gemini: Fix edge case when transforming MCP tool schema (#32373)

Closes #31766

Release Notes:

- Fixed an issue where some MCP tools would not work when using Gemini

crates/assistant_tool/src/tool_schema.rs

@@ -46,16 +46,20 @@ fn adapt_to_json_schema_subset(json: &mut Value) -> Result<()> {
             );
         }
 
-        const KEYS_TO_REMOVE: [&str; 5] = [
+        const KEYS_TO_REMOVE: [(&str, fn(&Value) -> bool); 5] = [
-            "format",
+            ("format", |value| value.is_string()),
-            "additionalProperties",
+            ("additionalProperties", |value| value.is_boolean()),
-            "exclusiveMinimum",
+            ("exclusiveMinimum", |value| value.is_number()),
-            "exclusiveMaximum",
+            ("exclusiveMaximum", |value| value.is_number()),
-            "optional",
+            ("optional", |value| value.is_boolean()),
         ];
-        for key in KEYS_TO_REMOVE {
+        for (key, predicate) in KEYS_TO_REMOVE {
+            if let Some(value) = obj.get(key) {
+                if predicate(value) {
                     obj.remove(key);
                 }
+            }
+        }
 
         // If a type is not specified for an input parameter, add a default type
         if matches!(obj.get("description"), Some(Value::String(_)))
@@ -153,6 +157,24 @@ mod tests {
                 "type": "integer"
             })
         );
+
+        // Ensure that we do not remove keys that are actually supported (e.g. "format" can just be used as another property)
+        let mut json = json!({
+            "description": "A test field",
+            "type": "integer",
+            "format": {},
+        });
+
+        adapt_to_json_schema_subset(&mut json).unwrap();
+
+        assert_eq!(
+            json,
+            json!({
+                "description": "A test field",
+                "type": "integer",
+                "format": {},
+            })
+        );
     }
 
     #[test]