ADR 0004 — F# owns parsing, domain, validation, relationships and projection

Status: Accepted (constraint, §1.5)

Context

The current core is 1,335 lines of JavaScript whose defects are type-shaped: silently dropped keys, silently dropped edges, defaults indistinguishable from data.

Decision

F# implements discovery, parsing, the domain model, validation, relationship resolution, projections, index generation and tests. JavaScript/TypeScript is limited to the Limen kernel.

Evidence

OBSERVED: the three largest defects (708/756 mistyped, 6 edges, 735 fabricated dates) are all cases where a value silently became something else. Discriminated unions and explicit option make each of them unrepresentable rather than merely unlikely.

Alternatives

Keep JS with stricter tests — rejected: the failures are contract failures, and §1.5 sets F# as the constraint.

Consequences

.NET toolchain in CI (already present — the lifecycle CLI is F#/net8.0). WASM payload becomes a real concern (R7), mitigated by the static HTML baseline.

Reversibility

High cost. This is a foundational choice.