fix(postgres): carry tree-sitter-sql in the postgres extra and surface grammar errors

The postgres introspection path synthesizes DDL and parses it with the SQL grammar, but
tree-sitter-sql was not in the postgres extra, so `pip install graphifyy[postgres]` left it
unable to parse and returned a silent empty result. Add tree-sitter-sql to the extra and
raise an actionable ImportError (with the install hint) when the grammar is missing or has
an incompatible ABI, instead of reporting zero nodes.

graphify/pg_introspect.py

@@ -154,4 +154,12 @@ def introspect_postgres(dsn: str | None = None) -> dict:
 
     # Pass virtual path and in-memory DDL content to extract_sql
     result = extract_sql(virtual_path, content=ddl_string)
+    # extract_sql() reports a missing grammar as an 'error' key with empty
+    # nodes/edges; surface it instead of letting the CLI print
+    # "PostgreSQL: 0 nodes" as if the database were empty.
+    if result.get("error"):
+        raise ImportError(
+            f"{result['error']} (required by --postgres; "
+            "install with: pip install 'graphifyy[postgres]')"
+        )
     return result

pyproject.toml

@@ -65,7 +65,10 @@ svg = ["matplotlib", "numpy>=2.0; python_version >= '3.13'"]
 leiden = ["graspologic; python_version < '3.13'"]
 office = ["python-docx", "openpyxl"]
 google = ["openpyxl"]
-postgres = ["psycopg[binary]"]
+# --postgres reconstructs DDL and feeds it to extract_sql(), which needs the
+# tree-sitter-sql grammar; without it introspection silently returns 0 nodes,
+# so the postgres extra must carry the grammar too.
+postgres = ["psycopg[binary]", "tree-sitter-sql"]
 video = ["faster-whisper; python_version >= '3.11'", "yt-dlp>=2026.6.9"]
 kimi = ["openai", "tiktoken"]
 ollama = ["openai"]

tests/test_pg_introspect.py

@@ -367,6 +367,26 @@ def test_pg_introspect_import_error():
     assert "graphifyy[postgres]" in str(exc_info.value)
 
 
+def test_pg_introspect_grammar_error_surfaces():
+    """If extract_sql reports an error (e.g. tree-sitter-sql missing), the
+    introspection must raise instead of returning an empty graph — otherwise
+    the CLI prints "PostgreSQL: 0 nodes" as if the database were empty."""
+    mock_psycopg = _make_mock_psycopg(
+        [("public", "users", "BASE TABLE")], [], [], []
+    )
+    with patch.dict("sys.modules", {"psycopg": mock_psycopg}):
+        with patch(
+            "graphify.pg_introspect.extract_sql",
+            return_value={
+                "nodes": [],
+                "edges": [],
+                "error": "tree_sitter_sql not installed. Run: pip install tree-sitter-sql",
+            },
+        ):
+            with pytest.raises(ImportError, match="tree_sitter_sql not installed"):
+                introspect_postgres("postgresql://myhost/mydb")
+
+
 def test_pg_introspect_uri_forward_slashes():
     """Assert that the virtual path in postgresql introspection output uses forward slashes on all platforms."""
     mock_psycopg = _make_mock_psycopg([], [], [], [], host="some-host", dbname="some-db")