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>
Move the dependency-free, semver-versioned half of the plugin contract into a
standalone workspace crate `crates/ocs_plugin_api`:
- manifest types: PluginManifest, ApiVersion, API_VERSION
- ribbon vocabulary: CadModule trait + ToolDef/RibbonGroup/RibbonItem/IconKind/
ModuleEvent/StyleKey
The host re-exports them from `crate::plugin::manifest` and `crate::modules`, so
every existing call site is unchanged. The acadrust-typed runtime surface
(HostSession) stays in the host binary; lifting it behind a HostApi trait in the
same crate is the remaining phase-1b step.
Part of #100. Docs updated in docs/plugin-architecture.md.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Sebastian