fix(antigravity): preserve string const constraints in tool schemas

backend/internal/pkg/antigravity/schema_cleaner.go

@@ -119,6 +119,27 @@ func cleanJSONSchemaRecursive(value any) any {
 	// 0. [NEW] 合并 allOf
 	mergeAllOf(schemaMap)
 
+	// Gemini's enum representation supports strings. Preserve string constants
+	// before the allowlist removes const, including schemas with no explicit type.
+	if constant, ok := schemaMap["const"].(string); ok {
+		values := []any{constant}
+		if existing, ok := schemaMap["enum"].([]any); ok {
+			// Both constraints apply: retain their intersection, not a wider enum.
+			values = []any{}
+			for _, value := range existing {
+				if text, ok := value.(string); ok && text == constant {
+					values = append(values, constant)
+					break
+				}
+			}
+		}
+		schemaMap["enum"] = values
+		if _, exists := schemaMap["type"]; !exists {
+			schemaMap["type"] = "string"
+		}
+		delete(schemaMap, "const")
+	}
+
 	// 1. [CRITICAL] 深度递归处理子项
 	if props, ok := schemaMap["properties"].(map[string]any); ok {
 		for _, v := range props {

backend/internal/pkg/antigravity/schema_const_test.go

@@ -0,0 +1,44 @@
+package antigravity
+
+import (
+	"encoding/json"
+	"testing"
+
+	"github.com/stretchr/testify/require"
+)
+
+func TestBuildToolsPreservesStringConst(t *testing.T) {
+	for _, tc := range []struct {
+		name   string
+		schema string
+		want   string
+	}{
+		{"typed", `{"type":"string","const":"browser"}`, `{"type":"string","enum":["browser"]}`},
+		{"inferred", `{"const":"browser"}`, `{"type":"string","enum":["browser"]}`},
+		{"empty", `{"type":"string","const":""}`, `{"type":"string","enum":[""]}`},
+		{"existing enum", `{"type":"string","const":"browser","enum":["browser","shell"]}`, `{"type":"string","enum":["browser"]}`},
+		{"conflicting enum", `{"type":"string","const":"browser","enum":["shell"]}`, `{"type":"string","enum":[]}`},
+		{"ordinary enum", `{"type":"string","enum":["browser","shell"]}`, `{"type":"string","enum":["browser","shell"]}`},
+		{"array items", `{"type":"array","items":{"type":"string","const":"browser"}}`, `{"type":"array","items":{"type":"string","enum":["browser"]}}`},
+		{"nested property named const", `{"type":"object","properties":{"const":{"const":"browser"}}}`, `{"type":"object","properties":{"const":{"type":"string","enum":["browser"]}}}`},
+		{"schema metadata", `{"type":"string","const":"browser","$schema":"https://json-schema.org/draft/2020-12/schema","description":"Tool kind"}`, `{"type":"string","enum":["browser"],"description":"Tool kind"}`},
+	} {
+		t.Run(tc.name, func(t *testing.T) {
+			var property map[string]any
+			require.NoError(t, json.Unmarshal([]byte(tc.schema), &property))
+			tools := buildTools([]ClaudeTool{{
+				Name: "dispatch",
+				InputSchema: map[string]any{
+					"type":       "object",
+					"properties": map[string]any{"action": property},
+				},
+			}})
+			require.Len(t, tools, 1)
+			require.Len(t, tools[0].FunctionDeclarations, 1)
+			properties := tools[0].FunctionDeclarations[0].Parameters["properties"].(map[string]any)
+			got, err := json.Marshal(properties["action"])
+			require.NoError(t, err)
+			require.JSONEq(t, tc.want, string(got))
+		})
+	}
+}