a two-tuple from encode_prompt is not always (embeds, negative)

Krea 2 returns (prompt_embeds, prompt_embeds_mask), and the generic path read
any 2-tuple as SD 1.x's (embeds, negative_embeds) -- so it handed the mask
over as a negative prompt and the pipeline answered

    If `prompt_embeds` are provided, `prompt_embeds_mask` also have to be
    passed.

which reads as a missing argument rather than a mislabelled one, and arrives
wrapped in "Failed to load image model" two and a half minutes into the load.

Told apart by the pipeline's own __call__ signature rather than a list of
family names, and the answer for those families is to pre-encode nothing:
weighted 75-token windows are a CLIP-pair feature that means nothing to them,
which is why Z-Image already takes that path.
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_014T3rZnLhydX9QqUcfBbqLu

codai/api/images.py

@@ -1655,7 +1655,20 @@ async def _generate_with_diffusers(pipeline, request, global_args, http_request=
                     _ep_kwargs["negative_prompt"] = neg_prompt or None
                 enc = pipeline.encode_prompt(**_ep_kwargs)
                 # enc is a tuple; length varies by pipeline type
-                if len(enc) == 2:
+                _call_params = set(
+                    _inspect.signature(pipeline.__call__).parameters)
+                if len(enc) == 2 and 'prompt_embeds_mask' in _call_params:
+                    # Krea 2 and the Qwen-Image family also return a 2-tuple,
+                    # but it is (prompt_embeds, prompt_embeds_mask) -- not a
+                    # negative. Passing the mask AS the negative is what the
+                    # pipeline reports as "If `prompt_embeds` are provided,
+                    # `prompt_embeds_mask` also have to be passed", which reads
+                    # like a missing argument rather than a mislabelled one.
+                    # These are not CLIP-pair pipelines, so weighted 75-token
+                    # windows mean nothing to them: let the pipeline encode the
+                    # prompt itself, the way Z-Image already does.
+                    embed_kwargs = {}
+                elif len(enc) == 2:
                     # SD 1.x: (prompt_embeds, negative_prompt_embeds)
                     embed_kwargs = {
                         'prompt_embeds': enc[0],

tests/test_prompt_embeds_mask.py

+"""A 2-tuple from encode_prompt is not always (embeds, negative).
+
+Krea 2 and the Qwen-Image family return ``(prompt_embeds, prompt_embeds_mask)``
+— the second element is a mask, not a negative prompt. Handing it over as
+``negative_prompt_embeds`` makes the pipeline answer
+
+    If `prompt_embeds` are provided, `prompt_embeds_mask` also have to be
+    passed. Make sure to generate `prompt_embeds_mask` from the same text
+    encoder that was used to generate `prompt_embeds`.
+
+which reads like a missing argument rather than a mislabelled one, and it
+arrives wrapped in "Failed to load image model", minutes into a 7.4B load.
+"""
+import inspect
+
+from codai.api import images as images_mod
+
+
+def _source():
+    return inspect.getsource(images_mod)
+
+
+def test_the_mask_families_are_told_apart_by_signature_not_by_name():
+    """A name list would have to grow for every new family; the pipelines that
+    need a mask say so in their own __call__ signature."""
+    src = _source()
+    assert "'prompt_embeds_mask' in _call_params" in src
+    # And the discriminator comes from the pipeline itself.
+    assert "_inspect.signature(pipeline.__call__).parameters" in src
+
+
+def test_a_mask_pipeline_falls_back_to_its_own_encoder():
+    """Weighted 75-token windows are a CLIP-pair feature and mean nothing to
+    these pipelines, so the right answer is to pass the raw prompt."""
+    src = _source()
+    i = src.index("'prompt_embeds_mask' in _call_params")
+    branch = src[i:i + 1200]
+    assert "embed_kwargs = {}" in branch
+    # The SD 1.x reading must still exist, just after it.
+    assert "elif len(enc) == 2:" in branch
+    assert "'negative_prompt_embeds': enc[1]," in branch
+
+
+def test_sd_one_x_still_gets_its_negative_embeds():
+    """The ordinary pair is untouched: enc[1] is a negative there."""
+    src = _source()
+    sd = src.index("# SD 1.x: (prompt_embeds, negative_prompt_embeds)")
+    after = src[sd:sd + 300]
+    assert "'prompt_embeds': enc[0]," in after
+    assert "'negative_prompt_embeds': enc[1]," in after