Coerce num_epochs in normalized() and use utf-8 for run records

num_epochs was only int-coerced for the range check, so a string value
from a dict-built config would reach resolve_train_steps' arithmetic;
normalized() now stores the coerced int. Run record reads/writes pass
encoding utf-8 explicitly so non-ASCII prompts survive on Windows

studio/backend/core/training/diffusion_train_common.py

@@ -407,6 +407,7 @@ class DiffusionLoraConfig:
             lora_target_modules = targets,
             max_grad_norm = float(self.max_grad_norm),
             hf_token = token or None,
+            num_epochs = int(self.num_epochs),
             cache_variants = int(self.cache_variants),
             compile_transformer = compile_transformer,
             base_precision = base_precision,

studio/backend/core/training/diffusion_training_service.py

@@ -99,7 +99,7 @@ def list_diffusion_runs(limit: int = 20) -> list[dict]:
     out: list[dict] = []
     for p in files[: max(0, int(limit))]:
         try:
-            rec = json.loads(p.read_text())
+            rec = json.loads(p.read_text(encoding = "utf-8"))
         except Exception:  # noqa: BLE001 -- a corrupt record never breaks the listing
             continue
         # A valid-JSON file with the wrong shape (an old or hand-edited record that is not a
@@ -124,7 +124,7 @@ def get_diffusion_run(job_id: str) -> Optional[dict]:
         return None
     p = _runs_dir() / f"{job_id}.json"
     try:
-        return json.loads(p.read_text())
+        return json.loads(p.read_text(encoding = "utf-8"))
     except Exception:  # noqa: BLE001 -- missing/corrupt record
         return None
 
@@ -403,7 +403,7 @@ class DiffusionTrainingService:
                 },
             }
             path = _runs_dir() / f"{s['job_id']}.json"
-            path.write_text(json.dumps(record))
+            path.write_text(json.dumps(record), encoding = "utf-8")
         except Exception:  # noqa: BLE001 -- persisting history must never break the run
             pass