feat(webapp): the hub can write the document back to the file

[ssowonny]

TL;DR

• "Whoever stops typing last writes the file" is what a relay leaves you with — close every laptop at once and unsaved keystrokes are gone.
• The hub holds the document now, so it can write it: on the last editor leaving, and on the room unloading.
• A safety net, not a replacement. The browser still saves on idle, and the duplicate is free because identical content journals nothing (perf(webapp): saving the same bytes twice is not two versions #238).
• Attributed to the human, never to the server.

What this actually adds

Not fewer versions — #238 already delivered that by making duplicate writes free. Durability. The one case no client can cover is every client going away at once, and until now that lost whatever hadn't reached the 700 ms idle save.

Two things it's careful about

Attribution. A version whose author is "the server" is a regression in History even when the server is holding the pen. The writer is recorded when their connection is authorized, and a room that nobody with write access ever joined writes nothing at all rather than guessing. Both pinned by tests.

The route in. The snapshot re-enters the API rather than calling the uploader directly, so quota, folder permissions, the no-op check, journaling and the change frame are all the same code every other write goes through. A second path into the file would be a second set of rules to keep in agreement — and they wouldn't stay agreed.

Also

Seeding moves from the persistence adapter to OnLoadDocument, which hands over the actual *crdt.Doc instead of encoded bytes — one fewer encode/decode round trip per room opened.

Tests

• the snapshot lands, and History attributes it to the human who typed it
• snapshotting text the file already holds adds no version
• a room with no write-capable joiner writes nothing

Full module: 12 packages ok, zero failures.

🤖 Generated with Claude Code