Checkpoint
One last thing before we move on. Same surface as a write step — but the lesson doesn't complete until this passes.
Stage 4, implemented: the running server holds v4 in MODEL; promote("churn", 5) flips the registry; show the server STILL serves v4; then implement reload_model() (a global MODEL refresh from load_production) and show it now serves v5. Print the three states: "serving v 4", "after promote, still serving v 4", "after reload, serving v 5". You just chose live-reload over restart — note that the tradeoff is added server complexity for zero-downtime model swaps.