refactor(subprocess): the dispose ladder moves to its one consumer

SubprocessHandle loses dispose(graces) and SubprocessDisposeGraces: the
stdin-EOF→SIGTERM→SIGKILL sequence is teardown POLICY encoding one
consumer's cooperation shape, not process vocabulary — the seam keeps
kill/terminate/waitForExit, and waitForExit(signal?) is the quiescence
probe a consumer ladder needs. dsh-subagent-acp owns disposeAcpChild()
over those public verbs (tier tests move into its suite; a never-exits
stub pins the fail-loud path); dsh-subprocess-local sheds the ladder,
its deadline import, and the dsh-timeout dependency. Every future
backend now owes four verbs and no teardown policy. New bilingual
ladder-ownership Agent Note records the decision; catalogs regenerated.

packages/subprocess/subprocess-local/src/index.ts

@@ -16,8 +16,8 @@ import type { SpawnInternals } from './spawn.ts'
 /**
  * Local subprocess service: detached process trees, Node-shaped stdio
  * dispositions (raw pipes, inherit, bounded tail-keep collection with spill
- * files), credential-scrubbed environment, tree-scoped signalling with
- * SIGTERM→grace→SIGKILL escalation, and the cooperative dispose ladder.
+ * files), credential-scrubbed environment, and tree-scoped signalling with
+ * SIGTERM→grace→SIGKILL escalation.
  */
 export class LocalSubprocessService extends SubprocessService {
   /** Live handles retained only so disposal can terminate and join them. */