oneOf ambiguities in schema cause validation to always fail for effects and precomp assets #84
Description
hit a few oneOf issues in the schema while building a validator. three separate bugs, all related:
1. effect-values/no-value matches everything
no-value is defined as {"type": "object"} which matches any object — including typed effect values like slider, checkbox, etc. so in the all-effect-values oneOf, every effect value matches both its own type AND no-value, which violates the exactly-one-match rule.
same issue also shows up in the base effect schema's ef.items.oneOf — it includes no-value alongside the typed refs there too.
Extra bit that really tripped me up: pro-levels-effect uses no-value refs in its prefixItems for spacer slots, and those slots DO have "ty": 0 in real AE exports. so you can't just globally add "not": {"required": ["ty"]} to no-value — it breaks pro-levels validation. the constraint needs to be scoped to the oneOf contexts only.
2. base effect in all-effects oneOf has no ty constraint
the base effect schema has no ty const, so it matches alongside every specific effect type (gaussian-blur-effect, drop-shadow-effect, etc.) in the all-effects oneOf. another oneOf violation.
fix that works for us: collect all known ty values from sibling schemas and inject "not": {"enum": [...]} on the base entry. similar to the unknown-layer pattern already in lottie-spec.
3. Sound matches precomp assets
sound inherits from file-asset which only requires "id". precomp assets also have "id", so they match both Precomposition and Sound in the all-assets oneOf.
constraining sound to "not": {"required": ["layers"]} works since only precomps have layers.
we're patching these at runtime in our validator right now. just flagging in case it's useful upstream. the lottie-spec build (schema-merge.py) might already handle some of these (as previously noted offline)