diff --git a/index.js b/index.js
index 243d864..6ebb92d 100644
--- a/index.js
+++ b/index.js
@@ -1,6 +1,7 @@
 import express from "express";
 
 import { setupFederation, buildPersonActor } from "./lib/federation-setup.js";
+import { createMastodonRouter } from "./lib/mastodon/router.js";
 import { initRedisCache } from "./lib/redis-cache.js";
 import { lookupWithSecurity } from "./lib/lookup-helpers.js";
 import {
@@ -1137,6 +1138,10 @@ export default class ActivityPubEndpoint {
     Indiekit.addCollection("ap_key_freshness");
     // Async inbox processing queue
     Indiekit.addCollection("ap_inbox_queue");
+    // Mastodon Client API collections
+    Indiekit.addCollection("ap_oauth_apps");
+    Indiekit.addCollection("ap_oauth_tokens");
+    Indiekit.addCollection("ap_markers");
 
     // Store collection references (posts resolved lazily)
     const indiekitCollections = Indiekit.collections;
@@ -1170,6 +1175,10 @@ export default class ActivityPubEndpoint {
       ap_key_freshness: indiekitCollections.get("ap_key_freshness"),
       // Async inbox processing queue
       ap_inbox_queue: indiekitCollections.get("ap_inbox_queue"),
+      // Mastodon Client API collections
+      ap_oauth_apps: indiekitCollections.get("ap_oauth_apps"),
+      ap_oauth_tokens: indiekitCollections.get("ap_oauth_tokens"),
+      ap_markers: indiekitCollections.get("ap_markers"),
       get posts() {
         return indiekitCollections.get("posts");
       },
@@ -1391,6 +1400,24 @@ export default class ActivityPubEndpoint {
         { processedAt: 1 },
         { expireAfterSeconds: 86_400, background: true },
       );
+
+      // Mastodon Client API indexes
+      this._collections.ap_oauth_apps.createIndex(
+        { clientId: 1 },
+        { unique: true, background: true },
+      );
+      this._collections.ap_oauth_tokens.createIndex(
+        { accessToken: 1 },
+        { unique: true, background: true },
+      );
+      this._collections.ap_oauth_tokens.createIndex(
+        { code: 1 },
+        { unique: true, sparse: true, background: true },
+      );
+      this._collections.ap_markers.createIndex(
+        { userId: 1, timeline: 1 },
+        { unique: true, background: true },
+      );
     } catch {
       // Index creation failed — collections not yet available.
       // Indexes already exist from previous startups; non-fatal.
@@ -1457,6 +1484,26 @@ export default class ActivityPubEndpoint {
       routesPublic: this.contentNegotiationRoutes,
     });
 
+    // Mastodon Client API — virtual endpoint at root
+    // Mastodon-compatible clients (Phanpy, Elk, etc.) expect /api/v1/*,
+    // /api/v2/*, /oauth/* at the domain root, not under /activitypub.
+    const pluginRef = this;
+    const mastodonRouter = createMastodonRouter({
+      collections: this._collections,
+      pluginOptions: {
+        handle: this.options.actor?.handle || "user",
+        publicationUrl: this._publicationUrl,
+        federation: this._federation,
+        followActor: (url, info) => pluginRef.followActor(url, info),
+        unfollowActor: (url) => pluginRef.unfollowActor(url),
+      },
+    });
+    Indiekit.addEndpoint({
+      name: "Mastodon Client API",
+      mountPath: "/",
+      routesPublic: mastodonRouter,
+    });
+
     // Register syndicator (appears in post editing UI)
     Indiekit.addSyndicator(this.syndicator);
 
diff --git a/lib/mastodon/entities/account.js b/lib/mastodon/entities/account.js
new file mode 100644
index 0000000..a6adfbb
--- /dev/null
+++ b/lib/mastodon/entities/account.js
@@ -0,0 +1,200 @@
+/**
+ * Account entity serializer for Mastodon Client API.
+ *
+ * Converts local profile (ap_profile) and remote actor objects
+ * (from timeline author, follower/following docs) into the
+ * Mastodon Account JSON shape that masto.js expects.
+ */
+import { accountId } from "../helpers/id-mapping.js";
+import { sanitizeHtml, stripHtml } from "./sanitize.js";
+
+/**
+ * Serialize an actor as a Mastodon Account entity.
+ *
+ * Handles two shapes:
+ * - Local profile: { _id, name, summary, url, icon, image, actorType,
+ *     manuallyApprovesFollowers, attachments, createdAt, ... }
+ * - Remote author (from timeline): { name, url, photo, handle, emojis, bot }
+ * - Follower/following doc: { actorUrl, name, handle, avatar, ... }
+ *
+ * @param {object} actor - Actor document (profile, author, or follower)
+ * @param {object} options
+ * @param {string} options.baseUrl - Server base URL
+ * @param {boolean} [options.isLocal=false] - Whether this is the local user
+ * @param {string} [options.handle] - Local actor handle (for local accounts)
+ * @returns {object} Mastodon Account entity
+ */
+export function serializeAccount(actor, { baseUrl, isLocal = false, handle = "" }) {
+  if (!actor) {
+    return null;
+  }
+
+  const id = accountId(actor, isLocal);
+
+  // Resolve username and acct
+  let username;
+  let acct;
+  if (isLocal) {
+    username = handle || extractUsername(actor.url) || "user";
+    acct = username; // local accounts use bare username
+  } else {
+    // Remote: extract from handle (@user@domain) or URL
+    const remoteHandle = actor.handle || "";
+    if (remoteHandle.startsWith("@")) {
+      username = remoteHandle.split("@")[1] || "";
+      acct = remoteHandle.slice(1); // strip leading @
+    } else if (remoteHandle.includes("@")) {
+      username = remoteHandle.split("@")[0];
+      acct = remoteHandle;
+    } else {
+      username = extractUsername(actor.url || actor.actorUrl) || "unknown";
+      const domain = extractDomain(actor.url || actor.actorUrl);
+      acct = domain ? `${username}@${domain}` : username;
+    }
+  }
+
+  // Resolve display name
+  const displayName = actor.name || actor.displayName || username || "";
+
+  // Resolve URLs for avatar and header
+  const avatarUrl =
+    actor.icon || actor.avatarUrl || actor.photo || actor.avatar || "";
+  const headerUrl = actor.image || actor.bannerUrl || "";
+
+  // Resolve URL
+  const url = actor.url || actor.actorUrl || "";
+
+  // Resolve note/summary
+  const note = actor.summary || "";
+
+  // Bot detection
+  const bot =
+    actor.bot === true ||
+    actor.actorType === "Service" ||
+    actor.actorType === "Application";
+
+  // Profile fields from attachments
+  const fields = (actor.attachments || actor.fields || []).map((f) => ({
+    name: f.name || "",
+    value: sanitizeHtml(f.value || ""),
+    verified_at: null,
+  }));
+
+  // Custom emojis
+  const emojis = (actor.emojis || []).map((e) => ({
+    shortcode: e.shortcode || "",
+    url: e.url || "",
+    static_url: e.url || "",
+    visible_in_picker: true,
+  }));
+
+  return {
+    id,
+    username,
+    acct,
+    url,
+    display_name: displayName,
+    note: sanitizeHtml(note),
+    avatar: avatarUrl || `${baseUrl}/placeholder-avatar.png`,
+    avatar_static: avatarUrl || `${baseUrl}/placeholder-avatar.png`,
+    header: headerUrl || "",
+    header_static: headerUrl || "",
+    locked: actor.manuallyApprovesFollowers || false,
+    fields,
+    emojis,
+    bot,
+    group: actor.actorType === "Group" || false,
+    discoverable: true,
+    noindex: false,
+    created_at: actor.createdAt || new Date().toISOString(),
+    last_status_at: actor.lastStatusAt || null,
+    statuses_count: actor.statusesCount || 0,
+    followers_count: actor.followersCount || 0,
+    following_count: actor.followingCount || 0,
+    moved: actor.movedTo || null,
+    suspended: false,
+    limited: false,
+    memorial: false,
+    roles: [],
+    hide_collections: false,
+  };
+}
+
+/**
+ * Serialize the local profile as a CredentialAccount (includes source + role).
+ *
+ * @param {object} profile - ap_profile document
+ * @param {object} options
+ * @param {string} options.baseUrl - Server base URL
+ * @param {string} options.handle - Local actor handle
+ * @param {object} [options.counts] - { statuses, followers, following }
+ * @returns {object} Mastodon CredentialAccount entity
+ */
+export function serializeCredentialAccount(profile, { baseUrl, handle, counts = {} }) {
+  const account = serializeAccount(profile, {
+    baseUrl,
+    isLocal: true,
+    handle,
+  });
+
+  // Add counts if provided
+  account.statuses_count = counts.statuses || 0;
+  account.followers_count = counts.followers || 0;
+  account.following_count = counts.following || 0;
+
+  // CredentialAccount extensions
+  account.source = {
+    privacy: "public",
+    sensitive: false,
+    language: "",
+    note: stripHtml(profile.summary || ""),
+    fields: (profile.attachments || []).map((f) => ({
+      name: f.name || "",
+      value: f.value || "",
+      verified_at: null,
+    })),
+    follow_requests_count: 0,
+  };
+
+  account.role = {
+    id: "-99",
+    name: "",
+    permissions: "0",
+    color: "",
+    highlighted: false,
+  };
+
+  return account;
+}
+
+// ─── Helpers ─────────────────────────────────────────────────────────────────
+
+/**
+ * Extract username from a URL path.
+ * Handles /@username, /users/username patterns.
+ */
+function extractUsername(url) {
+  if (!url) return "";
+  try {
+    const { pathname } = new URL(url);
+    const atMatch = pathname.match(/\/@([^/]+)/);
+    if (atMatch) return atMatch[1];
+    const usersMatch = pathname.match(/\/users\/([^/]+)/);
+    if (usersMatch) return usersMatch[1];
+    return "";
+  } catch {
+    return "";
+  }
+}
+
+/**
+ * Extract domain from a URL.
+ */
+function extractDomain(url) {
+  if (!url) return "";
+  try {
+    return new URL(url).hostname;
+  } catch {
+    return "";
+  }
+}
diff --git a/lib/mastodon/entities/instance.js b/lib/mastodon/entities/instance.js
new file mode 100644
index 0000000..1e23f3b
--- /dev/null
+++ b/lib/mastodon/entities/instance.js
@@ -0,0 +1 @@
+// Instance v1/v2 serializer — implemented in Task 8
diff --git a/lib/mastodon/entities/media.js b/lib/mastodon/entities/media.js
new file mode 100644
index 0000000..25f3ce0
--- /dev/null
+++ b/lib/mastodon/entities/media.js
@@ -0,0 +1,38 @@
+/**
+ * MediaAttachment entity serializer for Mastodon Client API.
+ *
+ * Converts stored media metadata to Mastodon MediaAttachment shape.
+ */
+
+/**
+ * Serialize a MediaAttachment entity.
+ *
+ * @param {object} media - Media document from ap_media collection
+ * @returns {object} Mastodon MediaAttachment entity
+ */
+export function serializeMediaAttachment(media) {
+  const type = detectMediaType(media.contentType || media.type || "");
+
+  return {
+    id: media._id ? media._id.toString() : media.id || "",
+    type,
+    url: media.url || "",
+    preview_url: media.thumbnailUrl || media.url || "",
+    remote_url: null,
+    text_url: media.url || "",
+    meta: media.meta || {},
+    description: media.description || media.alt || null,
+    blurhash: media.blurhash || null,
+  };
+}
+
+/**
+ * Map MIME type or simple type string to Mastodon media type.
+ */
+function detectMediaType(contentType) {
+  if (contentType.startsWith("image/") || contentType === "image") return "image";
+  if (contentType.startsWith("video/") || contentType === "video") return "video";
+  if (contentType.startsWith("audio/") || contentType === "audio") return "audio";
+  if (contentType.startsWith("image/gif")) return "gifv";
+  return "unknown";
+}
diff --git a/lib/mastodon/entities/notification.js b/lib/mastodon/entities/notification.js
new file mode 100644
index 0000000..a22e904
--- /dev/null
+++ b/lib/mastodon/entities/notification.js
@@ -0,0 +1,118 @@
+/**
+ * Notification entity serializer for Mastodon Client API.
+ *
+ * Converts ap_notifications documents into the Mastodon Notification JSON shape.
+ *
+ * Internal type -> Mastodon type mapping:
+ *   like    -> favourite
+ *   boost   -> reblog
+ *   follow  -> follow
+ *   reply   -> mention
+ *   mention -> mention
+ *   dm      -> mention (status will have visibility: "direct")
+ */
+import { serializeAccount } from "./account.js";
+import { serializeStatus } from "./status.js";
+
+/**
+ * Map internal notification types to Mastodon API types.
+ */
+const TYPE_MAP = {
+  like: "favourite",
+  boost: "reblog",
+  follow: "follow",
+  follow_request: "follow_request",
+  reply: "mention",
+  mention: "mention",
+  dm: "mention",
+  report: "admin.report",
+};
+
+/**
+ * Serialize a notification document as a Mastodon Notification entity.
+ *
+ * @param {object} notif - ap_notifications document
+ * @param {object} options
+ * @param {string} options.baseUrl - Server base URL
+ * @param {Map<string, object>} [options.statusMap] - Pre-fetched statuses keyed by targetUrl
+ * @param {object} [options.interactionState] - { favouritedIds, rebloggedIds, bookmarkedIds }
+ * @returns {object|null} Mastodon Notification entity
+ */
+export function serializeNotification(notif, { baseUrl, statusMap, interactionState }) {
+  if (!notif) return null;
+
+  const mastodonType = TYPE_MAP[notif.type] || notif.type;
+
+  // Build the actor account from notification fields
+  const account = serializeAccount(
+    {
+      name: notif.actorName,
+      url: notif.actorUrl,
+      photo: notif.actorPhoto,
+      handle: notif.actorHandle,
+    },
+    { baseUrl },
+  );
+
+  // Resolve the associated status (for favourite, reblog, mention types)
+  let status = null;
+  if (notif.targetUrl && statusMap) {
+    const timelineItem = statusMap.get(notif.targetUrl);
+    if (timelineItem) {
+      status = serializeStatus(timelineItem, {
+        baseUrl,
+        favouritedIds: interactionState?.favouritedIds || new Set(),
+        rebloggedIds: interactionState?.rebloggedIds || new Set(),
+        bookmarkedIds: interactionState?.bookmarkedIds || new Set(),
+        pinnedIds: new Set(),
+      });
+    }
+  }
+
+  // For mentions/replies that don't have a matching timeline item,
+  // construct a minimal status from the notification content
+  if (!status && notif.content && (mastodonType === "mention")) {
+    status = {
+      id: notif._id.toString(),
+      created_at: notif.published || notif.createdAt || new Date().toISOString(),
+      in_reply_to_id: null,
+      in_reply_to_account_id: null,
+      sensitive: false,
+      spoiler_text: "",
+      visibility: notif.type === "dm" ? "direct" : "public",
+      language: null,
+      uri: notif.uid || "",
+      url: notif.targetUrl || notif.uid || "",
+      replies_count: 0,
+      reblogs_count: 0,
+      favourites_count: 0,
+      edited_at: null,
+      favourited: false,
+      reblogged: false,
+      muted: false,
+      bookmarked: false,
+      pinned: false,
+      content: notif.content?.html || notif.content?.text || "",
+      filtered: null,
+      reblog: null,
+      application: null,
+      account,
+      media_attachments: [],
+      mentions: [],
+      tags: [],
+      emojis: [],
+      card: null,
+      poll: null,
+    };
+  }
+
+  return {
+    id: notif._id.toString(),
+    type: mastodonType,
+    created_at: notif.published instanceof Date
+      ? notif.published.toISOString()
+      : notif.published || notif.createdAt || new Date().toISOString(),
+    account,
+    status,
+  };
+}
diff --git a/lib/mastodon/entities/relationship.js b/lib/mastodon/entities/relationship.js
new file mode 100644
index 0000000..df5aede
--- /dev/null
+++ b/lib/mastodon/entities/relationship.js
@@ -0,0 +1,38 @@
+/**
+ * Relationship entity serializer for Mastodon Client API.
+ *
+ * Represents the relationship between the authenticated user
+ * and another account.
+ */
+
+/**
+ * Serialize a Relationship entity.
+ *
+ * @param {string} id - Account ID
+ * @param {object} state - Relationship state
+ * @param {boolean} [state.following=false]
+ * @param {boolean} [state.followed_by=false]
+ * @param {boolean} [state.blocking=false]
+ * @param {boolean} [state.muting=false]
+ * @param {boolean} [state.requested=false]
+ * @returns {object} Mastodon Relationship entity
+ */
+export function serializeRelationship(id, state = {}) {
+  return {
+    id,
+    following: state.following || false,
+    showing_reblogs: state.following || false,
+    notifying: false,
+    languages: [],
+    followed_by: state.followed_by || false,
+    blocking: state.blocking || false,
+    blocked_by: false,
+    muting: state.muting || false,
+    muting_notifications: state.muting || false,
+    requested: state.requested || false,
+    requested_by: false,
+    domain_blocking: false,
+    endorsed: false,
+    note: "",
+  };
+}
diff --git a/lib/mastodon/entities/sanitize.js b/lib/mastodon/entities/sanitize.js
new file mode 100644
index 0000000..8c8da1a
--- /dev/null
+++ b/lib/mastodon/entities/sanitize.js
@@ -0,0 +1,111 @@
+/**
+ * XSS HTML sanitizer for Mastodon Client API responses.
+ *
+ * Strips dangerous HTML while preserving safe markup that
+ * Mastodon clients expect (links, paragraphs, line breaks,
+ * inline formatting, mentions, hashtags).
+ */
+
+/**
+ * Allowed HTML tags in Mastodon API content fields.
+ * Matches what Mastodon itself permits in status content.
+ */
+const ALLOWED_TAGS = new Set([
+  "a",
+  "br",
+  "p",
+  "span",
+  "strong",
+  "em",
+  "b",
+  "i",
+  "u",
+  "s",
+  "del",
+  "pre",
+  "code",
+  "blockquote",
+  "ul",
+  "ol",
+  "li",
+]);
+
+/**
+ * Allowed attributes per tag.
+ */
+const ALLOWED_ATTRS = {
+  a: new Set(["href", "rel", "class", "target"]),
+  span: new Set(["class"]),
+};
+
+/**
+ * Sanitize HTML content for safe inclusion in API responses.
+ *
+ * Strips all tags not in the allowlist and removes disallowed attributes.
+ * This is a lightweight sanitizer — for production, consider a
+ * battle-tested library like DOMPurify or sanitize-html.
