fix(tasks): producer diagnostics name the seam, not one implementation

Review feedback (tianyicui, PR #657 inline): the missing-service message
should mention dsh-tasks, which defines ctx.tasks, rather than promoting a
specific backend. The seam's own surfaces (README, the direct-mount fence)
keep pointing at implementations, so the pointer chain still lands on
dsh-tasks-local without the producer strings going stale when another
backend becomes the recommended default. Agent Note updated accordingly
(en+zh, re-recorded).

packages/bash/tool-bash/README.md

@@ -139,7 +139,7 @@ Append-only; newly visible content follows the reusable request prefix and does
 
 #### What the model sees
 
-Validation and policy failures are normalized as `Error: <message>`. This package's stable messages are `invalid command: expected a non-empty string`, `invalid description: expected a non-empty string`, `invalid timeoutMs: expected a positive number, got <value>`, `invalid escalation: sandbox_permissions requires a justification`, `invalid escalation: justification is only valid together with sandbox_permissions`, `invalid justification: expected a non-empty sentence`, `background execution is disabled for this bash tool`, `background tasks unavailable: load @deepseek-ai/dsh-tasks-local and @deepseek-ai/dsh-tool-tasks`, `sandbox_permissions is not available in this composition (no sandboxing executor to escalate)`, `sandbox escalation to "<mode>" is not strictly wider than this call's current "<mode>" mode`, the approval-availability/rejection/cancellation variants, and `command aborted`.
+Validation and policy failures are normalized as `Error: <message>`. This package's stable messages are `invalid command: expected a non-empty string`, `invalid description: expected a non-empty string`, `invalid timeoutMs: expected a positive number, got <value>`, `invalid escalation: sandbox_permissions requires a justification`, `invalid escalation: justification is only valid together with sandbox_permissions`, `invalid justification: expected a non-empty sentence`, `background execution is disabled for this bash tool`, `background tasks unavailable: load @deepseek-ai/dsh-tasks and @deepseek-ai/dsh-tool-tasks`, `sandbox_permissions is not available in this composition (no sandboxing executor to escalate)`, `sandbox escalation to "<mode>" is not strictly wider than this call's current "<mode>" mode`, the approval-availability/rejection/cancellation variants, and `command aborted`.
 
 #### Token effect
 

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

@@ -533,7 +533,7 @@ 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-local and @deepseek-ai/dsh-tool-tasks')
+          throw new Error('background tasks unavailable: load @deepseek-ai/dsh-tasks and @deepseek-ai/dsh-tool-tasks')
         }
         // The caller owns cancellation until ctx.tasks commits detached ownership.
         if (exec.signal.aborted) {

packages/bash/tool-bash/tests/tools.spec.ts

@@ -475,7 +475,7 @@ describe('background execution through the task runtime', () => {
     const ctx = await setup() // no LocalTaskService / ToolTasks
     const result = await call(ctx, 'bash', { command: 'sleep 60', description: 'test command', run_in_background: true })
     expect(result.isError).toBe(true)
-    expect(text(result)).toContain('background tasks unavailable: load @deepseek-ai/dsh-tasks-local and @deepseek-ai/dsh-tool-tasks')
+    expect(text(result)).toContain('background tasks unavailable: load @deepseek-ai/dsh-tasks and @deepseek-ai/dsh-tool-tasks')
   })
 
   it('a pre-aborted call is skipped before the process starts', async () => {

packages/pty/tool-pty/README.md

@@ -66,4 +66,4 @@ Append-only; new results follow the reusable request prefix.
 ## Known Limitations and Deferred Work
 
 - No named key sequence, TUI, BEL, resize, auto-start, or cross-agent sharing schema is exposed.
-- Background mode requires both `@deepseek-ai/dsh-tasks-local` and the model-facing control surface from `@deepseek-ai/dsh-tool-tasks`.
+- Background mode requires both `@deepseek-ai/dsh-tasks` and its model-facing control surface.

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

@@ -250,7 +250,7 @@ export function apply(ctx: Context, config: Config = {}): void {
       if (args.run_in_background === true) {
         if (!enableRunInBackground) throw new Error('background terminal sends are disabled by tool-pty configuration')
         const tasks = ctx.get('tasks')
-        if (tasks === undefined) throw new Error('background terminal sends require @deepseek-ai/dsh-tasks-local and @deepseek-ai/dsh-tool-tasks')
+        if (tasks === undefined) throw new Error('background terminal sends require @deepseek-ai/dsh-tasks and @deepseek-ai/dsh-tool-tasks')
         let cancelRequested = false
         const taskId = tasks.start({
           kind: 'pty-send',

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-local and @deepseek-ai/dsh-tool-tasks')
+            throw new Error('background tasks unavailable: load @deepseek-ai/dsh-tasks 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

@@ -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-local')
+    expect(text(result)).toContain('background tasks unavailable: load @deepseek-ai/dsh-tasks')
   })
 
   it('skips background startup when the tool signal is already aborted', async () => {