feat(harness): manifest provider/model/thinking/name + session new options (BE-6/7)

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

harness/tests/test_manifest_pi_fields.py

@@ -0,0 +1,19 @@
+from tht.session.store import create_session
+from tht.session.models import SessionManifest
+
+
+def test_manifest_persists_pi_fields(tmp_path):
+    from tht.config import DatabaseConfig
+    db = DatabaseConfig(database="d", schema="s", transport="rest", user="u", password="p")
+    m = create_session("q", db, tmp_path, provider="zai", model="glm-5.2",
+                        thinking="medium", name="sessione test")
+    reload = SessionManifest.from_yaml(tmp_path / m.id / "session_manifest.yaml")
+    assert reload.provider == "zai" and reload.model == "glm-5.2"
+    assert reload.thinking == "medium" and reload.name == "sessione test"
+
+
+def test_manifest_pi_fields_optional(tmp_path):
+    from tht.config import DatabaseConfig
+    db = DatabaseConfig(database="d", schema="s", transport="rest", user="u", password="p")
+    m = create_session("q", db, tmp_path)
+    assert m.provider is None and m.model is None and m.thinking is None and m.name is None