diff --git a/DeepDrftPublic.Client/Common/SeoEnvironment.cs b/DeepDrftPublic.Client/Common/SeoEnvironment.cs
new file mode 100644
index 0000000..a9e017d
--- /dev/null
+++ b/DeepDrftPublic.Client/Common/SeoEnvironment.cs
@@ -0,0 +1,33 @@
+using Microsoft.AspNetCore.Components;
+
+namespace DeepDrftPublic.Client.Common;
+
+/// <summary>
+/// Environment-gated robots bridge (Phase 22 remediation §4). The beta/staging site is web-hosted and must
+/// not be crawled, so the <i>default</i> robots directive is environment-gated: <c>index,follow</c> only in
+/// Production, <c>noindex,nofollow</c> everywhere else. A per-page <see cref="SeoModel.Robots"/> override
+/// still wins — this only sets the default.
+///
+/// <para>
+/// Crawlers read the server-prerendered HTML, so correctness lives in the server prerender pass — but the
+/// value must be identical across the InteractiveAuto double render (AC6), so the WASM pass has to resolve
+/// the same flag. The WASM assembly has no <c>IWebHostEnvironment</c> (config comes from the server). This
+/// mirrors the DarkMode bridge exactly: a scoped service the server seeds during prerender (from
+/// <c>IWebHostEnvironment.IsProduction()</c>) and <c>[PersistentState]</c> rounds to the client, so both
+/// passes resolve the identical value. <c>SeoHead</c> injects this rather than an environment dependency,
+/// honouring the no-environment-in-the-component constraint.
+/// </para>
+/// </summary>
+public class SeoEnvironment
+{
+    /// <summary>
+    /// True only in Production. Seeded server-side and persisted across the WASM boot. Defaults to
+    /// <c>false</c> so the fail-safe is "do not index" — a missing bridge never accidentally opens a
+    /// non-production site to crawlers.
+    /// </summary>
+    [PersistentState]
+    public bool IsProduction { get; set; }
+
+    /// <summary>The environment-gated default robots directive. Explicit page values override this.</summary>
+    public string DefaultRobots => IsProduction ? "index,follow" : "noindex,nofollow";
+}
diff --git a/DeepDrftPublic.Client/Common/SeoJsonLd.cs b/DeepDrftPublic.Client/Common/SeoJsonLd.cs
new file mode 100644
index 0000000..9c256fa
--- /dev/null
+++ b/DeepDrftPublic.Client/Common/SeoJsonLd.cs
@@ -0,0 +1,127 @@
+using System.Text.Json;
+using System.Text.Json.Serialization;
+
+namespace DeepDrftPublic.Client.Common;
+
+/// <summary>
+/// Typed schema.org JSON-LD nodes (Phase 22, OQ5 — the typed-builder option). Each record mirrors one
+/// schema.org type; <see cref="SeoJsonLd.Serialize"/> renders a node to the <c>&lt;script type="application/ld+json"&gt;</c>
+/// body. Keeping the shape in C# (not hand-written JSON in pages) is what makes the medium→type mapping
+/// live in one place (DRY, §4.3) and the output unit-testable (AC5) rather than a manual validator pass.
+///
+/// <para>
+/// All nodes share <see cref="JsonLdNode"/> so the <c>@context</c>/<c>@type</c> pair serialises first and
+/// once. Null properties are omitted (the serializer ignores nulls) so partial data never emits an empty
+/// or broken node (C6/AC4).
+/// </para>
+/// </summary>
+public static class SeoJsonLd
+{
+    private static readonly JsonSerializerOptions Options = new()
+    {
+        DefaultIgnoreCondition = JsonIgnoreCondition.WhenWritingNull,
+        // schema.org keys are PascalCase ("@type", "byArtist", "datePublished"); JsonPropertyName drives
+        // each. Encoder relaxed so the JSON sits inline in HTML without over-escaping apostrophes etc.
+        // Note: the relaxed encoder leaves <, >, & raw — InlineSafe re-escapes exactly those before the
+        // body is injected into the <script> element. See Serialize.
+        Encoder = System.Text.Encodings.Web.JavaScriptEncoder.UnsafeRelaxedJsonEscaping,
+        WriteIndented = false,
+    };
+
+    /// <summary>
+    /// Renders a node to its compact JSON-LD script body. The host component wraps it in the script tag.
+    /// The body is run through <see cref="InlineSafe"/> so CMS-authored values containing
+    /// <c>&lt;/script&gt;</c> or <c>&lt;</c> cannot break out of the inline script element (XSS).
+    /// </summary>
+    public static string Serialize<TNode>(TNode node) where TNode : JsonLdNode =>
+        InlineSafe(JsonSerializer.Serialize(node, node.GetType(), Options));
+
+    /// <summary>
+    /// Escapes the three characters that can break out of an inline <c>&lt;script type="application/ld+json"&gt;</c>
+    /// element. Replacing <c>&lt;</c>/<c>&gt;</c>/<c>&amp;</c> with their <c>\uXXXX</c> JSON escapes keeps the
+    /// JSON byte-for-byte equivalent on parse (a JSON string treats <c><</c> and <c>&lt;</c> identically)
+    /// while making <c>&lt;/script&gt;</c> impossible to emit raw — the documented safe pattern for inline JSON-LD.
+    /// </summary>
+    internal static string InlineSafe(string json) => json
+        .Replace("<", "\\u003C")
+        .Replace(">", "\\u003E")
+        .Replace("&", "\\u0026");
+}
+
+/// <summary>Base for every schema.org node: emits <c>@context</c> and <c>@type</c> first.</summary>
+public abstract record JsonLdNode
+{
+    [JsonPropertyName("@context")]
+    [JsonPropertyOrder(-2)]
+    public string Context => "https://schema.org";
+
+    [JsonPropertyName("@type")]
+    [JsonPropertyOrder(-1)]
+    public abstract string Type { get; }
+}
+
+/// <summary>The Deep DRFT collective entity — the home/about node.</summary>
+public sealed record MusicGroupNode : JsonLdNode
+{
+    public override string Type => "MusicGroup";
+
+    [JsonPropertyName("name")] public string Name { get; init; } = string.Empty;
+    [JsonPropertyName("url")] public string? Url { get; init; }
+    [JsonPropertyName("genre")] public string? Genre { get; init; }
+    [JsonPropertyName("description")] public string? Description { get; init; }
+    [JsonPropertyName("logo")] public string? Logo { get; init; }
+    [JsonPropertyName("sameAs")] public IReadOnlyList<string>? SameAs { get; init; }
+}
+
+/// <summary>A studio cut or a live session release. <c>AlbumProductionType</c> distinguishes them.</summary>
+public sealed record MusicAlbumNode : JsonLdNode
+{
+    public override string Type => "MusicAlbum";
+
+    [JsonPropertyName("name")] public string Name { get; init; } = string.Empty;
+    [JsonPropertyName("byArtist")] public ArtistRef? ByArtist { get; init; }
+
+    /// <summary>schema.org <c>MusicAlbumProductionType</c> URI, e.g. <c>StudioAlbum</c> or <c>LiveAlbum</c>.</summary>
+    [JsonPropertyName("albumProductionType")] public string? AlbumProductionType { get; init; }
+
+    [JsonPropertyName("datePublished")] public string? DatePublished { get; init; }
+    [JsonPropertyName("genre")] public string? Genre { get; init; }
+    [JsonPropertyName("image")] public string? Image { get; init; }
+    [JsonPropertyName("url")] public string? Url { get; init; }
+
+    /// <summary>Ordered list of the album's recordings (cut track list, in TrackNumber order).</summary>
+    [JsonPropertyName("track")] public IReadOnlyList<MusicRecordingNode>? Track { get; init; }
+}
+
+/// <summary>A single recording — a mix release, or one track inside an album's <c>track</c> list.</summary>
+public sealed record MusicRecordingNode : JsonLdNode
+{
+    public override string Type => "MusicRecording";
+
+    [JsonPropertyName("name")] public string Name { get; init; } = string.Empty;
