- A preview cancelled while its file opens closes the handle and only
then ends the pin, so a doomed capture is never unlinked while open.
- An observe cancelled while capturing or reading releases the capture
instead of leaving it until the idle expiry.
- The model gate takes an on_skipped callback that runs once when the
work never starts; Generate passes the capture's release_use, so an
executor refusal no longer leaks a pin against the capture budget.
- The preview answers a single byte range with 206 and Content-Range
(416 for an unsatisfiable or multi-range header), still streamed inside
the pin, so Safari and WebKit can play video captures.
- _coded maps tag-limit (400), metadata-conflict and vocabulary-conflict,
and falls back to 409 with a fixed sentence for any other code instead
of raising KeyError.