feat: package continuity plugin MVP docs and receipt store

plugins/continuity/src/continuity/receipt-store.mjs

@@ -0,0 +1,44 @@
+import fs from "node:fs/promises";
+import path from "node:path";
+
+function isNonEmptyString(value) {
+  return typeof value === 'string' && value.trim().length > 0;
+}
+
+export function slugifyReceiptSegment(value) {
+  if (!isNonEmptyString(value)) return '';
+  return value
+    .trim()
+    .toLowerCase()
+    .replace(/[^a-z0-9._-]+/g, '-')
+    .replace(/-+/g, '-')
+    .replace(/^-+|-+$/g, '');
+}
+
+export function buildReceiptFilename({ planId, dispatchRunId }) {
+  const planIdSafe = slugifyReceiptSegment(planId);
+  const dispatchRunIdSafe = slugifyReceiptSegment(dispatchRunId);
+  return {
+    planIdSafe,
+    dispatchRunIdSafe,
+    filename: (planIdSafe && dispatchRunIdSafe)
+      ? `receipt-${planIdSafe}-${dispatchRunIdSafe}.json`
+      : '',
+  };
+}
+
+export async function writeReceipt({ receiptDir, receipt }) {
+  if (!isNonEmptyString(receiptDir)) {
+    throw new Error('receiptDir: expected non-empty string');
+  }
+
+  const { filename, planIdSafe, dispatchRunIdSafe } = buildReceiptFilename(receipt ?? {});
+  if (!filename) {
+    throw new Error(`receipt filename segments invalid: planId=${JSON.stringify(planIdSafe)}, dispatchRunId=${JSON.stringify(dispatchRunIdSafe)}`);
+  }
+
+  await fs.mkdir(receiptDir, { recursive: true });
+  const receiptPath = path.join(receiptDir, filename);
+  await fs.writeFile(receiptPath, `${JSON.stringify(receipt, null, 2)}\n`, 'utf8');
+  return receiptPath;
+}