Add model capability detection

- Add ModelCapabilities dataclass to represent model capabilities
- Add detect_model_capabilities() function to detect:
  - text_generation (LLM)
  - vision (image understanding)
  - image_generation (Stable Diffusion)
  - speech_to_text (whisper)
  - text_to_speech (TTS)
- Use capability detection for better error messages in image generation endpoint

coderai

@@ -35,6 +35,79 @@ queue_flags = {"model_1": False, "image_1": False, "audio_1": False, "tts_1": Fa
 # Model Cache Directory
 # =============================================================================
 
+# =============================================================================
+# Model Capability Detection
+# =============================================================================
+
+from typing import Set, Optional
+from dataclasses import dataclass, field
+
+@dataclass
+class ModelCapabilities:
+    """Represents what a model can do."""
+    text_generation: bool = False  # LLM/chat completion
+    vision: bool = False  # Image understanding
+    image_generation: bool = False  # Text-to-image (Stable Diffusion)
+    speech_to_text: bool = False  # Audio transcription
+    text_to_speech: bool = False  # Speech synthesis
+    
+    def __str__(self):
+        caps = []
+        if self.text_generation:
+            caps.append("text")
+        if self.vision:
+            caps.append("vision")
+        if self.image_generation:
+            caps.append("image")
+        if self.speech_to_text:
+            caps.append("speech-to-text")
+        if self.text_to_speech:
+            caps.append("text-to-speech")
+        return ", ".join(caps) if caps else "none"
+
+def detect_model_capabilities(model_name: str) -> ModelCapabilities:
+    """
+    Detect model capabilities based on model name/type.
+    
+    This is a heuristic detection - actual capabilities may vary.
+    """
+    caps = ModelCapabilities()
+    
+    if not model_name:
+        return caps
+    
+    name_lower = model_name.lower()
+    
+    # Check for image generation models (Stable Diffusion, SDXL, etc.)
+    if any(x in name_lower for x in ['stable-diffusion', 'sd15', 'sdxl', 'sd-xl', 'turbo', 'playground']):
+        caps.image_generation = True
+        return caps  # Usually SD models are dedicated
+    
+    # Check for vision models
+    if any(x in name_lower for x in ['vision', 'vl-', '-vl', 'llava', 'qwen2-vl', 'qwen-vl', 'phi-4-mini', 'pixtral', 'clip']):
+        caps.vision = True
+        caps.text_generation = True  # Vision models are also LLMs
+        return caps
+    
+    # Check for TTS models
+    if any(x in name_lower for x in ['kokoro', 'tts', 'speech', 'voice']):
+        caps.text_to_speech = True
+        return caps
+    
+    # Check for whisper models (speech-to-text)
+    if any(x in name_lower for x in ['whisper', 'faster-whisper', 'distil-whisper']):
+        caps.speech_to_text = True
+        return caps
+    
+    # Check for GGUF models (typically text models)
+    if '.gguf' in name_lower or 'gguf' in name_lower:
+        caps.text_generation = True
+        return caps
+    
+    # Default: assume text generation (most HF models are LLMs)
+    caps.text_generation = True
+    return caps
+
 def get_model_cache_dir() -> str:
     """Get or create the model cache directory."""
     # Use XDG_CACHE_HOME if set, otherwise use ~/.cache/coderai
@@ -3352,6 +3425,14 @@ async def create_image_generation(request: ImageGenerationRequest):
     
     # If still no image model configured, return an error
     if not image_model:
+        # Try to get capabilities of requested model for better error message
+        requested = request.model if request.model else "default"
+        caps = detect_model_capabilities(requested)
+        if caps.text_generation and not caps.image_generation:
+            raise HTTPException(
+                status_code=400,
+                detail=f"Model '{requested}' is a text generation model (capabilities: {caps}). Use --image-model to specify an image generation model like 'stable-diffusion-xl'."
+            )
         raise HTTPException(
             status_code=400,
             detail="Image generation not configured. Use --image-model to specify a model."