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.

packages/subagent/tool-subagent/package.json

@@ -46,6 +46,7 @@
     "@deepseek-ai/dsh-subagent": "workspace:^",
     "@deepseek-ai/dsh-system-prompt": "workspace:^",
     "@deepseek-ai/dsh-tasks": "workspace:^",
+    "@deepseek-ai/dsh-tasks-local": "workspace:^",
     "@deepseek-ai/dsh-tool-tasks": "workspace:^",
     "@deepseek-ai/dsh-tools": "workspace:^",
     "cordis": "^4.0.0-rc.7"

packages/subagent/tool-subagent/src/index.ts

@@ -323,7 +323,7 @@ export function apply(ctx: Context, config: Config): void {
           }
           const tasks = ctx.get('tasks')
           if (tasks === undefined) {
-            throw new Error('background tasks unavailable: load @deepseek-ai/dsh-tasks and @deepseek-ai/dsh-tool-tasks')
+            throw new Error('background tasks unavailable: load @deepseek-ai/dsh-tasks-local and @deepseek-ai/dsh-tool-tasks')
           }
           // Task preflight finishes before the starter can spawn a child.
           const id = tasks.start({

packages/subagent/tool-subagent/tests/tool-subagent.spec.ts

@@ -8,7 +8,7 @@ import { type Agent } from '@deepseek-ai/dsh-agent'
 import AgentRegistry from '@deepseek-ai/dsh-agent'
 import SubagentService from '@deepseek-ai/dsh-subagent'
 import type { SubagentStartRequest } from '@deepseek-ai/dsh-subagent'
-import TaskService from '@deepseek-ai/dsh-tasks'
+import LocalTaskService from '@deepseek-ai/dsh-tasks-local'
 import * as ToolTasks from '@deepseek-ai/dsh-tool-tasks'
 import * as mock from './scripted-provider.ts'
 import * as tool from '../src/index.ts'
@@ -641,7 +641,7 @@ describe('dsh-tool-subagent background mode', () => {
   async function backgroundSetup(toolConfig: tool.Config, mockConfig: Partial<mock.Config> = {}) {
     const ctx = await setup(toolConfig, mockConfig)
     await ctx.plugin(AgentRegistry)
-    await ctx.plugin(TaskService)
+    await ctx.plugin(LocalTaskService)
     await ctx.plugin(ToolTasks, {})
     return ctx
   }
@@ -680,7 +680,7 @@ describe('dsh-tool-subagent background mode', () => {
     const ctx = await setup({ provider: 'mock' })
     const result = await callSubagent(ctx, { description: 'd', prompt: 'p', run_in_background: true })
     expect(result.isError).toBe(true)
-    expect(text(result)).toContain('background tasks unavailable: load @deepseek-ai/dsh-tasks')
+    expect(text(result)).toContain('background tasks unavailable: load @deepseek-ai/dsh-tasks-local')
   })
 
   it('skips background startup when the tool signal is already aborted', async () => {
@@ -868,7 +868,7 @@ describe('background preflight failure (no orphaned child, by construction)', ()
     // With no control surface, task preflight fails before the provider can spawn.
     const ctx = await setup({ provider: 'mock' })
     await ctx.plugin(AgentRegistry)
-    await ctx.plugin(TaskService)
+    await ctx.plugin(LocalTaskService)
     const scopeFiber = ctx.plugin(() => {})
     const id = SessionId('sess-p')
     const parent = {