From 26833b9a2c9b6b4d8d3d36c9a73b3e08c9f31345 Mon Sep 17 00:00:00 2001
From: Uwe Fechner <u.fechner-1@tudelft.nl>
Date: Thu, 21 May 2026 16:46:54 +0200
Subject: [PATCH 01/16] Fix MakieExt and ControlPlotsExt define
 VortexStepMethod.plot_geometry for the same type Fixes #236

---
 ext/VortexStepMethodControlPlotsExt.jl | 20 ++++++---
 ext/VortexStepMethodMakieExt.jl        | 20 ++++++---
 src/VortexStepMethod.jl                | 57 +++++++++++++++++++++++++-
 3 files changed, 86 insertions(+), 11 deletions(-)

diff --git a/ext/VortexStepMethodControlPlotsExt.jl b/ext/VortexStepMethodControlPlotsExt.jl
index 46d5094e..8e168df5 100644
--- a/ext/VortexStepMethodControlPlotsExt.jl
+++ b/ext/VortexStepMethodControlPlotsExt.jl
@@ -6,6 +6,11 @@ import VortexStepMethod: calculate_filaments_for_plotting
 export plot_wing, plot_circulation_distribution, plot_geometry, plot_distribution,
        plot_polars, save_plot, show_plot, plot_polar_data, plot_combined_analysis
 
+# Set this extension as the active plotting backend when loaded
+function __init__()
+    VortexStepMethod._PLOT_BACKEND[] = VortexStepMethod.ControlPlotsBackend()
+end
+
 """
     set_plot_style(titel_size=16; use_tex=false)
 
@@ -284,7 +289,8 @@ Plot wing geometry from different viewpoints and optionally save/show plots.
 - `use_tex`: if the external `pdflatex` command shall be used (default: false)
 
 """
-function VortexStepMethod.plot_geometry(body_aero::BodyAerodynamics, title;
+function VortexStepMethod.plot_geometry(body_aero::BodyAerodynamics, title,
+    ::VortexStepMethod.ControlPlotsBackend;
     data_type=".pdf",
     save_path=nothing,
     is_save=false,
@@ -342,7 +348,8 @@ Plot spanwise distributions of aerodynamic properties.
 - `is_show`: Whether to display plots (default: true)
 - `use_tex`: if the external `pdflatex` command shall be used
 """
-function VortexStepMethod.plot_distribution(y_coordinates_list, results_list, label_list;
+function VortexStepMethod.plot_distribution(y_coordinates_list, results_list, label_list,
+    ::VortexStepMethod.ControlPlotsBackend;
     title="spanwise_distribution",
     data_type=".pdf",
     save_path=nothing,
@@ -547,7 +554,8 @@ Plot polar data comparing different solvers and configurations.
 function VortexStepMethod.plot_polars(
     solver_list,
     body_aero_list,
-    label_list;
+    label_list,
+    ::VortexStepMethod.ControlPlotsBackend;
     literature_path_list=String[],
     angle_range=range(0, 20, 2),
     angle_type="angle_of_attack",
@@ -755,7 +763,8 @@ relative to the 2d airfoil or panel chord line.
 - `is_show`: Whether to display plots (default: true)
 - `use_tex`: if the external `pdflatex` command shall be used
 """
-function VortexStepMethod.plot_polar_data(body_aero::BodyAerodynamics;
+function VortexStepMethod.plot_polar_data(body_aero::BodyAerodynamics,
+        ::VortexStepMethod.ControlPlotsBackend;
         alphas=collect(deg2rad.(-5:0.3:25)),
         delta_tes = collect(deg2rad.(-5:0.3:25)),
         is_show = true,
@@ -827,7 +836,8 @@ See individual functions for detailed parameter descriptions.
 function VortexStepMethod.plot_combined_analysis(
     solver,
     body_aero,
-    results;
+    results,
+    ::VortexStepMethod.ControlPlotsBackend;
     solver_label="VSM",
     labels=nothing,
     angle_range=range(0, 20, length=20),
diff --git a/ext/VortexStepMethodMakieExt.jl b/ext/VortexStepMethodMakieExt.jl
index fd37e52e..feec4db4 100644
--- a/ext/VortexStepMethodMakieExt.jl
+++ b/ext/VortexStepMethodMakieExt.jl
@@ -5,6 +5,11 @@ import VortexStepMethod: calculate_filaments_for_plotting
 export plot_geometry, plot_distribution, plot_polars, save_plot, show_plot,
     plot_polar_data, plot_combined_analysis
 
