= Solution
The superconducting order is a coherent pair amplitude, schematically $\Delta\propto\langle c_\downarrow c_\uparrow\rangle=|\Delta|e^{i\phi}$. Under a global <fermion> phase change $c\mapsto e^{i\alpha}c$, it acquires phase $2\alpha$. A symmetry-broken thermodynamic description selects a pair phase. This must be distinguished from electromagnetic gauge freedom: a local gauge transformation changes the phase and potentials together and is a redundancy of the description, not an observable symmetry that the material literally violates.
A conventional centrosymmetric <s-wave superconductor> usually has an even-parity orbital pair state and a <spin singlet state>, consistent with the antisymmetry of two <fermions>. Its ordinary zero-field equilibrium state preserves time reversal. The electromagnetic coupling makes phase dynamics and screening part of the <Anderson-Higgs mechanism in a superconductor>; the <Meissner effect> is a measurable consequence. The condensate phase description does not imply that electric charge is no longer conserved.
In an <unconventional superconductor>, the gap can transform nontrivially under the crystal point group or have other nonstandard pairing structure. A common example is <d-wave superconductivity>, with sign changes and possible nodes in the gap. This does not automatically imply an additional observable fourfold-rotation breaking: a rotation that reverses the gap's sign can be accompanied by a gauge phase change. A nematic superconducting state instead breaks an actual crystal rotation symmetry in its gauge-invariant responses.
A chiral combination such as $p_x+ip_y$ can break time reversal, while a spin-triplet <order parameter> can also distinguish spin directions when the applicable spin-rotation and spin-orbit constraints permit it. <Helium-3 superfluidity> illustrates paired-fermion order with richer spin and orbital structure. These possibilities must be tested rather than equated: \b[unconventional pairing does not by itself mean spin-triplet pairing, time-reversal breaking, or nematicity]. Gap angular dependence, phase-sensitive <interference>, spin response and spontaneous magnetic signatures probe different symmetry questions. The <phase-sensitive test of d-wave pairing> is more specific than inferring a gap sign merely from its magnitude.
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