feat: replace explore deck layout with full-width tabbed design

Replace the cramped deck/column layout on the explore page with a tabbed interface. Three tab types: Search (always first), Instance (pinned with local/federated badge), and Hashtag (aggregated across all pinned instances). - New ap_explore_tabs collection replaces ap_decks (clean start) - Tab CRUD API: add, remove, reorder with CSRF/SSRF validation - Per-tab infinite scroll with IntersectionObserver + AbortController - Hashtag tabs query up to 10 instances in parallel, merge by date, deduplicate by URL - WAI-ARIA tabs pattern with arrow key navigation - LRU cache (5 tabs) for tab content - Extract shared explore-utils.js (validators + status mapping) - Remove all old deck code (JS, CSS, controllers, locale strings)
2026-04-02 15:44:58 +02:00 · 2026-02-28 16:30:48 +01:00
parent f97e9a82f4
commit 55baa7cef5
13 changed files with 1924 additions and 857 deletions
--- a/assets/reader-decks.js
+++ b/assets/reader-decks.js
@@ -1,212 +0,0 @@
-/**
- * Deck components — Alpine.js components for the TweetDeck-style deck view.
- *
- * Registers:
- *   apDeckToggle  — star/favorite button to add/remove a deck on the Search tab
- *   apDeckColumn  — single deck column with its own infinite-scroll timeline
- */
-
-document.addEventListener("alpine:init", () => {
-  // ── apDeckToggle ──────────────────────────────────────────────────────────
-  //
-  // Star/favorite button that adds or removes a deck entry for the current
-  // instance+scope combination.
-  //
-  // Parameters (passed via x-data):
-  //   domain       — instance hostname (e.g. "mastodon.social")
-  //   scope        — "local" | "federated"
-  //   mountPath    — plugin mount path for API URL construction
-  //   csrfToken    — CSRF token from server session
-  //   deckCount    — current number of saved decks (for limit enforcement)
-  //   initialState — true if this instance+scope is already a deck
-  // eslint-disable-next-line no-undef
-  Alpine.data("apDeckToggle", (domain, scope, mountPath, csrfToken, deckCount, initialState) => ({
-    inDeck: initialState,
-    currentCount: deckCount,
-    loading: false,
-
-    get deckLimitReached() {
-      return this.currentCount >= 8 && !this.inDeck;
-    },
-
-    async toggle() {
-      if (this.loading) return;
-      if (!this.inDeck && this.deckLimitReached) return;
-
-      this.loading = true;
-      try {
-        const url = this.inDeck
-          ? `${mountPath}/admin/reader/api/decks/remove`
-          : `${mountPath}/admin/reader/api/decks`;
-
-        const res = await fetch(url, {
-          method: "POST",
-          headers: {
-            "Content-Type": "application/json",
-            "X-CSRF-Token": csrfToken,
-          },
-          body: JSON.stringify({ domain, scope }),
-        });
-
-        if (res.ok) {
-          this.inDeck = !this.inDeck;
-          // Track actual count so deckLimitReached stays accurate
-          this.currentCount += this.inDeck ? 1 : -1;
-        }
-      } catch {
-        // Network error — state unchanged, server is source of truth
-      } finally {
-        this.loading = false;
-      }
-    },
-  }));
-
-  // ── apDeckColumn ─────────────────────────────────────────────────────────
-  //
-  // Individual deck column component. Fetches timeline from the explore API
-  // and renders it in a scrollable column with infinite scroll.
-  //
-  // Uses its own IntersectionObserver referencing `this.$refs.sentinel`
-  // (NOT apExploreScroll which hardcodes document.getElementById).
-  //
-  // Parameters (passed via x-data):
-  //   domain    — instance hostname
-  //   scope     — "local" | "federated"
-  //   mountPath — plugin mount path
-  //   index     — column position (0-based), used for staggered loading delay
-  //   csrfToken — CSRF token for remove calls
-  // eslint-disable-next-line no-undef
-  Alpine.data("apDeckColumn", (domain, scope, mountPath, index, csrfToken) => ({
-    itemCount: 0,
-    html: "",
-    maxId: null,
-    loading: false,
-    done: false,
-    error: null,
-    observer: null,
-    abortController: null,
-
-    init() {
-      // Stagger initial fetch: column 0 loads immediately, column N waits N*200ms
-      const delay = index * 200;
-      if (delay === 0) {
-        this.loadMore();
-      } else {
-        setTimeout(() => {
-          this.loadMore();
-        }, delay);
-      }
-
-      // Set up IntersectionObserver scoped to this column's scrollable body
-      // (root must be the scroll container, not viewport, to avoid premature triggers)
-      this.$nextTick(() => {
-        const root = this.$refs.body || null;
-        this.observer = new IntersectionObserver(
-          (entries) => {
-            for (const entry of entries) {
-              if (entry.isIntersecting && !this.loading && !this.done && this.itemCount > 0) {
-                this.loadMore();
-              }
-            }
-          },
-          { root, rootMargin: "200px" },
-        );
-
-        if (this.$refs.sentinel) {
-          this.observer.observe(this.$refs.sentinel);
-        }
-      });
-    },
-
-    destroy() {
-      if (this.abortController) {
-        this.abortController.abort();
-        this.abortController = null;
-      }
-
-      if (this.observer) {
-        this.observer.disconnect();
-        this.observer = null;
-      }
-    },
-
-    async loadMore() {
-      if (this.loading || this.done) return;
-
-      this.loading = true;
-      this.error = null;
-
-      try {
-        this.abortController = new AbortController();
-
-        const url = new URL(`${mountPath}/admin/reader/api/explore`, window.location.origin);
-        url.searchParams.set("instance", domain);
-        url.searchParams.set("scope", scope);
-        if (this.maxId) url.searchParams.set("max_id", this.maxId);
-
-        const res = await fetch(url.toString(), {
-          headers: { Accept: "application/json" },
-          signal: this.abortController.signal,
-        });
-
-        if (!res.ok) {
-          throw new Error(`HTTP ${res.status}`);
-        }
-
-        const data = await res.json();
-
-        if (data.html && data.html.trim() !== "") {
-          this.html += data.html;
-          this.itemCount++;
-        }
-
-        if (data.maxId) {
-          this.maxId = data.maxId;
-        } else {
-          this.done = true;
-        }
-
-        // If no content came back on first load, mark as done
-        if (!data.html || data.html.trim() === "") {
-          this.done = true;
-        }
-      } catch (fetchError) {
-        this.error = fetchError.message || "Could not load timeline";
-      } finally {
-        this.loading = false;
-      }
-    },
-
-    async retryLoad() {
-      this.error = null;
-      this.done = false;
-      await this.loadMore();
-    },
-
-    async removeDeck() {
-      try {
-        const res = await fetch(`${mountPath}/admin/reader/api/decks/remove`, {
-          method: "POST",
-          headers: {
-            "Content-Type": "application/json",
-            "X-CSRF-Token": csrfToken,
-          },
-          body: JSON.stringify({ domain, scope }),
-        });
-
-        if (res.ok) {
-          // Remove column from DOM
-          if (this.observer) {
-            this.observer.disconnect();
-          }
-
-          this.$el.remove();
-        } else {
-          this.error = `Failed to remove (${res.status})`;
-        }
-      } catch {
-        this.error = "Network error — could not remove column";
-      }
-    },
-  }));
-});
--- a/assets/reader-infinite-scroll.js
+++ b/assets/reader-infinite-scroll.js
@@ -11,6 +11,7 @@ document.addEventListener("alpine:init", () => {
    maxId: null,
    instance: "",
    scope: "local",
+    hashtag: "",
    observer: null,

    init() {
@@ -18,6 +19,7 @@ document.addEventListener("alpine:init", () => {
      this.maxId = el.dataset.maxId || null;
      this.instance = el.dataset.instance || "";
      this.scope = el.dataset.scope || "local";
+      this.hashtag = el.dataset.hashtag || "";

      if (!this.maxId) {
        this.done = true;
@@ -53,6 +55,10 @@ document.addEventListener("alpine:init", () => {
        scope: this.scope,
        max_id: this.maxId,
      });
+      // Pass hashtag when in hashtag mode so infinite scroll stays on tag timeline
+      if (this.hashtag) {
+        params.set("hashtag", this.hashtag);
+      }

