Fix training start NameError, the load-order guard test and CPU-only diffusion tests

- start_training forwards resume_source_run_id to _start_training_impl, which
  reads it. Without it every start raised NameError.
- Restore main's anchor in the load-marker order test: the file now has an
  earlier `if config.is_gguf:`, so indexing the first one compared the wrong
  branch.
- The two diffusion tests that reach diffusers now skip when it is absent,
  matching the CPU repo-test env.
- The UI smoke finds nav rows that live in the sidebar's More flyout.

studio/backend/core/training/training.py

@@ -864,16 +864,24 @@ class TrainingBackend:
                 return False
             self._start_in_progress = True
         try:
-            return self._start_training_impl(job_id, before_spawn = before_spawn, **kwargs)
+            return self._start_training_impl(
+                job_id,
+                before_spawn = before_spawn,
+                resume_source_run_id = resume_source_run_id,
+                **kwargs,
+            )
         finally:
             with self._lock:
                 self._start_in_progress = False
 
+    # Named, not part of **kwargs: the body reads it directly, and it must not reach the
+    # worker config either (start_training's own signature keeps it out).
     def _start_training_impl(
         self,
         job_id: str,
         *,
         before_spawn = None,
+        resume_source_run_id: Optional[str] = None,
         **kwargs,
     ) -> bool:
         # Join prior pump thread — refuse to start if it won't die

studio/backend/tests/test_diffusion_dit_trainer_flow_shift.py

@@ -29,7 +29,8 @@ def _qwen_scheduler():
     # The Qwen/Qwen-Image scheduler config: shift=1.0 is SKIPPED at init because
     # use_dynamic_shifting is true, base_shift = max_shift = log 3 (constant inference mu),
     # exponential time shift, terminal stretch to 0.02.
-    from diffusers import FlowMatchEulerDiscreteScheduler
+    diffusers = pytest.importorskip("diffusers")
+    FlowMatchEulerDiscreteScheduler = diffusers.FlowMatchEulerDiscreteScheduler
     return FlowMatchEulerDiscreteScheduler(
         num_train_timesteps = 1000,
         shift = 1.0,

studio/backend/tests/test_diffusion_te_prequant.py

@@ -550,6 +550,7 @@ def test_cast_fp8_is_idempotent_on_precast_encoder():
     the engaged cast report as failed and status show no TE quant)."""
     import torch
 
+    pytest.importorskip("diffusers")  # _cast_fp8 installs diffusers' layerwise hooks
     from core.inference.diffusion_precision import _cast_fp8
 
     target = types.SimpleNamespace(dtype = torch.bfloat16)

studio/backend/tests/test_gguf_load_cache_reuse.py

@@ -785,7 +785,12 @@ class TestLoadHubDownloadExclusion:
 
     def test_load_marker_precedes_hub_guard_and_unload(self):
         source = (Path(__file__).resolve().parent.parent / "routes" / "inference.py").read_text()
-        gguf_branch = source[source.index("if config.is_gguf:") :]
+        # _load_model_impl has more than one `if config.is_gguf:`, so anchor on
+        # the branch that actually owns the load marker rather than the first
+        # one in the file, which belongs to an earlier check.
+        marker = source.index("enter_context(gguf_load_in_flight")
+        gguf_branch_start = source.rindex("if config.is_gguf:", 0, marker)
+        gguf_branch = source[gguf_branch_start:]
 
         # The gguf_load_in_flight marker must be entered before the hub-download
         # guard and the unload so a concurrent load can't race the download
@@ -794,7 +799,7 @@ class TestLoadHubDownloadExclusion:
         # inherited value (e.g. a carried --no-mmproj) shapes the guard's
         # require_mmproj. Anchor on the call form so the assertion pins the
         # endpoint's call site, not the function definition.
-        assert source.index("= _resolve_inherited_extra_args(") < source.index("if config.is_gguf:")
+        assert source.index("= _resolve_inherited_extra_args(") < gguf_branch_start
         assert (
             gguf_branch.index("enter_context(gguf_load_in_flight")
             < gguf_branch.index("_hub_download_blocks_gguf_load")

tests/studio/playwright_chat_ui.py

@@ -1155,6 +1155,23 @@ with sync_playwright() as p:
             if c.count() > 0:
                 btn = c
                 break
+        if btn is None:
+            # Unpinned rows (Video, Recipes, Export by default) live in the sidebar's
+            # "More" flyout. It opens on hover, so hover first; a click would toggle it
+            # straight back shut. Click is the fallback for a no-hover environment.
+            more_btn = page.get_by_role(
+                "button", name = re.compile(r"^\s*More\s*$", re.I)
+            ).first
+            if more_btn.count() > 0:
+                more_btn.hover()
+                page.wait_for_timeout(500)
+                item = page.get_by_role("menuitem", name = re.compile(label, re.I)).first
+                if item.count() == 0:
+                    more_btn.click(force = True)
+                    page.wait_for_timeout(500)
+                    item = page.get_by_role("menuitem", name = re.compile(label, re.I)).first
+                if item.count() > 0:
+                    btn = item
         if btn is None:
             soft_fail(f"nav '{label}' not found")
             return False