feat(web): integrate ecosystem social preview images

src/langbot/pkg/api/http/controller/main.py

@@ -174,9 +174,21 @@ class HTTPController:
 
         frontend_path = paths.get_frontend_path()
 
+        async def frontend_index():
+            from .social_preview import cloud_preview_html
+
+            response = await quart.send_from_directory(
+                frontend_path, 'index.html', mimetype='text/html', conditional=False
+            )
+            if quart.request.host.split(':', 1)[0].lower() == 'cloud.langbot.app':
+                response.set_data(cloud_preview_html(await response.get_data(as_text=True), quart.request.host))
+                response.headers.pop('ETag', None)
+                response.headers.pop('Last-Modified', None)
+            return response
+
         @self.quart_app.route('/')
         async def index():
-            response = await quart.send_from_directory(frontend_path, 'index.html', mimetype='text/html')
+            response = await frontend_index()
             response.headers['Cache-Control'] = 'no-cache, no-store, must-revalidate'
             response.headers['Pragma'] = 'no-cache'
             response.headers['Expires'] = '0'
@@ -207,7 +219,7 @@ class HTTPController:
                                 return response
 
                     # Fallback to index.html for SPA client-side routing
-                    response = await quart.send_from_directory(frontend_path, 'index.html', mimetype='text/html')
+                    response = await frontend_index()
                     response.headers['Cache-Control'] = 'no-cache, no-store, must-revalidate'
                     response.headers['Pragma'] = 'no-cache'
                     response.headers['Expires'] = '0'

src/langbot/pkg/api/http/controller/social_preview.py

@@ -0,0 +1,20 @@
+"""Crawler-visible preview for the hosted Cloud frontend only."""
+
+CLOUD_IMAGE = 'https://cloud.langbot.app/social/cloud-v3.png'
+
+
+def cloud_preview_html(html: str, hostname: str) -> str:
+    if hostname.split(':', 1)[0].lower() != 'cloud.langbot.app':
+        return html
+    tags = (
+        '<meta property="og:type" content="website">'
+        '<meta property="og:title" content="LangBot Cloud">'
+        '<meta property="og:description" content="Run LangBot in the cloud.">'
+        f'<meta property="og:image" content="{CLOUD_IMAGE}">'
+        '<meta property="og:image:width" content="1200">'
+        '<meta property="og:image:height" content="630">'
+        '<meta name="twitter:card" content="summary_large_image">'
+        '<meta name="twitter:title" content="LangBot Cloud">'
+        f'<meta name="twitter:image" content="{CLOUD_IMAGE}">'
+    )
+    return html.replace('</head>', tags + '</head>', 1)