fix(image): align Gemini hints with model capabilities

nanobot/providers/image_generation.py

@@ -33,13 +33,18 @@ _AIHUBMIX_ASPECT_RATIO_SIZES = {
 }
 _GEMINI_DEFAULT_TIMEOUT_S = 120.0
 _GEMINI_IMAGEN_ASPECT_RATIOS = {"1:1", "9:16", "16:9", "3:4", "4:3"}
-# Aspect ratios documented for every Gemini Flash image (generateContent) model.
-# The extreme ratios (1:4, 4:1, 1:8, 8:1) are only listed for the 3.1 Flash /
-# Flash Lite tables, so they are left out to avoid sending an unsupported value
-# to 2.5 Flash Image or 3.1 Pro Image.
-_GEMINI_FLASH_ASPECT_RATIOS = {
+# Aspect ratios documented for every Gemini image model using generateContent.
+_GEMINI_FLASH_COMMON_ASPECT_RATIOS = {
     "1:1", "2:3", "3:2", "3:4", "4:3", "4:5", "5:4", "9:16", "16:9", "21:9",
 }
+# Gemini 3.1 Flash and Flash Lite additionally accept extreme aspect ratios.
+_GEMINI_31_FLASH_ASPECT_RATIOS = {
+    *_GEMINI_FLASH_COMMON_ASPECT_RATIOS,
+    "1:4",
+    "4:1",
+    "1:8",
+    "8:1",
+}
 # Gemini 3 Pro image models accept these sizes. Gemini 3.1 Flash adds 512,
 # while Gemini 3.1 Flash Lite supports only 1K.
 _GEMINI_3_IMAGE_SIZES = {"1K", "2K", "4K"}
@@ -778,11 +783,12 @@ def _gemini_flash_image_config(
 ) -> dict[str, str]:
     """Build the ``responseFormat.image`` config for Gemini Flash image models.
 
-    Aspect ratio applies to all Flash image models; image size is only honored
-    by Gemini 3+ image models (``gemini-2.5-flash-image`` ignores it).
+    Capabilities are model-specific: Gemini 3.1 Flash variants support four
+    additional extreme ratios, while configurable image sizes are limited to
+    the documented Gemini 3 image model families.
     """
     config: dict[str, str] = {}
-    if aspect_ratio and aspect_ratio in _GEMINI_FLASH_ASPECT_RATIOS:
+    if aspect_ratio and aspect_ratio in _gemini_flash_supported_aspect_ratios(model):
         config["aspectRatio"] = aspect_ratio
     if image_size:
         normalized = image_size.strip().upper()
@@ -791,6 +797,19 @@ def _gemini_flash_image_config(
     return config
 
 
+def _gemini_flash_supported_aspect_ratios(model: str) -> set[str]:
+    """Return the documented aspect ratios for a generateContent image model."""
+    normalized = model.lower()
+    if (
+        "gemini-3.1-flash-lite-image" in normalized
+        or "gemini-3.1-flash-image" in normalized
+    ):
+        return _GEMINI_31_FLASH_ASPECT_RATIOS
+    if "gemini-" in normalized and "image" in normalized:
+        return _GEMINI_FLASH_COMMON_ASPECT_RATIOS
+    return set()
+
+
 def _gemini_flash_supported_image_sizes(model: str) -> set[str]:
     """Return the ``imageSize`` values documented for a Flash-path model.
 
@@ -802,7 +821,7 @@ def _gemini_flash_supported_image_sizes(model: str) -> set[str]:
         return _GEMINI_31_FLASH_LITE_IMAGE_SIZES
     if "gemini-3.1-flash-image" in normalized:
         return _GEMINI_31_FLASH_IMAGE_SIZES
-    if "gemini-3" in normalized:
+    if "gemini-3-pro-image" in normalized:
         return _GEMINI_3_IMAGE_SIZES
     return set()
 

tests/providers/test_image_generation.py

@@ -480,10 +480,39 @@ async def test_gemini_flash_2_0_drops_image_size() -> None:
     assert image_config == {"aspectRatio": "16:9"}
 
 
+@pytest.mark.parametrize(
+    ("model", "aspect_ratio", "expected"),
+    [
+        ("gemini-3.1-flash-image", "1:8", {"aspectRatio": "1:8"}),
+        ("gemini-3.1-flash-lite-image", "4:1", {"aspectRatio": "4:1"}),
+        ("gemini-3-pro-image", "1:8", None),
+        ("gemini-2.5-flash-image", "4:1", None),
+    ],
+)
+@pytest.mark.asyncio
+async def test_gemini_flash_scopes_extreme_aspect_ratios_by_model(
+    model: str,
+    aspect_ratio: str,
+    expected: dict[str, str] | None,
+) -> None:
+    fake = FakeClient(_gemini_flash_image_response())
+    client = GeminiImageGenerationClient(api_key="AIza-test", client=fake)  # type: ignore[arg-type]
+
+    await client.generate(
+        prompt="draw a cat",
+        model=model,
+        aspect_ratio=aspect_ratio,
+    )
+
+    response_format = fake.calls[0]["json"]["generationConfig"].get("responseFormat")
+    assert response_format == ({"image": expected} if expected else None)
+
+
 @pytest.mark.parametrize(
     ("model", "image_size", "expected"),
     [
         ("gemini-3-pro-image", "512", None),
+        ("gemini-3-pro", "2K", None),
         ("gemini-3.1-flash-lite-image", "2K", None),
         ("gemini-3.1-flash-lite-image", "1K", {"imageSize": "1K"}),
         ("gemini-3.1-flash-image", "512", {"imageSize": "512"}),