+# Set this extension as the active plotting backend when loaded
+function __init__()
+    VortexStepMethod._PLOT_BACKEND[] = VortexStepMethod.MakieBackend()
+end
+
 # Global storage for panel mesh observables (for dynamic plotting)
 const PANEL_MESH_OBSERVABLES = Ref{Union{Nothing,Dict}}(nothing)
 
@@ -479,7 +484,8 @@ Plot wing geometry from different viewpoints using Makie.
 - `view_azimuth`: View azimuth angle in degrees (default: -120)
 - `use_tex`: Ignored for Makie (default: false)
 """
-function VortexStepMethod.plot_geometry(body_aero::BodyAerodynamics, title;
+function VortexStepMethod.plot_geometry(body_aero::BodyAerodynamics, title,
+    ::VortexStepMethod.MakieBackend;
     data_type=nothing,
     save_path=nothing,
     is_save=false,
@@ -535,7 +541,8 @@ Plot spanwise distributions of aerodynamic properties using Makie.
 - `is_show`: Whether to display (default: true)
 - `use_tex`: Ignored for Makie (default: false)
 """
-function VortexStepMethod.plot_distribution(y_coordinates_list, results_list, label_list;
+function VortexStepMethod.plot_distribution(y_coordinates_list, results_list, label_list,
+    ::VortexStepMethod.MakieBackend;
     title="spanwise_distribution",
     data_type=nothing,
     save_path=nothing,
@@ -700,7 +707,8 @@ Plot polar data comparing different solvers using Makie.
 function VortexStepMethod.plot_polars(
     solver_list,
     body_aero_list,
-    label_list;
+    label_list,
+    ::VortexStepMethod.MakieBackend;
     literature_path_list=String[],
     angle_range=range(0, 20, 2),
     angle_type="angle_of_attack",
@@ -882,7 +890,8 @@ Plot polar data (Cl, Cd, Cm) as 3D surfaces using Makie.
 - `is_show`: Whether to display (default: true)
 - `use_tex`: Ignored for Makie (default: false)
 """
-function VortexStepMethod.plot_polar_data(body_aero::BodyAerodynamics;
+function VortexStepMethod.plot_polar_data(body_aero::BodyAerodynamics,
+    ::VortexStepMethod.MakieBackend;
     alphas=collect(deg2rad.(-5:0.3:25)),
     delta_tes=collect(deg2rad.(-5:0.3:25)),
     is_show=true,
@@ -972,7 +981,8 @@ Create combined multi-panel figure with geometry, polar data, distributions, and
 function VortexStepMethod.plot_combined_analysis(
     solver,
     body_aero,
-    results;
+    results,
+    ::VortexStepMethod.MakieBackend;
     solver_label="VSM",
     labels=nothing,
     angle_range=range(0, 20, length=20),
diff --git a/src/VortexStepMethod.jl b/src/VortexStepMethod.jl
index 5c5e3f4d..2466f878 100644
--- a/src/VortexStepMethod.jl
+++ b/src/VortexStepMethod.jl
@@ -46,7 +46,32 @@ export load_polar_data
 export plot_circulation_distribution, plot_combined_analysis, plot_distribution, plot_geometry,
     plot_polar_data, plot_polars, save_plot, show_plot
 
-# the following functions are defined in ext/VortexStepMethodExt.jl
+# Backend dispatch types for multi-backend support (Makie and ControlPlots can coexist)
+abstract type PlotBackend end
+struct MakieBackend <: PlotBackend end
+struct ControlPlotsBackend <: PlotBackend end
+export PlotBackend, MakieBackend, ControlPlotsBackend
+
+const _PLOT_BACKEND = Ref{Union{Nothing, PlotBackend}}(nothing)
+
+"""
+    set_plot_backend!(backend::PlotBackend)
+
+Select the active plotting backend when both Makie and ControlPlots are loaded.
+
+# Example
+```julia
+set_plot_backend!(MakieBackend())
+set_plot_backend!(ControlPlotsBackend())
+```
+"""
+function set_plot_backend!(backend::PlotBackend)
+    _PLOT_BACKEND[] = backend
+end
+export set_plot_backend!
+
+# Generic stubs — extended by MakieExt and ControlPlotsExt with a PlotBackend argument.
+# The no-backend-argument wrappers below route through the active backend.
 function plot_geometry end
 function plot_distribution end
 function plot_circulation_distribution end
@@ -56,6 +81,36 @@ function show_plot end
 function plot_polar_data end
 function plot_combined_analysis end
 
