BIDS-SRB Protocol Amendment A06: Infrastructure-invalid Attempt Replacement Rule v1.2

Post-registration, post-baseline-engineering and pre-fault amendment A06 to BIDS-SRB. A historical fMRIPrep baseline_A attempt is retained as infrastructure-invalid because Docker backend failure prevented any admissible terminal exit record. A06 prospectively permits one exact replacement of that logical baseline slot after external timestamping, with unchanged N=9, cases, input bundle, tool/image, seed, thread/environment controls, TemplateFlow authority, endpoints, pairwise checks, and success tripwire. No admitted metadata-fault execution or fault outcome has occurred.