[rig-sampler] Add type: "string" to all-string enum schemas

skills/rig/rig.ts

@@ -272,7 +272,9 @@ function serializeSchema(schema: Schema): JsonSchemaObject {
   const withDescription = (obj: JsonSchemaObject): JsonSchemaObject =>
     description === undefined ? obj : { ...obj, description };
   if ("enum" in schema) {
-    return withDescription({ enum: schema.enum });
+    const enumValues = schema.enum as readonly unknown[];
+    const allStrings = enumValues.length > 0 && enumValues.every((v) => typeof v === "string");
+    return withDescription(allStrings ? { type: "string", enum: schema.enum } : { enum: schema.enum });
   }
   if ("items" in schema) {
     return withDescription({ type: "array", items: serializeSchema(schema.items) });

src/rig.test.ts

@@ -1002,8 +1002,15 @@ describe("toJsonSchema", () => {
   });
 
   it("converts enum schemas", () => {
-    expect(toJsonSchema(s.enum("a", "b", "c"))).toEqual({ enum: ["a", "b", "c"] });
-    expect(toJsonSchema(s.enum(["x", "y"], "A choice"))).toEqual({ enum: ["x", "y"], description: "A choice" });
+    expect(toJsonSchema(s.enum("a", "b", "c"))).toEqual({ type: "string", enum: ["a", "b", "c"] });
+    expect(toJsonSchema(s.enum(["x", "y"], "A choice"))).toEqual({ type: "string", enum: ["x", "y"], description: "A choice" });
+  });
+
+  it("adds type:string to all-string enums but not mixed enums", () => {
+    expect(toJsonSchema(s.enum("low", "medium", "high"))).toEqual({ type: "string", enum: ["low", "medium", "high"] });
+    expect(toJsonSchema(s.enum(1, 2, 3))).toEqual({ enum: [1, 2, 3] });
+    expect(toJsonSchema(s.enum("yes", 1))).toEqual({ enum: ["yes", 1] });
+    expect(toJsonSchema(s.enum())).toEqual({ enum: [] });
   });
 
   it("converts array schemas", () => {