The oc_url_token has a ~50s effective lifetime and was only fetched once at
preview mount, so HTML/image/PDF previews cycled to 'authentication required'
when it expired and nothing forced a re-render with a fresh token.
Add a consumer-gated proactive refresh in runtime-auth: while at least one
url-token consumer is active, a single scheduler mints a fresh token just
before the skew window and swaps it in atomically (the previous token stays
valid until the new one lands — no empty-token window for other consumers).
acquire/release manage the consumer count; subscribe fires only on a real
token replacement.
FilesView consumes this via a shared useAssetAuthRefresh hook (replacing three
near-duplicate effects) and remounts the iframe/img only when the token
actually changes, not on a blind interval.
Bohdan Triapitsyn
57c5808ef2