+    [JsonPropertyName("byArtist")] public ArtistRef? ByArtist { get; init; }
+
+    /// <summary>ISO-8601 duration (e.g. <c>PT1H2M3S</c>) from <c>DurationSeconds</c>.</summary>
+    [JsonPropertyName("duration")] public string? Duration { get; init; }
+
+    [JsonPropertyName("genre")] public string? Genre { get; init; }
+    [JsonPropertyName("image")] public string? Image { get; init; }
+    [JsonPropertyName("url")] public string? Url { get; init; }
+}
+
+/// <summary>A browse/index surface listing releases (cuts/sessions/mixes/archive).</summary>
+public sealed record CollectionPageNode : JsonLdNode
+{
+    public override string Type => "CollectionPage";
+
+    [JsonPropertyName("name")] public string Name { get; init; } = string.Empty;
+    [JsonPropertyName("description")] public string? Description { get; init; }
+    [JsonPropertyName("url")] public string? Url { get; init; }
+}
+
+/// <summary>A nested <c>byArtist</c> reference — the collective as a MusicGroup, by name.</summary>
+public sealed record ArtistRef
+{
+    [JsonPropertyName("@type")] public string Type => "MusicGroup";
+    [JsonPropertyName("name")] public string Name { get; init; } = string.Empty;
+}
diff --git a/DeepDrftPublic.Client/Common/SeoModel.cs b/DeepDrftPublic.Client/Common/SeoModel.cs
new file mode 100644
index 0000000..1be1cae
--- /dev/null
+++ b/DeepDrftPublic.Client/Common/SeoModel.cs
@@ -0,0 +1,209 @@
+using DeepDrftModels.DTOs;
+using DeepDrftModels.Enums;
+
+namespace DeepDrftPublic.Client.Common;
+
+/// <summary>
+/// The OG <c>og:type</c> for a page. Releases map per medium (§3.4); everything else is a website.
+/// </summary>
+public enum SeoOgType
+{
+    Website,
+    MusicAlbum,
+    MusicSong,
+}
+
+/// <summary>
+/// The typed per-page SEO input (Phase 22). A page hands <c>SeoHead</c> one model instead of ~15 loose
+/// parameters; the named factories below encode the per-page / per-medium mapping (title, description,
+/// canonical path, og:type, JSON-LD node) in exactly one place each (DRY, §4.1/§4.2). The factories are
+/// pure functions over DTOs the page already holds — unit-testable without rendering.
+///
+/// <para>
+/// <see cref="CanonicalPath"/> is site-relative; <c>SeoHead</c> absolutises it against
+/// <see cref="SeoOptions.BaseUrl"/>. Release pages pass <see cref="ReleaseRoutes.DetailHref"/> so the
+/// canonical is the dedicated route regardless of alias/query routes (AC7). A null cover means the model
+/// carries no <see cref="ImagePath"/> and <c>SeoHead</c> falls back to the default OG image (C6/AC4).
+/// </para>
+/// </summary>
+public sealed record SeoModel
+{
+    /// <summary>Bare page title, no site suffix. <c>SeoHead</c> composes <c>"{Title} · {suffix}"</c>.</summary>
+    public required string Title { get; init; }
+
+    /// <summary>Meta/OG description. Null falls back to <see cref="SeoOptions.DefaultDescription"/>.</summary>
+    public string? Description { get; init; }
+
+    /// <summary>Site-relative canonical path. Null defaults to the current path in <c>SeoHead</c>.</summary>
+    public string? CanonicalPath { get; init; }
+
+    /// <summary>Relative cover <c>ImagePath</c>. Null → the default OG image.</summary>
+    public string? ImagePath { get; init; }
+
+    public SeoOgType OgType { get; init; } = SeoOgType.Website;
+
+    /// <summary>Robots directive. Null falls back to <see cref="SeoOptions.DefaultRobots"/>.</summary>
+    public string? Robots { get; init; }
+
+    /// <summary>Pre-serialised JSON-LD script body, or null to emit no structured-data script.</summary>
+    public string? JsonLd { get; init; }
+
+    // --- Music-vertical OG, release pages only (null elsewhere → tags omitted) ---
+    public string? Artist { get; init; }
+    public DateOnly? ReleaseDate { get; init; }
+    public double? DurationSeconds { get; init; }
+
+    // ------------------------------------------------------------------ Factories
+
+    /// <summary>Home page: the collective entity (MusicGroup JSON-LD), site-level OG.</summary>
+    public static SeoModel ForHome(SeoOptions options) => new()
+    {
+        Title = "Electronic Music Collective",
+        Description = options.DefaultDescription,
+        CanonicalPath = "/",
+        OgType = SeoOgType.Website,
+        JsonLd = SeoJsonLd.Serialize(MusicGroup(options)),
+    };
+
+    /// <summary>About page: the collective again, with the bio lede as description.</summary>
+    public static SeoModel ForAbout(SeoOptions options) => new()
+    {
+        Title = "The Collective",
+        Description =
+            "Two people, many hats. Deep DRFT brings the heart and soul of Midwest deep house to " +
+            "Charleston — informed by the founders of the style, and promising to push it forward.",
+        CanonicalPath = "/about",
+        OgType = SeoOgType.Website,
+        JsonLd = SeoJsonLd.Serialize(MusicGroup(options) with
+        {
+            Description =
+                "Two people, many hats. Deep DRFT brings the heart and soul of Midwest deep house to " +
+                "Charleston — informed by the founders of the style, and promising to push it forward.",
+        }),
+    };
+
+    /// <summary>A browse surface: <c>CollectionPage</c> JSON-LD, website OG.</summary>
+    public static SeoModel ForBrowse(SeoOptions options, ReleaseMedium? medium, string path)
+    {
+        var (title, description) = BrowseCopy(medium);
+        return new SeoModel
+        {
+            Title = title,
+            Description = description,
+            CanonicalPath = path,
+            OgType = SeoOgType.Website,
+            JsonLd = SeoJsonLd.Serialize(new CollectionPageNode
+            {
+                Name = title,
+                Description = description,
+                Url = SeoUrls.Absolute(options, path),
+            }),
+        };
+    }
+
+    /// <summary>The 404 page: no canonical, <c>noindex,follow</c>, no JSON-LD.</summary>
+    public static SeoModel ForNotFound(SeoOptions options) => new()
+    {
+        Title = "Not Found",
+        Description = options.DefaultDescription,
+        Robots = "noindex,follow",
+        OgType = SeoOgType.Website,
+    };
+
+    /// <summary>
+    /// A release detail page. The medium picks the schema (cut/session → MusicAlbum, mix → MusicRecording),
+    /// the og:type, and the music-vertical OG fields; the canonical is the dedicated route. The optional
+    /// <paramref name="tracks"/> seed the album's ordered <c>track</c> list (cut). <b>One call site, all tags.</b>
+    /// </summary>
+    public static SeoModel ForRelease(SeoOptions options, ReleaseDto release, IReadOnlyList<TrackDto>? tracks = null)
+    {
+        var canonicalPath = ReleaseRoutes.DetailHref(release.EntryKey, release.Medium);
+        var image = SeoUrls.CoverOrDefault(options, release.ImagePath);
+        // byArtist reflects the release's own artist, consistent with the music:musician OG tag (Daniel's
+        // call) — not the collective name. Album sub-recordings share it: the tracks are by this artist.
+        var artist = new ArtistRef { Name = release.Artist };
+        var description = string.IsNullOrWhiteSpace(release.Description) ? options.DefaultDescription : release.Description;
+
+        // A mix is a single recording; its duration comes from the (single) track when present.
+        var mixDurationSeconds = release.Medium == ReleaseMedium.Mix
