internal/storage, the package that parses store URLs and selects the backend, had no tests. Adds table-driven tests for URL parsing (each scheme, query parameters, malformed input, unknown scheme, backend type chosen); one shared conformance suite for the Storer interface, run against the file backend in a temp directory and the s3 backend on the in-process harness internal/s3 already uses, so a new backend inherits it; and rclone construction and argument tests using its in-process local backend. A comment records that rclone data operations need a configured remote and are not unit-tested. No production code changed and no defect surfaced. model: claude-opus-4-8 (implementation, review); claude-fable-5-1 (merge)