Leaving a deleted page drops its queued changes but left their image
uploads, and the bytes they hold, retrying later. An image placed after
the delete never got a change the server could take, so its staged
upload waited for a reference forever. Leaving now marks the strategy's
uploads for a check before their next attempt: one goes, with its
bytes, only if no queued change and no page on the server references
its image. Marks made offline wait for the connection. A check that
cannot prove the image unreferenced lets the upload go on.

Session tests now use a recording media queue: the real one had no
storage there, and nothing in them exercised it.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>