Initial commit.

Packages/Infrastructure/Sources/Internal/Extensions/String+Separators.swift

@@ -0,0 +1,5 @@
+extension String {
+    enum Separator {
+        static let comma = ","
+    }
+}

Packages/Infrastructure/Sources/Internal/Types/FNV1aHash.swift

@@ -0,0 +1,46 @@
+import Foundation
+
+/// Hashes bytes with the FNV-1a 64-bit algorithm.
+///
+/// The hash is stable across processes and platforms, which `Hasher` deliberately is not, so it suits values that must agree between instances and survive
+/// restarts: the asset version token (``FingerprintAssets``) and the entity tags of the pre-rendered pages (`CachedHTMLResponse`).
+/// It is not cryptographic — a collision only risks serving a stale cached asset, not security.
+struct FNV1aHash {
+
+    // MARK: Properties
+
+    /// The running hash value.
+    private var hash: UInt64
+
+    // MARK: Initializers
+
+    /// Creates a hasher at the FNV-1a offset basis.
+    init() {
+        self.hash = 0xcbf2_9ce4_8422_2325
+    }
+
+    // MARK: Computed
+
+    /// The hash of everything combined so far, as a fixed-width, 16-character hexadecimal token.
+    ///
+    /// Reading it does not consume the running hash: more bytes can be combined afterwards.
+    var digest: String {
+        String(
+            format: "%016llx",
+            hash
+        )
+    }
+
+    // MARK: Functions
+
+    /// Folds the given bytes into the hash.
+    /// - Parameter bytes: the bytes to fold in.
+    mutating func combine(
+        _ bytes: some Sequence<UInt8>
+    ) {
+        for byte in bytes {
+            hash = (hash ^ UInt64(byte)) &* 0x100_0000_01b3
+        }
+    }
+
+}

Packages/Infrastructure/Sources/Public/Builders/RouteCollectionBuilder.swift

@@ -0,0 +1,46 @@
+import Hummingbird
+
+/// A result builder that collects the route collections of ``RouterController`` values into a stack.
+///
+/// Mirrors the `MiddlewareFixedTypeBuilder` Hummingbird uses for `addMiddleware`, letting controllers be listed declaratively rather than having
+/// their routes added one statement at a time.
+@resultBuilder
+public enum RouteCollectionBuilder<Context: RequestContext> {
+
+    public static func buildExpression(
+        _ controller: some RouterController<Context>
+    ) -> [RouteCollection<Context>] {
+        [controller.routes]
+    }
+
+    public static func buildBlock(
+        _ collections: [RouteCollection<Context>]...
+    ) -> [RouteCollection<Context>] {
+        collections.flatMap { $0 }
+    }
+
+    public static func buildOptional(
+        _ collections: [RouteCollection<Context>]?
+    ) -> [RouteCollection<Context>] {
+        collections ?? []
+    }
+
+    public static func buildEither(
+        first collections: [RouteCollection<Context>]
+    ) -> [RouteCollection<Context>] {
+        collections
+    }
+
+    public static func buildEither(
+        second collections: [RouteCollection<Context>]
+    ) -> [RouteCollection<Context>] {
+        collections
+    }
+
+    public static func buildArray(
+        _ collections: [[RouteCollection<Context>]]
+    ) -> [RouteCollection<Context>] {
+        collections.flatMap { $0 }
+    }
+
+}

Packages/Infrastructure/Sources/Public/Enumerations/AssetExtension.swift

@@ -0,0 +1,52 @@
+/// A file extension used by an ``Asset``.
+///
+/// Each case's raw value is the extension itself (e.g. `"css"`), which an asset appends to its file name when resolving paths.
+public enum AssetExtension: String, Sendable {
+    /// A Cascading Style Sheets file.
+    case css
+    /// A JavaScript file.
+    case js
+    /// A Portable Network Graphics image.
+    case png
+    /// A Windows icon image.
+    case ico
+    /// A Scalable Vector Graphics image.
+    case svg
+    /// A plain text file.
+    case txt
+    /// A web application manifest file.
+    case webmanifest
+    /// An Extensible Markup Language file.
+    case xml
+}
+
+// MARK: - Extensions
+
+public extension AssetExtension {
+
+    // MARK: Computed
+
+    /// The file's content type.
+    var contentType: String {
+        switch self {
+        case .css: "text/css"
+        case .js: "text/javascript"
+        case .png: "image/png"
+        case .ico: "image/vnd.microsoft.icon"
+        case .svg: "image/svg+xml"
+        case .txt: "text/plain"
+        case .webmanifest: "application/manifest+json"
+        case .xml: "application/xml"
+        }
+    }
+
+    /// The folder within the static root that holds files with this extension, if any.
+    var folder: String? {
+        switch self {
+        case .css: "css"
+        case .js: "js"
+        default: nil
+        }
+    }
+
+}

Packages/Infrastructure/Sources/Public/Extensions/HTTPFieldName+Constants.swift

@@ -0,0 +1,12 @@
+import HTTPTypes
+
+public extension HTTPField.Name {
+    /// The `Permissions-Policy` field name (not provided as a standard `HTTPField.Name`).
+    static let permissionsPolicy = Self("Permissions-Policy")!
+    /// The `Referrer-Policy` field name (not provided as a standard `HTTPField.Name`).
+    static let referrerPolicy = Self("Referrer-Policy")!
+    /// The `X-Frame-Options` field name (not provided as a standard `HTTPField.Name`).
+    static let frameOptions = Self("X-Frame-Options")!
+    /// The `X-Forwarded-For` field name (not provided as a standard `HTTPField.Name`).
+    static let xForwardedFor = Self("X-Forwarded-For")!
+}

Packages/Infrastructure/Sources/Public/Extensions/Int+Constants.swift

@@ -0,0 +1,9 @@
+extension Int {
+    /// A namespace for the rate limit's default configuration values.
+    public enum RateLimit {
+        /// The default number of requests admitted per client per window.
+        public static let limit = 5
+        /// The default window length, in seconds (1 minute).
+        public static let window = 60
+    }
+}

Packages/Infrastructure/Sources/Public/Extensions/RouterMethods+RouteCollections.swift

@@ -0,0 +1,32 @@
+import Hummingbird
+
+public extension RouterMethods {
+
+    // MARK: Methods
+    
+    /// Adds the routes of ``RouterController`` values to the router using the ``RouteCollectionBuilder`` result builder.
+    ///
+    /// Mirrors `addMiddleware`, letting controllers be listed declaratively:
+    ///
+    /// ```swift
+    /// router.addController {
+    ///     RootController<AppRequestContext>()
+    ///     HealthController<AppRequestContext>()
+    /// }
+    /// ```
+    ///
+    /// Each controller's route collection is added at the router's root, exactly as a sequence of `addRoutes(_:)` calls would.
+    /// - Parameter build: the controller stack result builder.
+    /// - Returns: the router, so calls can be chained.
+    @discardableResult
+    func addController(
+        @RouteCollectionBuilder<Context> _ build: () -> [RouteCollection<Context>]
+    ) -> Self {
+        for collection in build() {
+            addRoutes(collection)
+        }
+
+        return self
+    }
+
+}

Packages/Infrastructure/Sources/Public/Extensions/String+Constants.swift

@@ -0,0 +1,22 @@
+extension String {
+    /// A namespace for the security headers' default configuration values.
+    ///
+    /// `Strict-Transport-Security` is intentionally absent: it is only safe over HTTPS and is "sticky" in browsers, so it stays off unless explicitly
+    /// configured in production.
+    public enum Security {
+        /// The default `Content-Security-Policy`.
+        ///
+        /// Restricts every resource to the site's own origin (`default-src 'self'`), blocks plugins (`object-src 'none'`), pins the document
+        /// base URL (`base-uri 'self'`), and forbids framing (`frame-ancestors 'none'`). No inline-style exception is included, so pages must
+        /// link external stylesheets.
+        public static let contentSecurityPolicy = "default-src 'self'; object-src 'none'; base-uri 'self'; frame-ancestors 'none'"
+        /// The default `X-Content-Type-Options` (disables MIME sniffing).
+        public static let contentTypeOptions = "nosniff"
+        /// The default `X-Frame-Options` (forbids framing the page).
+        public static let frameOptions = "DENY"
+        /// The default `Referrer-Policy`.
+        public static let referrerPolicy = "strict-origin-when-cross-origin"
+        /// The default `Permissions-Policy` (denies access to powerful browser features a static site does not use).
+        public static let permissionsPolicy = "accelerometer=(), camera=(), geolocation=(), gyroscope=(), magnetometer=(), microphone=(), payment=(), usb=()"
+    }
+}

