Complete Milestone 6 acceptance and runtime cleanup (#74)

docs/LEGACY_INSTABILITY_AUDIT.md

@@ -2,6 +2,13 @@
 
 This is the behavior contract used to implement Milestone 6. It is pinned to [Mystcraft Legacy source at commit `9bc8ddc`](https://github.com/Mystcraft/Mystcraft-Legacy/tree/9bc8ddc061845df0cd5ea47f4fdef773cff786ae). Values below are source defaults, not a claim that every historical config or server used them. Rivencraft now persists frozen writing-instability scores and provider plans and runs the implemented providers through a bounded, Age-scoped scheduler. The audit remains authoritative for Legacy behavior; the linked runtime documents identify modern adaptations and remaining gaps.
 
+Current new Age plans (schema 4) also implement Legacy's ordered period/phase
+consumption and +100 for each modifier kind still pending after the last
+celestial page. Repeated same-kind pages combine before consumption rather
+than charging a replacement penalty. Older plans keep their saved score and
+earlier stage-sorted time interpretation. The older #65 implementation notes
+below are historical where they mention a generic misplaced-modifier cost.
+
 ## Score, grammar, and selection in Legacy
 
 Legacy's [`AgeController`](https://github.com/Mystcraft/Mystcraft-Legacy/blob/9bc8ddc061845df0cd5ea47f4fdef773cff786ae/src/main/java/com/xcompwiz/mystcraft/world/AgeController.java) calculates `debug + symbol + block + book/base + bonus`, then applies difficulty 0/1/2/3 multipliers of 0.25/0.5/1/1.75. Global instability is enabled by default; an Age also has its own enable flag. The unmodified score is not simply “number of bad pages.” Block profiling may delay a usable score: `blockinstability` is null until **more than** 400 Age chunks are profiled, and `getInstabilityScore()` returns zero until then. It is recalculated after additional profiling. [`ChunkProfiler`](https://github.com/Mystcraft/Mystcraft-Legacy/blob/9bc8ddc061845df0cd5ea47f4fdef773cff786ae/src/main/java/com/xcompwiz/mystcraft/world/profiling/ChunkProfiler.java) compares watched block abundance with a baseline, subtracting only positive excess above each baseline. The baseline is profiled or read from balance config; [`InstabilityDataCalculator`](https://github.com/Mystcraft/Mystcraft-Legacy/blob/9bc8ddc061845df0cd5ea47f4fdef773cff786ae/src/main/java/com/xcompwiz/mystcraft/world/profiling/InstabilityDataCalculator.java) sets its default tolerance to 1.05, and default `useconfigs=false`. Rivencraft's later [bounded implementation](LIVE_BLOCK_INSTABILITY.md) retains the threshold and tolerance, but not Legacy's spatial accessibility formula or unbounded profiling.