Add detailed debugging for Gemini API response parsing

- Add debug logs to show response structure and candidates
- Log each part type and content to diagnose why images aren't being extracted
- Log text responses (error messages) from Gemini
- Log full response on failure for better error diagnosis
- This will help identify why Gemini is returning no image

src/core.py

@@ -167,27 +167,61 @@ def _call_gemini_edit(
 
     output_img: Image.Image | None = None
 
+    # Debug: log response structure
+    log.debug("Gemini response type: %s", type(response))
+    log.debug("Gemini response has candidates: %s", hasattr(response, "candidates"))
+    
     # Extract first image from response parts
     try:
-        for candidate in getattr(response, "candidates", []):
+        candidates = getattr(response, "candidates", [])
+        log.debug("Number of candidates: %d", len(candidates))
+        
+        for idx, candidate in enumerate(candidates):
+            log.debug("Candidate %d type: %s", idx, type(candidate))
             parts = getattr(candidate, "content", None)
-            if not parts or not getattr(parts, "parts", None):
+            if not parts:
+                log.debug("Candidate %d has no content", idx)
                 continue
-            for part in parts.parts:
+            response_parts = getattr(parts, "parts", None)
+            if not response_parts:
+                log.debug("Candidate %d content has no parts", idx)
+                continue
+            log.debug("Candidate %d has %d parts", idx, len(response_parts))
+            
+            for part_idx, part in enumerate(response_parts):
+                log.debug("Part %d type: %s", part_idx, type(part))
                 inline = getattr(part, "inline_data", None)
-                if inline and inline.data:
-                    data = inline.data
-                    if isinstance(data, str):
-                        data = base64.b64decode(data)
-                    output_img = Image.open(BytesIO(data)).convert("RGB")
-                    break
+                if inline:
+                    log.debug("Part %d has inline_data, mime_type: %s", part_idx, getattr(inline, "mime_type", None))
+                    if inline.data:
+                        data = inline.data
+                        if isinstance(data, str):
+                            data = base64.b64decode(data)
+                        output_img = Image.open(BytesIO(data)).convert("RGB")
+                        log.info("Successfully extracted image from Gemini response")
+                        break
+                else:
+                    # Check if part has text (might be an error message)
+                    text = getattr(part, "text", None)
+                    if text:
+                        log.warning("Gemini returned text instead of image in part %d: %s", part_idx, text[:200])
             if output_img:
                 break
     except Exception as err:
-        log.warning("Failed to parse Gemini response image: %s", err)
+        log.error("Failed to parse Gemini response image: %s", err, exc_info=True)
 
     if output_img is None:
-        raise RuntimeError("Gemini generate_content returned no image")
+        # Log full response for debugging
+        try:
+            response_text = str(response)
+            log.error("Gemini generate_content returned no image. Full response (first 500 chars): %s", response_text[:500])
+            # Try to extract any error messages
+            if hasattr(response, "prompt_feedback"):
+                feedback = response.prompt_feedback
+                log.error("Prompt feedback: %s", feedback)
+        except Exception:
+            pass
+        raise RuntimeError("Gemini generate_content returned no image. Check logs for details.")
 
     # Ensure output matches original dimensions if Gemini rescaled
     if output_img.size != target_size: