feat(api): add OpenAI compatibility for image models

- Introduced OpenAI-compatible image model support in the API, enabling integration through image generation and editing endpoints.
- Added registry type for OpenAIImageModelType to classify and validate compatibility.
- Implemented request handling for OpenAI-compatible image models, including JSON and multipart formats.
- Enhanced executor methods to support OpenAI-compatible image streaming and non-streaming requests.
- Included tests to validate model registration, streaming behavior, and multipart payload formatting.

internal/watcher/diff/model_hash.go

@@ -4,6 +4,7 @@ import (
 	"crypto/sha256"
 	"encoding/hex"
 	"encoding/json"
+	"fmt"
 	"sort"
 	"strings"
 
@@ -20,7 +21,7 @@ func ComputeOpenAICompatModelsHash(models []config.OpenAICompatibilityModel) str
 			if name == "" && alias == "" {
 				continue
 			}
-			out(strings.ToLower(name) + "|" + strings.ToLower(alias))
+			out(strings.ToLower(name) + "|" + strings.ToLower(alias) + "|" + fmt.Sprintf("image=%t", model.Image))
 		}
 	})
 	return hashJoined(keys)

internal/watcher/diff/model_hash_test.go

@@ -25,6 +25,17 @@ func TestComputeOpenAICompatModelsHash_Deterministic(t *testing.T) {
 	}
 }
 
+func TestComputeOpenAICompatModelsHash_IncludesImageFlag(t *testing.T) {
+	textModel := ComputeOpenAICompatModelsHash([]config.OpenAICompatibilityModel{{Name: "gpt-image", Alias: "image"}})
+	imageModel := ComputeOpenAICompatModelsHash([]config.OpenAICompatibilityModel{{Name: "gpt-image", Alias: "image", Image: true}})
+	if textModel == "" || imageModel == "" {
+		t.Fatal("hashes should not be empty")
+	}
+	if textModel == imageModel {
+		t.Fatal("hash should change when image flag changes")
+	}
+}
+
 func TestComputeOpenAICompatModelsHash_NormalizesAndDedups(t *testing.T) {
 	a := []config.OpenAICompatibilityModel{
 		{Name: "gpt-4", Alias: "gpt4"},

internal/watcher/diff/openai_compat.go

@@ -153,7 +153,7 @@ func openAICompatSignature(entry config.OpenAICompatibility) string {
 		if name == "" && alias == "" {
 			continue
 		}
-		models = append(models, strings.ToLower(name)+"|"+strings.ToLower(alias))
+		models = append(models, strings.ToLower(name)+"|"+strings.ToLower(alias)+"|"+fmt.Sprintf("image=%t", model.Image))
 	}
 	if len(models) > 0 {
 		sort.Strings(models)