ci: cache Rust dependencies in release Runner verification (#13194)

Cache external Rust dependencies in trusted master release verification after selecting the package-owned toolchain. Keep source compilation and all validation unconditional; restrict both restore and save to the matching master push.

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

.github/scripts/tests/release-runner-cache.test.mjs

@@ -0,0 +1,37 @@
+import test from "node:test";
+import assert from "node:assert/strict";
+import { readFileSync } from "node:fs";
+
+const workflow = readFileSync(new URL("../../workflows/release-verify.yml", import.meta.url), "utf8");
+const runner = workflow.split("  verify_paperclip_runner:")[1].split("  build:")[0];
+
+test("Runner dependency caching selects the package's pinned compiler before computing its key", () => {
+  const select = runner.indexOf("      - name: Select the pinned Runner Rust toolchain");
+  const cache = runner.indexOf("      - name: Cache Runner Rust dependencies");
+  assert.ok(select >= 0 && cache > select);
+  const setup = runner.slice(select, cache);
+  assert.match(setup, /working-directory: packages\/paperclip-runner/);
+  assert.match(setup, /rustup show active-toolchain/);
+  assert.match(setup, /echo "RUSTUP_TOOLCHAIN=\$toolchain" >> "\$GITHUB_ENV"/);
+  assert.match(runner, /uses: Swatinem\/rust-cache@[0-9a-f]{40} # v[0-9.]+/);
+  assert.match(runner, /workspaces: packages\/paperclip-runner\/runner -> target/);
+  assert.match(runner, /shared-key: release-runner-v1/);
+});
+
+test("the shared cache excludes workspace artifacts and only restores or saves the exact master-push source", () => {
+  assert.match(runner, /cache-workspace-crates: false/);
+  assert.match(runner, /cache-bin: false/);
+  const saveIf = runner.match(/^\s*save-if: (.+)$/m)?.[1];
+  assert.equal(saveIf, "${{ github.repository == 'paperclipai/paperclip' && github.event_name == 'push' && github.ref == 'refs/heads/master' && inputs.ref == github.sha }}");
+  const cacheStep = runner.split("      - name: Cache Runner Rust dependencies")[1].split("      - name: Install dependencies")[0];
+  assert.equal(cacheStep.match(/^\s*if: (.+)$/m)?.[1], saveIf);
+  assert.doesNotMatch(runner, /cache-on-failure: true|cache-all-crates: true/);
+});
+
+test("cache hits cannot bypass Runner verification", () => {
+  const verify = runner.split("      - name: Verify Paperclip Runner")[1];
+  assert.match(verify, /run: pnpm --filter @paperclipai\/paperclip-runner check:all/);
+  assert.doesNotMatch(verify, /if:|continue-on-error:/);
+  assert.ok(runner.indexOf("Cache Runner Rust dependencies") < runner.indexOf("      - name: Verify Paperclip Runner\n"));
+  assert.doesNotMatch(runner, /id-token: write|packages: write|secrets: inherit/);
+});