      try {
        const res = await fetch(
--- a/assets/reader-tabs.js
+++ b/assets/reader-tabs.js
@@ -0,0 +1,643 @@
+/**
+ * Tab components — Alpine.js component for the tabbed explore page.
+ *
+ * Registers:
+ *   apExploreTabs — tab management, timeline loading, infinite scroll
+ *
+ * Guard: init() exits early when .ap-explore-tabs-container is absent so
+ * this script is safe to load on all reader pages via the shared layout.
+ *
+ * Configuration is read from data-* attributes on the root element:
+ *   data-mount-path — plugin mount path for API URL construction
+ *   data-csrf       — CSRF token from server session
+ */
+
+document.addEventListener("alpine:init", () => {
+  // eslint-disable-next-line no-undef
+  Alpine.data("apExploreTabs", () => ({
+    // ── Tab list and active state ────────────────────────────────────────────
+    tabs: [],
+    activeTabId: null, // null = Search tab; string = user tab _id
+
+    // ── Tab management UI state ──────────────────────────────────────────────
+    pinning: false,
+    showHashtagForm: false,
+    hashtagInput: "",
+    error: null,
+
+    // ── Per-tab content state (keyed by tab _id) ─────────────────────────────
+    // Each entry: { loading, error, html, maxId, done, abortController }
+    // Hashtag tabs additionally carry: { cursors, sourceMeta }
+    //   cursors: { [domain]: maxId|null } — per-instance pagination cursors
+    //   sourceMeta: { instancesQueried, instancesTotal, instanceLabels }
+    tabState: {},
+
+    // ── Bounded content cache (last 5 tabs, LRU by access order) ────────────
+    _cacheOrder: [],
+
+    // ── Scroll observer for the active tab ───────────────────────────────────
+    _tabObserver: null,
+
+    // ── Configuration (read from data attributes) ────────────────────────────
+    _mountPath: "",
+    _csrfToken: "",
+    _reorderTimer: null,
+
+    // ── Lifecycle ────────────────────────────────────────────────────────────
+
+    init() {
+      if (!document.querySelector(".ap-explore-tabs-container")) return;
+      this._mountPath = this.$el.dataset.mountPath || "";
+      this._csrfToken = this.$el.dataset.csrf || "";
+      this._loadTabs();
+    },
+
+    destroy() {
+      if (this._tabObserver) {
+        this._tabObserver.disconnect();
+        this._tabObserver = null;
+      }
+      if (this._reorderTimer) {
+        clearTimeout(this._reorderTimer);
+        this._reorderTimer = null;
+      }
+      // Abort any in-flight requests
+      for (const state of Object.values(this.tabState)) {
+        if (state.abortController) state.abortController.abort();
+      }
+    },
+
+    async _loadTabs() {
+      try {
+        const res = await fetch(
+          `${this._mountPath}/admin/reader/api/tabs`,
+          { headers: { Accept: "application/json" } }
+        );
+        if (!res.ok) return;
+        const data = await res.json();
+        this.tabs = data.map((t) => ({ ...t, _id: String(t._id) }));
+      } catch {
+        // Non-critical — tab bar degrades gracefully to Search-only
+      }
+    },
+
+    // ── Tab content state helpers ─────────────────────────────────────────────
+
+    _getState(tabId) {
+      return this.tabState[tabId] || {
+        loading: false, error: null, html: "", maxId: null, done: false,
+        abortController: null,
+      };
+    },
+
+    _setState(tabId, update) {
+      const current = this._getState(tabId);
+      this.tabState = { ...this.tabState, [tabId]: { ...current, ...update } };
+    },
+
+    // LRU cache management — evict oldest when cache grows past 5 tabs
+    _touchCache(tabId) {
+      this._cacheOrder = this._cacheOrder.filter((id) => id !== tabId);
+      this._cacheOrder.push(tabId);
+
+      while (this._cacheOrder.length > 5) {
+        const evictId = this._cacheOrder.shift();
+        const evictedState = this.tabState[evictId];
+        if (evictedState) {
+          this._setState(evictId, {
+            html: "", maxId: null, done: false, loading: false,
+          });
+        }
+      }
+    },
+
+    // ── Tab switching ─────────────────────────────────────────────────────────
+
+    switchToSearch() {
+      this._abortActiveTabFetch();
+      this._teardownScrollObserver();
+      this.activeTabId = null;
+      this.error = null;
+    },
+
+    switchTab(tabId) {
+      if (this.activeTabId === tabId) return;
+      this._abortActiveTabFetch();
+      this._teardownScrollObserver();
+      this.activeTabId = tabId;
+      this.error = null;
+
+      const tab = this.tabs.find((t) => t._id === tabId);
+      if (!tab) return;
+
+      const state = this._getState(tabId);
+
+      if (tab.type === "instance") {
+        if (!state.html && !state.loading) {
+          // Cache miss — load first page
+          this.$nextTick(() => this._loadInstanceTab(tab));
+        } else if (state.html) {
+          // Cache hit — restore scroll observer
+          this._touchCache(tabId);
+          this.$nextTick(() => this._setupScrollObserver(tab));
+        }
+      } else if (tab.type === "hashtag") {
+        if (!state.html && !state.loading) {
+          this.$nextTick(() => this._loadHashtagTab(tab));
+        } else if (state.html) {
+          this._touchCache(tabId);
+          this.$nextTick(() => this._setupScrollObserver(tab));
+        }
+      }
+    },
+
+    _abortActiveTabFetch() {
+      if (!this.activeTabId) return;
+      const state = this._getState(this.activeTabId);
+      if (state.abortController) {
+        state.abortController.abort();
+        this._setState(this.activeTabId, {
+          abortController: null,
+          loading: false,
+        });
+      }
+    },
+
+    // ── Instance tab loading ──────────────────────────────────────────────────
+
+    async _loadInstanceTab(tab) {
+      const tabId = tab._id;
+      const abortController = new AbortController();
+      this._setState(tabId, {
+        loading: true, error: null, abortController,
+      });
+
+      try {
+        const url = new URL(
+          `${this._mountPath}/admin/reader/api/explore`,
+          window.location.origin
+        );
+        url.searchParams.set("instance", tab.domain);
+        url.searchParams.set("scope", tab.scope);
+
+        const res = await fetch(url.toString(), {
+          headers: { Accept: "application/json" },
+          signal: abortController.signal,
+        });
+
+        if (!res.ok) throw new Error(`HTTP ${res.status}`);
+
+        const data = await res.json();
+
+        this._setState(tabId, {
+          loading: false,
+          abortController: null,
+          html: data.html || "",
+          maxId: data.maxId || null,
+          done: !data.maxId,
+          error: null,
+        });
+
+        this._touchCache(tabId);
+
+        // Set up scroll observer after DOM updates
+        this.$nextTick(() => this._setupScrollObserver(tab));
+      } catch (err) {
+        if (err.name === "AbortError") return; // Tab was switched away — silent
+        this._setState(tabId, {
+          loading: false,
+          abortController: null,
+          error: err.message || "Could not load timeline",
+        });
+      }
+    },
+
+    async _loadMoreInstanceTab(tab) {
+      const tabId = tab._id;
+      const state = this._getState(tabId);
+      if (state.loading || state.done || !state.maxId) return;
+
+      const abortController = new AbortController();
+      this._setState(tabId, { loading: true, abortController });
+
+      try {
+        const url = new URL(
+          `${this._mountPath}/admin/reader/api/explore`,
+          window.location.origin
+        );
+        url.searchParams.set("instance", tab.domain);
+        url.searchParams.set("scope", tab.scope);
+        url.searchParams.set("max_id", state.maxId);
+
+        const res = await fetch(url.toString(), {
+          headers: { Accept: "application/json" },
+          signal: abortController.signal,
+        });
+
+        if (!res.ok) throw new Error(`HTTP ${res.status}`);
+
+        const data = await res.json();
+        const current = this._getState(tabId);
+
+        this._setState(tabId, {
+          loading: false,
+          abortController: null,
+          html: current.html + (data.html || ""),
+          maxId: data.maxId || null,
+          done: !data.maxId,
+        });
+      } catch (err) {
+        if (err.name === "AbortError") return;
+        this._setState(tabId, {
+          loading: false,
+          abortController: null,
+          error: err.message || "Could not load more posts",
+        });
+      }
+    },
+
+    // ── Hashtag tab loading ───────────────────────────────────────────────────
+
+    async _loadHashtagTab(tab) {
+      const tabId = tab._id;
+      const abortController = new AbortController();
+      this._setState(tabId, { loading: true, error: null, abortController });
+
+      try {
+        const url = new URL(
+          `${this._mountPath}/admin/reader/api/explore/hashtag`,
+          window.location.origin
+        );
+        url.searchParams.set("hashtag", tab.hashtag);
+        url.searchParams.set("cursors", "{}");
+
+        const res = await fetch(url.toString(), {
+          headers: { Accept: "application/json" },
+          signal: abortController.signal,
+        });
+
+        if (!res.ok) throw new Error(`HTTP ${res.status}`);
+
+        const data = await res.json();
+
+        this._setState(tabId, {
+          loading: false,
+          abortController: null,
+          html: data.html || "",
+          cursors: data.cursors || {},
+          sourceMeta: {
+            instancesQueried: data.instancesQueried || 0,
+            instancesTotal: data.instancesTotal || 0,
+            instanceLabels: data.instanceLabels || [],
+          },
+          done: !data.html || Object.values(data.cursors || {}).every((c) => !c),
+          error: null,
+        });
+
+        this._touchCache(tabId);
+        this.$nextTick(() => this._setupScrollObserver(tab));
+      } catch (err) {
+        if (err.name === "AbortError") return;
+        this._setState(tabId, {
+          loading: false,
+          abortController: null,
+          error: err.message || "Could not load hashtag timeline",
+        });
+      }
+    },
+
+    async _loadMoreHashtagTab(tab) {
+      const tabId = tab._id;
+      const state = this._getState(tabId);
+      if (state.loading || state.done) return;
+
+      const abortController = new AbortController();
+      this._setState(tabId, { loading: true, abortController });
+
+      try {
+        const url = new URL(
+          `${this._mountPath}/admin/reader/api/explore/hashtag`,
+          window.location.origin
+        );
+        url.searchParams.set("hashtag", tab.hashtag);
+        url.searchParams.set("cursors", JSON.stringify(state.cursors || {}));
+
+        const res = await fetch(url.toString(), {
+          headers: { Accept: "application/json" },
+          signal: abortController.signal,
+        });
+
+        if (!res.ok) throw new Error(`HTTP ${res.status}`);
+
+        const data = await res.json();
+        const current = this._getState(tabId);
+
+        const allCursorsExhausted = Object.values(data.cursors || {}).every(
+          (c) => !c
+        );
+
+        this._setState(tabId, {
+          loading: false,
+          abortController: null,
+          html: current.html + (data.html || ""),
+          cursors: data.cursors || {},
+          done: !data.html || allCursorsExhausted,
+        });
+      } catch (err) {
+        if (err.name === "AbortError") return;
+        this._setState(tabId, {
+          loading: false,
+          abortController: null,
+          error: err.message || "Could not load more posts",
+        });
+      }
+    },
+
+    async retryTab(tab) {
+      const tabId = tab._id;
+      this._setState(tabId, {
+        error: null, html: "", maxId: null, done: false,
+        cursors: {}, sourceMeta: null,
+      });
+      if (tab.type === "instance") {
+        await this._loadInstanceTab(tab);
+      } else if (tab.type === "hashtag") {
+        await this._loadHashtagTab(tab);
+      }
+    },
+
+    // ── Infinite scroll for tab panels ───────────────────────────────────────
+
+    _setupScrollObserver(tab) {
+      this._teardownScrollObserver();
+
+      const panel = this.$el.querySelector(`#ap-tab-panel-${tab._id}`);
+      if (!panel) return;
+
+      const sentinel = panel.querySelector(".ap-tab-sentinel");
+      if (!sentinel) return;
+
+      this._tabObserver = new IntersectionObserver(
+        (entries) => {
+          for (const entry of entries) {
+            if (entry.isIntersecting) {
+              const state = this._getState(tab._id);
+              if (!state.loading && !state.done) {
+                if (tab.type === "instance" && state.maxId) {
+                  this._loadMoreInstanceTab(tab);
+                } else if (tab.type === "hashtag") {
+                  this._loadMoreHashtagTab(tab);
+                }
+              }
+            }
+          }
+        },
+        { rootMargin: "200px" }
+      );
+      this._tabObserver.observe(sentinel);
+    },
+
+    _teardownScrollObserver() {
+      if (this._tabObserver) {
+        this._tabObserver.disconnect();
+        this._tabObserver = null;
+      }
+    },
+
+    // ── Tab label helpers ─────────────────────────────────────────────────────
+
+    tabLabel(tab) {
+      return tab.type === "instance" ? tab.domain : `#${tab.hashtag}`;
+    },
+
+    hashtagSourcesLine(tab) {
+      const state = this._getState(tab._id);
+      const meta = state.sourceMeta;
+      if (!meta || !meta.instancesQueried) return "";
+      const n = meta.instancesQueried;
+      const total = meta.instancesTotal;
+      const labels = meta.instanceLabels || [];
+      const tag = tab.hashtag || "";
+      const suffix = n === 1 ? "instance" : "instances";
+      let line = `Searching #${tag} across ${n} ${suffix}`;
+      if (n < total) {
+        line += ` (${n} of ${total} pinned)`;
+      }
+      if (labels.length > 0) {
+        line += `: ${labels.join(", ")}`;
+      }
+      return line;
+    },
+
+    // ── Keyboard navigation (WAI-ARIA Tabs pattern) ───────────────────────────
+
+    handleTabKeydown(event, currentIndex) {
+      const total = this.tabs.length + 1;
+      let nextIndex = null;
+
+      if (event.key === "ArrowRight") {
+        event.preventDefault();
+        nextIndex = (currentIndex + 1) % total;
+      } else if (event.key === "ArrowLeft") {
+        event.preventDefault();
+        nextIndex = (currentIndex - 1 + total) % total;
+      } else if (event.key === "Home") {
+        event.preventDefault();
+        nextIndex = 0;
+      } else if (event.key === "End") {
+        event.preventDefault();
+        nextIndex = total - 1;
+      }
+
+      if (nextIndex !== null) {
+        const tabEls = this.$el.querySelectorAll('[role="tab"]');
+        if (tabEls[nextIndex]) tabEls[nextIndex].focus();
+      }
+    },
+
+    // ── Pin current search result as instance tab ─────────────────────────────
+
+    async pinInstance(domain, scope) {
+      if (this.pinning) return;
+      this.pinning = true;
+      this.error = null;
+
+      try {
+        const res = await fetch(
+          `${this._mountPath}/admin/reader/api/tabs`,
+          {
+            method: "POST",
+            headers: {
+              "Content-Type": "application/json",
+              "X-CSRF-Token": this._csrfToken,
+            },
+            body: JSON.stringify({ type: "instance", domain, scope }),
+          }
+        );
+
+        if (res.status === 409) {
+          const existing = this.tabs.find(
+            (t) => t.type === "instance" && t.domain === domain && t.scope === scope
+          );
+          if (existing) this.switchTab(existing._id);
+          return;
+        }
+
+        if (res.status === 403) {
+          this.error = "Session expired — please refresh the page.";
+          return;
+        }
+
+        if (!res.ok) return;
+
+        const newTab = await res.json();
+        newTab._id = String(newTab._id);
+        this.tabs.push(newTab);
+        this.switchTab(newTab._id);
+      } catch {
+        // Network error — silent
+      } finally {
+        this.pinning = false;
+      }
+    },
+
+    // ── Add hashtag tab ───────────────────────────────────────────────────────
+
+    async submitHashtagTab() {
+      const hashtag = (this.hashtagInput || "").replace(/^#+/, "").trim();
+      if (!hashtag) return;
+
+      try {
+        const res = await fetch(
+          `${this._mountPath}/admin/reader/api/tabs`,
+          {
+            method: "POST",
+            headers: {
+              "Content-Type": "application/json",
+              "X-CSRF-Token": this._csrfToken,
+            },
+            body: JSON.stringify({ type: "hashtag", hashtag }),
+          }
+        );
+
+        if (res.status === 409) {
+          const existing = this.tabs.find(
+            (t) => t.type === "hashtag" && t.hashtag === hashtag
+          );
+          if (existing) {
+            this.switchTab(existing._id);
+            this.showHashtagForm = false;
+            this.hashtagInput = "";
+          }
+          return;
+        }
+
+        if (res.status === 403) {
+          this.error = "Session expired — please refresh the page.";
+          return;
+        }
+
+        if (!res.ok) return;
+
+        const newTab = await res.json();
+        newTab._id = String(newTab._id);
+        this.tabs.push(newTab);
+        this.hashtagInput = "";
+        this.showHashtagForm = false;
+        this.switchTab(newTab._id);
+      } catch {
+        // Network error — silent
+      }
+    },
+
+    // ── Remove a tab ──────────────────────────────────────────────────────────
+
+    async removeTab(tab) {
+      const body =
+        tab.type === "instance"
+          ? { type: "instance", domain: tab.domain, scope: tab.scope }
+          : { type: "hashtag", hashtag: tab.hashtag };
+
+      try {
+        const res = await fetch(
+          `${this._mountPath}/admin/reader/api/tabs/remove`,
+          {
+            method: "POST",
+            headers: {
+              "Content-Type": "application/json",
+              "X-CSRF-Token": this._csrfToken,
+            },
+            body: JSON.stringify(body),
+          }
+        );
+
+        if (res.status === 403) {
+          this.error = "Session expired — please refresh the page.";
+          return;
+        }
+
+        if (!res.ok) return;
+
+        // Clean up tab state
+        const { [tab._id]: _removed, ...remaining } = this.tabState;
+        this.tabState = remaining;
+        this._cacheOrder = this._cacheOrder.filter((id) => id !== tab._id);
+
+        this.tabs = this.tabs
+          .filter((t) => t._id !== tab._id)
+          .map((t, i) => ({ ...t, order: i }));
+
+        if (this.activeTabId === tab._id) {
+          this._teardownScrollObserver();
+          this.activeTabId = null;
+        }
+      } catch {
+        // Network error — silent
+      }
+    },
+
+    // ── Tab reordering ────────────────────────────────────────────────────────
+
+    moveUp(tab) {
+      const idx = this.tabs.findIndex((t) => t._id === tab._id);
+      if (idx <= 0) return;
+      const copy = [...this.tabs];
+      [copy[idx - 1], copy[idx]] = [copy[idx], copy[idx - 1]];
+      this.tabs = copy.map((t, i) => ({ ...t, order: i }));
+      this._scheduleReorder();
+    },
+
+    moveDown(tab) {
+      const idx = this.tabs.findIndex((t) => t._id === tab._id);
+      if (idx < 0 || idx >= this.tabs.length - 1) return;
+      const copy = [...this.tabs];
+      [copy[idx], copy[idx + 1]] = [copy[idx + 1], copy[idx]];
+      this.tabs = copy.map((t, i) => ({ ...t, order: i }));
+      this._scheduleReorder();
+    },
+
+    _scheduleReorder() {
+      if (this._reorderTimer) clearTimeout(this._reorderTimer);
+      this._reorderTimer = setTimeout(() => this._sendReorder(), 500);
+    },
+
+    async _sendReorder() {
+      try {
+        const tabIds = this.tabs.map((t) => t._id);
+        await fetch(
+          `${this._mountPath}/admin/reader/api/tabs/reorder`,
+          {
+            method: "PATCH",
+            headers: {
+              "Content-Type": "application/json",
+              "X-CSRF-Token": this._csrfToken,
+            },
+            body: JSON.stringify({ tabIds }),
+          }
+        );
+      } catch {
+        // Non-critical — reorder failure doesn't affect UX
+      }
+    },
+  }));
+});
--- a/assets/reader.css
+++ b/assets/reader.css
@@ -2060,189 +2060,294 @@
  font-weight: 600;
 }

