fix(runtime): prevent orphaned copilot processes on shutdown

src/core/agent-launcher.ts

@@ -5,6 +5,7 @@ import {
   AgentLauncher as FrameworkAgentLauncher,
   registerAgentBackendFactory,
   isCopilotCliInvocationError,
+  trackProcess,
   type BackendRuntimeConfig,
   type BackendLoggerLike,
   type AgentBackend,
@@ -277,6 +278,7 @@ function spawnAgent(command: string, args: string[], opts: { cwd: string; env: R
       stdio: ['pipe', 'pipe', 'pipe'],
       detached: true,
     });
+    trackProcess(child);
     child.unref();
 
     const stdoutChunks: Buffer[] = [];

src/core/runtime.ts

@@ -688,6 +688,7 @@ export class MigrationRuntime {
 
     process.on('SIGINT', () => void handler('SIGINT'));
     process.on('SIGTERM', () => void handler('SIGTERM'));
+    process.on('SIGHUP', () => void handler('SIGHUP'));
     process.on('exit', () => {
       this.releaseRunLockSync();
     });

tests/core/runtime.test.ts

@@ -825,7 +825,7 @@ describe('MigrationRuntime', () => {
       await rm(root, { recursive: true, force: true });
     });
 
-    it('setupShutdownHandlers registers SIGINT/SIGTERM handlers that flush and save state', async () => {
+    it('setupShutdownHandlers registers SIGINT/SIGTERM/SIGHUP handlers that flush and save state', async () => {
       const runtime = new MigrationRuntime() as any;
       const onSpy = vi.spyOn(process, 'on').mockReturnValue(process);
       const exitSpy = vi.spyOn(process, 'exit').mockImplementation((() => undefined) as never);
@@ -846,18 +846,22 @@ describe('MigrationRuntime', () => {
 
       const sigintHandler = onSpy.mock.calls.find(([signal]) => signal === 'SIGINT')?.[1] as (() => void) | undefined;
       const sigtermHandler = onSpy.mock.calls.find(([signal]) => signal === 'SIGTERM')?.[1] as (() => void) | undefined;
+      const sighupHandler = onSpy.mock.calls.find(([signal]) => signal === 'SIGHUP')?.[1] as (() => void) | undefined;
 
       expect(sigintHandler).toBeDefined();
       expect(sigtermHandler).toBeDefined();
+      expect(sighupHandler).toBeDefined();
 
       sigintHandler!();
       sigtermHandler!();
+      sighupHandler!();
       await new Promise(resolve => setTimeout(resolve, 0));
 
-      expect(runtime.logger.flush).toHaveBeenCalledTimes(2);
-      expect(runtime.checkpoint.save).toHaveBeenCalledTimes(2);
+      expect(runtime.logger.flush).toHaveBeenCalledTimes(3);
+      expect(runtime.checkpoint.save).toHaveBeenCalledTimes(3);
       expect(runtime.progress.appendEvent).toHaveBeenCalledWith('Migration interrupted by SIGINT');
       expect(runtime.progress.appendEvent).toHaveBeenCalledWith('Migration interrupted by SIGTERM');
+      expect(runtime.progress.appendEvent).toHaveBeenCalledWith('Migration interrupted by SIGHUP');
       expect(exitSpy).toHaveBeenCalledWith(130);
       expect(exitSpy).toHaveBeenCalledWith(143);