Summary

Implement orchestrator runtime that spawns/supervises loop child processes directly from Wiggum and supports PTY-based execution for interactive CLIs.

Part of #59.
Supports #34.

Scope

• Child process lifecycle management (start/stop/restart/exit reasons)
• PTY integration for CLIs requiring TTY semantics
• Stream routing (stdout/stderr) into monitor surfaces
• Graceful cancellation and cleanup
• Health/status channel for loop registry

Acceptance Criteria

• Loop can be launched and supervised by orchestrator runtime
• PTY-backed CLIs execute successfully under orchestrator
• Controlled stop/cancel works without orphan processes
• Exit reasons/status propagated to TUI accurately
• Runtime supports fallback to file-based action inbox path

Related

• #34
• #33
• #70