fix(ui): paste uses the event's clipboard text instead of re-reading it (#2021) (#2243)

The paste handler read the system clipboard synchronously (2 s timeout) even
though the paste event already carries that text, and discarded the read's
result. On the desktop, the clipboard bridge delivers `event_text` that it read
while the window thread was free; re-reading from the paste handler blocks that
same window thread - and when the app itself owns the clipboard (a self-paste),
its own data source can only be served by that very thread, so every self-paste
froze the window for the full 2 s read timeout on Linux/Wayland.

Prefer the event's text and only fall back to the synchronous read when the
platform handed over none (chords, image-only clipboard, context-menu paste).
A regression test pins that a paste event carrying text never triggers the
synchronous read.

crates/ui-egui/src/menus/clipboard.rs

@@ -7,8 +7,8 @@ use crate::i18n::trf;
 /// Paste: the system clipboard wins when it holds something newer than our own copy (layers copied
 /// from another design app, an image, SVG or text from another app); otherwise our copied layers.
 /// `event_text` is the text the platform handed over with the paste event (the browser has no
-/// other way to read it). `at`: the page point to paste at (Paste here); `None` pastes in the
-/// middle of the view.
+/// other way to read it; the desktop's clipboard bridge has already read it). `at`: the page
+/// point to paste at (Paste here); `None` pastes in the middle of the view.
 /// In Dev Mode only a comment's link pastes (it opens the thread); everything else would edit.
 pub fn paste(app: &mut FigApp, event_text: Option<&str>, at: Option<(f64, f64)>) {
     // A gesture injected through the control channel pastes only our own copied layers: it must not
@@ -47,7 +47,15 @@ pub fn paste(app: &mut FigApp, event_text: Option<&str>, at: Option<(f64, f64)>)
         }
         return;
     }
-    let sys_text = app.services.clipboard_get_text().or_else(|| event_text.map(str::to_string)).filter(|t| !t.is_empty());
+    // The text the platform handed over with the paste event is the system clipboard's text: the
+    // browser delivers it, and the desktop's async clipboard bridge read it while the window
+    // thread was free to serve the transfer. Never re-read the clipboard synchronously for it —
+    // on the desktop that read blocks the window thread for the read timeout, and when this app
+    // itself owns the clipboard (a self-paste) its own source can only be served by that very
+    // thread, so the read waits the full timeout and the window freezes for seconds (#2021).
+    // A paste the platform didn't hand text over (a chord, an image, the menu) reads it, as before.
+    let sys_text =
+        if let Some(t) = event_text { (!t.is_empty()).then(|| t.to_string()) } else { app.services.clipboard_get_text().filter(|t| !t.is_empty()) };
     // The text matching `last_copy` means the system clipboard still holds what we mirrored only
     // while the engine clipboard is the one we mirrored. A control-channel copy changes the engine
     // clipboard without writing the system clipboard, so its generation no longer matches and the

crates/ui-egui/src/web_clipboard_tests.rs

@@ -3,6 +3,9 @@
 //! whatever the system clipboard has. A copy that never reached the clipboard pasted the text that
 //! was there before as a text layer instead of the copied layers.
 
+use std::sync::Arc;
+use std::sync::atomic::{AtomicUsize, Ordering};
+
 use egui::{Event, Key, Modifiers, OutputCommand, Pos2, RawInput, Rect, vec2};
 use figcraft_doc::NodeKind;
 use figcraft_engine::Session;
@@ -223,3 +226,49 @@ fn a_mismatched_image_buffer_is_dropped() {
         assert!(out.platform_output.commands.is_empty(), "{w}x{h}");
     }
 }
+
+/// The system clipboard's text read, counted so a test can assert when it ran. The desktop's
+/// arboard read blocks the window thread up to `CLIPBOARD_TIMEOUT`; against the app's own Wayland
+/// source (a self-paste) it waits the full timeout — the whole UI freezes for seconds (#2021) —
+/// and its result is discarded in favour of the paste event's text. A paste whose platform event
+/// already carries the clipboard text must never perform that synchronous re-read.
+struct CountingReads {
+    /// How often the synchronous text read was asked for.
+    reads: Arc<AtomicUsize>,
+}
+
+impl Services for CountingReads {
+    fn clipboard_get_text(&mut self) -> Option<String> {
+        self.reads.fetch_add(1, Ordering::Relaxed);
+        None
+    }
+}
+
+#[test]
+fn a_paste_event_its_own_text_never_triggers_the_synchronous_text_read() {
+    // The platform (the desktop's async clipboard bridge, or the browser) already read the
+    // clipboard and handed the text with the paste event.
+    let reads = Arc::new(AtomicUsize::new(0));
+    let mut s = Session::new();
+    s.execute("shape.rectangle", &json!({"x": 10, "y": 10, "width": 100, "height": 50})).unwrap();
+    let mut p = Page {
+        ctx: egui::Context::default(),
+        app: FigApp::new(s, Box::new(CountingReads { reads: reads.clone() })),
+        time: 0.0,
+        clipboard: String::new(),
+    };
+    for _ in 0..3 {
+        p.frame(vec![]);
+    }
+
+    // The desktop delivers the copied layers' SVG as the paste event's text.
+    let text = "<svg width=\"100\" height=\"50\"><rect/></svg>";
+    p.frame(vec![Page::key(Key::V, true), Event::Paste(text.to_string())]);
+    p.frame(vec![Page::key(Key::V, false)]);
+    assert_eq!(reads.load(Ordering::Relaxed), 0, "the text came with the paste event: no blocking re-read of the system clipboard");
+
+    // Even a second paste must not re-read: the clipboard still holds the pasted text.
+    p.frame(vec![Page::key(Key::V, true), Event::Paste(text.to_string())]);
+    p.frame(vec![Page::key(Key::V, false)]);
+    assert_eq!(reads.load(Ordering::Relaxed), 0, "still the event's text: no blocking re-read");
+}