fix(sampler): record and restore Default instead of the None sentinel

The keep-current-scheduler sentinel leaked into user-facing surfaces:
infotexts and filenames recorded Sampler: None, restoring such an
infotext pushed an invalid value into the dropdown, and the API
samplers list never offered Default at all.

- infotext always records the sampler, mapping a stray None to Default
- parse maps legacy Sampler: None infotexts to Default
- api samplers list leads with Default; the remaining excluded config
  keys are shared templates, not samplers

modules/api/endpoints.py

@@ -15,9 +15,9 @@ def _format_tags(raw_tags):
 
 def get_samplers():
     from modules import sd_samplers_diffusers
-    all_samplers = []
+    all_samplers = [{'name': 'Default', 'options': {}}] # restores the model's own scheduler; first to match the ui dropdown order
     for k, v in sd_samplers_diffusers.config.items():
-        if k in ['All', 'Default', 'Res4Lyf']:
+        if k in ['All', 'Default', 'Res4Lyf']: # remaining keys are shared config templates, not samplers
             continue
         all_samplers.append({'name': k, 'options': v})
     return all_samplers

modules/infotext.py

@@ -83,6 +83,8 @@ def parse(infotext):
             params[key] = False
         elif key == 'VAE' and val == 'TAESD':
             params["VAE type"] = 'Tiny'
+        elif key == 'Sampler' and val == 'None':
+            params[key] = 'Default' # legacy infotexts recorded the keep-current-scheduler sentinel, which is not a dropdown choice
         elif size is not None:
             params[f"{key}-1"] = int(size.group(1))
             params[f"{key}-2"] = int(size.group(2))

modules/processing_info.py

@@ -54,7 +54,7 @@ def create_infotext(p: StableDiffusionProcessing, all_prompts=None, all_seeds=No
         # basic
         "Steps": p.steps,
         "Size": f"{p.width}x{p.height}" if hasattr(p, 'width') and hasattr(p, 'height') else None,
-        "Sampler": p.sampler_name if p.sampler_name != 'Default' else None,
+        "Sampler": p.sampler_name if p.sampler_name != 'None' else 'Default',
         "Scheduler": shared.sd_model.scheduler.__class__.__name__ if getattr(shared.sd_model, 'scheduler', None) is not None else None,
         "Seed": all_seeds[index],
         "Seed resize from": None if p.seed_resize_from_w <= 0 or p.seed_resize_from_h <= 0 else f"{p.seed_resize_from_w}x{p.seed_resize_from_h}",