[apply-patch] Fix lark grammar (#2651)

## 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

codex-rs/core/src/tool_apply_patch.lark

@@ -0,0 +1,19 @@
+start: begin_patch hunk+ end_patch
+begin_patch: "*** Begin Patch" LF
+end_patch: "*** End Patch" LF?
+
+hunk: add_hunk | delete_hunk | update_hunk
+add_hunk: "*** Add File: " filename LF add_line+
+delete_hunk: "*** Delete File: " filename LF
+update_hunk: "*** Update File: " filename LF change_move? change?
+
+filename: /(.+)/
+add_line: "+" /(.*)/ LF -> line
+
+change_move: "*** Move to: " filename LF
+change: (change_context | change_line)+ eof_line?
+change_context: ("@@" | "@@ " /(.+)/) LF
+change_line: ("+" | "-" | " ") /(.*)/ LF
+eof_line: "*** End of File" LF
+
+%import common.LF

codex-rs/core/src/tool_apply_patch.rs

@@ -8,6 +8,8 @@ use crate::openai_tools::JsonSchema;
 use crate::openai_tools::OpenAiTool;
 use crate::openai_tools::ResponsesApiTool;
 
+const APPLY_PATCH_LARK_GRAMMAR: &str = include_str!("tool_apply_patch.lark");
+
 #[derive(Serialize, Deserialize)]
 pub(crate) struct ApplyPatchToolArgs {
     pub(crate) input: String,
@@ -29,27 +31,7 @@ pub(crate) fn create_apply_patch_freeform_tool() -> OpenAiTool {
         format: FreeformToolFormat {
             r#type: "grammar".to_string(),
             syntax: "lark".to_string(),
-            definition: r#"start: begin_patch hunk+ end_patch
-begin_patch: "*** Begin Patch" LF
-end_patch: "*** End Patch" LF?
-
-hunk: add_hunk | delete_hunk | update_hunk
-add_hunk: "*** Add File: " filename LF add_line+
-delete_hunk: "*** Delete File: " filename LF
-update_hunk: "*** Update File: " filename LF change_move? change?
-
-filename: /(.+)/
-add_line: "+" /(.+)/ LF -> line
-
-change_move: "*** Move to: " filename LF
-change: (change_context | change_line)+ eof_line?
-change_context: ("@@" | "@@ " /(.+)/) LF
-change_line: ("+" | "-" | " ") /(.+)/ LF
-eof_line: "*** End of File" LF
-
-%import common.LF
-"#
-            .to_string(),
+            definition: APPLY_PATCH_LARK_GRAMMAR.to_string(),
         },
     })
 }