forked from 1b-agent/opencadstudio-upstream
Review of the drop-open and autosave commits surfaced one blocker and five majors; all are fixed here, and two claims in the autosave commit message are corrected by this one: tab close does NOT clear a snapshot (matches native .sv$ semantics — saving, restoring, discarding, exit, and the capped boot scan do), and serialization runs on the main thread between awaits, not off the paint path. - The restore prompt can no longer appear with no entries (empty "Recover Drawing" modal on every boot once the autosave dir exists). - Restore no longer consumes the snapshot before the open succeeds: the recovered drawing goes through the guarded drop queue, and the snapshot is deleted only after the tab opens; cancel or parse failure keeps the only copy. - Saving during an autosave round defers its snapshot cleanup until the round finishes, so a stale round can no longer resurrect a snapshot newer than the save. - The boot scan no longer deletes snapshots by mtime comparison (re-opening a drawing refreshes the recent copy's mtime, which silently destroyed wanted snapshots); GC is now a 16-entry cap with oldest-first eviction. - OPFS write failures abort the writable stream (a leaked lock could stall the same-key writer and disable autosave for the session), and DOMException errors now carry their name/message. - Empty (crash-window) snapshots are never offered; an unreadable one warns and stays discardable instead of looping forever. - Drop-open polish: reads start inside the handler and complete in drop order (legacy WebKit safety, deterministic multi-file order), dragenter is canceled too, the install guard only latches on success, non-drawing drops don't steal propagation, a lock-poison panic can't cross into JS, and re-dropping an open drawing no longer risks clobbering an in-flight open (it re-queues). - The model-space sheet floor is per-axis (a thin 8x400 mm profile keeps its length) and centers content on the enlarged page.