fix: check process group instead of parent PID in terminate

kill -0 ${pid} only checks if the parent is alive, but children may
survive SIGTERM. Changed to kill -0 ${negPid} to check if any process
in the group is still alive before deciding to send SIGKILL.

Author: ethanndickson

src/node/runtime/backgroundCommands.test.ts

@@ -133,7 +133,7 @@ describe("backgroundCommands", () => {
 
       expect(result).toContain("kill -15 -1234 2>/dev/null || true");
       expect(result).toContain("sleep 2");
-      expect(result).toContain("kill -0 1234");
+      expect(result).toContain("kill -0 -1234");
       expect(result).toContain("kill -9 -1234 2>/dev/null || true");
       expect(result).toContain("echo 137 >"); // SIGKILL exit code
       expect(result).toContain("echo 143 >"); // SIGTERM exit code (written after process exits)

src/node/runtime/backgroundCommands.ts

@@ -139,7 +139,7 @@ export function buildTerminateCommand(
   return (
     `kill -15 ${negPid} 2>/dev/null || true; ` +
     `sleep 2; ` +
-    `if kill -0 ${pid} 2>/dev/null; then ` +
+    `if kill -0 ${negPid} 2>/dev/null; then ` +
     `kill -9 ${negPid} 2>/dev/null || true; ` +
     `echo ${EXIT_CODE_SIGKILL} > ${quotePath(exitCodePath)}; ` +
     `else ` +