Modals now composite over a dimmed copy of the screen behind them instead of an opaque
scrim, so the transcript stays faintly visible around a modal (opencode-style). center()
stashes the frame's base (View sets m.lastBase), strips+dims it to a faint scrim, and
splices the modal box over it (ANSI-aware via ansi.Truncate/TruncateLeft so the side
margins keep the dimmed content). An idempotence guard passes an already-full-screen
modal through unchanged, so the existing double-center builders don't get re-dimmed.
Geometry tests assert the composite still fills the screen exactly.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
kami
26621567ac