fix(studio): watch external project dirs so preview ETag invalidates

Project dirs are symlinked into data/projects from anywhere on disk, but the
preview signature cache was only invalidated by Vite's watcher, whose roots
don't cover external paths. Edits hit disk while the cached ETag kept
serving 304s — the browser showed a stale preview after refresh and edits
looked lost. Register each project dir with the watcher when its signature
is first cached.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

Author: vanceingalls

packages/studio/vite.adapter.ts

@@ -92,6 +92,7 @@ export function createViteAdapter(dataDir: string, server: ViteDevServer): Studi
   };
 
   return {
+    // fallow-ignore-next-line complexity
     listProjects() {
       if (!existsSync(dataDir)) return [];
       const sessionsDir = resolve(dataDir, "../sessions");
@@ -130,6 +131,7 @@ export function createViteAdapter(dataDir: string, server: ViteDevServer): Studi
         .sort((a, b) => (a.title ?? "").localeCompare(b.title ?? ""));
     },
 
+    // fallow-ignore-next-line complexity
     resolveProject(id: string) {
       let projectDir = join(dataDir, id);
       if (!existsSync(projectDir)) {
@@ -177,6 +179,11 @@ export function createViteAdapter(dataDir: string, server: ViteDevServer): Studi
       const cacheKey = resolve(projectDir);
       const cached = projectSignatureCache.get(cacheKey);
       if (cached) return cached;
+      // Project dirs are symlinked from anywhere on disk (often outside the
+      // studio package), so Vite's default watch roots don't cover them.
+      // Without this, the signature cache never invalidates for external
+      // projects and the preview ETag serves stale 304s after edits.
+      server.watcher.add(cacheKey);
       const signature = createProjectSignature(cacheKey);
       projectSignatureCache.set(cacheKey, signature);
       return signature;
@@ -200,6 +207,7 @@ export function createViteAdapter(dataDir: string, server: ViteDevServer): Studi
       };
 
       const startTime = Date.now();
+      // fallow-ignore-next-line complexity
       (async () => {
         try {
           if (!process.env.PRODUCER_HEADLESS_SHELL_PATH) {
@@ -260,6 +268,7 @@ export function createViteAdapter(dataDir: string, server: ViteDevServer): Studi
       return null;
     },
 
+    // fallow-ignore-next-line complexity
     async listRegistryCatalog(): Promise<RegistryItem[]> {
       const registryRoot = resolve(__dirname, "../../registry");
       const items: RegistryItem[] = [];