src/filament/set_fila_tip_extension.jl

`MEDYAN.set_fila_tip_extension!`

set_fila_tip_extension!(c::Context, tip::FilaTipIdx, extension::Float64)

Set the tip extension for the given filament tip in monomer spacings.

The extension controls how far the tip position extends outward from the last monomer center. It affects both the chemistry tip position ([get_position] for FilaTipIdx) and the mechanical endpoint used in energy minimization (volume exclusion, equilibrium length):

0.0: tip at the monomer center
> 0.0: tip extends further outward (e.g. bulky end-binding protein)
< 0.0: tip moves inward past the monomer center

The node positions (fila_node_positions) are not affected by the extension. During energy minimization, end nodes are temporarily shifted to tip positions so volume exclusion sees the extension, then shifted back afterward. The extension is included in the rest length of an end cylinder when checking whether it is merged into its neighbor, see min_monomers_per_cylinder in FilamentMechParams.