config: make ServerArgs read-only with a single audited mutation entry (#31811)

test/registered/unit/layers/attention/test_gdn_prefill_backend_policy.py

@@ -35,6 +35,14 @@ def make_runner(
     for name, value in arg_overrides.items():
         setattr(args, name, value)
 
+    # The policy routes its load-time default through the audited mutation entry
+    # (server_args.override); mirror that on the stub so the write lands.
+    def _override(source, **fields):
+        for _field, _value in fields.items():
+            setattr(args, _field, _value)
+
+    args.override = _override
+
     return SimpleNamespace(
         server_args=args,
         model_config=SimpleNamespace(),

test/registered/unit/test_runtime_context_override.py

@@ -0,0 +1,88 @@
+"""Context-first mutation.
+
+``get_context().override(source, **fields)`` is the business mutation entry: it
+writes the resolved config bags (the single source of truth) and never touches
+``server_args`` (the pristine startup record). Routing is by NS metadata; a bad
+field aborts before any write; provenance is recorded.
+"""
+
+import unittest
+
+from sglang.srt import runtime_context as rc
+from sglang.srt.server_args import ServerArgs
+from sglang.test.ci.ci_register import register_cpu_ci
+from sglang.test.test_utils import CustomTestCase
+
+register_cpu_ci(est_time=5, suite="base-a-test-cpu")
+
+
+class TestContextOverride(CustomTestCase):
+    def setUp(self):
+        rc.reset_context()
+
+    def tearDown(self):
+        rc.reset_context()
+
+    def _publish(self):
+        sa = ServerArgs(model_path="dummy")
+        rc.get_context().set_server_args(sa)
+        return sa
+
+    def test_override_writes_bag_not_server_args(self):
+        sa = self._publish()
+        before = sa.hicache_ratio
+        rc.get_context().override("test", hicache_ratio=before + 1.0)
+        self.assertEqual(rc.get_memory().hicache_ratio, before + 1.0)
+        # server_args stays the pristine startup record.
+        self.assertEqual(sa.hicache_ratio, before)
+
+    def test_override_routes_across_namespaces(self):
+        self._publish()
+        rc.get_context().override(
+            "test",
+            moe_runner_backend="triton",
+            page_size=64,
+            disaggregation_mode="decode",
+        )
+        self.assertEqual(rc.get_exec().moe.moe_runner_backend, "triton")
+        self.assertEqual(rc.get_schedule().page_size, 64)
+        self.assertEqual(rc.get_disagg().disaggregation_mode, "decode")
+
+    def test_override_unknown_field_raises_and_is_atomic(self):
+        self._publish()
+        before = rc.get_memory().hicache_ratio
+        with self.assertRaises(ValueError):
+            rc.get_context().override(
+                "test", hicache_ratio=before + 5.0, not_a_real_field=1
+            )
+        # No partial write: the valid field was not applied.
+        self.assertEqual(rc.get_memory().hicache_ratio, before)
+
+    def test_override_before_publish_raises(self):
+        with self.assertRaises(ValueError):
+            rc.get_context().override("test", page_size=32)
+
+    def test_override_provenance_recorded(self):
+        self._publish()
+        rc.get_context().override("srcA", page_size=16)
+        log = rc.get_context().overrides_log()
+        self.assertEqual(log[-1], ("srcA", {"page_size": 16}))
+
+    def test_republish_resets_provenance(self):
+        self._publish()
+        rc.get_context().override("srcA", page_size=16)
+        self.assertTrue(rc.get_context().overrides_log())
+        self._publish()
+        self.assertEqual(rc.get_context().overrides_log(), [])
+
+    def test_bare_server_args_write_raises_after_resolution(self):
+        # server_args is read-only after resolution regardless of the
+        # SGLANG_STRICT_CONFIG_MUTATION env; write via override instead.
+        sa = ServerArgs(model_path="dummy")
+        object.__setattr__(sa, "_declarations_materialized", True)
+        with self.assertRaises(AttributeError):
+            sa.page_size = 999
+
+
+if __name__ == "__main__":
+    unittest.main()