Pass accesskit tree to after_step, drop on_accesskit_update

Replaces the separate on_accesskit_update hook with a `&TreeUpdate`
parameter on `after_step` — one hook per step, tree delivered inline.
`step_no_side_effects` now returns the TreeUpdate so plugins driving
the harness from within their own hook (where nested dispatches are
suppressed) can still see it.

Also adds `#[track_caller]` to the internal `_step` / `_step_no_side_effects`
/ `_try_run` so `Location::caller()` inside `step()` walks up to the
user's original call site when reached via `run()`.

crates/egui_kittest/src/lib.rs

@@ -210,10 +210,13 @@ impl<'a, State: 'static> Harness<'a, State> {
 
     /// Advance the harness by one frame without firing plugin hooks.
     ///
-    /// This is useful for running steps within a plugin, without ending in an infinite loop where
-    /// the plugin is called again.
-    pub fn step_no_side_effects(&mut self) {
-        self._step_no_side_effects(false);
+    /// Returns the AccessKit tree update produced by the frame. Useful for plugins driving
+    /// the harness from inside a hook: `after_step` normally delivers the tree, but nested
+    /// hook dispatches are suppressed, so plugins that call this from within their own
+    /// `after_step` need the return value to see the fresh tree.
+    #[track_caller]
+    pub fn step_no_side_effects(&mut self) -> egui::accesskit::TreeUpdate {
+        self._step_no_side_effects(false)
     }
 
     /// [`std::panic::Location`] of the most recent public `#[track_caller]` entry point
@@ -322,15 +325,17 @@ impl<'a, State: 'static> Harness<'a, State> {
     }
 
     /// Run a single step, firing `before_step` / `after_step` plugin hooks.
+    #[track_caller]
     fn _step(&mut self, sizing_pass: bool) {
         self.plugin_dispatch(|p, h| p.before_step(h));
-        self._step_no_side_effects(sizing_pass);
-        self.plugin_dispatch(|p, h| p.after_step(h));
+        let accesskit_update = self._step_no_side_effects(sizing_pass);
+        self.plugin_dispatch(|p, h| p.after_step(h, &accesskit_update));
     }
 
     /// Core frame advance. Does NOT fire plugin hooks — callable from within
     /// hooks via [`Self::step_no_side_effects`] without recursing.
-    fn _step_no_side_effects(&mut self, sizing_pass: bool) {
+    #[track_caller]
+    fn _step_no_side_effects(&mut self, sizing_pass: bool) -> egui::accesskit::TreeUpdate {
         self.input.predicted_dt = self.step_dt;
 
         let mut output = self.ctx.run_ui(self.input.take(), |ui| {
@@ -341,10 +346,10 @@ impl<'a, State: 'static> Harness<'a, State> {
             .accesskit_update
             .take()
             .expect("AccessKit was disabled");
-        self.plugin_dispatch(|p, h| p.on_accesskit_update(h, &accesskit_update));
-        self.kittest.update(accesskit_update);
+        self.kittest.update(accesskit_update.clone());
         self.renderer.handle_delta(&output.textures_delta);
         self.output = output;
+        accesskit_update
     }
 
     /// Calculate the rect that includes all popups and tooltips.
@@ -412,6 +417,7 @@ impl<'a, State: 'static> Harness<'a, State> {
         }
     }
 
+    #[track_caller]
     fn _try_run(&mut self, sleep: bool) -> Result<u64, ExceededMaxStepsError> {
         self.plugin_dispatch(|p, h| p.before_run(h));
 

crates/egui_kittest/src/plugin.rs

@@ -13,11 +13,12 @@ use crate::{ExceededMaxStepsError, Harness};
 /// State-agnostic plugins should impl for all `State` so they're reusable across harnesses:
 /// ```
 /// use egui_kittest::{Harness, Plugin};
+/// use egui::accesskit::TreeUpdate;
 ///
 /// struct MyPlugin;
 ///
 /// impl<S> Plugin<S> for MyPlugin {
-///     fn after_step(&mut self, _harness: &mut Harness<'_, S>) {
+///     fn after_step(&mut self, _harness: &mut Harness<'_, S>, _tree: &TreeUpdate) {
 ///         // ...
 ///     }
 /// }
@@ -48,17 +49,15 @@ pub trait Plugin<State = ()>: Send + 'static {
     fn before_step(&mut self, harness: &mut Harness<'_, State>) {}
 
     /// Called immediately after each single-frame step.
-    fn after_step(&mut self, harness: &mut Harness<'_, State>) {}
-
-    /// Called after each single-frame step with the AccessKit tree update egui produced
-    /// for that frame, before it's applied to the internal kittest state.
     ///
-    /// Plugins that need the tree (e.g. to stream it to an external debugger) should
-    /// clone it here — the harness no longer retains it after this hook returns.
-    fn on_accesskit_update(
+    /// `accesskit_update` is the AccessKit tree update egui produced for the frame that
+    /// just ran. Plugins that need to retain it (e.g. to stream it to an external
+    /// debugger) should clone it here — the harness doesn't hold on to it after this hook
+    /// returns.
+    fn after_step(
         &mut self,
         harness: &mut Harness<'_, State>,
-        tree: &egui::accesskit::TreeUpdate,
+        accesskit_update: &egui::accesskit::TreeUpdate,
     ) {
     }
 

crates/egui_kittest/tests/plugin.rs

@@ -41,7 +41,11 @@ impl<S> Plugin<S> for CountingPlugin {
     fn before_step(&mut self, _h: &mut Harness<'_, S>) {
         self.push("before_step");
     }
-    fn after_step(&mut self, _h: &mut Harness<'_, S>) {
+    fn after_step(
+        &mut self,
+        _h: &mut Harness<'_, S>,
+        _tree: &egui::accesskit::TreeUpdate,
+    ) {
         self.push("after_step");
     }
     fn on_event(&mut self, _h: &mut Harness<'_, S>, _event: &egui::Event) {
@@ -127,7 +131,7 @@ fn step_no_side_effects_skips_hooks() {
         drove: bool,
     }
     impl<S: 'static> Plugin<S> for DrivingPlugin {
-        fn after_step(&mut self, h: &mut Harness<'_, S>) {
+        fn after_step(&mut self, h: &mut Harness<'_, S>, _tree: &egui::accesskit::TreeUpdate) {
             self.log.lock().unwrap().push("after_step".into());
             if !self.drove {
                 self.drove = true;
@@ -164,7 +168,7 @@ fn mid_dispatch_registration_is_deferred() {
         registered: bool,
     }
     impl<S: 'static> Plugin<S> for Registrar {
-        fn after_step(&mut self, h: &mut Harness<'_, S>) {
+        fn after_step(&mut self, h: &mut Harness<'_, S>, _tree: &egui::accesskit::TreeUpdate) {
             self.log.lock().unwrap().push("registrar:after_step".into());
             if !self.registered {
                 self.registered = true;