fix: write exit code after process exits in terminate command

The EXIT trap in the process writes $? (which is 0 for SIGTERM) and would
overwrite our exit code if we wrote it immediately. Now we wait for the
process to exit before writing 143 (SIGTERM) or 137 (SIGKILL).

Author: ethanndickson

src/node/runtime/backgroundCommands.test.ts

@@ -135,12 +135,8 @@ describe("backgroundCommands", () => {
       expect(result).toContain("sleep 2");
       expect(result).toContain("kill -0 1234");
       expect(result).toContain("kill -9 -1234 2>/dev/null || true");
-    });
-
-    it("writes exit code 137 on force kill", () => {
-      const result = buildTerminateCommand(1234, "/tmp/exit_code");
-
-      expect(result).toContain("echo 137 > '/tmp/exit_code'");
+      expect(result).toContain("echo 137 >"); // SIGKILL exit code
+      expect(result).toContain("echo 143 >"); // SIGTERM exit code (written after process exits)
     });
 
     it("quotes exit code path with spaces", () => {

src/node/runtime/backgroundCommands.ts

@@ -133,12 +133,17 @@ export function buildTerminateCommand(
   quotePath: (p: string) => string = shellQuote
 ): string {
   const negPid = -pid; // Negative PID targets process group (PID === PGID due to set -m)
+  // Send SIGTERM, wait for process to exit, then write the correct exit code.
+  // We can't write immediately because the process's EXIT trap would overwrite it.
+  // After sleep 2, either the process exited (write SIGTERM code) or we escalate to SIGKILL.
   return (
     `kill -15 ${negPid} 2>/dev/null || true; ` +
     `sleep 2; ` +
     `if kill -0 ${pid} 2>/dev/null; then ` +
     `kill -9 ${negPid} 2>/dev/null || true; ` +
     `echo ${EXIT_CODE_SIGKILL} > ${quotePath(exitCodePath)}; ` +
+    `else ` +
+    `echo ${EXIT_CODE_SIGTERM} > ${quotePath(exitCodePath)}; ` +
     `fi`
   );
 }