Allow image_generation.size to be null for OpenAI and default it to that

The API spec for image creation and image editing says "string or null",
so we're allowing `null` now to trigger automatic selection.

docs/sample-provider-configs/openai-o1.yml

@@ -20,5 +20,5 @@ text_to_speech:
 image_generation:
   model_id: gpt-image-1
   style: null
-  size: 1024x1024
+  size: null
   quality: null

docs/sample-provider-configs/openai.yml

@@ -16,5 +16,5 @@ text_to_speech:
 image_generation:
   model_id: gpt-image-1
   style: null
-  size: 1024x1024
+  size: null
   quality: null

etc/app/config.yml.dist

@@ -93,7 +93,7 @@ agents:
     #     image_generation:
     #       model_id: gpt-image-1
     #       style: null
-    #       size: 1024x1024
+    #       size: null
     #       quality: null
     #
     # - id: localai

src/agent/provider/openai/config.rs

@@ -153,7 +153,7 @@ pub struct ImageGenerationConfig {
     pub style: Option<async_openai::types::ImageStyle>,
 
     #[serde(default = "default_image_size")]
-    pub size: async_openai::types::ImageSize,
+    pub size: Option<async_openai::types::ImageSize>,
 
     #[serde(default = "default_image_quality")]
     pub quality: Option<async_openai::types::ImageQuality>,
@@ -186,8 +186,8 @@ fn default_image_style() -> Option<async_openai::types::ImageStyle> {
     None
 }
 
-fn default_image_size() -> async_openai::types::ImageSize {
-    async_openai::types::ImageSize::S1024x1024
+fn default_image_size() -> Option<async_openai::types::ImageSize> {
+    None
 }
 
 fn default_image_quality() -> Option<async_openai::types::ImageQuality> {

src/agent/provider/openai/controller.rs

@@ -284,11 +284,8 @@ impl ControllerTrait for Controller {
 
         let size = params
             .size_override
-            .map(|s| {
-                convert_string_to_enum::<async_openai::types::ImageSize>(&s)
-                    .unwrap_or(image_generation_config.size)
-            })
-            .unwrap_or(image_generation_config.size);
+            .map(|s| convert_string_to_enum::<async_openai::types::ImageSize>(&s).unwrap())
+            .or(image_generation_config.size);
 
         let response_format = match model.clone() {
             ImageModel::DallE2 => Some(ImageResponseFormat::B64Json),
@@ -303,10 +300,7 @@ impl ControllerTrait for Controller {
 
         let mut request_builder = CreateImageRequestArgs::default();
 
-        request_builder
-            .model(model)
-            .prompt(prompt.to_owned())
-            .size(size);
+        request_builder.model(model).prompt(prompt.to_owned());
 
         if let Some(response_format) = response_format {
             request_builder.response_format(response_format);
@@ -320,6 +314,10 @@ impl ControllerTrait for Controller {
             request_builder.quality(quality.clone());
         }
 
+        if let Some(size) = size {
+            request_builder.size(size);
+        }
+
         let request = request_builder.build()?;
 
         tracing::trace!(
@@ -382,9 +380,9 @@ impl ControllerTrait for Controller {
         }
 
         let dalle2_size = match image_generation_config.size {
-            async_openai::types::ImageSize::S256x256 => Some(DallE2ImageSize::S256x256),
-            async_openai::types::ImageSize::S512x512 => Some(DallE2ImageSize::S512x512),
-            async_openai::types::ImageSize::S1024x1024 => Some(DallE2ImageSize::S1024x1024),
+            Some(async_openai::types::ImageSize::S256x256) => Some(DallE2ImageSize::S256x256),
+            Some(async_openai::types::ImageSize::S512x512) => Some(DallE2ImageSize::S512x512),
+            Some(async_openai::types::ImageSize::S1024x1024) => Some(DallE2ImageSize::S1024x1024),
             _ => None,
         };
 

src/agent/provider/openai_compat/config.rs

@@ -224,9 +224,11 @@ impl TryInto<OpenAIImageGenerationConfig> for ImageGenerationConfig {
 
     fn try_into(self) -> Result<OpenAIImageGenerationConfig, Self::Error> {
         let size = if let Some(size) = &self.size {
-            convert_string_to_enum::<async_openai::types::ImageSize>(size)?
+            Some(convert_string_to_enum::<async_openai::types::ImageSize>(
+                size,
+            )?)
         } else {
-            async_openai::types::ImageSize::S1024x1024
+            None
         };
 
         let style = if let Some(style) = &self.style {