[Bug]: edits made while the AI agent is running are overwritten when it answers

[EtienneLescot]

Describe the bug

Edits made in the editor while the AI agent is running are silently lost when the agent's turn finishes.

The chat sends a full document snapshot taken at Send time, the agent folds its edits onto that snapshot in the main process, and the renderer applies the returned document wholesale — setDocument + saveDocument — with no check that the live document has moved in the meantime. Last write wins on a stale base, so every user edit made during the turn (padding, background, a trim, a zoom, a clip move, a title change…) is overwritten on screen and on disk.

Where it happens:

• snapshot at send: LeftPanel.tsx:931 — useProjectStore.getState().document is captured once and passed to chatRun
• agent folds its tools onto that snapshot and returns holder.current (electron/ai-edition/deep-agent/service.ts, DocumentHolder)
• blind apply on return: LeftPanel.tsx:875-880 — applyAgentDocument does store.setDocument(parsed) then store.saveDocument(parsed)

Note this is not the torn-file race DocumentService.writeProject already guards against (that queue makes the two saves sequential and atomic — it just means the agent's stale document is written cleanly on top of the user's).

The one mitigation today is that setDocument pushes the previous document onto the undo stack, so a single Ctrl+Z restores the user's version — but it then throws away the agent's work, and nothing tells the user anything was clobbered.

Expected behavior

A user edit made during an agent turn must not be lost.

At minimum: detect the conflict (the store's revision already increments on every local mutation — capture it alongside the snapshot at send and compare on apply) and tell the user instead of silently overwriting. Better: rebase the agent's tool results onto the current document, or block/queue the conflicting local edit while a turn is in flight.

To Reproduce

1. Open a project in the editor and ask the AI a question that takes a while and edits the document (e.g. "remove the silences").
2. While the agent is still working, change something yourself — e.g. the padding in the inspector, or move a clip.
3. Wait for the agent to answer.
4. The change from step 2 is gone: it's absent from the timeline/inspector and from the saved .openscreen file.

OS

Windows

Additional context

Any of the direct document editors can lose an edit this way (timeline, inspector, transcript editor, captions pane) — they all write to the same projectStore document that the agent's return value replaces.