Demo 3: Tumble Tower — Stage 3 physics (sleeping + stack stability) #234
Description
Goal: implement sleeping and long-run stack stability deterministically.
Why
- Long-run drift is where many physics engines desync across machines.
Scope
- Sleep thresholds and wake rules.
- Deterministic island building and solver ordering.
- Stability tests that run for many ticks and assert no divergence.
Acceptance criteria
- A multi-thousand-tick test run stays deterministic and stable.
- No platform-dependent iteration order affects sleep/wake transitions.