Fix board creation failing silently on read-only filesystems (Vercel)

src/app/page.tsx

@@ -14,12 +14,13 @@ export default function HomePage() {
   // with the dev default so the server render and first client render match,
   // then corrected to the real origin after mount.
   const [baseUrl, setBaseUrl] = useState("http://localhost:4040");
+  const [error, setError] = useState<string | null>(null);
+  const [creating, setCreating] = useState(false);
   const router = useRouter();
 
   useEffect(() => {
     // window.location is only available client-side; syncing after mount keeps
     // the SSR/first-client render in agreement (no hydration mismatch).
-    // eslint-disable-next-line react-hooks/set-state-in-effect
     setBaseUrl(window.location.origin);
   }, []);
 
@@ -36,14 +37,25 @@ export default function HomePage() {
   const createBoard = async () => {
     const name = prompt("Board name:");
     if (!name) return;
-    const res = await fetch("/api/boards", {
-      method: "POST",
-      headers: { "Content-Type": "application/json" },
-      body: JSON.stringify({ name }),
-    });
-    const data = await res.json();
-    if (data.ok) {
-      router.push(`/boards/${data.data.id}`);
+    setError(null);
+    setCreating(true);
+    try {
+      const res = await fetch("/api/boards", {
+        method: "POST",
+        headers: { "Content-Type": "application/json" },
+        body: JSON.stringify({ name }),
+      });
+      const data = await res.json().catch(() => null);
+      if (res.ok && data?.ok) {
+        router.push(`/boards/${data.data.id}`);
+        return;
+      }
+      // Surface the failure instead of silently doing nothing.
+      setError(data?.error?.message || `Could not create board (HTTP ${res.status}). Please try again.`);
+    } catch {
+      setError("Could not reach the server. Check your connection and try again.");
+    } finally {
+      setCreating(false);
     }
   };
 
@@ -79,9 +91,10 @@ export default function HomePage() {
                 </button>
               ))}
             </div>
-            <Button onClick={createBoard} variant="outline" className="mt-4">
-              Create another board
+            <Button onClick={createBoard} variant="outline" className="mt-4" disabled={creating}>
+              {creating ? "Creating…" : "Create another board"}
             </Button>
+            {error && <p className="mt-3 text-sm text-destructive">{error}</p>}
           </div>
         </div>
       </div>
@@ -104,9 +117,10 @@ export default function HomePage() {
             </p>
           </div>
 
-          <Button onClick={createBoard} size="lg">
-            Create your first board
+          <Button onClick={createBoard} size="lg" disabled={creating}>
+            {creating ? "Creating…" : "Create your first board"}
           </Button>
+          {error && <p className="text-sm text-destructive">{error}</p>}
 
           <div className="text-left">
             <p className="text-sm text-muted-foreground mb-2">Or create via API:</p>

src/lib/server-utils.ts

@@ -1,6 +1,54 @@
+import fs from "fs";
 import path from "path";
 import os from "os";
 
+let cachedDataDir: string | null = null;
+
+function ensureWritableDir(dir: string): boolean {
+  try {
+    fs.mkdirSync(dir, { recursive: true });
+    fs.accessSync(dir, fs.constants.W_OK);
+    return true;
+  } catch {
+    return false;
+  }
+}
+
+/**
+ * Resolves the directory used for file-system JSON storage.
+ *
+ * Resolution order:
+ * 1. `AGENTBOARD_DATA_DIR` if set — explicit config always wins.
+ * 2. `~/.agentboard/data` when that location is writable (local/self-hosted).
+ * 3. `<os.tmpdir()>/agentboard/data` as a fallback when the home dir is
+ *    read-only — e.g. serverless platforms like Vercel, where only the temp
+ *    dir is writable. Without this, every write (createBoard, createTask, …)
+ *    throws EROFS/EACCES, the API returns 500, and the UI appears to "do
+ *    nothing." NOTE: the temp dir is ephemeral and per-instance on serverless,
+ *    so data is not durable there — a real backend is needed for persistence.
+ */
 export function getDataDir(): string {
-  return process.env.AGENTBOARD_DATA_DIR || path.join(os.homedir(), ".agentboard", "data");
+  if (process.env.AGENTBOARD_DATA_DIR) return process.env.AGENTBOARD_DATA_DIR;
+  if (cachedDataDir) return cachedDataDir;
+
+  const preferred = path.join(os.homedir(), ".agentboard", "data");
+  if (ensureWritableDir(preferred)) {
+    cachedDataDir = preferred;
+    return cachedDataDir;
+  }
+
+  const fallback = path.join(os.tmpdir(), "agentboard", "data");
+  if (ensureWritableDir(fallback)) {
+    console.warn(
+      `[agentboard] data dir ${preferred} is not writable; falling back to ${fallback}. ` +
+        `Data is ephemeral here (e.g. serverless) — set AGENTBOARD_DATA_DIR to a durable path for persistence.`,
+    );
+    cachedDataDir = fallback;
+    return cachedDataDir;
+  }
+
+  throw new Error(
+    `[agentboard] no writable data directory (tried ${preferred} and ${fallback}). ` +
+      `Set AGENTBOARD_DATA_DIR to a writable path.`,
+  );
 }