The onItems handler let unwrapWireItem's throw unwind through embind into the
C++ emitter — a bare pageerror, the whole batch lost, and flushDiff already
rebaselined so the dropped items could never be re-sent. Field-seen case:
Update PCB from Schematic emitted 67 changed entries, one an item-less board
envelope (pcbnew writes nothing for a standalone footprint field); all 67 were
dropped and two new footprints existed only on the syncing tab.
The conversion now skips un-resolvable entries per-entry (shared items-wire
fix), every conversion site warns via warnSkip, and the handler body is
wrapped so nothing escapes into the C++ caller again. The tests/web spec
drives the real serializer's empty envelope through onItems and holds that a
good entry batched with it still reaches the peer (proven red before the fix).
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_019daWLdW5xrRhjUvCUWoSAe
