While a line is on the banner the whole tree is paused, which freezes the
fleet, the enemies and GameState's own production and wave clocks, and stops
input reaching any node but the banner. So a press while a dialog is up
acknowledges it and does nothing else - it cannot also steer the fleet or
open a menu on the way through.
The pause is owned by NarrationBanner rather than by its callers: the thing
that must not get out of step is "a line is showing" and "the game is
stopped", and the banner is the only code that knows the first. It releases
on the last line, on clear(), and on leaving the tree - a scene swapped out
mid-line must not leave the game stopped with nothing left to start it.
Two consequences worth naming. A beat's deadline in the prologue is now game
time, so it can no longer run out from under an unread line; it remains the
way past a beat the player will not finish. And "the prologue leaves you
movement and nothing else" was applied by _process on the first frame, which
no longer comes - the prologue opens ON a dialog - so BuildController and
WorldMap apply it at _ready too.
