diff --git a/.github/workflows/refresh-community-data.yml b/.github/workflows/refresh-community-data.yml
index 7eb1c59b7..7a5e2e819 100644
--- a/.github/workflows/refresh-community-data.yml
+++ b/.github/workflows/refresh-community-data.yml
@@ -34,6 +34,10 @@ jobs:
       - uses: actions/setup-node@v7
         with:
           node-version-file: ".nvmrc"
+          cache: "npm"
+
+      - name: Install dependencies
+        run: npm ci
 
       - name: Fetch and update discussion posts
         run: node scripts/refresh-discussions.mjs
diff --git a/.github/workflows/refresh-community-sitemap.yml b/.github/workflows/refresh-community-sitemap.yml
index a11967f88..18a7d0136 100644
--- a/.github/workflows/refresh-community-sitemap.yml
+++ b/.github/workflows/refresh-community-sitemap.yml
@@ -34,6 +34,10 @@ jobs:
       - uses: actions/setup-node@v7
         with:
           node-version-file: ".nvmrc"
+          cache: "npm"
+
+      - name: Install dependencies
+        run: npm ci
 
       - name: Generate community sitemap
         run: node scripts/generate-community-sitemap.mjs
diff --git a/AGENTS.md b/AGENTS.md
index 53d97b01e..bb6ccb632 100644
--- a/AGENTS.md
+++ b/AGENTS.md
@@ -372,6 +372,22 @@ See [`ADVENTURES.md`](ADVENTURES.md). Add/extend the YAML, add per-level `*-post
 
 The `off-on-dev` org restricts third-party actions. Permitted: `actions/checkout`, `actions/cache`, `actions/setup-node`, `actions/create-github-app-token`, `JamesIves/github-pages-deploy-action`, `marocchino/sticky-pull-request-comment`, `rossjrw/pr-preview-action`, `fsfe/reuse-action`, actions owned by `off-on-dev`, actions created by GitHub, and Marketplace-verified actions. `withastro/action` and `actions/deploy-pages` are **NOT allowlisted**. Before adding a `uses:`, verify it is permitted.
 
+### Workflow convention: scripts/ require npm ci
+
+Any workflow job that invokes a script under `scripts/` via `node scripts/*.mjs` must run `npm ci` immediately after `setup-node`, before the first script step:
+
+```yaml
+- uses: actions/setup-node@v7
+  with:
+    node-version-file: ".nvmrc"
+    cache: "npm"
+
+- name: Install dependencies
+  run: npm ci
+```
+
+This is unconditional, even when the script currently uses only Node built-ins. Scripts acquire package imports over time; a workflow that skips `npm ci` breaks silently on the next scheduled run. With `cache: "npm"` a clean install takes a few seconds.
+
 ---
 
 ## Before Submitting Code
diff --git a/CLAUDE.md b/CLAUDE.md
index 96829f7db..4c5330e04 100644
--- a/CLAUDE.md
+++ b/CLAUDE.md
@@ -408,6 +408,22 @@ See [`ADVENTURES.md`](ADVENTURES.md). In brief: add/extend the YAML at `src/data
 
 The `off-on-dev` org restricts third-party actions. Permitted: `actions/checkout`, `actions/cache`, `actions/setup-node`, `actions/create-github-app-token`, `JamesIves/github-pages-deploy-action`, `marocchino/sticky-pull-request-comment`, `rossjrw/pr-preview-action`, `fsfe/reuse-action`, actions owned by `off-on-dev`, actions created by GitHub, and Marketplace-verified actions. **The official `withastro/action` and `actions/deploy-pages` are NOT allowlisted** — keep the JamesIves deploy flow. Before adding a `uses:`, verify it is permitted or use `gh`/shell.
 