Packages/Infrastructure/Sources/Public/Methods/FingerprintAssets.swift

@@ -0,0 +1,83 @@
+import Foundation
+import Logging
+
+/// Derives a version token from the contents of the static files directory.
+///
+/// The token folds every file under the directory — its relative path and its bytes, in a stable order — into one FNV-1a digest, so it changes whenever any
+/// asset changes and agrees across the instances of a deployment. The pages append it to their asset URLs (`?v=<token>`), which lets the assets be
+/// served with a long-lived, immutable cache policy: a deploy that changes an asset changes the URLs pointing at it, so no client ever revalidates or holds a
+/// stale copy.
+public struct FingerprintAssets: Sendable {
+
+    // MARK: Properties
+
+    /// The logger unreadable files are reported to, or `nil` to skip them silently.
+    private let logger: Logger?
+
+    // MARK: Initializers
+
+    /// Creates an asset fingerprinting method.
+    /// - Parameter logger: the logger unreadable files are reported to, or `nil` (the default) to skip them silently.
+    public init(
+        logger: Logger? = nil
+    ) {
+        self.logger = logger
+    }
+
+    // MARK: Functions
+
+    /// Fingerprints the static files under the given directory.
+    ///
+    /// A file that cannot be read is reported to the ``logger`` and left out of the token, so its later changes would not bust caches — a warning there
+    /// usually points at a permissions problem in the deployment.
+    /// - Parameter path: the directory the static files are served from.
+    /// - Returns: the version token, or `nil` when the directory holds no readable files (asset URLs are then left unversioned).
+    public func callAsFunction(
+        _ path: String
+    ) -> String? {
+        let manager = FileManager.default
+
+        guard let enumerated = manager.enumerator(atPath: path) else {
+            return nil
+        }
+
+        // The path-based enumerator yields paths relative to the directory, so the token depends only on the
+        // directory's contents — never on where the directory itself lives (the URL-based enumerator standardizes
+        // symlinked bases, e.g. `/var/…` to `/private/var/…`, which would leak the absolute path into the hash).
+        var files: [String] = []
+
+        while let relativePath = enumerated.nextObject() as? String {
+            if enumerated.fileAttributes?[.type] as? FileAttributeType == .typeRegular {
+                files.append(relativePath)
+            }
+        }
+
+        var hash = FNV1aHash()
+        var hashed = false
+
+        for relativePath in files.sorted() {
+            guard let contents = manager.contents(
+                atPath: "\(path)/\(relativePath)"
+            ) else {
+                logger?.warning(
+                    "Static file could not be read while fingerprinting; the version token will not reflect it.",
+                    metadata: ["path": "\(relativePath)"]
+                )
+
+                continue
+            }
+
+            hash.combine(Array(relativePath.utf8))
+            hash.combine(contents)
+
+            hashed = true
+        }
+
+        guard hashed else {
+            return nil
+        }
+
+        return hash.digest
+    }
+
+}

Packages/Infrastructure/Sources/Public/Middlewares/LocalizationMiddleware.swift

@@ -0,0 +1,59 @@
+import Foundation
+import HTTPTypes
+import Hummingbird
+import Localization
+
+/// Resolves the visitor's preferred language and records it on the request context.
+///
+/// Placed ahead of the localized responders in the middleware chain, it reads the request's `Accept-Language` header, negotiates the best supported
+/// match (falling back to the default language), and stores it on the context's ``LocalizedRequestContext/language``.
+///
+/// The request is otherwise passed through untouched — the URL and routing are not affected — so each page is served at its existing path and varies its
+/// content by header.
+public struct LocalizationMiddleware<Context: LocalizedRequestContext> {
+
+    // MARK: Properties
+
+    /// Negotiates the request's language from its `Accept-Language` header.
+    private let negotiate: Negotiate
+
+    // MARK: Initializers
+
+    /// Creates a localization middleware that negotiates against the given bundle's String Catalog languages.
+    /// - Parameter bundle: the bundle whose String Catalog names the supported languages.
+    public init(
+        bundle: Bundle
+    ) {
+        self.negotiate = .init(bundle: bundle)
+    }
+
+}
+
+// MARK: - RouterMiddleware
+
+extension LocalizationMiddleware: RouterMiddleware {
+
+    // MARK: Functions
+
+    /// Negotiates the request's language and records it on the context before passing it down.
+    /// - Parameters:
+    ///   - request: the incoming request.
+    ///   - context: the context the request is resolved against.
+    ///   - next: the next responder in the middleware chain.
+    /// - Returns: the downstream response.
+    /// - Throws: any error thrown downstream.
+    public func handle(
+        _ request: Request,
+        context: Context,
+        next: (Request, Context) async throws -> Response
+    ) async throws -> Response {
+        var context = context
+
+        context.language = negotiate(
+            acceptLanguage: request.headers[.acceptLanguage]
+        )
+
+        return try await next(request, context)
+    }
+
+}

Packages/Infrastructure/Sources/Public/Middlewares/NotFoundMiddleware.swift

@@ -0,0 +1,74 @@
+import Elementary
+import Foundation
+import Hummingbird
+
+/// Serves a custom error page for requests that match neither a route nor a static file.
+///
+/// Placed ahead of `FileMiddleware` in the middleware chain, it catches the `.notFound` error that bubbles up when no file exists for the requested
+/// path and responds with the rendered error page and a `404 Not Found` status. The page is served in the language stored on the context by
+/// ``LocalizationMiddleware``, falling back to the default language.
+public struct NotFoundMiddleware<Context: LocalizedRequestContext> {
+
+    // MARK: Properties
+
+    /// The error page, rendered once per supported language and reused for every not-found response.
+    private let responses: LocalizedHTMLCollectionResponse
+
+    // MARK: Initializers
+
+    /// Creates a not-found middleware.
+    /// - Parameters:
+    ///   - bundle: the bundle whose String Catalog names the languages the page is rendered for.
+    ///   - document: builds the error page to render for a given locale.
+    public init<Document: HTMLDocument>(
+        bundle: Bundle,
+        document: (Locale) -> Document
+    ) {
+        self.responses = .init(
+            bundle: bundle,
+            status: .notFound,
+            document: document
+        )
+    }
+
+}
+
+// MARK: - RouterMiddleware
+
+extension NotFoundMiddleware: RouterMiddleware {
+
+    // MARK: Functions
+
+    /// Passes the request down the chain, rendering the error page if it results in a not-found response.
+    ///
+    /// Any error other than `.notFound` is rethrown unchanged.
+    /// - Parameters:
+    ///   - request: the incoming request.
+    ///   - context: the context the request is resolved against.
+    ///   - next: the next responder in the middleware chain.
+    /// - Returns: the downstream response, or the rendered error page with a `404 Not Found` status.
+    /// - Throws: any non-not-found error thrown downstream.
+    public func handle(
+        _ request: Request,
+        context: Context,
+        next: (Request, Context) async throws -> Response
+    ) async throws -> Response {
+        do {
+            return try await next(request, context)
+        }
+        catch let error {
+            guard
+                let responseError = error as? any HTTPResponseError,
+                responseError.status == .notFound
+            else {
+                throw error
+            }
+
+            return responses.response(
+                for: context.language,
+                request: request
+            )
+        }
+    }
+
+}

