[arzafran]

What this does

Cmd+S (or View → Screenshot Mode) hides all the chrome — toolbar, tab strip, traffic lights — and floats the page as a rounded card inside an 8pt gutter of the window's glass, for clean captures. Modeled on the framed content look of remediate.ski / Arc. Cmd+S or Esc exits; Cmd+L and Cmd+T exit first since they need the chrome. Split screen stays split inside the frame.

Summary

• One self-contained block in bro_mac.mm + five small call sites: 173 insertions, 1 deletion, zero other files touched — first feature landed on the split structure, and it needed no new header surface
• Card radius derives from the concentric-corner rule (window radius minus gutter); the gutter reuses the existing glass-backdrop mechanism rather than adding a view
• Traffic lights capture their prior hidden state and restore it exactly on every exit path (fullscreen-safe)
• Both layout states derive absolutely from window bounds on every toggle — fixes a drift bug caught in live testing where each Cmd+S inset the content further (relative frame math compounding, amplified on viewport-reactive sites like darkroom.engineering)

Test plan

• Build clean, zero warnings
• AX: chrome elements 3→0→3 and traffic lights 3→0→3 across toggle cycles; menu checkmark tracks state; no crashes across rapid cycles
• Gutter measured by pixel scan: exactly 8pt on all four sides on a real page
• Geometric idempotence, instrumented: 14 toggle completions including mid-spring presses → exactly 1 distinct OFF frame and 1 distinct ON frame logged
• Human eyeball: enter the mode on darkroom.engineering — framed card look, repeated Cmd+S stable