feat(subagent): durable child catalog and list_agents

Implements the durable-subagent-catalog RFC: SubagentControlService.listChildren()
enumerates a parent's direct continuable children from one sessionQuery trace,
validates each child's sole subagent/descriptor event (now carrying the durable
creation label), and returns one ordered SubagentListEntry[] with per-child
corrupt/unsupported/unavailable diagnostics. The list_agents tool ships as a
separately loadable plugin of dsh-tool-subagent-control requiring sessionQuery
at load; send_message stays usable without it.

docs/tool-catalog.md

@@ -31,7 +31,7 @@ This table connects model-visible tool names to the plugin package and service s
 | `@deepseek-ai/dsh-tool-skill` | `skill` | `ctx.tools`, `ctx.agents`, `ctx.skills` | `tool/call`, `tool/result`, `user/message replacement catalogs via agent.inject()` | - | - |
 | `@deepseek-ai/dsh-tool-session-query` | `session_event_read`, `session_event_search`, `session_event_trace`, `session_search`, `session_trace` | `ctx.tools`, `ctx.systemPrompt`, `ctx.sessionQuery`, `a calling Agent for workspace authority` | `tool/call`, `tool/result` | - | The five read-only tools hide provider cursors and authorize every result from the immutable calling agent session. The package is opt-in; compositions that need enforced deadlines or bounded inline output also mount the generic timeout or spill policies. |
 | `@deepseek-ai/dsh-tool-subagent` | `subagent` | `ctx.tools`, `ctx.subagents` | `tool/call`, `tool/result`, `child session events through the chosen provider` | `subagent`, `subagent_fork` | The registered tool name is the load-time `toolName` config (default `subagent`); the schema above is that default. The shipped example agents load this package once per subagent backend, so the model additionally sees `subagent_fork` (bound to the fork backend) with an identical schema — see `apps/cli/config/base.cordis.yml` and `examples/acp-agent/cordis.yml`. |
-| `@deepseek-ai/dsh-tool-subagent-control` | `send_message` | `ctx.tools`, `ctx.subagents` | `tool/call`, `tool/result`, `child session events through ctx.subagents` | - | The one globally named follow-up tool over continuable background subagents: provider-bound `tool-subagent` instances register distinct delegation tools, while this package registers `send_message` once. |
+| `@deepseek-ai/dsh-tool-subagent-control` | `list_agents`, `send_message` | `ctx.tools`, `ctx.subagents`, `ctx.sessionQuery (list_agents only)` | `tool/call`, `tool/result`, `child session events through ctx.subagents` | - | The globally named control tools over continuable background subagents: provider-bound `tool-subagent` instances register distinct delegation tools, while this package registers `send_message` once, plus `list_agents` from its separately loaded `/list-agents` plugin (which additionally requires session query). |
 | `@deepseek-ai/dsh-tool-tasks` | `task_kill`, `task_list`, `task_output` | `ctx.tools`, `ctx.tasks`, `ctx.systemPrompt` | `tool/call`, `tool/result`, `user/message via agent.inject() for background completion notices` | - | The kind-agnostic background-task control surface: background bash commands, PTY sends, and subagents are read, listed, and killed through the same three tools. Loading the plugin attaches the control surface that arms producers' `ctx.tasks.start()`. |
 | `@deepseek-ai/dsh-tool-todo` | `todo_write` | `ctx.tools`, `owning Agent session` | `tool/call`, `todo/write`, `tool/result` | - | todo_write is session-owned state; UIs render the latest todo/write event as a checklist. |
 | `@deepseek-ai/dsh-tool-workflow` | `workflow` | `ctx.tools`, `ctx.workflows`, `ctx.systemPrompt`, `a calling Agent (exec.agent parents the script children)` | `tool/call`, `tool/result` | - | - |
@@ -1149,6 +1149,19 @@ The registered tool name is the load-time `toolName` config (default `subagent`)
 
 ## `@deepseek-ai/dsh-tool-subagent-control`
 
+### `list_agents`
+
+List your background subagents: every subagent you started that can receive `send_message`, whether it is still working (running) or has finished its current turn (complete — a follow-up message starts a new turn on the same conversation). Children that could not be read are reported as diagnostics instead of being silently dropped.
+
+```json
+{
+  "type": "object",
+  "properties": {}
+}
+```
+
+Source: [`packages/subagent/tool-subagent-control/src/index.ts`](../packages/subagent/tool-subagent-control/src/index.ts)
+
 ### `send_message`
 
 Send a message to a background subagent by its subagent id, continuing the same conversation. It becomes the subagent's next turn: if it is still working, the message waits until its current turn finishes, so it cannot redirect work already underway. The subagent does not reply to you, so use this only to give it more work. A failure means the message was NOT delivered.
@@ -1175,7 +1188,7 @@ Send a message to a background subagent by its subagent id, continuing the same
 
 Source: [`packages/subagent/tool-subagent-control/src/index.ts`](../packages/subagent/tool-subagent-control/src/index.ts)
 
-The one globally named follow-up tool over continuable background subagents: provider-bound `tool-subagent` instances register distinct delegation tools, while this package registers `send_message` once.
+The globally named control tools over continuable background subagents: provider-bound `tool-subagent` instances register distinct delegation tools, while this package registers `send_message` once, plus `list_agents` from its separately loaded `/list-agents` plugin (which additionally requires session query).
 
 ## `@deepseek-ai/dsh-tool-tasks`