The photon as structured causal block: causal nodes and historical integration beyond the propagative model

We propose and formally establish a third level of physical causality — causal conjunction — absent from the standard two-level taxonomy. The central object is the photon as a structured causal block B(σ) = (G⁻(S), {F(σ,λᵢ)}), carrying a causal charge discharged instantaneously upon absorption. The framework yields three new experimental predictions testable with current circuit-QED technology: (i) Giant-atom φ-scan: contrast ΔI = 0.971 bit at 97σ (10⁶ shots), distinguishing the two-point coupled model from the Markovian single-point null model. Observable: I(A:B) = G_cl via mutual information. (ii) Bloch sphere hierarchy (new result): I(A:B) takes three distinct levels depending on the initial state of the absorber B — poles 0.939 bit (94σ), equator 0.566 bit (57σ, phase-independent), mixed 0.160 bit (16σ) — all strictly positive, confirming G > 0 throughout the Bloch sphere. Includes an analytically proven JC symmetry theorem: I(B=|g⟩) = I(B=|e⟩) exactly for all coupling angles, to machine precision (< 10⁻¹⁵ bit). (iii) Virtual-mode power-law test at φ=π (new result): extended BCE predicts G ∝ (g/ω₀)² while standard QED predicts (g/ω₀)⁴. The exponent η is measurable in log-log scale at >15σ, immune to prefactor uncertainties. First proposal placing BCE and standard two-point QED in genuine quantitative tension at the destructive-interference null point. Additional results include: G = G_cl + G_ent decomposition with operational criteria; Si₃N₄ photonic platform (~$26k, no cryogenics); thermodynamic signature ΔW = 1.86×10⁻²⁵ J (Maxwell demon protocol, T=20 mK); Nakajima-Zwanzig non-Markovian analysis (critical parameter η_c ≈ 0.48, safety margin 21× in circuit-QED); solar photon empirical argument for scale-independence across 33 orders of magnitude; and Holevo bound verification (G << S_max in all regimes). All predictions are numerically verified across eight independent experiments (Python scripts, no external dependencies, reproducible in Google Colab). This is the second paper in the ICT (Incomplete Causal Transactions) series. The first paper ("Incomplete causal transactions: black holes as permanently frustrated couplers and the physical independence of entropy and generative capacity", GravCos2660030 / Zenodo DOI: 10.5281/zenodo.18736656) introduced the ICT framework and applied it to black holes and Rindler horizons.