s1124 — isospin carrier: T3 (Peirce ½ breaking) and T4 (which registered object flips u↔d)
  [PASS] [T3] Peirce-½ on a block is scalar: ‖P_½U − UP_½‖ = 0.0e+00 — it cannot distinguish u from d inside J₂₃
     ⇒ adding the Peirce ½ to the A1545 functional breaks U(54) only to the block-diagonal ∏U(8)×… — every block-internal
       rotation, u↔d included, is STILL a symmetry ⇒ the induced T(T+1) coefficient is exactly 0. T3: SCOPED NO-GO — the
       Peirce-½ route to isospin is closed. (This is why s1119's Coulomb works on N=Z and s1120 fails off it: the ½ sees
       'which cell', never 'which flavour'.)
  [PASS] [T4] the A689 conjugation e₇ → −e₇ maps H_u to H_d exactly (H_u^4 = e₇ ↦ −e₇ = H_d^4)
  [PASS] [T4] that map is an INVOLUTION (ℤ₂), not a one-parameter group: conj² = I
     ⇒ the ONLY registered object that exchanges up-type and down-type is a ℤ₂ (𝕆_s conjugation, H_u ↔ H_d, u^c ↔ d^c-type
       directions). A Casimir T(T+1) needs a continuous SU(2) acting on the (u,d) doublet at the level of the ENERGY functional.
       The dictionary has the doublet (Q is SU(2)_L), but no registered functional acts on it (A1545 T3) and the ℤ₂ cannot
       generate T(T+1). T4 verdict: at the registered level the framework carries a u↔d PARITY, not an isospin ROTATION.

VERDICT
  T3 no-go, T4 parity-only ⇒ the isospin sector is LOADED at present: χ = φ⁻⁶ T₃ (s1122) is a SELECTED registered weight that
  closes both fixed-Z chains (Ca 0.96 — fit target; Sn 1.09 — independent), not a derived coefficient. What a derivation would
  need: promote the e₇-conjugation ℤ₂ to the SU(2) it sits inside (the doublet SU(2)_L of Q) AND give the energy functional an
  action on that doublet — the same 'non-scalar internal Hamiltonian' A1545 named as the third missing map. So the isospin
  sector is not a fourth wall; it is the third wall (non-scalar Hamiltonian) seen from the flavour side. The exponent 6 in
  χ = φ⁻⁶T₃ is fodder until that Hamiltonian exists. Paper 9's scope line H→Zn stands; the blind lines (s1123) test the
  LOADED sector's predictive reach, not a derivation.

s1124: ALL CHECKS PASS
