Define canonical custom-game-settings JSON ingestion contract

[Teakowa]

Goal

Define the canonical workshop-rs ingestion contract for custom-game-settings JSON/lobby imports so source-language consumers can reach the canonical settings carrier, validation, and emitter without implementing private settings semantics.

Context

del-rs Issue #32 has corpus evidence for import "customGameSettings.json" and .lobby project imports. Released workshop-rs 0.1.1 exposes a canonical settings::Settings tree and settings emission, but no public contract for converting the JSON/lobby carrier used by source-language projects into that tree with stable diagnostics and provenance.

Scope

• Define accepted JSON/lobby input shape, merge semantics, canonical path/key validation, and locale handling.
• Define structured diagnostics for malformed input, unknown settings paths, wrong value kinds, and missing mappings.
• Preserve source-file and member provenance through the carrier and emission boundary.
• Add provenance-linked fixtures and parser/carrier/emitter round-trip evidence.

Non-goals

• DEL project loading or source-language import resolution.
• A DEL-local settings schema, table, locale map, or emitter.
• Presentation-only compiler options.

Acceptance criteria

• A reviewed public workshop-rs API/contract accepts or rejects the supported JSON/lobby form deterministically.
• Canonical settings validation/emission remains owned by workshop-rs.
• del-rs and other consumers can integrate through the public contract without copying settings data or semantics.

Evidence

• del-rs Define canonical embedded Workshop and comment preservation contract #32 and Draft PR Streamline README and centralize documentation navigation #42: feat(project): discover ds.toml entry points del-rs#42
• Released workshop-rs 0.1.1 exposes settings::Settings but not source-project JSON ingestion.