Ship the 0.8.0 first-hour and campaign milestone

Add the campaign shell, pause-safe checkpoint resume, post-shift campaign
continue, confirmed campaign reset, difficulty presets, searchable Help,
content-matrix validation, recovery events, contextual dialogue, policy/debrief
context and eligible-event previews. Extend persistence with atomic separate
files and add campaign/checkpoint/tutorial smokes. Headless 247/247, Python
94/94, tutorial/campaign/session/scenario smokes green.

src/autoload/save.gd

@@ -4,6 +4,8 @@ extends Node
 
 const SHIFT_RESULTS_FILE := "shift_results.json"
 const SETTINGS_FILE := "settings.json"
+const CAMPAIGN_FILE := "campaign.json"
+const SHIFT_STATE_FILE := "shift_state.json"
 
 func _load_json(file_name: String) -> Variant:
 	var path := "user://" + file_name
@@ -17,13 +19,17 @@ func _load_json(file_name: String) -> Variant:
 
 func _save_json(file_name: String, data: Variant) -> Error:
 	var path := "user://" + file_name
+	var temp := path + ".tmp"
 	var text := JSON.stringify(data, "\t")
-	var f := FileAccess.open(path, FileAccess.WRITE)
+	var f := FileAccess.open(temp, FileAccess.WRITE)
 	if f == null:
 		return FileAccess.get_open_error()
 	f.store_string(text)
 	f.close()
-	return OK
+	# Replace the target only after the complete JSON has been written, so a
+	# crash cannot leave a partial save in place.
+	return DirAccess.rename_absolute(ProjectSettings.globalize_path(temp),
+		ProjectSettings.globalize_path(path))
 
 ## Load previous shift results. Returns Array of Dictionaries or [].
 func load_shift_results() -> Array:
@@ -38,6 +44,29 @@ func save_shift_result(result: Dictionary) -> Error:
 	results.append(result)
 	return _save_json(SHIFT_RESULTS_FILE, results)
 
+## Campaign/session progression (separate from settings and shift history).
+func load_campaign() -> Dictionary:
+	var data = _load_json(CAMPAIGN_FILE)
+	return data if data is Dictionary else {}
+
+func save_campaign(data: Dictionary) -> Error:
+	return _save_json(CAMPAIGN_FILE, data)
+
+func reset_campaign() -> Error:
+	return _save_json(CAMPAIGN_FILE, {})
+
+## Mid-shift checkpoint. Kept separate so a completed shift history is never
+## overwritten by a resumable snapshot.
+func load_shift_state() -> Dictionary:
+	var data = _load_json(SHIFT_STATE_FILE)
+	return data if data is Dictionary else {}
+
+func save_shift_state(data: Dictionary) -> Error:
+	return _save_json(SHIFT_STATE_FILE, data)
+
+func clear_shift_state() -> Error:
+	return _save_json(SHIFT_STATE_FILE, {})
+
 ## Defaults for player settings. Kept in code so a missing or partial
 ## settings.json still produces a usable config.
 const DEFAULT_SETTINGS := {