test(tui): pin the update-service host to a published release target

McodeUpdateService.check() calls resolveMcodeReleaseTarget() with no override,
so it reads process.platform and process.arch. release.ts publishes only
darwin-arm64, darwin-x64, linux-x64, windows-x64 and windows-arm64, and a
host outside that set — linux-arm64, for example — fails every check with
"Unsupported MCode update host" regardless of what the test asserts.

Pin both properties with Object.defineProperty in beforeEach and restore the
captured host descriptors in afterEach, so the rest of the process is
untouched. The fallback is linux-x64, a real REQUIRED_V1_TARGETS entry, so the
tests keep exercising a shipped target instead of an invented one.

Hosts that already publish keep their own platform and arch, which leaves the
win32-only install test on Windows driving the real win32 branch of
resolveMcodeInstallRoot and detectMcodeInstallSource.

Purely test infrastructure; release.ts TARGETS is unchanged, so whether
linux-arm64 should become a published target stays a product decision.

Author: s39-dev

packages/tui/test/unit/update-service.test.ts

@@ -4,10 +4,10 @@ import { existsSync, mkdirSync, mkdtempSync, readFileSync, rmSync, writeFileSync
 import { createServer } from 'node:http';
 import { tmpdir } from 'node:os';
 import path from 'node:path';
-import { afterEach, describe, expect, it, vi } from 'vitest';
+import { afterEach, beforeEach, describe, expect, it, vi } from 'vitest';
 import { McodeUpdateService, type McodeUpdateDependencies } from '../../src/update/service.js';
 import { resolveMcodeNpmDistribution } from '../../src/update/install-source.js';
-import type { McodeReleaseManifestV1 } from '../../src/update/release.js';
+import { resolveMcodeReleaseTarget, type McodeReleaseManifestV1 } from '../../src/update/release.js';
 
 const temporaryRoots: string[] = [];
 
@@ -56,6 +56,43 @@ afterEach(() => {
   }
 });
 
+// McodeUpdateService.check() resolves the release target from the running
+// process, so this file only runs on a host release.ts actually publishes for.
+// A host outside that set (linux-arm64, for example) fails every check with
+// "Unsupported MCode update host" no matter what the test asserts. Pin the
+// reported platform and arch to a real required target for the duration of
+// each test, and restore the host descriptors afterwards so the rest of the
+// process is unaffected. Hosts that already publish keep their own values,
+// which leaves the win32-only install test exercising the real win32 branch.
+const hostIsRequiredTarget = (() => {
+  try {
+    resolveMcodeReleaseTarget();
+    return true;
+  } catch {
+    return false;
+  }
+})();
+const pinnedTarget = hostIsRequiredTarget
+  ? { platform: process.platform, arch: process.arch }
+  : { platform: 'linux', arch: 'x64' };
+const hostDescriptors = {
+  platform: Object.getOwnPropertyDescriptor(process, 'platform'),
+  arch: Object.getOwnPropertyDescriptor(process, 'arch'),
+};
+
+beforeEach(() => {
+  for (const [key, value] of Object.entries(pinnedTarget)) {
+    Object.defineProperty(process, key, { value, configurable: true });
+  }
+});
+
+afterEach(() => {
+  for (const [key, descriptor] of Object.entries(hostDescriptors)) {
+    if (!descriptor) continue;
+    Object.defineProperty(process, key, descriptor);
+  }
+});
+
 describe('McodeUpdateService', () => {
   it
     .skipIf(process.platform !== 'win32')