-/* ---------- Explore: deck toggle button ---------- */
+/* ==========================================================================
+   Explore: Tabbed Design
+   ========================================================================== */

-.ap-explore-deck-toggle {
-  display: flex;
-  justify-content: flex-end;
-  margin-bottom: var(--space-s);
+/* Tab bar wrapper: enables position:relative for fade gradient overlay */
+.ap-explore-tabs-container {
+  position: relative;
 }

-.ap-explore-deck-toggle__btn {
-  align-items: center;
-  background: none;
-  border: var(--border-width-thin) solid var(--color-outline);
-  border-radius: var(--border-radius-small);
-  color: var(--color-on-background);
-  cursor: pointer;
+/* Tab bar with right-edge fade to indicate horizontal overflow */
+.ap-explore-tabs-nav {
+  padding-right: var(--space-l);
+  position: relative;
+}
+
+.ap-explore-tabs-nav::after {
+  background: linear-gradient(to right, transparent, var(--color-background, #fff) 80%);
+  content: "";
+  height: 100%;
+  pointer-events: none;
+  position: absolute;
+  right: 0;
+  top: 0;
+  width: 40px;
+}
+
+/* Tab wrapper: holds tab button + reorder/close controls together */
+.ap-tab-wrapper {
+  align-items: stretch;
  display: inline-flex;
-  font-size: var(--font-size-s);
-  gap: var(--space-2xs);
-  padding: var(--space-xs) var(--space-s);
-  transition: background 0.15s, color 0.15s, border-color 0.15s;
+  position: relative;
 }

-.ap-explore-deck-toggle__btn:hover:not(:disabled) {
-  background: var(--color-offset);
-}
-
-.ap-explore-deck-toggle__btn--active {
-  background: var(--color-accent5);
-  border-color: var(--color-accent5);
-  color: var(--color-on-accent, #fff);
-}
-
-.ap-explore-deck-toggle__btn--active:hover:not(:disabled) {
-  background: var(--color-accent45);
-  border-color: var(--color-accent45);
-}
-
-.ap-explore-deck-toggle__btn:disabled {
-  cursor: not-allowed;
-  opacity: 0.5;
-}
-
-/* ---------- Deck grid layout ---------- */
-
-.ap-deck-grid {
-  display: grid;
-  gap: var(--space-m);
-  grid-template-columns: repeat(auto-fill, minmax(360px, 1fr));
-  margin-top: var(--space-m);
-  min-width: 0;
-}
-
-/* ---------- Deck column ---------- */
-
-.ap-deck-column {
-  background: var(--color-offset);
-  border: var(--border-width-thin) solid var(--color-outline);
-  border-radius: var(--border-radius-small);
-  display: flex;
-  flex-direction: column;
-  max-height: calc(100dvh - 220px);
-  min-height: 200px;
-  min-width: 0;
-  overflow: hidden;
-}
-
-.ap-deck-column__header {
+/* Show controls on hover or when the tab is active */
+.ap-tab-controls {
  align-items: center;
-  background: var(--color-background);
-  border-bottom: var(--border-width-thin) solid var(--color-outline);
-  display: flex;
-  flex-shrink: 0;
-  gap: var(--space-xs);
-  padding: var(--space-xs) var(--space-s);
+  display: none;
+  gap: 1px;
 }

-.ap-deck-column__domain {
+.ap-tab-wrapper:hover .ap-tab-controls,
+.ap-tab-wrapper:focus-within .ap-tab-controls {
+  display: flex;
+}
+
+/* Individual control buttons (↑ ↓ ×) */
+.ap-tab-control {
+  background: none;
+  border: none;
+  color: var(--color-on-offset);
+  cursor: pointer;
+  font-size: var(--font-size-xs);
+  line-height: 1;
+  padding: 2px 4px;
+}
+
+.ap-tab-control:hover {
+  color: var(--color-on-background);
+}
+
+.ap-tab-control:disabled {
+  cursor: default;
+  opacity: 0.3;
+}
+
+.ap-tab-control--remove {
+  color: var(--color-on-offset);
  font-size: var(--font-size-s);
-  font-weight: 600;
-  min-width: 0;
+}
+
+.ap-tab-control--remove:hover {
+  color: var(--color-red45);
+}
+
+/* Truncate long domain names in tab labels */
+.ap-tab__label {
+  display: inline-block;
+  max-width: 150px;
  overflow: hidden;
  text-overflow: ellipsis;
  white-space: nowrap;
 }

-.ap-deck-column__scope-badge {
-  border-radius: var(--border-radius-small);
-  flex-shrink: 0;
-  font-size: var(--font-size-xs);
-  font-weight: 600;
-  padding: 2px var(--space-xs);
+/* Scope badges on instance tabs */
+.ap-tab__badge {
+  border-radius: 3px;
+  font-size: 0.65em;
+  font-weight: 700;
+  letter-spacing: 0.02em;
+  margin-left: var(--space-xs);
+  padding: 1px 4px;
  text-transform: uppercase;
+  vertical-align: middle;
 }

-.ap-deck-column__scope-badge--local {
-  background: var(--color-blue10, #dbeafe);
-  color: var(--color-blue50, #1e40af);
+.ap-tab__badge--local {
+  background: color-mix(in srgb, var(--color-blue40, #2563eb) 15%, transparent);
+  color: var(--color-blue40, #2563eb);
 }

-.ap-deck-column__scope-badge--federated {
-  background: var(--color-purple10, #ede9fe);
-  color: var(--color-purple50, #5b21b6);
+.ap-tab__badge--federated {
+  background: color-mix(in srgb, var(--color-purple45, #7c3aed) 15%, transparent);
+  color: var(--color-purple45, #7c3aed);
 }

-.ap-deck-column__remove {
-  background: none;
-  border: none;
+/* +# button for adding hashtag tabs */
+.ap-tab--add {
+  font-family: monospace;
+  font-weight: 700;
+  letter-spacing: -0.05em;
+}
+
+/* Inline hashtag form that appears when +# is clicked */
+.ap-tab-add-hashtag {
+  align-items: center;
+  display: inline-flex;
+  gap: var(--space-xs);
+}
+
+.ap-tab-hashtag-form {
+  align-items: center;
+  display: flex;
+  gap: var(--space-xs);
+}
+
+.ap-tab-hashtag-form__prefix {
  color: var(--color-on-offset);
-  cursor: pointer;
-  flex-shrink: 0;
-  font-size: 1.2rem;
-  line-height: 1;
-  margin-left: auto;
-  padding: 0 2px;
+  font-weight: 600;
 }

-.ap-deck-column__remove:hover {
-  color: var(--color-red45);
-}
-
-.ap-deck-column__body {
-  flex: 1;
-  min-height: 0;
-  overflow-y: auto;
-  padding: var(--space-xs);
-}
-
-.ap-deck-column__loading,
-.ap-deck-column__loading-more,
-.ap-deck-column__error,
-.ap-deck-column__empty,
-.ap-deck-column__done {
-  color: var(--color-on-offset);
-  font-size: var(--font-size-s);
-  padding: var(--space-s);
-  text-align: center;
-}
-
-.ap-deck-column__retry {
-  background: none;
+.ap-tab-hashtag-form__input {
  border: var(--border-width-thin) solid var(--color-outline);
  border-radius: var(--border-radius-small);
-  color: var(--color-on-background);
+  font-family: inherit;
+  font-size: var(--font-size-s);
+  padding: 2px var(--space-s);
+  width: 8em;
+}
+
+.ap-tab-hashtag-form__input:focus {
+  border-color: var(--color-primary);
+  outline: 2px solid var(--color-primary);
+  outline-offset: -1px;
+}
+
+.ap-tab-hashtag-form__btn {
+  background: var(--color-primary);
+  border: none;
+  border-radius: var(--border-radius-small);
+  color: var(--color-on-primary);
  cursor: pointer;
+  font-family: inherit;
  font-size: var(--font-size-s);
-  margin-top: var(--space-xs);
-  padding: var(--space-xs) var(--space-s);
+  padding: 2px var(--space-s);
+  white-space: nowrap;
 }

-.ap-deck-column__retry:hover {
-  background: var(--color-offset);
+.ap-tab-hashtag-form__btn:hover {
+  opacity: 0.85;
 }

-/* Cards inside deck columns are more compact */
-.ap-deck-column__items .ap-item-card {
-  font-size: var(--font-size-s);
-}
-
-/* ---------- Deck empty state ---------- */
-
-.ap-deck-empty {
-  margin-top: var(--space-xl);
-  text-align: center;
-}
-
-.ap-deck-empty p {
-  color: var(--color-on-offset);
-  font-size: var(--font-size-s);
+/* "Pin as tab" button in search results area */
+.ap-explore-pin-bar {
  margin-bottom: var(--space-s);
 }

