Add engine_projection_mode as a distinct proto/wire/registry field
that carries pure V2 engine-derived local projection mode from VS
to master. Reads ONLY from CoreProjection — no ad-hoc fallback.
Separate from existing VolumeMode: EngineProjectionMode is VS-local
V2 engine truth, VolumeMode is the existing field that conflates V2
and V1 paths. Both exist during transition; only EngineProjectionMode
is V2-authoritative.
Clears stale value on primary turnover: when a newly promoted primary
heartbeats without the field, the old primary's projection is not
preserved (prevents synthetic master-side truth).
5 focused tests: propagation, distinctness (hard assertion), backward
compat preservation, turnover-clears, turnover-with-field.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
pingqiuandClaude Opus 4.6
85dad8e0c9