Module Host 

Vine::Host

VineHost is the embedder-facing seam between Vine and its consumer runtime. Mountain (Tauri runtime), Air (background daemon), and any Rust-side Cocoon client implement this trait to expose the minimum surface Vine’s notification handlers need: application-state access, renderer event emission, and an IPCProvider handle for cross-channel re-entrancy. Handlers operate on &dyn VineHost so a single handler tree can be hosted against any embedder runtime.

Design notes

• ApplicationState returns &dyn ApplicationStateAccess. Vine treats application state as opaque; embedders decide what their state exposes via embedder-local sub-traits and downcasting.
• EmitToRenderer is the single entry point for “send a value to the workbench / Sky window.” Mountain wires it to tauri::WebviewWindow::emit; Air leaves it as a no-op (no renderer).
• IPCProvider returns Arc<dyn IPCProvider> for handlers that need to re-enter the IPC bus.

Stability

Adding methods to VineHost is a compatible change so long as every impl is updated in the same revision. Removing a method requires sweeping every consumer.

Traits

ApplicationStateAccess

Opaque application-state handle exposed to Vine handlers.

IPCProvider

Cross-channel IPC provider abstraction.

RendererEmitter

Cheap-to-clone renderer event sink.

VineHost

The embedder-facing seam between Vine and its host runtime.