Drive a Mach-O inspection end-to-end: alice (SwiftUI) attaches, runs REPL probes, pins to notebook, shares the lab; bob (LumaGtk via DYLD_INSERT'd frida-gadget) joins and verifies notebook entries, sessions, REPL cells, and tracer events propagate. Includes the observed.c fixture and a Frida agent for GTK widget traversal.