This paper proposes that bilateral symmetry in ancient Egyptian hieroglyphic art and architecture encodes semantic structure rather than aesthetic preference. Analysis demonstrates that the mirror-axis observable in formal compositions scales down through line, word, and phoneme levels, terminating in eleven irreducible proto-phonemic structures: BA, DA, HA, KA, LA, MA, NA, RA, SHA, TA, WA. These structures center on the ayin (ꜥ), which functions not as a vowel marker but as a covenant point—the axis where reciprocity is either preserved or broken. The mathematical architecture is rigorous: eleven proto-phonemes correspond to the fifth prime; their summation with predecessor primes (2+3+5+7+11=28) produces the lunar month, validated architecturally in Dendera's bidirectional staircase. The paper demonstrates that standard Egyptological translation methodology, by reading bilateral compositions as independent parallel texts rather than coupled utterances, systematically flattens relational meaning. A test case examining Ma'at (mꜥꜣt) demonstrates recovered semantic depth when the ayin is treated as covenant-axis: "Truth-reflecting-into-I-Am" rather than merely "truth" or "cosmic order." Four falsifiable predictions are offered, including a stratification criterion: the corpus contains two distinct strata—one where bilateral structure carries semantic function, one where it is absent or merely decorative—which may not align with conventional chronological or dynastic boundaries. This paper extends "The Dendera Lunar Staircase as Phoneme Curriculum" (DOI: 10.5281/zenodo.18128781) by establishing the foundational principle underlying Egyptian phonemic transmission: the bilateral covenant structure.