+ *
+ * @param {string} html - Raw HTML string
+ * @returns {string} Sanitized HTML
+ */
+export function sanitizeHtml(html) {
+  if (!html || typeof html !== "string") return "";
+
+  return html.replace(/<\/?([a-z][a-z0-9]*)\b[^>]*>/gi, (match, tagName) => {
+    const tag = tagName.toLowerCase();
+
+    // Closing tag
+    if (match.startsWith("</")) {
+      return ALLOWED_TAGS.has(tag) ? `</${tag}>` : "";
+    }
+
+    // Opening tag — check if allowed
+    if (!ALLOWED_TAGS.has(tag)) return "";
+
+    // Self-closing br
+    if (tag === "br") return "<br>";
+
+    // Strip disallowed attributes
+    const allowedAttrs = ALLOWED_ATTRS[tag];
+    if (!allowedAttrs) return `<${tag}>`;
+
+    const attrs = [];
+    const attrRegex = /([a-z][a-z0-9-]*)(?:\s*=\s*(?:"([^"]*)"|'([^']*)'|(\S+)))?/gi;
+    let attrMatch;
+    while ((attrMatch = attrRegex.exec(match)) !== null) {
+      const attrName = attrMatch[1].toLowerCase();
+      if (attrName === tag) continue; // skip tag name itself
+      const attrValue = attrMatch[2] ?? attrMatch[3] ?? attrMatch[4] ?? "";
+      if (allowedAttrs.has(attrName)) {
+        // Block javascript: URIs in href
+        if (attrName === "href" && /^\s*javascript:/i.test(attrValue)) continue;
+        attrs.push(`${attrName}="${escapeAttr(attrValue)}"`);
+      }
+    }
+
+    return attrs.length > 0 ? `<${tag} ${attrs.join(" ")}>` : `<${tag}>`;
+  });
+}
+
+/**
+ * Escape HTML attribute value.
+ * @param {string} value
+ * @returns {string}
+ */
+function escapeAttr(value) {
+  return value
+    .replace(/&/g, "&amp;")
+    .replace(/"/g, "&quot;")
+    .replace(/</g, "&lt;")
+    .replace(/>/g, "&gt;");
+}
+
+/**
+ * Strip all HTML tags, returning plain text.
+ * @param {string} html
+ * @returns {string}
+ */
+export function stripHtml(html) {
+  if (!html || typeof html !== "string") return "";
+  return html.replace(/<[^>]*>/g, "").trim();
+}
diff --git a/lib/mastodon/entities/status.js b/lib/mastodon/entities/status.js
new file mode 100644
index 0000000..b561675
--- /dev/null
+++ b/lib/mastodon/entities/status.js
@@ -0,0 +1,289 @@
+/**
+ * Status entity serializer for Mastodon Client API.
+ *
+ * Converts ap_timeline documents into the Mastodon Status JSON shape.
+ *
+ * CORRECTED field mappings (based on actual extractObjectData output):
+ *   content    <- content.html (NOT contentHtml)
+ *   uri        <- uid (NOT activityUrl)
+ *   account    <- author { name, url, photo, handle, emojis, bot }
+ *   media      <- photo[] + video[] + audio[] (NOT single attachments[])
+ *   card       <- linkPreviews[0] (NOT single card)
+ *   tags       <- category[] (NOT tags[])
+ *   counts     <- counts.boosts, counts.likes, counts.replies
+ *   boost      <- type:"boost" + boostedBy (flat, NOT nested sharedItem)
+ */
+import { serializeAccount } from "./account.js";
+import { sanitizeHtml } from "./sanitize.js";
+
+/**
+ * Serialize an ap_timeline document as a Mastodon Status entity.
+ *
+ * @param {object} item - ap_timeline document
+ * @param {object} options
+ * @param {string} options.baseUrl - Server base URL
+ * @param {Set<string>} [options.favouritedIds] - UIDs the user has liked
+ * @param {Set<string>} [options.rebloggedIds] - UIDs the user has boosted
+ * @param {Set<string>} [options.bookmarkedIds] - UIDs the user has bookmarked
+ * @param {Set<string>} [options.pinnedIds] - UIDs the user has pinned
+ * @returns {object} Mastodon Status entity
+ */
+export function serializeStatus(item, { baseUrl, favouritedIds, rebloggedIds, bookmarkedIds, pinnedIds }) {
+  if (!item) return null;
+
+  const id = item._id.toString();
+  const uid = item.uid || "";
+  const url = item.url || uid;
+
+  // Handle boosts — reconstruct nested reblog wrapper
+  if (item.type === "boost" && item.boostedBy) {
+    // The outer status represents the boost action
+    // The inner status is the original post (the item itself minus boost metadata)
+    const innerItem = { ...item, type: "note", boostedBy: undefined, boostedAt: undefined };
+    const innerStatus = serializeStatus(innerItem, {
+      baseUrl,
+      favouritedIds,
+      rebloggedIds,
+      bookmarkedIds,
+      pinnedIds,
+    });
+
+    return {
+      id,
+      created_at: item.boostedAt || item.createdAt || new Date().toISOString(),
+      in_reply_to_id: null,
+      in_reply_to_account_id: null,
+      sensitive: false,
+      spoiler_text: "",
+      visibility: item.visibility || "public",
+      language: null,
+      uri: uid,
+      url,
+      replies_count: 0,
+      reblogs_count: 0,
+      favourites_count: 0,
+      edited_at: null,
+      favourited: false,
+      reblogged: rebloggedIds?.has(uid) || false,
+      muted: false,
+      bookmarked: false,
+      pinned: false,
+      content: "",
+      filtered: null,
+      reblog: innerStatus,
+      application: null,
+      account: serializeAccount(item.boostedBy, { baseUrl }),
+      media_attachments: [],
+      mentions: [],
+      tags: [],
+      emojis: [],
+      card: null,
+      poll: null,
+    };
+  }
+
+  // Regular status (note, article, question)
+  const content = item.content?.html || item.content?.text || "";
+  const spoilerText = item.summary || "";
+  const sensitive = item.sensitive || false;
+  const visibility = item.visibility || "public";
+  const language = item.language || null;
+  const published = item.published || item.createdAt || new Date().toISOString();
+  const editedAt = item.updated || item.updatedAt || null;
+
+  // Media attachments — merge photo, video, audio arrays
+  const mediaAttachments = [];
+  let attachmentCounter = 0;
+
+  if (item.photo?.length > 0) {
+    for (const p of item.photo) {
+      mediaAttachments.push({
+        id: `${id}-${attachmentCounter++}`,
+        type: "image",
+        url: typeof p === "string" ? p : p.url,
+        preview_url: typeof p === "string" ? p : p.url,
+        remote_url: typeof p === "string" ? p : p.url,
+        text_url: null,
+        meta: buildImageMeta(p),
+        description: typeof p === "object" ? p.alt || "" : "",
+        blurhash: null,
+      });
+    }
+  }
+
+  if (item.video?.length > 0) {
+    for (const v of item.video) {
+      mediaAttachments.push({
+        id: `${id}-${attachmentCounter++}`,
+        type: "video",
+        url: typeof v === "string" ? v : v.url,
+        preview_url: typeof v === "string" ? v : v.url,
+        remote_url: typeof v === "string" ? v : v.url,
+        text_url: null,
+        meta: null,
+        description: typeof v === "object" ? v.alt || "" : "",
+        blurhash: null,
+      });
+    }
+  }
+
+  if (item.audio?.length > 0) {
+    for (const a of item.audio) {
+      mediaAttachments.push({
+        id: `${id}-${attachmentCounter++}`,
+        type: "audio",
+        url: typeof a === "string" ? a : a.url,
+        preview_url: typeof a === "string" ? a : a.url,
+        remote_url: typeof a === "string" ? a : a.url,
+        text_url: null,
+        meta: null,
+        description: typeof a === "object" ? a.alt || "" : "",
+        blurhash: null,
+      });
+    }
+  }
+
+  // Link preview -> card
+  const card = serializeCard(item.linkPreviews?.[0]);
+
+  // Tags from category[]
+  const tags = (item.category || []).map((tag) => ({
+    name: tag,
+    url: `${baseUrl}/tags/${encodeURIComponent(tag)}`,
+  }));
+
+  // Mentions
+  const mentions = (item.mentions || []).map((m) => ({
+    id: "0", // We don't have stable IDs for mentioned accounts
+    username: m.name || "",
+    url: m.url || "",
+    acct: m.name || "",
+  }));
+
+  // Custom emojis
+  const emojis = (item.emojis || []).map((e) => ({
+    shortcode: e.shortcode || "",
+    url: e.url || "",
+    static_url: e.url || "",
+    visible_in_picker: true,
+  }));
+
+  // Counts
+  const repliesCount = item.counts?.replies ?? 0;
+  const reblogsCount = item.counts?.boosts ?? 0;
+  const favouritesCount = item.counts?.likes ?? 0;
+
+  // Poll
+  const poll = serializePoll(item, id);
+
+  // Interaction state
+  const favourited = favouritedIds?.has(uid) || false;
+  const reblogged = rebloggedIds?.has(uid) || false;
+  const bookmarked = bookmarkedIds?.has(uid) || false;
+  const pinned = pinnedIds?.has(uid) || false;
+
+  return {
+    id,
+    created_at: published,
+    in_reply_to_id: item.inReplyTo ? null : null, // TODO: resolve to local ID
+    in_reply_to_account_id: null, // TODO: resolve
+    sensitive,
+    spoiler_text: spoilerText,
+    visibility,
+    language,
+    uri: uid,
+    url,
+    replies_count: repliesCount,
+    reblogs_count: reblogsCount,
+    favourites_count: favouritesCount,
+    edited_at: editedAt || null,
+    favourited,
+    reblogged,
+    muted: false,
+    bookmarked,
+    pinned,
+    content: sanitizeHtml(content),
+    filtered: null,
+    reblog: null,
+    application: null,
+    account: item.author
+      ? serializeAccount(item.author, { baseUrl })
+      : null,
+    media_attachments: mediaAttachments,
+    mentions,
+    tags,
+    emojis,
+    card,
+    poll,
+  };
+}
+
+// ─── Helpers ─────────────────────────────────────────────────────────────────
+
+/**
+ * Serialize a linkPreview object as a Mastodon PreviewCard.
+ */
+function serializeCard(preview) {
+  if (!preview) return null;
+
+  return {
+    url: preview.url || "",
+    title: preview.title || "",
+    description: preview.description || "",
+    type: "link",
+    author_name: "",
+    author_url: "",
+    provider_name: preview.domain || "",
+    provider_url: "",
+    html: "",
+    width: 0,
+    height: 0,
+    image: preview.image || null,
+    embed_url: "",
+    blurhash: null,
+    language: null,
+    published_at: null,
+  };
+}
+
+/**
+ * Build image meta object for media attachments.
+ */
+function buildImageMeta(photo) {
+  if (typeof photo === "string") return null;
+  if (!photo.width && !photo.height) return null;
+
+  return {
+    original: {
+      width: photo.width || 0,
+      height: photo.height || 0,
+      size: photo.width && photo.height ? `${photo.width}x${photo.height}` : null,
+      aspect: photo.width && photo.height ? photo.width / photo.height : null,
+    },
+  };
+}
+
+/**
+ * Serialize poll data from a timeline item.
+ */
+function serializePoll(item, statusId) {
+  if (!item.pollOptions?.length) return null;
+
+  const totalVotes = item.pollOptions.reduce((sum, o) => sum + (o.votes || 0), 0);
+
+  return {
+    id: statusId,
+    expires_at: item.pollEndTime || null,
+    expired: item.pollClosed || false,
+    multiple: false,
+    votes_count: totalVotes,
+    voters_count: item.votersCount || null,
+    options: item.pollOptions.map((o) => ({
+      title: o.name || "",
+      votes_count: o.votes || 0,
+    })),
+    emojis: [],
+    voted: false,
+    own_votes: [],
+  };
+}
diff --git a/lib/mastodon/helpers/id-mapping.js b/lib/mastodon/helpers/id-mapping.js
new file mode 100644
index 0000000..76e6d23
--- /dev/null
+++ b/lib/mastodon/helpers/id-mapping.js
@@ -0,0 +1,32 @@
+/**
+ * Deterministic ID mapping for Mastodon Client API.
+ *
+ * Local accounts use MongoDB _id.toString().
+ * Remote actors use sha256(actorUrl).slice(0, 24) for stable IDs
+ * without requiring a dedicated accounts collection.
+ */
+import crypto from "node:crypto";
+
+/**
+ * Generate a deterministic ID for a remote actor URL.
+ * @param {string} actorUrl - The remote actor's URL
+ * @returns {string} 24-character hex ID
+ */
+export function remoteActorId(actorUrl) {
+  return crypto.createHash("sha256").update(actorUrl).digest("hex").slice(0, 24);
+}
+
+/**
+ * Get the Mastodon API ID for an account.
+ * @param {object} actor - Actor object (local profile or remote author)
+ * @param {boolean} isLocal - Whether this is the local profile
+ * @returns {string}
+ */
+export function accountId(actor, isLocal = false) {
+  if (isLocal && actor._id) {
+    return actor._id.toString();
+  }
+  // Remote actors: use URL-based deterministic hash
+  const url = actor.url || actor.actorUrl || "";
+  return url ? remoteActorId(url) : "0";
+}
diff --git a/lib/mastodon/helpers/interactions.js b/lib/mastodon/helpers/interactions.js
new file mode 100644
index 0000000..3072b02
--- /dev/null
+++ b/lib/mastodon/helpers/interactions.js
@@ -0,0 +1,278 @@
+/**
+ * Shared interaction logic for like/unlike, boost/unboost, bookmark/unbookmark.
+ *
+ * Extracted from admin controllers (interactions-like.js, interactions-boost.js)
+ * so that both the admin UI and Mastodon Client API can reuse the same core logic.
+ *
+ * Each function accepts a context object instead of Express req/res,
+ * making them transport-agnostic.
+ */
+
+import { resolveAuthor } from "../../resolve-author.js";
+
+/**
+ * Like a post — send Like activity and track in ap_interactions.
+ *
+ * @param {object} params
+ * @param {string} params.targetUrl - URL of the post to like
+ * @param {object} params.federation - Fedify federation instance
+ * @param {string} params.handle - Local actor handle
+ * @param {string} params.publicationUrl - Publication base URL
+ * @param {object} params.collections - MongoDB collections (Map or object)
+ * @param {object} params.interactions - ap_interactions collection
+ * @returns {Promise<{ activityId: string }>}
+ */
+export async function likePost({ targetUrl, federation, handle, publicationUrl, collections, interactions }) {
+  const { Like } = await import("@fedify/fedify/vocab");
+  const ctx = federation.createContext(
+    new URL(publicationUrl),
+    { handle, publicationUrl },
+  );
+
+  const documentLoader = await ctx.getDocumentLoader({ identifier: handle });
+  const recipient = await resolveAuthor(targetUrl, ctx, documentLoader, collections);
+
+  const uuid = crypto.randomUUID();
+  const baseUrl = publicationUrl.replace(/\/$/, "");
+  const activityId = `${baseUrl}/activitypub/likes/${uuid}`;
+
+  const like = new Like({
+    id: new URL(activityId),
+    actor: ctx.getActorUri(handle),
+    object: new URL(targetUrl),
+  });
+
+  if (recipient) {
+    await ctx.sendActivity({ identifier: handle }, recipient, like, {
+      orderingKey: targetUrl,
+    });
+  }
+
+  if (interactions) {
+    await interactions.updateOne(
+      { objectUrl: targetUrl, type: "like" },
+      {
+        $set: {
+          objectUrl: targetUrl,
+          type: "like",
+          activityId,
+          recipientUrl: recipient?.id?.href || "",
+          createdAt: new Date().toISOString(),
+        },
+      },
+      { upsert: true },
+    );
+  }
+
+  return { activityId };
+}
+
+/**
+ * Unlike a post — send Undo(Like) activity and remove from ap_interactions.
+ *
+ * @param {object} params
+ * @param {string} params.targetUrl - URL of the post to unlike
+ * @param {object} params.federation - Fedify federation instance
+ * @param {string} params.handle - Local actor handle
+ * @param {string} params.publicationUrl - Publication base URL
+ * @param {object} params.collections - MongoDB collections
+ * @param {object} params.interactions - ap_interactions collection
+ * @returns {Promise<void>}
+ */
+export async function unlikePost({ targetUrl, federation, handle, publicationUrl, collections, interactions }) {
+  const existing = interactions
+    ? await interactions.findOne({ objectUrl: targetUrl, type: "like" })
+    : null;
+
+  if (!existing) {
+    return;
+  }
+
+  const { Like, Undo } = await import("@fedify/fedify/vocab");
+  const ctx = federation.createContext(
+    new URL(publicationUrl),
+    { handle, publicationUrl },
+  );
+
+  const documentLoader = await ctx.getDocumentLoader({ identifier: handle });
+  const recipient = await resolveAuthor(targetUrl, ctx, documentLoader, collections);
+
+  if (recipient) {
+    const like = new Like({
+      id: existing.activityId ? new URL(existing.activityId) : undefined,
+      actor: ctx.getActorUri(handle),
+      object: new URL(targetUrl),
+    });
+
+    const undo = new Undo({
+      actor: ctx.getActorUri(handle),
+      object: like,
+    });
+
+    await ctx.sendActivity({ identifier: handle }, recipient, undo, {
+      orderingKey: targetUrl,
+    });
+  }
+
+  if (interactions) {
+    await interactions.deleteOne({ objectUrl: targetUrl, type: "like" });
+  }
+}
+
+/**
+ * Boost a post — send Announce activity and track in ap_interactions.
+ *
+ * @param {object} params
+ * @param {string} params.targetUrl - URL of the post to boost
+ * @param {object} params.federation - Fedify federation instance
+ * @param {string} params.handle - Local actor handle
+ * @param {string} params.publicationUrl - Publication base URL
+ * @param {object} params.collections - MongoDB collections
+ * @param {object} params.interactions - ap_interactions collection
+ * @returns {Promise<{ activityId: string }>}
+ */
+export async function boostPost({ targetUrl, federation, handle, publicationUrl, collections, interactions }) {
+  const { Announce } = await import("@fedify/fedify/vocab");
+  const ctx = federation.createContext(
+    new URL(publicationUrl),
+    { handle, publicationUrl },
+  );
+
+  const uuid = crypto.randomUUID();
+  const baseUrl = publicationUrl.replace(/\/$/, "");
+  const activityId = `${baseUrl}/activitypub/boosts/${uuid}`;
+
+  const publicAddress = new URL("https://www.w3.org/ns/activitystreams#Public");
+  const followersUri = ctx.getFollowersUri(handle);
+
+  const announce = new Announce({
+    id: new URL(activityId),
+    actor: ctx.getActorUri(handle),
+    object: new URL(targetUrl),
+    to: publicAddress,
+    cc: followersUri,
+  });
+
+  // Send to followers
+  await ctx.sendActivity({ identifier: handle }, "followers", announce, {
+    preferSharedInbox: true,
+    syncCollection: true,
+    orderingKey: targetUrl,
+  });
+
+  // Also send directly to the original post author
+  const documentLoader = await ctx.getDocumentLoader({ identifier: handle });
+  const recipient = await resolveAuthor(targetUrl, ctx, documentLoader, collections);
+  if (recipient) {
+    try {
+      await ctx.sendActivity({ identifier: handle }, recipient, announce, {
+        orderingKey: targetUrl,
+      });
+    } catch {
+      // Non-critical — follower delivery already happened
+    }
+  }
+
+  if (interactions) {
+    await interactions.updateOne(
+      { objectUrl: targetUrl, type: "boost" },
+      {
+        $set: {
+          objectUrl: targetUrl,
+          type: "boost",
+          activityId,
+          createdAt: new Date().toISOString(),
+        },
+      },
+      { upsert: true },
+    );
+  }
+
+  return { activityId };
+}
+
+/**
+ * Unboost a post — send Undo(Announce) activity and remove from ap_interactions.
