refactor(harness): route workflow persistence through repositories

harness/tests/test_decision_join_set_cli.py

@@ -28,15 +28,28 @@ def _walk_to_phase(session, target):
 
 def _configure_command(monkeypatch, sessions):
     import tht.cli.decision_cmd as mod
+    import tht.cli.session_cmd as session_mod
+    from tht.session.models import SessionManifest, SessionSnapshot
+
+    class _Repository:
+        def get(self, session_id):
+            return SessionSnapshot(
+                manifest=SessionManifest(id=session_id, created_at="2026-01-01T00:00:00Z", question="q", database="d", schema="s"),
+                decisions=list_decisions(sessions / session_id),
+            )
+
+        def append_decisions(self, session_id, decisions):
+            return append_decisions(sessions / session_id, list(decisions))
 
     class _Cfg:
-        class paths:
-            pass
+        pass
 
-    _Cfg.paths.sessions = sessions
+    repository = _Repository()
     monkeypatch.setattr(mod, "_load_config_or_exit", lambda _c: _Cfg())
     monkeypatch.setattr(mod, "load_session_or_exit", lambda _cfg, _s: None)
-    monkeypatch.setattr(mod, "session_dir", lambda _cfg, sid: sessions / sid)
+    monkeypatch.setattr(mod, "load_snapshot_or_exit", lambda _cfg, sid: repository.get(sid))
+    monkeypatch.setattr(mod, "session_repository", lambda _cfg: repository)
+    monkeypatch.setattr(session_mod, "load_snapshot_or_exit", lambda _cfg, sid: repository.get(sid))
 
 
 def test_add_join_set_rejects_the_whole_batch_when_one_item_is_invalid(tmp_path, monkeypatch):