+            ? tracks?.FirstOrDefault()?.DurationSeconds
+            : null;
+
+        JsonLdNode node = release.Medium switch
+        {
+            ReleaseMedium.Mix => new MusicRecordingNode
+            {
+                Name = release.Title,
+                ByArtist = artist,
+                Duration = SeoUrls.IsoDuration(mixDurationSeconds),
+                Genre = release.Genre,
+                Image = image,
+                Url = SeoUrls.Absolute(options, canonicalPath),
+            },
+            // Cut and Session are both albums; the production type distinguishes a live session.
+            _ => new MusicAlbumNode
+            {
+                Name = release.Title,
+                ByArtist = artist,
+                AlbumProductionType = release.Medium == ReleaseMedium.Session
+                    ? "https://schema.org/LiveAlbum"
+                    : "https://schema.org/StudioAlbum",
+                DatePublished = release.ReleaseDate?.ToString("yyyy-MM-dd"),
+                Genre = release.Genre,
+                Image = image,
+                Url = SeoUrls.Absolute(options, canonicalPath),
+                Track = AlbumTracks(options, artist, tracks),
+            },
+        };
+
+        return new SeoModel
+        {
+            Title = release.Title,
+            Description = description,
+            CanonicalPath = canonicalPath,
+            ImagePath = release.ImagePath,
+            OgType = release.Medium == ReleaseMedium.Mix ? SeoOgType.MusicSong : SeoOgType.MusicAlbum,
+            Artist = release.Artist,
+            ReleaseDate = release.ReleaseDate,
+            DurationSeconds = mixDurationSeconds,
+            JsonLd = SeoJsonLd.Serialize(node),
+        };
+    }
+
+    // The collective entity, built once from config — the home/about JSON-LD root.
+    private static MusicGroupNode MusicGroup(SeoOptions options) => new()
+    {
+        Name = options.SiteName,
+        Url = SeoUrls.Absolute(options, "/"),
+        Genre = options.Genre,
+        Description = options.DefaultDescription,
+        Logo = SeoUrls.Absolute(options, options.DefaultImageUrl),
+        SameAs = options.SameAs.Count > 0 ? options.SameAs : null,
+    };
+
+    // Ordered recording list for an album's `track` property. Null when there are no tracks so the
+    // property is omitted rather than emitting an empty array (C6).
+    private static IReadOnlyList<MusicRecordingNode>? AlbumTracks(
+        SeoOptions options, ArtistRef artist, IReadOnlyList<TrackDto>? tracks)
+    {
+        if (tracks is null || tracks.Count == 0) return null;
+
+        return tracks
+            .OrderBy(t => t.TrackNumber)
+            .Select(t => new MusicRecordingNode
+            {
+                Name = t.TrackName,
+                ByArtist = artist,
+                Duration = SeoUrls.IsoDuration(t.DurationSeconds),
+            })
+            .ToList();
+    }
+
+    private static (string Title, string Description) BrowseCopy(ReleaseMedium? medium) => medium switch
+    {
+        ReleaseMedium.Cut => ("Cuts", "Studio cuts from Deep DRFT — composed, layered, and finished."),
+        ReleaseMedium.Session => ("Sessions", "Live sessions from Deep DRFT — performances caught in the moment, unrepeatable and unedited."),
+        ReleaseMedium.Mix => ("Mixes", "DJ mixes from Deep DRFT — uninterrupted sets, one track bleeding into the next."),
+        _ => ("Archive", "The full Deep DRFT catalogue — cuts, sessions, and mixes, indexed and always expanding."),
+    };
+}
diff --git a/DeepDrftPublic.Client/Common/SeoOptions.cs b/DeepDrftPublic.Client/Common/SeoOptions.cs
new file mode 100644
index 0000000..b6f6150
--- /dev/null
+++ b/DeepDrftPublic.Client/Common/SeoOptions.cs
@@ -0,0 +1,52 @@
+namespace DeepDrftPublic.Client.Common;
+
+/// <summary>
+/// Site-wide SEO defaults (Phase 22). These are non-secret brand constants — a single canonical origin,
+/// the site name/suffix, the fallback share image, the social links — sourced once and injected into
+/// <c>SeoHead</c> so no page re-declares them. Registered as a singleton in
+/// <see cref="Startup.ConfigureDomainServices"/>, which runs in <b>both</b> the server prerender and the
+/// WASM passes, so both passes resolve identical values (the double-render-identity requirement, §5/AC6).
+///
+/// <para>
+/// <see cref="BaseUrl"/> is the load-bearing field: absolute canonical / <c>og:url</c> / <c>og:image</c>
+/// origins all come from here, never from a browser API — there is no <c>window.location</c> during
+/// server prerender, and the request host is unreliable behind the nginx reverse proxy (§5, OQ1).
+/// </para>
+/// </summary>
+public sealed record SeoOptions
+{
+    /// <summary>Canonical production origin, no trailing slash. Absolute URLs are this + a resolved path (OQ1).</summary>
+    public string BaseUrl { get; init; } = "https://deepdrft.com";
+
+    /// <summary>The brand name used in <c>og:site_name</c>, <c>application-name</c>, and the JSON-LD MusicGroup.</summary>
+    public string SiteName { get; init; } = "Deep DRFT";
+
+    /// <summary>Appended to a page's bare title as <c>"{Title} · {TitleSuffix}"</c>. Resolves the prior suffix inconsistency (OQ4).</summary>
+    public string TitleSuffix { get; init; } = "Deep DRFT";
+
+    /// <summary>Fallback meta/OG description for pages that supply none.</summary>
+    public string DefaultDescription { get; init; } =
+        "Deep DRFT — an electronic music collective from Charleston, South Carolina. Studio cuts, live sessions, and DJ mixes.";
+
+    /// <summary>
+    /// Absolute or root-relative URL of the default 1200×630 share image used when a page has no cover (OQ2).
+    /// A placeholder path until the real asset is dropped in; swapping it is a one-value change.
+    /// </summary>
+    public string DefaultImageUrl { get; init; } = "/img/og-default.png";
+
+    /// <summary>OG locale. Optional surface tag.</summary>
+    public string Locale { get; init; } = "en_US";
+
+    /// <summary>The collective's primary genre, used in the MusicGroup JSON-LD node.</summary>
+    public string Genre { get; init; } = "Electronic";
+
+    // The default robots directive is NOT a static option — it is environment-gated (Production →
+    // index,follow; non-production → noindex,nofollow) via SeoEnvironment so the beta/staging site is
+    // never crawled. A page's explicit SeoModel.Robots still overrides that default.
+
+    /// <summary>
+    /// Public social profile URLs for the MusicGroup <c>sameAs</c> array (OQ3). Instagram only —
+    /// no Twitter/X account exists, so no <c>twitter:site</c>/<c>twitter:creator</c> handle is emitted.
+    /// </summary>
+    public IReadOnlyList<string> SameAs { get; init; } = ["https://instagram.com/deepdrft.music"];
+}
diff --git a/DeepDrftPublic.Client/Common/SeoUrls.cs b/DeepDrftPublic.Client/Common/SeoUrls.cs
new file mode 100644
index 0000000..3945ee1
--- /dev/null
+++ b/DeepDrftPublic.Client/Common/SeoUrls.cs
@@ -0,0 +1,44 @@
+namespace DeepDrftPublic.Client.Common;
+
+/// <summary>
+/// Absolute-URL composition for SEO tags (Phase 22). Canonical / <c>og:url</c> / <c>og:image</c> origins
+/// all come from <see cref="SeoOptions.BaseUrl"/> (config), never from a browser API — there is no
+/// <c>window.location</c> during server prerender and the request host is unreliable behind nginx
