Make release asset guard idempotent

scripts/release_asset_guard.js

@@ -0,0 +1,17 @@
+"use strict";
+
+const IMMUTABLE_RELEASE_ASSETS = ["cmux-macos.dmg", "appcast.xml"];
+
+function evaluateReleaseAssetGuard({ existingAssetNames, immutableAssetNames = IMMUTABLE_RELEASE_ASSETS }) {
+  const existing = new Set(existingAssetNames || []);
+  const conflicts = immutableAssetNames.filter((assetName) => existing.has(assetName));
+  return {
+    conflicts,
+    shouldSkipUpload: conflicts.length > 0,
+  };
+}
+
+module.exports = {
+  IMMUTABLE_RELEASE_ASSETS,
+  evaluateReleaseAssetGuard,
+};

scripts/release_asset_guard.test.js

@@ -0,0 +1,36 @@
+"use strict";
+
+const test = require("node:test");
+const assert = require("node:assert/strict");
+
+const {
+  IMMUTABLE_RELEASE_ASSETS,
+  evaluateReleaseAssetGuard,
+} = require("./release_asset_guard");
+
+test("skips upload when immutable assets already exist", () => {
+  const result = evaluateReleaseAssetGuard({
+    existingAssetNames: ["cmux-macos.dmg", "appcast.xml", "notes.txt"],
+  });
+
+  assert.deepEqual(result.conflicts, IMMUTABLE_RELEASE_ASSETS);
+  assert.equal(result.shouldSkipUpload, true);
+});
+
+test("allows upload when immutable assets are not present", () => {
+  const result = evaluateReleaseAssetGuard({
+    existingAssetNames: ["notes.txt", "checksums.txt"],
+  });
+
+  assert.deepEqual(result.conflicts, []);
+  assert.equal(result.shouldSkipUpload, false);
+});
+
+test("skips upload when any immutable asset would conflict", () => {
+  const result = evaluateReleaseAssetGuard({
+    existingAssetNames: ["appcast.xml"],
+  });
+
+  assert.deepEqual(result.conflicts, ["appcast.xml"]);
+  assert.equal(result.shouldSkipUpload, true);
+});