A Strategy Is a Document, Not a Mood
A profile names the seams an experiment is allowed to vary: instruction depth, instruction budget, context length, truncation, compaction, tool set, guards, parallelism, orchestrator, routing, limits. It is hashed into session_start and rides every request. Changing a live session's soul mid-flight is not an experiment. It is editing the instrument while you claim to measure the specimen.
Want a different strategy? Open a new session on a new profile, or fork a prefix and continue under a recorded change. Reseed and fork copy a verified prefix into a new identifier. The source notebook is not rewritten. A later reader can say which hash was in force when a step ran.
What Frozen Does Not Mean
Operator transitions still append: model change, identity change, policy change. Those are lines. They are not silent mutations of the birth profile. Resume folds the latest state. The birth line remains what it was. Confusing the two is how a brain switch left metadata describing the birth brain — the record track already closed that hole.