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diff --git a/src/tagstrip.h b/src/tagstrip.h
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+/*
+ * qtmaildir - a Qt6 mail client for notmuch-indexed Maildirs
+ * Copyright (C) 2026 Danilo M. <danix@danix.xyz>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
+ */
+
+#pragma once
+
+#include <QStringList>
+#include <QWidget>
+
+class TagColors;
+
+/// One row of tag chips under the message pane.
+///
+/// A single row by design: the message area must not shift as you move between
+/// threads with different numbers of tags. Whatever does not fit collapses
+/// into a trailing "+N" chip whose tooltip names the hidden tags.
+class TagStrip : public QWidget
+{
+    Q_OBJECT
+public:
+    explicit TagStrip(QWidget *parent = nullptr);
+
+    /// Not owned; must outlive the strip.
+    void setTagColors(const TagColors *colours);
+
+    /// Account tags are filtered out: they belong to the thread list chip,
+    /// being a different taxonomy from the functional tags shown here.
+    void setTags(const QStringList &tags);
+
+    QSize sizeHint() const override;
+
+    /// The tags actually drawn, in order. Exposed for testing the overflow
+    /// split without rendering.
+    QStringList visibleTags() const { return m_visible; }
+    QStringList hiddenTags() const { return m_hidden; }
+
+protected:
+    void paintEvent(QPaintEvent *event) override;
+    void resizeEvent(QResizeEvent *event) override;
+
+private:
+    /// Recomputes the visible/hidden split for the current width.
+    void relayout();
+
+    QStringList m_tags;     ///< Functional tags only, account ones removed.
+    QStringList m_visible;
+    QStringList m_hidden;
+    const TagColors *m_tagColors = nullptr;
+};