feat(store): set_schema_linking validates then writes the F4 artifact

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

harness/tht/session/store.py

@@ -1,3 +1,4 @@
+import json
 import os
 import shutil
 from datetime import UTC, datetime
@@ -158,6 +159,28 @@ def set_question(
     return path
 
 
+def set_schema_linking(
+    session_id: str,
+    data: dict,
+    sessions_root: Path,
+) -> Path:
+    """Valida e scrive schema_linking.json (Fase 4) in modo deterministico.
+
+    Valida `data` contro il modello SchemaLinking (ValidationError se invalido) PRIMA
+    di scrivere, così un artefatto malformato non tocca mai il disco. Ritorna il path.
+    """
+    from tht.session.models import SchemaLinking
+
+    load_session(session_id, sessions_root)
+    model = SchemaLinking.model_validate(data)
+    path = sessions_root / session_id / "schema_linking.json"
+    path.write_text(
+        json.dumps(model.model_dump(by_alias=True), indent=2, ensure_ascii=False)
+    )
+    touch_manifest(session_id, sessions_root)
+    return path
+
+
 def load_session(session_id: str, sessions_root: Path) -> SessionManifest:
     path = sessions_root / session_id / MANIFEST
     if not path.exists():