feat(scale): CompactEnum + JAM compact codec for >256-variant enums#184
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feat(scale): CompactEnum + JAM compact codec for >256-variant enums#184pgherveou wants to merge 1 commit into
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The MessagePayload enum used scale-ts `Enum`, which writes the variant discriminant as a single byte, capping the protocol at 256 variants. We are at 130 and growing. Add `CompactEnum`, a drop-in replacement that encodes the discriminant as a SCALE-compact integer, lifting the cap into the u16 range while keeping single-byte tags for indices 0..=63. BREAKING: not wire-compatible with the u8 form. Index 0 still encodes as [0], but every other index differs (e.g. 76 -> [49, 1]), so both ends of the protocol must run this version.
pgherveou
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Summary
The host-api
MessagePayloadenum is built with scale-tsEnum, whose discriminant is a single byte — capping the protocol at 256 variants (we're at 130, and indices 128/129 are already in use). This adds a compact-discriminant path without changing the meaning of the standardEnum.Design
Two distinct codecs rather than overloading
Enum:Enumu8CompactEnumcompactcompact(new) — the JAM general-natural-number codec (see jam-codec'sCompact). Byte-identical to au8for values0..=127, spilling into more bytes above that.CompactEnum(new) — tagged-union codec that encodes the discriminant withcompact, lifting the 256 cap. Used only by theMessagePayloadenvelope.Enumstays theu8codec and now rejects >256 variants at construction, mirroring jam-codec's compile-time guard.TODO before un-drafting
docs/design/host-api-protocol.mdto document the compact discriminant on the message envelope.u8encoding of indices 128/129.