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

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

src/utils/custom-fields.ts

@@ -46,3 +46,36 @@ export function decodeCustomFields(raw: string | null): {
     return { custom_fields: [], field_order: [] };
   }
 }
+
+/**
+ * Per-document selection of which COMPANY custom fields print on a PDF.
+ * Stored positionally (matching the `custom_<i>` keys the PDF builder emits)
+ * as a JSON array string, e.g. "[0,2]". Null/empty means "none selected".
+ */
+export function encodeSelectedCustomFields(indices: unknown): string | null {
+  const clean = normalizeIndices(indices);
+  return clean.length > 0 ? JSON.stringify(clean) : null;
+}
+
+/** Decode the stored selection (string OR defensive array) into a clean number[]. */
+export function parseSelectedCustomFields(raw: unknown): number[] {
+  if (raw == null) return [];
+  if (Array.isArray(raw)) return normalizeIndices(raw);
+  if (typeof raw !== "string" || raw.trim() === "") return [];
+  try {
+    return normalizeIndices(JSON.parse(raw));
+  } catch {
+    // Malformed JSON in a selection column degrades to "none" (expected
+    // condition — a hand-edited/legacy row should never 500 a PDF render).
+    return [];
+  }
+}
+
+function normalizeIndices(input: unknown): number[] {
+  if (!Array.isArray(input)) return [];
+  const set = new Set<number>();
+  for (const v of input) {
+    if (typeof v === "number" && Number.isInteger(v) && v >= 0) set.add(v);
+  }
+  return [...set].sort((a, b) => a - b);
+}