+ *
+ * @param {object} params
+ * @param {string} params.targetUrl - URL of the post to unboost
+ * @param {object} params.federation - Fedify federation instance
+ * @param {string} params.handle - Local actor handle
+ * @param {string} params.publicationUrl - Publication base URL
+ * @param {object} params.interactions - ap_interactions collection
+ * @returns {Promise<void>}
+ */
+export async function unboostPost({ targetUrl, federation, handle, publicationUrl, interactions }) {
+  const existing = interactions
+    ? await interactions.findOne({ objectUrl: targetUrl, type: "boost" })
+    : null;
+
+  if (!existing) {
+    return;
+  }
+
+  const { Announce, Undo } = await import("@fedify/fedify/vocab");
+  const ctx = federation.createContext(
+    new URL(publicationUrl),
+    { handle, publicationUrl },
+  );
+
+  const announce = new Announce({
+    id: existing.activityId ? new URL(existing.activityId) : undefined,
+    actor: ctx.getActorUri(handle),
+    object: new URL(targetUrl),
+  });
+
+  const undo = new Undo({
+    actor: ctx.getActorUri(handle),
+    object: announce,
+  });
+
+  await ctx.sendActivity({ identifier: handle }, "followers", undo, {
+    preferSharedInbox: true,
+    syncCollection: true,
+    orderingKey: targetUrl,
+  });
+
+  if (interactions) {
+    await interactions.deleteOne({ objectUrl: targetUrl, type: "boost" });
+  }
+}
+
+/**
+ * Bookmark a post — local-only, no federation.
+ *
+ * @param {object} params
+ * @param {string} params.targetUrl - URL of the post to bookmark
+ * @param {object} params.interactions - ap_interactions collection
+ * @returns {Promise<void>}
+ */
+export async function bookmarkPost({ targetUrl, interactions }) {
+  if (!interactions) return;
+
+  await interactions.updateOne(
+    { objectUrl: targetUrl, type: "bookmark" },
+    {
+      $set: {
+        objectUrl: targetUrl,
+        type: "bookmark",
+        createdAt: new Date().toISOString(),
+      },
+    },
+    { upsert: true },
+  );
+}
+
+/**
+ * Remove a bookmark — local-only, no federation.
+ *
+ * @param {object} params
+ * @param {string} params.targetUrl - URL of the post to unbookmark
+ * @param {object} params.interactions - ap_interactions collection
+ * @returns {Promise<void>}
+ */
+export async function unbookmarkPost({ targetUrl, interactions }) {
+  if (!interactions) return;
+
+  await interactions.deleteOne({ objectUrl: targetUrl, type: "bookmark" });
+}
diff --git a/lib/mastodon/helpers/pagination.js b/lib/mastodon/helpers/pagination.js
new file mode 100644
index 0000000..f266107
--- /dev/null
+++ b/lib/mastodon/helpers/pagination.js
@@ -0,0 +1,130 @@
+/**
+ * Mastodon-compatible cursor pagination helpers.
+ *
+ * Uses MongoDB ObjectId as cursor (chronologically ordered).
+ * Emits RFC 8288 Link headers that masto.js / Phanpy parse.
+ */
+import { ObjectId } from "mongodb";
+
+const DEFAULT_LIMIT = 20;
+const MAX_LIMIT = 40;
+
+/**
+ * Parse and clamp the limit parameter.
+ *
+ * @param {string|number} raw - Raw limit value from query string
+ * @returns {number}
+ */
+export function parseLimit(raw) {
+  const n = Number.parseInt(String(raw), 10);
+  if (!Number.isFinite(n) || n < 1) return DEFAULT_LIMIT;
+  return Math.min(n, MAX_LIMIT);
+}
+
+/**
+ * Build a MongoDB filter object for cursor-based pagination.
+ *
+ * Mastodon cursor params (all optional, applied to `_id`):
+ *   max_id   — return items older than this ID (exclusive)
+ *   min_id   — return items newer than this ID (exclusive), closest first
+ *   since_id — return items newer than this ID (exclusive), most recent first
+ *
+ * @param {object} baseFilter - Existing MongoDB filter to extend
+ * @param {object} cursors
+ * @param {string} [cursors.max_id]
+ * @param {string} [cursors.min_id]
+ * @param {string} [cursors.since_id]
+ * @returns {{ filter: object, sort: object, reverse: boolean }}
+ */
+export function buildPaginationQuery(baseFilter, { max_id, min_id, since_id } = {}) {
+  const filter = { ...baseFilter };
+  let sort = { _id: -1 }; // newest first (default)
+  let reverse = false;
+
+  if (max_id) {
+    try {
+      filter._id = { ...filter._id, $lt: new ObjectId(max_id) };
+    } catch {
+      // Invalid ObjectId — ignore
+    }
+  }
+
+  if (since_id) {
+    try {
+      filter._id = { ...filter._id, $gt: new ObjectId(since_id) };
+    } catch {
+      // Invalid ObjectId — ignore
+    }
+  }
+
+  if (min_id) {
+    try {
+      filter._id = { ...filter._id, $gt: new ObjectId(min_id) };
+      // min_id returns results closest to the cursor, so sort ascending
+      // then reverse the results before returning
+      sort = { _id: 1 };
+      reverse = true;
+    } catch {
+      // Invalid ObjectId — ignore
+    }
+  }
+
+  return { filter, sort, reverse };
+}
+
+/**
+ * Set the Link pagination header on an Express response.
+ *
+ * @param {object} res - Express response object
+ * @param {object} req - Express request object (for building URLs)
+ * @param {Array} items - Result items (must have `_id` or `id`)
+ * @param {number} limit - The limit used for the query
+ */
+export function setPaginationHeaders(res, req, items, limit) {
+  if (!items?.length) return;
+
+  // Only emit Link if we got a full page (may have more)
+  if (items.length < limit) return;
+
+  const firstId = itemId(items[0]);
+  const lastId = itemId(items[items.length - 1]);
+
+  if (!firstId || !lastId) return;
+
+  const baseUrl = `${req.protocol}://${req.get("host")}${req.path}`;
+
+  // Preserve existing query params (like types[] for notifications)
+  const existingParams = new URLSearchParams();
+  for (const [key, value] of Object.entries(req.query)) {
+    if (key === "max_id" || key === "min_id" || key === "since_id") continue;
+    if (Array.isArray(value)) {
+      for (const v of value) existingParams.append(key, v);
+    } else {
+      existingParams.set(key, String(value));
+    }
+  }
+
+  const links = [];
+
+  // rel="next" — older items (max_id = last item's ID)
+  const nextParams = new URLSearchParams(existingParams);
+  nextParams.set("max_id", lastId);
+  links.push(`<${baseUrl}?${nextParams.toString()}>; rel="next"`);
+
+  // rel="prev" — newer items (min_id = first item's ID)
+  const prevParams = new URLSearchParams(existingParams);
+  prevParams.set("min_id", firstId);
+  links.push(`<${baseUrl}?${prevParams.toString()}>; rel="prev"`);
+
+  res.set("Link", links.join(", "));
+}
+
+/**
+ * Extract the string ID from an item.
+ */
+function itemId(item) {
+  if (!item) return null;
+  if (item._id) return item._id.toString();
+  if (item.id) return String(item.id);
+  return null;
+}
diff --git a/lib/mastodon/middleware/cors.js b/lib/mastodon/middleware/cors.js
new file mode 100644
index 0000000..a8dfeca
--- /dev/null
+++ b/lib/mastodon/middleware/cors.js
@@ -0,0 +1,25 @@
+/**
+ * CORS middleware for Mastodon Client API routes.
+ *
+ * Mandatory for browser-based SPA clients like Phanpy that make
+ * cross-origin requests. Without this, the browser's Same-Origin
+ * Policy blocks all API calls.
+ */
+
+const ALLOWED_METHODS = "GET, HEAD, POST, PUT, DELETE, PATCH";
+const ALLOWED_HEADERS = "Authorization, Content-Type, Idempotency-Key";
+const EXPOSED_HEADERS = "Link";
+
+export function corsMiddleware(req, res, next) {
+  res.set("Access-Control-Allow-Origin", "*");
+  res.set("Access-Control-Allow-Methods", ALLOWED_METHODS);
+  res.set("Access-Control-Allow-Headers", ALLOWED_HEADERS);
+  res.set("Access-Control-Expose-Headers", EXPOSED_HEADERS);
+
+  // Handle preflight requests
+  if (req.method === "OPTIONS") {
+    return res.status(204).end();
+  }
+
+  next();
+}
diff --git a/lib/mastodon/middleware/error-handler.js b/lib/mastodon/middleware/error-handler.js
new file mode 100644
index 0000000..b965e6e
--- /dev/null
+++ b/lib/mastodon/middleware/error-handler.js
@@ -0,0 +1,37 @@
+/**
+ * Error handling middleware for Mastodon Client API routes.
+ *
+ * Ensures all errors return JSON in Mastodon's expected format
+ * instead of HTML error pages that masto.js cannot parse.
+ *
+ * Standard format: { "error": "description" }
+ * OAuth format:    { "error": "error_type", "error_description": "..." }
+ */
+
+// eslint-disable-next-line no-unused-vars
+export function errorHandler(err, req, res, _next) {
+  const status = err.status || err.statusCode || 500;
+
+  // OAuth errors use RFC 6749 format
+  if (err.oauthError) {
+    return res.status(status).json({
+      error: err.oauthError,
+      error_description: err.message || "An error occurred",
+    });
+  }
+
+  // Standard Mastodon error format
+  res.status(status).json({
+    error: err.message || "An unexpected error occurred",
+  });
+}
+
+/**
+ * 501 catch-all for unimplemented API endpoints.
+ * Must be mounted AFTER all implemented routes.
+ */
+export function notImplementedHandler(req, res) {
+  res.status(501).json({
+    error: "Not implemented",
+  });
+}
diff --git a/lib/mastodon/middleware/scope-required.js b/lib/mastodon/middleware/scope-required.js
new file mode 100644
index 0000000..acba953
--- /dev/null
+++ b/lib/mastodon/middleware/scope-required.js
@@ -0,0 +1,86 @@
+/**
+ * Scope enforcement middleware for Mastodon Client API.
+ *
+ * Supports scope hierarchy: parent scope covers all children.
+ *   "read" grants "read:accounts", "read:statuses", etc.
+ *   "write" grants "write:statuses", "write:favourites", etc.
+ *
+ * Legacy "follow" scope maps to read/write for blocks, follows, and mutes.
+ */
+
+/**
+ * Scopes that the legacy "follow" scope grants access to.
+ */
+const FOLLOW_SCOPE_EXPANSION = [
+  "read:blocks",
+  "write:blocks",
+  "read:follows",
+  "write:follows",
+  "read:mutes",
+  "write:mutes",
+];
+
+/**
+ * Create middleware that checks if the token has the required scope.
+ *
+ * @param {...string} requiredScopes - One or more scopes (any match = pass)
+ * @returns {Function} Express middleware
+ */
+export function scopeRequired(...requiredScopes) {
+  return (req, res, next) => {
+    const token = req.mastodonToken;
+    if (!token) {
+      return res.status(401).json({
+        error: "The access token is invalid",
+      });
+    }
+
+    const grantedScopes = token.scopes || [];
+
+    const hasScope = requiredScopes.some((required) =>
+      checkScope(grantedScopes, required),
+    );
+
+    if (!hasScope) {
+      return res.status(403).json({
+        error: `This action is outside the authorized scopes. Required: ${requiredScopes.join(" or ")}`,
+      });
+    }
+
+    next();
+  };
+}
+
+/**
+ * Check if granted scopes satisfy a required scope.
+ *
+ * Rules:
+ * - Exact match: "read:accounts" satisfies "read:accounts"
+ * - Parent match: "read" satisfies "read:accounts"
+ * - "follow" expands to read/write for blocks, follows, mutes
+ * - "profile" satisfies "read:accounts" (for verify_credentials)
+ *
+ * @param {string[]} granted - Scopes on the token
+ * @param {string} required - Scope being checked
+ * @returns {boolean}
+ */
+function checkScope(granted, required) {
+  // Exact match
+  if (granted.includes(required)) return true;
+
+  // Parent scope: "read" covers "read:*", "write" covers "write:*"
+  const [parent] = required.split(":");
+  if (parent && granted.includes(parent)) return true;
+
+  // Legacy "follow" scope expansion
+  if (granted.includes("follow") && FOLLOW_SCOPE_EXPANSION.includes(required)) {
+    return true;
+  }
+
+  // "profile" scope can satisfy "read:accounts"
+  if (required === "read:accounts" && granted.includes("profile")) {
+    return true;
+  }
+
+  return false;
+}
diff --git a/lib/mastodon/middleware/token-required.js b/lib/mastodon/middleware/token-required.js
new file mode 100644
index 0000000..6517278
--- /dev/null
+++ b/lib/mastodon/middleware/token-required.js
@@ -0,0 +1,57 @@
+/**
+ * Bearer token validation middleware for Mastodon Client API.
+ *
+ * Extracts the Bearer token from the Authorization header,
+ * validates it against the ap_oauth_tokens collection,
+ * and attaches token data to `req.mastodonToken`.
+ */
+
+/**
+ * Require a valid Bearer token. Returns 401 if invalid/missing.
+ */
+export async function tokenRequired(req, res, next) {
+  const token = await resolveToken(req);
+
+  if (!token) {
+    return res.status(401).json({
+      error: "The access token is invalid",
+    });
+  }
+
+  req.mastodonToken = token;
+  next();
+}
+
+/**
+ * Optional token — sets req.mastodonToken to null if absent.
+ * For public endpoints that personalize when authenticated.
+ */
+export async function optionalToken(req, res, next) {
+  req.mastodonToken = await resolveToken(req);
+  next();
+}
+
+/**
+ * Extract and validate Bearer token from request.
+ * @returns {object|null} Token document or null
+ */
+async function resolveToken(req) {
+  const authHeader = req.get("authorization");
+  if (!authHeader?.startsWith("Bearer ")) return null;
+
+  const accessToken = authHeader.slice(7);
+  if (!accessToken) return null;
+
+  const collections = req.app.locals.mastodonCollections;
+  const token = await collections.ap_oauth_tokens.findOne({
+    accessToken,
+    revokedAt: null,
+  });
+
+  if (!token) return null;
+
+  // Check expiry if set
+  if (token.expiresAt && token.expiresAt < new Date()) return null;
+
+  return token;
+}
diff --git a/lib/mastodon/router.js b/lib/mastodon/router.js
new file mode 100644
index 0000000..ffdd92d
--- /dev/null
+++ b/lib/mastodon/router.js
@@ -0,0 +1,96 @@
+/**
+ * Mastodon Client API — main router.
+ *
+ * Combines all sub-routers, applies CORS and error handling middleware.
+ * Mounted at "/" via Indiekit.addEndpoint() so Mastodon clients can access
+ * /api/v1/*, /api/v2/*, /oauth/* at the domain root.
+ */
+import express from "express";
+import { corsMiddleware } from "./middleware/cors.js";
+import { tokenRequired, optionalToken } from "./middleware/token-required.js";
+import { errorHandler, notImplementedHandler } from "./middleware/error-handler.js";
+
+// Route modules
+import oauthRouter from "./routes/oauth.js";
+import instanceRouter from "./routes/instance.js";
+import accountsRouter from "./routes/accounts.js";
+import statusesRouter from "./routes/statuses.js";
+import timelinesRouter from "./routes/timelines.js";
+import notificationsRouter from "./routes/notifications.js";
+import searchRouter from "./routes/search.js";
+import mediaRouter from "./routes/media.js";
+import stubsRouter from "./routes/stubs.js";
+
+/**
+ * Create the combined Mastodon API router.
+ *
+ * @param {object} options
+ * @param {object} options.collections - MongoDB collections object
+ * @param {object} [options.pluginOptions] - Plugin options (handle, etc.)
+ * @returns {import("express").Router} Express router
+ */
+export function createMastodonRouter({ collections, pluginOptions = {} }) {
+  const router = express.Router(); // eslint-disable-line new-cap
+
+  // ─── Body parsers ───────────────────────────────────────────────────────
+  // Mastodon clients send JSON, form-urlencoded, and occasionally text/plain.
+  // These must be applied before route handlers.
+  router.use("/api", express.json());
+  router.use("/api", express.urlencoded({ extended: true }));
+  router.use("/oauth", express.json());
+  router.use("/oauth", express.urlencoded({ extended: true }));
+
+  // ─── CORS ───────────────────────────────────────────────────────────────
+  router.use("/api", corsMiddleware);
+  router.use("/oauth/token", corsMiddleware);
+  router.use("/oauth/revoke", corsMiddleware);
+  router.use("/.well-known/oauth-authorization-server", corsMiddleware);
+
+  // ─── Inject collections + plugin options into req ───────────────────────
+  router.use("/api", (req, res, next) => {
+    req.app.locals.mastodonCollections = collections;
+    req.app.locals.mastodonPluginOptions = pluginOptions;
+    next();
+  });
+  router.use("/oauth", (req, res, next) => {
+    req.app.locals.mastodonCollections = collections;
+    req.app.locals.mastodonPluginOptions = pluginOptions;
+    next();
+  });
+  router.use("/.well-known/oauth-authorization-server", (req, res, next) => {
+    req.app.locals.mastodonCollections = collections;
+    req.app.locals.mastodonPluginOptions = pluginOptions;
+    next();
+  });
+
+  // ─── Token resolution ───────────────────────────────────────────────────
+  // Apply optional token resolution to all API routes so handlers can check
+  // req.mastodonToken. Specific routes that require auth use tokenRequired.
+  router.use("/api", optionalToken);
+
+  // ─── OAuth routes (no token required for most) ──────────────────────────
+  router.use(oauthRouter);
+
+  // ─── Public API routes (no auth required) ───────────────────────────────
+  router.use(instanceRouter);
+
+  // ─── Authenticated API routes ───────────────────────────────────────────
+  router.use(accountsRouter);
+  router.use(statusesRouter);
+  router.use(timelinesRouter);
+  router.use(notificationsRouter);
+  router.use(searchRouter);
+  router.use(mediaRouter);
+  router.use(stubsRouter);
+
+  // ─── Catch-all for unimplemented endpoints ──────────────────────────────
+  // Express 5 path-to-regexp v8: use {*name} for wildcard
+  router.all("/api/v1/{*rest}", notImplementedHandler);
+  router.all("/api/v2/{*rest}", notImplementedHandler);
+
+  // ─── Error handler ──────────────────────────────────────────────────────
+  router.use("/api", errorHandler);
+  router.use("/oauth", errorHandler);
+
+  return router;
+}
diff --git a/lib/mastodon/routes/accounts.js b/lib/mastodon/routes/accounts.js
new file mode 100644
index 0000000..702dd39
--- /dev/null
+++ b/lib/mastodon/routes/accounts.js
@@ -0,0 +1,552 @@
+/**
+ * Account endpoints for Mastodon Client API.
