/README.md

@@ -40,7 +40,7 @@ The bridge multiplexes N sessions over one connection. Live sessions are held in
 
 ## Session config options
 
-The bridge advertises one independent `select` per composable knob in the `session/new`/`session/load` responses — `sandbox-mode` (`read-only`/`workspace-write`/`danger-full-access`, category `mode`) iff the mounted executor confines (`ctx.get('bash')?.sandboxMode` defined), `approval-policy` (`ask`/`never`) iff the approval seam is composed — with each session's `currentValue` folded from its OWN log (`effectiveSandboxMode`/`effectiveApprovalPolicy` ?? the composition default), so `session/load` reports a resumed session's overrides with no catch-up machinery. `session/set_config_option` validates the value against the same closed vocabulary, routes to the domain's write path (`setSandboxMode`/`setApprovalPolicy` — ONE log-only event on that session's log), and returns the complete refreshed state per the spec. Anchoring honors turn-enclosure: a switch while a turn is open appends immediately (openness read from the LOG — `agent.status` stays `running` between queued turns); an idle switch is held on the session record and anchored at the next turn's `agent/prompt-submit` (inside the turn, before anything assembles, last write per knob — an idle flip-flop anchors as one event), because appending from inside a `session/event` listener would reorder events for later-registered peers. Until anchored the switch lives in bridge memory only: responses overlay it truthfully, and a crash before the next turn reverts it — `session/load` then reports the fold's truth. Design: [the sandbox RFC § Per-session mode switching](../../../docs/rfc/proposed/feature/2026-07-06-sandbox.md); protocol matrix: [acp-feature-support.md](acp-feature-support.md) § 6.
+The bridge advertises one independent `select` per composable knob in the `session/new`/`session/load` responses — `sandbox-mode` (`read-only`/`workspace-write`/`danger-full-access`, category `mode`) iff the mounted executor confines (`ctx.get('bash')?.sandboxMode` defined), `approval-policy` (`ask`/`never`) iff the approval seam is composed — with each session's `currentValue` folded from its OWN log (`effectiveSandboxMode`/`effectiveApprovalPolicy` ?? the composition default), so `session/load` reports a resumed session's overrides with no catch-up machinery. `session/set_config_option` validates the value against the same closed vocabulary, routes to the domain's write path (`setSandboxMode`/`setApprovalPolicy` — ONE log-only event on that session's log), and returns the complete refreshed state per the spec. Anchoring honors turn-enclosure: a switch while a turn is open appends immediately (openness read from the LOG — `agent.status` stays `running` between queued turns); an idle switch is held on the session record and anchored at the next turn's `agent/prompt-submit` (inside the turn, before anything assembles, last write per knob — an idle flip-flop anchors as one event), because appending from inside a `session/event` listener would reorder events for later-registered peers. Until anchored the switch lives in bridge memory only: responses overlay it truthfully, and a crash before the next turn reverts it — `session/load` then reports the fold's truth. Design: [the sandbox RFC § Per-session mode switching](../../../docs/rfc/implemented/feature/2026-07-06-sandbox.md); protocol matrix: [acp-feature-support.md](acp-feature-support.md) § 6.
 
 Background-task isolation rides on `dsh-tool-bash`: bash task ids are global and predictable, so each task carries an opaque owner token — the owning agent's `session.header.id` — stored on the task inside the executor (`dsh-bash`'s `ownerOf(id)` seam). `bash_output`/`bash_kill` reject a task whose token differs from the caller's session token, so one session's agent can't read or kill another's task. Ownership is by session TOKEN, not `Agent` object identity — a different `Agent` object on the same session may access the task — and because the token lives on the executor's task it survives a `tool-bash` HMR reload.