Save The Tree implementation and acceptance work in progress

Preserve production code, regression fixtures, audio assets and provenance, test infrastructure, and the original-completion plan and progress ledger. Final game and Windows acceptance remain pending; excluded local artifacts and native experiments are not part of this snapshot.

scripts/economy/economy_service.gd

@@ -23,6 +23,8 @@ var _transaction_ids: Dictionary = {}
 var _idempotency_keys: Dictionary = {}
 var _next_transaction_sequence := 1
 var _pending_transaction_notifications: Dictionary = {}
+# Transient nested observer boundary; never serialized as gameplay state.
+var _notification_scopes: Array[Array] = []
 
 
 func _init(account_definitions: Dictionary = {}) -> void:
@@ -308,7 +310,10 @@ func post(
 		_next_transaction_sequence = generated_sequence + 1
 	var posted_entries := get_transaction_entries(effective_id)
 	if emit_notification:
-		transaction_posted.emit(effective_id, posted_entries)
+		if _notification_scopes.is_empty():
+			transaction_posted.emit(effective_id, posted_entries)
+		else:
+			_notification_scopes.back().append(effective_id)
 	else:
 		_pending_transaction_notifications[effective_id] = true
 	return CommandResultType.succeeded(0, {
@@ -318,6 +323,36 @@ func post(
 	})
 
 
+## Retain ordinary post semantics while postponing observer delivery through a
+## complete event effect/cost boundary. Explicit emit_notification=false remains
+## owned by its existing caller, including Operations and supply transactions.
+func notification_scope_depth() -> int:
+	return _notification_scopes.size()
+
+
+func begin_notification_scope() -> void:
+	_notification_scopes.append([])
+
+
+func end_notification_scope() -> void:
+	assert(not _notification_scopes.is_empty(), "Balanced notification scope required.")
+	if _notification_scopes.is_empty():
+		return
+	var queued: Array = _notification_scopes.pop_back()
+	if not _notification_scopes.is_empty():
+		_notification_scopes.back().append_array(queued)
+		return
+	var seen: Dictionary = {}
+	for raw_id: Variant in queued:
+		var transaction_id := StringName(raw_id)
+		# Restoring a ledger removes rolled-back IDs. A failure branch can reuse
+		# an ID; deliver the surviving final receipt once in insertion order.
+		if seen.has(transaction_id) or not _transaction_ids.has(transaction_id):
+			continue
+		seen[transaction_id] = true
+		transaction_posted.emit(transaction_id, get_transaction_entries(transaction_id))
+
+
 func has_pending_transaction_notification(transaction_id: StringName) -> bool:
 	return _pending_transaction_notifications.has(transaction_id)