fix(tauri): pump the macOS main run loop so WebKit schedules work on a headless runner (#540)

.github/workflows/_ci-package.reusable.yml

@@ -244,6 +244,19 @@ jobs:
       # Run package tests using test-package.ts script
       # All apps are built in isolated environments (Electron always, Tauri if not skipBuild)
       # Tauri uses skipBuild to copy pre-built binaries from separate build jobs
+      # #540 investigation (temporary): capture the WebKit unified log during the macOS Tauri package
+      # test so we can classify its intermittent failure — same idle-run-loop stall class as the e2e
+      # DirectEval flake, or a different flake (e.g. session-create/teardown). Scoped to macOS + tauri.
+      - name: 🩺 Start WebKit log stream [Package]
+        if: runner.os == 'macOS' && inputs.service == 'tauri'
+        shell: bash
+        run: |
+          mkdir -p "$GITHUB_WORKSPACE/logs/package-tests"
+          /usr/bin/log stream --level debug --style compact \
+            --predicate 'subsystem == "com.apple.WebKit" OR process == "com.apple.WebKit.WebContent" OR process == "com.apple.WebKit.GPU"' \
+            > "$GITHUB_WORKSPACE/logs/package-tests/webkit-log.log" 2>&1 &
+          echo $! > /tmp/webkit-log-pkg.pid
+
       - name: 🧪 Execute Package Tests
         id: package-tests
         # WebView2 Runtime 150 dropped the CDP --remote-debugging-port for elevated
@@ -315,6 +328,26 @@ jobs:
               ;;
           esac
 
+      - name: 🩺 Collect WebKit diagnostics [Package]
+        if: always() && runner.os == 'macOS' && inputs.service == 'tauri'
+        shell: bash
+        run: |
+          if [ -f /tmp/webkit-log-pkg.pid ]; then
+            kill "$(cat /tmp/webkit-log-pkg.pid)" 2>/dev/null || true
+          fi
+          mkdir -p "$GITHUB_WORKSPACE/logs/package-tests"
+          shopt -s nullglob
+          for dir in "$HOME/Library/Logs/DiagnosticReports" "/Library/Logs/DiagnosticReports"; do
+            for f in "$dir"/*.ips "$dir"/*.crash; do
+              case "$(basename "$f")" in
+                *tauri*|*WebContent*|*WebKit*|*GPU*|*Networking*)
+                  sudo -n cp "$f" "$GITHUB_WORKSPACE/logs/package-tests/$(basename "$f").log" 2>/dev/null \
+                    || cp "$f" "$GITHUB_WORKSPACE/logs/package-tests/$(basename "$f").log" 2>/dev/null || true ;;
+              esac
+            done
+          done
+          echo "package diag:"; ls -la "$GITHUB_WORKSPACE/logs/package-tests" 2>/dev/null || true
+
       - name: ⚠️ Note allowed WebView2-150 Windows failure
         if: always() && (inputs.service == 'tauri' || inputs.service == 'electrobun') && runner.os == 'Windows' && steps.package-tests.outcome == 'failure'
         shell: bash

packages/tauri-plugin-webdriver/Cargo.toml

@@ -42,7 +42,7 @@ block2 = "0.6"
 
 [target."cfg(target_os = \"macos\")".dependencies.objc2-foundation]
 version = "0.3"
-features = [ "NSString", "NSData", "NSError", "NSArray", "NSDictionary" ]
+features = [ "NSString", "NSData", "NSError", "NSArray", "NSDictionary", "NSTimer", "NSRunLoop", "NSDate", "block2" ]
 
 [target."cfg(target_os = \"macos\")".dependencies.objc2-app-kit]
 version = "0.3"

packages/tauri-plugin-webdriver/src/platform/macos.rs

@@ -1,3 +1,4 @@
+use std::ptr::NonNull;
 use std::sync::Arc;
 
 use async_trait::async_trait;
@@ -8,7 +9,10 @@ use objc2::rc::Retained;
 use objc2::runtime::{AnyObject, ProtocolObject};
 use objc2::{define_class, msg_send, DefinedClass, MainThreadMarker, MainThreadOnly};
 use objc2_app_kit::{NSBitmapImageFileType, NSBitmapImageRep, NSImage};
-use objc2_foundation::{NSData, NSDictionary, NSError, NSObject, NSObjectProtocol, NSString};
+use objc2_foundation::{
+    NSData, NSDictionary, NSError, NSObject, NSObjectProtocol, NSRunLoop, NSRunLoopCommonModes,
+    NSString, NSTimer,
+};
 use objc2_web_kit::{
     WKContentWorld, WKFrameInfo, WKPDFConfiguration, WKScriptMessage, WKScriptMessageHandler,
     WKSnapshotConfiguration, WKUIDelegate, WKUserContentController, WKWebView,
@@ -89,10 +93,36 @@ pub fn register_webview_handlers<R: Runtime>(webview: &tauri::Webview<R>) {
             .userContentController()
             .addScriptMessageHandler_name(&eval_proto, &NSString::from_str("wdioEvalResult"));
 
+        start_runloop_pump();
+
         tracing::debug!("Registered UI delegate + eval message handler for webview");
     });
 }
 
+/// Keep the app's main run loop waking on a headless/off-screen runner.
+///
+/// With no display, the app parks in `-[NSApplication run]` waiting for events, so WebKit doesn't
+/// promptly service WebContent's URL-scheme resource requests (page-load subresources) or eval
+/// dispatches — a DirectEval can then stall for tens of seconds and time out. A low-frequency no-op
+/// timer in the run loop's common modes forces it to wake, draining that pending work each tick; the
+/// interval only bounds worst-case servicing latency (well under the command timeout), so it is kept
+/// coarse to minimise idle wakeups. Harmless with a real display (the loop already pumps
+/// continuously). This plugin ships only in WebDriver-automation builds. Scheduled once.
+/// https://github.com/webdriverio/desktop-mobile/issues/540
+///
+/// # Safety
+/// Must be called on the main thread (schedules on the main run loop).
+unsafe fn start_runloop_pump() {
+    use std::sync::Once;
+    static PUMP: Once = Once::new();
+    PUMP.call_once(|| {
+        let block = RcBlock::new(|_timer: NonNull<NSTimer>| {});
+        let timer = NSTimer::timerWithTimeInterval_repeats_block(0.05, true, &block);
+        NSRunLoop::mainRunLoop().addTimer_forMode(&timer, NSRunLoopCommonModes);
+        tracing::debug!("Started macOS main run-loop pump for headless WebKit scheduling");
+    });
+}
+
 #[async_trait]
 impl<R: Runtime + 'static> PlatformExecutor<R> for MacOSExecutor<R> {
     // =========================================================================