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.

docs/cordis-catalog/services.md

@@ -1988,7 +1988,7 @@ sendMessage(parent: Agent, childId: SessionId, message: ContentBlock[]): SendMes
 
 Types: [Agent](../core-data-structures/core.md) · [ContentBlock](../core-data-structures/core.md) · [ContinuableStart](../core-data-structures/subagent.md) · [ContinuableStartSpec](../core-data-structures/subagent.md) · [SendMessageResult](../core-data-structures/subagent.md) · [SessionId](../core-data-structures/core.md)
 
-Source: [`packages/subagent/subagent-control/src/index.ts:152`](../../packages/subagent/subagent-control/src/index.ts)
+Source: [`packages/subagent/subagent-control/src/index.ts:156`](../../packages/subagent/subagent-control/src/index.ts)
 
 ## `ctx.subagents` — `SubagentService`