fix(anime): restore bridge install after validation failure

- Preserve the previous install when post-swap validation fails
- Cover rollback behavior with an installer regression test

src/main/runtime/anime-bridge-installer.test.ts

@@ -1,6 +1,6 @@
 import test from 'node:test';
 import assert from 'node:assert/strict';
-import { access, mkdir, mkdtemp, readdir, rename, writeFile } from 'node:fs/promises';
+import { access, mkdir, mkdtemp, readdir, rename, rm, writeFile } from 'node:fs/promises';
 import { tmpdir } from 'node:os';
 import path from 'node:path';
 import {
@@ -288,3 +288,28 @@ test('stageBridgeUpdate commit restores the existing install when activation fai
     [],
   );
 });
+
+test('stageBridgeUpdate commit restores the existing install when post-swap validation fails', async () => {
+  const root = await tempRoot();
+  const managed = path.join(root, 'managed');
+  await writeBundle(managed, 'MExtensionServer-v1.0.5.0.jar');
+  await writeBundleMarker(managed, 'v1.0.5.0');
+  const { options } = fakeUpstream();
+  const staged = await stageBridgeUpdate({ ...options, installDir: managed, systemDirs: [] });
+  const stagedJar = path.join(`${managed}.next`, `MExtensionServer-${LATEST}.jar`);
+  await rm(stagedJar);
+
+  await assert.rejects(
+    staged.commit(),
+    /The updated anime bridge is missing its java runtime or jar/,
+  );
+
+  assert.ok(await exists(path.join(managed, 'MExtensionServer-v1.0.5.0.jar')));
+  assert.equal(await readBundleMarker(managed), 'v1.0.5.0');
+  assert.ok(await exists(`${managed}.next`));
+  assert.ok(!(await exists(stagedJar)));
+  assert.deepEqual(
+    (await readdir(root)).filter((entry) => entry.startsWith('managed.backup-')),
+    [],
+  );
+});

src/main/runtime/anime-bridge-installer.ts

@@ -324,8 +324,23 @@ export async function stageBridgeUpdate(options: EnsureBridgeOptions): Promise<S
         }
 
         const binaries = await findBundleBinaries(options.installDir);
-        if (!binaries)
-          throw new Error('The updated anime bridge is missing its java runtime or jar.');
+        if (!binaries) {
+          const validationError = new Error(
+            'The updated anime bridge is missing its java runtime or jar.',
+          );
+          try {
+            await renameImpl(options.installDir, stagingDir);
+            await renameImpl(backupDir, options.installDir);
+            backupHoldsInstall = false;
+          } catch (restoreError) {
+            throw new AggregateError(
+              [validationError, restoreError],
+              `The updated anime bridge failed validation and the previous install could not be ` +
+                `restored. The previous install remains at ${backupDir}.`,
+            );
+          }
+          throw validationError;
+        }
         await rm(backupRoot, { recursive: true, force: true });
         backupHoldsInstall = false;
         return describeInstall(binaries, options.installDir, 'managed');