evals: Add system prompt to edit agent evals + fix edit agent (#31082)

1. Add system prompt: this is how it's called from threads. Previously,
we were sending
2. Fix an issue with writing agent thought into a newly created empty
file.

Release Notes:

- N/A

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Co-authored-by: Ben Brandt <benjamin.j.brandt@gmail.com>
Co-authored-by: Antonio Scandurra <me@as-cii.com>
91bc5aefa4Oleksiy Syvokon committed on 5/21/2025, 10:14:58 AM· committed by GitHubparent2f3564b
4 files changedLine totals unavailable