feat(documents): selected-custom-fields encode/decode helpers

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

src/__tests__/selected-custom-fields.test.ts

@@ -0,0 +1,38 @@
+import { describe, it, expect } from "vitest";
+import {
+  encodeSelectedCustomFields,
+  parseSelectedCustomFields,
+} from "../utils/custom-fields";
+
+describe("selected custom fields encode/decode", () => {
+  it("encodes a non-empty index array to a JSON string", () => {
+    expect(encodeSelectedCustomFields([0, 2])).toBe("[0,2]");
+  });
+
+  it("encodes empty / non-array to null", () => {
+    expect(encodeSelectedCustomFields([])).toBeNull();
+    expect(encodeSelectedCustomFields(undefined)).toBeNull();
+    expect(encodeSelectedCustomFields("nope")).toBeNull();
+  });
+
+  it("dedupes, sorts, and drops invalid entries before encoding", () => {
+    expect(encodeSelectedCustomFields([2, 0, 2, -1, 1.5, 3])).toBe("[0,2,3]");
+  });
+
+  it("parses a stored string back to a number array", () => {
+    expect(parseSelectedCustomFields("[0,2]")).toEqual([0, 2]);
+  });
+
+  it("parses null / malformed to an empty array", () => {
+    expect(parseSelectedCustomFields(null)).toEqual([]);
+    expect(parseSelectedCustomFields("")).toEqual([]);
+    expect(parseSelectedCustomFields("{garbage")).toEqual([]);
+    expect(parseSelectedCustomFields('"x"')).toEqual([]);
+  });
+
+  it("parses already-array input (defensive) and filters invalid", () => {
+    expect(parseSelectedCustomFields([0, "1", 2, -3] as unknown)).toEqual([
+      0, 2,
+    ]);
+  });
+});