fix: detect missing checkpoint file and surface clear error

User report on a different machine: 'AttributeError: NoneType has no attribute
lower' at comfy/utils.py:126 inside load_torch_file. Root cause: manifest's
meta.model references a checkpoint that isn't installed on this machine —
folder_paths.get_full_path returns None, that None propagates through
load_checkpoint_guess_config to load_torch_file, crashes cryptically.

Two defensive checks:

1. upscale_runner._run_upscale_thread: validates the session checkpoint
   resolves to a real file BEFORE calling load_checkpoint. If not, sets
   job['error'] with a clear actionable message ('Copy the .safetensors
   file over, or regenerate the images on this machine') and exits early.

2. florence2_hires._get_or_load_checkpoint_lora: same check before the
   fresh-load path (different per-item model). On missing file, falls back
   to the session base with a one-line log so the upscale still completes
   instead of crashing the whole job.

Tests: added folder_paths.get_full_path to the root conftest stub returning
a synthetic path so mocked-loader tests don't trip the new file-check.
96/96 still passing.

conftest.py

@@ -58,6 +58,12 @@ def _install_stubs():
     fp = sys.modules["folder_paths"]
     if not hasattr(fp, "get_output_directory"):
         fp.get_output_directory = lambda: os.path.join(_NODE_ROOT, "_test_output")  # type: ignore
+    if not hasattr(fp, "get_full_path"):
+        # Stub returns a synthetic path for any (folder, name) lookup so tests
+        # that don't care about file existence (e.g. mocked loaders) don't trip
+        # the "file not found -> fall back" guard in florence2_hires. Tests that
+        # specifically want to exercise the missing-file path can monkeypatch.
+        fp.get_full_path = lambda folder, name: f"<stubbed>/{folder}/{name}" if name else None  # type: ignore
 
     # server.PromptServer
     if "server" not in sys.modules:

florence2_hires.py

@@ -401,7 +401,25 @@ def _get_or_load_checkpoint_lora(item, fallback, model_source, cache, session_mo
         cache[key] = result
         return result
 
-    # Different model — full load.
+    # Different model — full load. Validate the file exists first; without this
+    # guard a missing checkpoint hits comfy/utils.load_torch_file(None,...) and
+    # crashes with "'NoneType' has no attribute 'lower'". Common scenario: manifest
+    # was generated on a different machine that had the per-item checkpoint
+    # installed.
+    try:
+        import folder_paths as _fp_check
+        ckpt_path_check = _fp_check.get_full_path("checkpoints", model_name)
+    except Exception:
+        ckpt_path_check = None
+    if ckpt_path_check is None:
+        print(
+            f"[Florence2HiResFix] Item references model '{model_name}' but the "
+            f"file is not installed in ComfyUI/models/checkpoints/. Falling back to "
+            f"session default."
+        )
+        cache[key] = fallback
+        return fallback
+
     try:
         model, clip, vae = ckpt_fn(
             target_model_name=model_name,

upscale_runner.py

@@ -124,9 +124,30 @@ def _run_upscale_thread(job, target_items, upscale_config, meta, manifest_data,
         _ext = "jpg" if _fmt in ("jpg", "jpeg") else _fmt
 
         # Load model, VAE, CLIP for conditioning
-        model_name = meta.get("model", "")
+        model_name = meta.get("model", "") or ""
         vae_name = meta.get("vae", "")
 
+        # Validate the checkpoint exists before calling load_checkpoint. Without
+        # this guard, a missing file ends up at comfy/utils.py:load_torch_file(None,
+        # ...) and crashes with the cryptic "'NoneType' object has no attribute
+        # 'lower'". Common cause: manifest copied from another machine where the
+        # checkpoint isn't installed; or manifest entry has model=None.
+        try:
+            import folder_paths as _fp_check
+            ckpt_path_check = _fp_check.get_full_path("checkpoints", model_name) if model_name else None
+        except Exception:
+            ckpt_path_check = None
+        if not model_name or ckpt_path_check is None:
+            job["status"] = "error"
+            job["error"] = (
+                f"Checkpoint '{model_name or '(empty)'}' not found in "
+                f"ComfyUI/models/checkpoints/. The session manifest references it but "
+                f"the file is not installed on this machine. Copy the .safetensors "
+                f"file over, or regenerate the images on this machine first."
+            )
+            print(f"[DashboardUpscale] ❌ {job['error']}")
+            return
+
         # VRAM hygiene before load_checkpoint: the previous workflow's model handles
         # may still be Python-referenced and won't be evicted by ComfyUI's LRU on a
         # new load_checkpoint call. soft_empty_cache + gc.collect releases those