v2.0.1 — cache_control_sticky (#33)

Adds cache_control_sticky — preserves historical cache_control marker positions across turns. CC drops previous marker positions (~43 bytes per) as it moves the marker to each new last user message, causing tail-of-message byte drift. This extension tracks up to 3 historical positions by stable message hash and reinstates them.

16 total cache-stability fixes. 160 tests. Credit: @deafsquad (PR #33).