fix(runtime): prevent orphaned copilot processes on shutdown

[jafreck]

Problem

When the AAMF runtime is terminated (e.g. terminal killed, SIGHUP), copilot CLI agent processes are left running as orphans. In one observed case, 55 copilot processes survived after killing the migration terminal.

Root cause (two issues):

1. Copilot children not tracked for cleanup. spawnAgent() in agent-launcher.ts spawns copilot CLI processes with { detached: true } and child.unref(), making them independent of the parent Node process. However, these children were not registered with the framework's trackProcess() mechanism. The shutdown handler calls killAllActiveProcesses(), but that only kills tracked processes — the copilot agents were invisible to it.

2. No SIGHUP handler. The runtime handles SIGINT and SIGTERM but not SIGHUP. When a terminal is closed/killed, the OS sends SIGHUP. Without a handler, the Node process dies without running cleanup, and detached children survive unconditionally.

Fix

• Track copilot children: Call trackProcess(child) immediately after spawn in spawnAgent() so copilot CLI processes are registered with the framework process tracker and cleaned up by killAllActiveProcesses() on shutdown.
• Handle SIGHUP: Add process.on('SIGHUP', ...) in setupShutdownHandlers() alongside SIGINT/SIGTERM so terminal-close scenarios trigger the same graceful shutdown path.

Changes

File	Change
src/core/agent-launcher.ts	Import trackProcess, call it after copilot child spawn
src/core/runtime.ts	Add SIGHUP handler in setupShutdownHandlers()
tests/core/runtime.test.ts	Update shutdown test to verify SIGHUP registration

Testing

• All 1498 unit tests pass
• tsc --noEmit clean