forked from 1b-agent/opencadstudio-upstream
Plugins targeted the host's concrete HostSession type. Add a HostApi trait in ocs_plugin_api behind an optional `host` feature (the only thing that pulls acadrust, so the core crate stays dependency-free). HostSession implements it and BuiltinPlugin::dispatch now takes `&mut dyn HostApi`, so an out-of-tree add-on compiles against the contract crate alone. Per-tab plugin state is reached through object-safe plugin_state* helpers. Completes the phase-1 host-surface extraction in the #100 epic. Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>