“Revoice this conversation as GLaDOS” sounds like a request to rewrite the final answer. For ordinary dialogue, that may even appear to work.
Tool traces make the shortcut obvious. The assistant may reason about what to do, issue several calls, read the results and only then answer. Rewriting the last paragraph leaves the decisions, tool arguments and reactions untouched. The conversation ends in character but reaches that ending as a different assistant.
The GLaDOS pipeline now regenerates the complete assistant side while keeping the user messages and tool results fixed. Each assistant slot is produced from the context available at that point; later tool output cannot leak backwards into an earlier decision.
This is slower than a style pass and much easier to get wrong. It is also the only version which teaches the model to remain GLaDOS while doing the work, rather than adding the voice after the work is already finished.