New files:
- fs9p.go: FS9P struct with /proc-based execution model
- /proc/new (rdwr): blocking tool execution
- /proc/new.bg: background/detached execution
- /proc/<pid>/out, wait, stat, ctl: process management
- /tools, /ctl, /info: tool registry and host info
- Payload format: key=value lines, newline delimited
- exec9p.go: Decoupled tool execution
- ExecuteTool: standalone function for tool execution
- executeSandboxed: sandbox execution without Server deps
- executeBypassDirect: bypass broker without Server deps
- fs9p_test.go: Unit tests for FS9P
Design notes:
- Background execution is the internal model
- Foreground (/proc/new rdwr) blocks until completion
- No per-connection state (cwd/env passed per-call or at attach)
- Session ID scoping via registry, not env propagation
This is the foundation - actual 9P serving and integration pending.
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