With no current list the proof goes only through a provider the member names, never the
session's sign-in provider: a sign-in through an unlinked provider makes Heimdall mint an
orphan account holding that login. Link buttons need a current list. The unlink completion
must say a step-up was requested. POST /auth/heimdall/complete answers no-store. The fake
Heimdall now models orphan minting, derives step_up_at from the start's stepUp flag, and
enforces the app secret, sign_in-only, unsupported-provider and 600 s rules.
Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>
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