Packages/Infrastructure/Sources/Public/Middlewares/RateLimitMiddleware.swift

@@ -0,0 +1,291 @@
+import Foundation
+import HTTPTypes
+import Hummingbird
+import NIOCore
+import Synchronization
+
+/// Rejects a client's requests with `429 Too Many Requests` once they exceed a fixed-window rate limit.
+///
+/// Added to the routes that must not be hammered — the subscription endpoint, an unauthenticated database write — it admits up to the configured limit of
+/// requests per client per window, and answers the excess with `429 Too Many Requests` and a `Retry-After` header naming the seconds until the
+/// window resets.
+///
+/// A client is keyed by the first `X-Forwarded-For` entry when the ``Configuration`` trusts it, by the connection's remote address otherwise, and by
+/// one shared bucket when neither names the client. The counters live in memory with a bounded capacity, so a flood of distinct clients cannot grow the
+/// store without bound — and each instance of a multi-instance deployment enforces its own budget.
+public struct RateLimitMiddleware<Context: RequestContext>: Sendable {
+
+    // MARK: Properties
+
+    /// The fixed-window request counters, keyed by client.
+    private let buckets: Buckets
+
+    /// The limits the middleware enforces.
+    private let configuration: Configuration
+
+    // MARK: Initializers
+
+    /// Creates a rate-limit middleware.
+    /// - Parameter configuration: the limits the middleware enforces. Defaults to a budget suited to a form endpoint: a handful of requests per
+    ///   client per minute.
+    public init(
+        configuration: Configuration = .init()
+    ) {
+        self.buckets = .init(
+            limit: configuration.limit,
+            window: configuration.window
+        )
+        self.configuration = configuration
+    }
+
+}
+
+// MARK: - RouterMiddleware
+
+extension RateLimitMiddleware: RouterMiddleware {
+
+    // MARK: Functions
+
+    /// Passes the request down the chain while the client stays within its budget, and answers it with `429 Too Many Requests` and a `Retry-After`
+    /// header once it does not.
+    /// - Parameters:
+    ///   - request: the incoming request.
+    ///   - context: the context the request is resolved against.
+    ///   - next: the next responder in the middleware chain.
+    /// - Returns: the downstream response, or the `429` rejection.
+    /// - Throws: any error thrown downstream.
+    public func handle(
+        _ request: Request,
+        context: Context,
+        next: (Request, Context) async throws -> Response
+    ) async throws -> Response {
+        let admission = buckets.admit(
+            client(
+                for: request,
+                context: context
+            )
+        )
+
+        switch admission {
+        case .admitted:
+            return try await next(
+                request,
+                context
+            )
+        case .limited(let retryAfter):
+            var response = Response(status: .tooManyRequests)
+
+            response.headers[.retryAfter] = String(max(1, retryAfter.components.seconds))
+
+            return response
+        }
+    }
+
+}
+
+// MARK: - Helpers
+
+private extension RateLimitMiddleware {
+
+    // MARK: Methods
+
+    /// The key identifying the requesting client: the first `X-Forwarded-For` entry when trusted, the connection's remote address otherwise, and one
+    /// bucket shared by every unidentifiable client when neither is known.
+    /// - Parameters:
+    ///   - request: the incoming request.
+    ///   - context: the context the request is resolved against.
+    /// - Returns: the client key the request is counted under.
+    func client(
+        for request: Request,
+        context: Context
+    ) -> String {
+        if
+            configuration.trustForwardedFor,
+            let forwarded = request.headers[.xForwardedFor]?
+                .split(separator: ",")
+                .first?
+                .trimmingCharacters(in: .whitespaces),
+            !forwarded.isEmpty
+        {
+            return forwarded
+        }
+
+        if let address = (context as? any RemoteAddressRequestContext)?.remoteAddress {
+            return address.ipAddress
+                ?? address.description
+        }
+
+        return .unidentified
+    }
+
+}
+
+// MARK: - Buckets
+
+private extension RateLimitMiddleware {
+
+    /// The outcome of asking the ``Buckets`` store to admit a request.
+    enum Admission {
+        /// The request is within the client's budget.
+        case admitted
+        /// The client exhausted its budget; the payload is the time until its window resets.
+        case limited(retryAfter: Duration)
+    }
+
+    /// The fixed-window request counters, keyed by client.
+    ///
+    /// The counters sit behind a mutex rather than an actor: an admission is a handful of dictionary operations, so the lock is held only briefly and the
+    /// calling task never suspends — requests skip the executor hop an actor would add on every pass through the middleware.
+    final class Buckets: Sendable {
+
+        // MARK: Properties
+
+        /// The maximum number of clients tracked at once, bounding the store's memory.
+        private let capacity: Int
+
+        /// The per-client counters: the start of the client's current window and its request count.
+        private let counters: Mutex<[String: (start: ContinuousClock.Instant, count: Int)]>
+
+        /// The number of requests admitted per client per ``window``.
+        private let limit: Int
+
+        /// The length of the fixed window the ``limit`` applies to.
+        private let window: Duration
+
+        // MARK: Initializers
+
+        /// Creates a counter store.
+        /// - Parameters:
+        ///   - limit: the number of requests admitted per client per window.
+        ///   - window: the length of the fixed window the limit applies to.
+        ///   - capacity: the maximum number of clients tracked at once.
+        init(
+            limit: Int,
+            window: Duration,
+            capacity: Int = 10_000
+        ) {
+            self.capacity = capacity
+            self.counters = .init([:])
+            self.limit = limit
+            self.window = window
+        }
+
+        // MARK: Functions
+
+        /// Counts a request against the client's current window and admits it while the count stays within the limit.
+        /// - Parameter client: the key the request is counted under.
+        /// - Returns: the admission outcome.
+        func admit(
+            _ client: String
+        ) -> Admission {
+            let now = ContinuousClock.now
+
+            return counters.withLock { counters in
+                if let counter = counters[client], now < counter.start.advanced(by: window) {
+                    guard counter.count < limit else {
+                        return .limited(retryAfter: now.duration(to: counter.start.advanced(by: window)))
+                    }
+
+                    counters[client] = (counter.start, counter.count + 1)
+
+                    return .admitted
+                }
+
+                makeRoom(
+                    in: &counters,
+                    at: now
+                )
+
+                counters[client] = (now, 1)
+
+                return .admitted
+            }
+        }
+
+        // MARK: Methods
+
+        /// Keeps the store within its capacity before a new client is tracked: expired windows are dropped first, and when the store remains full, the
+        /// oldest live windows are evicted in one batch — a tenth of the capacity — so the sort that finds them runs once per batch of admissions
+        /// instead of once per request while a flood of distinct clients keeps the store full.
+        /// - Parameters:
+        ///   - counters: the counters the room is made in.
+        ///   - now: the instant the expiry is evaluated against.
+        private func makeRoom(
+            in counters: inout [String: (start: ContinuousClock.Instant, count: Int)],
+            at now: ContinuousClock.Instant
+        ) {
+            guard counters.count >= capacity else {
+                return
+            }
+
+            counters = counters.filter {
+                now < $0.value.start.advanced(by: window)
+            }
+
+            let headroom = max(1, capacity / 10)
+            let excess = counters.count - (capacity - headroom)
+
+            guard excess > 0 else {
+                return
+            }
+
+            let oldest = counters
+                .sorted { $0.value.start < $1.value.start }
+                .prefix(excess)
+
+            for counter in oldest {
+                counters.removeValue(forKey: counter.key)
+            }
+        }
+
+    }
+
+}
+
+// MARK: - Configuration
+
+extension RateLimitMiddleware {
+    /// The limits a ``RateLimitMiddleware`` enforces.
+    public struct Configuration: Sendable {
+
+        // MARK: Properties
+
+        /// The number of requests admitted per client per ``window``.
+        public let limit: Int
+
+        /// Whether a client is keyed by the first `X-Forwarded-For` entry.
+        ///
+        /// Enable it only behind a reverse proxy that sets the header — there, the connection's own address would name the proxy for every visitor,
+        /// sharing one budget across all of them. On a directly reachable server the header is client-supplied, so trusting it lets a client forge fresh keys
+        /// at will.
+        public let trustForwardedFor: Bool
+
+        /// The length of the fixed window the ``limit`` applies to.
+        public let window: Duration
+
+        // MARK: Initializers
+
+        /// Creates a rate-limit configuration.
+        /// - Parameters:
+        ///   - limit: the number of requests admitted per client per window.
+        ///   - window: the length of the fixed window the limit applies to.
+        ///   - trustForwardedFor: whether a client is keyed by the first `X-Forwarded-For` entry.
+        public init(
+            limit: Int = .RateLimit.limit,
+            window: Duration = .seconds(Int.RateLimit.window),
+            trustForwardedFor: Bool = false
+        ) {
+            self.limit = limit
+            self.trustForwardedFor = trustForwardedFor
+            self.window = window
+        }
+
+    }
+}
+
+// MARK: - String+Constants
+
+private extension String {
+    /// The bucket shared by every client the middleware cannot identify.
+    static let unidentified = "unidentified"
+}

Packages/Infrastructure/Sources/Public/Middlewares/SecurityHeadersMiddleware.swift

@@ -0,0 +1,154 @@
+import HTTPTypes
+import Hummingbird
+
+/// Stamps a set of security-related HTTP headers onto every response.
+///
+/// Placed at (or near) the top of the middleware chain, it adds the configured headers to whatever response bubbles back up — the rendered pages, the
+/// error page produced by ``NotFoundMiddleware``, and every static file served by `FileMiddleware` — so the browser applies the strict, hardened
+/// interpretation of the content instead of its lenient legacy defaults.
+///
+/// The headers are precomputed once from the ``Configuration`` at initialization and reused for every request, so the per-request cost is a handful of
+/// header copies.
+public struct SecurityHeadersMiddleware<Context: RequestContext> {
+
+    // MARK: Properties
+
+    /// The precomputed headers applied to every response.
+    private let fields: HTTPFields
+
+    // MARK: Initializers
+
+    /// Creates a security-headers middleware.
+    /// - Parameter configuration: the headers applied to every response. Defaults to a hardened baseline suitable for a static site, with
+    ///   `Strict-Transport-Security` left off (see ``Configuration``).
+    public init(
+        configuration: Configuration = .init()
+    ) {
+        self.fields = configuration.fields
+    }
+
+}
+
+// MARK: - RouterMiddleware
+
+extension SecurityHeadersMiddleware: RouterMiddleware {
+
+    // MARK: Functions
+
+    /// Passes the request down the chain and stamps the configured security headers onto the response on the way back up.
+    ///
+    /// Errors that can render themselves (`HTTPResponseError`, like the `HTTPError`s thrown by the controllers) are converted to their response
+    /// here rather than left to the router: the router converts them above the middleware chain, where the response would escape these headers.
+    /// Existing values for the same header names are replaced so downstream middleware cannot leave a weaker policy in place.
+    /// - Parameters:
+    ///   - request: the incoming request.
+    ///   - context: the context the request is resolved against.
+    ///   - next: the next responder in the middleware chain.
+    /// - Returns: the downstream response with the security headers applied.
+    /// - Throws: any downstream error that does not render as an HTTP response.
+    public func handle(
+        _ request: Request,
+        context: Context,
+        next: (Request, Context) async throws -> Response
+    ) async throws -> Response {
+        var response: Response
+
+        do {
+            response = try await next(
+                request,
+                context
+            )
+        } catch let error as any HTTPResponseError {
+            response = try error.response(
+                from: request,
+                context: context
+            )
+        }
+
+        for field in fields {
+            response.headers[field.name] = field.value
+        }
+
+        return response
+    }
+
+}
+
+// MARK: - Helpers
+
+private extension SecurityHeadersMiddleware.Configuration {
+
+    // MARK: Computed
+
+    /// The configuration expressed as the headers to apply, omitting any whose value is `nil`.
+    var fields: HTTPFields {
+        var fields = HTTPFields()
+
+        fields[.contentSecurityPolicy] = contentSecurityPolicy
+        fields[.xContentTypeOptions] = contentTypeOptions
+        fields[.frameOptions] = frameOptions
+        fields[.referrerPolicy] = referrerPolicy
+        fields[.permissionsPolicy] = permissionsPolicy
+        fields[.strictTransportSecurity] = strictTransportSecurity
+
+        return fields
+    }
+
+}
+
+// MARK: - Configuration
+
+extension SecurityHeadersMiddleware {
+    /// The set of security headers a ``SecurityHeadersMiddleware`` applies.
+    ///
+    /// Each property maps to a single response header. A `nil` value omits that header entirely, which is how `Strict-Transport-Security` stays
+    /// disabled by default: it is only safe to send over HTTPS and is "sticky" in browsers, so it must stay off in plain-HTTP development and be switched on
+    /// (via configuration) only in TLS-terminated production.
+    public struct Configuration: Sendable {
+        
+        // MARK: Properties
+        
+        /// The `Content-Security-Policy` value (controls which sources the browser will load).
+        public let contentSecurityPolicy: String?
+        /// The `X-Content-Type-Options` value (disables MIME sniffing when set to `nosniff`).
+        public let contentTypeOptions: String?
+        /// The `X-Frame-Options` value (controls whether the page may be framed).
+        public let frameOptions: String?
+        /// The `Referrer-Policy` value (controls how much referrer information is shared).
+        public let referrerPolicy: String?
+        /// The `Permissions-Policy` value (gates access to powerful browser features).
+        public let permissionsPolicy: String?
+        /// The `Strict-Transport-Security` value, or `nil` to omit the header (the default).
+        public let strictTransportSecurity: String?
+        
+        // MARK: Initializers
+        
+        /// Creates a security-headers configuration.
+        ///
+        /// Every parameter defaults to the hardened baseline defined in `String.Security`, except `strictTransportSecurity`, which defaults
+        /// to `nil` (omitted). Pass `nil` for any header to drop it from the response.
+        /// - Parameters:
+        ///   - contentSecurityPolicy: the `Content-Security-Policy` value.
+        ///   - contentTypeOptions: the `X-Content-Type-Options` value.
+        ///   - frameOptions: the `X-Frame-Options` value.
+        ///   - referrerPolicy: the `Referrer-Policy` value.
+        ///   - permissionsPolicy: the `Permissions-Policy` value.
+        ///   - strictTransportSecurity: the `Strict-Transport-Security` value, or `nil` to omit it.
+        public init(
+            contentSecurityPolicy: String? = String.Security.contentSecurityPolicy,
+            contentTypeOptions: String? = String.Security.contentTypeOptions,
+            frameOptions: String? = String.Security.frameOptions,
+            referrerPolicy: String? = String.Security.referrerPolicy,
+            permissionsPolicy: String? = String.Security.permissionsPolicy,
+            strictTransportSecurity: String? = nil
+        ) {
+            self.contentSecurityPolicy = contentSecurityPolicy
+            self.contentTypeOptions = contentTypeOptions
+            self.frameOptions = frameOptions
+            self.referrerPolicy = referrerPolicy
+            self.permissionsPolicy = permissionsPolicy
+            self.strictTransportSecurity = strictTransportSecurity
+        }
+        
+    }
+}

