Description This paper operationalises the projective Z2 parity identified in Paper 11 within the Finite Reversible Closure framework. Minimal Involutive Plaquette Tag In compact U(1), the only self-inverse elements satisfy W squared equals 1. Therefore W equals plus or minus 1. The unique nontrivial involutive element is W = -1. This provides a structurally robust binary curvature tag closed under multiplication and inversion. We restrict attention to composite sectors containing a local plaquette defect with Wp = -1. Minimal Charge Quantisation Gauge-compatible matter sectors (established in Paper 5) imply integer spectra for the electric flux or charge operator. We normalise units so that the minimal nonzero gauge charge equals 1. Intrinsic Minimal Composite We define a composite excitation by combining;- A minimal charge insertion at lattice site x, A neighbouring plaquette defect restricted to the Wp = -1 sector. This composite introduces no new primitive degrees of freedom. Wilson-Line Transport and Discrete Linking For an oriented lattice path gamma, we define Wilson-line transport as the ordered product of link variables along gamma. On the cubic lattice, a closed loop gamma links a plaquette p once if it winds once around the dual edge piercing that plaquette. This defines a discrete linking number L(gamma, p) equal to 0 or 1. Internal Derivation of Minus-One Holonomy For any closed loop gamma bounding a lattice surface S, the Abelian surface identity gives;- Wilson loop of gamma equals the product of plaquette holonomies over S. If exactly one plaquette in S has Wp = -1 and all others have Wp = +1, then the Wilson loop equals -1. Equivalently: W(gamma) equals (-1) to the power L(gamma, p_star). Operational Z2 Holonomy If a state contains the minimal composite with Wp = -1, then transport around a loop linking once yields a minus sign: Transport operator acting on the state equals minus the state. This produces an observable Z2 holonomy entirely within the lattice theory. Projective Frame Parity The symmetric gauge-invariant tensor constructed in Paper 11 has eigenframes defined only up to global sign. The Z2 holonomy flips the projective frame label but leaves eigenvalues invariant. Thus rotation and exchange behaviour emerge operationally at composite level while primitive recurrence remains strictly integer-wound. Programme Flow;- Paper 9 - U(1) recurrence universalityPaper 10 - Composite excitation and effective massPaper 11 - Projective Z2 parity from composite structurePaper 12 - Operational Z2 holonomy via transportPaper 14 onward - Spin-statistics and curvature response Paper 12 closes the gap between abstract projective parity and measurable transport holonomy.

Composite Transport, Projective Holonomy and Operational Spin in Finite Reversible Closure - Paper 12 Abstract Paper 11 established that driver-level U(1) recurrence is integer-wound while composite frames are generically projective, producing a Z2 parity at the emergent matter level. Paper 12 makes that parity operational. We construct an explicit minimal charge-flux composite, define a strictly local finite-depth transport operator and derive internally at lattice level that closed-loop transport yields a measurable minus-one holonomy in the unique nontrivial involutive sector of compact U(1), namely Wp = -1 (equivalently plaquette phase equal to pi modulo 2pi). No new primitive degrees of freedom are introduced and no SU(2) structure is assumed. The Z2 holonomy arises directly from Abelian surface-product identities and discrete linking on the lattice. This operationalises the projective frame parity identified in Paper 11 and prepares the ground for emergent spinor structure and transport-based spin tests in subsequent papers. Introduction The Finite Reversible Closure (FRC) programme develops a strictly local, finite-dimensional, constraint-defined substrate in which physical structure emerges through admissible reversible update. Paper 9 established minimal U(1) recurrence and infrared universality. Paper 10 constructed the first gauge-invariant charge-flux composite. Paper 11 showed that primitive recurrence is integer-quantised while composite structure is generically projective, yielding a Z2 parity fibre. Paper 12 addresses the next structural question;- How does the Z2 parity identified in Paper 11 become operational and measurable within the lattice theory itself? To answer this, we construct;- A minimal composite excitation combining a unit gauge charge with a local involutive plaquette defect Wp = -1; A strictly local Wilson-line transport operator along oriented lattice paths and A discrete linking notion between loops and plaquette defects. We then derive internally that a closed loop linking the defect once produces a minus-one holonomy acting on the composite state. This derivation uses only;- Compact U(1) group structure; Abelian surface-product identities; Discrete linking on the cubic lattice and Finite-depth local update assumptions. No additional covering groups or spinor primitives are inserted.