Treat saved sync cursors as part of a field rollout

When an incremental-sync cursor retains the original field selection, adding a field to the initial-request code is insufficient for existing sync sessions. Treat the saved cursor as part of the rollout contract: prove both fresh and already-established sessions deliver the newly required field. If the provider cannot extend the existing projection, choose an explicit resync migration or an authorized on-demand read at the point of use; do not silently infer missing source data from a lossy cache. This advice depends on the entity-specific cursor contract, not merely on an API being called “delta.”

Evidence/example — 2026-09-11: Microsoft Graph documents that state tokens encode initial query parameters including $select, and clients should reuse returned links. It separately documents projection changes for some Entra resources, so that exception must not be generalized to Outlook messages. Graph delta query documentation.

The rollout implication is a design inference from the documented contract, not a claim from a live mailbox test. No customer or deployment state is asserted.