The messages between a Craft app's web build and the page that hosts it
(ready, host, open, save, saved, dirty, failed, handoff, handoff-done),
as proposed on #358. The contract part (message kinds, the version, the
?host=parent / data-host="page" switch, file-name clean-up) builds
everywhere and is tested natively; the web module (wasm32) is the bridge
an app's web shell calls: same-origin parent only, files as bytes or a
Blob without copying, saves as a transferred ArrayBuffer, dirty repeats
suppressed. Compatible with the bridges shipped before it: optional
fields stay optional, and a host treats an unknown ready.version as 1.
Helen Kwok