Improve describeSchemaType to show array item type in error messages (#132)

When a required array field is missing, the validation error now reads
'missing required field (expected array of string)' instead of
'missing required field (expected array)'. This makes repair prompts
more precise and helps the model produce the correct item type on retry.

Co-authored-by: github-actions[bot] <41898282+github-actions[bot]@users.noreply.github.com>
Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: github-actions[bot]

skills/rig/rig.ts

@@ -2306,15 +2306,16 @@ function describeSchemaType(schema: Schema): string {
   if ("nullable" in schema && schema.nullable === true) {
     return `${describeSchemaType((schema as NullableSchema).inner)} | null`;
   }
+  if ("items" in schema) {
+    const itemType = describeSchemaType((schema as ArraySchema).items);
+    return `array of ${itemType}`;
+  }
   if ("type" in schema) {
     return (schema as { type: string }).type;
   }
   if ("enum" in schema) {
     return (schema as EnumSchema).enum.map((v: Json) => JSON.stringify(v)).join(" | ");
   }
-  if ("items" in schema) {
-    return "array";
-  }
   if ("properties" in schema || "additionalProperties" in schema) {
     return "object";
   }

src/rig.test.ts

@@ -1684,14 +1684,25 @@ describe("missing required field error message", () => {
     }
   });
 
-  it("reports a missing required array field with type 'array'", () => {
+  it("reports a missing required array field with item type 'array of string'", () => {
     const schema = s.object({ items: s.array(s.string), name: s.string });
     const result = analyzeResponse(JSON.stringify({ name: "x" }), schema, "test", 1);
     expect(result.ok).toBe(false);
     if (!result.ok) {
       expect(result.error.message).toContain("missing required field");
       expect(result.error.message).toContain("$.items");
-      expect(result.error.message).toContain("array");
+      expect(result.error.message).toContain("array of string");
+    }
+  });
+
+  it("reports a missing required array-of-numbers field with item type 'array of number'", () => {
+    const schema = s.object({ scores: s.array(s.number), name: s.string });
+    const result = analyzeResponse(JSON.stringify({ name: "x" }), schema, "test", 1);
+    expect(result.ok).toBe(false);
+    if (!result.ok) {
+      expect(result.error.message).toContain("missing required field");
+      expect(result.error.message).toContain("$.scores");
+      expect(result.error.message).toContain("array of number");
     }
   });