scion-smoke Agent Plugins fixture

A minimal Agent Plugins 1.0.0 bundle for the live smoke test of native plugin install (hub.agent_plugins; see the design's §5.3). Text files only, no dependencies beyond python3.

• skills/smoke-hello: asked for the smoke word, the agent answers PLUM-7.
• bin/stdio-mcp: stdio MCP server with one tool, whereami, returning the server's cwd, PLUGIN_ROOT, PLUGIN_DATA, whether PLUGIN_DATA is writable, and its argv. mcp.json omits cwd on purpose, to test the spec's default (the plugin root).
• bin/http-mcp: minimal streamable-http MCP server on 127.0.0.1:8765 with one tool, ping, returning pong. Start it by hand from the native plugin root during the smoke test.

To use it, copy this directory to plugins/scion-smoke/ in a test template whose scion-agent.yaml declares:

agent_plugins:
  - path: plugins/scion-smoke