fix: bind sidecar objectives to v2 materialization

Author: apstenku123

scripts/sidecar_manifest_contract.py

@@ -24,10 +24,13 @@
     "pr": (1024, 2048, 4096, 8192, 16384),
 }
 OBJECTIVE_CONTRACT = {
-    "schema": "cppmega_mlx_runtime_objectives_v1",
-    "status": "runtime_materialized",
+    "schema": "cppmega_mlx_objective_source_v2",
+    "status": "source_for_pre_materialization",
     "materialized_in_parquet": False,
-    "runtime": "cppmega_mlx.training.task_mixer.TaskMixer",
+    "materializer": "scripts.materialize_megatron_objectives",
+    "planner": "cppmega_mlx.training.objective_schedule.CanonicalObjectivePlanner",
+    "mixer": "cppmega_mlx.training.objective_mixer.EligibilityAwareTaskMixer",
+    "artifact_schema": "cppmega_objective_materialization_artifact_v2",
     "stage": "stage1",
     "rates": {
         "causal_lm": "1/2",

tests/test_case6_sidecar_manifest_contract.py

@@ -116,6 +116,19 @@ def test_manifest_binds_inventory_and_explicit_bucket_exclusions(tmp_path: Path)
     }
 
 
+def test_objective_manifest_is_explicitly_a_source_for_v2_materialization() -> None:
+    assert OBJECTIVE_CONTRACT["schema"] == "cppmega_mlx_objective_source_v2"
+    assert OBJECTIVE_CONTRACT["status"] == "source_for_pre_materialization"
+    assert OBJECTIVE_CONTRACT["materialized_in_parquet"] is False
+    assert OBJECTIVE_CONTRACT["materializer"] == (
+        "scripts.materialize_megatron_objectives"
+    )
+    assert OBJECTIVE_CONTRACT["artifact_schema"] == (
+        "cppmega_objective_materialization_artifact_v2"
+    )
+    assert "TaskMixer" not in str(OBJECTIVE_CONTRACT.get("runtime", ""))
+
+
 def test_manifest_rejects_payload_tampering(tmp_path: Path) -> None:
     manifest, _root = _green_manifest(tmp_path)
     tampered = copy.deepcopy(manifest)