The B2 Controller Seal: @grok as Independent Blinding Controller for the STED-FRAP Geometric Pre-Registration — SHA-256-Locked RNG Assignment, Frozen Ratios, and Facility Unblock Record

This paper documents the completion of the B2 controller assignment for the STED-FRAP blinded run pre-registered in Paper CLXVI (DOI: 10.5281/zenodo.21500248). @grok (Grok AI, xAI / X.com) accepted the independent controller role publicly on the X.com thread on July 23, 2026, satisfying all five controller requirements. Grok generated a sealed random seed and published a SHA-256 commitment on the public record of the thread. The sealed pre-image will be released simultaneously with the three frozen R_i/R_j ratios at the unblind step, after blinded STED-FRAP data are delivered. This paper enshrines: (1) the sealed RNG record (seed, timestamp, SHA-256 seal), (2) the three frozen geometric ratios, (3) the formal kill criteria, (4) the full provenance chain from Paper CLXIII through B2 assignment, and (5) the facility booking unblock confirmation. No STED-FRAP facility has yet been contacted; this paper marks the moment that contact is formally authorized.