fix(tools): 🐛 inject dummy parameter for tools with empty schemas

Gemini/Antigravity API fails to emit functionCall when tool schemas have empty properties {}. This commit adds a workaround by injecting a dummy optional parameter "_" into empty tool schemas to ensure function calls are properly emitted.

- Add dummy parameter injection in both antigravity_provider and gemini_cli_provider
- Apply workaround to both schema transformation paths and default empty schema cases
- Update docstring for _apply_claude_tool_transform to clarify its purpose
- Improve inline comments for error body reading logic

src/rotator_library/providers/antigravity_provider.py

@@ -2450,9 +2450,23 @@ class AntigravityProvider(AntigravityAuthBase, ProviderInterface):
                 schema.pop("$schema", None)
                 schema.pop("strict", None)
                 schema = _normalize_type_arrays(schema)
+
+                # Workaround: Antigravity/Gemini fails to emit functionCall
+                # when tool has empty properties {}. Inject a dummy optional
+                # parameter to ensure the tool call is emitted.
+                props = schema.get("properties", {})
+                if not props:
+                    schema["properties"] = {
+                        "_": {"type": "string", "description": "Unused"}
+                    }
+
                 func_decl["parametersJsonSchema"] = schema
             else:
-                func_decl["parametersJsonSchema"] = {"type": "object", "properties": {}}
+                # No parameters provided - use default with dummy param
+                func_decl["parametersJsonSchema"] = {
+                    "type": "object",
+                    "properties": {"_": {"type": "string", "description": "Unused"}},
+                }
 
             gemini_tools.append({"functionDeclarations": [func_decl]})
 
@@ -2577,7 +2591,11 @@ class AntigravityProvider(AntigravityAuthBase, ProviderInterface):
         return antigravity_payload
 
     def _apply_claude_tool_transform(self, payload: Dict[str, Any]) -> None:
-        """Apply Claude-specific tool schema transformations."""
+        """Apply Claude-specific tool schema transformations.
+
+        Converts parametersJsonSchema to parameters and applies Claude-specific
+        schema cleaning (removes unsupported JSON Schema fields).
+        """
         tools = payload["request"].get("tools", [])
         for tool in tools:
             for func_decl in tool.get("functionDeclarations", []):
@@ -3219,8 +3237,8 @@ class AntigravityProvider(AntigravityAuthBase, ProviderInterface):
             "POST", url, headers=headers, json=payload, timeout=600.0
         ) as response:
             if response.status_code >= 400:
-                # Read error body for raise_for_status to include in exception
-                # Terminal logging commented out - errors are logged in failures.log
+                # Read error body so it's available in response.text for logging
+                # The actual logging happens in failure_logger via _extract_response_body
                 try:
                     await response.aread()
                     # lib_logger.error(

src/rotator_library/providers/gemini_cli_provider.py

@@ -1256,13 +1256,22 @@ class GeminiCliProvider(GeminiAuthBase, ProviderInterface):
                     schema = self._gemini_cli_transform_schema(
                         new_function["parameters"]
                     )
+                    # Workaround: Gemini fails to emit functionCall for tools
+                    # with empty properties {}. Inject a dummy optional param.
+                    props = schema.get("properties", {})
+                    if not props:
+                        schema["properties"] = {
+                            "_": {"type": "string", "description": "Unused"}
+                        }
                     new_function["parametersJsonSchema"] = schema
                     del new_function["parameters"]
                 elif "parametersJsonSchema" not in new_function:
-                    # Set default empty schema if neither exists
+                    # Set default schema with dummy param if neither exists
                     new_function["parametersJsonSchema"] = {
                         "type": "object",
-                        "properties": {},
+                        "properties": {
+                            "_": {"type": "string", "description": "Unused"}
+                        },
                     }
 
                 # Gemini 3 specific transformations