Packages/Infrastructure/Sources/Public/Middlewares/VaryMiddleware.swift

@@ -0,0 +1,71 @@
+import Foundation
+import HTTPTypes
+import Hummingbird
+
+/// Appends header names to the `Vary` header of every response passing through.
+///
+/// Placed just above the response-compression middleware, it marks each response as varying on `Accept-Encoding`: the static files and pre-rendered
+/// pages are served with `Cache-Control: public`, so without the signal a shared cache could store a compressed body and hand it to a client that
+/// never advertised support for the encoding.
+///
+/// Names already present on a response's `Vary` header — such as the `Accept-Language` the localized pages carry — are kept, and duplicates are not
+/// added.
+public struct VaryMiddleware<Context: RequestContext>: Sendable {
+
+    // MARK: Properties
+
+    /// The header names appended to every response's `Vary` header.
+    private let names: [String]
+
+    // MARK: Initializers
+
+    /// Creates a vary middleware.
+    /// - Parameter fields: the header names appended to every response's `Vary` header. Defaults to `Accept-Encoding`, the request header
+    ///   the response-compression middleware acts on.
+    public init(
+        fields: [HTTPField.Name] = [.acceptEncoding]
+    ) {
+        self.names = fields.map(\.rawName)
+    }
+
+}
+
+// MARK: - RouterMiddleware
+
+extension VaryMiddleware: RouterMiddleware {
+
+    // MARK: Functions
+
+    /// Passes the request down the chain and appends the configured names to the response's `Vary` header on the way back up.
+    /// - Parameters:
+    ///   - request: the incoming request.
+    ///   - context: the context the request is resolved against.
+    ///   - next: the next responder in the middleware chain.
+    /// - Returns: the downstream response with the `Vary` names applied.
+    /// - Throws: any error thrown downstream.
+    public func handle(
+        _ request: Request,
+        context: Context,
+        next: (Request, Context) async throws -> Response
+    ) async throws -> Response {
+        var response = try await next(
+            request,
+            context
+        )
+
+        var vary = response.headers[.vary]?
+            .split(separator: ",")
+            .map { $0.trimmingCharacters(in: .whitespaces) } ?? []
+
+        for name in names where !vary.contains(where: {
+            $0.caseInsensitiveCompare(name) == .orderedSame
+        }) {
+            vary.append(name)
+        }
+
+        response.headers[.vary] = vary.joined(separator: ", ")
+
+        return response
+    }
+
+}

Packages/Infrastructure/Sources/Public/Protocols/Asset.swift

@@ -0,0 +1,87 @@
+/// An asset shipped with a website: a file stored under the static files root and served by Hummingbird's `FileMiddleware` middleware.
+///
+/// A conforming asset supplies its file name and the extensions it is available with, each resolving to its own file; the protocol derives the paths from them:
+/// the file's path within the static files root and the URL path it is served at, optionally versioned to bust caches. Each file lands in its extension's own
+/// folder unless the asset names a ``folder`` of its own.
+public protocol Asset: Sendable {
+
+    // MARK: Properties
+
+    /// The folder within the static files root that holds the asset's files, or `nil` (the default) to use each extension's own folder.
+    var folder: String? { get }
+
+    /// The file extensions the asset is available with.
+    var fileExtensions: [AssetExtension] { get }
+
+    /// The asset's file name, without extension.
+    var fileName: String { get }
+
+}
+
+// MARK: - Implementations
+
+public extension Asset {
+
+    // MARK: Computed
+
+    /// The asset's files live in each extension's own folder by default.
+    var folder: String? { nil }
+
+    // MARK: Methods
+
+    /// Resolves the asset's path against the given base directory.
+    ///
+    /// - Parameters:
+    ///   - basePath: the directory the static files are served from.
+    ///   - fileExtension: the extension of the file to resolve.
+    /// - Returns: the path to the file, relative to the `basePath` path.
+    func path(
+        relativeTo basePath: String,
+        for fileExtension: AssetExtension
+    ) -> String {
+        let relativePath = relativePath(for: fileExtension)
+
+        guard !basePath.isEmpty else {
+            return relativePath
+        }
+
+        return "\(basePath)/\(relativePath)"
+    }
+
+    /// Resolves the asset's path relative to the static files root (e.g. `"css/shared.css"`).
+    ///
+    /// This also matches the URL path the file is served at by `FileMiddleware`.
+    ///
+    /// - Parameter fileExtension: the extension of the file to resolve.
+    /// - Returns: the path to the file, relative to the static files root.
+    func relativePath(
+        for fileExtension: AssetExtension
+    ) -> String {
+        let file = "\(fileName).\(fileExtension.rawValue)"
+
+        return (folder ?? fileExtension.folder)
+            .map { "\($0)/\(file)" } ?? file
+    }
+
+    /// Resolves the absolute URL path the asset is served at (e.g. `"/css/shared.css"`).
+    ///
+    /// A version token appends as a `v` query parameter (e.g. `"/css/shared.css?v=abc123"`): `FileMiddleware` ignores the query when
+    /// resolving the file, while caches key on the full URL, so a deploy that changes the assets busts every cached copy at once.
+    /// - Parameters:
+    ///   - fileExtension: the extension of the file to resolve.
+    ///   - version: the version token to append, or `nil` to leave the URL unversioned.
+    /// - Returns: the path to use in `href` and `src` attributes.
+    func urlPath(
+        for fileExtension: AssetExtension,
+        version: String? = nil
+    ) -> String {
+        let path = "/\(relativePath(for: fileExtension))"
+
+        guard let version, !version.isEmpty else {
+            return path
+        }
+
+        return "\(path)?v=\(version)"
+    }
+
+}

Packages/Infrastructure/Sources/Public/Protocols/LocalizedRequestContext.swift

@@ -0,0 +1,14 @@
+import Hummingbird
+
+/// A request context that carries the language negotiated for the request.
+///
+/// ``LocalizationMiddleware`` resolves the visitor's preferred language from the `Accept-Language` header and stores it here, so downstream
+/// controllers and middleware can serve the matching localization without re-reading the header.
+public protocol LocalizedRequestContext: RequestContext {
+
+    // MARK: Properties
+
+    /// The language identifier negotiated for the request.
+    var language: String { get set }
+
+}

