feat: harden runtime readiness and session workflow

harness/tests/test_adapter_factory.py

@@ -125,6 +125,20 @@ def test_factory_builds_writer_only_direct_vector_when_write_is_required():
     assert store.capabilities.upsert is True
 
 
+def test_factory_reuses_legacy_direct_connection_for_server_writes_only():
+    server = _config(vector_type="pgvector_direct", writer=False)
+    server.vectors.connection = server.vectors.reader
+    server.vectors.reader = None
+
+    store = build_vector_store(server, require_write=True)
+    assert store.capabilities.search is True
+    assert store.capabilities.upsert is True
+
+    server.profile = "workstation"
+    with pytest.raises(ConfigError, match="writer"):
+        build_vector_store(server, require_write=True)
+
+
 def test_factory_propagates_non_default_statement_timeout():
     config = _config(dwh_type="postgres_direct")
     config.execution.statement_timeout_ms = 12_345