The shell's VersionsSource (shell/node-versions-source.ts) reads GET
/api/history through the sync and shows one version per distinct content
(a restore's copy folds into the entry it copies; the blank page is none),
numbered as they first appeared, with what changed since the one before.
The entry the server says is on the canvas marks the version; undo and
redo of the newest version restore the one before it, or it again, through
POST /api/restore, so hand edits stay as versions of their own. The cards
sit in a panel beside the canvas (toggle in the header); the strip and
Compare come from the shared canvas components. The sync tells listeners
once per server version, and when History changed without one, so the
list is read again only then.
A write taken in place that leaves the canvas as it is gets no autosave from draw.io, so the marker for its copy stayed armed and ate the user's next paper-size edit: arm it only when the write changed the document. The 15 s export timeout now retires the export's sequence number, so a result POST that answers late no longer restores the document a second time.
A recovery loads the server's diagram in full and waits for draw.io's
load report, as the classic page does: whether the canvas takes a write
in place is decided inside DiagramProvider, and an autosave of the
canvas being replaced went to the server as an edit when the decision
was wrong. A paper size change alone is pushed again: autosaves are
compared as documents only for draw.io's own copy of a committed write.
A projection stays on screen until draw.io reports the restore load
(5 s at most), the whole export ends in 15 s even when its result POST
hangs, and an export in flight is dropped when draw.io starts over. A
refused poll shows the tab offline. With several pages and the page on
screen unknown, a write loads in full. hasLoadOnlySettings and the
highlight of an AI change are shared with the editor bridge.
The recovery, thumbnail, size limit and History cases of
tests/unit/mcp-preview-recovery.test.ts, driven against mcp-sync-core.ts
with a stubbed server and canvas, plus the stale 409 recovery, an export
request answered once, a projection that ignores edits and restores the
document, the thumbnail of a write loaded before draw.io was ready, writes
taken in place as commits (draw.io's own copy is not pushed), and the
commit-or-load decision table of decideLoad.
dayuan.jiang