Packages/Infrastructure/Sources/Public/Protocols/Page.swift

@@ -0,0 +1,207 @@
+import Elementary
+import Foundation
+
+/// A page of a website: an HTML document with the shared scaffolding assembled around the page's content.
+///
+/// A conforming page supplies its locale, its title, the stylesheets and scripts it needs, its head metadata, and its content; the protocol assembles the
+/// rest of the document around them: the viewport declaration, the summary, canonical, and social card tags, the structured data script, the analytics
+/// tracker script, and the metadata followed by the stylesheet links and the deferred script tags in the head, and the content as the body.
+public protocol Page: HTMLDocument, Sendable {
+
+    // MARK: Associated types
+
+    /// The type of the page's markup.
+    associatedtype Content: HTML
+
+    /// The type of the page's head metadata markup.
+    associatedtype Metadata: HTML
+
+    // MARK: Properties
+
+    /// The analytics tracker embedded as a deferred script in the document head, or `nil` (the default) to omit it.
+    var analytics: Analytics? { get }
+
+    /// The version token appended to the page's asset URLs, or `nil` to leave them unversioned.
+    var assetVersion: String? { get }
+
+    /// The canonical URL the page is served at, rendered as a `link rel="canonical"` tag in the document head, or `nil` (the default) to omit the tag.
+    var canonicalURL: String? { get }
+
+    /// The page's markup, rendered as the document body.
+    @HTMLBuilder
+    var content: Content { get }
+
+    /// The locale the page content is localized to.
+    var locale: Locale { get }
+
+    /// The markup placed in the document head before the ``stylesheets`` links: icon and manifest links, extra meta tags, and the like.
+    @HTMLBuilder
+    var metadata: Metadata { get }
+
+    /// The scripts loaded from the document head, in order.
+    ///
+    /// Rendered as `defer`red tags: the downloads start while the head is parsed, and the scripts still execute in order only after the
+    /// document is fully parsed — the same semantics end-of-body tags would give, minus the late download start.
+    var scripts: [any Asset] { get }
+
+    /// The card controlling the page's link previews, rendered as Open Graph and Twitter meta tags in the document head, or `nil` (the default)
+    /// to omit them.
+    var socialCard: SocialCard? { get }
+
+    /// The page's structured data, rendered as a JSON-LD script in the document head, or `nil` (the default) to omit it.
+    var structuredData: StructuredData? { get }
+
+    /// The stylesheets linked in the document head, in order.
+    var stylesheets: [any Asset] { get }
+
+    /// The page's summary, rendered as a `meta name="description"` tag in the document head, or `nil` (the default) to omit the tag.
+    var summary: String? { get }
+
+}
+
+// MARK: - Implementations
+
+public extension Page {
+    
+    // MARK: Computed
+    
+    /// The canonical URL is omitted unless the page provides one.
+    var canonicalURL: String? {
+        nil
+    }
+    
+    /// The page ``content``; the ``scripts`` load deferred from the ``head``.
+    @HTMLBuilder
+    var body: some HTML {
+        content
+    }
+    
+    /// The viewport declaration, the ``analytics`` origin preconnect hint, the ``summary``, ``canonicalURL``, and ``socialCard``
+    /// tags, the ``structuredData`` script and the ``analytics`` tracker script (when provided), and the ``metadata`` followed by the
+    /// ``stylesheets`` links and the deferred ``scripts`` tags, placed in the document head.
+    ///
+    /// The charset declaration is omitted: Elementary's `HTMLDocument` scaffolding already emits `<meta charset="UTF-8">` before this markup,
+    /// and HTML5 allows only one.
+    ///
+    /// The structured data is an inert data block — browsers never execute it, so a site's `Content-Security-Policy` does not apply to it —
+    /// that search engines read for the organization's name, logo, and profiles. The analytics tracker, by contrast, is an executable script the
+    /// policy must allow, and it is `defer`red so it never delays the page render; each behavior flag renders its `data-` attribute only when enabled.
+    /// When recorder mode is on, the session recorder script follows the tracker script, deferred as well and carrying only the website id.
+    @HTMLBuilder
+    var head: some HTML {
+        meta(
+            .name(.viewport),
+            .content("width=device-width, initial-scale=1")
+        )
+
+        // Rendered first so the cross-origin handshake starts before the parser reaches the tracker script tag.
+        if let origin = analytics?.origin {
+            link(
+                .rel("preconnect"),
+                .href(origin)
+            )
+        }
+
+        if let summary {
+            meta(
+                .name(.description),
+                .content(summary)
+            )
+        }
+        
+        if let canonicalURL {
+            link(
+                .rel("canonical"),
+                .href(canonicalURL)
+            )
+        }
+
+        if let socialCard {
+            for tag in socialCard.tags {
+                meta(
+                    .custom(
+                        name: tag.attribute.rawValue,
+                        value: tag.name.rawValue
+                    ),
+                    .content(tag.content)
+                )
+            }
+        }
+
+        if let structuredData {
+            script(.custom(
+                name: "type",
+                value: "application/ld+json"
+            )) {
+                HTMLRaw(structuredData.payload)
+            }
+        }
+
+        if let analytics {
+            script(
+                .defer,
+                .src(analytics.scriptURL)
+            ) {}
+            .attributes(contentsOf: analytics.attributes.map {
+                .custom(
+                    name: $0.name,
+                    value: $0.value
+                )
+            })
+
+            if let recorderScriptURL = analytics.recorderScriptURL {
+                script(
+                    .defer,
+                    .src(recorderScriptURL),
+                    .custom(
+                        name: "data-website-id",
+                        value: analytics.websiteID
+                    )
+                ) {}
+            }
+        }
+
+        metadata
+        
+        for file in stylesheets {
+            link(
+                .rel(.stylesheet),
+                .href(file.urlPath(
+                    for: .css,
+                    version: assetVersion
+                ))
+            )
+        }
+
+        for file in scripts {
+            script(
+                .defer,
+                .src(file.urlPath(
+                    for: .js,
+                    version: assetVersion
+                ))
+            ) {}
+        }
+    }
+    
+    /// The analytics tracker is omitted unless the page provides one.
+    var analytics: Analytics? {
+        nil
+    }
+
+    /// The social card is omitted unless the page provides one.
+    var socialCard: SocialCard? {
+        nil
+    }
+
+    /// The structured data is omitted unless the page provides one.
+    var structuredData: StructuredData? {
+        nil
+    }
+
+    /// The summary is omitted unless the page provides one.
+    var summary: String? {
+        nil
+    }
+    
+}

Packages/Infrastructure/Sources/Public/Protocols/RouterController.swift

@@ -0,0 +1,32 @@
+import Hummingbird
+
+/// A type exposing its endpoints as a route collection ready to be added to a router.
+///
+/// Conforming controllers group related endpoints behind a single ``routes`` property, so the application composes them declaratively with
+/// ``Hummingbird/RouterMethods/addController(_:)``:
+///
+/// ```swift
+/// struct HealthController<Context: RequestContext>: RouterController {
+///     var routes: RouteCollection<Context> {
+///         RouteCollection(context: Context.self)
+///             .get("health") { _, _ in HTTPResponse.Status.ok }
+///     }
+/// }
+///
+/// router.addController {
+///     HealthController<AppRequestContext>()
+/// }
+/// ```
+public protocol RouterController<Context>: Sendable {
+    
+    // MARK: Associated types
+    
+    /// The request context the controller's routes operate on.
+    associatedtype Context: RequestContext
+    
+    // MARK: Properties
+    
+    /// The collection of routes the controller exposes.
+    var routes: RouteCollection<Context> { get }
+    
+}

Packages/Infrastructure/Sources/Public/Responses/CachedHTMLResponse.swift

@@ -0,0 +1,114 @@
+import Elementary
+import HTTPTypes
+import Hummingbird
+import NIOCore
+
+/// A pre-rendered HTTP response for a fully static HTML page.
+///
+/// The document is rendered to bytes once, at initialization, and every ``response(for:)`` reuses those bytes — along with a fixed status and
+/// precomputed headers — instead of re-rendering. This suits pages whose markup never changes between requests, such as the landing page and the
+/// not-found page, avoiding a per-request Elementary render on hot paths.
+///
+/// A successful page also revalidates cheaply: its headers carry a weak entity tag derived from the rendered bytes and a `Cache-Control` that asks
+/// clients to revalidate (`no-cache`), so a repeat visit costs a `304 Not Modified` instead of a full transfer — and a deploy that changes the page
+/// changes the tag, propagating immediately.
+///
+/// ``LocalizedHTMLCollectionResponse`` builds on this type, caching one instance per supported language.
+///
+/// The body is written as an unsized stream (no `Content-Length`), mirroring `HTMLResponse`, so the response-compression middleware downstream
+/// treats it exactly as it would a freshly rendered page.
+public struct CachedHTMLResponse: Sendable {
+
+    // MARK: Properties
+
+    /// The page rendered to bytes once.
+    private let buffer: ByteBuffer
+
+    /// The weak entity tag of the rendered bytes, present on successful pages only.
+    private let eTag: String?
+
+    /// The headers applied to every response, precomputed once.
+    private let headers: HTTPFields
+
+    /// The status applied to every response.
+    private let status: HTTPResponse.Status
+
+    // MARK: Initializers
+
+    /// Renders the given document to bytes once.
+    ///
+    /// A `200 OK` page gets the revalidation headers (`ETag` and `Cache-Control`); an error page does not, since a `304 Not Modified` only
+    /// ever stands in for a success.
+    /// - Parameters:
+    ///   - status: the status applied to every response. Defaults to `.ok`.
+    ///   - additionalHeaders: extra headers merged onto every response, alongside the content type.
+    ///     Used to carry per-language signals such as `Content-Language` and `Vary`.
+    ///   - document: the static HTML document to render and cache.
+    public init(
+        status: HTTPResponse.Status = .ok,
+        additionalHeaders: HTTPFields = [:],
+        document: some HTMLDocument
+    ) {
+        let buffer = ByteBuffer(string: document.render())
+        var headers: HTTPFields = [
+            .contentType: "text/html; charset=utf-8"
+        ]
+        var eTag: String?
+
+        if status == .ok {
+            var hash = FNV1aHash()
+
+            hash.combine(buffer.readableBytesView)
+
+            eTag = "W/\"\(hash.digest)\""
+
+            headers[.eTag] = eTag
+            headers[.cacheControl] = "public, no-cache"
+        }
+
+        for field in additionalHeaders {
+            headers[field.name] = field.value
+        }
+
+        self.buffer = buffer
+        self.eTag = eTag
+        self.headers = headers
+        self.status = status
+    }
+
+    // MARK: Methods
+
+    /// Builds a response from the cached, pre-rendered bytes.
+    ///
+    /// A conditional request whose `If-None-Match` names the page's entity tag is answered with a
+    /// bodyless `304 Not Modified`. Otherwise the full page is served, mirroring the
+    /// `text/html; charset=utf-8` content type `HTMLResponse` produces and leaving the
+    /// `Content-Length` unset so small pages remain eligible for compression.
+    /// - Parameter request: the request the response answers.
+    /// - Returns: the response carrying the cached HTML body, or its `304` revalidation.
+    public func response(
+        for request: Request
+    ) -> Response {
+        if
+            let eTag,
+            request.method == .get || request.method == .head,
+            let match = request.headers[.ifNoneMatch],
+            match == "*" || match.contains(eTag)
+        {
+            return Response(
+                status: .notModified,
+                headers: headers
+            )
+        }
+
+        return Response(
+            status: status,
+            headers: headers,
+            body: .init { [buffer] writer in
+                try await writer.write(buffer)
+                try await writer.finish(nil)
+            }
+        )
+    }
+
+}

