docs: document the independent subagent daemon (start/continue/interrupt)

claude-plugins/plugins/base/skills/claude-subagents/SKILL.md

@@ -3,11 +3,11 @@ name: claude-subagents
 description: Spin up a short-lived headless `claude` sub-instance to grind through a well-scoped, mechanical batch (bulk relabeling, a repetitive find/replace, a mechanical migration) instead of burning your own context on it inline. Use this when a task has a clear, describable recipe and is either big enough to eat your context or long enough that you'd rather not babysit it. Not for judgement-heavy work, anything needing operator back-and-forth, or a task whose blast radius you can't bound up front.
 ---
 
-# Ephemeral Sub-Agents via the Claude CLI
+# Ephemeral Sub-Agents
 
-`claude` is on `PATH` in your container, and a sub-instance you spawn
-inherits the same filesystem and credentials you have. This is a
-first-class tool for offloading a bounded, mechanical batch - not a hack.
+A sub-instance you spawn inherits the same filesystem and credentials you
+have. This is a first-class tool for offloading a bounded, mechanical
+batch - not a hack.
 
 ## When to use it
 
@@ -18,7 +18,36 @@ first-class tool for offloading a bounded, mechanical batch - not a hack.
 - **No:** judgement-heavy work, anything needing back-and-forth with a
   human, or a task whose blast radius you can't bound up front.
 
-## The spawn command
+## The `subagent` MCP tools
+
+Your container's `subagent` MCP server (`hive-subagent-daemon`) is this
+skill's recipe as MCP calls — no manual shell-wrapping, no hand-rolled
+backgrounding:
+
+```
+start(name, prompt_file, model?, trigger?)
+continue(name, prompt, model?)
+interrupt(name, force?)
+```
+
+`name` ↔ `--name`, `model` ↔ `--model`, `prompt_file` ↔
+`--append-system-prompt-file`, `trigger`/`prompt` ↔ `-p`. `start` returns
+once the process is confirmed running, not once it finishes — a
+completion lands as a todo (`get_loose_ends`), same as any other producer.
+There's no `status` poll: check on a subagent by `continue`-ing it (refused
+while it's still running, which is itself the "still going" signal) or by
+reading its completion todo. `interrupt` genuinely stops a running turn
+(`force: true` for SIGKILL) — unlike bash tasks' `kill`, this isn't
+limited to a still-pending state.
+
+Everything else in this skill (model choice, prompt hygiene, splitting
+big batches, verify-then-report) applies unchanged; only the launch
+mechanics differ from a raw shell invocation.
+
+No `subagent` MCP server on this container? Fall back to the manual
+command below — same recipe, you drive the backgrounding yourself.
+
+## The spawn command (manual fallback)
 
 Put the task recipe in a file and pass it as a path, with a short `-p`
 trigger: