fix(api): commit a mislabelled data-URL image under its sniffed type

Mechanism: commit_api_images refused the whole batch (RuntimeStoreError
invalid_params, then HTTP 409) when a data URL's declared mime differed from
the sniffed bytes. Many SDKs hardcode `data:image/png;base64,` for JPEG bytes;
on main the same request only had to start with `data:image/` and reached the
provider.

Fix: the sniffed type decides the committed mime and extension; only bytes
that are no supported image (png/jpeg/gif/webp) are refused, before any byte
is staged (invalid_params, now 400 via the shared status table).

Test (red on r13-base2: RuntimeStoreError invalid_params):
tests/gateway/test_api_image_mislabelled_mime.py admits a png-labelled JPEG
through the real admission path and asserts the committed .jpg bytes; the
existing non-image refusal case in test_api_media_admission_bounds still holds.

Review: ahrazzle B1-21

gateway/session_api_media.py

@@ -34,12 +34,15 @@ def commit_api_images(content):
     from gateway.platforms.base import get_inbound_media_max_bytes
     from gateway.session_ingress_media import capture_native_media, sniff_image_mime
     from hermes_state_runtime import RuntimeStoreError
-    images = [decoded for decoded in map(_data_url_bytes, _image_urls(content)) if decoded is not None]
+    # The bytes decide the committed type: SDKs often label JPEG bytes ``data:image/png`` and
+    # main forwarded those to the provider; only bytes that are no supported image are refused.
+    images = [(sniff_image_mime(decoded[1]), decoded[1])
+              for decoded in map(_data_url_bytes, _image_urls(content)) if decoded is not None]
     # Validate the whole batch before one byte lands on disk: a refused request must not
-    # leave staged or committed bytes behind, and the declared type must be the real one.
+    # leave staged or committed bytes behind.
     limit = max(0, get_inbound_media_max_bytes())
     if (len(images) > _IMAGE_LIMIT or (limit and sum(len(data) for _, data in images) > limit)
-            or any(sniff_image_mime(data) != mime for mime, data in images)):
+            or any(mime is None for mime, _ in images)):
         raise RuntimeStoreError('invalid_params')
     staged = []
     for mime, data in images:

tests/gateway/test_api_image_mislabelled_mime.py

@@ -0,0 +1,17 @@
+"""A data URL whose label disagrees with its image bytes (``data:image/png`` carrying JPEG, a
+common SDK default) is admitted under the sniffed type, as main forwarded it to the provider."""
+import base64
+from pathlib import Path
+
+from gateway.session_api_turn import admit_api_turn
+
+JPEG = b'\xff\xd8\xff\xe0\x00\x10JFIF\x00\x01\x01\x00\x00\x01\x00\x01\x00\x00\xff\xd9'
+
+
+def test_mislabelled_image_commits_under_sniffed_type(api, owner):
+    url = 'data:image/png;base64,' + base64.b64encode(JPEG).decode()
+    parts = [{'type': 'text', 'text': 'look'}, {'type': 'image_url', 'image_url': {'url': url}}]
+    _, _, row = admit_api_turn(api, session_id='api-mislabel', user_message=parts, conversation_history=[])
+    media = row['payload']['api_turn_v1']['media']
+    assert len(media) == 1 and Path(media[0]['path']).read_bytes() == JPEG
+    assert Path(media[0]['path']).suffix == '.jpg'