## Summary
Fixes an issue with the lark grammar definition for the apply_patch
freeform tool. This does NOT change the defaults, merely patches the
root cause of the issue we were seeing with empty lines, and an issue
with config flowing through correctly.
Specifically, the following requires that a line is non-empty:
```
add_line: "+" /(.+)/ LF -> line
```
but many changes _should_ involve creating/updating empty lines. The new
definition is:
```
add_line: "+" /(.*)/ LF -> line
```
## Testing
- [x] Tested locally, reproduced the issue without the update and
confirmed that the model will produce empty lines wiht the new lark
grammar
## Summary
GPT-5 introduced the concept of [custom
tools](https://platform.openai.com/docs/guides/function-calling#custom-tools),
which allow the model to send a raw string result back, simplifying
json-escape issues. We are migrating gpt-5 to use this by default.
However, gpt-oss models do not support custom tools, only normal
functions. So we keep both tool definitions, and provide whichever one
the model family supports.
## Testing
- [x] Tested locally with various models
- [x] Unit tests pass
