Brummel
ae96c903a1
P2 entry: Stateful a b first-class type + !Mut effect + mut syntactic block, with uniqueness inference at the boundary. Motivated by the 2026-05-15 myc-vs-AILang analysis showing AILang's pure-only model cannot match the stateful-closure-plus-pipe idiom for online / streaming workloads (rolling indicators, IIR filters, online stats). The signature-as-contract thesis is *better* served by explicit Stateful + !Mut annotations than by myc's implicit closure-mutation: time-identity becomes visible in signatures without body inspection. Decision 10's no-shared-mutable-refs forbids aliased mutation; it does not forbid uniqueness-bounded mutation, which is the Lean 4 / Roc / Haskell-ST / Koka layered-design pattern. Ten blockers identified, from effect-handler infrastructure (the first non-IO/non-Diverge effect) through uniqueness inference for var captures, mutable-array primitive, runST-equivalent escape discharge, Form-A surface design, codegen for mutable struct-field writes, escape analysis for var/ref values, Decision-10 amendment vs. Decision 12, streaming bench corpus, and LLM-utility fieldtest.