Add MultiplyFunction to worker and show const flag in catalog CLI

- Add MultiplyFunction to ExampleWorker's functions list
- Update arrow_schema_to_json to extract and display const metadata
  for ConstParam arguments

Now the catalog CLI shows:
- multiply: {"name": "factor", "type": "int64", "const": true}
- polars_multiply: {"name": "factor", "type": "any", "const": true}

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Author: rustyconover

vgi/client/cli_utils.py

@@ -172,7 +172,7 @@ def arrow_schema_to_json(serialized: bytes) -> list[dict[str, Any]]:
         serialized: Serialized Arrow schema bytes
 
     Returns:
-        List of column definitions with name, type, and optional varargs flag
+        List of column definitions with name, type, and optional flags (varargs, const)
 
     """
     reader = pa.BufferReader(serialized)
@@ -181,6 +181,7 @@ def arrow_schema_to_json(serialized: bytes) -> list[dict[str, Any]]:
     for f in schema:
         type_str = str(f.type)
         is_varargs = False
+        is_const = False
         if f.metadata:
             # Check for vgi:any metadata (output schema)
             if f.metadata.get(b"vgi:any") == b"true":
@@ -193,10 +194,15 @@ def arrow_schema_to_json(serialized: bytes) -> list[dict[str, Any]]:
             # Check for varargs metadata
             if f.metadata.get(b"vgi_varargs") == b"true":
                 is_varargs = True
+            # Check for const metadata (ConstParam)
+            if f.metadata.get(b"vgi_const") == b"true":
+                is_const = True
 
         entry: dict[str, Any] = {"name": f.name, "type": type_str}
         if is_varargs:
             entry["varargs"] = True
+        if is_const:
+            entry["const"] = True
         result.append(entry)
     return result
 

vgi/examples/worker.py

@@ -24,6 +24,7 @@
 from vgi.examples.scalar import (
     AddValuesFunction,
     DoubleFunction,
+    MultiplyFunction,
     NullHandlingFunction,
     RandomIntFunction,
     SumValuesFunction,
@@ -108,6 +109,7 @@ class Settings:
         # ScalarFunctionGenerator - transform to single-column output
         AddValuesFunction,
         DoubleFunction,
+        MultiplyFunction,
         NullHandlingFunction,
         RandomIntFunction,
         SumValuesFunction,