Proposal: Investigate HTML-in-Canvas (CanvasDrawElement) support via Chromium/CEF flags

## Summary

This issue proposes exploring support for the experimental *HTML-in-Canvas* API (CanvasDrawElement) from the [Web Incubator Community Group](https://wicg.io/) in Kurogane via Chromium/CEF feature flags.

Rather than committing to adoption, the goal is to evaluate feasibility, performance impact and alignment with Kurogane’s rendering-focused use cases.

## Background

The HTML-in-Canvas proposal (incubated in WICG) introduces APIs that allow rendering DOM elements directly into `` contexts, including:

* `drawElementImage()`
* `layoutsubtree` attribute
* `canvas.onpaint` event
* `captureElementImage()` for OffscreenCanvas workflows

The feature is currently:

* Implemented behind a Chromium flag (`canvas-draw-element`)
* Available in experimental builds (e.g. Chromium Canary)
* Not standardized and subject to change

Reference:
[https://github.com/WICG/html-in-canvas](https://github.com/WICG/html-in-canvas)

## Why is this relevant?

Kurogane is explicitly designed for:

* High-frequency rendering workloads (WebGL, Canvas, WASM)
* Direct control over the Chromium rendering pipeline
* Cross-platform GPU consistency (especially on Linux)

HTML-in-Canvas aligns strongly with these goals by enabling:

* Rendering complex, styled DOM content into GPU-backed canvas contexts
* More consistent accessibility vs traditional canvas text rendering
* New hybrid rendering patterns (DOM -> GPU surface -> 2D/3D composition)
* Potential use in:

* In-app UI layers
* Game-like interfaces
* Visualization overlays
* Media export pipelines

## Proposal

Investigate whether Kurogane can expose this feature **optionally** via Chromium/CEF flags.

### Exploration areas

1. **CEF / Chromium compatibility**

* Identify the Chromium version where `canvas-draw-element` exists
* Map to corresponding CEF version(s)
* Verify whether the feature is compiled into CEF builds

2. **Flag support**

* Test enabling via:

```
chrome://flags/#canvas-draw-element
```

Read more over https://html-in-canvas.dev/docs/browser-support/

3. **Runtime behavior**

* Validate basic demos from the WICG repo
* Test:

* 2D canvas usage
* OffscreenCanvas + worker flows
* WebGL/WebGPU interop (if available)

4. **Performance characteristics**

* Compare against:

* Manual canvas text/layout rendering
* DOM overlays
* Measure:

* Frame consistency
* GPU utilization
* Latency

5. **Platform consistency**

* Especially Linux vs Windows behavior
* Any compositor / vsync interactions

## Non-goals

* Shipping this as a stable or default feature
* Building abstractions around the API (yet)
* Guaranteeing long-term support

This is strictly exploratory.

## Risks

* API is unstable
* Potential mismatch between Chromium and CEF exposure
* Behavior may change or be removed upstream
* Additional maintenance burden if relied upon too early

## Potential outcome

If viable, Kurogane could:

* Expose experimental rendering capabilities ahead of mainstream frameworks
* Enable advanced GPU/DOM hybrid rendering patterns
* Further differentiate from WebView-based approaches and higher-level runtimes

## Next steps

* [x] Identify minimum Chromium + CEF version
* [x] Attempt flag enablement in a dev build
* [x] Run WICG demos inside Kurogane
* [ ] Document findings (working / broken / missing)

Le ticket est une proposition d'exploration. Commencez par vérifier le dépôt WICG lié et la documentation html-in-canvas.dev pour la prise en charge par les navigateurs. Identifiez les versions de Chromium et CEF qui incluent le drapeau 'canvas-draw-element'. Exécutez les démos WICG dans une version de développement Kurogane pour voir si la fonctionnalité fonctionne. Documentez toutes les découvertes sur la compatibilité, les performances et la cohérence entre les plateformes.

Rédigé par le modèle d'indexation à partir du texte de l'issue.