Context
The general monoid/group EchoAggregation landed in echo-types (proofs/agda/EchoAggregation.agda, #175). EchoTypes.jl (hyperpolymath/EchoTypes.jl) is the executable Julia companion that mirrors echo-types' finite-domain shadow and falsifies-by-counterexample on concrete data — the Agda stays the source of truth. The EchoAggregation result is not yet mirrored there.
A paste-ready handoff prompt is committed at docs/handoffs/ECHOTYPES-JL-MIRROR-NEXT-CLAUDE-2026-06-27.adoc (PR #279, merged). Open a fresh session in an EchoTypes.jl checkout and paste the block under [#the-prompt].
Scope note
The work happens in the separate EchoTypes.jl repo, which is outside the current agent MCP repo-scope (cf. #263's new ordinal repo). This issue tracks the disposition; echo-types only holds the spec being mirrored.
What to build (Julia, executable, property-tested)
- A
Monoid struct (carrier / ε / ⊕) + ⊕fold over a Vector, with a property test of the homomorphism law ⊕fold(m, vcat(xs, ys)) == ⊕fold(m, xs) ⊕ ⊕fold(m, ys) on random finite data.
- Instances
sumMonoid / countMonoid / maxMonoid over Int and minMonoid over Union{Nothing,Int} (nothing = ∞); property-test each one's identity + associativity laws.
aggregate_values(agg, kvs) + a test of aggregation-as-fold.pairsum((a,b)) = a + b with tests: pairsum_is_fold (equals the sumMonoid fold of [a,b]), non-injectivity, and no-canonical-disaggregation (no raise satisfies raise ∘ pairsum == id — two pairs share a total).
Honest scope (preserve — do not overclaim)
aggregation-as-fold is the fold's monoid-homomorphism law, NOT SQL GROUP-BY operational semantics.avg is deliberately absent (not a monoid) — express as sum / count.- no-canonical-disaggregation refutes a section (a LEFT inverse), not the existence of some representative choice. Do not restate it as a failed surjection (the aggregate map is onto).
Acceptance
Filed at owner request to capture remaining work on the master scheduler.
Context
The general monoid/group
EchoAggregationlanded in echo-types (proofs/agda/EchoAggregation.agda, #175).EchoTypes.jl(hyperpolymath/EchoTypes.jl) is the executable Julia companion that mirrors echo-types' finite-domain shadow and falsifies-by-counterexample on concrete data — the Agda stays the source of truth. TheEchoAggregationresult is not yet mirrored there.A paste-ready handoff prompt is committed at
docs/handoffs/ECHOTYPES-JL-MIRROR-NEXT-CLAUDE-2026-06-27.adoc(PR #279, merged). Open a fresh session in anEchoTypes.jlcheckout and paste the block under[#the-prompt].Scope note
The work happens in the separate
EchoTypes.jlrepo, which is outside the current agent MCP repo-scope (cf. #263's new ordinal repo). This issue tracks the disposition; echo-types only holds the spec being mirrored.What to build (Julia, executable, property-tested)
Monoidstruct (carrier /ε/⊕) +⊕foldover aVector, with a property test of the homomorphism law⊕fold(m, vcat(xs, ys)) == ⊕fold(m, xs) ⊕ ⊕fold(m, ys)on random finite data.sumMonoid/countMonoid/maxMonoidoverIntandminMonoidoverUnion{Nothing,Int}(nothing= ∞); property-test each one's identity + associativity laws.aggregate_values(agg, kvs)+ a test ofaggregation-as-fold.pairsum((a,b)) = a + bwith tests:pairsum_is_fold(equals thesumMonoidfold of[a,b]), non-injectivity, and no-canonical-disaggregation (noraisesatisfiesraise ∘ pairsum == id— two pairs share a total).Honest scope (preserve — do not overclaim)
aggregation-as-foldis the fold's monoid-homomorphism law, NOT SQL GROUP-BY operational semantics.avgis deliberately absent (not a monoid) — express assum / count.Acceptance
EchoAggregationmodule +@testsetadded to EchoTypes.jl;Pkg.test()green.pairsumtrio (is-fold / non-injective / no-canonical-disaggregation) witnessed on concrete collisions.claude/ecstatic-wright-OBEvx, cross-referencing echo-types Add EchoAggregation module — Monoid + GroupAggregator carriers for SQL aggregation-as-fold (consumer: affinescript db-theory #3) #175.Filed at owner request to capture remaining work on the master scheduler.