fsllisted

# FSL Core — Language, Verifier, and Repair Loop FSL is a language not present in training data. **Do not write from memory; follow this guide and reference.md.** Read `reference.md` in the same directory for syntax details, the full expression catalog, and the idiom collection (always read it before writing a spec). Within the repository, `docs/LANGUAGE.md` is the complete reference and `specs/*.fsl` are working examples (cart_v1 is the basic form, mutex_queue is Seq+leadsTo, and bank_* are refinement+compose examples). **What makes FSL different — connectivity, not just per-spec checking.** Classic formal methods describe one hard spot and verify it in isolation (the "island" model). FSL's distinctive value is stitching business ⊒ requirements ⊒ design together with refinement, so **cross-layer alignment (traceability) is itself checkable** — the dominant question moves from "is this spec correct?" to "do these layers still mean the same thing?" Verify a one-off hard spot with a single spec; when the value is keeping the layers aligned, reach for the connected workflow (`fslc chain`) and the `fsl-delivery` skill. The two workflows are juxtaposed below. ## First, decide whether FSL fits (self-check) Before reaching for a spec, run this filter. FSL is not for every task, and forcing it where it does not fit wastes effort and produces hollow specs. **This is a judgment aid, not a gate**: when neither payoff below applies, say so and recommend the better tool (usually ordin