+/// (§5, OQ1). Shared by the <c>SeoModel</c> factories (which absolutise JSON-LD <c>url</c>/<c>image</c>)
+/// and <c>SeoHead</c> (which absolutises the meta/OG tags) so the rule lives in exactly one place.
+/// </summary>
+public static class SeoUrls
+{
+    /// <summary>BaseUrl + a site-relative path. Both sides are trimmed so the join never doubles or drops the slash.</summary>
+    public static string Absolute(SeoOptions options, string path)
+    {
+        var origin = options.BaseUrl.TrimEnd('/');
+        if (string.IsNullOrEmpty(path)) return origin;
+        return $"{origin}/{path.TrimStart('/')}";
+    }
+
+    /// <summary>
+    /// Absolute URL of a release/track cover from its FileDatabase <c>ImagePath</c>, via the public image
+    /// route (<c>api/image/{escaped}</c>). Returns the configured default share image when no cover exists
+    /// (C6/AC4 — a default guarantees <c>og:image</c> presence).
+    /// </summary>
+    public static string CoverOrDefault(SeoOptions options, string? imagePath)
+    {
+        if (string.IsNullOrWhiteSpace(imagePath))
+            return Absolute(options, options.DefaultImageUrl);
+
+        return Absolute(options, $"api/image/{Uri.EscapeDataString(imagePath)}");
+    }
+
+    /// <summary>
+    /// ISO-8601 duration (e.g. <c>PT1H2M3S</c>) from a seconds value, for JSON-LD <c>duration</c> and the
+    /// <c>music:duration</c> OG tag. Null / non-finite / non-positive input yields null (omit the tag).
+    /// </summary>
+    public static string? IsoDuration(double? seconds)
+    {
+        if (seconds is null || double.IsNaN(seconds.Value) || double.IsInfinity(seconds.Value) || seconds.Value <= 0)
+            return null;
+
+        return System.Xml.XmlConvert.ToString(TimeSpan.FromSeconds(seconds.Value));
+    }
+}
diff --git a/DeepDrftPublic.Client/Controls/SeoHead.razor b/DeepDrftPublic.Client/Controls/SeoHead.razor
new file mode 100644
index 0000000..4abd4fd
--- /dev/null
+++ b/DeepDrftPublic.Client/Controls/SeoHead.razor
@@ -0,0 +1,116 @@
+@using DeepDrftPublic.Client.Common
+@inject SeoOptions Seo
+@inject SeoEnvironment SeoEnv
+@inject NavigationManager Nav
+
+@*
+   The single reusable SEO head surface (Phase 22). Presentational and parameter-fed — owns no fetch and
+   no business logic (C4); it reads the injected SeoOptions for defaults and NavigationManager for the
+   current path. Renders <PageTitle> (the sole title source — pages drop their bare <PageTitle>) plus a
+   <HeadContent> block carrying the full standard/OG/Twitter/JSON-LD surface (§3), projected into the
+   <HeadOutlet> in App.razor so it is present in the prerendered HTML a crawler sees (C2/AC1).
+
+   Identical output across the InteractiveAuto double render (AC6): every value comes from the parameter
+   Model (built from the page's bridged PersistentComponentState) and config — never a browser API — so
+   the prerender and WASM passes render byte-identical tags.
+
+   Partial data (C6/AC4): a missing value falls back to config or omits its tag; og:image always resolves
+   (the default guarantees presence) so there is never a content="" attribute or a broken node.
+*@
+
+<PageTitle>@_fullTitle</PageTitle>
+
+<HeadContent>
+    @* Standard / search *@
+    <meta name="description" content="@_description" />
+    <link rel="canonical" href="@_canonical" />
+    <meta name="robots" content="@_robots" />
+    <meta name="application-name" content="@Seo.SiteName" />
+
+    @* Open Graph *@
+    <meta property="og:title" content="@Model.Title" />
+    <meta property="og:description" content="@_description" />
+    <meta property="og:url" content="@_canonical" />
+    <meta property="og:type" content="@_ogType" />
+    <meta property="og:site_name" content="@Seo.SiteName" />
+    <meta property="og:locale" content="@Seo.Locale" />
+    <meta property="og:image" content="@_image" />
+    @if (_hasCover)
+    {
+        <meta property="og:image:alt" content="@($"{Model.Title} cover art")" />
+    }
+
+    @* Music-vertical OG (release pages only) *@
+    @if (!string.IsNullOrWhiteSpace(Model.Artist))
+    {
+        <meta property="music:musician" content="@Model.Artist" />
+    }
+    @if (Model.ReleaseDate is not null)
+    {
+        <meta property="music:release_date" content="@Model.ReleaseDate.Value.ToString("yyyy-MM-dd")" />
+    }
+    @if (_isoDuration is not null)
+    {
+        <meta property="music:duration" content="@_isoDuration" />
+    }
+
+    @* Twitter Card. No twitter:site / twitter:creator — no X account exists (OQ3). *@
+    <meta name="twitter:card" content="summary_large_image" />
+    <meta name="twitter:title" content="@Model.Title" />
+    <meta name="twitter:description" content="@_description" />
+    <meta name="twitter:image" content="@_image" />
+
+    @* JSON-LD structured data *@
+    @if (!string.IsNullOrEmpty(Model.JsonLd))
+    {
+        <script type="application/ld+json">@((MarkupString)Model.JsonLd)</script>
+    }
+</HeadContent>
+
+@code {
+    /// <summary>The page's resolved SEO input, built via a <see cref="SeoModel"/> factory.</summary>
+    [Parameter, EditorRequired] public required SeoModel Model { get; set; }
+
+    private string _fullTitle = string.Empty;
+    private string _description = string.Empty;
+    private string _canonical = string.Empty;
+    private string _robots = string.Empty;
+    private string _ogType = "website";
+    private string _image = string.Empty;
+    private bool _hasCover;
+    private string? _isoDuration;
+
+    protected override void OnParametersSet()
+    {
+        _fullTitle = $"{Model.Title} · {Seo.TitleSuffix}";
+        _description = string.IsNullOrWhiteSpace(Model.Description) ? Seo.DefaultDescription : Model.Description;
+        // Default robots is environment-gated (non-production → noindex,nofollow) so beta/staging is never
+        // crawled; an explicit per-page Robots still wins (e.g. the 404's / soft-404's noindex,follow).
+        _robots = string.IsNullOrWhiteSpace(Model.Robots) ? SeoEnv.DefaultRobots : Model.Robots;
+        _ogType = OgTypeString(Model.OgType);
+
+        // Canonical: BaseUrl + the model's path, defaulting to the current relative path. The origin is
+        // always config (no browser API) so prerender and WASM agree (§5).
+        var path = Model.CanonicalPath ?? RelativePath();
+        _canonical = SeoUrls.Absolute(Seo, path);
+
+        _hasCover = !string.IsNullOrWhiteSpace(Model.ImagePath);
+        _image = SeoUrls.CoverOrDefault(Seo, Model.ImagePath);
+        _isoDuration = SeoUrls.IsoDuration(Model.DurationSeconds);
+    }
+
+    private string RelativePath()
+    {
+        var path = Nav.ToBaseRelativePath(Nav.Uri);
+        var query = path.IndexOf('?');
+        if (query >= 0) path = path[..query];
+        return "/" + path;
+    }
+
+    private static string OgTypeString(SeoOgType type) => type switch
+    {
+        SeoOgType.MusicAlbum => "music.album",
+        SeoOgType.MusicSong => "music.song",
+        _ => "website",
+    };
+}
diff --git a/DeepDrftPublic.Client/Pages/About.razor b/DeepDrftPublic.Client/Pages/About.razor
index 57247ca..5e13d18 100644
--- a/DeepDrftPublic.Client/Pages/About.razor
+++ b/DeepDrftPublic.Client/Pages/About.razor
@@ -2,8 +2,9 @@
 @using DeepDrftPublic.Client.Controls
 @implements IAsyncDisposable
 @inject IJSRuntime JsRuntime
+@inject SeoOptions Seo
 
