diff --git a/plugins/codex/scripts/lib/process.mjs b/plugins/codex/scripts/lib/process.mjs
index af28d1cf..06f043af 100644
--- a/plugins/codex/scripts/lib/process.mjs
+++ b/plugins/codex/scripts/lib/process.mjs
@@ -16,7 +16,10 @@ export function runCommand(command, args = [], options = {}) {
   return {
     command,
     args,
-    status: result.status ?? 0,
+    // A process killed by a signal reports status === null. Treat that as a
+    // failure (not success) so runCommandChecked/binaryAvailable don't silently
+    // accept truncated output; the signal itself is preserved below.
+    status: result.status ?? (result.signal ? 1 : 0),
     signal: result.signal ?? null,
     stdout: result.stdout ?? "",
     stderr: result.stderr ?? "",
diff --git a/tests/process.test.mjs b/tests/process.test.mjs
index 80e0715b..26107aa8 100644
--- a/tests/process.test.mjs
+++ b/tests/process.test.mjs
@@ -1,7 +1,48 @@
 import test from "node:test";
 import assert from "node:assert/strict";
 
-import { terminateProcessTree } from "../plugins/codex/scripts/lib/process.mjs";
+import {
+  formatCommandFailure,
+  runCommand,
+  runCommandChecked,
+  terminateProcessTree
+} from "../plugins/codex/scripts/lib/process.mjs";
+
+test("runCommand reports a signal-terminated process as a non-zero failure", () => {
+  const result = runCommand(process.execPath, ["-e", "process.kill(process.pid, 'SIGKILL')"]);
+  assert.notEqual(result.status, 0);
+  assert.equal(result.signal, "SIGKILL");
+});
+
+test("runCommandChecked throws when the child is killed by a signal", () => {
+  assert.throws(
+    () => runCommandChecked(process.execPath, ["-e", "process.kill(process.pid, 'SIGKILL')"]),
+    /signal=SIGKILL/
+  );
+});
+
+test("runCommand still reports a clean exit as status 0", () => {
+  const result = runCommand(process.execPath, ["-e", "process.exit(0)"]);
+  assert.equal(result.status, 0);
+  assert.equal(result.signal, null);
+});
+
+test("runCommand preserves a non-zero exit code", () => {
+  const result = runCommand(process.execPath, ["-e", "process.exit(3)"]);
+  assert.equal(result.status, 3);
+});
+
+test("formatCommandFailure surfaces the signal for a signal-killed command", () => {
+  const failure = formatCommandFailure({
+    command: "git",
+    args: ["status"],
+    status: 1,
+    signal: "SIGKILL",
+    stdout: "",
+    stderr: ""
+  });
+  assert.match(failure, /signal=SIGKILL/);
+});
 
 test("terminateProcessTree uses taskkill on Windows", () => {
   let captured = null;