This PR adds logging when the chat runner retries and exits because of
an error. It also adds a 15-minute task timeout to ensure that stuck
tasks do not hang forever.
Chat watch events publish through Postgres NOTIFY, so embedding the full
REST chat payload can exceed the payload limit when
`last_injected_context` grows. Strip `LastInjectedContext` from watch
payloads, matching the existing `Files` omission, while keeping
`DiffStatus` populated for `diff_status_change` events and leaving `GET
/chats/{id}` unchanged.
A previous attempt in #26368 introduced a separate summary type for
watch events. This avoids making that API change prematurely: one large
optional field is not enough reason to split the shared `Chat` shape by
endpoint, so this keeps the existing type and omits the heavy detail
field from pubsub payloads.
Closes CODAGT-501
Hugo Dutka