feat(codebase): auto-select the best entry point file on load so preview isn't empty

vibn-frontend/app/[workspace]/project/[projectId]/(home)/code/page.tsx

@@ -183,6 +183,9 @@ export default function CodeTab() {
                           <GiteaFileTree
                             projectId={projectId}
                             rootPath={cb.path}
+                            autoSelect={
+                              codebases.length > 0 && cb.id === codebases[0].id
+                            }
                             selectedPath={
                               selection?.type === "file" &&
                               selection.codebaseId === cb.id

vibn-frontend/components/project/gitea-file-tree.tsx

@@ -9,7 +9,7 @@
  * Gitea's web UI on click.
  */
 
-import { useEffect, useState, useCallback } from "react";
+import { useEffect, useState, useCallback, useRef } from "react";
 import { Loader2, AlertCircle } from "lucide-react";
 import { Tree, Folder, File } from "@/components/ui/file-tree";
 import { THEME } from "@/components/project/dashboard-ui";
@@ -36,6 +36,8 @@ interface GiteaFileTreeProps {
   onSelectFile?: (path: string) => void;
   /** Path of the currently-selected file, used to highlight the row. */
   selectedPath?: string;
+  /** If true, automatically selects the best available file (e.g. page.tsx, package.json) on mount. */
+  autoSelect?: boolean;
 }
 
 // ── In-memory cache to persist tree state across tab navigations ──
@@ -48,13 +50,45 @@ const treeCache: Record<
   }
 > = {};
 
+function pickBestFile(paths: string[]): string | undefined {
+  const PREFERRED = [
+    "src/app/page.tsx",
+    "src/app/page.jsx",
+    "app/page.tsx",
+    "app/page.jsx",
+    "src/pages/index.tsx",
+    "src/pages/index.jsx",
+    "pages/index.tsx",
+    "pages/index.jsx",
+    "src/App.tsx",
+    "src/App.jsx",
+    "src/main.tsx",
+    "src/main.jsx",
+    "src/index.ts",
+    "src/index.js",
+    "package.json",
+    "README.md",
+  ];
+  for (const p of PREFERRED) {
+    if (paths.includes(p)) return p;
+  }
+  const fallbackExts = [".tsx", ".ts", ".jsx", ".js", ".json"];
+  for (const ext of fallbackExts) {
+    const found = paths.find((p) => p.endsWith(ext));
+    if (found) return found;
+  }
+  return paths[0];
+}
+
 export function GiteaFileTree({
   projectId,
   rootPath,
   onSelectFile,
   selectedPath,
+  autoSelect,
 }: GiteaFileTreeProps) {
   const cacheKey = `${projectId}::${rootPath}`;
+  const autoSelectedRef = useRef(false);
 
   const [rootItems, setRootItems] = useState<TreeItem[] | null>(() => {
     return treeCache[cacheKey]?.rootItems ?? null;
@@ -101,7 +135,22 @@ export function GiteaFileTree({
   // Load root whenever projectId or rootPath changes
   useEffect(() => {
     // If we already loaded this from cache on mount, skip fetching again
-    if (treeCache[cacheKey]) return;
+    if (treeCache[cacheKey]) {
+      if (autoSelect && !autoSelectedRef.current && onSelectFile) {
+        autoSelectedRef.current = true;
+        const cached = treeCache[cacheKey];
+        const allItems = [
+          ...cached.rootItems,
+          ...Object.values(cached.childrenByPath).flat(),
+        ];
+        const filePaths = allItems
+          .filter((i) => i.type === "file")
+          .map((i) => i.path);
+        const best = pickBestFile(filePaths);
+        if (best) onSelectFile(best);
+      }
+      return;
+    }
 
     let cancelled = false;
     setLoading(true);
@@ -184,6 +233,19 @@ export function GiteaFileTree({
           );
         }
 
+        if (autoSelect && !autoSelectedRef.current && onSelectFile) {
+          autoSelectedRef.current = true;
+          const allItems = [
+            ...items,
+            ...Object.values(newChildrenByPath).flat(),
+          ];
+          const filePaths = allItems
+            .filter((i) => i.type === "file")
+            .map((i) => i.path);
+          const best = pickBestFile(filePaths);
+          if (best) onSelectFile(best);
+        }
+
         if (cancelled) return;
 
         setRootItems(items);