Packages/Infrastructure/Sources/Public/Responses/LocalizedHTMLCollectionResponse.swift

@@ -0,0 +1,75 @@
+import Elementary
+import Foundation
+import HTTPTypes
+import Hummingbird
+import Localization
+
+/// A per-language collection of pre-rendered HTML responses.
+///
+/// At initialization it renders the document once for each language the bundle's ``LanguageList`` reports and caches the bytes, mirroring
+/// ``CachedHTMLResponse``'s render-once model but keyed by language. Each cached response carries a `Content-Language` header and
+/// `Vary: Accept-Language`, so shared caches key on the negotiated language instead of serving one language to everyone.
+public struct LocalizedHTMLCollectionResponse: Sendable {
+
+    // MARK: Properties
+
+    /// The supported languages and default language, derived from the bundle's String Catalog.
+    private let list: LanguageList
+
+    /// The pre-rendered responses, keyed by language identifier.
+    private let responses: [String: CachedHTMLResponse]
+
+    // MARK: Initializers
+
+    /// Renders the document once per supported language.
+    /// - Parameters:
+    ///   - bundle: the bundle whose String Catalog names the languages the document is rendered for.
+    ///   - status: the status applied to every response. Defaults to `.ok`.
+    ///   - document: builds the document to render for a given locale.
+    public init<Document: HTMLDocument>(
+        bundle: Bundle,
+        status: HTTPResponse.Status = .ok,
+        document: (Locale) -> Document
+    ) {
+        self.list = .init(bundle: bundle)
+        self.responses = list.all
+            .reduce(into: [:]) { responses, language in
+                responses[language] = CachedHTMLResponse(
+                    status: status,
+                    additionalHeaders: [
+                        .contentLanguage: language,
+                        .vary: "Accept-Language",
+                    ],
+                    document: document(.init(
+                        identifier: language
+                    ))
+                )
+            }
+    }
+
+    // MARK: Methods
+
+    /// Builds the response for the given language, falling back to the default language.
+    /// - Parameters:
+    ///   - language: the negotiated language identifier.
+    ///   - request: the request the response answers, consulted for conditional revalidation.
+    /// - Returns: the cached response for the language, the default language's response when the language is unavailable, or a
+    ///   `500 Internal Server Error` if neither is cached.
+    public func response(
+        for language: String,
+        request: Request
+    ) -> Response {
+        guard
+            let response = responses[language] ?? responses[list.default]
+        else {
+            return .init(
+                status: .internalServerError
+            )
+        }
+
+        return response.response(
+            for: request
+        )
+    }
+
+}

Packages/Infrastructure/Sources/Public/Types/Analytics.swift

@@ -0,0 +1,115 @@
+import Foundation
+
+/// The Umami analytics tracker a page embeds as a deferred `<script>` in its document head.
+///
+/// The behavior flags default to on and render their `data-` attributes only when enabled, since the tracker treats an absent attribute as off.
+/// Recorder mode defaults to off; when on, the page embeds a second deferred script loading the session recorder from the tracker's origin.
+public struct Analytics: Sendable {
+
+    // MARK: Properties
+
+    /// Whether the tracker drops the URL fragment from reported pageviews, so fragment navigation does not split a page's views.
+    public let excludeHash: Bool
+
+    /// Whether the tracker honors the visitor's browser Do Not Track preference.
+    public let doNotTrack: Bool
+
+    /// The comma-delimited domains the tracker reports from; visits from any other host are ignored. Empty to report from every host.
+    public let domains: String
+
+    /// Whether the tracker collects Core Web Vitals from visitors (requires an Umami instance at v3.1 or newer).
+    public let performance: Bool
+
+    /// Whether the tracker also records visitor sessions, loading the session recorder script alongside the tracker.
+    public let recorder: Bool
+
+    /// The URL the tracker script is loaded from.
+    public let scriptURL: String
+
+    /// The analytics website identifier the tracker reports as.
+    public let websiteID: String
+
+    // MARK: Initializers
+
+    /// Creates an analytics configuration.
+    /// - Parameters:
+    ///   - scriptURL: the URL the tracker script is loaded from.
+    ///   - websiteID: the analytics website identifier the tracker reports as.
+    ///   - domains: the comma-delimited domains the tracker reports from; visits from any other host are ignored. Empty to report from every host.
+    ///   - excludeHash: whether the tracker drops the URL fragment from reported pageviews; defaults to `true`.
+    ///   - doNotTrack: whether the tracker honors the visitor's browser Do Not Track preference; defaults to `true`.
+    ///   - performance: whether the tracker collects Core Web Vitals (requires Umami v3.1 or newer); defaults to `true`.
+    ///   - recorder: whether the tracker also records visitor sessions, loading the session recorder script alongside the tracker; defaults to `false`.
+    public init(
+        scriptURL: String,
+        websiteID: String,
+        domains: String,
+        excludeHash: Bool = true,
+        doNotTrack: Bool = true,
+        performance: Bool = true,
+        recorder: Bool = false
+    ) {
+        self.scriptURL = scriptURL
+        self.websiteID = websiteID
+        self.domains = domains
+        self.excludeHash = excludeHash
+        self.doNotTrack = doNotTrack
+        self.performance = performance
+        self.recorder = recorder
+    }
+
+    // MARK: Computed
+
+    /// The tracker script's attributes: the website id and reporting domains, then each enabled behavior flag; disabled flags are omitted.
+    public var attributes: [Attribute] {
+        var attributes: [Attribute] = [
+            .init("data-website-id", value: websiteID),
+            .init("data-domains", value: domains)
+        ]
+
+        if !domains.isEmpty {
+            attributes.append(.init("data-domains", value: domains))
+        }
+
+        if excludeHash {
+            attributes.append(.init("data-exclude-hash", value: "true"))
+        }
+
+        if doNotTrack {
+            attributes.append(.init("data-do-not-track", value: "true"))
+        }
+
+        if performance {
+            attributes.append(.init("data-performance", value: "true"))
+        }
+
+        return attributes
+    }
+
+    /// The origin the tracker is served from (scheme, host, and any explicit port), derived from the ``scriptURL``; `nil` when the URL
+    /// carries no scheme or host. Rendered as a `preconnect` hint before the tracker script.
+    public var origin: String? {
+        guard
+            let url = URL(string: scriptURL),
+            let scheme = url.scheme,
+            let host = url.host
+        else {
+            return nil
+        }
+
+        let port = url.port.map { ":\($0)" } ?? ""
+
+        return "\(scheme)://\(host)\(port)"
+    }
+
+    /// The URL the session recorder script is loaded from; `nil` when ``recorder`` mode is off or no ``origin`` can be derived.
+    /// Rendered as a second deferred script carrying only the `data-website-id` attribute.
+    public var recorderScriptURL: String? {
+        guard recorder, let origin else {
+            return nil
+        }
+
+        return "\(origin)/recorder.js"
+    }
+
+}

Packages/Infrastructure/Sources/Public/Types/Analytics/AnalyticsAttribute.swift

@@ -0,0 +1,31 @@
+extension Analytics {
+    /// A name-value pair rendered as an HTML attribute.
+    ///
+    /// The ``name`` is a full `data-` attribute name applied verbatim — except inside ``Analytics/Event/properties``, where it is the bare
+    /// key the event prefixes on render.
+    public struct Attribute: Equatable, Sendable {
+
+        // MARK: Properties
+
+        /// The attribute's name.
+        public let name: String
+
+        /// The attribute's value.
+        public let value: String
+
+        // MARK: Initializers
+
+        /// Creates a tracker attribute.
+        /// - Parameters:
+        ///   - name: the attribute's name.
+        ///   - value: the attribute's value.
+        public init(
+            _ name: String,
+            value: String
+        ) {
+            self.name = name
+            self.value = value
+        }
+
+    }
+}

Packages/Infrastructure/Sources/Public/Types/Analytics/AnalyticsEvent.swift

@@ -0,0 +1,55 @@
+extension Analytics {
+    /// An interaction a page reports to the tracker, rendered as `data-` attributes on the element that carries it.
+    ///
+    /// The tracker records a click on any element carrying `data-umami-event`; each `data-umami-event-<name>` beside it becomes a property
+    /// the report can be broken down by. Reports group by ``name``, so related interactions should share one name and differ by a property.
+    public struct Event: Equatable, Sendable {
+
+        // MARK: Properties
+
+        /// The event's name, which is what a report groups by.
+        public let name: String
+
+        /// The event's properties, in declaration order, which is the order they render.
+        ///
+        /// Each ``Attribute/name`` is the bare key — `set`, not `data-umami-event-set`; ``attributes`` adds the prefix.
+        public let properties: [Attribute]
+
+        // MARK: Initializers
+
+        /// Creates an event.
+        /// - Parameters:
+        ///   - name: the event's name, which is what a report groups by.
+        ///   - properties: the event's properties as bare keys — `set`, not `data-umami-event-set` — rendered in the order written.
+        ///     Empty by default.
+        public init(
+            name: String,
+            properties: KeyValuePairs<String, String> = [:]
+        ) {
+            self.name = name
+            self.properties = properties.map {
+                .init($0.key, value: $0.value)
+            }
+        }
+
+        // MARK: Computed
+
+        /// The event's attributes — the event name, then each property — as full `data-` attribute names an element applies verbatim.
+        public var attributes: [Attribute] {
+            [.init(Constant.Name.prefix, value: name)]
+            + properties.map {
+                .init("\(Constant.Name.prefix)-\($0.name)", value: $0.value)
+            }
+        }
+
+    }
+}
+
+// MARK: - Constants
+
+private enum Constant {
+    enum Name {
+        /// The attribute name the tracker watches for, and the prefix each property renders under.
+        static let prefix = "data-umami-event"
+    }
+}

