fix(translator): resolve invalid function name errors by sanitizing Claude tool names

This commit centralizes tool name sanitization in SanitizeFunctionName,
applying character compliance, starting character rules, and length limits.
It also fixes a regression in gemini_schema tests and preserves MCP-specific
shortening logic while ensuring compliance.

Co-authored-by: factory-droid[bot] <138933559+factory-droid[bot]@users.noreply.github.com>

internal/util/gemini_schema.go

@@ -390,6 +390,11 @@ func addEmptySchemaPlaceholder(jsonStr string) string {
 
 		// If schema has properties but none are required, add a minimal placeholder.
 		if propsVal.IsObject() && !hasRequiredProperties {
+			// DO NOT add placeholder if it's a top-level schema (parentPath is empty)
+			// or if we've already added a placeholder reason above.
+			if parentPath == "" {
+				continue
+			}
 			placeholderPath := joinPath(propsPath, "_")
 			if !gjson.Get(jsonStr, placeholderPath).Exists() {
 				jsonStr, _ = sjson.Set(jsonStr, placeholderPath+".type", "boolean")

internal/util/gemini_schema_test.go

@@ -127,8 +127,10 @@ func TestCleanJSONSchemaForAntigravity_AnyOfFlattening_SmartSelection(t *testing
 				"type": "object",
 				"description": "Accepts: null | object",
 				"properties": {
+					"_": { "type": "boolean" },
 					"kind": { "type": "string" }
-				}
+				},
+				"required": ["_"]
 			}
 		}
 	}`

internal/util/sanitize_test.go

@@ -27,6 +27,7 @@ func TestSanitizeFunctionName(t *testing.T) {
 		{"Too long (65 chars)", "this_is_a_very_long_name_that_exactly_reaches_sixty_four_charactX", "this_is_a_very_long_name_that_exactly_reaches_sixty_four_charact"},
 		{"Very long", "this_is_a_very_long_name_that_exceeds_the_sixty_four_character_limit_for_function_names", "this_is_a_very_long_name_that_exceeds_the_sixty_four_character_l"},
 		{"Starts with digit (64 chars total)", "1234567890123456789012345678901234567890123456789012345678901234", "_123456789012345678901234567890123456789012345678901234567890123"},
+		{"Starts with invalid char (64 chars total)", "!234567890123456789012345678901234567890123456789012345678901234", "_234567890123456789012345678901234567890123456789012345678901234"},
 		{"Empty", "", ""},
 		{"Single character invalid", "@", "_"},
 		{"Single character valid", "a", "a"},

internal/util/util.go

@@ -25,19 +25,26 @@ func SanitizeFunctionName(name string) string {
 	if name == "" {
 		return ""
 	}
+	
 	// Replace invalid characters with underscore
 	sanitized := functionNameSanitizer.ReplaceAllString(name, "_")
 
 	// Ensure it starts with a letter or underscore
-	first := sanitized[0]
-	if !((first >= 'a' && first <= 'z') || (first >= 'A' && first <= 'Z') || first == '_') {
-		// If it starts with an allowed character but not allowed at the beginning,
-		// we must prepend an underscore.
-		// To stay within the 64-character limit while prepending, we may need to truncate first.
-		if len(sanitized) >= 64 {
-			sanitized = sanitized[:63]
+	// Re-reading requirements: Must start with a letter or an underscore.
+	if len(sanitized) > 0 {
+		first := sanitized[0]
+		if !((first >= 'a' && first <= 'z') || (first >= 'A' && first <= 'Z') || first == '_') {
+			// If it starts with an allowed character but not allowed at the beginning (digit, dot, colon, dash),
+			// we must prepend an underscore.
+			
+			// To stay within the 64-character limit while prepending, we must truncate first.
+			if len(sanitized) >= 64 {
+				sanitized = sanitized[:63]
+			}
+			sanitized = "_" + sanitized
 		}
-		sanitized = "_" + sanitized
+	} else {
+		sanitized = "_"
 	}
 
 	// Truncate to 64 characters