test(spec): pin the WRITE refusal on the generator's diagnostic

`refuses to WRITE the artifact when the document is inconsistent` asserted only
a non-zero exit status and a missing artifact. A subprocess that never starts
satisfies both, so the case stayed green in exactly the scenario where the gate
it exists to pin never ran at all — measured by parking tsx aside, where 8 of
the 9 spawn tests go red and this one is among the 13 that still pass.

Assert the generator's own dangling-ref diagnostic as well, which is the shape
its three sibling spawn tests already carry.

Claude-Session: https://claude.ai/code/session_01JbZnqu8bt6YqfJsr9vaFb3
Co-authored-by: Claude <noreply@anthropic.com>

Author: claude

packages/spec/scripts/openapi-self-consistency.test.ts

@@ -375,6 +375,14 @@ describe('build-openapi.ts end to end', () => {
       ),
     );
     expect(run.status).not.toBe(0);
+    // A non-zero status and a missing artifact are BOTH satisfied by a subprocess
+    // that never started, so on their own they cannot tell "the gate refused the
+    // write" apart from "the spawn failed to launch" — which is how this case
+    // stayed green while the gate it pins never ran once. The generator's own
+    // diagnostic is what pins the refusal to the gate, and it is the assertion
+    // the three siblings above already carry.
+    expect(run.output).toMatch(/unresolvable \$ref/);
+    expect(run.output).toContain('#/components/schemas/ApiErrorTypo');
     // The gate runs before the write, so no half-broken document is published.
     expect(fs.existsSync(run.artifact)).toBe(false);
   });