Kept the prototype out of search engines in the Website service.

Services/Website/Sources/App/Extensions/App+Build.swift

@@ -64,6 +64,7 @@ func application(
             cacheControl: reader.cacheControl,
             compressionMinResponseSize: reader.compressionMinResponseSize,
             httpsRedirect: reader.httpsRedirect,
+            isIndexable: reader.isIndexable,
             rateLimit: reader.rateLimit,
             securityHeaders: reader.securityHeaders,
             // An unset origin leaves the pages without canonical URLs and language alternates, rather than
@@ -181,6 +182,7 @@ private func logger(
 ///   - analytics: the analytics tracker both pages embed, or `nil` to omit it.
 ///   - cacheControl: the cache-control directives applied to the served static files.
 ///   - compressionMinResponseSize: the minimum response body size, in bytes, before compression is applied.
+///   - isIndexable: whether search engines may index the site; while `false`, every response is marked `noindex`.
 ///   - httpsRedirect: the origin plain-HTTP requests are redirected to, and whether the forwarded-protocol header is trusted.
 ///   - rateLimit: the rate limit configuration, currently applied to no route.
 ///   - securityHeaders: the security headers applied to every response.
@@ -201,6 +203,7 @@ private func router(
     cacheControl: CacheControl,
     compressionMinResponseSize: Int,
     httpsRedirect: HTTPSRedirectMiddleware<AppRequestContext>.Configuration,
+    isIndexable: Bool,
     rateLimit: RateLimitMiddleware<AppRequestContext>.Configuration,
     securityHeaders: SecurityHeadersMiddleware<AppRequestContext>.Configuration,
     siteOrigin: String?,
@@ -241,6 +244,11 @@ private func router(
         await home.refresh(with: .init(from: listings))
     }
 
+    // Outermost, so the mark reaches redirects, errors, and served files alike.
+    if !isIndexable {
+        router.add(middleware: NoIndexMiddleware())
+    }
+
     router.addMiddleware {
         LogRequestsMiddleware(logLevel)
         SecurityHeadersMiddleware(

Services/Website/Sources/App/Extensions/ConfigReader+Properties.swift

@@ -264,6 +264,16 @@ package extension ConfigReader {
         )
     }
 
+    /// Whether search engines may index the site, read from the `site.indexable` key.
+    ///
+    /// Off by default: the prototype holds demo data, and a sign-in anyone can use. While off, every response is marked `noindex`.
+    var isIndexable: Bool {
+        bool(
+            forKey: .Site.indexable,
+            default: false
+        )
+    }
+
     /// The origin passkeys are bound to, read from the `passkeys.origin` key.
     var passkeysOrigin: String {
         string(

Services/Website/Sources/Library/Public/Extensions/AbsoluteConfigKey+Constants.swift

@@ -82,6 +82,11 @@ extension AbsoluteConfigKey {
         /// The absolute configuration key for the directory the static files are served from.
         public static let staticFiles: AbsoluteConfigKey = .init(.Path.staticFiles)
     }
+    /// A namespace for the site configuration keys, as absolute keys.
+    public enum Site {
+        /// The absolute configuration key for letting search engines index the site.
+        public static let indexable: AbsoluteConfigKey = .init(.Site.indexable)
+    }
     /// A namespace for the security headers configuration keys, as absolute keys.
     public enum Security {
         /// The absolute configuration key for the `Content-Security-Policy` header value.

Services/Website/Sources/Library/Public/Extensions/ConfigKey+Constants.swift

@@ -107,5 +107,7 @@ extension ConfigKey {
     public enum Site {
         /// The configuration key for the public origin the site is served at (scheme and host, no trailing slash).
         public static let origin: ConfigKey = "site.origin"
+        /// The configuration key for letting search engines index the site.
+        public static let indexable: ConfigKey = "site.indexable"
     }
 }

Services/Website/Sources/Library/Public/Middlewares/NoIndexMiddleware.swift

@@ -0,0 +1,43 @@
+import Hummingbird
+import Infrastructure
+
+/// Keeps the site out of search engines: every response — pages, files, redirects, errors — is marked `X-Robots-Tag: noindex, nofollow`.
+///
+/// A header rather than `robots.txt`, which stays open on purpose: a crawler barred from a page never reads its `noindex`, and may still
+/// list the bare URL from links elsewhere. A header also covers what carries no markup, such as the photos sellers upload.
+public struct NoIndexMiddleware<Context: RequestContext>: RouterMiddleware {
+
+    // MARK: Constants
+
+    /// The directive stamped on every response.
+    public static var directive: String { "noindex, nofollow" }
+
+    // MARK: Initializers
+
+    /// Creates the middleware.
+    public init() {}
+
+    // MARK: Methods
+
+    public func handle(
+        _ request: Request,
+        context: Context,
+        next: (Request, Context) async throws -> Response
+    ) async throws -> Response {
+        do {
+            var response = try await next(request, context)
+
+            response.headers[.robotsTag] = Self.directive
+
+            return response
+        } catch let error as HTTPError {
+            // An error thrown past this point becomes a response further out: the mark travels with it.
+            var error = error
+
+            error.headers[.robotsTag] = Self.directive
+
+            throw error
+        }
+    }
+
+}