v0 Preview repeatedly breaks: duplicate Vite dev servers, port changes and SANDBOX_NOT_FOUND

I'm having a persistent problem with the Preview Pane in v0 when working on an existing GitHub-connected React/Vite application. I'm hoping someone can confirm whether this is a known issue or explain the supported configuration/workaround. The application itself is healthy and deploys/runs normally through Vercel. The problem appears specific to v0's embedded Preview/sandbox. Initially, the Preview Pane was intermittently blank. After extensive diagnosis with the v0 agent, we found that on each vm:files_synced event v0 was starting another pnpm run dev process without terminating the existing Vite dev server. This produced the following sequence: 5173 → 5174 → 5175 → 5176 Each existing server remained alive and retained its port, while the newly spawned server simply moved to the next available port. This caused two visible problems:

the Preview Pane became unreliable/blank because the active server port kept changing;
I had to sign back into the application after virtually every edit. The application uses Supabase Auth, and changing the port changes the browser origin, so the existing localStorage session is no longer available. The v0 agent verified that the application itself was healthy: Vite served the real app successfully both on localhost and the sandbox network interface, required environment variables were present, and there were no application/runtime errors. We also established that the host proxy could reach the sandbox gateway, but Preview routing was not reliably reaching the active Vite server. As a diagnostic experiment, the agent tried strictPort: true. This successfully stopped duplicate servers climbing to higher ports: the original server remained healthy on 5173 and the duplicate failed as expected. Unfortunately, v0 then surfaced that deliberately rejected duplicate as “Server failed to start”, despite the original server still running correctly. The Preview subsequently deteriorated to: 404: SANDBOX_NOT_FOUND The agent's own conclusion was that the underlying problem is v0's sandbox/dev-server lifecycle and Preview routing, not the React application itself. It also confirmed that simply cleaning up orphaned processes isn't durable: on the next file sync v0 starts another pnpm run dev without stopping the existing one. I don't want to modify the application's normal package.json dev lifecycle to kill existing processes merely to compensate for this behaviour. At the moment I'm working around the problem by opening the external Vercel branch Preview in a separate browser window. That works, but it rather defeats the purpose of v0's rapid visual Preview/iteration workflow. Has anyone encountered this with an existing Vite project in v0? In particular, is v0 expected to terminate/reuse the existing supervised dev server on file sync, and is there a supported configuration that prevents these duplicate dev-server processes? I've already spent considerable v0 agent time/credits diagnosing this, so I'd particularly appreciate guidance from Vercel/v0 staff rather than another round of application-side troubleshooting.

Sandbox not found.png

the Preview Pane became unreliable/blank because the active server port kept changing;
I had to sign back into the application after virtually every edit. The application uses Supabase Auth, and changing the port changes the browser origin, so the existing localStorage session is no longer available. The v0 agent verified that the application itself was healthy: Vite served the real app successfully both on localhost and the sandbox network interface, required environment variables were present, and there were no application/runtime errors. We also established that the host proxy could reach the sandbox gateway, but Preview routing was not reliably reaching the active Vite server. As a diagnostic experiment, the agent tried strictPort: true. This successfully stopped duplicate servers climbing to higher ports: the original server remained healthy on 5173 and the duplicate failed as expected. Unfortunately, v0 then surfaced that deliberately rejected duplicate as “Server failed to start”, despite the original server still running correctly. The Preview subsequently deteriorated to: 404: SANDBOX_NOT_FOUND The agent's own conclusion was that the underlying problem is v0's sandbox/dev-server lifecycle and Preview routing, not the React application itself. It also confirmed that simply cleaning up orphaned processes isn't durable: on the next file sync v0 starts another pnpm run dev without stopping the existing one. I don't want to modify the application's normal package.json dev lifecycle to kill existing processes merely to compensate for this behaviour. At the moment I'm working around the problem by opening the external Vercel branch Preview in a separate browser window. That works, but it rather defeats the purpose of v0's rapid visual Preview/iteration workflow. Has anyone encountered this with an existing Vite project in v0? In particular, is v0 expected to terminate/reuse the existing supervised dev server on file sync, and is there a supported configuration that prevents these duplicate dev-server processes? I've already spent considerable v0 agent time/credits diagnosing this, so I'd particularly appreciate guidance from Vercel/v0 staff rather than another round of application-side troubleshooting.

Sandbox not found.png