[apply_patch] freeform apply_patch tool (#2576)

## 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

codex-rs/core/src/model_family.rs

@@ -1,3 +1,5 @@
+use crate::tool_apply_patch::ApplyPatchToolType;
+
 /// A model family is a group of models that share certain characteristics.
 #[derive(Debug, Clone, PartialEq, Eq, Hash)]
 pub struct ModelFamily {
@@ -24,9 +26,9 @@ pub struct ModelFamily {
     // See https://platform.openai.com/docs/guides/tools-local-shell
     pub uses_local_shell_tool: bool,
 
-    /// True if the model performs better when `apply_patch` is provided as
-    /// a tool call instead of just a bash command.
-    pub uses_apply_patch_tool: bool,
+    /// Present if the model performs better when `apply_patch` is provided as
+    /// a tool call instead of just a bash command
+    pub apply_patch_tool_type: Option<ApplyPatchToolType>,
 }
 
 macro_rules! model_family {
@@ -40,7 +42,7 @@ macro_rules! model_family {
             needs_special_apply_patch_instructions: false,
             supports_reasoning_summaries: false,
             uses_local_shell_tool: false,
-            uses_apply_patch_tool: false,
+            apply_patch_tool_type: None,
         };
         // apply overrides
         $(
@@ -60,7 +62,7 @@ macro_rules! simple_model_family {
             needs_special_apply_patch_instructions: false,
             supports_reasoning_summaries: false,
             uses_local_shell_tool: false,
-            uses_apply_patch_tool: false,
+            apply_patch_tool_type: None,
         })
     }};
 }
@@ -88,6 +90,7 @@ pub fn find_family_for_model(slug: &str) -> Option<ModelFamily> {
         model_family!(
             slug, slug,
             supports_reasoning_summaries: true,
+            apply_patch_tool_type: Some(ApplyPatchToolType::Freeform),
         )
     } else if slug.starts_with("gpt-4.1") {
         model_family!(
@@ -95,7 +98,7 @@ pub fn find_family_for_model(slug: &str) -> Option<ModelFamily> {
             needs_special_apply_patch_instructions: true,
         )
     } else if slug.starts_with("gpt-oss") {
-        model_family!(slug, "gpt-oss", uses_apply_patch_tool: true)
+        model_family!(slug, "gpt-oss", apply_patch_tool_type: Some(ApplyPatchToolType::Function))
     } else if slug.starts_with("gpt-4o") {
         simple_model_family!(slug, "gpt-4o")
     } else if slug.starts_with("gpt-3.5") {
@@ -104,6 +107,7 @@ pub fn find_family_for_model(slug: &str) -> Option<ModelFamily> {
         model_family!(
             slug, "gpt-5",
             supports_reasoning_summaries: true,
+            apply_patch_tool_type: Some(ApplyPatchToolType::Freeform),
         )
     } else {
         None