+function _active_backend()
+    b = _PLOT_BACKEND[]
+    isnothing(b) && error(
+        "No plotting backend loaded. Load Makie or ControlPlots first, " *
+        "or call set_plot_backend!(MakieBackend()) / set_plot_backend!(ControlPlotsBackend()) " *
+        "when both are loaded."
+    )
+    b
+end
+
+function plot_geometry(body_aero, title; kwargs...)
+    plot_geometry(body_aero, title, _active_backend(); kwargs...)
+end
+
+function plot_distribution(y_coordinates_list, results_list, label_list; kwargs...)
+    plot_distribution(y_coordinates_list, results_list, label_list, _active_backend(); kwargs...)
+end
+
+function plot_polars(solver_list, body_aero_list, label_list; kwargs...)
+    plot_polars(solver_list, body_aero_list, label_list, _active_backend(); kwargs...)
+end
+
+function plot_polar_data(body_aero; kwargs...)
+    plot_polar_data(body_aero, _active_backend(); kwargs...)
+end
+
+function plot_combined_analysis(solver, body_aero, results; kwargs...)
+    plot_combined_analysis(solver, body_aero, results, _active_backend(); kwargs...)
+end
+
 """
    const MVec3    = MVector{3, Float64}
 

From 5012f7ed554eff1dc2b4cac0e638059c30aa8ade Mon Sep 17 00:00:00 2001
From: Uwe Fechner <u.fechner-1@tudelft.nl>
Date: Thu, 21 May 2026 18:15:32 +0200
Subject: [PATCH 02/16] Fix test

---
 test/solver/test_forwarddiff.jl | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/test/solver/test_forwarddiff.jl b/test/solver/test_forwarddiff.jl
index e17ba29f..104e1dc3 100644
--- a/test/solver/test_forwarddiff.jl
+++ b/test/solver/test_forwarddiff.jl
@@ -76,7 +76,7 @@ using Test
         )
 
         v_a = 15.0
-        aoa_rad = deg2rad(8.0)
+        aoa_rad = deg2rad(7.5)  # off-grid (grid is every 1°) to avoid piecewise-linear node discontinuities
         y_op = [zeros(4);
                 [cos(aoa_rad), 0.0, sin(aoa_rad)] * v_a;
                 zeros(3)]

From 0dfc6afd5a4e88163aaed33ba204e4d0b58d3919 Mon Sep 17 00:00:00 2001
From: Uwe Fechner <u.fechner-1@tudelft.nl>
Date: Thu, 21 May 2026 18:23:18 +0200
Subject: [PATCH 03/16] Fix docstrings

---
 ext/VortexStepMethodControlPlotsExt.jl |  28 ++++---
 ext/VortexStepMethodMakieExt.jl        |  20 ++---
 src/VortexStepMethod.jl                | 109 +++++++++++++++++++++++++
 3 files changed, 134 insertions(+), 23 deletions(-)

diff --git a/ext/VortexStepMethodControlPlotsExt.jl b/ext/VortexStepMethodControlPlotsExt.jl
index 8e168df5..c34af63f 100644
--- a/ext/VortexStepMethodControlPlotsExt.jl
+++ b/ext/VortexStepMethodControlPlotsExt.jl
@@ -268,16 +268,16 @@ function create_geometry_plot(body_aero::BodyAerodynamics, title, view_elevation
 end
 
 """
-    plot_geometry(body_aero::BodyAerodynamics, title;
+    plot_geometry(body_aero::BodyAerodynamics, title, ::ControlPlotsBackend;
                   data_type=".pdf", save_path=nothing,
                   is_save=false, is_show=false,
                   view_elevation=15, view_azimuth=-120, use_tex=false)
 
-Plot wing geometry from different viewpoints and optionally save/show plots.
+ControlPlots backend implementation of [`plot_geometry`](@ref).
 
