The adapter retains a Runtime Host subscription after the first prompt. Cancellation and close use the subscription's current root identity, including a Turn started by another Host client while the ACP attachment was idle. Close releases the subscription and connection-local ownership; it does not delete or archive the durable Session.
ACP v1 message chunks are append-only. Matching replay and prefix extensions are supported. If a completed or recovered message changes text or thinking that was already streamed (including clearing it), the adapter rejects the prompt with JSON-RPC error -32603 and error.data.code: unsupported_stream_revision and requests a stop of that prompt's exact live root. It never represents a replacement by inventing a new message ID or reports end_turn for that failed projection. The client may still display the already delivered partial text; ACP v1 cannot retract it. The Session remains owned and can accept another prompt or be closed.
Local resource links must identify regular files. Filesystem admission rejects non-regular files, including POSIX FIFOs, before reading their content. After live attachment succeeds, the adapter uploads each linked file through the Host's existing Session Artifact protocol and uses its canonical attachment reference for Turn admission. Cancellation or close during an upload aborts staged content and prevents that prompt from starting a Turn.
When a dispatched start loses its response, the adapter retries admission queries with bounded deadlines instead of replaying the start. Only a matching Turn or authoritative not_found settles admission. Exhausted reads report outcome_unknown; explicit cancellation still returns cancelled, with the failed Stop diagnostic retained. Shutdown can cancel an initial attachment waiting for transcript hydration or reconnection without waiting for the Host to become available.
Interaction mapping remains deferred to the next ACP capability increment. If a pending permission, question, form, sandbox-boundary, or client-capability request belongs to an active ACP prompt, the adapter rejects it with JSON-RPC -32603 and error.data.code: unsupported_interaction (error.data.kind identifies the request). It retires the attachment and uses the existing failure path to request Stop for that prompt‘s exact Host Turn. It does not answer or approve the interaction; Host remains responsible for settlement. A failed Stop retains the Host diagnostic. The durable Session remains owned and can be prompted again or closed. Interactions belonging to another client’s Turn keep the idle attachment available so ACP cancellation and close can still stop the observed root.