-<PageTitle>The Collective - Deep DRFT</PageTitle>
+<SeoHead Model="@SeoModel.ForAbout(Seo)" />
 
 @* ──────────────────────────────────────────────────────────────────────────────
    THE LINER NOTES — a numbered three-movement editorial essay.
diff --git a/DeepDrftPublic.Client/Pages/AlbumsView.razor b/DeepDrftPublic.Client/Pages/AlbumsView.razor
index 071ee68..d9d2a1a 100644
--- a/DeepDrftPublic.Client/Pages/AlbumsView.razor
+++ b/DeepDrftPublic.Client/Pages/AlbumsView.razor
@@ -1,7 +1,9 @@
 @page "/cuts"
+@using DeepDrftModels.Enums
 @using DeepDrftPublic.Client.Controls
+@inject SeoOptions Seo
 
-<PageTitle>DeepDrft Cuts</PageTitle>
+<SeoHead Model="@SeoModel.ForBrowse(Seo, ReleaseMedium.Cut, "/cuts")" />
 
 @* The shared release-card grid; each card routes to /cuts/{entryKey} via the one ReleaseRoutes table.
    Cuts show a track count where other media show the artist, supplied via SubtitleResolver. *@
diff --git a/DeepDrftPublic.Client/Pages/ArchiveView.razor b/DeepDrftPublic.Client/Pages/ArchiveView.razor
index 2a5069e..9b121d4 100644
--- a/DeepDrftPublic.Client/Pages/ArchiveView.razor
+++ b/DeepDrftPublic.Client/Pages/ArchiveView.razor
@@ -1,8 +1,9 @@
 @page "/archive"
 @using DeepDrftModels.Enums
 @using DeepDrftPublic.Client.Controls
+@inject SeoOptions Seo
 
-<PageTitle>DeepDrft Archive</PageTitle>
+<SeoHead Model="@SeoModel.ForBrowse(Seo, null, "/archive")" />
 
 <div>
     <MudContainer MaxWidth="MaxWidth.Large" Class="archive-view-container">
diff --git a/DeepDrftPublic.Client/Pages/CutDetail.razor b/DeepDrftPublic.Client/Pages/CutDetail.razor
index 8d2809b..67721de 100644
--- a/DeepDrftPublic.Client/Pages/CutDetail.razor
+++ b/DeepDrftPublic.Client/Pages/CutDetail.razor
@@ -3,8 +3,7 @@
 @using DeepDrftPublic.Client.Controls
 @using DeepDrftPublic.Client.Services
 @inherits CutDetailBase
-
-<PageTitle>@(ViewModel.Release?.Title ?? "Cut") - DeepDrft</PageTitle>
+@inject SeoOptions Seo
 
 @if (ViewModel.IsLoading)
 {
@@ -17,6 +16,9 @@
 }
 else if (ViewModel.NotFound || ViewModel.Release is null)
 {
+    @* Soft-404: a bad key renders a 200 "not found" view, so it must carry noindex so it is not indexed
+       (mirrors the dedicated /404 NotFound page). *@
+    <SeoHead Model="@SeoModel.ForNotFound(Seo)" />
     <div class="deepdrft-track-detail-container">
         <div class="deepdrft-track-detail-masthead">
             <MudText Typo="Typo.h4" Align="Align.Center">Cut not found.</MudText>
@@ -37,6 +39,10 @@ else
     var hasYear = release.ReleaseDate is not null;
     var firstTrack = ViewModel.Tracks.Count > 0 ? ViewModel.Tracks[0] : null;
 
+    @* SEO head — fed from the same bridged release + ordered tracks, so the prerender and WASM passes
+       render identical tags (AC6). MusicAlbum/StudioAlbum with the ordered track list (§3.4). *@
+    <SeoHead Model="@SeoModel.ForRelease(Seo, release, ViewModel.Tracks)" />
+
     @* Full-screen content body (Phase 20 Wave 2 §1): the scaffold has no Class param, so a thin wrapper
        carries the min-height. dd-detail-fill keeps the body >= viewport height (below the nav) so the
        ambient visualizer reads full-screen and the site footer is pushed below the fold. *@
diff --git a/DeepDrftPublic.Client/Pages/Home.razor b/DeepDrftPublic.Client/Pages/Home.razor
index 4e24e94..65feb10 100644
--- a/DeepDrftPublic.Client/Pages/Home.razor
+++ b/DeepDrftPublic.Client/Pages/Home.razor
@@ -1,8 +1,9 @@
 @page "/"
 @using DeepDrftPublic.Client.Controls
 @using DeepDrftPublic.Client.Services
+@inject SeoOptions Seo
 
-<PageTitle>Deep DRFT - Electronic Music Collective</PageTitle>
+<SeoHead Model="@SeoModel.ForHome(Seo)" />
 
 @* Hero - split 50/50 *@
 <section class="hero">
diff --git a/DeepDrftPublic.Client/Pages/MixDetail.razor b/DeepDrftPublic.Client/Pages/MixDetail.razor
index 1800076..85ade2e 100644
--- a/DeepDrftPublic.Client/Pages/MixDetail.razor
+++ b/DeepDrftPublic.Client/Pages/MixDetail.razor
@@ -2,8 +2,7 @@
 @using DeepDrftPublic.Client.Controls
 @using DeepDrftPublic.Client.Services
 @inherits ReleaseDetailBase
-
-<PageTitle>@(ViewModel.Release?.Title ?? "Mix") - DeepDrft</PageTitle>
+@inject SeoOptions Seo
 
 @if (ViewModel.IsLoading)
 {
@@ -16,6 +15,9 @@
 }
 else if (ViewModel.NotFound || ViewModel.Release is null)
 {
+    @* Soft-404: a bad key renders a 200 "not found" view, so it must carry noindex so it is not indexed
+       (mirrors the dedicated /404 NotFound page). *@
+    <SeoHead Model="@SeoModel.ForNotFound(Seo)" />
     <div class="deepdrft-track-detail-container">
         <div class="deepdrft-track-detail-masthead">
             <MudText Typo="Typo.h4" Align="Align.Center">Mix not found.</MudText>
@@ -32,6 +34,11 @@ else if (ViewModel.NotFound || ViewModel.Release is null)
 else
 {
     var release = ViewModel.Release;
+    var mixTracks = ViewModel.Track is not null ? new[] { ViewModel.Track } : null;
+
+    @* SEO head — fed from the same bridged release + single track, so prerender and WASM render identical
+       tags (AC6). MusicRecording with ISO-8601 duration from the track (§3.4). *@
+    <SeoHead Model="@SeoModel.ForRelease(Seo, release, mixTracks)" />
 
     @* Full-page waveform sits behind the scaffold content. The scaffold's container is positioned
        above it via the mix-detail-foreground stacking context. TrackId lets the visualizer couple to
diff --git a/DeepDrftPublic.Client/Pages/MixesView.razor b/DeepDrftPublic.Client/Pages/MixesView.razor
index b4eb946..d5dac4c 100644
--- a/DeepDrftPublic.Client/Pages/MixesView.razor
+++ b/DeepDrftPublic.Client/Pages/MixesView.razor
@@ -1,8 +1,10 @@
 @page "/mixes"
+@using DeepDrftModels.Enums
 @using DeepDrftPublic.Client.Controls
 @inherits MediumBrowseBase
+@inject SeoOptions Seo
 
-<PageTitle>DeepDrft Mixes</PageTitle>
+<SeoHead Model="@SeoModel.ForBrowse(Seo, ReleaseMedium.Mix, "/mixes")" />
 
 <ReleaseGallery Releases="@Releases"
                 Loading="@Loading"
diff --git a/DeepDrftPublic.Client/Pages/NotFound.razor b/DeepDrftPublic.Client/Pages/NotFound.razor
index 0d95497..dd71b3d 100644
--- a/DeepDrftPublic.Client/Pages/NotFound.razor
+++ b/DeepDrftPublic.Client/Pages/NotFound.razor
@@ -1,4 +1,9 @@
 @page "/404"
+@using DeepDrftPublic.Client.Controls
+@inject SeoOptions Seo
+
+@* The 404 must not be indexed (AC8): noindex,follow — no canonical, no JSON-LD. *@
+<SeoHead Model="@SeoModel.ForNotFound(Seo)" />
 
