Sud: server always starts empty; sude/*.json is purely a client concern

Several sude/*.json schedules can exist on disk; only one runs at a
time, chosen by a client Load. Sud no longer takes a path at all - it
starts empty (EMPTY_SUD) and the server config no longer names a
specific schedule file, removing the implicit link to sud_0010.json
in particular. Reading/writing sude/*.json is now entirely the
client's job (e.g. the GUI's Load/Save file dialogs); the server's Sud
only ever holds whatever was last Load()ed, in memory, until replaced
or the server restarts.

Updates demo_sud.py/demo_sud_save_load.py to construct an empty Sud()
and load() a schedule explicitly, matching the new constructor.

scripts/demos/sud/demo_sud.py

@@ -1,3 +1,4 @@
+import json
 import numpy as np
 from matplotlib.pyplot import plot, step, figure, subplot, grid, show, legend, yticks
 from components.sud import Sud, SudState
@@ -33,7 +34,9 @@ if __name__ == '__main__':
 		}
 	}
 
-	sud = Sud("sude/sud_0010.json")
+	sud = Sud()
+	with open("sude/sud_0010.json") as f:
+		sud.load(json.load(f))
 
 	first_step = sud.schedule[0]
 	plant_params = {

scripts/demos/sud/demo_sud_save_load.py

@@ -1,45 +1,44 @@
 import json
-import shutil
-import tempfile
-from pathlib import Path
 
 from components.sud import Sud, SudState
 
 # Console-only walkthrough of Sud.save()/load() (no plot - there's no
-# numeric data here, just JSON plumbing). Runs against a scratch copy of a
-# real sud.json so sude/sud_0010.json itself is never touched.
+# numeric data here, just JSON plumbing). load()/save() are purely
+# in-memory - Sud itself never reads or writes anything under sude/.
 
 if __name__ == '__main__':
-	with tempfile.TemporaryDirectory() as tmp:
-		path = Path(tmp) / "sud.json"
-		shutil.copy("sude/sud_0010.json", path)
+	sud = Sud()
+	print(f"Starts out empty: '{sud.name}', {len(sud.schedule)} steps")
 
-		sud = Sud(str(path))
-		print(f"Loaded '{sud.name}', {len(sud.schedule)} steps")
+	with open("sude/sud_0010.json") as f:
+		doc = json.load(f)
+	assert sud.load(doc) is True
+	print(f"Loaded '{sud.name}', {len(sud.schedule)} steps")
 
-		doc = sud.save()
-		assert doc['Name'] == sud.name
-		print("save() returned the on-disk document")
+	saved = sud.save()
+	assert saved['Name'] == sud.name
+	print("save() returned the running document")
 
-		sud.state = SudState.RAMPING
-		assert sud.load(doc) is False
-		print("load() refused while RAMPING")
+	sud.state = SudState.RAMPING
+	assert sud.load(saved) is False
+	print("load() refused while RAMPING")
 
-		sud.state = SudState.IDLE
-		doc['Name'] = 'Sud-Renamed'
-		doc['steps'][0]['descr'] = 'Edited step'
-		assert sud.load(doc) is True
-		assert sud.name == 'Sud-Renamed'
-		assert sud.schedule[0]['descr'] == 'Edited step'
-		assert sud.state == SudState.IDLE
-		print("load() applied the edit and reset to IDLE")
+	sud.state = SudState.IDLE
+	saved['Name'] = 'Sud-Renamed'
+	saved['steps'][0]['descr'] = 'Edited step'
+	assert sud.load(saved) is True
+	assert sud.name == 'Sud-Renamed'
+	assert sud.schedule[0]['descr'] == 'Edited step'
+	assert sud.state == SudState.IDLE
+	print("load() applied the edit, purely in memory")
 
-		on_disk = json.loads(path.read_text())
-		assert on_disk['Name'] == 'Sud-Renamed'
-		print("load() persisted the edit to disk")
+	with open("sude/sud_0010.json") as f:
+		on_disk = json.load(f)
+	assert on_disk['Name'] != 'Sud-Renamed'
+	print("sude/sud_0010.json on disk is untouched")
 
-		assert sud.load({'Name': 'broken'}) is False
-		assert sud.name == 'Sud-Renamed'
-		print("load() rejected malformed data, left schedule untouched")
+	assert sud.load({'Name': 'broken'}) is False
+	assert sud.name == 'Sud-Renamed'
+	print("load() rejected malformed data, left schedule untouched")
 
 	print("All sud save/load checks passed")