feat(preview): add 1-click start dev server button to empty state

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

@@ -174,6 +174,8 @@ export default function PreviewTab() {
     bridge.registerPreviewIframe(iframeDomRef.current, iframeSrc);
   }, [bridge, iframeSrc]);
 
+  const [isForceStarting, setIsForceStarting] = useState(false);
+
   // Determine which empty state to show.
   const emptyContent = (() => {
     if (loading && !anatomy) return <InitialLoader />;
@@ -190,7 +192,11 @@ export default function PreviewTab() {
         />
       );
     }
-    if (ensureStatus === "calling" || ensureStatus === "starting") {
+    if (
+      ensureStatus === "calling" ||
+      ensureStatus === "starting" ||
+      isForceStarting
+    ) {
       return (
         <WarmingUpState
           startedAt={undefined}
@@ -200,7 +206,19 @@ export default function PreviewTab() {
       );
     }
     // Never had a dev server — needs the AI to start one.
-    return <NotRunningState />;
+    return (
+      <NotRunningState
+        onStart={() => {
+          setIsForceStarting(true);
+          fetch(
+            `/api/projects/${projectId}/dev-server/ensure?forceStart=true`,
+            {
+              method: "POST",
+            },
+          ).catch(() => setIsForceStarting(false));
+        }}
+      />
+    );
   })();
 
   return (
@@ -421,7 +439,7 @@ function FailedState({
   );
 }
 
-function NotRunningState() {
+function NotRunningState({ onStart }: { onStart: () => void }) {
   return (
     <div style={{ textAlign: "center", maxWidth: 260 }}>
       <div
@@ -443,9 +461,25 @@ function NotRunningState() {
       </div>
       <p style={emptyTitle}>Preview not running</p>
       <p style={emptySubtext}>No dev server found on port 3000.</p>
-      <p style={{ ...emptySubtext, marginTop: 4 }}>
-        Ask the AI to start the dev server.
-      </p>
+      <button
+        onClick={onStart}
+        style={{
+          marginTop: 16,
+          background: "#18181b",
+          color: "white",
+          border: "none",
+          padding: "8px 16px",
+          borderRadius: 8,
+          fontSize: "0.8rem",
+          fontWeight: 500,
+          cursor: "pointer",
+          display: "inline-flex",
+          alignItems: "center",
+          gap: 6,
+        }}
+      >
+        ⚡ Start Dev Server
+      </button>
     </div>
   );
 }

vibn-frontend/app/api/projects/[projectId]/dev-server/ensure/route.ts

@@ -23,7 +23,7 @@ import {
 } from "@/lib/dev-container";
 
 export async function POST(
-  _req: Request,
+  request: Request,
   { params }: { params: Promise<{ projectId: string }> },
 ) {
   const { projectId } = await params;
@@ -96,7 +96,10 @@ export async function POST(
     [projectId],
   );
 
-  if (!last) {
+  const forceStart =
+    new URL(request.url).searchParams.get("forceStart") === "true";
+
+  if (!last && !forceStart) {
     return NextResponse.json({ status: "no_history" });
   }
 
@@ -111,13 +114,12 @@ export async function POST(
   }
 
   // 4. Fire restart in background — don't block the response.
-  //    The probe (up to 300s) runs in background; anatomy polling at 5s
-  //    will surface state='starting' immediately, then 'running' when ready.
+  //    If forceStart is true but we have no history, default to Next.js start command.
   const restartOpts = {
     projectId: project.id,
     projectSlug: project.slug,
-    command: last.command,
-    port: last.port,
+    command: last?.command || "next dev -H 0.0.0.0 --no-turbopack",
+    port: last?.port || 3000,
     workspace,
   };