+### Workflow convention: scripts/ require npm ci
+
+Any workflow job that invokes a script under `scripts/` via `node scripts/*.mjs` must run `npm ci` immediately after `setup-node`, before the first script step:
+
+```yaml
+- uses: actions/setup-node@v7
+  with:
+    node-version-file: ".nvmrc"
+    cache: "npm"
+
+- name: Install dependencies
+  run: npm ci
+```
+
+This is unconditional, even when the script currently uses only Node built-ins. Scripts acquire package imports over time; a workflow that skips `npm ci` breaks silently on the next scheduled run. With `cache: "npm"` a clean install takes a few seconds.
+
 ---
 
 ## Before Submitting Code
diff --git a/scripts/sync-adventure.mjs b/scripts/sync-adventure.mjs
index 320b27b57..cc51aefb0 100644
--- a/scripts/sync-adventure.mjs
+++ b/scripts/sync-adventure.mjs
@@ -60,9 +60,10 @@ function fail(msg) {
   process.exit(1);
 }
 
-function currentMonth() {
+export function currentMonth() {
+  const ABBR = ["JAN","FEB","MAR","APR","MAY","JUN","JUL","AUG","SEP","OCT","NOV","DEC"];
   const d = new Date();
-  return d.toLocaleString("en-GB", { month: "short" }).toUpperCase() + " " + d.getFullYear();
+  return ABBR[d.getUTCMonth()] + " " + d.getUTCFullYear();
 }
 
 function parseAdventureUrl(url) {
@@ -594,7 +595,9 @@ async function main() {
   console.log(`\nDone: ${adventureName} (live: ${activeLevels.map((l) => l.level).join(", ")}${upcomingLevels.length > 0 ? ` | upcoming: ${upcomingLevels.map((u) => u.difficulty).join(", ")}` : ""})`);
 }
 
-main().catch((err) => {
-  console.error(err);
-  process.exit(1);
-});
+if (process.argv[1] === fileURLToPath(import.meta.url)) {
+  main().catch((err) => {
+    console.error(err);
+    process.exit(1);
+  });
+}
diff --git a/src/test/scripts/sync-adventure.test.ts b/src/test/scripts/sync-adventure.test.ts
new file mode 100644
index 000000000..35b948c9b
--- /dev/null
+++ b/src/test/scripts/sync-adventure.test.ts
@@ -0,0 +1,56 @@
+// SPDX-FileCopyrightText: 2025 OffOn contributors
+// SPDX-License-Identifier: MIT
+
+/**
+ * Unit tests for currentMonth() in scripts/sync-adventure.mjs.
+ *
+ * Non-vacuous check: the old implementation used
+ *   new Date().toLocaleString("en-GB", { month: "short" }).toUpperCase()
+ * Node 26 CLDR returns "Sept" (4 letters) for September, so "SEPT 2026"
+ * fails the adventure schema regex /^[A-Z]{3} \d{4}$/.
+ *
+ * The it.each test pins the system clock to every month of the year so
+ * the suite catches a revert to toLocaleString regardless of when it runs.
+ * The old-implementation test always asserts "SEPT 2026" against the
+ * schema, providing a second revert-catch that does not depend on the clock.
+ */
+
+import { describe, it, expect, vi, afterEach } from "vitest";
+import { currentMonth } from "../../../scripts/sync-adventure.mjs";
+
+const MONTH_SCHEMA = /^[A-Z]{3} \d{4}$/;
+
+const ALL_MONTHS: [number, string][] = [
+  [0, "JAN"], [1, "FEB"], [2, "MAR"], [3, "APR"],
+  [4, "MAY"], [5, "JUN"], [6, "JUL"], [7, "AUG"],
+  [8, "SEP"], [9, "OCT"], [10, "NOV"], [11, "DEC"],
+];
+
+describe("currentMonth", () => {
+  afterEach(() => {
+    vi.useRealTimers();
+  });
+
+  it.each(ALL_MONTHS)(
+    "month %i (%s): produces correct abbreviation and passes schema regex",
+    (monthIndex, abbr) => {
+      vi.useFakeTimers();
+      vi.setSystemTime(new Date(2026, monthIndex, 15));
+      expect(currentMonth()).toBe(`${abbr} 2026`);
+      expect(currentMonth()).toMatch(MONTH_SCHEMA);
+    },
+  );
+
+  it("old toLocaleString implementation produces 'SEPT 2026' for September, failing the schema", () => {
+    // Inline the old implementation so this assertion is always true regardless
+    // of the current month. A revert of the fix causes the it.each test above
+    // to fail for September; this test makes the cause immediately legible.
+    const oldImpl = (d: Date) =>
+      d.toLocaleString("en-GB", { month: "short" }).toUpperCase() +
+      " " +
+      d.getFullYear();
+    const result = oldImpl(new Date(2026, 8, 15));
+    expect(result).toBe("SEPT 2026");
+    expect(result).not.toMatch(MONTH_SCHEMA);
+  });
+});