-.ap-deck-empty__link {
+.ap-explore-pin-btn {
+  background: none;
+  border: var(--border-width-thin) solid var(--color-primary);
+  border-radius: var(--border-radius-small);
+  color: var(--color-primary);
+  cursor: pointer;
+  font-family: inherit;
+  font-size: var(--font-size-s);
+  padding: var(--space-xs) var(--space-m);
+}
+
+.ap-explore-pin-btn:hover {
+  background: color-mix(in srgb, var(--color-primary) 10%, transparent);
+}
+
+.ap-explore-pin-btn:disabled {
+  cursor: default;
+  opacity: 0.6;
+}
+
+/* Hashtag form row inside the search form */
+.ap-explore-form__hashtag-row {
+  align-items: center;
+  display: flex;
+  flex-wrap: wrap;
+  gap: var(--space-xs);
+  margin-top: var(--space-s);
+}
+
+.ap-explore-form__hashtag-label {
+  color: var(--color-on-offset);
+  font-size: var(--font-size-s);
+  white-space: nowrap;
+}
+
+.ap-explore-form__hashtag-prefix {
+  color: var(--color-on-offset);
+  font-weight: 600;
+}
+
+.ap-explore-form__hashtag-hint {
+  color: var(--color-on-offset);
+  font-size: var(--font-size-xs);
+  flex-basis: 100%;
+}
+
+.ap-explore-form__input--hashtag {
+  max-width: 200px;
+  width: auto;
+}
+
+/* Tab panel containers */
+.ap-explore-instance-panel,
+.ap-explore-hashtag-panel {
+  min-height: 120px;
+}
+
+/* Loading state */
+.ap-explore-tab-loading {
+  align-items: center;
+  color: var(--color-on-offset);
+  display: flex;
+  justify-content: center;
+  padding: var(--space-xl);
+}
+
+.ap-explore-tab-loading--more {
+  padding-block: var(--space-m);
+}
+
+.ap-explore-tab-loading__text {
  font-size: var(--font-size-s);
 }

-/* ---------- Deck responsive ---------- */
-
-@media (max-width: 767px) {
-  .ap-deck-grid {
-    grid-template-columns: 1fr;
-  }
-
-  .ap-deck-column {
-    max-height: 60vh;
-  }
+/* Error state */
+.ap-explore-tab-error {
+  align-items: center;
+  display: flex;
+  flex-direction: column;
+  gap: var(--space-s);
+  padding: var(--space-xl);
 }
+
+.ap-explore-tab-error__message {
+  color: var(--color-red45);
+  font-size: var(--font-size-s);
+  margin: 0;
+}
+
+.ap-explore-tab-error__retry {
+  background: none;
+  border: 1px solid var(--color-accent);
+  border-radius: var(--border-radius-small);
+  color: var(--color-accent);
+  cursor: pointer;
+  font-size: var(--font-size-s);
+  padding: var(--space-xs) var(--space-s);
+}
+
+.ap-explore-tab-error__retry:hover {
+  background: color-mix(in srgb, var(--color-accent) 10%, transparent);
+}
+
+/* Empty state */
+.ap-explore-tab-empty {
+  color: var(--color-on-offset);
+  font-size: var(--font-size-s);
+  padding: var(--space-xl);
+  text-align: center;
+}
+
+/* Infinite scroll sentinel — zero height, invisible */
+.ap-tab-sentinel {
+  height: 1px;
+  visibility: hidden;
+}
+
+/* Hashtag tab sources info line */
+.ap-hashtag-sources {
+  color: var(--color-on-offset);
+  font-size: var(--font-size-s);
+  margin: 0;
+  padding: var(--space-s) 0 var(--space-xs);
+}
+
--- a/index.js
+++ b/index.js
@@ -70,10 +70,12 @@ import {
 } from "./lib/controllers/explore.js";
 import { followTagController, unfollowTagController } from "./lib/controllers/follow-tag.js";
 import {
-  listDecksController,
-  addDeckController,
-  removeDeckController,
-} from "./lib/controllers/decks.js";
+  listTabsController,
+  addTabController,
+  removeTabController,
+  reorderTabsController,
+} from "./lib/controllers/tabs.js";
+import { hashtagExploreApiController } from "./lib/controllers/hashtag-explore.js";
 import { publicProfileController } from "./lib/controllers/public-profile.js";
 import { authorizeInteractionController } from "./lib/controllers/authorize-interaction.js";
 import { myProfileController } from "./lib/controllers/my-profile.js";
@@ -238,12 +240,14 @@ export default class ActivityPubEndpoint {
    router.get("/admin/reader/api/timeline", apiTimelineController(mp));
    router.get("/admin/reader/explore", exploreController(mp));
    router.get("/admin/reader/api/explore", exploreApiController(mp));
+    router.get("/admin/reader/api/explore/hashtag", hashtagExploreApiController(mp));
    router.get("/admin/reader/api/instances", instanceSearchApiController(mp));
    router.get("/admin/reader/api/instance-check", instanceCheckApiController(mp));
    router.get("/admin/reader/api/popular-accounts", popularAccountsApiController(mp));
-    router.get("/admin/reader/api/decks", listDecksController(mp));
-    router.post("/admin/reader/api/decks", addDeckController(mp));
-    router.post("/admin/reader/api/decks/remove", removeDeckController(mp));
+    router.get("/admin/reader/api/tabs", listTabsController(mp));
+    router.post("/admin/reader/api/tabs", addTabController(mp));
+    router.post("/admin/reader/api/tabs/remove", removeTabController(mp));
+    router.patch("/admin/reader/api/tabs/reorder", reorderTabsController(mp));
    router.post("/admin/reader/follow-tag", followTagController(mp));
    router.post("/admin/reader/unfollow-tag", unfollowTagController(mp));
    router.get("/admin/reader/notifications", notificationsController(mp));
@@ -884,8 +888,8 @@ export default class ActivityPubEndpoint {
    Indiekit.addCollection("ap_interactions");
    Indiekit.addCollection("ap_notes");
    Indiekit.addCollection("ap_followed_tags");
-    // Deck collections
-    Indiekit.addCollection("ap_decks");
+    // Explore tab collections
+    Indiekit.addCollection("ap_explore_tabs");

    // Store collection references (posts resolved lazily)
    const indiekitCollections = Indiekit.collections;
@@ -906,8 +910,8 @@ export default class ActivityPubEndpoint {
      ap_interactions: indiekitCollections.get("ap_interactions"),
      ap_notes: indiekitCollections.get("ap_notes"),
      ap_followed_tags: indiekitCollections.get("ap_followed_tags"),
-      // Deck collections
-      ap_decks: indiekitCollections.get("ap_decks"),
+      // Explore tab collections
+      ap_explore_tabs: indiekitCollections.get("ap_explore_tabs"),
      get posts() {
        return indiekitCollections.get("posts");
      },
@@ -1032,11 +1036,19 @@ export default class ActivityPubEndpoint {
        { background: true },
      );

-      // Deck index — compound unique ensures same instance can appear at most once per scope
-      this._collections.ap_decks.createIndex(
-        { domain: 1, scope: 1 },
+      // Explore tab indexes
+      // Compound unique on (type, domain, scope, hashtag) prevents duplicate tabs.
+      // ALL insertions must explicitly set all four fields (unused fields = null)
+      // because MongoDB treats missing fields differently from null in unique indexes.
+      this._collections.ap_explore_tabs.createIndex(
+        { type: 1, domain: 1, scope: 1, hashtag: 1 },
        { unique: true, background: true },
      );
+      // Order index for efficient sorting of tab bar
+      this._collections.ap_explore_tabs.createIndex(
+        { order: 1 },
+        { background: true },
+      );
    } catch {
      // Index creation failed — collections not yet available.
      // Indexes already exist from previous startups; non-fatal.
--- a/lib/controllers/decks.js
+++ b/lib/controllers/decks.js
@@ -1,137 +0,0 @@
-/**
- * Deck CRUD controller — manages favorited instance deck entries.
- * Stored in the ap_decks MongoDB collection.
- */
-
-import { validateToken } from "../csrf.js";
-import { validateInstance } from "./explore.js";
-
-const MAX_DECKS = 8;
-
-/**
- * GET /admin/reader/api/decks
- * Returns all deck entries sorted by addedAt ascending.
- */
-export function listDecksController(_mountPath) {
-  return async (request, response, next) => {
-    try {
-      const { application } = request.app.locals;
-      const collection = application?.collections?.get("ap_decks");
-      if (!collection) {
-        return response.json([]);
-      }
-
-      const decks = await collection
-        .find({}, { projection: { _id: 0 } })
-        .sort({ addedAt: 1 })
-        .toArray();
-
-      return response.json(decks);
-    } catch (error) {
-      return next(error);
-    }
-  };
-}
-
-/**
- * POST /admin/reader/api/decks
- * Adds a new deck entry for the given domain + scope.
- * Body: { domain, scope }
- */
-export function addDeckController(_mountPath) {
-  return async (request, response, next) => {
-    try {
-      // CSRF protection
-      if (!validateToken(request)) {
-        return response.status(403).json({ error: "Invalid CSRF token" });
-      }
-
-      const { application } = request.app.locals;
-      const collection = application?.collections?.get("ap_decks");
-      if (!collection) {
-        return response.status(500).json({ error: "Deck storage unavailable" });
-      }
-
-      const { domain: rawDomain, scope: rawScope } = request.body;
-
-      // Validate domain (SSRF prevention)
-      const domain = validateInstance(rawDomain);
-      if (!domain) {
-        return response.status(400).json({ error: "Invalid instance domain" });
-      }
-
-      // Validate scope
-      const scope = rawScope === "federated" ? "federated" : "local";
-
-      // Enforce max deck limit
-      const count = await collection.countDocuments();
-      if (count >= MAX_DECKS) {
-        return response.status(400).json({
-          error: `Maximum of ${MAX_DECKS} decks reached`,
-        });
-      }
-
-      // Insert (unique index on domain+scope will throw on duplicate)
-      const deck = {
-        domain,
-        scope,
-        addedAt: new Date().toISOString(),
-      };
-
-      try {
-        await collection.insertOne(deck);
-      } catch (insertError) {
-        if (insertError.code === 11_000) {
-          // Duplicate key — deck already exists
-          return response.status(409).json({
-            error: "Deck already exists for this domain and scope",
-          });
-        }
-
-        throw insertError;
-      }
-
-      return response.status(201).json(deck);
-    } catch (error) {
-      return next(error);
-    }
-  };
-}
-
-/**
- * POST /admin/reader/api/decks/remove
- * Removes the deck entry for the given domain + scope.
- * Body: { domain, scope }
- */
-export function removeDeckController(_mountPath) {
-  return async (request, response, next) => {
-    try {
-      // CSRF protection
-      if (!validateToken(request)) {
-        return response.status(403).json({ error: "Invalid CSRF token" });
-      }
-
-      const { application } = request.app.locals;
-      const collection = application?.collections?.get("ap_decks");
-      if (!collection) {
-        return response.status(500).json({ error: "Deck storage unavailable" });
-      }
-
-      const { domain: rawDomain, scope: rawScope } = request.body;
-
-      // Validate domain (SSRF prevention)
-      const domain = validateInstance(rawDomain);
-      if (!domain) {
-        return response.status(400).json({ error: "Invalid instance domain" });
-      }
-
-      const scope = rawScope === "federated" ? "federated" : "local";
-
-      await collection.deleteOne({ domain, scope });
-
-      return response.json({ success: true });
-    } catch (error) {
-      return next(error);
-    }
-  };
-}
--- a/lib/controllers/explore-utils.js
+++ b/lib/controllers/explore-utils.js
@@ -0,0 +1,122 @@
+/**
+ * Shared utilities for explore controllers.
+ *
+ * Extracted to break the circular dependency between explore.js and tabs.js:
+ *   - explore.js needs validateHashtag (was in tabs.js)
+ *   - tabs.js needs validateInstance (was in explore.js)
+ *   - hashtag-explore.js needs mapMastodonStatusToItem (was duplicated)
+ */
+
+import sanitizeHtml from "sanitize-html";
+import { sanitizeContent } from "../timeline-store.js";
+
+/**
+ * Validate the instance parameter to prevent SSRF.
+ * Only allows hostnames — no IPs, no localhost, no port numbers.
+ * @param {string} instance - Raw instance parameter from query string
+ * @returns {string|null} Validated hostname or null
+ */
+export function validateInstance(instance) {
+  if (!instance || typeof instance !== "string") return null;
+
+  try {
+    const url = new URL(`https://${instance.trim()}`);
+    const hostname = url.hostname;
+    if (
+      hostname === "localhost" ||
+      hostname === "127.0.0.1" ||
+      hostname === "0.0.0.0" ||
+      hostname === "::1" ||
+      hostname.startsWith("192.168.") ||
+      hostname.startsWith("10.") ||
+      hostname.startsWith("169.254.") ||
+      /^172\.(1[6-9]|2\d|3[01])\./.test(hostname) ||
+      /^[0-9]{1,3}(\.[0-9]{1,3}){3}$/.test(hostname) ||
+      hostname.includes("[")
+    ) {
+      return null;
+    }
+
+    return hostname;
+  } catch {
+    return null;
+  }
+}
+
+/**
+ * Validates a hashtag value.
+ * Returns the cleaned hashtag (leading # stripped) or null if invalid.
+ *
+ * Rules match Mastodon's hashtag character rules:
+ *   - Alphanumeric + underscore only (\w+)
+ *   - 1–100 characters after stripping leading #
+ */
+export function validateHashtag(raw) {
+  if (typeof raw !== "string") return null;
+  const cleaned = raw.replace(/^#+/, "");
+  if (!cleaned || cleaned.length > 100) return null;
+  if (!/^[\w]+$/.test(cleaned)) return null;
+  return cleaned;
+}
+
+/**
+ * Map a Mastodon API status object to our timeline item format.
+ * @param {object} status - Mastodon API status
+ * @param {string} instance - Instance hostname (for handle construction)
+ * @returns {object} Timeline item compatible with ap-item-card.njk
+ */
+export function mapMastodonStatusToItem(status, instance) {
+  const account = status.account || {};
+  const acct = account.acct || "";
+  const handle = acct.includes("@") ? `@${acct}` : `@${acct}@${instance}`;
+
+  const mentions = (status.mentions || []).map((m) => ({
+    name: m.acct.includes("@") ? m.acct : `${m.acct}@${instance}`,
+    url: m.url || "",
+  }));
+
+  const category = (status.tags || []).map((t) => t.name || "");
+
+  const photo = [];
+  const video = [];
+  const audio = [];
+  for (const att of status.media_attachments || []) {
+    const url = att.url || att.remote_url || "";
+    if (!url) continue;
+    if (att.type === "image" || att.type === "gifv") {
+      photo.push(url);
+    } else if (att.type === "video") {
+      video.push(url);
+    } else if (att.type === "audio") {
+      audio.push(url);
+    }
+  }
+
+  return {
+    uid: status.url || status.uri || "",
+    url: status.url || status.uri || "",
+    type: "note",
+    name: "",
+    content: {
+      text: (status.content || "").replace(/<[^>]*>/g, ""),
+      html: sanitizeContent(status.content || ""),
+    },
+    summary: status.spoiler_text || "",
+    sensitive: status.sensitive || false,
+    published: status.created_at || new Date().toISOString(),
+    author: {
+      name: sanitizeHtml(account.display_name || account.username || "Unknown", { allowedTags: [], allowedAttributes: {} }),
+      url: account.url || "",
+      photo: account.avatar || account.avatar_static || "",
+      handle,
+    },
+    category,
+    mentions,
+    photo,
+    video,
+    audio,
+    inReplyTo: status.in_reply_to_id ? `https://${instance}/web/statuses/${status.in_reply_to_id}` : "",
+    createdAt: new Date().toISOString(),
+    _explore: true,
+  };
+}
--- a/lib/controllers/explore.js
+++ b/lib/controllers/explore.js
@@ -5,117 +5,15 @@
 * Remote HTML is always passed through sanitizeContent() before storage.
 */

