⚡ Fix progressive render budget when timestamp is stale

Pass performance.now from finalize/debounce and re-anchor the WASM
budget if the stamp is 0 or already past max_blocking_time, so HQ
tiles are not yielded after a few nodes with almost no real work.

frontend/src/app/render_wasm/api.cljs

@@ -1417,7 +1417,7 @@
     ;; this implicitly (`zoom_changed`); this extends it to pan/resize-triggered
     ;; ends (e.g. selecting a shape opens the options panel and resizes the
     ;; viewport), which previously blanked.
-    (internal-render 0 RENDER-FLAG-SYNC-TILES)
+    (internal-render (js/performance.now) RENDER-FLAG-SYNC-TILES)
     ;; The direct render above bypasses the rAF `render` loop, so repaint the
     ;; editor overlay explicitly. Only when this was a full frame: a progressive
     ;; render keeps painting through the rAF loop and its partial frames must not
@@ -1432,7 +1432,7 @@
               (if (view-gesture-active?)
                 ;; Pan/zoom pause: render without ending the interaction.
                 (do
-                  (internal-render 0 RENDER-FLAG-SYNC-TILES)
+                  (internal-render (js/performance.now) RENDER-FLAG-SYNC-TILES)
                   (render-text-editor-overlay-after-frame!))
                 (finalize-view-interaction!))))]
     (fns/debounce do-render DEBOUNCE_DELAY_MS)))

render-wasm/src/render.rs

@@ -2368,6 +2368,7 @@ impl RenderState {
         allow_stop: bool,
     ) -> Result<FrameType> {
         performance::begin_measure!("continue_render_loop");
+        let timestamp = self.render_budget_start(timestamp);
         let frame_type =
             self.render_shape_tree_partial(base_object, tree, timestamp, allow_stop)?;
 
@@ -2433,6 +2434,7 @@ impl RenderState {
         tree: ShapesPoolRef,
         timestamp: i32,
     ) -> Result<FrameType> {
+        let timestamp = self.render_budget_start(timestamp);
         self.render_shape_tree_partial(base_object, tree, timestamp, false)?;
 
         // Same composition as `continue_render_loop` for full frames: snapshot only the
@@ -2567,6 +2569,24 @@ impl RenderState {
         Ok((data.as_bytes().to_vec(), width, height))
     }
 
+    /// Anchor the progressive render budget to wall-clock now when the
+    /// caller-provided timestamp is unusable:
+    /// - Frontend sometimes passes `0` (finalize-view / debounced zoom-end).
+    /// - rAF may hand a timestamp that is already older than the budget when
+    ///   the handler runs late. Using that stamp made `should_stop_rendering`
+    ///   yield after a few nodes with ~0ms of real work.
+    #[inline]
+    fn render_budget_start(&self, timestamp: i32) -> i32 {
+        let now = performance::get_time();
+        if timestamp <= 0 {
+            return now;
+        }
+        if now - timestamp > self.options.max_blocking_time_ms {
+            return now;
+        }
+        timestamp
+    }
+
     #[inline]
     pub fn should_stop_rendering(&self, iteration: i32, timestamp: i32) -> bool {
         if iteration % self.options.node_batch_threshold != 0 {