fix(rebase): migrate the replayed stack onto current master APIs

The linear replay carried each commit's own lineage, so this checkpoint
restores the master-owned surfaces the conflicted regions clobbered and
migrates branch-owned code to master's post-rebase APIs:

- rebuild subprocess-local spawn.ts on master's tree-exit-observer
  machinery, keeping the branch's win32 childEnv key semantics and the
  Linux zombie-quiescence probe; the zombie test reaps its survivor
  directly since a confirmed-absent verdict is a permanent
  no-more-signals boundary
- migrate pty-local test stubs to the Inbox-model Agent interface,
  Session.create, runnerFailureRules, and the new turn/start payload
- implement the seam's resolveExecutable/spawnTerminal abstracts in the
  new pwsh-local and tool-fs-search test fakes
- restore code-runtime, atomic-write, pwsh-local, and app-boot to
  master's exact content (the net-zero code-runtime churn is pruned
  from this history) and drop rename-detection graft debris
- re-apply the PR's architecture rows and execution-world paragraph,
  re-record bilingual pairings, regenerate catalogs, and reconcile the
  lockfile

packages/fs/tool-fs-search/tests/tools.spec.ts

@@ -148,6 +148,8 @@ class FakeHandle implements SubprocessHandle {
  */
 class FakeSubprocess extends SubprocessService {
   spawns: SubprocessSpawnSpec[] = []
+  override async resolveExecutable(command: string): Promise<string> { return command }
+  override spawnTerminal(): Promise<never> { throw new Error('search tools spawn pipes, never terminals') }
   handles: FakeHandle[] = []
   /** Arms the per-spawn script; a `{ reject }` return scripts a spawn-level failure. */
   handler: (spec: SubprocessSpawnSpec) => ScriptedRun | { reject: Error } = () => runResult('')