iris: turn the phone bind-group-layout crash into a diagnostic, drop force-gles from phone builds

UiRenderNode::new used to let a wgpu validation error reach the default
uncaptured-error handler and panic, which is what aborted the P0 bench APK
on Iris's phone in AndroidRenderer::new with only "wgpu error: Validation
Error" surviving into the truncated crash report. It now wraps creation in
wgpu error scopes and returns Result<Self, String>; the Android backend
turns a failure into the adapter's identity, the limits/downlevel flags a
layout validates against, and wgpu's own error chain, logged as one logcat
line and shown on screen (IrisView.showRendererError) instead of crashing.

Auditing every bind-group-layout entry against wgpu-core's own validation
source names the likely cause: masks_layout's move_offsets storage buffer
is visible to the vertex stage, which Vulkan grants unconditionally but
GLES gates on the driver's own vertex-stage SSBO support -- and the
delivered APK was built with force-gles, a flag meant only to force the
*emulator* onto GLES for one frame-time measurement, that build-apk.sh's
default feature list applied to every arm64 build regardless of target.
Its default no longer includes force-gles.

Testing the diagnostic (by inducing an artificial validation error) also
found and fixed a real reentrancy bug: calling Activity.setContentView
synchronously from inside a ViewPeer callback re-enters the same peer's
RefCell borrow through onFocusChanged, aborting with "RefCell already
borrowed". Deferred through the same push_dynamic_deferred_callback
mechanism raise_if_enabled already uses.

Full audit, verification, and the named hypothesis are in RUST.md's P0
box ("iris bench crash on the phone, 2026-09-06"); the API change is in
IRIS.md. Nobody on this session has the phone, so this is unconfirmed
against real hardware -- the point of (1) is that the next run says so
either way.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

iris/android-app/Cargo.lock

@@ -1785,6 +1785,7 @@ dependencies = [
  "fxhash",
  "image",
  "parley",
+ "pollster",
  "swash",
  "wgpu",
 ]

iris/android-app/app/src/main/java/dev/iris/android/demo/IrisView.java

@@ -1,6 +1,10 @@
 package dev.iris.android.demo;
 
+import android.app.Activity;
 import android.content.Context;
+import android.view.Gravity;
+import android.widget.ScrollView;
+import android.widget.TextView;
 
 import org.linebender.android.rustview.RustView;
 
@@ -33,4 +37,35 @@ public final class IrisView extends RustView {
         unregisterInsetsNative(mViewPeer);
         super.onDetachedFromWindow();
     }
+
+    /**
+     * Called from the Rust side (iris/src/android/view.rs's
+     * `show_renderer_error`) when `AndroidRenderer::new` fails instead of
+     * drawing -- an ordinary instance method rather than a `native` one,
+     * since this call is Rust reaching into Java rather than the other
+     * direction. Replaces the whole activity content with plain,
+     * selectable, scrollable text rather than leaving the last frame (or a
+     * blank surface) on screen with no way to report what happened:
+     * UI_RULES.md's "a failure is reported where it happened, and says
+     * what to do next." No dialog and no styling beyond what is needed to
+     * read and copy the text -- this path exists for exactly the crash it
+     * replaces, so it must not depend on anything that could itself fail
+     * to render.
+     */
+    void showRendererError(String report) {
+        Context context = getContext();
+        if (!(context instanceof Activity)) {
+            return;
+        }
+        Activity activity = (Activity) context;
+        TextView text = new TextView(activity);
+        text.setText(report);
+        text.setTextIsSelectable(true);
+        text.setGravity(Gravity.TOP | Gravity.START);
+        int pad = (int) (16 * activity.getResources().getDisplayMetrics().density);
+        text.setPadding(pad, pad, pad, pad);
+        ScrollView scroll = new ScrollView(activity);
+        scroll.addView(text);
+        activity.setContentView(scroll);
+    }
 }

iris/android-app/build-apk.sh

@@ -12,13 +12,25 @@
 #   emulator stays on debug" rule -- pass `release` explicitly for a phone
 #   build). --abi defaults to arm64-v8a (a phone/real device); pass
 #   x86_64 for this checkout's own AVD. --features defaults to
-#   "transcript-screen force-gles bench", P0's exact combination.
+#   "transcript-screen bench" -- deliberately *without* `force-gles`, unlike
+#   an earlier version of this default. `force-gles` (`iris/Cargo.toml`'s
+#   own doc) exists only to force the emulator off its default software
+#   Vulkan and onto GLES for one specific measurement (RUST.md's I5, "Where
+#   iris's frame time goes") -- it was never meant to reach a real device,
+#   but this script's old default put it in every arm64 build regardless,
+#   so the P0 bench APK delivered to Iris's phone forced GLES there too.
+#   That is the named hypothesis in RUST.md's P0 box ("iris bench crash on
+#   the phone, 2026-09-06"): a real Vulkan driver is what a phone should
+#   run, and GLES is the backend the same box's own SwiftShader finding
+#   already flagged as the fragile one for this shader's storage buffers.
+#   Pass `--features "transcript-screen force-gles bench"` explicitly for
+#   an emulator backend-isolation run; never for a build meant for a phone.
 set -eu
 cd "$(dirname "$0")"
 
 BUILD_TYPE="debug"
 ABI="arm64-v8a"
-FEATURES="transcript-screen force-gles bench"
+FEATURES="transcript-screen bench"
 case "${1:-}" in
     debug|release) BUILD_TYPE="$1"; shift ;;
 esac