Covers the dialogs' credential contract: a credential goes in and never comes back, a malformed one is refused before it is sent, a stored one is offered as Replace/Remove, an environment-set one is reported rather than editable, a failed save claims nothing, and the enable toggle writes through regardless.

## Before writing SPEC.md files

Read https://raw.githubusercontent.com/brillout/sdd/refs/heads/main/sdd.md
