v26.6.1.0

Features

• The "voltage as a state" option is now registered centrally in BaseBatteryModel and supports all operating modes. SPM/SPMe promote "surface form" to "algebraic" automatically when a particle-size distribution is used (previously an error) as well as for non-default kinetics. CasadiSolver integrator failures on DAE models solved without algebraic initial-condition perturbation now include an actionable hint. (#5572)

Bug fixes

• Fixed CasADi conversion of a differentiated Interpolant, which returned the original function. (#5583)
• Fixed the "explicit power" and "explicit resistance" operating modes, which failed to build with a ModelError. These modes now default "voltage as a state" to "true", which breaks the circular dependency between current and voltage (I = P/V), and raise a clear OptionError if it is explicitly disabled. (#5572)
• Fixed latexify() crashing with a NotImplementedError for models whose boundary conditions contain boundary_gradient nodes (e.g. DFN with {"surface form": "algebraic"}). (#5572)
• Fixed unified experiment crash when the ambient-temperature parameter value is a pybamm.Scalar. (#5587)
• Unified experiment calculate_sensitivities no longer leaks internal control inputs into the parameter Jacobian. (#5587)
• Corrected the overflow-clamp threshold in the lithium-ion OCP asymptote helper so the softplus and its linear continuation match exactly. (#5588)
• Fixed unified experiment building redundant control branches and a dense switching-control Jacobian. (#5589)