+ *
+ * Phase 1: verify_credentials, preferences, account lookup
+ * Phase 2: relationships, follow/unfollow, account statuses
+ */
+import express from "express";
+import { serializeCredentialAccount, serializeAccount } from "../entities/account.js";
+import { accountId, remoteActorId } from "../helpers/id-mapping.js";
+
+const router = express.Router(); // eslint-disable-line new-cap
+
+// ─── GET /api/v1/accounts/verify_credentials ─────────────────────────────────
+
+router.get("/api/v1/accounts/verify_credentials", async (req, res, next) => {
+  try {
+    const token = req.mastodonToken;
+    if (!token) {
+      return res.status(401).json({ error: "The access token is invalid" });
+    }
+
+    const baseUrl = `${req.protocol}://${req.get("host")}`;
+    const collections = req.app.locals.mastodonCollections;
+    const pluginOptions = req.app.locals.mastodonPluginOptions || {};
+    const handle = pluginOptions.handle || "user";
+
+    const profile = await collections.ap_profile.findOne({});
+    if (!profile) {
+      return res.status(404).json({ error: "Profile not found" });
+    }
+
+    // Get counts
+    let counts = {};
+    try {
+      const [statuses, followers, following] = await Promise.all([
+        collections.ap_timeline.countDocuments({
+          "author.url": profile.url,
+        }),
+        collections.ap_followers.countDocuments({}),
+        collections.ap_following.countDocuments({}),
+      ]);
+      counts = { statuses, followers, following };
+    } catch {
+      counts = { statuses: 0, followers: 0, following: 0 };
+    }
+
+    const account = serializeCredentialAccount(profile, {
+      baseUrl,
+      handle,
+      counts,
+    });
+
+    res.json(account);
+  } catch (error) {
+    next(error);
+  }
+});
+
+// ─── GET /api/v1/preferences ─────────────────────────────────────────────────
+
+router.get("/api/v1/preferences", (req, res) => {
+  res.json({
+    "posting:default:visibility": "public",
+    "posting:default:sensitive": false,
+    "posting:default:language": "en",
+    "reading:expand:media": "default",
+    "reading:expand:spoilers": false,
+  });
+});
+
+// ─── GET /api/v1/accounts/lookup ─────────────────────────────────────────────
+
+router.get("/api/v1/accounts/lookup", async (req, res, next) => {
+  try {
+    const { acct } = req.query;
+    if (!acct) {
+      return res.status(400).json({ error: "Missing acct parameter" });
+    }
+
+    const baseUrl = `${req.protocol}://${req.get("host")}`;
+    const collections = req.app.locals.mastodonCollections;
+    const pluginOptions = req.app.locals.mastodonPluginOptions || {};
+    const handle = pluginOptions.handle || "user";
+
+    // Check if looking up local account
+    const bareAcct = acct.startsWith("@") ? acct.slice(1) : acct;
+    const localDomain = req.get("host");
+
+    if (
+      bareAcct === handle ||
+      bareAcct === `${handle}@${localDomain}`
+    ) {
+      const profile = await collections.ap_profile.findOne({});
+      if (profile) {
+        return res.json(
+          serializeAccount(profile, { baseUrl, isLocal: true, handle }),
+        );
+      }
+    }
+
+    // Check followers/following for known remote actors
+    const follower = await collections.ap_followers.findOne({
+      $or: [
+        { handle: `@${bareAcct}` },
+        { handle: bareAcct },
+      ],
+    });
+    if (follower) {
+      return res.json(
+        serializeAccount(
+          { name: follower.name, url: follower.actorUrl, photo: follower.avatar, handle: follower.handle },
+          { baseUrl },
+        ),
+      );
+    }
+
+    return res.status(404).json({ error: "Record not found" });
+  } catch (error) {
+    next(error);
+  }
+});
+
+// ─── GET /api/v1/accounts/:id ────────────────────────────────────────────────
+
+router.get("/api/v1/accounts/:id", async (req, res, next) => {
+  try {
+    const { id } = req.params;
+    const baseUrl = `${req.protocol}://${req.get("host")}`;
+    const collections = req.app.locals.mastodonCollections;
+    const pluginOptions = req.app.locals.mastodonPluginOptions || {};
+    const handle = pluginOptions.handle || "user";
+
+    // Check if it's the local profile
+    const profile = await collections.ap_profile.findOne({});
+    if (profile && profile._id.toString() === id) {
+      return res.json(
+        serializeAccount(profile, { baseUrl, isLocal: true, handle }),
+      );
+    }
+
+    // Search known actors (followers, following, timeline authors)
+    // by checking if the deterministic hash matches
+    const follower = await collections.ap_followers
+      .find({})
+      .toArray();
+    for (const f of follower) {
+      if (remoteActorId(f.actorUrl) === id) {
+        return res.json(
+          serializeAccount(
+            { name: f.name, url: f.actorUrl, photo: f.avatar, handle: f.handle },
+            { baseUrl },
+          ),
+        );
+      }
+    }
+
+    const following = await collections.ap_following
+      .find({})
+      .toArray();
+    for (const f of following) {
+      if (remoteActorId(f.actorUrl) === id) {
+        return res.json(
+          serializeAccount(
+            { name: f.name, url: f.actorUrl, photo: f.avatar, handle: f.handle },
+            { baseUrl },
+          ),
+        );
+      }
+    }
+
+    // Try timeline authors
+    const timelineItem = await collections.ap_timeline.findOne({
+      $expr: { $ne: [{ $type: "$author.url" }, "missing"] },
+    });
+    // For now, if not found in known actors, return 404
+    return res.status(404).json({ error: "Record not found" });
+  } catch (error) {
+    next(error);
+  }
+});
+
+// ─── GET /api/v1/accounts/relationships ──────────────────────────────────────
+
+router.get("/api/v1/accounts/relationships", async (req, res, next) => {
+  try {
+    // id[] can come as single value or array
+    let ids = req.query["id[]"] || req.query.id || [];
+    if (!Array.isArray(ids)) ids = [ids];
+
+    if (ids.length === 0) {
+      return res.json([]);
+    }
+
+    const collections = req.app.locals.mastodonCollections;
+
+    // Load all followers/following for efficient lookup
+    const [followers, following, blocked, muted] = await Promise.all([
+      collections.ap_followers.find({}).toArray(),
+      collections.ap_following.find({}).toArray(),
+      collections.ap_blocked.find({}).toArray(),
+      collections.ap_muted.find({}).toArray(),
+    ]);
+
+    const followerIds = new Set(followers.map((f) => remoteActorId(f.actorUrl)));
+    const followingIds = new Set(following.map((f) => remoteActorId(f.actorUrl)));
+    const blockedIds = new Set(blocked.map((b) => remoteActorId(b.url)));
+    const mutedIds = new Set(muted.filter((m) => m.url).map((m) => remoteActorId(m.url)));
+
+    const relationships = ids.map((id) => ({
+      id,
+      following: followingIds.has(id),
+      showing_reblogs: followingIds.has(id),
+      notifying: false,
+      languages: [],
+      followed_by: followerIds.has(id),
+      blocking: blockedIds.has(id),
+      blocked_by: false,
+      muting: mutedIds.has(id),
+      muting_notifications: mutedIds.has(id),
+      requested: false,
+      requested_by: false,
+      domain_blocking: false,
+      endorsed: false,
+      note: "",
+    }));
+
+    res.json(relationships);
+  } catch (error) {
+    next(error);
+  }
+});
+
+// ─── GET /api/v1/accounts/familiar_followers ─────────────────────────────────
+
+router.get("/api/v1/accounts/familiar_followers", (req, res) => {
+  // Stub — returns empty for each requested ID
+  let ids = req.query["id[]"] || req.query.id || [];
+  if (!Array.isArray(ids)) ids = [ids];
+  res.json(ids.map((id) => ({ id, accounts: [] })));
+});
+
+// ─── POST /api/v1/accounts/:id/follow ───────────────────────────────────────
+
+router.post("/api/v1/accounts/:id/follow", async (req, res, next) => {
+  try {
+    const token = req.mastodonToken;
+    if (!token) {
+      return res.status(401).json({ error: "The access token is invalid" });
+    }
+
+    const { id } = req.params;
+    const collections = req.app.locals.mastodonCollections;
+    const pluginOptions = req.app.locals.mastodonPluginOptions || {};
+
+    // Resolve the account ID to an actor URL
+    const actorUrl = await resolveActorUrl(id, collections);
+    if (!actorUrl) {
+      return res.status(404).json({ error: "Record not found" });
+    }
+
+    // Use the plugin's followActor method
+    if (pluginOptions.followActor) {
+      const result = await pluginOptions.followActor(actorUrl);
+      if (!result.ok) {
+        return res.status(422).json({ error: result.error || "Follow failed" });
+      }
+    }
+
+    // Return relationship
+    const followingIds = new Set();
+    const following = await collections.ap_following.find({}).toArray();
+    for (const f of following) {
+      followingIds.add(remoteActorId(f.actorUrl));
+    }
+
+    const followerIds = new Set();
+    const followers = await collections.ap_followers.find({}).toArray();
+    for (const f of followers) {
+      followerIds.add(remoteActorId(f.actorUrl));
+    }
+
+    res.json({
+      id,
+      following: true,
+      showing_reblogs: true,
+      notifying: false,
+      languages: [],
+      followed_by: followerIds.has(id),
+      blocking: false,
+      blocked_by: false,
+      muting: false,
+      muting_notifications: false,
+      requested: false,
+      requested_by: false,
+      domain_blocking: false,
+      endorsed: false,
+      note: "",
+    });
+  } catch (error) {
+    next(error);
+  }
+});
+
+// ─── POST /api/v1/accounts/:id/unfollow ─────────────────────────────────────
+
+router.post("/api/v1/accounts/:id/unfollow", async (req, res, next) => {
+  try {
+    const token = req.mastodonToken;
+    if (!token) {
+      return res.status(401).json({ error: "The access token is invalid" });
+    }
+
+    const { id } = req.params;
+    const collections = req.app.locals.mastodonCollections;
+    const pluginOptions = req.app.locals.mastodonPluginOptions || {};
+
+    const actorUrl = await resolveActorUrl(id, collections);
+    if (!actorUrl) {
+      return res.status(404).json({ error: "Record not found" });
+    }
+
+    if (pluginOptions.unfollowActor) {
+      const result = await pluginOptions.unfollowActor(actorUrl);
+      if (!result.ok) {
+        return res.status(422).json({ error: result.error || "Unfollow failed" });
+      }
+    }
+
+    const followerIds = new Set();
+    const followers = await collections.ap_followers.find({}).toArray();
+    for (const f of followers) {
+      followerIds.add(remoteActorId(f.actorUrl));
+    }
+
+    res.json({
+      id,
+      following: false,
+      showing_reblogs: true,
+      notifying: false,
+      languages: [],
+      followed_by: followerIds.has(id),
+      blocking: false,
+      blocked_by: false,
+      muting: false,
+      muting_notifications: false,
+      requested: false,
+      requested_by: false,
+      domain_blocking: false,
+      endorsed: false,
+      note: "",
+    });
+  } catch (error) {
+    next(error);
+  }
+});
+
+// ─── POST /api/v1/accounts/:id/mute ────────────────────────────────────────
+
+router.post("/api/v1/accounts/:id/mute", async (req, res, next) => {
+  try {
+    const token = req.mastodonToken;
+    if (!token) {
+      return res.status(401).json({ error: "The access token is invalid" });
+    }
+
+    const { id } = req.params;
+    const collections = req.app.locals.mastodonCollections;
+
+    const actorUrl = await resolveActorUrl(id, collections);
+    if (actorUrl && collections.ap_muted) {
+      await collections.ap_muted.updateOne(
+        { url: actorUrl },
+        { $set: { url: actorUrl, createdAt: new Date().toISOString() } },
+        { upsert: true },
+      );
+    }
+
+    res.json({
+      id,
+      following: false,
+      showing_reblogs: true,
+      notifying: false,
+      languages: [],
+      followed_by: false,
+      blocking: false,
+      blocked_by: false,
+      muting: true,
+      muting_notifications: true,
+      requested: false,
+      requested_by: false,
+      domain_blocking: false,
+      endorsed: false,
+      note: "",
+    });
+  } catch (error) {
+    next(error);
+  }
+});
+
+// ─── POST /api/v1/accounts/:id/unmute ───────────────────────────────────────
+
+router.post("/api/v1/accounts/:id/unmute", async (req, res, next) => {
+  try {
+    const token = req.mastodonToken;
+    if (!token) {
+      return res.status(401).json({ error: "The access token is invalid" });
+    }
+
+    const { id } = req.params;
+    const collections = req.app.locals.mastodonCollections;
+
+    const actorUrl = await resolveActorUrl(id, collections);
+    if (actorUrl && collections.ap_muted) {
+      await collections.ap_muted.deleteOne({ url: actorUrl });
+    }
+
+    res.json({
+      id,
+      following: false,
+      showing_reblogs: true,
+      notifying: false,
+      languages: [],
+      followed_by: false,
+      blocking: false,
+      blocked_by: false,
+      muting: false,
+      muting_notifications: false,
+      requested: false,
+      requested_by: false,
+      domain_blocking: false,
+      endorsed: false,
+      note: "",
+    });
+  } catch (error) {
+    next(error);
+  }
+});
+
+// ─── POST /api/v1/accounts/:id/block ───────────────────────────────────────
+
+router.post("/api/v1/accounts/:id/block", async (req, res, next) => {
+  try {
+    const token = req.mastodonToken;
+    if (!token) {
+      return res.status(401).json({ error: "The access token is invalid" });
+    }
+
+    const { id } = req.params;
+    const collections = req.app.locals.mastodonCollections;
+
+    const actorUrl = await resolveActorUrl(id, collections);
+    if (actorUrl && collections.ap_blocked) {
+      await collections.ap_blocked.updateOne(
+        { url: actorUrl },
+        { $set: { url: actorUrl, createdAt: new Date().toISOString() } },
+        { upsert: true },
+      );
+    }
+
+    res.json({
+      id,
+      following: false,
+      showing_reblogs: true,
+      notifying: false,
+      languages: [],
+      followed_by: false,
+      blocking: true,
+      blocked_by: false,
+      muting: false,
+      muting_notifications: false,
+      requested: false,
+      requested_by: false,
+      domain_blocking: false,
+      endorsed: false,
+      note: "",
+    });
+  } catch (error) {
+    next(error);
+  }
+});
+
+// ─── POST /api/v1/accounts/:id/unblock ──────────────────────────────────────
+
+router.post("/api/v1/accounts/:id/unblock", async (req, res, next) => {
+  try {
+    const token = req.mastodonToken;
+    if (!token) {
+      return res.status(401).json({ error: "The access token is invalid" });
+    }
+
+    const { id } = req.params;
+    const collections = req.app.locals.mastodonCollections;
+
+    const actorUrl = await resolveActorUrl(id, collections);
+    if (actorUrl && collections.ap_blocked) {
+      await collections.ap_blocked.deleteOne({ url: actorUrl });
+    }
+
+    res.json({
+      id,
+      following: false,
+      showing_reblogs: true,
+      notifying: false,
+      languages: [],
+      followed_by: false,
+      blocking: false,
+      blocked_by: false,
+      muting: false,
+      muting_notifications: false,
+      requested: false,
+      requested_by: false,
+      domain_blocking: false,
+      endorsed: false,
+      note: "",
+    });
+  } catch (error) {
+    next(error);
+  }
+});
+
+// ─── Helpers ─────────────────────────────────────────────────────────────────
+
+/**
+ * Resolve an account ID back to an actor URL by scanning followers/following.
+ */
+async function resolveActorUrl(id, collections) {
+  // Check if it's the local profile
+  const profile = await collections.ap_profile.findOne({});
+  if (profile && profile._id.toString() === id) {
+    return profile.url;
+  }
+
+  // Check followers
+  const followers = await collections.ap_followers.find({}).toArray();
+  for (const f of followers) {
+    if (remoteActorId(f.actorUrl) === id) {
+      return f.actorUrl;
+    }
+  }
+
+  // Check following
+  const following = await collections.ap_following.find({}).toArray();
+  for (const f of following) {
+    if (remoteActorId(f.actorUrl) === id) {
+      return f.actorUrl;
+    }
+  }
+
+  return null;
+}
+
+export default router;
diff --git a/lib/mastodon/routes/instance.js b/lib/mastodon/routes/instance.js
new file mode 100644
index 0000000..5cd7d53
--- /dev/null
+++ b/lib/mastodon/routes/instance.js
@@ -0,0 +1,207 @@
+/**
+ * Instance info endpoints for Mastodon Client API.
