FPF Agent Stack

Feature: Guard tri-state discipline Guards return pass, degrade, or abstain; unknown evidence never coerces to pass. @guard Scenario: Missing required evidence causes abstain Given the tool "write_file" requires evidence carrier "session_open" And evidence carrier "session_open" is missing When the guard is evaluated Then the guard decision should be "abstain" @guard Scenario: Execution failure results in degrade Given the guard decision is "pass" When the tool execution fails with error "disk full" Then the guard decision should be "degrade" And the evidence should include the captured error