test(webui): keep a Mini App's view URL stable across a proxy restart

Closes #255's stability criterion with evidence. The page's `localStorage` and
`IndexedDB` are keyed by its origin, so a port that moved between runs would silently
discard the page's own state. The derived port is a pure function of the plugin id, and
this asserts the property end to end: start on the derived port, close, start again from
a fresh derivation, and the view URL is identical.

Verified: pnpm typecheck:webui; the focused suite (9 cases).

Author: Fectivnfy112357

packages/webui/test/unit/miniapp-proxy.test.ts

@@ -148,6 +148,28 @@ describe('Mini App proxy', () => {
     expect(seen.at(-1)?.headers[CREDENTIAL_HEADER]).toBe(CREDENTIAL);
   });
 
+  it('keeps one plugin on the same port across a restart, so the page storage survives', async () => {
+    const derived = deriveMiniAppProxyPort('fixture.miniapp');
+    const target = {
+      pluginId: 'fixture.miniapp',
+      upstreamOrigin: `http://127.0.0.1:${upstreamPort}`,
+      credential: CREDENTIAL,
+      credentialHeader: CREDENTIAL_HEADER,
+    };
+
+    const first = await startMiniAppProxy({ target, port: derived });
+    const firstUrl = first.viewUrl;
+    await first.close();
+
+    const second = await startMiniAppProxy({ target, port: deriveMiniAppProxyPort('fixture.miniapp') });
+    try {
+      expect(second.viewUrl).toBe(firstUrl);
+      expect(second.port).toBe(derived);
+    } finally {
+      await second.close();
+    }
+  });
+
   it('derives a stable loopback port per plugin', () => {
     const first = deriveMiniAppProxyPort('fixture.miniapp');