Fix/adjust diffusion: clear stale metadata on failed swap for PR #5754

When a swap load fails after the previous pipeline is released,
status() previously reported is_loaded=false on top of the OLD
repo/family/base_repo metadata, which the frontend then rendered
as a misleading 'still loaded: X' label. Clear all metadata
atomically with the pipe drop so a failed swap reports a clean
empty status plus last_error. Add regression test.

studio/backend/core/inference/diffusion.py

@@ -334,9 +334,10 @@ class DiffusionBackend:
         for VAE / text encoders. ``family_override`` short-circuits the
         substring matcher when an exotic repo name confuses it.
 
-        Raises ``RuntimeError`` on failure with a user-facing message;
-        the previous pipeline (if any) stays loaded so a failed swap
-        does not leave Studio in an unusable state.
+        Raises ``RuntimeError`` on failure with a user-facing message.
+        On a failed swap the previous pipeline is also released to
+        keep peak VRAM bounded; status() reports is_loaded=false with
+        last_error set so the caller can react.
         """
         from huggingface_hub import hf_hub_download
         import diffusers
@@ -469,7 +470,19 @@ class DiffusionBackend:
                 old = self._pipe
                 if old is not None:
                     with self._lock:
+                        # Clear ALL metadata together so a failed swap
+                        # cannot leave status() reporting the previous
+                        # repo / family / base_repo on top of an empty
+                        # pipe. The except block below will restore
+                        # last_error so the caller knows what happened.
                         self._pipe = None
+                        self._family = None
+                        self._repo_id = None
+                        self._gguf_path = None
+                        self._base_repo = None
+                        self._device = None
+                        self._dtype = None
+                        self._loaded_at = None
                     _release(old)
                     old = None
 

studio/backend/tests/test_diffusion_backend.py

@@ -417,6 +417,49 @@ def test_load_model_recovers_after_failure(monkeypatch):
     assert s["last_error"] and "simulated load failure" in s["last_error"]
 
 
+def test_failed_swap_clears_previous_metadata(monkeypatch):
+    """After a successful load, a subsequent failing load must NOT
+    leave status() reporting the OLD repo/family/base_repo on top of
+    is_loaded=false. The clear must be atomic with the pipe drop."""
+    import sys
+
+    _install_fake_diffusers(monkeypatch)
+    from core.inference.diffusion import get_diffusion_backend
+
+    backend = get_diffusion_backend()
+    # First load succeeds.
+    backend.load_model(
+        "unsloth/FLUX.2-klein-4B-GGUF",
+        gguf_filename = "flux-2-klein-4b-Q4_K_S.gguf",
+    )
+    s_before = backend.status()
+    assert s_before["is_loaded"] is True
+    assert s_before["repo_id"] == "unsloth/FLUX.2-klein-4B-GGUF"
+
+    # Replace from_pretrained on the SAME fake module with a raising one
+    # without re-installing the rest of the fakes.
+    fake = sys.modules["diffusers"]
+    def _boom(cls, *a, **kw):
+        raise RuntimeError("simulated swap failure")
+    fake.Flux2KleinPipeline.from_pretrained = classmethod(_boom)
+
+    with pytest.raises(RuntimeError, match = "Failed to load diffusion model"):
+        backend.load_model(
+            "unsloth/FLUX.2-dev-GGUF",
+            gguf_filename = "flux2-dev-Q4_K_S.gguf",
+        )
+
+    s_after = backend.status()
+    assert s_after["is_loaded"] is False
+    # Critically: stale metadata from the previous successful load
+    # must be cleared, not just the pipe.
+    assert s_after["repo_id"] is None
+    assert s_after["family"] is None
+    assert s_after["base_repo"] is None
+    assert s_after["gguf_filename"] is None
+    assert s_after["last_error"] and "simulated swap failure" in s_after["last_error"]
+
+
 def test_load_model_swap_drops_previous(monkeypatch):
     _install_fake_diffusers(monkeypatch)
     from core.inference.diffusion import get_diffusion_backend