40400 — message_not_found

GET /messages/:id — or the versions / reactions for that id — found no row in this project, or the id was not a positive integer. Not terminal.

At a glance — HTTP 404 · REST only.

What to do

• Check the id and the project scope: a message that exists in another project is a 404 here.
• The id must be a positive integer; a malformed id is a 404, not a 400.
• Nullable for UI: "not found" is a normal answer for detail endpoints, not an incident.