Module codec 

Serialization codecs for cache entries.

Implement CacheCodecImpl on concrete types, then use CacheCodec::from_impl to produce a type-erased codec for the cache.

Wire format

Every serialized entry begins with a small hand-framed envelope so the reader can validate it before trusting the body:

[magic: 4B = b"LCE1"]
[envelope_version: u8]
[type_id_len: u16 LE][type_id: utf8]   # stable, author-assigned
[type_version: u32 LE]                 # per-type body schema version
<body, written by the type's CacheCodecImpl::serialize>

The envelope is deliberately not protobuf: it is the most stability-critical part, must parse robustly against arbitrary bytes (including data written by older, pre-stabilization builds), and never changes shape. Bodies use protobuf headers, where field-number evolution pays off.

Decode outcome

Deserialization never propagates a parse failure as a hard error into the cache path. Anything the reader cannot confidently interpret — absent or wrong magic, an unknown envelope_version, a type_id mismatch, an unsupported type_version, or a body decode error — becomes CacheDecode::Miss. A backend turns Miss into a normal cache miss and recomputes the value. This is what lets data written by an older format self-heal: it simply fails the magic check and is regenerated.

Structs

CacheCodec

Type-erased codec for serializing and deserializing cache entries.

Enums

CacheDecode

Outcome of deserializing a cache entry.

CacheMissReason

Why a cache entry could not be decoded into the expected type.

Constants

MAGIC

Magic bytes that prefix every stabilized cache entry.

Traits

CacheCodecImpl

Serialization trait for cache entries.

Functions

has_cache_envelope

Returns true if data begins with the cache-entry MAGIC.