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.

docs/capability-seams.md

@@ -117,6 +117,7 @@ flowchart LR
   pkg_tool_ralph["tool-ralph"]
   pkg_tasks["tasks"]
   svc_tasks["ctx.tasks<br/>Background task registry"]
+  pkg_tasks_local["tasks-local"]
   pkg_tool_tasks["tool-tasks"]
   pkg_web["web"]
   svc_web["ctx.web<br/>Web access provider registry"]
@@ -192,6 +193,7 @@ flowchart LR
   pkg_subagent_spawn --> svc_subagents
   pkg_system_prompt --> svc_systemPrompt
   pkg_tasks --> svc_tasks
+  pkg_tasks_local --> svc_tasks
   pkg_token_meter --> svc_tokenMeter
   pkg_tool_bash --> svc_bashEnv
   pkg_tools --> svc_tools
@@ -326,7 +328,7 @@ flowchart LR
 | `ctx.fs` | `seam` | [`fs`](../packages/fs/fs) | [`fs-local`](../packages/fs/fs-local), [`fs-sandbox`](../packages/fs/fs-sandbox) | [`tool-fs`](../packages/fs/tool-fs) | [`fs-policy`](../packages/fs/fs-policy) | tool-fs executes read/write/edit through ctx.fs; fs-sandbox fences mutations by the shared sandbox mode; fs-policy contributes observed-state checks through the fs/* event gate. |
 | `ctx.compact` | `seam` | [`compact`](../packages/compact/compact) | [`compact-basic`](../packages/compact/compact-basic) | [`compact-basic`](../packages/compact/compact-basic) | - | The basic backend consumes post-step pressure and request-error recovery events; a model-facing compact tool remains deferred. |
 | `ctx.subagents` | `seam` | [`subagent`](../packages/subagent/subagent) | [`subagent-spawn`](../packages/subagent/subagent-spawn), [`subagent-fork`](../packages/subagent/subagent-fork), [`subagent-acp`](../packages/subagent/subagent-acp) | [`tool-subagent`](../packages/subagent/tool-subagent), [`tool-ralph`](../packages/workflow/tool-ralph) | - | Providers implement transports; tool-subagent exposes configured delegation while tool-ralph requires one fresh structured-output route. |
-| `ctx.tasks` | `core` | [`tasks`](../packages/tasks/tasks) | - | [`tool-bash`](../packages/bash/tool-bash), [`tool-pty`](../packages/pty/tool-pty), [`tool-subagent`](../packages/subagent/tool-subagent), [`tool-tasks`](../packages/tasks/tool-tasks) | - | Producers (background bash, PTY sends, and subagent delegations) register running work; tool-tasks is the model-facing control surface that reads, lists, and kills it. |
+| `ctx.tasks` | `seam` | [`tasks`](../packages/tasks/tasks) | [`tasks-local`](../packages/tasks/tasks-local) | [`tool-bash`](../packages/bash/tool-bash), [`tool-pty`](../packages/pty/tool-pty), [`tool-subagent`](../packages/subagent/tool-subagent), [`tool-tasks`](../packages/tasks/tool-tasks) | - | Producers (background bash, PTY sends, and subagent delegations) register running work; tool-tasks is the model-facing control surface that reads, lists, and kills it; tasks-local is the process-local registry. |
 | `ctx.web` | `seam` | [`web`](../packages/web/web) | [`web-search-exa`](../packages/web/web-search-exa), [`web-search-perplexity`](../packages/web/web-search-perplexity), [`web-search-deepseek`](../packages/web/web-search-deepseek), [`web-fetch-local`](../packages/web/web-fetch-local) | [`tool-web`](../packages/web/tool-web) | - | Search and fetch providers register into one ctx.web seam; tool-web owns the stable model-facing names. |
 | `ctx.spillStore` | `seam` | [`spill`](../packages/spill/spill) | [`spill-local`](../packages/spill/spill-local) | [`spill-policy`](../packages/spill/spill-policy) | - | The backend saves oversized tool text and returns a model-facing locator plus retrieval hint; spill-policy is the tools/post-execute consumer that decides when to spill. |
 | `ctx.httpServer` | `core` | `webserver` | - | `connection`, `modules`, `hmr` | - | Plain node:http carrier: named-route registry, index transform taps, and the static dist fallback; web-transport plugins register their own routes. |