feat(#1132): complete contribution hook prerequisite

Closes #1132

tests/run-tests-harness.test.cjs

@@ -314,6 +314,30 @@ test('ambient GSD workstream vars are stripped by the runner', () => {
         `expected chunking marker in stderr; STDERR (tail):\n${r.stderr.split('\n').slice(-20).join('\n')}`,
       );
     });
+
+    test('chunks by file count even when argv length is below the ceiling', () => {
+      const names = Array.from({ length: 7 }, (_, i) => `tiny-${String(i).padStart(2, '0')}.test.cjs`);
+      seed(tmpDir, names);
+      const r = runHarness(tmpDir, [], {
+        RUN_TESTS_MAX_CMDLINE_CHARS: '100000',
+        RUN_TESTS_MAX_FILES_PER_CHUNK: '3',
+      });
+      assert.strictEqual(
+        r.status,
+        0,
+        `expected zero exit; got status=${r.status} signal=${r.signal}\nSTDERR:\n${r.stderr}`,
+      );
+      assert.match(
+        r.stderr,
+        /run-tests: chunk 1\/3 — 3 files/,
+        `expected file-count chunking marker in stderr; STDERR:\n${r.stderr}`,
+      );
+      assert.match(
+        r.stderr,
+        /run-tests: chunk 3\/3 — 1 files/,
+        `expected final file-count chunking marker in stderr; STDERR:\n${r.stderr}`,
+      );
+    });
   });
 
   describe('per-chunk timeout + force-exit (windows hang guard, #1051)', () => {