fix: late-branch guidance no longer leaks the model

Its step wrapper held its own ModelPatcher, a cycle only a full gc frees;
that gc clears ComfyUI's weak link to the parent copy first, leaving it
tracking a dead model ("memory leak with model MiniMaxH3").

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

samplers.py

@@ -8633,6 +8633,11 @@ class FunPackLTXAVSceneChainSampler:
             old_wrapper = patched.model_options.get("model_function_wrapper")
             _w = float(w)
             stats = {"guided": 0, "why": None}
+            # The wrapper lives in patched.model_options, so it must not hold `patched`: that
+            # cycle is only freed by a full gc, which clears ComfyUI's weak link to the
+            # parent copy first and leaves it tracking a dead model ("memory leak with model").
+            # The shapes live on the shared base model, which holds no patcher.
+            span_source = types.SimpleNamespace(model=patched.model)
 
             def _guided(apply_fn, cond_only):
                 def _apply(x, t, **c):
@@ -8650,7 +8655,7 @@ class FunPackLTXAVSceneChainSampler:
                         weak = apply_fn(x, t, **{**c, "transformer_options": weak_to})
                     finally:
                         saved.pop("h", None)
-                    span = _video_span(patched, normal)
+                    span = _video_span(span_source, normal)
                     if span is None:
                         # A plain 5-D latent is picture only; an unreadable packed one is
                         # left alone rather than guessed at.

tests/test_late_guidance.py

@@ -143,3 +143,39 @@ def test_strength_learns_from_ratings(monkeypatch, tmp_path):
     assert d.commit("k", -1.0) is None
     assert d.choose("k", "off", 0.5)[0] is None
     assert d.choose("", "learned", 0.5)[0] is None          # no key: off
+
+
+def test_installed_copies_free_without_a_full_gc():
+    """A hook that holds its own ModelPatcher is a cycle: only a full gc frees it, and that
+    clears ComfyUI's weak link to the parent copy first -> "memory leak with model".
+    Real ComfyUI in a subprocess: this suite stubs `comfy`."""
+    import os
+    import subprocess
+    import pytest
+    root = Path(os.environ.get("COMFYUI_DIR", Path.home() / "Documents" / "ComfyUI"))
+    if not (root / "comfy" / "model_patcher.py").exists():
+        pytest.skip("no ComfyUI checkout to test against")
+    code = f"""
+import sys, gc, weakref
+sys.path[:0] = [{str(Path(__file__).resolve().parents[1])!r}, {str(root)!r}]
+import torch, comfy.model_patcher as mp, samplers
+gc.disable()
+class Net(torch.nn.Module):
+    def __init__(self):
+        super().__init__()
+        self.blocks = torch.nn.ModuleList([torch.nn.Identity() for _ in range(6)])
+class Base(torch.nn.Module):
+    def __init__(self):
+        super().__init__()
+        self.diffusion_model = Net()
+root = mp.ModelPatcher(Base(), torch.device("cpu"), torch.device("cpu"))
+s = samplers.FunPackLTXAVSceneChainSampler()
+for name, install in (("late", lambda m: s._install_late_branch(m, 3, 0.5)[0]),
+                      ("stas", lambda m: s._install_stas(m, 2, 2.0, torch.zeros(1, 24, 2, 4, 6))[0])):
+    p = install(root.clone())
+    ref = weakref.ref(p)
+    del p
+    assert ref() is None, name + " copy is in a reference cycle"
+"""
+    done = subprocess.run([sys.executable, "-c", code], cwd=root, capture_output=True, text=True)
+    assert done.returncode == 0, done.stderr[-2000:]