fix(tasks): fail loud when the abstract seam is mounted directly

Review finding (Codex round 1): abstract erases at runtime and
@deepseek-ai/dsh-tasks used to be the mountable registry, so a stale
composition row would register a ctx.tasks with no method implementations
and fail far from the misconfiguration. The seam constructor now rejects
direct mounts with a load-time pointer at dsh-tasks-local; the seam suite
pins the fence, the Agent Note cost paragraph records the actual behavior,
and the stale tool-pty README requirement line names the implementation
package.

.agents/notes/implemented/architecture/2026-07-26-task-registry-seam.i18n.yaml

@@ -2,5 +2,5 @@
 # side as of the last confirmed-consistent state. Both languages carry equal authority;
 # after editing either side, bring the other along and re-record with:
 #   pnpm run verify-translation-pairing --write
-2026-07-26-task-registry-seam.md: b785eb75a632503def10fad583f6a68477cffef6
-2026-07-26-task-registry-seam.zh.md: bfb733a5e1060c9bfe2acc6c4769aa47443d0c9e
+2026-07-26-task-registry-seam.md: d550b5b081a7980cceddd3c1eb65c3a9a175906f
+2026-07-26-task-registry-seam.zh.md: 1088465b908fd905900aa11479a48632fff3fe6f

.agents/notes/implemented/architecture/2026-07-26-task-registry-seam.md

@@ -32,4 +32,4 @@ The seam keeps the in-process contract semantics unchanged: `TaskStart.run()` st
 
 Bought: the task registry now matches the repository-wide seam shape; a durable, remote, or instrumented registry is a sibling package implementing eight abstract methods, and no producer, control surface, or `TaskKindMap` extender changes when one lands. The seam README states the contract; the implementation README owns the lifecycle bookkeeping facts. The registry behavior suite (owner cleanup, settlement, waits, teardown) lives with `dsh-tasks-local`; the seam keeps a stub-subclass test pinning registration under `ctx.tasks` and single-service duplication behavior, plus the probe-based invariant suite.
 
-Cost: one more package (manifest, tsconfig, README, invariant companion), and compositions must name the implementation package — a boot that loads only `@deepseek-ai/dsh-tasks` gets a pending `ctx.tasks` and producers fail with the standard missing-service behavior rather than a bespoke message. The misconfiguration diagnostics naming `dsh-tasks-local` accept staleness if a different backend becomes the recommended default.
+Cost: one more package (manifest, tsconfig, README, invariant companion), and compositions must name the implementation package. `abstract` erases at runtime and this package name used to be the mountable registry, so the seam constructor fails loudly when mounted directly — a stale composition row gets "load an implementation such as @deepseek-ai/dsh-tasks-local" at load time instead of a half-registered `ctx.tasks` failing far from the misconfiguration. The misconfiguration diagnostics naming `dsh-tasks-local` accept staleness if a different backend becomes the recommended default.

.agents/notes/implemented/architecture/2026-07-26-task-registry-seam.zh.md

@@ -32,4 +32,4 @@ Status: implemented
 
 换来的是：任务注册表如今与全仓库通行的 seam 形态一致；持久化、远程或带插桩的注册表将是一个实现八个抽象方法的兄弟包，这样的注册表落地时，任何生产方、控制接口或 `TaskKindMap` 扩展方都无需改动。seam 包的 README 陈述契约；生命周期簿记方面的事实归实现包的 README 所有。注册表行为测试套件（所有者清理、结算、等待、拆除）随 `dsh-tasks-local` 存放；seam 包保留一个桩子类（stub subclass）测试，固定 `ctx.tasks` 下的注册行为与单一服务的重复注册行为，外加基于探针的不变式测试套件。
 
-代价是：多出一个包，即多一份 manifest（元数据清单）、tsconfig、README 与不变式配套插件；同时各组合必须点名实现包。若某次启动只加载 `@deepseek-ai/dsh-tasks`，`ctx.tasks` 将保持挂起，生产方会按标准的服务缺失行为失败，而不会收到一条专门定制的消息。若日后另一个后端成为推荐的默认选择，点名 `dsh-tasks-local` 的配置错误诊断信息将随之陈旧；这一点已被接受。
+代价是：多出一个包，即多一份 manifest（元数据清单）、tsconfig、README 与不变式配套插件；同时各组合必须点名实现包。`abstract` 在运行时会被擦除，而这个包名过去正是可挂载的具体注册表，因此 seam 的构造函数在被直接挂载时会响亮失败——一条过期的组合配置行会在加载时得到「load an implementation such as @deepseek-ai/dsh-tasks-local」，而不是一个方法残缺的 `ctx.tasks` 在远离错误配置处才失败。若日后另一个后端成为推荐的默认选择，点名 `dsh-tasks-local` 的配置错误诊断信息将随之陈旧；这一点已被接受。

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` and its model-facing control surface.
+- Background mode requires both `@deepseek-ai/dsh-tasks-local` and the model-facing control surface from `@deepseek-ai/dsh-tool-tasks`.

packages/tasks/tasks/src/index.ts

@@ -49,6 +49,13 @@ declare module 'cordis' {
  */
 export abstract class TaskService extends Service {
   constructor(ctx: Context) {
+    // `abstract` erases at runtime, and this package name used to be the
+    // mountable concrete registry — a stale composition row would otherwise
+    // register a ctx.tasks with no method implementations and fail far from
+    // the misconfiguration. Fail loud at load instead.
+    if (new.target === TaskService) {
+      throw new Error('@deepseek-ai/dsh-tasks is the abstract task registry seam; load an implementation such as @deepseek-ai/dsh-tasks-local instead')
+    }
     super(ctx, 'tasks')
   }
 

packages/tasks/tasks/tests/service.spec.ts

@@ -79,4 +79,10 @@ describe('TaskService seam', () => {
     class SecondTaskService extends StubTaskService {}
     await expect(ctx.plugin(SecondTaskService)).rejects.toThrow(/service "tasks" has been registered/)
   })
+
+  it('mounting the abstract seam directly fails loudly at load (stale-composition fence)', async () => {
+    const ctx = new Context()
+    await expect(ctx.plugin(TaskService as unknown as typeof StubTaskService))
+      .rejects.toThrow(/abstract task registry seam; load an implementation such as @deepseek-ai\/dsh-tasks-local/)
+  })
 })