Fix mcp-serve to read connection from sidemantic.yaml config (#129)

mcp-serve was ignoring the config file's connection settings, so
init_sql with ATTACH/LOAD statements and non-default connections
didn't work. Now resolves connection string from config like the
query and api-serve commands do.

Author: nicosuave

sidemantic/cli.py

@@ -268,14 +268,24 @@ def mcp_serve(
     else:
         db_path = str(db) if db else None
 
-    # Merge CLI --init-sql with config-based init_sql
+    # Resolve connection from CLI args or config
+    connection_str = None
     effective_init_sql: list[str] | None = init_sql if init_sql else None
-    if not effective_init_sql and _loaded_config:
+
+    if db_path and db_path != ":memory:":
+        connection_str = f"duckdb:///{Path(db_path).absolute()}"
+    elif db_path == ":memory:":
+        connection_str = "duckdb:///:memory:"
+    elif _loaded_config and _loaded_config.connection:
+        connection_str = build_connection_string(_loaded_config)
+        if not effective_init_sql:
+            effective_init_sql = get_init_sql(_loaded_config)
+    elif not effective_init_sql and _loaded_config:
         effective_init_sql = get_init_sql(_loaded_config)
 
     try:
         # Initialize the semantic layer
-        initialize_layer(str(directory), db_path, init_sql=effective_init_sql)
+        initialize_layer(str(directory), connection=connection_str, init_sql=effective_init_sql)
 
         # If demo mode, populate with demo data
         if demo:

sidemantic/mcp_server.py

@@ -19,14 +19,14 @@
 def initialize_layer(
     directory: str,
     db_path: str | None = None,
+    connection: str | None = None,
     init_sql: list[str] | None = None,
 ) -> SemanticLayer:
     """Initialize the semantic layer with models from directory."""
     global _layer
 
-    # Create connection string
-    connection = None
-    if db_path:
+    # Use explicit connection string, or build one from db_path
+    if connection is None and db_path:
         if db_path == ":memory:":
             connection = "duckdb:///:memory:"
         else:

tests/test_cli_commands.py

@@ -157,9 +157,10 @@ def test_mcp_serve_calls_initialize(monkeypatch, tmp_path):
     pytest.importorskip("mcp")
     called = {}
 
-    def fake_initialize_layer(directory, db_path=None, init_sql=None):
+    def fake_initialize_layer(directory, db_path=None, connection=None, init_sql=None):
         called["directory"] = directory
         called["db_path"] = db_path
+        called["connection"] = connection
         called["init_sql"] = init_sql
 
     def fake_run(*args, **kwargs):