fix
We don't post an answer twice when we can't confirm the agent's reply
If the agent's reply for a turn can't be matched to a comment it posted, the task now reports that instead of posting the answer itself.
Before, when we couldn't find the agent's own reply, we posted the answer ourselves, which could leave the same answer in the thread twice. This is a tightening: you now see an error saying the reply couldn't be verified, so check the issue or PR before you retry. A reply we can't check only because GitHub or Linear is briefly unavailable still counts as posted.
#1592, #1625