Decide the conversation virtualization architecture and rollout route

[chuks-qua]

Parent

#1544

Question

Should Mcode retain 3.13.23, upgrade TanStack, or replace it with vlist, and what rollout route follows from the evidence?

Required evidence

• Choose one architecture from the child evidence.
• If a change wins, define the implementation boundary, state and measurement ownership, focus ownership, rollout slices, rollback condition, and regression gates.
• Decide whether the evidence warrants a separate map for other virtualized surfaces.
• Keep the decision tied to the accepted behavior and comparison contracts.

Blocked by

• Run the paired MessageList virtualization comparison #1549: Run the paired MessageList virtualization comparison

Out of scope

Do not implement or ship the chosen architecture in this issue.