(autofix) Fix anthropic error with tool_use blocks

[trillville]

https://sentry.sentry.io/issues/6046082278/?project=6178942&query=is:unresolved%20issue.priority:%5Bhigh,%20medium%5D&sort=date&statsPeriod=14d&stream_index=2

Notes on the observed occurrence:

• got all the way to change describer step, but it looks like the step was interrupted by rethink in root cause step
• went back to root cause analysis and errored immediately
• seems like the memory already has a root cause offered up, ends with a user "." placeholder, and we try to generate anyway, and this causes an error.