The compatibility obligation belongs to the released target format.
An incoming converter can be fixed or support more historical inputs after
the target ships, as long as its output preserves that target's meaning.
Alpha releases may reject valid historical cases without an implemented,
evidenced mapping instead of expanding the format for speculative inputs.
Record the native-writer oracle, pre-normalization comparison, supported
flat V4 tool-result representation, uniform plugin naming, owner collision
rules, retained source files and read-only private corpus handling in the
migration cookbook. Align the existing architecture note with this rule;
keep native target changes and source conversion fixes distinct.
This updates contributor guidance only. It does not change finalization
checkpoint machinery, existing V4 schemas, or any released codec.
Tianyi Cui
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