feat(server): select bounded background work fairly across companies

Preserve each owner's ordering while rotating company turns between bounded batches.

Co-Authored-By: Paperclip <noreply@paperclip.ing>

server/src/services/company-work-batch.ts

@@ -0,0 +1,28 @@
+export function takeCompanyWorkBatch<T extends { companyId: string }>(
+  ordered: readonly T[],
+  limit: number,
+  afterCompany: string | null = null,
+): { entries: T[]; lastCompany: string | null } {
+  const grouped = new Map<string, T[]>();
+  for (const entry of ordered) {
+    const group = grouped.get(entry.companyId);
+    if (group) group.push(entry); else grouped.set(entry.companyId, [entry]);
+  }
+  const companies = [...grouped.keys()].sort();
+  const next = afterCompany === null ? 0 : companies.findIndex(id => id > afterCompany);
+  const start = next < 0 ? 0 : next;
+  const rotation = [...companies.slice(start), ...companies.slice(0, start)];
+  const entries: T[] = [];
+  let lastCompany = afterCompany;
+  for (let round = 0; entries.length < limit; round++) {
+    let added = false;
+    for (const companyId of rotation) {
+      const entry = grouped.get(companyId)![round];
+      if (!entry) continue;
+      entries.push(entry); lastCompany = companyId; added = true;
+      if (entries.length === limit) break;
+    }
+    if (!added) break;
+  }
+  return { entries, lastCompany };
+}