Compositor-backed canvas contexts keep their transports tied to a single
Compositor connection. When that connection dies, the 2D backing
storage and WebGL GL objects disappear with it, but WebContent does not
surface the loss to canvas contexts or create fresh host contexts after
reconnect.
Track compositor loss through the WebContent connection, mark WebGL
contexts lost, dispatch the standard context events, and rebuild the
remote proxy when the page opts into restoration. For 2D canvas, queue
the canvas context loss steps, discard the dead backing storage, and
create new storage before firing contextrestored.
Canvas rendering is a major remaining path where WebContent directly
owns GPU-facing drawing state. Back 2D and WebGL canvas contexts with
remote Compositor transports, so WebContent talks to canvas surfaces
through IPC while the Compositor owns the rasterization resources.
This is a large step toward GPU sandboxing because canvas GPU work now
lives behind the Compositor boundary. It also gives OffscreenCanvas the
process-independent canvas plumbing that HTMLCanvasElement now uses,
making worker-owned canvases possible without another WebContent-local
rendering path.
Moving WebGL execution into the Compositor needs a serializable command
stream and a client-side proxy that can queue commands before sending
them over IPC. The existing generator metadata only described direct GL
wrappers, so generated code could not distinguish async commands from
sync calls or object factory methods.
This teaches the WebGL metadata and generators about command streams and
adds the unused LibWeb proxy/list types. No rendering behavior changes
yet; the later host wiring can build on these generated interfaces
without mixing the metadata churn into that commit.
