Mirrors capture: when membership is non-empty and the project has no .rpp,
Main_SaveProject(proj, true) prompts Save-As before persisting; cancel leaves
the in-session tag state intact and warns via console.
Design View actions mutated the model but never pushed it to ext-state, so
tags/active-mode/snapshots were lost on save/reopen. Add persistViewState()
(saveToActiveProject) after each handler's apply/reapply.
Register toggle/activate/tag/untag/show-both actions driving the D2
shell and D3 model; reapply saved active mode on project load via a
persist load-signal seam. Shared guidString helper; pure nextModeId
unit-tested.
daniel