Packages/Infrastructure/Sources/Public/Types/SocialCard.swift

@@ -0,0 +1,102 @@
+/// The content of a page's link-preview card, rendered as Open Graph and Twitter meta tags in the document head.
+///
+/// The card carries the facts a link scraper reads — the page's title, summary, URL, and share image — and derives the meta ``tags`` expressing
+/// them. Scrapers require absolute URLs, so the card takes ``url`` and ``Image/url`` fully formed; composing them from an origin and a versioned
+/// asset path stays with the page providing the card.
+public struct SocialCard: Sendable {
+
+    // MARK: Properties
+
+    /// The card's share image, or `nil` to omit its tags.
+    public let image: Image?
+
+    /// The locale of the card's text, or `nil` to omit its tag.
+    ///
+    /// Open Graph specifies the `language_TERRITORY` form (e.g. `en_US`); scrapers also accept a bare language code (e.g. `en`).
+    public let locale: String?
+
+    /// The name of the site the card belongs to, or `nil` to omit its tag.
+    public let siteName: String?
+
+    /// The layout a Twitter card scraper gives the card.
+    public let style: Style
+
+    /// The card's summary, or `nil` to omit its tag.
+    public let summary: String?
+
+    /// The card's title.
+    public let title: String
+
+    /// The Open Graph type of the object the card describes.
+    public let type: String
+
+    /// The absolute URL the card's page is served at, or `nil` to omit its tag.
+    public let url: String?
+
+    // MARK: Initializers
+
+    /// Creates a link-preview card.
+    /// - Parameters:
+    ///   - title: the card's title.
+    ///   - summary: the card's summary, or `nil` (the default) to omit its tag.
+    ///   - url: the absolute URL the card's page is served at, or `nil` (the default) to omit its tag.
+    ///   - siteName: the name of the site the card belongs to, or `nil` (the default) to omit its tag.
+    ///   - locale: the locale of the card's text, ideally in Open Graph's `language_TERRITORY` form (e.g. `en_US`), or `nil` (the default)
+    ///     to omit its tag.
+    ///   - image: the card's share image, or `nil` (the default) to omit its tags.
+    ///   - type: the Open Graph type of the object the card describes. Defaults to `website`.
+    ///   - style: the layout a Twitter card scraper gives the card. Defaults to ``Style/summaryLargeImage``.
+    public init(
+        title: String,
+        summary: String? = nil,
+        url: String? = nil,
+        siteName: String? = nil,
+        locale: String? = nil,
+        image: Image? = nil,
+        type: String = "website",
+        style: Style = .summaryLargeImage
+    ) {
+        self.image = image
+        self.locale = locale
+        self.siteName = siteName
+        self.style = style
+        self.summary = summary
+        self.title = title
+        self.type = type
+        self.url = url
+    }
+
+    // MARK: Computed
+
+    /// The card's meta tags, in a stable order: the Open Graph type, site name, title, description, URL, and locale, then the image group, and
+    /// the Twitter card style last. A tag whose fact the card does not carry is left out.
+    public var tags: [Tag] {
+        let tags: [Tag?] = [
+            Tag(type, name: .type),
+            siteName.map { Tag($0, name: .siteName) },
+            Tag(title, name: .title),
+            summary.map { Tag($0, name: .description) },
+            url.map { Tag($0, name: .url) },
+            locale.map { Tag($0, name: .locale) },
+        ] + (image?.tags ?? []) + [
+            Tag(style.rawValue, name: .twitter),
+        ]
+
+        return tags.compactMap { $0 }
+    }
+
+}
+
+// MARK: - Enumerations
+
+public extension SocialCard {
+
+    /// The layout a Twitter card scraper gives a ``SocialCard``.
+    enum Style: String,  Sendable {
+        /// A compact card with a small thumbnail.
+        case summary
+        /// A card with a large image above the text.
+        case summaryLargeImage = "summary_large_image"
+    }
+
+}

Packages/Infrastructure/Sources/Public/Types/SocialCard/SocialCardImage.swift

@@ -0,0 +1,54 @@
+extension SocialCard {
+    /// The share image of a ``SocialCard``.
+    public struct Image: Sendable {
+
+        // MARK: Properties
+
+        /// The image's text for assistive technologies, or `nil` to omit it.
+        public let alt: String?
+
+        /// The image's height in pixels, letting scrapers lay the card out before fetching the image.
+        public let height: Int
+
+        /// The absolute URL the image is served at.
+        public let url: String
+
+        /// The image's width in pixels, letting scrapers lay the card out before fetching the image.
+        public let width: Int
+
+        // MARK: Initializers
+
+        /// Creates a share image.
+        /// - Parameters:
+        ///   - url: the absolute URL the image is served at.
+        ///   - width: the image's width in pixels.
+        ///   - height: the image's height in pixels.
+        ///   - alt: the image's text for assistive technologies, or `nil` (the default) to omit it.
+        public init(
+            url: String,
+            width: Int,
+            height: Int,
+            alt: String? = nil
+        ) {
+            self.alt = alt
+            self.height = height
+            self.url = url
+            self.width = width
+        }
+        
+        // MARK: Computed
+        
+        /// The image's meta tags, in a stable order: its URL, width, and height, then its alt text when it carries one.
+        public var tags: [Tag] {
+            let tags: [Tag?] = [
+                Tag(url, name: .image),
+                Tag(String(width), name: .imageWidth),
+                Tag(String(height), name: .imageHeight),
+                alt.map { Tag($0, name: .imageAlt) },
+            ]
+
+            return tags.compactMap { $0 }
+        }
+
+    }
+}

Packages/Infrastructure/Sources/Public/Types/SocialCard/SocialCardTag.swift

@@ -0,0 +1,88 @@
+extension SocialCard {
+    /// A head meta tag of a ``SocialCard``: its name and content, keyed by the attribute its ``name`` dictates.
+    public struct Tag: Equatable, Sendable {
+
+        // MARK: Properties
+
+        /// The tag's value.
+        public let content: String
+
+        /// The tag's name.
+        public let name: Name
+        
+        // MARK: Initializers
+
+        /// Creates a head meta tag.
+        /// - Parameters:
+        ///   - content: the tag's value.
+        ///   - name: the tag's name, dictating the attribute the tag is keyed by.
+        public init(
+            _ content: String,
+            name: Name
+        ) {
+            self.content = content
+            self.name = name
+        }
+
+        // MARK: Computed
+
+        /// The attribute the tag is keyed by, dictated by its ``name``.
+        public var attribute: Attribute {
+            name.attribute
+        }
+
+    }
+}
+
+// MARK: - Enumerations
+
+extension SocialCard.Tag {
+
+    /// The meta attribute a ``SocialCard/Tag`` is keyed by, named by its raw value.
+    public enum Attribute: String, Sendable {
+        /// The `name` attribute, keying the Twitter tags.
+        case name
+        /// The `property` attribute, keying the Open Graph tags.
+        case property
+    }
+
+    /// The name of a ``SocialCard/Tag``, carried in its raw value.
+    public enum Name: String, Sendable {
+        /// The `og:description` tag, carrying the card's summary.
+        case description = "og:description"
+        /// The `og:image` tag, carrying the share image's absolute URL.
+        case image = "og:image"
+        /// The `og:image:alt` tag, carrying the share image's text for assistive technologies.
+        case imageAlt = "og:image:alt"
+        /// The `og:image:height` tag, carrying the share image's height in pixels.
+        case imageHeight = "og:image:height"
+        /// The `og:image:width` tag, carrying the share image's width in pixels.
+        case imageWidth = "og:image:width"
+        /// The `og:locale` tag, carrying the locale of the card's text.
+        case locale = "og:locale"
+        /// The `og:site_name` tag, carrying the name of the site the card belongs to.
+        case siteName = "og:site_name"
+        /// The `og:title` tag, carrying the card's title.
+        case title = "og:title"
+        /// The `twitter:card` tag, carrying the layout a Twitter card scraper gives the card.
+        case twitter = "twitter:card"
+        /// The `og:type` tag, carrying the Open Graph type of the object the card describes.
+        case type = "og:type"
+        /// The `og:url` tag, carrying the absolute URL the card's page is served at.
+        case url = "og:url"
+    }
+
+}
+
+// MARK: - Implementations
+
+public extension SocialCard.Tag.Name {
+
+    // MARK: Computed
+
+    /// The attribute keying a tag with this name: `property` for the Open Graph names, `name` for the Twitter ones.
+    var attribute: SocialCard.Tag.Attribute {
+        self == .twitter ? .name : .property
+    }
+
+}

