fix(ci): reuse npm downloads across lockfile updates

.github/workflows/node-ci.yml

@@ -268,11 +268,30 @@ jobs:
       - *checkout-repository
       - &set-up-node-js
         name: Set up Node.js
+        id: node
         uses: actions/setup-node@949feb2413d6458794dcd2491c4babbbce0c15c1 # v7.1.0
         with:
           node-version: ${{ matrix.node }}
           cache: npm
           cache-dependency-path: sdk/typescript/pnpm-lock.yaml
+      - &resolve-npm-cache
+        name: Resolve npm download cache
+        id: npm-cache
+        if: steps.node.outputs.cache-hit != 'true'
+        shell: bash
+        env:
+          PRIMARY_CACHE_KEY: ${{ steps.node.outputs.cache-primary-key }}
+        run: |
+          echo "path=$(npm config get cache)" >> "$GITHUB_OUTPUT"
+          echo "restore-prefix=${PRIMARY_CACHE_KEY%-*}-" >> "$GITHUB_OUTPUT"
+      - &restore-npm-cache
+        name: Restore previous npm downloads
+        if: steps.node.outputs.cache-hit != 'true'
+        uses: actions/cache/restore@55cc8345863c7cc4c66a329aec7e433d2d1c52a9 # v6.1.0
+        with:
+          path: ${{ steps.npm-cache.outputs.path }}
+          key: ${{ steps.node.outputs.cache-primary-key }}
+          restore-keys: ${{ steps.npm-cache.outputs.restore-prefix }}
       - *download-package-for-this-commit
       - name: Inspect installed package
         working-directory: sdk/typescript
@@ -556,6 +575,8 @@ jobs:
       - *checkout-repository
       - *set-up-python
       - *set-up-node-js
+      - *resolve-npm-cache
+      - *restore-npm-cache
       - *download-package-for-this-commit
       - name: Inspect installed package
         working-directory: sdk/typescript

sdk/typescript/tests-ts/cli-skills.test.ts

@@ -158,7 +158,7 @@ describe("CLI skill commands", () => {
   );
 
   test.each([0, 2])(
-    "combines inline, file, and directory context and cleans up after exit %s",
+    "combines inline, file, and directory context and cleans up after exit %d",
     async (status) => {
       const directory = await temporaryDirectory("validation-context-");
       await mkdir(join(directory, "context", "nested"), { recursive: true });

sdk/typescript/tests-ts/scan-skill-paths.test.ts

@@ -40,7 +40,7 @@ async function fixture() {
 }
 
 test.each([false, true])(
-  "disables cached skill files while preserving effective selection (profile=%s)",
+  "disables cached skill files while preserving effective selection (profile=%j)",
   async (profile) => {
     const { root, home, plugin, blocked } = await fixture();
     const unrelated = {
@@ -117,7 +117,7 @@ test("leaves plugins outside the credential home and absent skills unchanged", a
 });
 
 test.each([false, true])(
-  "preserves malformed native skill settings (profile=%s)",
+  "preserves malformed native skill settings (profile=%j)",
   async (profile) => {
     const { home, plugin } = await fixture();
     for (const skills of [

sdk/typescript/tests-ts/skeleton.test.ts

@@ -1,4 +1,6 @@
-import { readFile } from "node:fs/promises";
+import { mkdtemp, readFile, rm } from "node:fs/promises";
+import { tmpdir } from "node:os";
+import { join } from "node:path";
 import { describe, expect, test } from "bun:test";
 import { parse } from "smol-toml";
 import {
@@ -10,9 +12,11 @@ import {
 } from "../src/index.js";
 import { main } from "../src/cli.js";
 import { capture } from "./cli-fixtures.js";
+import { bashCommand, runCommand } from "./support/shell.js";
 
 interface WorkflowStep {
   name?: string;
+  id?: string;
   uses?: string;
   with?: Record<string, unknown>;
   run?: string;
@@ -206,6 +210,85 @@ describe("TypeScript package skeleton", () => {
     }
   });
 
+  test("reuses npm downloads after lockfile changes without skipping package installation", async () => {
+    const { jobs } = await workflow("node-ci.yml");
+    for (const name of ["compatibility", "windows-verify"]) {
+      const steps = jobs[name]!.steps!;
+      const setup = steps.findIndex(({ id }) => id === "node");
+      const resolver = steps.findIndex(({ id }) => id === "npm-cache");
+      const restore = steps.findIndex(({ uses }) =>
+        uses?.startsWith("actions/cache/restore@"),
+      );
+      const inspection = steps.findIndex(
+        ({ name }) => name === "Inspect installed package",
+      );
+      expect(setup).toBeGreaterThanOrEqual(0);
+      expect(setup).toBeLessThan(resolver);
+      expect(resolver).toBeLessThan(restore);
+      expect(restore).toBeLessThan(inspection);
+      expect(steps[setup]?.with?.["cache"]).toBe("npm");
+      expect(steps[resolver]?.env).toEqual({
+        PRIMARY_CACHE_KEY: "${{ steps.node.outputs.cache-primary-key }}",
+      });
+      for (const index of [resolver, restore]) {
+        expect(steps[index]?.if).toBe("steps.node.outputs.cache-hit != 'true'");
+      }
+      expect(steps[restore]?.with).toEqual({
+        path: "${{ steps.npm-cache.outputs.path }}",
+        key: "${{ steps.node.outputs.cache-primary-key }}",
+        "restore-keys": "${{ steps.npm-cache.outputs.restore-prefix }}",
+      });
+      expect(steps[inspection]).not.toHaveProperty("if");
+    }
+  });
+
+  test("npm cache fallback shares lockfile versions within each platform and architecture", async () => {
+    const { jobs } = await workflow("node-ci.yml");
+    const script = jobs["compatibility"]!.steps!.find(
+      ({ id }) => id === "npm-cache",
+    )!.run!;
+    const directory = await mkdtemp(join(tmpdir(), "npm-cache-workflow-"));
+    try {
+      for (const platform of ["Windows-x64", "Windows-arm64", "Linux-x64"]) {
+        for (const hash of ["a".repeat(64), "b".repeat(64)]) {
+          const cachePath = platform.startsWith("Windows")
+            ? "C:\\npm cache"
+            : "/tmp/npm cache";
+          const output = join(directory, "output.txt");
+          await rm(output, { force: true });
+          const result = await runCommand(
+            bashCommand(),
+            [
+              "-e",
+              "-o",
+              "pipefail",
+              "-c",
+              `npm() { test "$*" = "config get cache" && printf '%s\\n' "$TEST_NPM_CACHE"; }\n${script}`,
+            ],
+            {
+              cwd: directory,
+              env: {
+                ...process.env,
+                PRIMARY_CACHE_KEY: `node-cache-${platform}-npm-${hash}`,
+                GITHUB_OUTPUT: "output.txt",
+                TEST_NPM_CACHE: cachePath,
+              },
+            },
+          );
+          expect(result.status, result.stderr).toBe(0);
+          expect(
+            (await readFile(output, "utf8")).trim().split(/\r?\n/u),
+          ).toEqual([
+            `path=${cachePath}`,
+            `restore-prefix=node-cache-${platform}-npm-`,
+          ]);
+        }
+      }
+    } finally {
+      await rm(directory, { recursive: true, force: true });
+    }
+  });
+
   test("randomizes tests and keeps the default and Windows CI timeouts", async () => {
     const packageJson = JSON.parse(
       await readFile(new URL("../package.json", import.meta.url), "utf8"),