fix(tasks-local): layer control surfaces and listeners by registering scope

One host registry serves every composition in the process, so its two
service-wide collections answered per-owner questions process-wide. `start()`
asked only whether SOME surface was attached, so an agent whose own composition
loads no `tool-tasks` could start work it has no tool to collect or stop as soon
as any other preset attached one — and the answer changed depending on which
sessions happened to be open. `settle()` walked every registered listener, so a
task settling without a waiter injected one completion notice per mounted
preset into the same owner.

Both collections now sit in `ScopedLayers`, the layered-registry primitive
`tools` and `skills` already use: a registration files into its registering
context's scope, and a read unions the global layer with the owner's scope
chain. A surface or listener registered from an unscoped context lands in the
global layer and serves every owner, which is exactly the host-plane
composition's own controls, so the TUI path is unchanged without a special
case.

This supersedes the consumer-side filter in the previous commit. That filter
produced the right notices but sat in the wrong layer: it left the `start()`
gate process-wide, it could not be enforced against a producer that resolves
the registry directly, and it made a Consumer carry scope knowledge that the
other layered registries keep in the registry. `tool-tasks` is scope-agnostic
again and the `dsh-scope` edge moves to `tasks-local`.

`start()`'s refusal is now owner-relative, so its model-visible text names the
agent rather than the process. The shipped `minimal` preset keeps
`enableRunInBackground: false`, no longer as the safety boundary — the registry
owns that now — but so an agent that could never collect a task is not offered
the parameter at all.

Refs #2141

packages/tasks/tasks/src/index.ts

@@ -44,8 +44,13 @@ declare module 'cordis' {
  * - Settlement is first-wins: one terminal record, one round of contained
  *   listener notification, and released waiters, even against a late
  *   producer outcome.
- * - {@link start} refuses work while no control surface is attached, so a
- *   producer cannot start work that callers cannot collect or stop.
+ * - {@link start} refuses work while no attached control surface serves the
+ *   spec's owner, so a producer cannot start work that owner cannot collect
+ *   or stop. One registry serves every composition in the process, so this
+ *   question — and completion-listener delivery — is owner-relative rather
+ *   than process-wide: registrations made from an unscoped context serve
+ *   every owner, and registrations made under an agent composition's scope
+ *   serve exactly the agents composed under it.
  */
 export abstract class TaskService extends Service {
   constructor(ctx: Context) {
@@ -120,17 +125,19 @@ export abstract class TaskService extends Service {
   abstract wait(id: TaskId, timeoutMs: number, caller?: Agent, signal?: AbortSignal): Promise<TaskSnapshot>
 
   /**
-   * Register an effect-scoped completion listener. Each listener is contained;
-   * returned promises are observed but not awaited. No listener runs after
-   * service disposal.
+   * Register an effect-scoped completion listener. It receives the settlements
+   * of the owners its registering context's scope covers; each listener is
+   * contained; returned promises are observed but not awaited. No listener runs
+   * after service disposal.
    * @param listener - receives each terminal snapshot and its exact owner.
    * @returns disposer that unregisters the listener.
    */
   abstract onTaskDone(listener: TaskDoneListener): () => void
 
   /**
-   * Attach an effect-scoped surface that can read and stop tasks. {@link start}
-   * refuses work while none is attached.
+   * Attach an effect-scoped surface that can read and stop tasks. It serves the
+   * owners its registering context's scope covers, and {@link start} refuses an
+   * owner no attached surface serves.
    * @param name - diagnostic label; duplicate names remain independent.
    * @returns disposer that detaches this surface.
    */