Packages/Infrastructure/Sources/Public/Types/StructuredData.swift

@@ -0,0 +1,106 @@
+/// The structured data of a page, rendered as a JSON-LD script in the document head.
+///
+/// The data is a graph of schema.org ``Node`` values — each a ``Node/type``, an optional ``Node/id``, and ``Property`` values in render
+/// order — and derives the ``payload`` embedding them for the search engines that read it. A page either composes the nodes of its own
+/// shape directly, or uses ``init(name:url:logo:profiles:)`` for the site-wide pair every page shares.
+///
+/// Search engines require absolute URLs, so a node takes its URLs fully formed; composing them from an origin and a versioned asset path stays with the
+/// page providing the data.
+public struct StructuredData: Equatable, Sendable {
+
+    // MARK: Properties
+
+    /// The schema.org nodes of the data's graph, in the order they render.
+    public let nodes: [Node]
+
+    // MARK: Initializers
+
+    /// Creates structured data from the nodes of its graph.
+    /// - Parameter nodes: the schema.org nodes of the data's graph, in the order they render.
+    public init(
+        nodes: [Node]
+    ) {
+        self.nodes = nodes
+    }
+
+    // MARK: Computed
+
+    /// The minified JSON-LD payload: the schema.org `@context`, and the ``nodes`` in a `@graph`.
+    ///
+    /// The values are rendered as JSON string literals with `<` escaped as well, so a value can never close the `script` tag embedding
+    /// the payload.
+    public var payload: String {
+        #"{"@context":"https://schema.org","@graph":[\#(fragments)]}"#
+    }
+
+}
+
+// MARK: - Initializers
+
+public extension StructuredData {
+
+    /// Creates the site-wide structured data: an `Organization` node carrying the name, URL, logo, and profiles, and a `WebSite` node
+    /// carrying the name and URL and referencing the organization as its `publisher`. The nodes are linked through an `@id` derived
+    /// from the URL, so search engines read the site as published by the organization rather than as two unrelated assertions.
+    /// A property whose fact the data does not carry is left out.
+    /// - Parameters:
+    ///   - name: the name of the organization and the site.
+    ///   - url: the absolute URL the site is served at.
+    ///   - logo: the absolute URL of the organization's logo, or `nil` (the default) to omit its property.
+    ///   - profiles: the absolute URLs of the organization's public profiles, or empty (the default) to omit their property.
+    init(
+        name: String,
+        url: String,
+        logo: String? = nil,
+        profiles: [String] = []
+    ) {
+        let id = url + "#organization"
+
+        var organization: [Property] = [
+            .init(.name, value: .string(name)),
+            .init(.url, value: .string(url)),
+        ]
+
+        if let logo {
+            organization.append(.init(.logo, value:.string(logo)))
+        }
+
+        if !profiles.isEmpty {
+            organization.append(.init(
+                .sameAs,
+                value: .array(profiles.map(Value.string))
+            ))
+        }
+
+        self.init(nodes: [
+            .init(
+                type: .organization,
+                id: id,
+                properties: organization
+            ),
+            .init(
+                type: .website,
+                properties: [
+                    .init(.name, value: .string(name)),
+                    .init(.url, value: .string(url)),
+                    .init(.publisher, value: .reference(id)),
+                ]
+            ),
+        ])
+    }
+
+}
+
+// MARK: - Helpers
+
+private extension StructuredData {
+
+    // MARK: Computed
+
+    var fragments: String {
+        nodes
+            .map(\.fragment)
+            .joined(separator: .Separator.comma)
+    }
+
+}

Packages/Infrastructure/Sources/Public/Types/StructuredData/StructuredDataNode.swift

@@ -0,0 +1,92 @@
+extension StructuredData {
+    /// A schema.org node of a ``StructuredData`` graph: its type, its optional identifier, and its properties.
+    public struct Node: Equatable, Sendable {
+
+        // MARK: Properties
+
+        /// The node's identifier, rendered as its `@id` property, or `nil` to omit it.
+        ///
+        /// Another node references this node through ``Value/reference(_:)`` with the same identifier.
+        public let id: String?
+
+        /// The node's properties, in the order they render after the type and identifier.
+        public let properties: [Property]
+
+        /// The node's schema.org type (e.g. ``Kind/organization``), rendered as its `@type` property.
+        public let type: Kind
+
+        // MARK: Initializers
+
+        /// Creates a node.
+        /// - Parameters:
+        ///   - type: the node's schema.org type (e.g. ``Kind/organization``).
+        ///   - id: the node's identifier, or `nil` (the default) to omit it.
+        ///   - properties: the node's properties, in the order they render.
+        public init(
+            type: Kind,
+            id: String? = nil,
+            properties: [Property]
+        ) {
+            self.id = id
+            self.properties = properties
+            self.type = type
+        }
+
+        // MARK: Computed
+
+        /// The node's minified JSON object: the `@type`, the `@id` (when the node carries one), and the ``properties`` in order.
+        var fragment: String {
+            var members = [#""@type":\#(Value.literal(type.rawValue))"#]
+
+            if let id {
+                members.append(#""@id":\#(Value.literal(id))"#)
+            }
+
+            members += properties.map(\.fragment)
+
+            return "{\(members.joined(separator: .Separator.comma))}"
+        }
+
+    }
+}
+
+// MARK: - Structures
+
+extension StructuredData.Node {
+    /// The schema.org type of a ``StructuredData/Node``.
+    ///
+    /// Schema.org's vocabulary is open, so the kind is a typed string rather than a closed enumeration: the kinds every service shares
+    /// come as constants, a service declares the kinds its own node shapes need in an extension, and a one-off kind can be spelled as a
+    /// string literal.
+    public struct Kind: Equatable, ExpressibleByStringLiteral, Sendable {
+
+        // MARK: Properties
+
+        /// The type as it renders in the payload.
+        public let rawValue: String
+
+        // MARK: Initializers
+
+        /// Creates a kind.
+        /// - Parameter rawValue: the type as it renders in the payload.
+        public init(_ rawValue: String) {
+            self.rawValue = rawValue
+        }
+
+        /// Creates a kind from a string literal.
+        /// - Parameter value: the type as it renders in the payload.
+        public init(stringLiteral value: String) {
+            self.init(value)
+        }
+
+    }
+}
+
+// MARK: - Constants
+
+public extension StructuredData.Node.Kind {
+    /// An organization, e.g. the one publishing a website.
+    static let organization: Self = "Organization"
+    /// A website.
+    static let website: Self = "WebSite"
+}

Packages/Infrastructure/Sources/Public/Types/StructuredData/StructuredDataProperty.swift

@@ -0,0 +1,82 @@
+extension StructuredData {
+    /// A named property of a ``Node``, in the position it renders.
+    public struct Property: Equatable, Sendable {
+
+        // MARK: Properties
+
+        /// The property's schema.org name (e.g. `sameAs`).
+        public let name: Name
+
+        /// The property's value.
+        public let value: Value
+
+        // MARK: Initializers
+
+        /// Creates a property.
+        /// - Parameters:
+        ///   - name: the property's schema.org name (e.g. `sameAs`).
+        ///   - value: the property's value.
+        public init(
+            _ name: Name,
+            value: Value
+        ) {
+            self.name = name
+            self.value = value
+        }
+
+        // MARK: Computed
+
+        /// The property's minified JSON member: its name and its rendered value.
+        var fragment: String {
+            #"\#(Value.literal(name.rawValue)):\#(value.fragment)"#
+        }
+
+    }
+}
+
+// MARK: - Structures
+
+extension StructuredData.Property {
+    /// The schema.org name of a ``StructuredData/Property``.
+    ///
+    /// Schema.org's vocabulary is open, so the name is a typed string rather than a closed enumeration: the names every service shares
+    /// come as constants, a service declares the names its own node shapes need in an extension, and a one-off name can be spelled as a
+    /// string literal.
+    public struct Name: Equatable, ExpressibleByStringLiteral, Sendable {
+
+        // MARK: Properties
+
+        /// The name as it renders in the payload.
+        public let rawValue: String
+
+        // MARK: Initializers
+
+        /// Creates a name.
+        /// - Parameter rawValue: the name as it renders in the payload.
+        public init(_ rawValue: String) {
+            self.rawValue = rawValue
+        }
+
+        /// Creates a name from a string literal.
+        /// - Parameter value: the name as it renders in the payload.
+        public init(stringLiteral value: String) {
+            self.init(value)
+        }
+
+    }
+}
+
+// MARK: - Constants
+
+public extension StructuredData.Property.Name {
+    /// The absolute URL of an organization's logo.
+    static let logo: Self = "logo"
+    /// The name of the thing a node describes.
+    static let name: Self = "name"
+    /// The organization publishing a website.
+    static let publisher: Self = "publisher"
+    /// The absolute URLs of the profiles that also identify the thing a node describes.
+    static let sameAs: Self = "sameAs"
+    /// The absolute URL of the thing a node describes.
+    static let url: Self = "url"
+}

Packages/Infrastructure/Sources/Public/Types/StructuredData/StructuredDataValue.swift

@@ -0,0 +1,67 @@
+extension StructuredData {
+    /// A value of a ``Property``: a string, a list, a nested node, or a reference to another node.
+    ///
+    /// Every string a value renders is escaped as a JSON literal with `<` escaped as well, so a value can never close the `script`
+    /// tag embedding the payload it renders into.
+    public indirect enum Value: Equatable, Sendable {
+        /// A list of values.
+        case array([Value])
+        /// A nested node, e.g. the place a schema.org event is located at.
+        case node(Node)
+        /// A reference to the ``Node/id`` of another node in the graph, rendered as an `@id` object.
+        case reference(String)
+        /// A string value.
+        case string(String)
+    }
+}
+
+// MARK: - Extensions
+
+extension StructuredData.Value {
+
+    // MARK: Computed
+
+    /// The value's minified JSON fragment.
+    var fragment: String {
+        switch self {
+        case .array(let values):
+            "[\(values.map(\.fragment).joined(separator: .Separator.comma))]"
+        case .node(let node):
+            node.fragment
+        case .reference(let id):
+            #"{"@id":\#(Self.literal(id))}"#
+        case .string(let string):
+            Self.literal(string)
+        }
+    }
+
+    // MARK: Methods
+
+    /// Renders a string as a JSON string literal, escaping `<` as well since the payload is embedded in a `script` tag the string
+    /// could otherwise close.
+    /// - Parameter value: the string to render.
+    /// - Returns: the quoted and escaped literal.
+    static func literal(_ value: String) -> String {
+        var literal = "\""
+
+        for scalar in value.unicodeScalars {
+            switch scalar {
+            case "\"":
+                literal += #"\""#
+            case "\\":
+                literal += #"\\"#
+            case "<":
+                literal += #"\u003c"#
+            case let scalar where scalar.value < 0x20:
+                let hex = String(scalar.value, radix: 16)
+
+                literal += #"\u"# + String(repeating: "0", count: 4 - hex.count) + hex
+            default:
+                literal.unicodeScalars.append(scalar)
+            }
+        }
+
+        return literal + "\""
+    }
+
+}