feat(details): rebuild the message details dialog as rows

A text box could not carry a per-value context menu without parsing displayed
text back into structure, and the user did not want a text box. Each row now
holds its own value, its message index and its query, built from the parsed
message.

Every value label states Qt::PlainText. The QPlainTextEdit this replaced was
plain by design rather than by style: header values come from strangers, and a
QLabel guesses the format under AutoText.

1 files changed, 87 insertions, 0 deletions

diff --git a/src/messagedetailsdialog.h b/src/messagedetailsdialog.h
new file mode 100644
index 0000000..f865913
--- /dev/null
+++ b/src/messagedetailsdialog.h
@@ -0,0 +1,87 @@
+/*
+ * 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 <QDialog>
+#include <QList>
+#include <QString>
+
+#include "htmlbuilder.h"
+
+/// One header of one message, as shown and as searched for.
+///
+/// The query is built when the row is, from the parsed value, so nothing has
+/// to parse displayed text back into structure. That is the whole reason this
+/// dialog stopped being a text box.
+struct HeaderRow
+{
+    /// notmuch's field name, or empty for a header with no searchable form.
+    /// Wire format, never translated.
+    QString field;
+
+    /// Translated label shown at the start of the row, e.g. "From:".
+    QString label;
+
+    /// The header's value, verbatim and untrusted.
+    QString value;
+
+    /// The finished query, empty when the header has no searchable form.
+    QString query;
+
+    /// Which message of the thread this row belongs to, zero-based.
+    int messageIndex = 0;
+};
+
+/// The full headers of every message in a thread, read-only.
+///
+/// Rows rather than one text box, so a value can carry its own context menu
+/// without anything parsing rendered text back into structure. The user also
+/// asked not to be shown a text box.
+///
+/// **Every value label is explicitly `Qt::PlainText`.** This replaced a
+/// `QPlainTextEdit` whose plain-textness was a security property rather than a
+/// style: header values come from strangers, and plain text cannot interpret
+/// markup, so there is nothing to escape and nothing that can render. A QLabel
+/// guesses under `Qt::AutoText`, so stating the format is what preserves that.
+class MessageDetailsDialog : public QDialog
+{
+    Q_OBJECT
+public:
+    explicit MessageDetailsDialog(const QList<ThreadRenderItem> &items,
+                                  QWidget *parent = nullptr);
+
+    /// The rows on display, in order. Exposed for testing without rendering.
+    QList<HeaderRow> rows() const { return m_rows; }
+
+    /// Emits searchRequested for `row`, or nothing when the row carries no
+    /// searchable query. The menu entries call this; a test can too, without
+    /// popping a menu.
+    void requestSearch(const HeaderRow &row, bool extend);
+
+signals:
+    /// The user chose a search from a row's menu. `extend` narrows the current
+    /// query rather than replacing it.
+    void searchRequested(const QString &query, bool extend);
+
+private:
+    /// Builds the rows from the thread, one group per message.
+    void buildRows(const QList<ThreadRenderItem> &items);
+
+    QList<HeaderRow> m_rows;
+};