On-glass caught a runtime panic the box compile couldn't: `VirtualDisplayManager used before a
backend initialised it`. Step 3 put the preempt (`vdm().begin_idd_setup`) BEFORE
`vdisplay::open` in virtual_stream, but vdisplay::open is what constructs the backend that calls
manager::init() — so vdm() was reached before init and panicked on the first IDD-push session.
(The old IDD_SETUP_LOCK/IDD_SESSION_STOP globals needed no init, so the prior ordering was fine.)
Fix: open the backend first (it does no monitor work — just constructs the marker + opens the
control device, initialising the manager), THEN run the preempt, THEN build the pipeline (which
creates the monitor). The preempt still precedes this session's monitor creation, so the
semantics are unchanged. Validates why §2.5 needs the on-glass gate, not just the compile.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
enricobuehler
683c81be03