Merge remote-tracking branch 'origin/master' into worktree/web-background-tasks-display-258f7e

# Conflicts:
#	docs/subsystems/tasks.i18n.yaml
#	docs/subsystems/tasks.md
#	docs/subsystems/tasks.zh.md
#	packages/host/apiproxy/README.i18n.yaml
#	packages/host/apiproxy/README.md
#	packages/host/apiproxy/README.zh.md
#	packages/host/apiproxy/src/api-proxy.ts
#	packages/tasks/tasks-local/src/index.ts
#	packages/tasks/tasks/README.i18n.yaml
#	packages/tasks/tasks/README.md
#	packages/tasks/tasks/README.zh.md
#	packages/tasks/tasks/src/index.ts

packages/host/apiproxy/src/api/events.ts

@@ -145,6 +145,18 @@ export type HostFrame =
    * background rather than diffing.
    */
   | { type: 'host/commands-changed' }
+  /**
+   * One blank session was recomposed onto another agent preset (the logged
+   * `agent-preset/selected` commit point, read off the session stream). The
+   * registry-wide `host/commands-changed` cannot stand in for it: recomposing
+   * re-parents that agent's scope without registering anything, so a
+   * preset already mounted for another session produces no registry change
+   * at all. Clients refetch the catalogs this session's composition decides
+   * (`command.list`, `skill.list`) for this sessionId alone, and fold the
+   * preset id into their session row — the RPC echo reaches only the client
+   * that issued the switch, so the row is where every other one learns it.
+   */
+  | { type: 'host/session-preset-changed'; sessionId: SessionId; agentPreset: string }
   /**
    * One settings namespace's resolved value changed (`settings/updated`
    * passthrough) — an RPC write, an external `settings.yaml` edit, or a