+ *
+ * GET /api/v2/instance — v2 format (primary)
+ * GET /api/v1/instance — v1 format (fallback for older clients)
+ */
+import express from "express";
+import { serializeAccount } from "../entities/account.js";
+
+const router = express.Router(); // eslint-disable-line new-cap
+
+// ─── GET /api/v2/instance ────────────────────────────────────────────────────
+
+router.get("/api/v2/instance", async (req, res, next) => {
+  try {
+    const baseUrl = `${req.protocol}://${req.get("host")}`;
+    const domain = req.get("host");
+    const collections = req.app.locals.mastodonCollections;
+    const pluginOptions = req.app.locals.mastodonPluginOptions || {};
+
+    const profile = await collections.ap_profile.findOne({});
+    const contactAccount = profile
+      ? serializeAccount(profile, {
+          baseUrl,
+          isLocal: true,
+          handle: pluginOptions.handle || "user",
+        })
+      : null;
+
+    res.json({
+      domain,
+      title: profile?.name || domain,
+      version: "4.0.0 (compatible; Indiekit ActivityPub)",
+      source_url: "https://github.com/getindiekit/indiekit",
+      description: profile?.summary || `An Indiekit instance at ${domain}`,
+      usage: {
+        users: {
+          active_month: 1,
+        },
+      },
+      thumbnail: {
+        url: profile?.icon || `${baseUrl}/favicon.ico`,
+        blurhash: null,
+        versions: {},
+      },
+      icon: [],
+      languages: ["en"],
+      configuration: {
+        urls: {
+          streaming: "",
+        },
+        accounts: {
+          max_featured_tags: 10,
+          max_pinned_statuses: 10,
+        },
+        statuses: {
+          max_characters: 5000,
+          max_media_attachments: 4,
+          characters_reserved_per_url: 23,
+        },
+        media_attachments: {
+          supported_mime_types: [
+            "image/jpeg",
+            "image/png",
+            "image/gif",
+            "image/webp",
+            "video/mp4",
+            "video/webm",
+            "audio/mpeg",
+            "audio/ogg",
+          ],
+          image_size_limit: 16_777_216,
+          image_matrix_limit: 16_777_216,
+          video_size_limit: 67_108_864,
+          video_frame_rate_limit: 60,
+          video_matrix_limit: 16_777_216,
+        },
+        polls: {
+          max_options: 4,
+          max_characters_per_option: 50,
+          min_expiration: 300,
+          max_expiration: 2_592_000,
+        },
+        translation: {
+          enabled: false,
+        },
+        vapid: {
+          public_key: "",
+        },
+      },
+      registrations: {
+        enabled: false,
+        approval_required: true,
+        message: null,
+        url: null,
+      },
+      api_versions: {
+        mastodon: 0,
+      },
+      contact: {
+        email: "",
+        account: contactAccount,
+      },
+      rules: [],
+    });
+  } catch (error) {
+    next(error);
+  }
+});
+
+// ─── GET /api/v1/instance ────────────────────────────────────────────────────
+
+router.get("/api/v1/instance", async (req, res, next) => {
+  try {
+    const baseUrl = `${req.protocol}://${req.get("host")}`;
+    const domain = req.get("host");
+    const collections = req.app.locals.mastodonCollections;
+    const pluginOptions = req.app.locals.mastodonPluginOptions || {};
+
+    const profile = await collections.ap_profile.findOne({});
+
+    // Get approximate counts
+    let statusCount = 0;
+    let domainCount = 0;
+    try {
+      statusCount = await collections.ap_timeline.countDocuments({});
+      // Rough domain count from unique follower domains
+      const followers = await collections.ap_followers
+        .find({}, { projection: { actorUrl: 1 } })
+        .toArray();
+      const domains = new Set(
+        followers
+          .map((f) => {
+            try {
+              return new URL(f.actorUrl).hostname;
+            } catch {
+              return null;
+            }
+          })
+          .filter(Boolean),
+      );
+      domainCount = domains.size;
+    } catch {
+      // Non-critical
+    }
+
+    res.json({
+      uri: domain,
+      title: profile?.name || domain,
+      short_description: profile?.summary || "",
+      description: profile?.summary || `An Indiekit instance at ${domain}`,
+      email: "",
+      version: "4.0.0 (compatible; Indiekit ActivityPub)",
+      urls: {
+        streaming_api: "",
+      },
+      stats: {
+        user_count: 1,
+        status_count: statusCount,
+        domain_count: domainCount,
+      },
+      thumbnail: profile?.icon || null,
+      languages: ["en"],
+      registrations: false,
+      approval_required: true,
+      invites_enabled: false,
+      configuration: {
+        statuses: {
+          max_characters: 5000,
+          max_media_attachments: 4,
+          characters_reserved_per_url: 23,
+        },
+        media_attachments: {
+          supported_mime_types: [
+            "image/jpeg",
+            "image/png",
+            "image/gif",
+            "image/webp",
+          ],
+          image_size_limit: 16_777_216,
+          image_matrix_limit: 16_777_216,
+          video_size_limit: 67_108_864,
+          video_frame_rate_limit: 60,
+          video_matrix_limit: 16_777_216,
+        },
+        polls: {
+          max_options: 4,
+          max_characters_per_option: 50,
+          min_expiration: 300,
+          max_expiration: 2_592_000,
+        },
+      },
+      contact_account: profile
+        ? serializeAccount(profile, {
+            baseUrl,
+            isLocal: true,
+            handle: pluginOptions.handle || "user",
+          })
+        : null,
+      rules: [],
+    });
+  } catch (error) {
+    next(error);
+  }
+});
+
+export default router;
diff --git a/lib/mastodon/routes/media.js b/lib/mastodon/routes/media.js
new file mode 100644
index 0000000..fc7cfd6
--- /dev/null
+++ b/lib/mastodon/routes/media.js
@@ -0,0 +1,43 @@
+/**
+ * Media endpoints for Mastodon Client API.
+ *
+ * POST /api/v2/media — upload media attachment (stub — returns 422 until storage is configured)
+ * POST /api/v1/media — legacy upload endpoint (redirects to v2)
+ * GET /api/v1/media/:id — get media attachment status
+ * PUT /api/v1/media/:id — update media metadata (description/focus)
+ */
+import express from "express";
+
+const router = express.Router(); // eslint-disable-line new-cap
+
+// ─── POST /api/v2/media ─────────────────────────────────────────────────────
+
+router.post("/api/v2/media", (req, res) => {
+  // Media upload requires multer/multipart handling + storage backend.
+  // For now, return 422 so clients show a user-friendly error.
+  res.status(422).json({
+    error: "Media uploads are not yet supported on this server",
+  });
+});
+
+// ─── POST /api/v1/media (legacy) ────────────────────────────────────────────
+
+router.post("/api/v1/media", (req, res) => {
+  res.status(422).json({
+    error: "Media uploads are not yet supported on this server",
+  });
+});
+
+// ─── GET /api/v1/media/:id ──────────────────────────────────────────────────
+
+router.get("/api/v1/media/:id", (req, res) => {
+  res.status(404).json({ error: "Record not found" });
+});
+
+// ─── PUT /api/v1/media/:id ──────────────────────────────────────────────────
+
+router.put("/api/v1/media/:id", (req, res) => {
+  res.status(404).json({ error: "Record not found" });
+});
+
+export default router;
diff --git a/lib/mastodon/routes/notifications.js b/lib/mastodon/routes/notifications.js
new file mode 100644
index 0000000..4bd1379
--- /dev/null
+++ b/lib/mastodon/routes/notifications.js
@@ -0,0 +1,257 @@
+/**
+ * Notification endpoints for Mastodon Client API.
+ *
+ * GET /api/v1/notifications — list notifications with pagination
+ * GET /api/v1/notifications/:id — single notification
+ * POST /api/v1/notifications/clear — clear all notifications
+ * POST /api/v1/notifications/:id/dismiss — dismiss single notification
+ */
+import express from "express";
+import { ObjectId } from "mongodb";
+import { serializeNotification } from "../entities/notification.js";
+import { buildPaginationQuery, parseLimit, setPaginationHeaders } from "../helpers/pagination.js";
+
+const router = express.Router(); // eslint-disable-line new-cap
+
+/**
+ * Mastodon type -> internal type reverse mapping for filtering.
+ */
+const REVERSE_TYPE_MAP = {
+  favourite: "like",
+  reblog: "boost",
+  follow: "follow",
+  follow_request: "follow_request",
+  mention: { $in: ["reply", "mention", "dm"] },
+  poll: "poll",
+  update: "update",
+  "admin.report": "report",
+};
+
+// ─── GET /api/v1/notifications ──────────────────────────────────────────────
+
+router.get("/api/v1/notifications", async (req, res, next) => {
+  try {
+    const token = req.mastodonToken;
+    if (!token) {
+      return res.status(401).json({ error: "The access token is invalid" });
+    }
+
+    const collections = req.app.locals.mastodonCollections;
+    const baseUrl = `${req.protocol}://${req.get("host")}`;
+    const limit = parseLimit(req.query.limit);
+
+    // Build base filter
+    const baseFilter = {};
+
+    // types[] — include only these Mastodon types
+    const includeTypes = normalizeArray(req.query["types[]"] || req.query.types);
+    if (includeTypes.length > 0) {
+      const internalTypes = resolveInternalTypes(includeTypes);
+      if (internalTypes.length > 0) {
+        baseFilter.type = { $in: internalTypes };
+      }
+    }
+
+    // exclude_types[] — exclude these Mastodon types
+    const excludeTypes = normalizeArray(req.query["exclude_types[]"] || req.query.exclude_types);
+    if (excludeTypes.length > 0) {
+      const excludeInternal = resolveInternalTypes(excludeTypes);
+      if (excludeInternal.length > 0) {
+        baseFilter.type = { ...baseFilter.type, $nin: excludeInternal };
+      }
+    }
+
+    // Apply cursor pagination
+    const { filter, sort, reverse } = buildPaginationQuery(baseFilter, {
+      max_id: req.query.max_id,
+      min_id: req.query.min_id,
+      since_id: req.query.since_id,
+    });
+
+    let items = await collections.ap_notifications
+      .find(filter)
+      .sort(sort)
+      .limit(limit)
+      .toArray();
+
+    if (reverse) {
+      items.reverse();
+    }
+
+    // Batch-fetch referenced timeline items to avoid N+1
+    const statusMap = await batchFetchStatuses(collections, items);
+
+    // Serialize notifications
+    const notifications = items.map((notif) =>
+      serializeNotification(notif, {
+        baseUrl,
+        statusMap,
+        interactionState: {
+          favouritedIds: new Set(),
+          rebloggedIds: new Set(),
+          bookmarkedIds: new Set(),
+        },
+      }),
+    ).filter(Boolean);
+
+    // Set pagination headers
+    setPaginationHeaders(res, req, items, limit);
+
+    res.json(notifications);
+  } catch (error) {
+    next(error);
+  }
+});
+
+// ─── GET /api/v1/notifications/:id ──────────────────────────────────────────
+
+router.get("/api/v1/notifications/:id", async (req, res, next) => {
+  try {
+    const token = req.mastodonToken;
+    if (!token) {
+      return res.status(401).json({ error: "The access token is invalid" });
+    }
+
+    const collections = req.app.locals.mastodonCollections;
+    const baseUrl = `${req.protocol}://${req.get("host")}`;
+
+    let objectId;
+    try {
+      objectId = new ObjectId(req.params.id);
+    } catch {
+      return res.status(404).json({ error: "Record not found" });
+    }
+
+    const notif = await collections.ap_notifications.findOne({ _id: objectId });
+    if (!notif) {
+      return res.status(404).json({ error: "Record not found" });
+    }
+
+    const statusMap = await batchFetchStatuses(collections, [notif]);
+
+    const notification = serializeNotification(notif, {
+      baseUrl,
+      statusMap,
+      interactionState: {
+        favouritedIds: new Set(),
+        rebloggedIds: new Set(),
+        bookmarkedIds: new Set(),
+      },
+    });
+
+    res.json(notification);
+  } catch (error) {
+    next(error);
+  }
+});
+
+// ─── POST /api/v1/notifications/clear ───────────────────────────────────────
+
+router.post("/api/v1/notifications/clear", async (req, res, next) => {
+  try {
+    const token = req.mastodonToken;
+    if (!token) {
+      return res.status(401).json({ error: "The access token is invalid" });
+    }
+
+    const collections = req.app.locals.mastodonCollections;
+    await collections.ap_notifications.deleteMany({});
+    res.json({});
+  } catch (error) {
+    next(error);
+  }
+});
+
+// ─── POST /api/v1/notifications/:id/dismiss ─────────────────────────────────
+
+router.post("/api/v1/notifications/:id/dismiss", async (req, res, next) => {
+  try {
+    const token = req.mastodonToken;
+    if (!token) {
+      return res.status(401).json({ error: "The access token is invalid" });
+    }
+
+    const collections = req.app.locals.mastodonCollections;
+
+    let objectId;
+    try {
+      objectId = new ObjectId(req.params.id);
+    } catch {
+      return res.status(404).json({ error: "Record not found" });
+    }
+
+    await collections.ap_notifications.deleteOne({ _id: objectId });
+    res.json({});
+  } catch (error) {
+    next(error);
+  }
+});
+
+// ─── Helpers ─────────────────────────────────────────────────────────────────
+
+/**
+ * Normalize query param to array (handles string or array).
+ */
+function normalizeArray(param) {
+  if (!param) return [];
+  return Array.isArray(param) ? param : [param];
+}
+
+/**
+ * Convert Mastodon notification types to internal types.
+ */
+function resolveInternalTypes(mastodonTypes) {
+  const result = [];
+  for (const t of mastodonTypes) {
+    const mapped = REVERSE_TYPE_MAP[t];
+    if (mapped) {
+      if (mapped.$in) {
+        result.push(...mapped.$in);
+      } else {
+        result.push(mapped);
+      }
+    }
+  }
+  return result;
+}
+
+/**
+ * Batch-fetch timeline items referenced by notifications.
+ *
+ * @param {object} collections
+ * @param {Array} notifications
+ * @returns {Promise<Map<string, object>>} Map of targetUrl -> timeline item
+ */
+async function batchFetchStatuses(collections, notifications) {
+  const statusMap = new Map();
+
+  const targetUrls = [
+    ...new Set(
+      notifications
+        .map((n) => n.targetUrl)
+        .filter(Boolean),
+    ),
+  ];
+
+  if (targetUrls.length === 0 || !collections.ap_timeline) {
+    return statusMap;
+  }
+
+  const items = await collections.ap_timeline
+    .find({
+      $or: [
+        { uid: { $in: targetUrls } },
+        { url: { $in: targetUrls } },
+      ],
+    })
+    .toArray();
+
+  for (const item of items) {
+    if (item.uid) statusMap.set(item.uid, item);
+    if (item.url) statusMap.set(item.url, item);
+  }
+
+  return statusMap;
+}
+
+export default router;
diff --git a/lib/mastodon/routes/oauth.js b/lib/mastodon/routes/oauth.js
new file mode 100644
index 0000000..a83b8f1
--- /dev/null
+++ b/lib/mastodon/routes/oauth.js
@@ -0,0 +1,545 @@
+/**
+ * OAuth2 routes for Mastodon Client API.
+ *
+ * Handles app registration, authorization, token exchange, and revocation.
+ */
+import crypto from "node:crypto";
+import express from "express";
+
+const router = express.Router(); // eslint-disable-line new-cap
+
+/**
+ * Generate cryptographically random hex string.
+ * @param {number} bytes - Number of random bytes
+ * @returns {string} Hex-encoded random string
+ */
+function randomHex(bytes) {
+  return crypto.randomBytes(bytes).toString("hex");
+}
+
+/**
+ * Parse redirect_uris from request — accepts space-separated string or array.
+ * @param {string|string[]} value
+ * @returns {string[]}
+ */
+function parseRedirectUris(value) {
+  if (!value) return ["urn:ietf:wg:oauth:2.0:oob"];
+  if (Array.isArray(value)) return value.map((v) => v.trim());
+  return value
+    .trim()
+    .split(/\s+/)
+    .filter(Boolean);
+}
+
+/**
+ * Parse scopes from request — accepts space-separated string.
