Dioxus embedded driver: blank screenshots; no alerts, print, frames or shadow roots #721

Problem

The Dioxus embedded driver runs every command as JavaScript in the page and has no native handle to the webview. Compared with Tauri's embedded driver (tauri-plugin-webdriver), it's missing:

Running through the page also means anything that stops the page's JavaScript stalls the driver. That includes a native alert(), a long-running script, and a hidden window whose timers get throttled.

The silent blank screenshot is the worst of these: saveScreenshot(), screenshots taken on test failure and visual comparison all get an empty image without any error. The docs claimed screenshots work on every platform until #703. e2e/test/dioxus/visual.spec.ts doesn't catch it: it calls saveScreen, which saves a baseline without comparing anything, so it passes on a blank image.

Fix

• Screenshots, print and alerts: these need the native webview handle, the same prerequisite as Dioxus: embedded driver keys arrive isTrusted:false on Windows/WebView2 #720. With it, port Tauri's code:
  • WebView2: CapturePreview, PrintToPdf, ScriptDialogOpening.
  • WKWebView: takeSnapshot, createPDF.
  • WebKitGTK: snapshot.
• Frames and shadow roots: Tauri does frames in page JavaScript, so both may port without the handle.
• In the meantime: a screenshot should return an error, not a blank image. Make the visual spec compare against a committed baseline (checkScreen), so it fails on a blank image.

Related

• Dioxus: embedded driver keys arrive isTrusted:false on Windows/WebView2 #720: trusted keys on Windows, which needs the same native handle.
• Dioxus 'external' provider: enable it on Windows and Linux #713: the external provider gives all of this on Windows. Whether embedded can catch up decides whether external is worth building.