Preview PNGs and card JPEGs go stale two ways. Editing a document and
forgetting to refresh is the obvious one. The other leaves no trace at
all: the renderer changes, the document does not, and every previously
saved image is silently wrong while git is clean, the tests are green
and the gate passes. That is what happened to three minimal-keynote
frames whose content matched HEAD exactly but whose pixels no longer
did, because the desktop binary had been rebuilt underneath them.
Nothing but re-rendering and comparing bytes can see the second case, so
that is the only criterion here. It rests on rendering being
deterministic — two runs of one document must be byte-identical, which
`--selftest` checks; if that ever stops holding, this tool's verdicts
are void and the renderer is the thing to fix.
Claude-Session: https://claude.ai/code/session_01FqKQqNj8exYwopGDpYUU7x
ad1ed80a8d