Make GUI checkboxes clickable

Clicking a checkbox glyph toggles its state and writes the change back.
DocumentModel::toggleCheckbox(row, ordinal) finds the Nth checkbox cookie
in the section body (document order), flips [ ]/[-] -> [X] and [X] -> [ ],
writes the body via /body, and refreshes the row.

The body parser assigns each checkbox item a stable ordinal across the
whole section, and the list delegate wires a pointer-cursor MouseArea on
the glyph (checkbox items only) to the model toggle.

ui/qml/OutlineView.qml

@@ -94,7 +94,9 @@ ListView {
 
             // Push a run of text, splitting out any contiguous list items into
             // dedicated "list" parts so they render with bullets/checkboxes.
-            function pushText(text) {
+            // `cbCounter` is a single-element array used as a mutable counter so
+            // checkbox ordinals are stable across the whole section body.
+            function pushText(text, cbCounter) {
                 if (!text) return;
                 let lines = text.split('\n');
                 let buf = [];
@@ -116,6 +118,9 @@ ListView {
                     let item = parseListItem(ln);
                     if (item) {
                         flushBuf();
+                        // Assign a stable ordinal to checkbox-bearing items.
+                        item.checkboxOrdinal = (item.checkbox !== "")
+                            ? cbCounter[0]++ : -1;
                         items.push(item);
                     } else {
                         flushItems();
@@ -126,6 +131,9 @@ ListView {
                 flushBuf();
             }
 
+            // Running checkbox ordinal across the whole section body.
+            let cbCounter = [0];
+
             let lines = body.split('\n');
             let currentText = [];
             let inCode = false;
@@ -143,7 +151,7 @@ ListView {
                 if (!inCode && !inTable && trimmed.toUpperCase().startsWith("#+BEGIN_SRC")) {
                     // Flush pending text
                     if (currentText.length > 0) {
-                        pushText(currentText.join('\n').trim());
+                        pushText(currentText.join('\n').trim(), cbCounter);
                         currentText = [];
                     }
                     inCode = true;
@@ -162,7 +170,7 @@ ListView {
                 else if (!inTable && trimmed.startsWith("|")) {
                     // Flush pending text
                     if (currentText.length > 0) {
-                        pushText(currentText.join('\n').trim());
+                        pushText(currentText.join('\n').trim(), cbCounter);
                         currentText = [];
                     }
                     inTable = true;
@@ -212,7 +220,7 @@ ListView {
                 }
                 parts.push({type: "table", rows: rows, hasHeader: hasHeader});
             } else if (currentText.length > 0) {
-                pushText(currentText.join('\n').trim());
+                pushText(currentText.join('\n').trim(), cbCounter);
             }
             
             return parts;
@@ -447,6 +455,7 @@ ListView {
 
                                         // Checkbox glyph, or a plain bullet when no checkbox.
                                         Label {
+                                            id: cbGlyph
                                             readonly property string cb: modelData.checkbox ?? ""
                                             text: {
                                                 switch (cb) {
@@ -463,6 +472,16 @@ ListView {
                                                    : theme.placeholderTextColor
                                             font.pointSize: outline.baseFontSize + 1
                                             font.bold: cb !== ""
+
+                                            // Clickable only for checkbox items; toggles via the model.
+                                            MouseArea {
+                                                anchors.fill: parent
+                                                enabled: cbGlyph.cb !== ""
+                                                visible: enabled
+                                                cursorShape: Qt.PointingHandCursor
+                                                onClicked: docModel.toggleCheckbox(
+                                                    del.index, modelData.checkboxOrdinal ?? -1)
+                                            }
                                         }
 
                                         // Item text; checked items are dimmed and struck through.

ui/src/documentmodel.cpp

@@ -2,6 +2,7 @@
 #include "orkclient.h"
 
 #include <QDebug>
+#include <QRegularExpression>
 
 static const QStringList DONE_KEYWORDS = {"DONE", "CANCELLED", "CANCELED"};
 
@@ -186,6 +187,66 @@ bool DocumentModel::isLanguageSupported(const QString &lang)
     return m_supportedLanguages.contains(lang.trimmed().toLower());
 }
 
+bool DocumentModel::toggleCheckbox(int row, int checkboxOrdinal)
+{
+    if (!m_client || row < 0 || row >= m_visibleRows.size())
+        return false;
+
+    const QString &id = m_visibleRows[row];
+    if (!m_sections.contains(id))
+        return false;
+
+    Section &sec = m_sections[id];
+    if (!sec.bodyLoaded)
+        loadBody(sec);
+
+    // Match a list item's checkbox cookie: leading indent, a bullet (- / +) or
+    // ordered marker (N. / N)), then a [ ]/[x]/[X]/[-] cookie.
+    static const QRegularExpression cookieRe(
+        QStringLiteral("^(\\s*(?:[-+]|\\d+[.)])\\s+\\[)([ xX-])(\\])"));
+
+    const QStringList lines = sec.body.split('\n');
+    QStringList out;
+    out.reserve(lines.size());
+
+    int seen = -1;
+    bool toggled = false;
+    for (const QString &line : lines) {
+        QRegularExpressionMatch m = cookieRe.match(line);
+        if (m.hasMatch()) {
+            ++seen;
+            if (seen == checkboxOrdinal) {
+                const QString state = m.captured(2);
+                const QString next = (state == QLatin1String("X") ||
+                                      state == QLatin1String("x"))
+                                         ? QStringLiteral(" ")
+                                         : QStringLiteral("X");
+                QString updated = line;
+                updated.replace(m.capturedStart(2), m.capturedLength(2), next);
+                out.append(updated);
+                toggled = true;
+                continue;
+            }
+        }
+        out.append(line);
+    }
+
+    if (!toggled)
+        return false;
+
+    const QString newBody = out.join('\n');
+    if (!m_client->write(sec.path + QStringLiteral("/body"), newBody))
+        return false;
+
+    // Refresh from the server so the parsed state matches what was written.
+    sec.bodyLoaded = false;
+    loadBody(sec);
+
+    const QModelIndex idx = index(row);
+    emit dataChanged(idx, idx, {BodyRole});
+    return true;
+}
+
 void DocumentModel::loadDocument()
 {
     beginResetModel();

ui/src/documentmodel.h

@@ -70,6 +70,12 @@ public:
     // `/ctl languages` (loaded once and cached). Case-insensitive.
     Q_INVOKABLE bool isLanguageSupported(const QString &lang);
 
+    // Toggle the Nth checkbox (0-based, in document order, counting only list
+    // items that carry a `[ ]`/`[X]`/`[-]` cookie) in the section at the given
+    // visible row. Flips [ ]/[-] -> [X] and [X] -> [ ], writes the section body
+    // back via /body, and refreshes the row. Returns true on success.
+    Q_INVOKABLE bool toggleCheckbox(int row, int checkboxOrdinal);
+
 signals:
     void documentChanged();