fix: normalize aspect ratio per model, surface invalid_params in errors

Models like mystic, flux-pro-1.1, and seedream-v4/v4-5 require named
aspect ratio slugs (e.g. "square_1_1", "widescreen_16_9") while other
models accept the "W:H" format directly.

- Add normalize_aspect_ratio() mapping W:H strings to slugs for affected models
- Apply normalization in generate-image before building the request payload
- Improve FreepikAPIError to surface invalid_params field details from the API
  response, so "Validation error" now also shows which field failed and why

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

freepik_cli/api/client.py

@@ -34,10 +34,17 @@ class FreepikAPIError(Exception):
             or f"HTTP {response.status_code}"
         )
 
+        # Append individual field validation errors when present
+        invalid = body.get("invalid_params", [])
+        if invalid:
+            details = "\n".join(
+                f"  • {p.get('field', '?')}: {p.get('reason', '')}" for p in invalid
+            )
+            message = f"{message}\n\n{details}"
+
         hints = {
             401: "Check your API key — set FREEPIK_API_KEY or use --api-key.",
             403: "Your plan may not support this feature. Check your Freepik subscription.",
-            422: "Invalid request parameters. Check the options you provided.",
             429: "Rate limit exceeded. Please wait before retrying.",
         }
         hint = hints.get(response.status_code)

freepik_cli/api/models.py

@@ -124,6 +124,45 @@ VIDEO_UPSCALE_POST_ENDPOINTS: dict[VideoUpscaleMode, str] = {
 VIDEO_UPSCALE_STATUS_ENDPOINT = "/v1/ai/video-upscaler/{task_id}"
 
 
+# ---------------------------------------------------------------------------
+# Aspect ratio normalization
+# ---------------------------------------------------------------------------
+
+# Models that require named slug aspect ratios instead of "W:H" strings
+SLUG_ASPECT_RATIO_MODELS: set[ImageModel] = {
+    ImageModel.MYSTIC,
+    ImageModel.FLUX_PRO_1_1,
+    ImageModel.SEEDREAM_V4,
+    ImageModel.SEEDREAM_V4_5,
+}
+
+# User-friendly "W:H" → API slug mapping
+_RATIO_TO_SLUG: dict[str, str] = {
+    "1:1":   "square_1_1",
+    "16:9":  "widescreen_16_9",
+    "9:16":  "social_story_9_16",
+    "4:3":   "classic_4_3",
+    "3:4":   "traditional_3_4",
+    "3:2":   "standard_3_2",
+    "2:3":   "portrait_2_3",
+    "2:1":   "horizontal_2_1",
+    "1:2":   "vertical_1_2",
+    "4:5":   "social_post_4_5",
+    "21:9":  "widescreen_16_9",   # closest match
+}
+
+
+def normalize_aspect_ratio(ratio: str, model: ImageModel) -> str:
+    """Convert a user-facing aspect ratio to the format required by the model."""
+    if model not in SLUG_ASPECT_RATIO_MODELS:
+        return ratio  # free-form models accept "1:1" directly
+    slug = _RATIO_TO_SLUG.get(ratio)
+    if slug:
+        return slug
+    # Already a slug (user passed "square_1_1" directly) — pass through
+    return ratio
+
+
 # ---------------------------------------------------------------------------
 # Response normalization helpers
 # ---------------------------------------------------------------------------