-import sanitizeHtml from "sanitize-html";
-import { sanitizeContent } from "../timeline-store.js";
 import { searchInstances, checkInstanceTimeline, getPopularAccounts } from "../fedidb.js";
 import { getToken } from "../csrf.js";
+import { validateInstance, validateHashtag, mapMastodonStatusToItem } from "./explore-utils.js";

 const FETCH_TIMEOUT_MS = 10_000;
 const MAX_RESULTS = 20;

-/**
- * Validate the instance parameter to prevent SSRF.
- * Only allows hostnames — no IPs, no localhost, no port numbers for exotic attacks.
- * @param {string} instance - Raw instance parameter from query string
- * @returns {string|null} Validated hostname or null
- */
-export function validateInstance(instance) {
-  if (!instance || typeof instance !== "string") return null;
-
-  try {
-    // Prepend https:// to parse as URL
-    const url = new URL(`https://${instance.trim()}`);
-
-    // Must be a plain hostname — no IP addresses, no localhost
-    const hostname = url.hostname;
-    if (
-      hostname === "localhost" ||
-      hostname === "127.0.0.1" ||
-      hostname === "0.0.0.0" ||
-      hostname === "::1" ||
-      hostname.startsWith("192.168.") ||
-      hostname.startsWith("10.") ||
-      hostname.startsWith("169.254.") ||
-      /^172\.(1[6-9]|2\d|3[01])\./.test(hostname) ||
-      /^[0-9]{1,3}(\.[0-9]{1,3}){3}$/.test(hostname) || // IPv4
-      hostname.includes("[") // IPv6
-    ) {
-      return null;
-    }
-
-    // Only allow the hostname (no path, no port override)
-    return hostname;
-  } catch {
-    return null;
-  }
-}
-
-/**
- * Map a Mastodon API status object to our timeline item format.
- * @param {object} status - Mastodon API status
- * @param {string} instance - Instance hostname (for handle construction)
- * @returns {object} Timeline item compatible with ap-item-card.njk
- */
-function mapMastodonStatusToItem(status, instance) {
-  const account = status.account || {};
-  const acct = account.acct || "";
-  // Mastodon acct is "user" for local, "user@remote" for remote
-  const handle = acct.includes("@") ? `@${acct}` : `@${acct}@${instance}`;
-
-  // Map mentions — store without leading @ (template prepends it)
-  const mentions = (status.mentions || []).map((m) => ({
-    name: m.acct.includes("@") ? m.acct : `${m.acct}@${instance}`,
-    url: m.url || "",
-  }));
-
-  // Map hashtags
-  const category = (status.tags || []).map((t) => t.name || "");
-
-  // Map media attachments
-  const photo = [];
-  const video = [];
-  const audio = [];
-  for (const att of status.media_attachments || []) {
-    const url = att.url || att.remote_url || "";
-    if (!url) continue;
-    if (att.type === "image" || att.type === "gifv") {
-      photo.push(url);
-    } else if (att.type === "video") {
-      video.push(url);
-    } else if (att.type === "audio") {
-      audio.push(url);
-    }
-  }
-
-  return {
-    uid: status.url || status.uri || "",
-    url: status.url || status.uri || "",
-    type: "note",
-    name: "",
-    content: {
-      text: (status.content || "").replace(/<[^>]*>/g, ""),
-      html: sanitizeContent(status.content || ""),
-    },
-    summary: status.spoiler_text || "",
-    sensitive: status.sensitive || false,
-    published: status.created_at || new Date().toISOString(),
-    author: {
-      name: sanitizeHtml(account.display_name || account.username || "Unknown", { allowedTags: [], allowedAttributes: {} }),
-      url: account.url || "",
-      photo: account.avatar || account.avatar_static || "",
-      handle,
-    },
-    category,
-    mentions,
-    photo,
-    video,
-    audio,
-    inReplyTo: status.in_reply_to_id ? `https://${instance}/web/statuses/${status.in_reply_to_id}` : "",
-    createdAt: new Date().toISOString(),
-    // Explore-specific: track source instance
-    _explore: true,
-  };
-}
+// Re-export validateInstance for backward compatibility (used by tabs.js, index.js)
+export { validateInstance } from "./explore-utils.js";

 export function exploreController(mountPath) {
  return async (request, response, next) => {
@@ -123,24 +21,10 @@ export function exploreController(mountPath) {
      const rawInstance = request.query.instance || "";
      const scope = request.query.scope === "federated" ? "federated" : "local";
      const maxId = request.query.max_id || "";
-      const activeTab = request.query.tab === "decks" ? "decks" : "search";
-
-      // Fetch deck list for both tabs (needed for star button state + deck tab)
-      const { application } = request.app.locals;
-      const decksCollection = application?.collections?.get("ap_decks");
-      let decks = [];
-      try {
-        decks = await decksCollection
-          .find({})
-          .sort({ addedAt: 1 })
-          .toArray();
-      } catch {
-        // Collection unavailable — non-fatal, decks defaults to []
-      }
+      const rawHashtag = request.query.hashtag || "";
+      const hashtag = rawHashtag ? validateHashtag(rawHashtag) : null;

      const csrfToken = getToken(request.session);
-      const deckCount = decks.length;
-
      const readerParent = { href: `${mountPath}/admin/reader`, text: response.locals.__("activitypub.reader.title") };

      // No instance specified — render clean initial page (no error)
@@ -150,14 +34,11 @@ export function exploreController(mountPath) {
          readerParent,
          instance: "",
          scope,
+          hashtag: hashtag || "",
          items: [],
          maxId: null,
          error: null,
          mountPath,
-          activeTab,
-          decks,
-          deckCount,
-          isInDeck: false,
          csrfToken,
        });
      }
@@ -169,22 +50,25 @@ export function exploreController(mountPath) {
          readerParent,
          instance: rawInstance,
          scope,
+          hashtag: hashtag || "",
          items: [],
          maxId: null,
          error: response.locals.__("activitypub.reader.explore.invalidInstance"),
          mountPath,
-          activeTab,
-          decks,
-          deckCount,
-          isInDeck: false,
          csrfToken,
        });
      }

-      // Fetch public timeline from remote instance
+      // Build API URL: hashtag timeline or public timeline
      const isLocal = scope === "local";
-      const apiUrl = new URL(`https://${instance}/api/v1/timelines/public`);
+      let apiUrl;
+      if (hashtag) {
+        apiUrl = new URL(`https://${instance}/api/v1/timelines/tag/${encodeURIComponent(hashtag)}`);
        apiUrl.searchParams.set("local", isLocal ? "true" : "false");
+      } else {
+        apiUrl = new URL(`https://${instance}/api/v1/timelines/public`);
+        apiUrl.searchParams.set("local", isLocal ? "true" : "false");
+      }
      apiUrl.searchParams.set("limit", String(MAX_RESULTS));
      if (maxId) apiUrl.searchParams.set("max_id", maxId);

@@ -226,23 +110,16 @@ export function exploreController(mountPath) {
        error = msg;
      }

-      const isInDeck = decks.some(
-        (d) => d.domain === instance && d.scope === scope,
-      );
-
      response.render("activitypub-explore", {
        title: response.locals.__("activitypub.reader.explore.title"),
        readerParent,
        instance,
        scope,
+        hashtag: hashtag || "",
        items,
        maxId: nextMaxId,
        error,
        mountPath,
-        activeTab,
-        decks,
-        deckCount,
-        isInDeck,
        csrfToken,
        // Pass empty interactionMap — explore posts are not in our DB
        interactionMap: {},
@@ -263,15 +140,24 @@ export function exploreApiController(mountPath) {
      const rawInstance = request.query.instance || "";
      const scope = request.query.scope === "federated" ? "federated" : "local";
      const maxId = request.query.max_id || "";
+      const rawHashtag = request.query.hashtag || "";
+      const hashtag = rawHashtag ? validateHashtag(rawHashtag) : null;

      const instance = validateInstance(rawInstance);
      if (!instance) {
        return response.status(400).json({ error: "Invalid instance" });
      }