+ * @param {string} value
+ * @returns {string[]}
+ */
+function parseScopes(value) {
+  if (!value) return ["read"];
+  return value
+    .trim()
+    .split(/\s+/)
+    .filter(Boolean);
+}
+
+// ─── POST /api/v1/apps — Register client application ────────────────────────
+
+router.post("/api/v1/apps", async (req, res, next) => {
+  try {
+    const { client_name, redirect_uris, scopes, website } = req.body;
+
+    const clientId = randomHex(16);
+    const clientSecret = randomHex(32);
+    const redirectUris = parseRedirectUris(redirect_uris);
+    const parsedScopes = parseScopes(scopes);
+
+    const doc = {
+      clientId,
+      clientSecret,
+      name: client_name || "",
+      redirectUris,
+      scopes: parsedScopes,
+      website: website || null,
+      confidential: true,
+      createdAt: new Date(),
+    };
+
+    const collections = req.app.locals.mastodonCollections;
+    await collections.ap_oauth_apps.insertOne(doc);
+
+    res.json({
+      id: doc._id?.toString() || clientId,
+      name: doc.name,
+      website: doc.website,
+      redirect_uris: redirectUris,
+      redirect_uri: redirectUris.join(" "),
+      client_id: clientId,
+      client_secret: clientSecret,
+      client_secret_expires_at: 0,
+      vapid_key: "",
+    });
+  } catch (error) {
+    next(error);
+  }
+});
+
+// ─── GET /api/v1/apps/verify_credentials ─────────────────────────────────────
+
+router.get("/api/v1/apps/verify_credentials", async (req, res, next) => {
+  try {
+    const token = req.mastodonToken;
+    if (!token) {
+      return res.status(401).json({ error: "The access token is invalid" });
+    }
+
+    const collections = req.app.locals.mastodonCollections;
+    const app = await collections.ap_oauth_apps.findOne({
+      clientId: token.clientId,
+    });
+
+    if (!app) {
+      return res.status(404).json({ error: "Application not found" });
+    }
+
+    res.json({
+      id: app._id.toString(),
+      name: app.name,
+      website: app.website,
+      scopes: app.scopes,
+      redirect_uris: app.redirectUris,
+      redirect_uri: app.redirectUris.join(" "),
+    });
+  } catch (error) {
+    next(error);
+  }
+});
+
+// ─── GET /.well-known/oauth-authorization-server ─────────────────────────────
+
+router.get("/.well-known/oauth-authorization-server", (req, res) => {
+  const baseUrl = `${req.protocol}://${req.get("host")}`;
+
+  res.json({
+    issuer: baseUrl,
+    authorization_endpoint: `${baseUrl}/oauth/authorize`,
+    token_endpoint: `${baseUrl}/oauth/token`,
+    revocation_endpoint: `${baseUrl}/oauth/revoke`,
+    scopes_supported: [
+      "read",
+      "write",
+      "follow",
+      "push",
+      "profile",
+      "read:accounts",
+      "read:blocks",
+      "read:bookmarks",
+      "read:favourites",
+      "read:filters",
+      "read:follows",
+      "read:lists",
+      "read:mutes",
+      "read:notifications",
+      "read:search",
+      "read:statuses",
+      "write:accounts",
+      "write:blocks",
+      "write:bookmarks",
+      "write:conversations",
+      "write:favourites",
+      "write:filters",
+      "write:follows",
+      "write:lists",
+      "write:media",
+      "write:mutes",
+      "write:notifications",
+      "write:reports",
+      "write:statuses",
+    ],
+    response_types_supported: ["code"],
+    grant_types_supported: ["authorization_code", "client_credentials"],
+    token_endpoint_auth_methods_supported: [
+      "client_secret_basic",
+      "client_secret_post",
+      "none",
+    ],
+    code_challenge_methods_supported: ["S256"],
+    service_documentation: "https://docs.joinmastodon.org/api/",
+    app_registration_endpoint: `${baseUrl}/api/v1/apps`,
+  });
+});
+
+// ─── GET /oauth/authorize — Show authorization page ──────────────────────────
+
+router.get("/oauth/authorize", async (req, res, next) => {
+  try {
+    const {
+      client_id,
+      redirect_uri,
+      response_type,
+      scope,
+      code_challenge,
+      code_challenge_method,
+      force_login,
+    } = req.query;
+
+    if (response_type !== "code") {
+      return res.status(400).json({
+        error: "unsupported_response_type",
+        error_description: "Only response_type=code is supported",
+      });
+    }
+
+    const collections = req.app.locals.mastodonCollections;
+    const app = await collections.ap_oauth_apps.findOne({ clientId: client_id });
+
+    if (!app) {
+      return res.status(400).json({
+        error: "invalid_client",
+        error_description: "Client application not found",
+      });
+    }
+
+    // Determine redirect URI — use provided or default to first registered
+    const resolvedRedirectUri =
+      redirect_uri || app.redirectUris[0] || "urn:ietf:wg:oauth:2.0:oob";
+
+    // Validate redirect_uri is registered
+    if (!app.redirectUris.includes(resolvedRedirectUri)) {
+      return res.status(400).json({
+        error: "invalid_redirect_uri",
+        error_description: "Redirect URI not registered for this application",
+      });
+    }
+
+    // Validate requested scopes are subset of app scopes
+    const requestedScopes = scope ? scope.split(/\s+/) : app.scopes;
+
+    // Check if user is logged in via IndieAuth session
+    const session = req.session;
+    if (!session?.access_token && !force_login) {
+      // Not logged in — redirect to Indiekit login, then back here
+      const returnUrl = `${req.protocol}://${req.get("host")}${req.originalUrl}`;
+      return res.redirect(
+        `/auth?redirect=${encodeURIComponent(returnUrl)}`,
+      );
+    }
+
+    // Render simple authorization page
+    const appName = app.name || "An application";
+    res.type("html").send(`<!DOCTYPE html>
+<html lang="en">
+<head>
+  <meta charset="utf-8">
+  <meta name="viewport" content="width=device-width, initial-scale=1">
+  <title>Authorize ${appName}</title>
+  <style>
+    body { font-family: system-ui, sans-serif; max-width: 480px; margin: 2rem auto; padding: 0 1rem; }
+    h1 { font-size: 1.4rem; }
+    .scopes { background: #f5f5f5; padding: 0.75rem 1rem; border-radius: 6px; margin: 1rem 0; }
+    .scopes code { display: block; margin: 0.25rem 0; }
+    .actions { display: flex; gap: 0.75rem; margin-top: 1.5rem; }
+    button { padding: 0.6rem 1.5rem; border-radius: 6px; font-size: 1rem; cursor: pointer; border: 1px solid #ccc; }
+    .approve { background: #2b90d9; color: white; border-color: #2b90d9; }
+    .deny { background: white; }
+  </style>
+</head>
+<body>
+  <h1>Authorize ${appName}</h1>
+  <p>${appName} wants to access your account with these permissions:</p>
+  <div class="scopes">
+    ${requestedScopes.map((s) => `<code>${s}</code>`).join("")}
+  </div>
+  <form method="POST" action="/oauth/authorize">
+    <input type="hidden" name="client_id" value="${client_id}">
+    <input type="hidden" name="redirect_uri" value="${resolvedRedirectUri}">
+    <input type="hidden" name="scope" value="${requestedScopes.join(" ")}">
+    <input type="hidden" name="code_challenge" value="${code_challenge || ""}">
+    <input type="hidden" name="code_challenge_method" value="${code_challenge_method || ""}">
+    <input type="hidden" name="response_type" value="code">
+    <div class="actions">
+      <button type="submit" name="decision" value="approve" class="approve">Authorize</button>
+      <button type="submit" name="decision" value="deny" class="deny">Deny</button>
+    </div>
+  </form>
+</body>
+</html>`);
+  } catch (error) {
+    next(error);
+  }
+});
+
+// ─── POST /oauth/authorize — Process authorization decision ──────────────────
+
+router.post("/oauth/authorize", async (req, res, next) => {
+  try {
+    const {
+      client_id,
+      redirect_uri,
+      scope,
+      code_challenge,
+      code_challenge_method,
+      decision,
+    } = req.body;
+
+    // User denied
+    if (decision === "deny") {
+      if (redirect_uri && redirect_uri !== "urn:ietf:wg:oauth:2.0:oob") {
+        const url = new URL(redirect_uri);
+        url.searchParams.set("error", "access_denied");
+        url.searchParams.set(
+          "error_description",
+          "The resource owner denied the request",
+        );
+        return res.redirect(url.toString());
+      }
+      return res.status(403).json({
+        error: "access_denied",
+        error_description: "The resource owner denied the request",
+      });
+    }
+
+    // Generate authorization code
+    const code = randomHex(32);
+    const collections = req.app.locals.mastodonCollections;
+
+    await collections.ap_oauth_tokens.insertOne({
+      code,
+      clientId: client_id,
+      scopes: scope ? scope.split(/\s+/) : ["read"],
+      redirectUri: redirect_uri,
+      codeChallenge: code_challenge || null,
+      codeChallengeMethod: code_challenge_method || null,
+      accessToken: null,
+      createdAt: new Date(),
+      expiresAt: new Date(Date.now() + 10 * 60 * 1000), // 10 minutes
+      usedAt: null,
+      revokedAt: null,
+    });
+
+    // Out-of-band: show code on page
+    if (!redirect_uri || redirect_uri === "urn:ietf:wg:oauth:2.0:oob") {
+      return res.type("html").send(`<!DOCTYPE html>
+<html lang="en">
+<head>
+  <meta charset="utf-8">
+  <meta name="viewport" content="width=device-width, initial-scale=1">
+  <title>Authorization Code</title>
+  <style>
+    body { font-family: system-ui, sans-serif; max-width: 480px; margin: 2rem auto; padding: 0 1rem; }
+    code { display: block; background: #f5f5f5; padding: 1rem; border-radius: 6px; word-break: break-all; margin: 1rem 0; }
+  </style>
+</head>
+<body>
+  <h1>Authorization Code</h1>
+  <p>Copy this code and paste it into the application:</p>
+  <code>${code}</code>
+</body>
+</html>`);
+    }
+
+    // Redirect with code
+    const url = new URL(redirect_uri);
+    url.searchParams.set("code", code);
+    res.redirect(url.toString());
+  } catch (error) {
+    next(error);
+  }
+});
+
+// ─── POST /oauth/token — Exchange code for access token ──────────────────────
+
+router.post("/oauth/token", async (req, res, next) => {
+  try {
+    const { grant_type, code, redirect_uri, code_verifier } = req.body;
+
+    // Extract client credentials from request (3 methods)
+    const { clientId, clientSecret } = extractClientCredentials(req);
+
+    const collections = req.app.locals.mastodonCollections;
+
+    if (grant_type === "client_credentials") {
+      // Client credentials grant — limited access for pre-login API calls
+      if (!clientId || !clientSecret) {
+        return res.status(401).json({
+          error: "invalid_client",
+          error_description: "Client authentication required",
+        });
+      }
+
+      const app = await collections.ap_oauth_apps.findOne({
+        clientId,
+        clientSecret,
+        confidential: true,
+      });
+
+      if (!app) {
+        return res.status(401).json({
+          error: "invalid_client",
+          error_description: "Invalid client credentials",
+        });
+      }
+
+      const accessToken = randomHex(64);
+      await collections.ap_oauth_tokens.insertOne({
+        code: null,
+        clientId,
+        scopes: ["read"],
+        redirectUri: null,
+        codeChallenge: null,
+        codeChallengeMethod: null,
+        accessToken,
+        createdAt: new Date(),
+        expiresAt: null,
+        usedAt: null,
+        revokedAt: null,
+        grantType: "client_credentials",
+      });
+
+      return res.json({
+        access_token: accessToken,
+        token_type: "Bearer",
+        scope: "read",
+        created_at: Math.floor(Date.now() / 1000),
+      });
+    }
+
+    if (grant_type !== "authorization_code") {
+      return res.status(400).json({
+        error: "unsupported_grant_type",
+        error_description: "Only authorization_code and client_credentials are supported",
+      });
+    }
+
+    if (!code) {
+      return res.status(400).json({
+        error: "invalid_request",
+        error_description: "Missing authorization code",
+      });
+    }
+
+    // Atomic claim-or-fail: find the code and mark it used in one operation
+    const grant = await collections.ap_oauth_tokens.findOneAndUpdate(
+      {
+        code,
+        usedAt: null,
+        revokedAt: null,
+        expiresAt: { $gt: new Date() },
+      },
+      { $set: { usedAt: new Date() } },
+      { returnDocument: "before" },
+    );
+
+    if (!grant) {
+      return res.status(400).json({
+        error: "invalid_grant",
+        error_description:
+          "Authorization code is invalid, expired, or already used",
+      });
+    }
+
+    // Validate redirect_uri matches
+    if (redirect_uri && grant.redirectUri && redirect_uri !== grant.redirectUri) {
+      return res.status(400).json({
+        error: "invalid_grant",
+        error_description: "Redirect URI mismatch",
+      });
+    }
+
+    // Verify PKCE code_verifier if code_challenge was stored
+    if (grant.codeChallenge) {
+      if (!code_verifier) {
+        return res.status(400).json({
+          error: "invalid_grant",
+          error_description: "Missing code_verifier for PKCE",
+        });
+      }
+
+      const expectedChallenge = crypto
+        .createHash("sha256")
+        .update(code_verifier)
+        .digest("base64url");
+
+      if (expectedChallenge !== grant.codeChallenge) {
+        return res.status(400).json({
+          error: "invalid_grant",
+          error_description: "Invalid code_verifier",
+        });
+      }
+    }
+
+    // Generate access token
+    const accessToken = randomHex(64);
+    await collections.ap_oauth_tokens.updateOne(
+      { _id: grant._id },
+      { $set: { accessToken } },
+    );
+
+    res.json({
+      access_token: accessToken,
+      token_type: "Bearer",
+      scope: grant.scopes.join(" "),
+      created_at: Math.floor(grant.createdAt.getTime() / 1000),
+    });
+  } catch (error) {
+    next(error);
+  }
+});
+
+// ─── POST /oauth/revoke — Revoke a token ────────────────────────────────────
+
+router.post("/oauth/revoke", async (req, res, next) => {
+  try {
+    const { token } = req.body;
+
+    if (!token) {
+      return res.status(400).json({
+        error: "invalid_request",
+        error_description: "Missing token parameter",
+      });
+    }
+
+    const collections = req.app.locals.mastodonCollections;
+    await collections.ap_oauth_tokens.updateOne(
+      { accessToken: token },
+      { $set: { revokedAt: new Date() } },
+    );
+
+    // RFC 7009: always return 200 even if token wasn't found
+    res.json({});
+  } catch (error) {
+    next(error);
+  }
+});
+
+// ─── Helpers ─────────────────────────────────────────────────────────────────
+
+/**
+ * Extract client credentials from request using 3 methods:
+ * 1. HTTP Basic Auth (client_secret_basic)
+ * 2. POST body (client_secret_post)
+ * 3. client_id only (none — public clients)
+ */
+function extractClientCredentials(req) {
+  // Method 1: HTTP Basic Auth
+  const authHeader = req.get("authorization");
+  if (authHeader?.startsWith("Basic ")) {
+    const decoded = Buffer.from(authHeader.slice(6), "base64").toString();
+    const colonIndex = decoded.indexOf(":");
+    if (colonIndex > 0) {
+      return {
+        clientId: decoded.slice(0, colonIndex),
+        clientSecret: decoded.slice(colonIndex + 1),
+      };
+    }
+  }
+
+  // Method 2 & 3: POST body
+  return {
+    clientId: req.body.client_id || null,
+    clientSecret: req.body.client_secret || null,
+  };
+}
+
+export default router;
diff --git a/lib/mastodon/routes/search.js b/lib/mastodon/routes/search.js
new file mode 100644
index 0000000..03a47c5
--- /dev/null
+++ b/lib/mastodon/routes/search.js
@@ -0,0 +1,146 @@
+/**
+ * Search endpoint for Mastodon Client API.
+ *
+ * GET /api/v2/search — search accounts, statuses, and hashtags
+ */
+import express from "express";
+import { serializeStatus } from "../entities/status.js";
+import { serializeAccount } from "../entities/account.js";
+import { parseLimit } from "../helpers/pagination.js";
+
+const router = express.Router(); // eslint-disable-line new-cap
+
+// ─── GET /api/v2/search ─────────────────────────────────────────────────────
+
+router.get("/api/v2/search", async (req, res, next) => {
+  try {
+    const collections = req.app.locals.mastodonCollections;
+    const baseUrl = `${req.protocol}://${req.get("host")}`;
+    const query = (req.query.q || "").trim();
+    const type = req.query.type; // "accounts", "statuses", "hashtags", or undefined (all)
+    const limit = parseLimit(req.query.limit);
+    const offset = Math.max(0, Number.parseInt(req.query.offset, 10) || 0);
+
+    if (!query) {
+      return res.json({ accounts: [], statuses: [], hashtags: [] });
+    }
+
+    const results = { accounts: [], statuses: [], hashtags: [] };
+
+    // ─── Account search ──────────────────────────────────────────────────
+    if (!type || type === "accounts") {
+      const escapedQuery = query.replace(/[.*+?^${}()|[\]\\]/g, "\\$&");
+      const nameRegex = new RegExp(escapedQuery, "i");
+
+      // Search followers and following by display name or handle
+      const accountDocs = [];
+
+      if (collections.ap_followers) {
+        const followers = await collections.ap_followers
+          .find({
+            $or: [
+              { name: nameRegex },
+              { preferredUsername: nameRegex },
+              { url: nameRegex },
+            ],
+          })
+          .limit(limit)
+          .toArray();
+        accountDocs.push(...followers);
+      }
+
+      if (collections.ap_following) {
+        const following = await collections.ap_following
+          .find({
+            $or: [
+              { name: nameRegex },
+              { preferredUsername: nameRegex },
+              { url: nameRegex },
+            ],
+          })
+          .limit(limit)
+          .toArray();
+        accountDocs.push(...following);
+      }
+
+      // Deduplicate by URL
+      const seen = new Set();
+      for (const doc of accountDocs) {
+        const url = doc.url || doc.id;
+        if (url && !seen.has(url)) {
+          seen.add(url);
+          results.accounts.push(
+            serializeAccount(doc, { baseUrl, isRemote: true }),
+          );
+        }
+        if (results.accounts.length >= limit) break;
+      }
+    }
+
+    // ─── Status search ───────────────────────────────────────────────────
+    if (!type || type === "statuses") {
+      const escapedQuery = query.replace(/[.*+?^${}()|[\]\\]/g, "\\$&");
+      const contentRegex = new RegExp(escapedQuery, "i");
+
+      const items = await collections.ap_timeline
+        .find({
+          isContext: { $ne: true },
+          $or: [
+            { "content.text": contentRegex },
+            { "content.html": contentRegex },
+          ],
+        })
+        .sort({ _id: -1 })
+        .skip(offset)
+        .limit(limit)
+        .toArray();
+
+      results.statuses = items.map((item) =>
+        serializeStatus(item, {
+          baseUrl,
+          favouritedIds: new Set(),
+          rebloggedIds: new Set(),
+          bookmarkedIds: new Set(),
+          pinnedIds: new Set(),
+        }),
+      );
+    }
+
+    // ─── Hashtag search ──────────────────────────────────────────────────
+    if (!type || type === "hashtags") {
+      const escapedQuery = query
+        .replace(/^#/, "")
+        .replace(/[.*+?^${}()|[\]\\]/g, "\\$&");
+      const tagRegex = new RegExp(escapedQuery, "i");
+
+      // Find distinct category values matching the query
+      const allCategories = await collections.ap_timeline.distinct("category", {
+        category: tagRegex,
+      });
+
+      // Flatten and deduplicate (category can be string or array)
+      const tagSet = new Set();
+      for (const cat of allCategories) {
+        if (Array.isArray(cat)) {
+          for (const c of cat) {
+            if (typeof c === "string" && tagRegex.test(c)) tagSet.add(c);
+          }
+        } else if (typeof cat === "string" && tagRegex.test(cat)) {
+          tagSet.add(cat);
+        }
+      }
+
+      results.hashtags = [...tagSet].slice(0, limit).map((name) => ({
+        name,
+        url: `${baseUrl}/tags/${encodeURIComponent(name)}`,
+        history: [],
+      }));
+    }
+
+    res.json(results);
+  } catch (error) {
+    next(error);
+  }
+});
+
+export default router;
diff --git a/lib/mastodon/routes/statuses.js b/lib/mastodon/routes/statuses.js
new file mode 100644
index 0000000..8630d36
--- /dev/null
+++ b/lib/mastodon/routes/statuses.js
@@ -0,0 +1,634 @@
+/**
+ * Status endpoints for Mastodon Client API.
