Short, stable machine code for the failure category, e.g. "rejected",
"too_large", "rate_limited", "invalid_recipient", or the generic
"send_failed". Used for logging/diagnostics, not shown verbatim to users.
OptionalmessageHuman-readable, user-safe explanation to show beside "Failed to send" (e.g. "Recipient address rejected"). Null/omitted when the connector has no safe message to surface — the app then shows just "Failed to send".
Reports that an outbound send / write-back for a note could not be delivered to the external system, so Plot can surface it to the user.
Returned (not thrown) from a write-back hook — see
NoteWriteBackResult.deliveryErrorandNewLinkWithNotes.originatingNote— after the connector has exhausted its own retries (or immediately for a permanent failure such as a rejected recipient). The runtime records it on the note (the app then shows a "Failed to send" affordance with Retry / Discard) and marks the thread unread so the user notices.