+      // Build API URL: hashtag timeline or public timeline
      const isLocal = scope === "local";
-      const apiUrl = new URL(`https://${instance}/api/v1/timelines/public`);
+      let apiUrl;
+      if (hashtag) {
+        apiUrl = new URL(`https://${instance}/api/v1/timelines/tag/${encodeURIComponent(hashtag)}`);
        apiUrl.searchParams.set("local", isLocal ? "true" : "false");
+      } else {
+        apiUrl = new URL(`https://${instance}/api/v1/timelines/public`);
+        apiUrl.searchParams.set("local", isLocal ? "true" : "false");
+      }
      apiUrl.searchParams.set("limit", String(MAX_RESULTS));
      if (maxId) apiUrl.searchParams.set("max_id", maxId);

--- a/lib/controllers/hashtag-explore.js
+++ b/lib/controllers/hashtag-explore.js
@@ -0,0 +1,223 @@
+/**
+ * Hashtag explore API — aggregates a hashtag timeline across all pinned instance tabs.
+ *
+ * GET /admin/reader/api/explore/hashtag
+ *   ?hashtag={tag}
+ *   &cursors={json}   — JSON-encoded { domain: maxId } cursor map for pagination
+ *
+ * Returns JSON:
+ *   {
+ *     html: string,             — server-rendered HTML cards
+ *     cursors: { [domain]: string|null },  — updated cursor map
+ *     sources: { [domain]: "ok" | "error:N" },
+ *     instancesQueried: number,
+ *     instancesTotal: number,
+ *     instanceLabels: string[],
+ *   }
+ */
+
+import { validateHashtag, mapMastodonStatusToItem } from "./explore-utils.js";
+
+const FETCH_TIMEOUT_MS = 10_000;
+const PAGE_SIZE = 20;
+const MAX_HASHTAG_INSTANCES = 10;
+
+/**
+ * Fetch hashtag timeline from one instance.
+ * Returns { statuses, nextMaxId, error }.
+ */
+async function fetchHashtagFromInstance(domain, scope, hashtag, maxId) {
+  try {
+    const isLocal = scope === "local";
+    const url = new URL(
+      `https://${domain}/api/v1/timelines/tag/${encodeURIComponent(hashtag)}`
+    );
+    url.searchParams.set("local", isLocal ? "true" : "false");
+    url.searchParams.set("limit", "20");
+    if (maxId) url.searchParams.set("max_id", maxId);
+
+    const controller = new AbortController();
+    const timeoutId = setTimeout(() => controller.abort(), FETCH_TIMEOUT_MS);
+
+    const res = await fetch(url.toString(), {
+      headers: { Accept: "application/json" },
+      signal: controller.signal,
+    });
+    clearTimeout(timeoutId);
+
+    if (!res.ok) {
+      return { statuses: [], nextMaxId: null, error: `error:${res.status}` };
+    }
+
+    const statuses = await res.json();
+    if (!Array.isArray(statuses)) {
+      return { statuses: [], nextMaxId: null, error: "error:invalid" };
+    }
+
+    const nextMaxId =
+      statuses.length === 20 && statuses.length > 0
+        ? statuses[statuses.length - 1].id || null
+        : null;
+
+    return { statuses, nextMaxId, error: null };
+  } catch {
+    return { statuses: [], nextMaxId: null, error: "error:timeout" };
+  }
+}
+
+/**
+ * Hashtag explore API controller.
+ * Queries up to MAX_HASHTAG_INSTANCES pinned instance tabs in parallel.
+ */
+export function hashtagExploreApiController(mountPath) {
+  return async (request, response, next) => {
+    try {
+      // Validate hashtag
+      const rawHashtag = request.query.hashtag || "";
+      const hashtag = validateHashtag(rawHashtag);
+      if (!hashtag) {
+        return response.status(400).json({ error: "Invalid hashtag" });
+      }
+
+      const tabsCollection = request.app.locals.application?.collections?.get("ap_explore_tabs");
+      if (!tabsCollection) {
+        return response.json({
+          html: "", cursors: {}, sources: {}, instancesQueried: 0, instancesTotal: 0, instanceLabels: [],
+        });
+      }
+
+      // Parse cursors map — { [domain]: maxId | null }
+      let cursors = {};
+      try {
+        const raw = request.query.cursors || "{}";
+        const parsed = JSON.parse(raw);
+        if (parsed && typeof parsed === "object" && !Array.isArray(parsed)) {
+          cursors = parsed;
+        }
+      } catch {
+        // Invalid JSON — use empty cursors (start from beginning)
+      }
+
+      // Load instance tabs, capped at MAX_HASHTAG_INSTANCES by order
+      const instanceTabs = await tabsCollection
+        .find({ type: "instance" })
+        .sort({ order: 1 })
+        .limit(MAX_HASHTAG_INSTANCES)
+        .toArray();
+
+      const instancesTotal = await tabsCollection.countDocuments({
+        type: "instance",
+      });
+
+      if (instanceTabs.length === 0) {
+        return response.json({
+          html: "",
+          cursors: {},
+          sources: {},
+          instancesQueried: 0,
+          instancesTotal,
+          instanceLabels: [],
+        });
+      }
+
+      // Fetch from all instances in parallel
+      const fetchResults = await Promise.allSettled(
+        instanceTabs.map((tab) =>
+          fetchHashtagFromInstance(
+            tab.domain,
+            tab.scope,
+            hashtag,
+            cursors[tab.domain] || null
+          )
+        )
+      );
+
+      // Build sources map and collect all statuses with their domain
+      const sources = {};
+      const updatedCursors = {};
+      const allItems = [];
+
+      for (let i = 0; i < instanceTabs.length; i++) {
+        const tab = instanceTabs[i];
+        const result = fetchResults[i];
+
+        if (result.status === "fulfilled") {
+          const { statuses, nextMaxId, error } = result.value;
+          sources[tab.domain] = error || "ok";
+          updatedCursors[tab.domain] = nextMaxId;
+
+          if (!error) {
+            for (const status of statuses) {
+              allItems.push({ status, domain: tab.domain });
+            }
+          }
+        } else {
+          sources[tab.domain] = "error:rejected";
+          updatedCursors[tab.domain] = cursors[tab.domain] || null;
+        }
+      }
+
+      // Merge by published date descending
+      allItems.sort((a, b) => {
+        const dateA = new Date(a.status.created_at || 0).getTime();
+        const dateB = new Date(b.status.created_at || 0).getTime();
+        return dateB - dateA;
+      });
+
+      // Deduplicate by post URL (first occurrence wins)
+      const seenUrls = new Set();
+      const dedupedItems = [];
+      for (const { status, domain } of allItems) {
+        const uid = status.url || status.uri || "";
+        if (uid && seenUrls.has(uid)) continue;
+        if (uid) seenUrls.add(uid);
+        dedupedItems.push({ status, domain });
+      }
+
+      // Paginate: take first PAGE_SIZE items
+      const pageItems = dedupedItems.slice(0, PAGE_SIZE);
+
+      // Map to timeline item format
+      const items = pageItems.map(({ status, domain }) =>
+        mapMastodonStatusToItem(status, domain)
+      );
+
+      // Render HTML AFTER merge/dedup/paginate (don't waste CPU on discarded items)
+      const templateData = {
+        ...response.locals,
+        mountPath,
+        csrfToken: "",
+        interactionMap: {},
+      };
+
+      const htmlParts = await Promise.all(
+        items.map(
+          (item) =>
+            new Promise((resolve, reject) => {
+              request.app.render(
+                "partials/ap-item-card.njk",
+                { ...templateData, item },
+                (err, html) => {
+                  if (err) reject(err);
+                  else resolve(html);
+                }
+              );
+            })
+        )
+      );
+
+      const instanceLabels = instanceTabs.map((t) => t.domain);
+
+      response.json({
+        html: htmlParts.join(""),
+        cursors: updatedCursors,
+        sources,
+        instancesQueried: instanceTabs.length,
+        instancesTotal,
+        instanceLabels,
+      });
+    } catch (error) {
+      next(error);
+    }
+  };
+}
--- a/lib/controllers/tabs.js
+++ b/lib/controllers/tabs.js
@@ -0,0 +1,245 @@
+/**
+ * Tab CRUD controller — manages explore tab entries.
+ * Stored in the ap_explore_tabs MongoDB collection.
+ *
+ * Tab types:
+ *   - "instance": pinned Mastodon-compatible instance with scope (local/federated)
+ *   - "hashtag": aggregated hashtag across all pinned instance tabs
+ *
+ * IMPORTANT: All insertions must explicitly set all four indexed fields.
+ * Missing fields and null are treated differently by MongoDB compound unique indexes.
+ * Instance tabs: { type, domain, scope, hashtag: null, order, addedAt }
+ * Hashtag tabs:  { type, domain: null, scope: null, hashtag, order, addedAt }
+ */
+
+import { ObjectId } from "mongodb";
+import { validateToken } from "../csrf.js";
+import { validateInstance, validateHashtag } from "./explore-utils.js";
+
+// Re-export for consumers that imported from tabs.js
+export { validateHashtag };
+
+/**
+ * GET /admin/reader/api/tabs
+ * Returns all tab entries sorted by order ascending.
+ */
+export function listTabsController(_mountPath) {
+  return async (request, response, next) => {
+    try {
+      const { application } = request.app.locals;
+      const collection = application?.collections?.get("ap_explore_tabs");
+      if (!collection) {
+        return response.json([]);
+      }
+
+      const tabs = await collection
+        .find({}, { projection: { _id: 1, type: 1, domain: 1, scope: 1, hashtag: 1, order: 1, addedAt: 1 } })
+        .sort({ order: 1 })
+        .toArray();
+
+      return response.json(tabs);
+    } catch (error) {
+      return next(error);
+    }
+  };
+}
+
+/**
+ * POST /admin/reader/api/tabs
+ * Adds a new tab entry.
+ * Body (instance tab): { type: "instance", domain, scope }
+ * Body (hashtag tab):  { type: "hashtag", hashtag }
+ */
+export function addTabController(_mountPath) {
+  return async (request, response, next) => {
+    try {
+      // CSRF protection
+      if (!validateToken(request)) {
+        return response.status(403).json({ error: "Invalid CSRF token" });
+      }
+
+      const { application } = request.app.locals;
+      const collection = application?.collections?.get("ap_explore_tabs");
+      if (!collection) {
+        return response.status(500).json({ error: "Tab storage unavailable" });
+      }
+
+      const { type } = request.body;
+
+      if (type !== "instance" && type !== "hashtag") {
+        return response.status(400).json({ error: "Invalid tab type" });
+      }
+
+      // Determine the next order value atomically
+      const lastTab = await collection
+        .find({})
+        .sort({ order: -1 })
+        .limit(1)
+        .toArray();
+      const nextOrder = lastTab.length > 0 ? lastTab[0].order + 1 : 0;
+
+      let tab;
+
+      if (type === "instance") {
+        const { domain: rawDomain, scope: rawScope } = request.body;
+
+        // Validate domain (SSRF prevention)
+        const domain = validateInstance(rawDomain);
+        if (!domain) {
+          return response.status(400).json({ error: "Invalid instance domain" });
+        }
+
+        // Validate scope
+        const scope = rawScope === "federated" ? "federated" : "local";
+
+        // All four indexed fields must be explicitly set
+        tab = {
+          type: "instance",
+          domain,
+          scope,
+          hashtag: null,       // explicit null — required for unique index
+          order: nextOrder,
+          addedAt: new Date().toISOString(),
+        };
+      } else {
+        // type === "hashtag"
+        const { hashtag: rawHashtag } = request.body;
+
+        const hashtag = validateHashtag(rawHashtag);
+        if (!hashtag) {
+          return response.status(400).json({
+            error:
+              "Invalid hashtag. Use alphanumeric characters and underscores only (max 100 chars).",
+          });
+        }
+
+        // All four indexed fields must be explicitly set
+        tab = {
+          type: "hashtag",
+          domain: null,        // explicit null — required for unique index
+          scope: null,         // explicit null — required for unique index
+          hashtag,
+          order: nextOrder,
+          addedAt: new Date().toISOString(),
+        };
+      }
+
+      try {
+        const result = await collection.insertOne(tab);
+        // Return with the MongoDB _id included
+        return response.status(201).json({ ...tab, _id: result.insertedId });
+      } catch (insertError) {
+        if (insertError.code === 11_000) {
+          return response.status(409).json({ error: "Tab already exists" });
+        }
+        throw insertError;
+      }
+    } catch (error) {
+      return next(error);
+    }
+  };
+}
+
+/**
+ * POST /admin/reader/api/tabs/remove
+ * Removes a tab entry and re-compacts order numbers.
+ * Body (instance tab): { type: "instance", domain, scope }
+ * Body (hashtag tab):  { type: "hashtag", hashtag }
+ */
+export function removeTabController(_mountPath) {
+  return async (request, response, next) => {
+    try {
+      // CSRF protection
+      if (!validateToken(request)) {
+        return response.status(403).json({ error: "Invalid CSRF token" });
+      }
+
+      const { application } = request.app.locals;
+      const collection = application?.collections?.get("ap_explore_tabs");
+      if (!collection) {
+        return response.status(500).json({ error: "Tab storage unavailable" });
+      }
+
+      const { type } = request.body;
+      let filter;
+
+      if (type === "instance") {
+        const domain = validateInstance(request.body.domain);
+        if (!domain) {
+          return response.status(400).json({ error: "Invalid instance domain" });
+        }
+        const scope = request.body.scope === "federated" ? "federated" : "local";
+        filter = { type: "instance", domain, scope };
+      } else if (type === "hashtag") {
+        const hashtag = validateHashtag(request.body.hashtag);
+        if (!hashtag) {
+          return response.status(400).json({ error: "Invalid hashtag" });
+        }
+        filter = { type: "hashtag", hashtag };
+      } else {
+        return response.status(400).json({ error: "Invalid tab type" });
+      }
+
+      await collection.deleteOne(filter);
+
+      // Re-compact order numbers to avoid gaps
+      const remaining = await collection.find({}).sort({ order: 1 }).toArray();
+      await Promise.all(
+        remaining.map((tab, index) =>
+          collection.updateOne({ _id: tab._id }, { $set: { order: index } }),
+        ),
+      );
+
+      return response.json({ success: true });
+    } catch (error) {
+      return next(error);
+    }
+  };
+}
+
+/**
+ * PATCH /admin/reader/api/tabs/reorder
+ * Reorders tabs by accepting an array of tab IDs in the desired order.
+ * Body: { tabIds: ["<mongoId1>", "<mongoId2>", ...] }
+ * Sets order = index for each tab ID.
+ */
+export function reorderTabsController(_mountPath) {
+  return async (request, response, next) => {
+    try {
+      // CSRF protection
+      if (!validateToken(request)) {
+        return response.status(403).json({ error: "Invalid CSRF token" });
+      }
+
+      const { application } = request.app.locals;
+      const collection = application?.collections?.get("ap_explore_tabs");
+      if (!collection) {
+        return response.status(500).json({ error: "Tab storage unavailable" });
+      }
+
+      const { tabIds } = request.body;
+      if (!Array.isArray(tabIds) || tabIds.length > 100) {
+        return response.status(400).json({ error: "tabIds must be an array (max 100)" });
+      }
+
+      // Validate each ID is a valid ObjectId hex string
+      const objectIdPattern = /^[a-f\d]{24}$/;
+      if (tabIds.some((id) => typeof id !== "string" || !objectIdPattern.test(id))) {
+        return response.status(400).json({ error: "Invalid tab ID format" });
+      }
+
+      await Promise.all(
+        tabIds.map((id, index) =>
+          collection.updateOne(
+            { _id: new ObjectId(id) },
+            { $set: { order: index } },
+          ),
+        ),
+      );
+
+      return response.json({ success: true });
+    } catch (error) {
+      return next(error);
+    }
+  };
+}
--- a/locales/en.json
+++ b/locales/en.json
@@ -240,22 +240,25 @@
        "mauLabel": "MAU",
        "timelineSupported": "Public timeline available",
        "timelineUnsupported": "Public timeline not available",
+        "hashtagLabel": "Hashtag (optional)",
+        "hashtagPlaceholder": "e.g. indieweb",
+        "hashtagHint": "Filter results to a specific hashtag",
        "tabs": {
+          "label": "Explore tabs",
          "search": "Search",
-          "decks": "Decks"
-        },
-        "deck": {
-          "addToDeck": "Add to deck",
-          "removeFromDeck": "Remove from deck",
-          "inDeck": "In deck",
-          "deckLimitReached": "Maximum of 8 decks reached",
-          "localBadge": "Local",
-          "federatedBadge": "Federated",
-          "removeColumn": "Remove column",
+          "pinAsTab": "Pin as tab",
+          "pinned": "Pinned",
+          "remove": "Remove tab",
+          "moveUp": "Move up",
+          "moveDown": "Move down",
+          "addHashtag": "Add hashtag tab",
+          "hashtagTabPlaceholder": "Enter hashtag",
+          "addTab": "Add",
          "retry": "Retry",
-          "loadError": "Could not load timeline from this instance.",
-          "emptyState": "No decks yet. Browse an instance in the Search tab and click the star to add it.",
-          "emptyStateLink": "Go to Search"
+          "noInstances": "Pin some instances first to use hashtag tabs.",
+          "sources": "Searching #%s across %d instance",
+          "sources_plural": "Searching #%s across %d instances",
+          "sourcesPartial": "%d of %d instances responded"
        }
      },
      "tagTimeline": {
--- a/views/activitypub-explore.njk
+++ b/views/activitypub-explore.njk
@@ -9,22 +9,115 @@
    <p class="ap-explore-header__desc">{{ __("activitypub.reader.explore.description") }}</p>
  </header>

