internal/storage had no tests. This adds table-driven ParseStorageURL
coverage and a shared Storer conformance suite, defined once in
conformance_test.go and run against every backend that can run
in-process: file:// over a temp dir and s3:// over the same in-memory
S3 harness (gofakes3 + s3mem) that internal/s3 and the not-found test
use, so a new backend inherits the contract by passing its constructor.
The rclone backend gets construction and argument-shaping tests via
rclone's in-process ":local" backend, plus the missing-remote error
path; a comment records that its data-plane operations need a configured
remote and so cannot run in a unit test.
Tests only; no production code changed and no defect surfaced.
Model: opus-4-8
The Storer interface documents that Get and Stat return storage.ErrNotFound for a missing object. The file and rclone backends did; the s3 backend returned the raw SDK error, so callers testing for ErrNotFound behaved differently on s3.
S3Storer.Get and Stat now wrap ErrNotFound when the SDK reports a missing object and leave every other error untouched. The SDK reports a missing key two ways (NoSuchKey from Get, NotFound from Head); both are recognised in one helper, s3.IsNotFound, which HeadObject now also uses. The mapping lives in the storage package because internal/s3 cannot import it.
model: claude-opus-4-8 (implementation, review); claude-fable-5-1 (merge)