A hijacked session is authenticated by definition, which is why credential controls do not detect it: the token is real, the MFA prompt already succeeded, and only the operator has changed. Token theft, adversary-in-the-middle phishing kits, malicious browser extensions, and infostealer malware all target the artifact issued after authentication rather than the password or second factor. Detection therefore has to come from the behavior of whoever is now driving the session. When the operator changes, cadence variance shifts, cursor micro-corrections change shape or disappear under scripted control, hesitation structure moves, and entropy collapses toward linearity when automation is driving. MagenTrust compares the live signature against the session's established signature and gates the sensitive action on the result, so a wire transfer, role change, bulk export, or privileged configuration change blocks on the verdict rather than being logged after execution. Soft policy fails open on unclear signal; hard policy fails closed for high-risk actions.