F6 §6.5 PUC-1. Detects the baseline diff tab (original scheme cowriting-baseline,
modified == the doc) to close-and-reveal; else opens vscode.diff with an epoch
title. Live document on the right — editor state preserved by construction.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
F6 §6.2/§6.4, INV-18/INV-19. ensure/advance/pin capture buffer text, persist
via BaselineStore, refresh the open diff via onDidChange. Storage-unavailable
degrades to in-memory + one warning. toggle UX lands in SLICE-3.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Ben Stull