 <MudText Typo="Typo.h3">
     Not Found
diff --git a/DeepDrftPublic.Client/Pages/SessionDetail.razor b/DeepDrftPublic.Client/Pages/SessionDetail.razor
index dd954ae..1a16c77 100644
--- a/DeepDrftPublic.Client/Pages/SessionDetail.razor
+++ b/DeepDrftPublic.Client/Pages/SessionDetail.razor
@@ -3,8 +3,7 @@
 @using DeepDrftPublic.Client.Controls
 @using DeepDrftPublic.Client.Services
 @inherits ReleaseDetailBase
-
-<PageTitle>@(ViewModel.Release?.Title ?? "Session") - DeepDrft</PageTitle>
+@inject SeoOptions Seo
 
 @if (ViewModel.IsLoading)
 {
@@ -20,6 +19,9 @@
 }
 else if (ViewModel.NotFound || ViewModel.Release is null)
 {
+    @* Soft-404: a bad key renders a 200 "not found" view, so it must carry noindex so it is not indexed
+       (mirrors the dedicated /404 NotFound page). *@
+    <SeoHead Model="@SeoModel.ForNotFound(Seo)" />
     <div class="deepdrft-track-detail-container">
         <div class="deepdrft-track-detail-masthead">
             <MudText Typo="Typo.h4" Align="Align.Center">Session not found.</MudText>
@@ -40,6 +42,10 @@ else
     // Hero image precedence: the session's dedicated hero, then the release cover, then a placeholder.
     var heroImage = !string.IsNullOrEmpty(heroKey) ? heroKey : release.ImagePath;
 
+    @* SEO head — fed from the same bridged release, so prerender and WASM render identical tags (AC6).
+       MusicAlbum/LiveAlbum (a session is a live release, §3.4/OQ6). *@
+    <SeoHead Model="@SeoModel.ForRelease(Seo, release)" />
+
     @* Ambient living waveform behind the hero overlay (Phase 12 §3e option b / §3f mode B). Session does
        NOT compose ReleaseDetailScaffold, so it mounts the shared engine directly with its own thin
        full-bleed wrapper — the engine is single-source either way, only the mount differs (§3b). The
diff --git a/DeepDrftPublic.Client/Pages/SessionsView.razor b/DeepDrftPublic.Client/Pages/SessionsView.razor
index 626497e..d2e9768 100644
--- a/DeepDrftPublic.Client/Pages/SessionsView.razor
+++ b/DeepDrftPublic.Client/Pages/SessionsView.razor
@@ -1,8 +1,10 @@
 @page "/sessions"
+@using DeepDrftModels.Enums
 @using DeepDrftPublic.Client.Controls
 @inherits MediumBrowseBase
+@inject SeoOptions Seo
 
-<PageTitle>DeepDrft Sessions</PageTitle>
+<SeoHead Model="@SeoModel.ForBrowse(Seo, ReleaseMedium.Session, "/sessions")" />
 
 <ReleaseGallery Releases="@Releases"
                 Loading="@Loading"
diff --git a/DeepDrftPublic.Client/Startup.cs b/DeepDrftPublic.Client/Startup.cs
index 55781aa..59ebd23 100644
--- a/DeepDrftPublic.Client/Startup.cs
+++ b/DeepDrftPublic.Client/Startup.cs
@@ -45,6 +45,16 @@ public static class Startup
         services.AddScoped<IAnonIdProvider, AnonIdProvider>();
         services.AddScoped<IPlayEventSink, BeaconPlayEventSink>();
         services.AddScoped<ShareTracker>();
+
+        // Phase 22 SEO defaults — non-secret brand constants (canonical origin, site name, default share
+        // image, social links). Singleton: stateless config, identical in the server-prerender and WASM
+        // passes (this method runs in both), which is what makes SeoHead's double-render output identical.
+        services.AddSingleton(new SeoOptions());
+
+        // Environment-gated robots bridge. Scoped + [PersistentState] like DarkModeSettings: the server
+        // seeds IsProduction during prerender and it rounds to the WASM pass, so SeoHead resolves the same
+        // default robots in both render passes (non-production → noindex,nofollow, keeping beta uncrawled).
+        services.AddScoped<SeoEnvironment>();
     }
 
     public static void ConfigureApiHttpClient(IServiceCollection services, string baseAddress)
diff --git a/DeepDrftPublic/Components/App.razor b/DeepDrftPublic/Components/App.razor
index e36ba5b..bbec5d5 100644
--- a/DeepDrftPublic/Components/App.razor
+++ b/DeepDrftPublic/Components/App.razor
@@ -1,4 +1,5 @@
 @using DeepDrftPublic.Client
+@using DeepDrftPublic.Client.Common
 @using DeepDrftPublic.Services
 @using DeepDrftShared.Client.Components
 <!DOCTYPE html>
@@ -34,11 +35,16 @@
 @code {
 
     [Inject] public required DarkModeService DarkModeService { get; set; }
+    [Inject] public required SeoEnvironment SeoEnvironment { get; set; }
+    [Inject] public required IWebHostEnvironment HostEnvironment { get; set; }
 
     protected override void OnInitialized()
     {
         base.OnInitialized();
         DarkModeService.CheckDarkMode();
+        // Seed the environment-gated robots bridge during prerender; [PersistentState] rounds it to WASM
+        // so both render passes resolve the same default robots (Production → index, else noindex).
+        SeoEnvironment.IsProduction = HostEnvironment.IsProduction();
     }
 
