refactor(tasks): split the task registry into seam and local implementation

The tasks/ family now matches the capability-seam shape: @deepseek-ai/dsh-tasks
keeps the abstract TaskService (ctx.tasks contract, vocabulary types, snapshot
invariant companion) and the new @deepseek-ai/dsh-tasks-local carries the
process-local registry (LocalTaskService: in-memory store, settlement,
owner-cleanup effects, teardown, TASK_WAIT_TIMEOUT). Compositions and test
harnesses now load dsh-tasks-local; producers, TaskKindMap merges, and
dsh-tool-tasks keep importing the seam only.

Producer misconfiguration diagnostics name dsh-tasks-local because loading the
implementation is the fix. The registry behavior suite moves to tasks-local;
the seam keeps a stub-subclass registration test and the probe-based invariant
suite.

.agents/notes/implemented/architecture/2026-06-20-generic-long-running-tool-runtime.md

@@ -19,7 +19,7 @@ The `tasks/` package group owns background-task semantics:
 
 Long-running tools are producers. `dsh-tool-bash` adapts a `BashProcess` into incremental output and process cancellation; `dsh-tool-subagent` adapts a child run into final output and child disposal. The execution seams remain independent of sessions and the task registry.
 
-`TaskService` is a concrete, process-local service. TODO(task-service-backend): separate its public contract from the implementation when a second backend defines the required lifecycle; a systemd-backed runtime is one plausible driver, but this PR does not speculate about its durability, reconnect, ownership, or observation semantics.
+`TaskService` is the abstract seam in `@deepseek-ai/dsh-tasks`; the process-local registry is `LocalTaskService` in `@deepseek-ai/dsh-tasks-local` (the [task-registry seam Agent Note](2026-07-26-task-registry-seam.md) records that split).
 
 ## Runtime contract
 
@@ -103,7 +103,7 @@ Separate bash and subagent output/stop tools duplicate ids, isolation, cleanup,
 
 ### An immediate abstract task-runtime backend
 
-The current `TaskStart.run()` contract passes in-process callbacks and exact `Agent` objects. A durable backend changes identity, restart, ownership, and observation semantics, so extracting an interface before a second implementation exists would freeze the wrong boundary.
+The current `TaskStart.run()` contract passes in-process callbacks and exact `Agent` objects. A durable backend changes identity, restart, ownership, and observation semantics, so at introduction time the registry stayed one concrete service rather than freezing the wrong boundary. The [task-registry seam Agent Note](2026-07-26-task-registry-seam.md) later separated the contract from the process-local implementation without changing these in-process semantics.
 
 ### Consumer-owned authorization or cleanup events