A measurement child that already holds a value when the pumpingStation
registers it (e.g. a once:true inject that fired during startup before the
parent subscribed) was never surfaced — the emitter only delivers future
updates. _subscribeMeasurement now seeds from the child's current sample via
getLaggedSample(0), so late subscribers pick up present state. This is what
makes a measured upstream inflow register as inflow on a clean startup.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