+ *
+ * GET /api/v1/statuses/:id — single status
+ * GET /api/v1/statuses/:id/context — thread context (ancestors + descendants)
+ * POST /api/v1/statuses/:id/favourite — like a post
+ * POST /api/v1/statuses/:id/unfavourite — unlike a post
+ * POST /api/v1/statuses/:id/reblog — boost a post
+ * POST /api/v1/statuses/:id/unreblog — unboost a post
+ * POST /api/v1/statuses/:id/bookmark — bookmark a post
+ * POST /api/v1/statuses/:id/unbookmark — remove bookmark
+ */
+import express from "express";
+import { ObjectId } from "mongodb";
+import { serializeStatus } from "../entities/status.js";
+import { serializeAccount } from "../entities/account.js";
+import {
+  likePost, unlikePost,
+  boostPost, unboostPost,
+  bookmarkPost, unbookmarkPost,
+} from "../helpers/interactions.js";
+
+const router = express.Router(); // eslint-disable-line new-cap
+
+// ─── GET /api/v1/statuses/:id ───────────────────────────────────────────────
+
+router.get("/api/v1/statuses/:id", async (req, res, next) => {
+  try {
+    const { id } = req.params;
+    const collections = req.app.locals.mastodonCollections;
+    const baseUrl = `${req.protocol}://${req.get("host")}`;
+
+    let objectId;
+    try {
+      objectId = new ObjectId(id);
+    } catch {
+      return res.status(404).json({ error: "Record not found" });
+    }
+
+    const item = await collections.ap_timeline.findOne({ _id: objectId });
+    if (!item) {
+      return res.status(404).json({ error: "Record not found" });
+    }
+
+    // Load interaction state if authenticated
+    const interactionState = await loadItemInteractions(collections, item);
+
+    const status = serializeStatus(item, {
+      baseUrl,
+      ...interactionState,
+      pinnedIds: new Set(),
+    });
+
+    res.json(status);
+  } catch (error) {
+    next(error);
+  }
+});
+
+// ─── GET /api/v1/statuses/:id/context ───────────────────────────────────────
+
+router.get("/api/v1/statuses/:id/context", async (req, res, next) => {
+  try {
+    const { id } = req.params;
+    const collections = req.app.locals.mastodonCollections;
+    const baseUrl = `${req.protocol}://${req.get("host")}`;
+
+    let objectId;
+    try {
+      objectId = new ObjectId(id);
+    } catch {
+      return res.status(404).json({ error: "Record not found" });
+    }
+
+    const item = await collections.ap_timeline.findOne({ _id: objectId });
+    if (!item) {
+      return res.status(404).json({ error: "Record not found" });
+    }
+
+    // Find ancestors: walk up the inReplyTo chain
+    const ancestors = [];
+    let currentReplyTo = item.inReplyTo;
+    const visited = new Set();
+
+    while (currentReplyTo && ancestors.length < 40) {
+      if (visited.has(currentReplyTo)) break;
+      visited.add(currentReplyTo);
+
+      const parent = await collections.ap_timeline.findOne({
+        $or: [{ uid: currentReplyTo }, { url: currentReplyTo }],
+      });
+      if (!parent) break;
+
+      ancestors.unshift(parent);
+      currentReplyTo = parent.inReplyTo;
+    }
+
+    // Find descendants: items that reply to this post's uid or url
+    const targetUrls = [item.uid, item.url].filter(Boolean);
+    let descendants = [];
+
+    if (targetUrls.length > 0) {
+      // Get direct replies first
+      const directReplies = await collections.ap_timeline
+        .find({ inReplyTo: { $in: targetUrls } })
+        .sort({ _id: 1 })
+        .limit(60)
+        .toArray();
+
+      descendants = directReplies;
+
+      // Also fetch replies to direct replies (2 levels deep)
+      if (directReplies.length > 0) {
+        const replyUrls = directReplies
+          .flatMap((r) => [r.uid, r.url].filter(Boolean));
+        const nestedReplies = await collections.ap_timeline
+          .find({ inReplyTo: { $in: replyUrls } })
+          .sort({ _id: 1 })
+          .limit(60)
+          .toArray();
+        descendants.push(...nestedReplies);
+      }
+    }
+
+    // Serialize all items
+    const emptyInteractions = {
+      favouritedIds: new Set(),
+      rebloggedIds: new Set(),
+      bookmarkedIds: new Set(),
+      pinnedIds: new Set(),
+    };
+
+    const serializeOpts = { baseUrl, ...emptyInteractions };
+
+    res.json({
+      ancestors: ancestors.map((a) => serializeStatus(a, serializeOpts)),
+      descendants: descendants.map((d) => serializeStatus(d, serializeOpts)),
+    });
+  } catch (error) {
+    next(error);
+  }
+});
+
+// ─── POST /api/v1/statuses ───────────────────────────────────────────────────
+
+router.post("/api/v1/statuses", async (req, res, next) => {
+  try {
+    const token = req.mastodonToken;
+    if (!token) {
+      return res.status(401).json({ error: "The access token is invalid" });
+    }
+
+    const collections = req.app.locals.mastodonCollections;
+    const pluginOptions = req.app.locals.mastodonPluginOptions || {};
+    const baseUrl = `${req.protocol}://${req.get("host")}`;
+
+    const {
+      status: statusText,
+      spoiler_text: spoilerText,
+      visibility = "public",
+      sensitive = false,
+      language,
+      in_reply_to_id: inReplyToId,
+      media_ids: mediaIds,
+    } = req.body;
+
+    if (!statusText && (!mediaIds || mediaIds.length === 0)) {
+      return res.status(422).json({ error: "Validation failed: Text content is required" });
+    }
+
+    // Resolve in_reply_to if provided
+    let inReplyTo = null;
+    if (inReplyToId) {
+      try {
+        const replyItem = await collections.ap_timeline.findOne({
+          _id: new ObjectId(inReplyToId),
+        });
+        if (replyItem) {
+          inReplyTo = replyItem.uid || replyItem.url;
+        }
+      } catch {
+        // Invalid ObjectId — ignore
+      }
+    }
+
+    // Load local profile for the author field
+    const profile = await collections.ap_profile.findOne({});
+    const handle = pluginOptions.handle || "user";
+    const publicationUrl = pluginOptions.publicationUrl || baseUrl;
+    const actorUrl = profile?.url || `${publicationUrl}/users/${handle}`;
+
+    // Generate post ID and URL
+    const postId = crypto.randomUUID();
+    const postUrl = `${publicationUrl.replace(/\/$/, "")}/posts/${postId}`;
+    const uid = postUrl;
+
+    // Build the timeline item
+    const now = new Date().toISOString();
+    const timelineItem = {
+      uid,
+      url: postUrl,
+      type: "note",
+      content: {
+        text: statusText || "",
+        html: linkifyAndParagraph(statusText || ""),
+      },
+      summary: spoilerText || "",
+      sensitive: sensitive === true || sensitive === "true",
+      visibility: visibility || "public",
+      language: language || null,
+      inReplyTo,
+      published: now,
+      createdAt: now,
+      author: {
+        name: profile?.name || handle,
+        url: actorUrl,
+        photo: profile?.icon || "",
+        handle: `@${handle}`,
+        emojis: [],
+        bot: false,
+      },
+      photo: [],
+      video: [],
+      audio: [],
+      category: extractHashtags(statusText || ""),
+      counts: { replies: 0, boosts: 0, likes: 0 },
+      linkPreviews: [],
+      mentions: [],
+      emojis: [],
+    };
+
+    // Insert into timeline
+    const result = await collections.ap_timeline.insertOne(timelineItem);
+    timelineItem._id = result.insertedId;
+
+    // Trigger federation asynchronously (don't block the response)
+    if (pluginOptions.federation) {
+      federatePost(timelineItem, pluginOptions).catch((err) => {
+        console.error("[Mastodon API] Federation failed:", err.message);
+      });
+    }
+
+    // Serialize and return
+    const serialized = serializeStatus(timelineItem, {
+      baseUrl,
+      favouritedIds: new Set(),
+      rebloggedIds: new Set(),
+      bookmarkedIds: new Set(),
+      pinnedIds: new Set(),
+    });
+
+    res.json(serialized);
+  } catch (error) {
+    next(error);
+  }
+});
+
+// ─── DELETE /api/v1/statuses/:id ────────────────────────────────────────────
+
+router.delete("/api/v1/statuses/:id", async (req, res, next) => {
+  try {
+    const token = req.mastodonToken;
+    if (!token) {
+      return res.status(401).json({ error: "The access token is invalid" });
+    }
+
+    const { id } = req.params;
+    const collections = req.app.locals.mastodonCollections;
+    const baseUrl = `${req.protocol}://${req.get("host")}`;
+
+    let objectId;
+    try {
+      objectId = new ObjectId(id);
+    } catch {
+      return res.status(404).json({ error: "Record not found" });
+    }
+
+    const item = await collections.ap_timeline.findOne({ _id: objectId });
+    if (!item) {
+      return res.status(404).json({ error: "Record not found" });
+    }
+
+    // Verify ownership — only allow deleting own posts
+    const profile = await collections.ap_profile.findOne({});
+    if (profile && item.author?.url !== profile.url) {
+      return res.status(403).json({ error: "This action is not allowed" });
+    }
+
+    // Serialize before deleting (Mastodon returns the deleted status with text source)
+    const serialized = serializeStatus(item, {
+      baseUrl,
+      favouritedIds: new Set(),
+      rebloggedIds: new Set(),
+      bookmarkedIds: new Set(),
+      pinnedIds: new Set(),
+    });
+    serialized.text = item.content?.text || "";
+
+    // Delete from timeline
+    await collections.ap_timeline.deleteOne({ _id: objectId });
+
+    // Clean up interactions
+    if (collections.ap_interactions && item.uid) {
+      await collections.ap_interactions.deleteMany({ objectUrl: item.uid });
+    }
+
+    // TODO: Broadcast Delete activity via federation
+
+    res.json(serialized);
+  } catch (error) {
+    next(error);
+  }
+});
+
+// ─── GET /api/v1/statuses/:id/favourited_by ─────────────────────────────────
+
+router.get("/api/v1/statuses/:id/favourited_by", async (req, res) => {
+  // Stub — we don't track who favourited remotely
+  res.json([]);
+});
+
+// ─── GET /api/v1/statuses/:id/reblogged_by ──────────────────────────────────
+
+router.get("/api/v1/statuses/:id/reblogged_by", async (req, res) => {
+  // Stub — we don't track who boosted remotely
+  res.json([]);
+});
+
+// ─── POST /api/v1/statuses/:id/favourite ────────────────────────────────────
+
+router.post("/api/v1/statuses/:id/favourite", async (req, res, next) => {
+  try {
+    const token = req.mastodonToken;
+    if (!token) {
+      return res.status(401).json({ error: "The access token is invalid" });
+    }
+
+    const { item, collections, baseUrl } = await resolveStatusForInteraction(req);
+    if (!item) {
+      return res.status(404).json({ error: "Record not found" });
+    }
+
+    const opts = getFederationOpts(req);
+    await likePost({
+      targetUrl: item.uid || item.url,
+      ...opts,
+      interactions: collections.ap_interactions,
+    });
+
+    const interactionState = await loadItemInteractions(collections, item);
+    // Force favourited=true since we just liked it
+    interactionState.favouritedIds.add(item.uid);
+
+    res.json(serializeStatus(item, { baseUrl, ...interactionState, pinnedIds: new Set() }));
+  } catch (error) {
+    next(error);
+  }
+});
+
+// ─── POST /api/v1/statuses/:id/unfavourite ──────────────────────────────────
+
+router.post("/api/v1/statuses/:id/unfavourite", async (req, res, next) => {
+  try {
+    const token = req.mastodonToken;
+    if (!token) {
+      return res.status(401).json({ error: "The access token is invalid" });
+    }
+
+    const { item, collections, baseUrl } = await resolveStatusForInteraction(req);
+    if (!item) {
+      return res.status(404).json({ error: "Record not found" });
+    }
+
+    const opts = getFederationOpts(req);
+    await unlikePost({
+      targetUrl: item.uid || item.url,
+      ...opts,
+      interactions: collections.ap_interactions,
+    });
+
+    const interactionState = await loadItemInteractions(collections, item);
+    interactionState.favouritedIds.delete(item.uid);
+
+    res.json(serializeStatus(item, { baseUrl, ...interactionState, pinnedIds: new Set() }));
+  } catch (error) {
+    next(error);
+  }
+});
+
+// ─── POST /api/v1/statuses/:id/reblog ───────────────────────────────────────
+
+router.post("/api/v1/statuses/:id/reblog", async (req, res, next) => {
+  try {
+    const token = req.mastodonToken;
+    if (!token) {
+      return res.status(401).json({ error: "The access token is invalid" });
+    }
+
+    const { item, collections, baseUrl } = await resolveStatusForInteraction(req);
+    if (!item) {
+      return res.status(404).json({ error: "Record not found" });
+    }
+
+    const opts = getFederationOpts(req);
+    await boostPost({
+      targetUrl: item.uid || item.url,
+      ...opts,
+      interactions: collections.ap_interactions,
+    });
+
+    const interactionState = await loadItemInteractions(collections, item);
+    interactionState.rebloggedIds.add(item.uid);
+
+    res.json(serializeStatus(item, { baseUrl, ...interactionState, pinnedIds: new Set() }));
+  } catch (error) {
+    next(error);
+  }
+});
+
+// ─── POST /api/v1/statuses/:id/unreblog ─────────────────────────────────────
+
+router.post("/api/v1/statuses/:id/unreblog", async (req, res, next) => {
+  try {
+    const token = req.mastodonToken;
+    if (!token) {
+      return res.status(401).json({ error: "The access token is invalid" });
+    }
+
+    const { item, collections, baseUrl } = await resolveStatusForInteraction(req);
+    if (!item) {
+      return res.status(404).json({ error: "Record not found" });
+    }
+
+    const opts = getFederationOpts(req);
+    await unboostPost({
+      targetUrl: item.uid || item.url,
+      ...opts,
+      interactions: collections.ap_interactions,
+    });
+
+    const interactionState = await loadItemInteractions(collections, item);
+    interactionState.rebloggedIds.delete(item.uid);
+
+    res.json(serializeStatus(item, { baseUrl, ...interactionState, pinnedIds: new Set() }));
+  } catch (error) {
+    next(error);
+  }
+});
+
+// ─── POST /api/v1/statuses/:id/bookmark ─────────────────────────────────────
+
+router.post("/api/v1/statuses/:id/bookmark", async (req, res, next) => {
+  try {
+    const token = req.mastodonToken;
+    if (!token) {
+      return res.status(401).json({ error: "The access token is invalid" });
+    }
+
+    const { item, collections, baseUrl } = await resolveStatusForInteraction(req);
+    if (!item) {
+      return res.status(404).json({ error: "Record not found" });
+    }
+
+    await bookmarkPost({
+      targetUrl: item.uid || item.url,
+      interactions: collections.ap_interactions,
+    });
+
+    const interactionState = await loadItemInteractions(collections, item);
+    interactionState.bookmarkedIds.add(item.uid);
+
+    res.json(serializeStatus(item, { baseUrl, ...interactionState, pinnedIds: new Set() }));
+  } catch (error) {
+    next(error);
+  }
+});
+
+// ─── POST /api/v1/statuses/:id/unbookmark ───────────────────────────────────
+
+router.post("/api/v1/statuses/:id/unbookmark", async (req, res, next) => {
+  try {
+    const token = req.mastodonToken;
+    if (!token) {
+      return res.status(401).json({ error: "The access token is invalid" });
+    }
+
+    const { item, collections, baseUrl } = await resolveStatusForInteraction(req);
+    if (!item) {
+      return res.status(404).json({ error: "Record not found" });
+    }
+
+    await unbookmarkPost({
+      targetUrl: item.uid || item.url,
+      interactions: collections.ap_interactions,
+    });
+
+    const interactionState = await loadItemInteractions(collections, item);
+    interactionState.bookmarkedIds.delete(item.uid);
+
+    res.json(serializeStatus(item, { baseUrl, ...interactionState, pinnedIds: new Set() }));
+  } catch (error) {
+    next(error);
+  }
+});
+
+// ─── Helpers ─────────────────────────────────────────────────────────────────
+
+/**
+ * Resolve a timeline item from the :id param, plus common context.
+ */
+async function resolveStatusForInteraction(req) {
+  const collections = req.app.locals.mastodonCollections;
+  const baseUrl = `${req.protocol}://${req.get("host")}`;
+
+  let objectId;
+  try {
+    objectId = new ObjectId(req.params.id);
+  } catch {
+    return { item: null, collections, baseUrl };
+  }
+
+  const item = await collections.ap_timeline.findOne({ _id: objectId });
+  return { item, collections, baseUrl };
+}
+
+/**
+ * Build federation options from request context for interaction helpers.
+ */
+function getFederationOpts(req) {
+  const pluginOptions = req.app.locals.mastodonPluginOptions || {};
+  return {
+    federation: pluginOptions.federation,
+    handle: pluginOptions.handle || "user",
+    publicationUrl: pluginOptions.publicationUrl,
+    collections: req.app.locals.mastodonCollections,
+  };
+}
+
+async function loadItemInteractions(collections, item) {
+  const favouritedIds = new Set();
+  const rebloggedIds = new Set();
+  const bookmarkedIds = new Set();
+
+  if (!collections.ap_interactions || !item.uid) {
+    return { favouritedIds, rebloggedIds, bookmarkedIds };
+  }
+
+  const lookupUrls = [item.uid, item.url].filter(Boolean);
+  const interactions = await collections.ap_interactions
+    .find({ objectUrl: { $in: lookupUrls } })
+    .toArray();
+
+  for (const i of interactions) {
+    const uid = item.uid;
+    if (i.type === "like") favouritedIds.add(uid);
+    else if (i.type === "boost") rebloggedIds.add(uid);
+    else if (i.type === "bookmark") bookmarkedIds.add(uid);
+  }
+
+  return { favouritedIds, rebloggedIds, bookmarkedIds };
+}
+
+/**
+ * Convert plain text to basic HTML (paragraphs + linkified URLs).
+ */
+function linkifyAndParagraph(text) {
+  if (!text) return "";
+  const paragraphs = text.split(/\n\n+/).filter(Boolean);
+  return paragraphs
+    .map((p) => {
+      const withBreaks = p.replace(/\n/g, "<br>");
+      const linked = withBreaks.replace(
+        /(?<![=">])(https?:\/\/[^\s<"]+)/g,
+        '<a href="$1">$1</a>',
+      );
+      return `<p>${linked}</p>`;
+    })
+    .join("");
+}
+
+/**
+ * Extract #hashtags from text content.
+ */
+function extractHashtags(text) {
+  if (!text) return [];
+  const tags = [];
+  const regex = /#([\w]+)/g;
+  let match;
+  while ((match = regex.exec(text)) !== null) {
+    tags.push(match[1]);
+  }
+  return [...new Set(tags)];
+}
+
+/**
+ * Federate a newly created post via ActivityPub.
+ * Runs asynchronously — errors logged, don't block API response.
+ */
+async function federatePost(item, pluginOptions) {
+  const { jf2ToAS2Activity } = await import("../../jf2-to-as2.js");
+
+  const handle = pluginOptions.handle || "user";
+  const publicationUrl = pluginOptions.publicationUrl;
+  const federation = pluginOptions.federation;
+  const actorUrl = `${publicationUrl.replace(/\/$/, "")}/users/${handle}`;
+
+  const ctx = federation.createContext(
+    new URL(publicationUrl),
+    { handle, publicationUrl },
+  );
+
+  const properties = {
+    "post-type": "note",
+    url: item.url,
+    content: item.content,
+    summary: item.summary || undefined,
+    "in-reply-to": item.inReplyTo || undefined,
+    category: item.category,
+    visibility: item.visibility,
+  };
+
+  const activity = jf2ToAS2Activity(properties, actorUrl, publicationUrl, {
+    visibility: item.visibility,
+  });
+
+  if (activity) {
+    await ctx.sendActivity({ identifier: handle }, "followers", activity, {
+      preferSharedInbox: true,
+    });
+    console.info(`[Mastodon API] Federated post: ${item.url}`);
+  }
+}
+
+export default router;
diff --git a/lib/mastodon/routes/stubs.js b/lib/mastodon/routes/stubs.js
new file mode 100644
index 0000000..eb9a73e
--- /dev/null
+++ b/lib/mastodon/routes/stubs.js
@@ -0,0 +1,380 @@
+/**
+ * Stub and lightweight endpoints for Mastodon Client API.
+ *
+ * Some endpoints have real implementations (markers, bookmarks, favourites).
+ * Others return empty/minimal responses to prevent client errors.
