Previously, lastAgentTimestamp was updated regardless of whether
runAgent succeeded or failed. This caused messages to be skipped
on retry after a failure since they were already marked as processed.
Now the timestamp is only advanced when the agent returns a valid
response, ensuring failed messages will be included in the next retry.
https://claude.ai/code/session_0118wNAJCKY2Asr17Lb91TE2
