SSR manifest: vite build --app --watch embeds the previous round's client index.html #705

Follow-up to #696 (fixed in #697 for normal builds). Found while reviewing #697.

In vite build --app --watch the server environment reads the client index.html in its own buildStart. The client of the same round only writes the new page later, in generateBundle. So every round embeds the page from the round before:

round 1   embeds /src/main.ts (source page)   disk: index-CDAm_wYV.js
round 2   embeds index-CDAm_wYV.js            disk: index-DK41E1g1.js
round 3   embeds index-DK41E1g1.js            disk: index-CheYs2QK.js
→ the SSR page loads a script that is 404 and never hydrates

#697 prints a warning each round, so this is not silent, but the output is still wrong. In watch mode the two environments run at the same time, so listing client first doesn't help.

Possible fix: each client round resolves a promise in its generateBundle. The server embeds a placeholder at transform time and fills it in renderChunk / generateBundle after awaiting that promise. A client-only change also needs to rebuild (or patch) the server output.