Behaviour for key input handlers in the focus stack.

Each handler module decides whether to consume a key press or pass it through to the next handler in the stack. Handlers self-gate: they return {:passthrough, state} when their feature is inactive (e.g., the picker handler passes through when no picker is open).

State contract

Input handlers receive a handler_state() which is currently MingaEditor.State.t(). This type alias is the narrowing point: as the shell independence refactor progresses, it will be replaced by a focused contract struct containing only what handlers need (workspace, capabilities, layout, shell_state). Handlers should avoid accessing fields outside these four to prepare for that narrowing.

Implementing a handler

defmodule MyHandler do
  @behaviour MingaEditor.Input.Handler

  @impl true
  def handle_key(state, _codepoint, _modifiers) do
    if my_feature_active?(state) do
      {:handled, do_something(state)}
    else
      {:passthrough, state}
    end
  end
end