test(config): signal-killed spawns map to -1, not exit 0

Both cfg() helpers defaulted a null spawn status to 0 — a child killed by
signal would read as success and mask real failures.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

test/gstack-config-cross-project.test.ts

@@ -23,7 +23,8 @@ function cfg(args: string[]): { code: number; out: string; err: string } {
     encoding: "utf8",
     env: { ...process.env, GSTACK_STATE_ROOT: stateRoot },
   });
-  return { code: r.status ?? 0, out: r.stdout ?? "", err: r.stderr ?? "" };
+  // null status = killed by signal, never success — map to -1, not 0.
+  return { code: r.status ?? -1, out: r.stdout ?? "", err: r.stderr ?? "" };
 }
 
 beforeEach(() => {

test/gstack-config-redact-keys.test.ts

@@ -18,7 +18,8 @@ function cfg(args: string[]): { code: number; out: string; err: string } {
     env: { ...process.env, GSTACK_HOME: home },
     timeout: 30_000,
   });
-  return { code: r.status ?? 0, out: r.stdout ?? "", err: r.stderr ?? "" };
+  // null status = killed by signal, never success — map to -1, not 0.
+  return { code: r.status ?? -1, out: r.stdout ?? "", err: r.stderr ?? "" };
 }
 
 beforeEach(() => {