Write refused on the hosted Studio: stale base revision (409)

On a team Studio, your save was refused with a 409: someone else saved the same file after you opened it. Nothing of theirs was overwritten, and your draft is kept. This page says how to see what changed and how to save yours.

Symptom

• In the Studio: a dialog "The file changed since you read it", with "Someone saved rooms/kitchen.ts meanwhile (revision 42): this is what changed since you read it at revision 40. Your draft is kept: apply it on the latest version, or copy it."
• Through the API, the CLI or the MCP: HTTP 409, {"error": "rooms/kitchen.ts changed since revision 40 (now 42)", "path", "readAt", "head", "before", "now"}: the file as you read it and as it is now, when it is text.

Possible causes

Each write says which revision its editor read, in the header x-studio-base; every read answers with its revision in x-studio-revision. If one of the files the write changes was saved by someone else after that revision, the write is refused:

1. Another member saved the same file after you opened it. The most common case.
2. You saved it yourself from somewhere else: another tab, or an AI agent working for you through the MCP. Only the writes of the same tab, CLI or MCP session never refuse each other.
3. Undo or redo of an operation whose file someone else changed since: refused the same way, "cannot undo …: <file> changed since".

Diagnosis

• The dialog shows what changed between the revision you read and now.
• Through the API, readAt is the revision you read, head the current one, before and now the file at each.
• If the error has no path but says "changed while this edit was being prepared" or "while this edit was being checked", another write landed during yours: try again, nothing else to do.

Fix

1. Read what changed in the dialog: it may already hold what you wanted, or clash with it.

2. For an edit the server makes on the file (a text, a value, a note, a voice line): click "Apply my edit on the latest version". Your edit is applied on top of theirs; nothing of theirs is lost.

3. For a whole document (a room's layout, the storyboard): either click "Replace with my version (drops their change)", knowing it removes theirs, or copy your draft, reload the file, and redo your change on the new version.

4. Through the API, read the file again (its answer gives the new x-studio-revision), redo the change, and send it with that revision as x-studio-base. Nothing is sent again unless you ask.

Check it is fixed

The save goes through, with a revision after the one in the error's head. GET /api/ops lists both operations, theirs and yours.

Neighbouring cases

• 423, "… is held by …": someone holds the span right now; that is a lock, not a stale read. See Write refused on the hosted Studio: span locked (423).
• The Reality Bridge's 409 has nothing to do with the Studio: a pairing code confirmed twice, a speedrun run sent twice. See Bridge and connector troubleshooting.
• Other 409s of the Studio Server: "… already exists in room …" (an id already taken), and "another epoch: resynchronise" on GET /api/ops?epoch=… when the project is not the one the client knew (read the history again from the start).