pub fn install(
ctx: &ModeContext,
buffer: BufferId,
mode_id: &str,
) -> Option<(MagitHeaderlineHandle, HeaderlineRegistration)>Expand description
Build a headerline for buffer and register it as a virtual-row
provider. Returns the handle the mode keeps (to set fields as its
data lands) and the registration whose drop tears the row down.
Synchronous and cheap — call it above the first .await in
on_activate, alongside the state publish, so the row exists (and
stays hidden, rendering None) from the moment the buffer opens.
Returns None only in a harness with no virtual-row registrar.