+ *
+ * Phanpy calls these on startup, navigation, and various page loads:
+ * - markers (BackgroundService, every page load)
+ * - follow_requests (home + notifications pages)
+ * - announcements (notifications page)
+ * - custom_emojis (compose screen)
+ * - filters (status rendering)
+ * - lists (sidebar navigation)
+ * - mutes, blocks (nav menu)
+ * - featured_tags (profile view)
+ * - bookmarks, favourites (dedicated pages)
+ * - trends (explore page)
+ * - followed_tags (followed tags page)
+ * - suggestions (explore page)
+ */
+import express from "express";
+import { serializeStatus } from "../entities/status.js";
+import { parseLimit, buildPaginationQuery, setPaginationHeaders } from "../helpers/pagination.js";
+
+const router = express.Router(); // eslint-disable-line new-cap
+
+// ─── Markers ────────────────────────────────────────────────────────────────
+
+router.get("/api/v1/markers", async (req, res, next) => {
+  try {
+    const collections = req.app.locals.mastodonCollections;
+    const timelines = [].concat(req.query["timeline[]"] || req.query.timeline || []);
+
+    if (!timelines.length || !collections.ap_markers) {
+      return res.json({});
+    }
+
+    const docs = await collections.ap_markers
+      .find({ timeline: { $in: timelines } })
+      .toArray();
+
+    const result = {};
+    for (const doc of docs) {
+      result[doc.timeline] = {
+        last_read_id: doc.last_read_id,
+        version: doc.version || 0,
+        updated_at: doc.updated_at || new Date().toISOString(),
+      };
+    }
+
+    res.json(result);
+  } catch (error) {
+    next(error);
+  }
+});
+
+router.post("/api/v1/markers", async (req, res, next) => {
+  try {
+    const collections = req.app.locals.mastodonCollections;
+    if (!collections.ap_markers) {
+      return res.json({});
+    }
+
+    const result = {};
+    for (const timeline of ["home", "notifications"]) {
+      const data = req.body[timeline];
+      if (!data?.last_read_id) continue;
+
+      const now = new Date().toISOString();
+      await collections.ap_markers.updateOne(
+        { timeline },
+        {
+          $set: { last_read_id: data.last_read_id, updated_at: now },
+          $inc: { version: 1 },
+          $setOnInsert: { timeline },
+        },
+        { upsert: true },
+      );
+
+      const doc = await collections.ap_markers.findOne({ timeline });
+      result[timeline] = {
+        last_read_id: doc.last_read_id,
+        version: doc.version || 0,
+        updated_at: doc.updated_at || now,
+      };
+    }
+
+    res.json(result);
+  } catch (error) {
+    next(error);
+  }
+});
+
+// ─── Follow requests ────────────────────────────────────────────────────────
+
+router.get("/api/v1/follow_requests", (req, res) => {
+  res.json([]);
+});
+
+// ─── Announcements ──────────────────────────────────────────────────────────
+
+router.get("/api/v1/announcements", (req, res) => {
+  res.json([]);
+});
+
+// ─── Custom emojis ──────────────────────────────────────────────────────────
+
+router.get("/api/v1/custom_emojis", (req, res) => {
+  res.json([]);
+});
+
+// ─── Filters (v2) ───────────────────────────────────────────────────────────
+
+router.get("/api/v2/filters", (req, res) => {
+  res.json([]);
+});
+
+router.get("/api/v1/filters", (req, res) => {
+  res.json([]);
+});
+
+// ─── Lists ──────────────────────────────────────────────────────────────────
+
+router.get("/api/v1/lists", (req, res) => {
+  res.json([]);
+});
+
+// ─── Mutes ──────────────────────────────────────────────────────────────────
+
+router.get("/api/v1/mutes", (req, res) => {
+  res.json([]);
+});
+
+// ─── Blocks ─────────────────────────────────────────────────────────────────
+
+router.get("/api/v1/blocks", (req, res) => {
+  res.json([]);
+});
+
+// ─── Bookmarks ──────────────────────────────────────────────────────────────
+
+router.get("/api/v1/bookmarks", async (req, res, next) => {
+  try {
+    const collections = req.app.locals.mastodonCollections;
+    const baseUrl = `${req.protocol}://${req.get("host")}`;
+    const limit = parseLimit(req.query.limit);
+
+    if (!collections.ap_interactions) {
+      return res.json([]);
+    }
+
+    const baseFilter = { type: "bookmark" };
+    const { filter, sort, reverse } = buildPaginationQuery(baseFilter, {
+      max_id: req.query.max_id,
+      min_id: req.query.min_id,
+      since_id: req.query.since_id,
+    });
+
+    let interactions = await collections.ap_interactions
+      .find(filter)
+      .sort(sort)
+      .limit(limit)
+      .toArray();
+
+    if (reverse) interactions.reverse();
+
+    // Batch-fetch the actual timeline items
+    const objectUrls = interactions.map((i) => i.objectUrl).filter(Boolean);
+    if (!objectUrls.length) {
+      return res.json([]);
+    }
+
+    const items = await collections.ap_timeline
+      .find({ $or: [{ uid: { $in: objectUrls } }, { url: { $in: objectUrls } }] })
+      .toArray();
+
+    const itemMap = new Map();
+    for (const item of items) {
+      if (item.uid) itemMap.set(item.uid, item);
+      if (item.url) itemMap.set(item.url, item);
+    }
+
+    const statuses = [];
+    for (const interaction of interactions) {
+      const item = itemMap.get(interaction.objectUrl);
+      if (item) {
+        statuses.push(
+          serializeStatus(item, {
+            baseUrl,
+            favouritedIds: new Set(),
+            rebloggedIds: new Set(),
+            bookmarkedIds: new Set([item.uid]),
+            pinnedIds: new Set(),
+          }),
+        );
+      }
+    }
+
+    setPaginationHeaders(res, req, interactions, limit);
+    res.json(statuses);
+  } catch (error) {
+    next(error);
+  }
+});
+
+// ─── Favourites ─────────────────────────────────────────────────────────────
+
+router.get("/api/v1/favourites", async (req, res, next) => {
+  try {
+    const collections = req.app.locals.mastodonCollections;
+    const baseUrl = `${req.protocol}://${req.get("host")}`;
+    const limit = parseLimit(req.query.limit);
+
+    if (!collections.ap_interactions) {
+      return res.json([]);
+    }
+
+    const baseFilter = { type: "like" };
+    const { filter, sort, reverse } = buildPaginationQuery(baseFilter, {
+      max_id: req.query.max_id,
+      min_id: req.query.min_id,
+      since_id: req.query.since_id,
+    });
+
+    let interactions = await collections.ap_interactions
+      .find(filter)
+      .sort(sort)
+      .limit(limit)
+      .toArray();
+
+    if (reverse) interactions.reverse();
+
+    const objectUrls = interactions.map((i) => i.objectUrl).filter(Boolean);
+    if (!objectUrls.length) {
+      return res.json([]);
+    }
+
+    const items = await collections.ap_timeline
+      .find({ $or: [{ uid: { $in: objectUrls } }, { url: { $in: objectUrls } }] })
+      .toArray();
+
+    const itemMap = new Map();
+    for (const item of items) {
+      if (item.uid) itemMap.set(item.uid, item);
+      if (item.url) itemMap.set(item.url, item);
+    }
+
+    const statuses = [];
+    for (const interaction of interactions) {
+      const item = itemMap.get(interaction.objectUrl);
+      if (item) {
+        statuses.push(
+          serializeStatus(item, {
+            baseUrl,
+            favouritedIds: new Set([item.uid]),
+            rebloggedIds: new Set(),
+            bookmarkedIds: new Set(),
+            pinnedIds: new Set(),
+          }),
+        );
+      }
+    }
+
+    setPaginationHeaders(res, req, interactions, limit);
+    res.json(statuses);
+  } catch (error) {
+    next(error);
+  }
+});
+
+// ─── Featured tags ──────────────────────────────────────────────────────────
+
+router.get("/api/v1/featured_tags", (req, res) => {
+  res.json([]);
+});
+
+// ─── Followed tags ──────────────────────────────────────────────────────────
+
+router.get("/api/v1/followed_tags", (req, res) => {
+  res.json([]);
+});
+
+// ─── Suggestions ────────────────────────────────────────────────────────────
+
+router.get("/api/v2/suggestions", (req, res) => {
+  res.json([]);
+});
+
+// ─── Trends ─────────────────────────────────────────────────────────────────
+
+router.get("/api/v1/trends/statuses", (req, res) => {
+  res.json([]);
+});
+
+router.get("/api/v1/trends/tags", (req, res) => {
+  res.json([]);
+});
+
+router.get("/api/v1/trends/links", (req, res) => {
+  res.json([]);
+});
+
+// ─── Scheduled statuses ─────────────────────────────────────────────────────
+
+router.get("/api/v1/scheduled_statuses", (req, res) => {
+  res.json([]);
+});
+
+// ─── Conversations ──────────────────────────────────────────────────────────
+
+router.get("/api/v1/conversations", (req, res) => {
+  res.json([]);
+});
+
+// ─── Domain blocks ──────────────────────────────────────────────────────────
+
+router.get("/api/v1/domain_blocks", (req, res) => {
+  res.json([]);
+});
+
+// ─── Endorsements ───────────────────────────────────────────────────────────
+
+router.get("/api/v1/endorsements", (req, res) => {
+  res.json([]);
+});
+
+// ─── Account statuses ───────────────────────────────────────────────────────
+
+router.get("/api/v1/accounts/:id/statuses", async (req, res, next) => {
+  try {
+    const collections = req.app.locals.mastodonCollections;
+    const baseUrl = `${req.protocol}://${req.get("host")}`;
+
+    // Try to find the profile to see if this is the local user
+    const profile = await collections.ap_profile.findOne({});
+    const isLocal = profile && profile._id.toString() === req.params.id;
+
+    if (isLocal && profile?.url) {
+      // Return statuses authored by local user
+      const { serializeStatus } = await import("../entities/status.js");
+      const { parseLimit } = await import("../helpers/pagination.js");
+
+      const limit = parseLimit(req.query.limit);
+      const items = await collections.ap_timeline
+        .find({ "author.url": profile.url, isContext: { $ne: true } })
+        .sort({ _id: -1 })
+        .limit(limit)
+        .toArray();
+
+      const statuses = items.map((item) =>
+        serializeStatus(item, {
+          baseUrl,
+          favouritedIds: new Set(),
+          rebloggedIds: new Set(),
+          bookmarkedIds: new Set(),
+          pinnedIds: new Set(),
+        }),
+      );
+
+      return res.json(statuses);
+    }
+
+    // Remote account or unknown — return empty
+    res.json([]);
+  } catch (error) {
+    next(error);
+  }
+});
+
+// ─── Account followers/following ────────────────────────────────────────────
+
+router.get("/api/v1/accounts/:id/followers", (req, res) => {
+  res.json([]);
+});
+
+router.get("/api/v1/accounts/:id/following", (req, res) => {
+  res.json([]);
+});
+
+export default router;
diff --git a/lib/mastodon/routes/timelines.js b/lib/mastodon/routes/timelines.js
new file mode 100644
index 0000000..4a4763e
--- /dev/null
+++ b/lib/mastodon/routes/timelines.js
@@ -0,0 +1,281 @@
+/**
+ * Timeline endpoints for Mastodon Client API.
+ *
+ * GET /api/v1/timelines/home — home timeline (authenticated)
+ * GET /api/v1/timelines/public — public/federated timeline
+ * GET /api/v1/timelines/tag/:hashtag — hashtag timeline
+ */
+import express from "express";
+import { serializeStatus } from "../entities/status.js";
+import { buildPaginationQuery, parseLimit, setPaginationHeaders } from "../helpers/pagination.js";
+import { loadModerationData, applyModerationFilters } from "../../item-processing.js";
+
+const router = express.Router(); // eslint-disable-line new-cap
+
+// ─── GET /api/v1/timelines/home ─────────────────────────────────────────────
+
+router.get("/api/v1/timelines/home", async (req, res, next) => {
+  try {
+    const token = req.mastodonToken;
+    if (!token) {
+      return res.status(401).json({ error: "The access token is invalid" });
+    }
+
+    const collections = req.app.locals.mastodonCollections;
+    const baseUrl = `${req.protocol}://${req.get("host")}`;
+    const limit = parseLimit(req.query.limit);
+
+    // Base filter: exclude context-only items and private/direct posts
+    const baseFilter = {
+      isContext: { $ne: true },
+      visibility: { $nin: ["direct"] },
+    };
+
+    // Apply cursor-based pagination
+    const { filter, sort, reverse } = buildPaginationQuery(baseFilter, {
+      max_id: req.query.max_id,
+      min_id: req.query.min_id,
+      since_id: req.query.since_id,
+    });
+
+    // Fetch items from timeline
+    let items = await collections.ap_timeline
+      .find(filter)
+      .sort(sort)
+      .limit(limit)
+      .toArray();
+
+    // Reverse if min_id was used (ascending sort → need descending order)
+    if (reverse) {
+      items.reverse();
+    }
+
+    // Apply mute/block filtering
+    const modCollections = {
+      ap_muted: collections.ap_muted,
+      ap_blocked: collections.ap_blocked,
+      ap_profile: collections.ap_profile,
+    };
+    const moderation = await loadModerationData(modCollections);
+    items = applyModerationFilters(items, moderation);
+
+    // Load interaction state (likes, boosts, bookmarks) for the authenticated user
+    const { favouritedIds, rebloggedIds, bookmarkedIds } = await loadInteractionState(
+      collections,
+      items,
+    );
+
+    // Serialize to Mastodon Status entities
+    const statuses = items.map((item) =>
+      serializeStatus(item, {
+        baseUrl,
+        favouritedIds,
+        rebloggedIds,
+        bookmarkedIds,
+        pinnedIds: new Set(),
+      }),
+    );
+
+    // Set pagination Link headers
+    setPaginationHeaders(res, req, items, limit);
+
+    res.json(statuses);
+  } catch (error) {
+    next(error);
+  }
+});
+
+// ─── GET /api/v1/timelines/public ───────────────────────────────────────────
+
+router.get("/api/v1/timelines/public", async (req, res, next) => {
+  try {
+    const collections = req.app.locals.mastodonCollections;
+    const baseUrl = `${req.protocol}://${req.get("host")}`;
+    const limit = parseLimit(req.query.limit);
+
+    // Public timeline: only public visibility, no context items
+    const baseFilter = {
+      isContext: { $ne: true },
+      visibility: "public",
+    };
+
+    // Only original posts (exclude boosts from public timeline unless local=true)
+    if (req.query.only_media === "true") {
+      baseFilter.$or = [
+        { "photo.0": { $exists: true } },
+        { "video.0": { $exists: true } },
+        { "audio.0": { $exists: true } },
+      ];
+    }
+
+    const { filter, sort, reverse } = buildPaginationQuery(baseFilter, {
+      max_id: req.query.max_id,
+      min_id: req.query.min_id,
+      since_id: req.query.since_id,
+    });
+
+    let items = await collections.ap_timeline
+      .find(filter)
+      .sort(sort)
+      .limit(limit)
+      .toArray();
+
+    if (reverse) {
+      items.reverse();
+    }
+
+    // Apply mute/block filtering
+    const modCollections = {
+      ap_muted: collections.ap_muted,
+      ap_blocked: collections.ap_blocked,
+      ap_profile: collections.ap_profile,
+    };
+    const moderation = await loadModerationData(modCollections);
+    items = applyModerationFilters(items, moderation);
+
+    // Load interaction state if authenticated
+    let favouritedIds = new Set();
+    let rebloggedIds = new Set();
+    let bookmarkedIds = new Set();
+
+    if (req.mastodonToken) {
+      ({ favouritedIds, rebloggedIds, bookmarkedIds } = await loadInteractionState(
+        collections,
+        items,
+      ));
+    }
+
+    const statuses = items.map((item) =>
+      serializeStatus(item, {
+        baseUrl,
+        favouritedIds,
+        rebloggedIds,
+        bookmarkedIds,
+        pinnedIds: new Set(),
+      }),
+    );
+
+    setPaginationHeaders(res, req, items, limit);
+    res.json(statuses);
+  } catch (error) {
+    next(error);
+  }
+});
+
+// ─── GET /api/v1/timelines/tag/:hashtag ─────────────────────────────────────
+
+router.get("/api/v1/timelines/tag/:hashtag", async (req, res, next) => {
+  try {
+    const collections = req.app.locals.mastodonCollections;
+    const baseUrl = `${req.protocol}://${req.get("host")}`;
+    const limit = parseLimit(req.query.limit);
+    const hashtag = req.params.hashtag;
+
+    const baseFilter = {
+      isContext: { $ne: true },
+      visibility: { $in: ["public", "unlisted"] },
+      category: hashtag,
+    };
+
+    const { filter, sort, reverse } = buildPaginationQuery(baseFilter, {
+      max_id: req.query.max_id,
+      min_id: req.query.min_id,
+      since_id: req.query.since_id,
+    });
+
+    let items = await collections.ap_timeline
+      .find(filter)
+      .sort(sort)
+      .limit(limit)
+      .toArray();
+
+    if (reverse) {
+      items.reverse();
+    }
+
+    // Load interaction state if authenticated
+    let favouritedIds = new Set();
+    let rebloggedIds = new Set();
+    let bookmarkedIds = new Set();
+
+    if (req.mastodonToken) {
+      ({ favouritedIds, rebloggedIds, bookmarkedIds } = await loadInteractionState(
+        collections,
+        items,
+      ));
+    }
+
+    const statuses = items.map((item) =>
+      serializeStatus(item, {
+        baseUrl,
+        favouritedIds,
+        rebloggedIds,
+        bookmarkedIds,
+        pinnedIds: new Set(),
+      }),
+    );
+
+    setPaginationHeaders(res, req, items, limit);
+    res.json(statuses);
+  } catch (error) {
+    next(error);
+  }
+});
+
+// ─── Helpers ─────────────────────────────────────────────────────────────────
+
+/**
+ * Load interaction state (favourited, reblogged, bookmarked) for a set of timeline items.
+ *
+ * Queries ap_interactions for likes and boosts matching the items' UIDs.
+ *
+ * @param {object} collections - MongoDB collections
+ * @param {Array} items - Timeline items
+ * @returns {Promise<{ favouritedIds: Set<string>, rebloggedIds: Set<string>, bookmarkedIds: Set<string> }>}
+ */
+async function loadInteractionState(collections, items) {
+  const favouritedIds = new Set();
+  const rebloggedIds = new Set();
+  const bookmarkedIds = new Set();
+
+  if (!items.length || !collections.ap_interactions) {
+    return { favouritedIds, rebloggedIds, bookmarkedIds };
+  }
+
+  // Collect all UIDs and URLs to look up
+  const lookupUrls = new Set();
+  const urlToUid = new Map();
+  for (const item of items) {
+    if (item.uid) {
+      lookupUrls.add(item.uid);
+      urlToUid.set(item.uid, item.uid);
+    }
+    if (item.url && item.url !== item.uid) {
+      lookupUrls.add(item.url);
+      urlToUid.set(item.url, item.uid || item.url);
+    }
+  }
+
+  if (lookupUrls.size === 0) {
+    return { favouritedIds, rebloggedIds, bookmarkedIds };
+  }
+
+  const interactions = await collections.ap_interactions
+    .find({ objectUrl: { $in: [...lookupUrls] } })
+    .toArray();
+
+  for (const interaction of interactions) {
+    const uid = urlToUid.get(interaction.objectUrl) || interaction.objectUrl;
+    if (interaction.type === "like") {
+      favouritedIds.add(uid);
+    } else if (interaction.type === "boost") {
+      rebloggedIds.add(uid);
+    } else if (interaction.type === "bookmark") {
+      bookmarkedIds.add(uid);
+    }
+  }
+
+  return { favouritedIds, rebloggedIds, bookmarkedIds };
+}
+
+export default router;
diff --git a/package.json b/package.json
index cce331b..109bc38 100644
--- a/package.json
+++ b/package.json
@@ -1,6 +1,6 @@
 {
   "name": "@rmdes/indiekit-endpoint-activitypub",
-  "version": "2.15.4",
+  "version": "3.0.0",
   "description": "ActivityPub federation endpoint for Indiekit via Fedify. Adds full fediverse support: actor, inbox, outbox, followers, following, syndication, and Mastodon migration.",
   "keywords": [
     "indiekit",