-  {# Tab navigation #}
-  {% set exploreBase = mountPath + "/admin/reader/explore" %}
-  <nav class="ap-tabs">
-    <a href="{{ exploreBase }}" class="ap-tab{% if activeTab != 'decks' %} ap-tab--active{% endif %}">
-      {{ __("activitypub.reader.explore.tabs.search") }}
-    </a>
-    <a href="{{ exploreBase }}?tab=decks" class="ap-tab{% if activeTab == 'decks' %} ap-tab--active{% endif %}">
-      {{ __("activitypub.reader.explore.tabs.decks") }}
-      {% if decks and decks.length > 0 %}
-        <span class="ap-tab__count">{{ decks.length }}</span>
-      {% endif %}
-    </a>
-  </nav>
+  {# ── Tabbed explore container (Alpine.js component) ──────────────────── #}
+  <div class="ap-explore-tabs-container"
+    data-mount-path="{{ mountPath }}"
+    data-csrf="{{ csrfToken }}"
+    x-data="apExploreTabs()">

-  {# ── Search tab ────────────────────────────────────────────────── #}
-  {% if activeTab != 'decks' %}
+    {# ── Tab bar ──────────────────────────────────────────────────────────── #}
+    <nav class="ap-tabs ap-explore-tabs-nav"
+      id="ap-explore-tab-bar"
+      role="tablist"
+      aria-label="{{ __('activitypub.reader.explore.tabs.label') }}">
+
+      {# Search tab — always first, not removable #}
+      <button
+        type="button"
+        class="ap-tab"
+        :class="{ 'ap-tab--active': activeTabId === null }"
+        role="tab"
+        :aria-selected="activeTabId === null ? 'true' : 'false'"
+        aria-controls="ap-tab-panel-search"
+        id="ap-tab-btn-search"
+        @click="switchToSearch()"
+        @keydown="handleTabKeydown($event, 0)">
+        {{ __("activitypub.reader.explore.tabs.search") }}
+      </button>
+
+      {# User-created instance and hashtag tabs #}
+      <template x-for="(tab, index) in tabs" :key="tab._id">
+        <div class="ap-tab-wrapper">
+          {# Tab button #}
+          <button
+            type="button"
+            class="ap-tab ap-tab--user"
+            :class="{ 'ap-tab--active': activeTabId === tab._id }"
+            role="tab"
+            :aria-selected="activeTabId === tab._id ? 'true' : 'false'"
+            :aria-controls="'ap-tab-panel-' + tab._id"
+            :id="'ap-tab-btn-' + tab._id"
+            @click="switchTab(tab._id)"
+            @keydown="handleTabKeydown($event, index + 1)">
+            <span class="ap-tab__label" :title="tabLabel(tab)" x-text="tabLabel(tab)"></span>
+            <span
+              x-show="tab.type === 'instance'"
+              class="ap-tab__badge"
+              :class="tab.scope === 'local' ? 'ap-tab__badge--local' : 'ap-tab__badge--federated'"
+              x-text="tab.scope"></span>
+          </button>
+
+          {# Reorder and close controls #}
+          <div class="ap-tab-controls">
+            <button
+              type="button"
+              class="ap-tab-control ap-tab-control--up"
+              @click.stop="moveUp(tab)"
+              :disabled="index === 0"
+              :aria-label="'{{ __('activitypub.reader.explore.tabs.moveUp') }}: ' + tabLabel(tab)">↑</button>
+            <button
+              type="button"
+              class="ap-tab-control ap-tab-control--down"
+              @click.stop="moveDown(tab)"
+              :disabled="index === tabs.length - 1"
+              :aria-label="'{{ __('activitypub.reader.explore.tabs.moveDown') }}: ' + tabLabel(tab)">↓</button>
+            <button
+              type="button"
+              class="ap-tab-control ap-tab-control--remove"
+              @click.stop="removeTab(tab)"
+              :aria-label="'{{ __('activitypub.reader.explore.tabs.remove') }}: ' + tabLabel(tab)">×</button>
+          </div>
+        </div>
+      </template>
+
+      {# +# button — add a hashtag tab #}
+      <div class="ap-tab-add-hashtag">
+        <button
+          type="button"
+          class="ap-tab ap-tab--add"
+          @click="showHashtagForm = !showHashtagForm"
+          :aria-expanded="showHashtagForm ? 'true' : 'false'"
+          title="{{ __('activitypub.reader.explore.tabs.addHashtag') }}">+#</button>
+        <form
+          x-show="showHashtagForm"
+          x-cloak
+          class="ap-tab-hashtag-form"
+          @submit.prevent="submitHashtagTab()"
+          @keydown.escape.prevent="showHashtagForm = false; hashtagInput = ''">
+          <span class="ap-tab-hashtag-form__prefix">#</span>
+          <input
+            type="text"
+            x-model="hashtagInput"
+            class="ap-tab-hashtag-form__input"
+            placeholder="{{ __('activitypub.reader.explore.tabs.hashtagTabPlaceholder') }}"
+            aria-label="{{ __('activitypub.reader.explore.tabs.addHashtag') }}"
+            autocomplete="off"
+            maxlength="100">
+          <button type="submit" class="ap-tab-hashtag-form__btn">
+            {{ __("activitypub.reader.explore.tabs.addTab") }}
+          </button>
+        </form>
+      </div>
+    </nav>{# end tab bar nav #}
+
+    {# Error message (CSRF expiry, network errors) #}
+    <p x-show="error" x-cloak class="ap-explore-error" x-text="error"></p>
+
+    {# ── Search tab panel ─────────────────────────────────────────────────── #}
+    <div id="ap-tab-panel-search"
+      role="tabpanel"
+      aria-labelledby="ap-tab-btn-search"
+      x-show="activeTabId === null">

      {# Instance form with autocomplete #}
      <form action="{{ mountPath }}/admin/reader/explore" method="get" class="ap-explore-form"
@@ -98,6 +191,24 @@
            {{ __("activitypub.reader.explore.browse") }}
          </button>
        </div>
+        <div class="ap-explore-form__hashtag-row">
+          <label class="ap-explore-form__hashtag-label" for="ap-explore-hashtag">
+            {{ __("activitypub.reader.explore.hashtagLabel") }}
+          </label>
+          <span class="ap-explore-form__hashtag-prefix">#</span>
+          <input
+            type="text"
+            id="ap-explore-hashtag"
+            name="hashtag"
+            value="{{ hashtag }}"
+            class="ap-explore-form__input ap-explore-form__input--hashtag"
+            placeholder="{{ __('activitypub.reader.explore.hashtagPlaceholder') }}"
+            aria-label="{{ __('activitypub.reader.explore.hashtagPlaceholder') }}"
+            autocomplete="off"
+            pattern="[\w]+"
+            maxlength="100">
+          <span class="ap-explore-form__hashtag-hint">{{ __("activitypub.reader.explore.hashtagHint") }}</span>
+        </div>
      </form>

