fix(second pass): name the upsampler ComfyUI cannot load, instead of its traceback

Core's latent-upscale loader is an if/elif with no else, so an unrecognised file
falls off the end as "cannot access local variable 'model'". The architectures it
knows are probed here first, and an unknown one is reported by name and key shape.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

detailing.py

@@ -207,7 +207,7 @@ def load_latent_upsampler(model_name):
     if "post_upsample_res_blocks.0.conv2.bias" not in sd:
         # Not Lightricks' architecture. ComfyUI's own loader knows the others (and will know
         # the next one), so hand it over rather than declaring the file unusable here.
-        return _load_upsampler_via_core(model_name)
+        return _load_upsampler_via_core(model_name, sd)
     config = json.loads(metadata["config"])
     # ComfyUI v0.29.0 (upstream f8a3fd9d) moved the upsampler onto DynamicVram and made
     # `operations` a required argument of from_config; older cores build nn.Modules
@@ -225,7 +225,30 @@ def load_latent_upsampler(model_name):
     return model
 
 
-def _load_upsampler_via_core(model_name):
+# The state-dict keys ComfyUI's own loader branches on, and what each one is.
+# Its execute() is an if/elif/elif with NO else, so a file matching none of them falls off
+# the end and raises `cannot access local variable 'model'` — a Python internal that names
+# neither the file nor the problem. Probing here means an unknown architecture is reported
+# as what it is, and it also means we never depend on that missing else.
+CORE_UPSAMPLER_SIGNATURES = (
+    ("blocks.0.block.0.conv.weight", "Hunyuan Video 1.5 SR (720p)"),
+    ("up.0.block.0.conv1.conv.weight", "Hunyuan Video 1.5 SR (1080p)"),
+)
+
+
+def _key_families(sd, limit=6):
+    """A few distinguishing top-level key prefixes, to identify an unknown file by."""
+    seen = []
+    for key in sd:
+        head = str(key).split(".")[0]
+        if head not in seen:
+            seen.append(head)
+        if len(seen) >= limit:
+            break
+    return ", ".join(seen) or "no keys"
+
+
+def _load_upsampler_via_core(model_name, sd=None):
     """ComfyUI's Load Latent Upscale Model, for every architecture that is not LTX's."""
     try:
         from comfy_extras.nodes_hunyuan import LatentUpscaleModelLoader
@@ -233,6 +256,13 @@ def _load_upsampler_via_core(model_name):
         raise ValueError(
             f"{model_name} is not an LTX latent upsampler, and this ComfyUI has no other "
             "latent upscale model loader to try") from exc
+    if sd is not None and not any(k in sd for k, _ in CORE_UPSAMPLER_SIGNATURES):
+        known = ", ".join(name for _, name in CORE_UPSAMPLER_SIGNATURES)
+        raise ValueError(
+            f"{model_name} is not an architecture this ComfyUI can load as a latent "
+            f"upscale model. It knows Lightricks LatentUpsampler and {known}; this file's "
+            f"keys start with: {_key_families(sd)}. Either it is not a latent upsampler, or "
+            "it needs the custom node pack it shipped with")
     out = LatentUpscaleModelLoader.execute(model_name)
     result = getattr(out, "result", out)
     if isinstance(result, (tuple, list)):

tests/test_second_pass.py

@@ -16,6 +16,7 @@ import sys
 import types
 from pathlib import Path
 
+import pytest
 import torch
 
 sys.path.insert(0, str(Path(__file__).resolve().parents[1]))
@@ -291,3 +292,33 @@ def test_auto_says_what_to_install_when_nothing_fits(monkeypatch):
 def test_an_explicitly_chosen_file_is_always_honoured(monkeypatch):
     _installed(monkeypatch, [])
     assert detailing.resolve_upsampler_name("my_upsampler.safetensors", 24) == "my_upsampler.safetensors"
+
+
+# ── an upsampler ComfyUI cannot load at all ───────────────────────────────────
+
+def test_an_unknown_upsampler_architecture_is_named_not_a_python_error(monkeypatch):
+    """Core's loader is an if/elif with no else, so a file it does not recognise falls off
+    the end as `cannot access local variable 'model'` — which names neither the file nor
+    the problem, and reads like a FunPack bug."""
+    called = []
+    monkeypatch.setitem(
+        sys.modules, "comfy_extras.nodes_hunyuan",
+        types.SimpleNamespace(LatentUpscaleModelLoader=types.SimpleNamespace(
+            execute=lambda name: called.append(name))))
+    sd = {"encoder.layers.0.weight": object(), "decoder.out.bias": object()}
+    with pytest.raises(ValueError) as exc:
+        detailing._load_upsampler_via_core("h3_upsampler.safetensors", sd)
+    msg = str(exc.value)
+    assert "h3_upsampler.safetensors" in msg
+    assert "encoder, decoder" in msg          # what the file actually looks like
+    assert "Hunyuan Video 1.5 SR (720p)" in msg
+    assert not called, "core's loader should not be reached with a file it cannot branch on"
+
+
+def test_an_architecture_core_does_know_is_still_handed_over(monkeypatch):
+    monkeypatch.setitem(
+        sys.modules, "comfy_extras.nodes_hunyuan",
+        types.SimpleNamespace(LatentUpscaleModelLoader=types.SimpleNamespace(
+            execute=lambda name: ("loaded",))))
+    sd = {"blocks.0.block.0.conv.weight": object()}
+    assert detailing._load_upsampler_via_core("hunyuan_sr.safetensors", sd) == "loaded"