The plan follows the one of the Go reference: the codec first, then the
reader together with the testdata of spec-v0.10 in one commit, as the
v0.9 did, since the guard of the harness wants every synced file read by
a test; then the writer, the ZIP of the page and the two pages.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
