feat(v2): builder-agent self-modification WIP + container-config as per-group file

Checkpoints the builder-agent dev-agent/worktree/swap flow (create_dev_agent,
request_swap, classifier, deadman, promote) before pivoting to a unified
draft-activate approach with OS-level RO enforcement. Lifts container_config
out of the agent_groups row into groups/<folder>/container.json so install_packages,
add_mcp_server, and rebuild flows can eventually route through the same draft
path as source edits.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

container/agent-runner/src/mcp-tools/agents.ts

@@ -31,7 +31,7 @@ export const createAgent: McpToolDefinition = {
   tool: {
     name: 'create_agent',
     description:
-      'Create a new child agent with a given name. The name you choose becomes the destination name you use to message this agent. Admin-only. Fire-and-forget — you will receive a notification when the agent is created.',
+      "Create a long-lived companion sub-agent (research assistant, task manager, specialist) — the name becomes your destination for it. NOT for source-code changes — use `create_dev_agent` for those. Admin-only. Fire-and-forget.",
     inputSchema: {
       type: 'object' as const,
       properties: {