      {# Error state #}
@@ -107,28 +218,24 @@

      {# Results #}
      {% if instance and not error %}
-    {# Add to deck toggle button (shown when browsing results) #}
-    {% if items.length > 0 %}
-      <div class="ap-explore-deck-toggle"
-        x-data="apDeckToggle('{{ instance }}', '{{ scope }}', '{{ mountPath }}', '{{ csrfToken }}', {{ deckCount }}, {{ 'true' if isInDeck else 'false' }})">
+        {# Pin as tab button — outside form, inside apExploreTabs scope #}
+        <div class="ap-explore-pin-bar">
          <button
            type="button"
-          class="ap-explore-deck-toggle__btn"
-          :class="{ 'ap-explore-deck-toggle__btn--active': inDeck }"
-          @click="toggle()"
-          :disabled="!inDeck && deckLimitReached"
-          :title="!inDeck && deckLimitReached ? '{{ __('activitypub.reader.explore.deck.deckLimitReached') }}' : (inDeck ? '{{ __('activitypub.reader.explore.deck.removeFromDeck') }}' : '{{ __('activitypub.reader.explore.deck.addToDeck') }}')"
-          :aria-label="!inDeck && deckLimitReached ? '{{ __('activitypub.reader.explore.deck.deckLimitReached') }}' : (inDeck ? '{{ __('activitypub.reader.explore.deck.removeFromDeck') }}' : '{{ __('activitypub.reader.explore.deck.addToDeck') }}')"
-          x-text="inDeck ? '★ {{ __('activitypub.reader.explore.deck.inDeck') }}' : '☆ {{ __('activitypub.reader.explore.deck.addToDeck') }}'">
+            class="ap-explore-pin-btn"
+            @click="pinInstance('{{ instance }}', '{{ scope }}')"
+            :disabled="pinning">
+            <span x-show="!pinning">{{ __("activitypub.reader.explore.tabs.pinAsTab") }}</span>
+            <span x-show="pinning" x-cloak>…</span>
          </button>
        </div>
-    {% endif %}

        {% if items.length > 0 %}
          <div class="ap-timeline ap-explore-timeline"
            id="ap-explore-timeline"
            data-instance="{{ instance }}"
            data-scope="{{ scope }}"
+            data-hashtag="{{ hashtag }}"
            data-mount-path="{{ mountPath }}"
            data-max-id="{{ maxId if maxId else '' }}">
            {% for item in items %}
@@ -136,13 +243,14 @@
            {% endfor %}
          </div>

-      {# Infinite scroll for explore page #}
+          {# Infinite scroll for explore search tab #}
          {% if maxId %}
            <div class="ap-load-more"
              id="ap-explore-load-more"
              data-max-id="{{ maxId }}"
              data-instance="{{ instance }}"
              data-scope="{{ scope }}"
+              data-hashtag="{{ hashtag }}"
              x-data="apExploreScroll()"
              x-init="init()">
              <div class="ap-load-more__sentinel" x-ref="sentinel"></div>
@@ -158,61 +266,124 @@
        {% endif %}
      {% endif %}

-  {% endif %}{# end Search tab #}
+    </div>{# end Search tab panel #}

-  {# ── Decks tab ──────────────────────────────────────────────────── #}
-  {% if activeTab == 'decks' %}
-    {% if decks and decks.length > 0 %}
-      <div class="ap-deck-grid" data-csrf-token="{{ csrfToken }}">
-        {% for deck in decks %}
-          <div class="ap-deck-column"
-            x-data="apDeckColumn('{{ deck.domain }}', '{{ deck.scope }}', '{{ mountPath }}', {{ loop.index0 }}, '{{ csrfToken }}')"
-            x-init="init()">
-            <header class="ap-deck-column__header">
-              <span class="ap-deck-column__domain">{{ deck.domain }}</span>
-              <span class="ap-deck-column__scope-badge ap-deck-column__scope-badge--{{ deck.scope }}">
-                {{ __("activitypub.reader.explore.deck." + deck.scope + "Badge") }}
-              </span>
-              <button
-                type="button"
-                class="ap-deck-column__remove"
-                @click="removeDeck()"
-                title="{{ __('activitypub.reader.explore.deck.removeColumn') }}"
-                aria-label="{{ __('activitypub.reader.explore.deck.removeColumn') }}">×</button>
-            </header>
-            <div class="ap-deck-column__body" x-ref="body">
-              <div x-show="loading && itemCount === 0" class="ap-deck-column__loading">
-                <span>{{ __("activitypub.reader.pagination.loading") }}</span>
+    {# ── Dynamic tab panels (instance + hashtag) ──────────────────────────── #}
+    <template x-for="tab in tabs" :key="tab._id + '-panel'">
+      <div
+        :id="'ap-tab-panel-' + tab._id"
+        role="tabpanel"
+        :aria-labelledby="'ap-tab-btn-' + tab._id"
+        x-show="activeTabId === tab._id"
+        x-cloak>
+
+        {# ── Instance tab panel ───────────────────────────────────────────── #}
+        <template x-if="tab.type === 'instance'">
+          <div class="ap-explore-instance-panel">
+
+            {# Loading spinner — first load, no content yet #}
+            <div class="ap-explore-tab-loading"
+              x-show="tabState[tab._id] && tabState[tab._id].loading && !tabState[tab._id].html">
+              <span class="ap-explore-tab-loading__text">{{ __("activitypub.reader.pagination.loading") }}</span>
            </div>
-              <div x-show="error" class="ap-deck-column__error" x-cloak>
-                <p x-text="error"></p>
-                <button type="button" class="ap-deck-column__retry" @click="retryLoad()">
-                  {{ __("activitypub.reader.explore.deck.retry") }}
+
+            {# Error state with retry #}
+            <div class="ap-explore-tab-error"
+              x-show="tabState[tab._id] && tabState[tab._id].error && !tabState[tab._id].html">
+              <p class="ap-explore-tab-error__message" x-text="tabState[tab._id] && tabState[tab._id].error"></p>
+              <button type="button" class="ap-explore-tab-error__retry" @click="retryTab(tab)">
+                {{ __("activitypub.reader.explore.tabs.retry") }}
              </button>
            </div>
-              <div x-show="!loading && !error && itemCount === 0" class="ap-deck-column__empty" x-cloak>
-                {{ __("activitypub.reader.explore.noResults") }}
+
+            {# Timeline content — server-rendered cards injected via x-html #}
+            <div class="ap-timeline ap-explore-tab-timeline"
+              x-show="tabState[tab._id] && tabState[tab._id].html"
+              x-html="tabState[tab._id] ? tabState[tab._id].html : ''">
            </div>
-              <div x-html="html" class="ap-deck-column__items"></div>
-              <div class="ap-deck-column__sentinel" x-ref="sentinel"></div>
-              <div x-show="loading && itemCount > 0" class="ap-deck-column__loading-more" x-cloak>
-                <span>{{ __("activitypub.reader.pagination.loading") }}</span>
+
+            {# Inline loading spinner for subsequent pages #}
+            <div class="ap-explore-tab-loading ap-explore-tab-loading--more"
+              x-show="tabState[tab._id] && tabState[tab._id].loading && tabState[tab._id].html">
+              <span class="ap-explore-tab-loading__text">{{ __("activitypub.reader.pagination.loading") }}</span>
            </div>
-              <p x-show="done && itemCount > 0" class="ap-deck-column__done" x-cloak>
+
+            {# Empty state — loaded successfully but no posts #}
+            <div class="ap-explore-tab-empty"
+              x-show="tabState[tab._id] && tabState[tab._id].done && !tabState[tab._id].html && !tabState[tab._id].loading && !tabState[tab._id].error">
+              <p>{{ __("activitypub.reader.explore.noResults") }}</p>
+            </div>
+
+            {# End of feed message #}
+            <p class="ap-load-more__done"
+              x-show="tabState[tab._id] && tabState[tab._id].done && tabState[tab._id].html"
+              x-cloak>
              {{ __("activitypub.reader.pagination.noMore") }}
            </p>
+
+            {# Infinite scroll sentinel — watched by IntersectionObserver #}
+            <div class="ap-tab-sentinel"></div>
          </div>
+        </template>
+
+        {# ── Hashtag tab panel ────────────────────────────────────────────── #}
+        <template x-if="tab.type === 'hashtag'">
+          <div class="ap-explore-hashtag-panel">
+
+            {# Source info line — shows which instances are being searched #}
+            <p class="ap-hashtag-sources"
+              x-show="tabState[tab._id] && tabState[tab._id].sourceMeta && tabState[tab._id].sourceMeta.instancesQueried > 0"
+              x-text="hashtagSourcesLine(tab)"
+              x-cloak></p>
+
+            {# Loading spinner — first load, no content yet #}
+            <div class="ap-explore-tab-loading"
+              x-show="tabState[tab._id] && tabState[tab._id].loading && !tabState[tab._id].html">
+              <span class="ap-explore-tab-loading__text">{{ __("activitypub.reader.pagination.loading") }}</span>
            </div>
-        {% endfor %}
+
+            {# Error state with retry #}
+            <div class="ap-explore-tab-error"
+              x-show="tabState[tab._id] && tabState[tab._id].error && !tabState[tab._id].html">
+              <p class="ap-explore-tab-error__message" x-text="tabState[tab._id] && tabState[tab._id].error"></p>
+              <button type="button" class="ap-explore-tab-error__retry" @click="retryTab(tab)">
+                {{ __("activitypub.reader.explore.tabs.retry") }}
+              </button>
            </div>
-    {% else %}
-      <div class="ap-deck-empty">
-        <p>{{ __("activitypub.reader.explore.deck.emptyState") }}</p>
-        <a href="{{ exploreBase }}" class="ap-deck-empty__link">
-          {{ __("activitypub.reader.explore.deck.emptyStateLink") }}
-        </a>
+
+            {# Timeline content #}
+            <div class="ap-timeline ap-explore-tab-timeline"
+              x-show="tabState[tab._id] && tabState[tab._id].html"
+              x-html="tabState[tab._id] ? tabState[tab._id].html : ''">
            </div>
-    {% endif %}
-  {% endif %}{# end Decks tab #}
+
+            {# Inline loading spinner for subsequent pages #}
+            <div class="ap-explore-tab-loading ap-explore-tab-loading--more"
+              x-show="tabState[tab._id] && tabState[tab._id].loading && tabState[tab._id].html">
+              <span class="ap-explore-tab-loading__text">{{ __("activitypub.reader.pagination.loading") }}</span>
+            </div>
+
+            {# Empty state — no instance tabs pinned yet #}
+            <div class="ap-explore-tab-empty"
+              x-show="tabState[tab._id] && tabState[tab._id].done && !tabState[tab._id].html && !tabState[tab._id].loading && !tabState[tab._id].error">
+              <p>{{ __("activitypub.reader.explore.tabs.noInstances") }}</p>
+            </div>
+
+            {# End of feed message #}
+            <p class="ap-load-more__done"
+              x-show="tabState[tab._id] && tabState[tab._id].done && tabState[tab._id].html"
+              x-cloak>
+              {{ __("activitypub.reader.pagination.noMore") }}
+            </p>
+
+            {# Infinite scroll sentinel #}
+            <div class="ap-tab-sentinel"></div>
+          </div>
+        </template>
+
+      </div>
+    </template>
+
+  </div>{# end ap-explore-tabs-container #}

 {% endblock %}
--- a/views/layouts/ap-reader.njk
+++ b/views/layouts/ap-reader.njk
@@ -5,8 +5,8 @@
  <script defer src="/assets/@rmdes-indiekit-endpoint-activitypub/reader-infinite-scroll.js"></script>
  {# Autocomplete components for explore + popular accounts #}
  <script defer src="/assets/@rmdes-indiekit-endpoint-activitypub/reader-autocomplete.js"></script>
-  {# Deck components — apDeckToggle and apDeckColumn #}
-  <script defer src="/assets/@rmdes-indiekit-endpoint-activitypub/reader-decks.js"></script>
+  {# Tab components — apExploreTabs #}
+  <script defer src="/assets/@rmdes-indiekit-endpoint-activitypub/reader-tabs.js"></script>

  {# Alpine.js for client-side reactivity (CW toggles, interaction buttons, infinite scroll) #}
  <script defer src="https://cdn.jsdelivr.net/npm/alpinejs@3.14.9/dist/cdn.min.js"></script>