Function translate_mode_keymap 

pub fn translate_mode_keymap(
    handle: &KeymapHandle,
    mode_id: ModeId,
    mode: &Arc<dyn DynMode>,
    command_registry: &CommandRegistry,
)

Translate one mode’s Keymap contribution and push it as a layer. Symmetric with translate_mode_keymaps but scoped to a single mode — the entry point a future plugin host or dynamic ModeRegistry::register call site uses to hot-attach a newly-loaded mode without re-walking the full registry.

Today no production caller exists for the dynamic path (plugins are post-1.0); the helper is provided here so the translation logic has one shape rather than two drift-prone copies.