Add egui_inspection protocol and plugin (#8234)

Introduces live inspection for running egui apps over a small TCP
request/response protocol, plus the `egui::Plugin` that serves it.

This is the minimal surface to get the egui mcp in, we may want to
extend this in the future to add support for the inspection gui.

---------

Co-authored-by: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

crates/eframe/Cargo.toml

@@ -116,6 +116,12 @@ x11 = [
 ## This is used to generate images for examples.
 __screenshot = []
 
+## Enable the [`egui_inspection`] plugin. When the `EGUI_INSPECTION` (or
+## `EGUI_INSPECTION_ADDR`) env var is set, eframe opens a TCP inspection port on startup that
+## lets an external tool (e.g. the `egui_mcp` server) read the AccessKit tree, inject input,
+## and capture screenshots. Off unless the env var is set; no-op on wasm.
+inspection = ["dep:egui_inspection", "accesskit"]
+
 [dependencies]
 egui = { workspace = true, default-features = false, features = ["bytemuck"] }
 
@@ -131,6 +137,7 @@ web-time.workspace = true
 # Optional dependencies
 
 egui_glow = { workspace = true, optional = true, default-features = false }
+egui_inspection = { workspace = true, optional = true, features = ["plugin"] }
 glow = { workspace = true, optional = true }
 ron = { workspace = true, optional = true, features = ["integer128"] }
 serde = { workspace = true, optional = true }

crates/eframe/src/lib.rs

@@ -209,6 +209,35 @@ pub use native::file_storage::storage_dir;
 #[cfg(not(target_arch = "wasm32"))]
 pub mod icon_data;
 
+// ----------------------------------------------------------------------------
+
+/// Attach an [`egui_inspection::InspectionPlugin`] to `ctx` when enabled via the environment.
+#[cfg(all(feature = "inspection", not(target_arch = "wasm32")))]
+pub(crate) fn maybe_attach_inspection_plugin(ctx: &egui::Context, label: Option<String>) {
+    match egui_inspection::attach_from_env(ctx, label) {
+        Ok(true) => log::info!("egui_inspection plugin attached"),
+        Ok(false) => {}
+        Err(err) => log::warn!("egui_inspection attach failed: {err}"),
+    }
+}
+
+/// Fallback for native builds without the `inspection` feature. Logs warning if inspection env
+/// var was set.
+#[cfg(all(
+    not(feature = "inspection"),
+    not(target_arch = "wasm32"),
+    any(feature = "glow", feature = "wgpu_no_default_features")
+))]
+pub(crate) fn maybe_attach_inspection_plugin(_ctx: &egui::Context, _label: Option<String>) {
+    if let Ok(value) = std::env::var("EGUI_INSPECTION")
+        && value != "0"
+        && value != "false"
+        && !value.is_empty()
+    {
+        log::warn!("Inspection env var set but app was compiled without eframe/inspection feature");
+    }
+}
+
 /// This is how you start a native (desktop) app.
 ///
 /// The first argument is name of your app, which is an identifier

crates/eframe/src/native/glow_integration.rs

@@ -299,6 +299,9 @@ impl<'app> GlowWinitApp<'app> {
         let app_creator = std::mem::take(&mut self.app_creator)
             .expect("Single-use AppCreator has unexpectedly already been taken");
 
+        #[cfg(all(not(feature = "inspection"), not(target_arch = "wasm32")))]
+        crate::maybe_attach_inspection_plugin(&integration.egui_ctx, Some(self.app_name.clone()));
+
         let app: Box<dyn 'app + App> = {
             // Use latest raw_window_handle for eframe compatibility
             use raw_window_handle::{HasDisplayHandle as _, HasWindowHandle as _};

crates/eframe/src/native/wgpu_integration.rs

@@ -291,6 +291,9 @@ impl<'app> WgpuWinitApp<'app> {
 
         let app_creator = std::mem::take(&mut self.app_creator)
             .expect("Single-use AppCreator has unexpectedly already been taken");
+
+        crate::maybe_attach_inspection_plugin(&egui_ctx, Some(self.app_name.clone()));
+
         let cc = CreationContext {
             egui_ctx: egui_ctx.clone(),
             integration_info: integration.frame.info().clone(),