 }
diff --git a/DeepDrftTests/SeoModelTests.cs b/DeepDrftTests/SeoModelTests.cs
new file mode 100644
index 0000000..b6dc92a
--- /dev/null
+++ b/DeepDrftTests/SeoModelTests.cs
@@ -0,0 +1,308 @@
+using System.Text.Json;
+using DeepDrftModels.DTOs;
+using DeepDrftModels.Enums;
+using DeepDrftPublic.Client.Common;
+
+namespace DeepDrftTests;
+
+/// <summary>
+/// Unit tests for the Phase 22 SEO typed builders (<see cref="SeoModel"/> factories + <see cref="SeoJsonLd"/>
+/// nodes + <see cref="SeoUrls"/>). These are pure functions over the DTOs a page already holds — the
+/// medium→schema mapping (AC3), graceful partial data (AC4), JSON-LD validity (AC5), and canonical
+/// correctness (AC7) are all testable here without rendering. The JSON-LD is parsed back to a document so
+/// each assertion checks real structure, not a substring.
+/// </summary>
+[TestFixture]
+public class SeoModelTests
+{
+    private static readonly SeoOptions Options = new()
+    {
+        BaseUrl = "https://deepdrft.com",
+        SiteName = "Deep DRFT",
+        TitleSuffix = "Deep DRFT",
+        DefaultDescription = "default description",
+        DefaultImageUrl = "/img/og-default.png",
+        Genre = "Electronic",
+        SameAs = ["https://instagram.com/deepdrft.music"],
+    };
+
+    private static ReleaseDto Release(
+        ReleaseMedium medium,
+        string? image = "cover.jpg",
+        string? description = "desc",
+        string title = "Test Release",
+        string artist = "Aphex Twin") => new()
+    {
+        EntryKey = "abc-key",
+        Title = title,
+        Artist = artist,
+        Genre = "House",
+        Description = description,
+        ImagePath = image,
+        ReleaseDate = new DateOnly(2026, 3, 14),
+        Medium = medium,
+    };
+
+    private static JsonElement Parse(string? json)
+    {
+        Assert.That(json, Is.Not.Null.And.Not.Empty, "expected a JSON-LD body");
+        return JsonDocument.Parse(json!).RootElement;
+    }
+
+    // --- AC3: per-medium schema -------------------------------------------------
+
+    [Test]
+    public void ForRelease_Cut_IsMusicAlbum_StudioAlbum_WithOrderedTrackList()
+    {
+        var tracks = new List<TrackDto>
+        {
+            new() { TrackName = "Second", TrackNumber = 2, DurationSeconds = 60 },
+            new() { TrackName = "First", TrackNumber = 1, DurationSeconds = 30 },
+        };
+
+        var model = SeoModel.ForRelease(Options, Release(ReleaseMedium.Cut), tracks);
+        var node = Parse(model.JsonLd);
+
+        Assert.Multiple(() =>
+        {
+            Assert.That(node.GetProperty("@type").GetString(), Is.EqualTo("MusicAlbum"));
+            Assert.That(node.GetProperty("albumProductionType").GetString(), Is.EqualTo("https://schema.org/StudioAlbum"));
+            Assert.That(model.OgType, Is.EqualTo(SeoOgType.MusicAlbum));
+
+            var trackArray = node.GetProperty("track");
+            Assert.That(trackArray.GetArrayLength(), Is.EqualTo(2));
+            // Ordered by TrackNumber, not input order.
+            Assert.That(trackArray[0].GetProperty("name").GetString(), Is.EqualTo("First"));
+            Assert.That(trackArray[1].GetProperty("name").GetString(), Is.EqualTo("Second"));
+            Assert.That(trackArray[0].GetProperty("duration").GetString(), Is.EqualTo("PT30S"));
+        });
+    }
+
+    [Test]
+    public void ForRelease_Session_IsMusicAlbum_LiveAlbum()
+    {
+        var model = SeoModel.ForRelease(Options, Release(ReleaseMedium.Session));
+        var node = Parse(model.JsonLd);
+
+        Assert.Multiple(() =>
+        {
+            Assert.That(node.GetProperty("@type").GetString(), Is.EqualTo("MusicAlbum"));
+            Assert.That(node.GetProperty("albumProductionType").GetString(), Is.EqualTo("https://schema.org/LiveAlbum"));
+            Assert.That(model.OgType, Is.EqualTo(SeoOgType.MusicAlbum));
+        });
+    }
+
+    [Test]
+    public void ForRelease_Mix_IsMusicRecording_WithIsoDuration()
+    {
+        var tracks = new List<TrackDto> { new() { TrackName = "The Mix", DurationSeconds = 3723 } }; // 1h 2m 3s
+        var model = SeoModel.ForRelease(Options, Release(ReleaseMedium.Mix), tracks);
+        var node = Parse(model.JsonLd);
+
+        Assert.Multiple(() =>
+        {
+            Assert.That(node.GetProperty("@type").GetString(), Is.EqualTo("MusicRecording"));
+            Assert.That(node.GetProperty("duration").GetString(), Is.EqualTo("PT1H2M3S"));
+            Assert.That(model.OgType, Is.EqualTo(SeoOgType.MusicSong));
+            Assert.That(model.DurationSeconds, Is.EqualTo(3723));
+            // A mix is one recording, not an album — it carries no track list.
+            Assert.That(node.TryGetProperty("track", out _), Is.False);
+        });
+    }
+
+    [Test]
+    public void ForRelease_AllNodes_DeclareSchemaOrgContext()
+    {
+        foreach (var medium in Enum.GetValues<ReleaseMedium>())
+        {
+            var node = Parse(SeoModel.ForRelease(Options, Release(medium)).JsonLd);
+            Assert.That(node.GetProperty("@context").GetString(), Is.EqualTo("https://schema.org"),
+                $"{medium} node must declare the schema.org context");
+        }
+    }
+
+    // --- AC4: graceful partial data ---------------------------------------------
+
+    [Test]
+    public void ForRelease_NoDescription_FallsBackToDefault()
+    {
+        var model = SeoModel.ForRelease(Options, Release(ReleaseMedium.Cut, description: null));
+        Assert.That(model.Description, Is.EqualTo(Options.DefaultDescription));
+    }
+
+    [Test]
+    public void ForRelease_NoCover_OmitsImagePath_SoHeadFallsBackToDefault()
+    {
+        var model = SeoModel.ForRelease(Options, Release(ReleaseMedium.Cut, image: null));
+        // The model carries no relative ImagePath; the JSON-LD image is absolutised to the default.
+        var node = Parse(model.JsonLd);
+
+        Assert.Multiple(() =>
+        {
+            Assert.That(model.ImagePath, Is.Null);
+            Assert.That(node.GetProperty("image").GetString(), Is.EqualTo("https://deepdrft.com/img/og-default.png"));
+        });
+    }
+
+    [Test]
+    public void ForRelease_NoGenre_OmitsGenreProperty_NoEmptyValue()
+    {
+        var release = Release(ReleaseMedium.Cut);
+        release.Genre = null;
+
+        var node = Parse(SeoModel.ForRelease(Options, release).JsonLd);
+        Assert.That(node.TryGetProperty("genre", out _), Is.False, "a null genre must be omitted, not emitted empty");
+    }
+
+    [Test]
+    public void ForRelease_Mix_NoTrack_OmitsDuration()
+    {
+        var node = Parse(SeoModel.ForRelease(Options, Release(ReleaseMedium.Mix), tracks: null).JsonLd);
+        Assert.That(node.TryGetProperty("duration", out _), Is.False, "a mix with no track must omit duration");
+    }
+
+    // --- AC7: canonical correctness ---------------------------------------------
+
+    [TestCase(ReleaseMedium.Cut, "https://deepdrft.com/cuts/abc-key")]
+    [TestCase(ReleaseMedium.Session, "https://deepdrft.com/sessions/abc-key")]
+    [TestCase(ReleaseMedium.Mix, "https://deepdrft.com/mixes/abc-key")]
+    public void ForRelease_CanonicalPath_IsDedicatedRoute_AndJsonLdUrlAgrees(ReleaseMedium medium, string expectedAbsolute)
+    {
+        var model = SeoModel.ForRelease(Options, Release(medium));
+        var node = Parse(model.JsonLd);
+
+        Assert.Multiple(() =>
+        {
+            Assert.That(SeoUrls.Absolute(Options, model.CanonicalPath!), Is.EqualTo(expectedAbsolute));
+            // The JSON-LD url must be the same absolute canonical (AC7: canonical == og:url == node url).
+            Assert.That(node.GetProperty("url").GetString(), Is.EqualTo(expectedAbsolute));
+        });
+    }
+
+    // --- Home / About / Browse / NotFound ---------------------------------------
+
+    [Test]
+    public void ForHome_IsMusicGroup_WithSameAs()
+    {
