Reuse canonical artifact chunk reads across hash, snapshot, range and publication, leaving cleanup to the exact owner. Let the reader own cancellation, preserve same-read physical failures, and classify growth past the input allowance through the existing typed admission failure.
Validation: 46 focused tests across four files, docs checks and five conformance tests. Native file IO with controlled faults; no Linux firmware engines verified. Shared post-cleanup error projection remains tracked in #4628. Refs #4619, #4475