fix: address codex review round 2

- Wire the control service and send_message tool into every shipped
  composition with a resumable provider and background enabled
  (headless-agent, tui-agent, and the SDK helper's subagent feature
  base resources); jsonrpc-agent disables background and is unchanged.
- Resolve the send_message availability check in the CALLER's tool
  scope so a restriction that removes the follow-up tool from one
  agent also blocks that agent's continuable start.
- Control-service disposal now cancels live activations and awaits
  producer settlement instead of stranding them: TaskService keeps
  producer Tasks across a reload, so the disposing service aborts each
  activation-owned controller, resolves its terminal gate (the
  effect-scoped onTaskDone listener is already gone), and awaits done.
  A new test kills a mid-start activation through HMR disposal.

pnpm-lock.yaml

@@ -384,6 +384,9 @@ importers:
       '@deepseek-ai/dsh-subagent':
         specifier: workspace:^
         version: link:../../packages/subagent/subagent
+      '@deepseek-ai/dsh-subagent-control':
+        specifier: workspace:^
+        version: link:../../packages/subagent/subagent-control
       '@deepseek-ai/dsh-subagent-fork':
         specifier: workspace:^
         version: link:../../packages/subagent/subagent-fork
@@ -441,6 +444,9 @@ importers:
       '@deepseek-ai/dsh-tool-subagent':
         specifier: workspace:^
         version: link:../../packages/subagent/tool-subagent
+      '@deepseek-ai/dsh-tool-subagent-control':
+        specifier: workspace:^
+        version: link:../../packages/subagent/tool-subagent-control
       '@deepseek-ai/dsh-tool-tasks':
         specifier: workspace:^
         version: link:../../packages/tasks/tool-tasks