+        var model = SeoModel.ForHome(Options);
+        var node = Parse(model.JsonLd);
+
+        Assert.Multiple(() =>
+        {
+            Assert.That(node.GetProperty("@type").GetString(), Is.EqualTo("MusicGroup"));
+            Assert.That(node.GetProperty("name").GetString(), Is.EqualTo("Deep DRFT"));
+            Assert.That(node.GetProperty("sameAs")[0].GetString(), Is.EqualTo("https://instagram.com/deepdrft.music"));
+            Assert.That(model.CanonicalPath, Is.EqualTo("/"));
+        });
+    }
+
+    [Test]
+    public void ForAbout_IsMusicGroup()
+    {
+        var node = Parse(SeoModel.ForAbout(Options).JsonLd);
+        Assert.That(node.GetProperty("@type").GetString(), Is.EqualTo("MusicGroup"));
+    }
+
+    [TestCase(ReleaseMedium.Cut, "/cuts")]
+    [TestCase(ReleaseMedium.Session, "/sessions")]
+    [TestCase(ReleaseMedium.Mix, "/mixes")]
+    public void ForBrowse_IsCollectionPage_WithAbsoluteUrl(ReleaseMedium medium, string path)
+    {
+        var model = SeoModel.ForBrowse(Options, medium, path);
+        var node = Parse(model.JsonLd);
+
+        Assert.Multiple(() =>
+        {
+            Assert.That(node.GetProperty("@type").GetString(), Is.EqualTo("CollectionPage"));
+            Assert.That(node.GetProperty("url").GetString(), Is.EqualTo($"https://deepdrft.com{path}"));
+            Assert.That(model.CanonicalPath, Is.EqualTo(path));
+        });
+    }
+
+    [Test]
+    public void ForBrowse_NullMedium_IsArchive()
+    {
+        var model = SeoModel.ForBrowse(Options, null, "/archive");
+        Assert.That(model.Title, Is.EqualTo("Archive"));
+    }
+
+    [Test]
+    public void ForNotFound_IsNoindex_NoCanonical_NoJsonLd()
+    {
+        var model = SeoModel.ForNotFound(Options);
+
+        Assert.Multiple(() =>
+        {
+            Assert.That(model.Robots, Is.EqualTo("noindex,follow"));
+            Assert.That(model.CanonicalPath, Is.Null);
+            Assert.That(model.JsonLd, Is.Null);
+        });
+    }
+
+    // --- byArtist consistency: per-release artist, matching music:musician -------
+
+    [TestCase(ReleaseMedium.Cut)]
+    [TestCase(ReleaseMedium.Session)]
+    [TestCase(ReleaseMedium.Mix)]
+    public void ForRelease_ByArtist_IsPerReleaseArtist_NotCollectiveName(ReleaseMedium medium)
+    {
+        var model = SeoModel.ForRelease(Options, Release(medium, artist: "Aphex Twin"));
+        var node = Parse(model.JsonLd);
+
+        Assert.Multiple(() =>
+        {
+            // byArtist mirrors the OG music:musician value (the release's own artist), not the SiteName.
+            Assert.That(node.GetProperty("byArtist").GetProperty("name").GetString(), Is.EqualTo("Aphex Twin"));
+            Assert.That(node.GetProperty("byArtist").GetProperty("name").GetString(), Is.Not.EqualTo(Options.SiteName));
+            Assert.That(model.Artist, Is.EqualTo("Aphex Twin"));
+        });
+    }
+
+    [Test]
+    public void ForRelease_Cut_AlbumTracks_ByArtist_IsPerReleaseArtist()
+    {
+        var tracks = new List<TrackDto> { new() { TrackName = "Track", TrackNumber = 1, DurationSeconds = 30 } };
+        var node = Parse(SeoModel.ForRelease(Options, Release(ReleaseMedium.Cut, artist: "Aphex Twin"), tracks).JsonLd);
+
+        Assert.That(node.GetProperty("track")[0].GetProperty("byArtist").GetProperty("name").GetString(),
+            Is.EqualTo("Aphex Twin"));
+    }
+
+    // --- Critical: inline JSON-LD script-breakout escaping (XSS) -----------------
+
+    [Test]
+    public void ForRelease_TitleWithScriptClose_DoesNotEmitRawAngleBracket()
+    {
+        // A CMS-authored title containing </script> / < must not survive raw in the inline script body —
+        // that is a breakout/XSS vector. The escaped < keeps the JSON parseable while neutralising it.
+        var release = Release(ReleaseMedium.Cut, title: "Evil</script><script>alert(1)</script>");
+        var body = SeoModel.ForRelease(Options, release).JsonLd;
+
+        Assert.That(body, Is.Not.Null);
+        Assert.Multiple(() =>
+        {
+            Assert.That(body, Does.Not.Contain("<"), "no raw < may appear in the inline JSON-LD body");
+            Assert.That(body, Does.Not.Contain(">"), "no raw > may appear in the inline JSON-LD body");
+            Assert.That(body, Does.Contain("\\u003C"), "< must be emitted as its \\u003C JSON escape");
+            // The escaped body still parses as JSON and round-trips the original value.
+            var node = Parse(body);
+            Assert.That(node.GetProperty("name").GetString(), Is.EqualTo("Evil</script><script>alert(1)</script>"));
+        });
+    }
+
+    [Test]
+    public void ForRelease_TitleWithAmpersand_EscapesAmpersand_StillParses()
+    {
+        // The title is serialized into the JSON-LD `name`, so an ampersand there exercises the & escape.
+        var release = Release(ReleaseMedium.Mix, title: "Sound & Vision");
+        var body = SeoModel.ForRelease(Options, release).JsonLd;
+
+        Assert.That(body, Is.Not.Null);
+        Assert.Multiple(() =>
+        {
+            Assert.That(body, Does.Not.Contain("&"), "no raw & may appear in the inline JSON-LD body");
+            Assert.That(body, Does.Contain("\\u0026"), "& must be emitted as its \\u0026 JSON escape");
+            Assert.That(Parse(body).GetProperty("name").GetString(), Is.EqualTo("Sound & Vision"));
+        });
+    }
+}
diff --git a/DeepDrftTests/SeoUrlsTests.cs b/DeepDrftTests/SeoUrlsTests.cs
new file mode 100644
index 0000000..fd2ad4c
--- /dev/null
+++ b/DeepDrftTests/SeoUrlsTests.cs
@@ -0,0 +1,68 @@
+using DeepDrftPublic.Client.Common;
+
+namespace DeepDrftTests;
+
+/// <summary>
+/// Unit tests for <see cref="SeoUrls"/> — the absolute-URL composition shared by the SeoModel factories
+/// and SeoHead (Phase 22). Origin always comes from config (never a browser API), so these pin the
+/// slash-join, the cover-vs-default fallback (C6/AC4), and the ISO-8601 duration edge cases.
+/// </summary>
+[TestFixture]
+public class SeoUrlsTests
+{
+    private static readonly SeoOptions Options = new()
+    {
+        BaseUrl = "https://deepdrft.com",
+        DefaultImageUrl = "/img/og-default.png",
+    };
+
+    [TestCase("/cuts/key", "https://deepdrft.com/cuts/key")]
+    [TestCase("cuts/key", "https://deepdrft.com/cuts/key")]
+    [TestCase("/", "https://deepdrft.com/")]
+    [TestCase("", "https://deepdrft.com")]
+    public void Absolute_JoinsOriginAndPath_WithoutDoublingOrDroppingSlash(string path, string expected)
+    {
+        Assert.That(SeoUrls.Absolute(Options, path), Is.EqualTo(expected));
+    }
+
+    [Test]
+    public void Absolute_TrimsTrailingSlashOnBaseUrl()
+    {
+        var withSlash = Options with { BaseUrl = "https://deepdrft.com/" };
+        Assert.That(SeoUrls.Absolute(withSlash, "/cuts"), Is.EqualTo("https://deepdrft.com/cuts"));
+    }
+
+    [Test]
+    public void CoverOrDefault_WithCover_BuildsEscapedImageRoute()
+    {
+        Assert.That(SeoUrls.CoverOrDefault(Options, "my cover.jpg"),
+            Is.EqualTo("https://deepdrft.com/api/image/my%20cover.jpg"));
+    }
+
+    [TestCase(null)]
+    [TestCase("")]
+    [TestCase("   ")]
+    public void CoverOrDefault_WithoutCover_FallsBackToDefaultImage(string? image)
+    {
+        Assert.That(SeoUrls.CoverOrDefault(Options, image),
+            Is.EqualTo("https://deepdrft.com/img/og-default.png"));
+    }
+
+    [TestCase(30.0, "PT30S")]
+    [TestCase(90.0, "PT1M30S")]
+    [TestCase(3723.0, "PT1H2M3S")]
+    public void IsoDuration_PositiveSeconds_RendersIso8601(double seconds, string expected)
+    {
+        Assert.That(SeoUrls.IsoDuration(seconds), Is.EqualTo(expected));
+    }
+
+    [TestCase(null)]
+    [TestCase(0.0)]
+    [TestCase(-5.0)]
+    [TestCase(double.NaN)]
+    [TestCase(double.PositiveInfinity)]
+    public void IsoDuration_NonPositiveOrNonFinite_ReturnsNull(double? seconds)
+    {
+        Assert.That(SeoUrls.IsoDuration(seconds), Is.Null);
+    }
+}