context_input: middle-click pastes the X11 PRIMARY selection

Joe (X11) reported that middle-click paste did nothing in the ticket and
node-ID fields. iced's base text_input only binds Ctrl+V to the Standard
(CLIPBOARD) selection and never reads PRIMARY or binds mouse button 2, so
the "select text, middle-click to paste" workflow was dead.

Add a Button::Middle branch to ContextInput::update that reads
clipboard::Kind::Primary, sanitizes it, and pastes at the cursor (reusing
the already-tested pure paste()). Factor the control-char stripping into a
shared, unit-tested sanitize_clip() helper also used by the menu Paste, so
a trailing newline on the PRIMARY selection is dropped. Respects `locked`
so read-only display fields still reject paste.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/widget/context_input.rs

@@ -70,6 +70,13 @@ pub fn paste(value: &str, start: usize, end: usize, clip: &str) -> Edit {
     }
 }
 
+/// Strip control characters (e.g. a trailing newline on an X11 PRIMARY
+/// selection) from clipboard text before it is pasted. Shared by the
+/// right-click menu Paste and the middle-click PRIMARY paste.
+pub fn sanitize_clip(raw: &str) -> String {
+    raw.chars().filter(|c| !c.is_control()).collect()
+}
+
 pub fn select_all_range(value: &str) -> (usize, usize) {
     let value = text_input::Value::new(value);
 
@@ -362,6 +369,48 @@ where
             return;
         }
 
+        // Middle-click pastes the X11 PRIMARY selection at the cursor. iced's
+        // base text_input only wires Ctrl+V to the Standard (CLIPBOARD)
+        // selection, so without this the common "select text, middle-click to
+        // paste" workflow does nothing on X11.
+        let middle_click_on_input = matches!(
+            event,
+            Event::Mouse(mouse::Event::ButtonPressed(mouse::Button::Middle))
+        ) && cursor.is_over(layout.bounds());
+
+        if middle_click_on_input && !self.locked {
+            let clip = sanitize_clip(&clipboard.read(clipboard::Kind::Primary).unwrap_or_default());
+
+            if !clip.is_empty() {
+                let value = text_input::Value::new(&self.value);
+                let input_state = tree.children[0]
+                    .state
+                    .downcast_mut::<text_input::State<Renderer::Paragraph>>();
+                let (start, end) = match input_state.cursor().state(&value) {
+                    text_input::cursor::State::Index(index) => {
+                        let index = index.min(value.len());
+                        (index, index)
+                    }
+                    text_input::cursor::State::Selection { start, end } => {
+                        normalized_range(&value, start, end)
+                    }
+                };
+
+                let edit = paste(&self.value, start, end, &clip);
+                input_state.move_cursor_to(edit.cursor);
+
+                if let Some(on_paste) = &self.on_paste {
+                    shell.publish(on_paste.as_ref()(edit.value));
+                } else if let Some(on_input) = &self.on_input {
+                    shell.publish(on_input.as_ref()(edit.value));
+                }
+            }
+
+            shell.capture_event();
+            shell.request_redraw();
+            return;
+        }
+
         Widget::update(
             &mut self.input,
             &mut tree.children[0],
@@ -717,12 +766,7 @@ where
                 }
             }
             MenuAction::Paste => {
-                let clip = clipboard
-                    .read(clipboard::Kind::Standard)
-                    .unwrap_or_default()
-                    .chars()
-                    .filter(|c| !c.is_control())
-                    .collect::<String>();
+                let clip = sanitize_clip(&clipboard.read(clipboard::Kind::Standard).unwrap_or_default());
                 let edit = paste(self.value, start, end, &clip);
 
                 self.publish_paste(edit, shell);
@@ -842,6 +886,16 @@ mod tests {
         assert_eq!(clip, None);
     }
 
+    #[test]
+    fn sanitize_clip_strips_control_chars_keeps_text() {
+        // An X11 PRIMARY selection commonly carries a trailing newline.
+        assert_eq!(sanitize_clip("pixelpassF1:abc\n"), "pixelpassF1:abc");
+        assert_eq!(sanitize_clip("a\tb\r\nc"), "abc");
+        // Non-control unicode is preserved.
+        assert_eq!(sanitize_clip("héllo🦀"), "héllo🦀");
+        assert_eq!(sanitize_clip(""), "");
+    }
+
     #[test]
     fn paste_replaces_selection_or_inserts_at_cursor() {
         assert_eq!(