# Bounded per-call scalar digest cache

SimulationDigest now reuses canonical encodings for integers (up to512 values), short strings and StringNames (separate type-tagged caches, up to256 values each, length<=128). Caches exist only for one canonical encoding call. Mutable containers and floats are not cached; the v1 byte format and digest contract are unchanged.

Final compatibility75 checks PASS, including reference-byte equality, dictionary order/type tags, depth/invalid values, long histories, cache saturation and changed inputs across calls. Synthetic5000-record history median129.949ms versus272.166ms in the original reference encoder; this ratio includes earlier optimizations and is not the gain from this patch alone.

Same production scenario diagnostic: x1 average63.616ms before /62.711ms after, x3 P95 234.396ms before /228.869ms after; digest average26.328ms before /25.983ms after. Single-run differences are small and may include timing noise; no substantial production performance improvement is established. Both remain outside the4ms/12ms budgets. Main performance defect remains open.

Evidence: digest-scalar-final.log, production-scalar-profile.json and production-scalar-profile.log under artifacts/facility-dimensions-2026-09-29. Next work should address the dominant complete snapshot/digest traversal and redundant infrastructure work without weakening replay correctness.