Per-model service tier default (codex: gpt-6.1-sol -> fast), tier:<x> / tier:none labels

executors.<x>.tier_defaults maps a model to the tier used when no label sets one;
a tier:<name> label sets it explicitly and tier:none drops the tier argument.

tests/test_core.py

@@ -362,5 +362,32 @@ class EnvFailureTest(unittest.TestCase):
         h.close()
 
 
+
+class TierDefaultTest(unittest.TestCase):
+    """executors.<x>.tier_defaults: tier per model unless a label (`tier:<x>`, `tier:none`) sets one."""
+    def run_with(self, labels):
+        data = config_data()
+        data["executors"]["codex"]["tier_defaults"] = {"sol": "fast"}
+        h = Harness(data)
+        try:
+            iid = h.plane.add_issue(1, labels=labels)
+            h.tick()
+            return h.execs[("win10", "codex")].started[0].tier, h.plane.texts(iid)[-1]
+        finally:
+            h.close()
+
+    def test_default_model_gets_its_tier(self):
+        tier, text = self.run_with(())
+        self.assertEqual(tier, "fast")
+        self.assertIn("codex / sol / medium / fast @ win10", text)
+
+    def test_other_model_has_no_default(self):
+        self.assertIsNone(self.run_with(("model:astra",))[0])
+
+    def test_labels_override(self):
+        self.assertEqual(self.run_with(("tier:flex",))[0], "flex")
+        self.assertIsNone(self.run_with(("tier:none",))[0])
+
+
 if __name__ == "__main__":
     unittest.main()