Multilayer Cipher Architecture in Fontana's *Secretum* and *Bellicorum*: A Twenty-Lens Template Return with Negative-Control Differential

Giovanni Fontana (Venice, c.1395 – c.1455; Padua medical doctorate 1421) produced two surviving cipher-bearing manuscripts: the Bellicorum instrumentorum liber (Munich, Bayerische Staatsbibliothek, Cod.icon. 242) and the Secretum de thesauro experimentorum imaginationis hominum (Paris, Bibliothèque nationale de France, NAL 635) [1, 2]. A third Fontana witness, the autograph-candidate De trigono balistario in Bodleian Canon Misc 47, is plain Latin with embedded astronomical and trigonometric apparatus [3]. Battisti and Battisti (1984) decoded the substitution layer of the cipher works [4]. This paper reports an internal twenty-lens rescore and a small negative-control comparison documented in the 2026-06-11 close-pass receipt [10]; both remain Candidate-tier pending blinded inter-rater scoring and category-matched controls. Its structural-development line is a contemporaneous-network proposal rather than a documented transmission chain. Separately, Guzy documents a March 1599 Augsburg Hofkammer book transaction and presents Voynich inclusion and a Rauwolf-estate route as conditional inferences [14]; this paper does not treat the transaction as a documented Voynich ownership record. Keywords: Giovanni Fontana, Bellicorum instrumentorum liber, Secretum de thesauro, NAL 635, Bayerische Staatsbibliothek Cod.icon. 242, Bodleian Canon Misc 47, twenty-lens template, negative-control corpus, Cgm 7958, Hartlieb Kräuterbuch, Cermisone Consilia, Padua institutional density, Trithemius, Polygraphiae, Vigenère, Traicté des Chiffres, Augsburg Hoffinanz, Carl Widemann, Leonard Rauwolf, Voynich Manuscript, multilayer cipher.