 # Arguments:
 - `body_aero`: the [BodyAerodynamics](@ref) to plot
-- title: plot title
+- `title`: plot title
 
 # Keyword arguments:
 - `data_type``: string with the file type postfix (default: ".pdf")
@@ -329,11 +329,11 @@ function VortexStepMethod.plot_geometry(body_aero::BodyAerodynamics, title,
 end
 
 """
-    plot_distribution(y_coordinates_list, results_list, label_list;
+    plot_distribution(y_coordinates_list, results_list, label_list, ::ControlPlotsBackend;
                       title="spanwise_distribution", data_type=".pdf",
                       save_path=nothing, is_save=false, is_show=true, use_tex=false)
 
-Plot spanwise distributions of aerodynamic properties.
+ControlPlots backend implementation of [`plot_distribution`](@ref).
 
 # Arguments
 - `y_coordinates_list`: List of spanwise coordinates
@@ -522,14 +522,14 @@ Generate polar data for aerodynamic analysis over a range of angles.
 """
 
 """
-    plot_polars(solver_list, body_aero_list, label_list;
+    plot_polars(solver_list, body_aero_list, label_list, ::ControlPlotsBackend;
                 literature_path_list=String[],
                 angle_range=range(0, 20, 2), angle_type="angle_of_attack",
                 angle_of_attack=0.0, side_slip=0.0, v_a=10.0,
                 title="polar", data_type=".pdf", save_path=nothing,
                 is_save=true, is_show=true, use_tex=false)
 
-Plot polar data comparing different solvers and configurations.
+ControlPlots backend implementation of [`plot_polars`](@ref).
 
 # Arguments
 - `solver_list`: List of aerodynamic solvers
@@ -749,10 +749,12 @@ function VortexStepMethod.plot_polars(
 end
 
 """
-    plot_polar_data(body_aero::BodyAerodynamics; alphas=collect(deg2rad.(-5:0.3:25)), delta_tes=collect(deg2rad.(-5:0.3:25)))
+    plot_polar_data(body_aero::BodyAerodynamics, ::ControlPlotsBackend;
+                    alphas=collect(deg2rad.(-5:0.3:25)),
+                    delta_tes=collect(deg2rad.(-5:0.3:25)))
 
-Plot polar data (Cl, Cd, Cm) as 3D surfaces against alpha and delta_te angles. delta_te is the trailing edge deflection angle
-relative to the 2d airfoil or panel chord line.
+ControlPlots backend implementation of [`plot_polar_data`](@ref). Plots Cl, Cd, Cm as 3D surfaces
+against angle of attack and trailing edge deflection angle.
 
 # Arguments
 - `body_aero`: Wing aerodynamics struct
@@ -821,10 +823,10 @@ function VortexStepMethod.plot_polar_data(body_aero::BodyAerodynamics,
 end
 
 """
-    plot_combined_analysis(solver, body_aero, results; kwargs...)
+    plot_combined_analysis(solver, body_aero, results, ::ControlPlotsBackend; kwargs...)
 
-Create combined analysis by calling plot_geometry, plot_distribution,
-and plot_polars sequentially. Each creates a separate matplotlib window.
+ControlPlots backend implementation of [`plot_combined_analysis`](@ref).
+Calls `plot_geometry`, `plot_distribution`, and `plot_polars` sequentially.
 
 # Arguments
 - `solver`: Solver or array of solvers
diff --git a/ext/VortexStepMethodMakieExt.jl b/ext/VortexStepMethodMakieExt.jl
index feec4db4..598d44c6 100644
--- a/ext/VortexStepMethodMakieExt.jl
+++ b/ext/VortexStepMethodMakieExt.jl
@@ -464,12 +464,12 @@ function create_geometry_plot_makie(body_aero::BodyAerodynamics, title,
 end
 
 """
-    plot_geometry(body_aero::BodyAerodynamics, title;
+    plot_geometry(body_aero::BodyAerodynamics, title, ::MakieBackend;
                   data_type=nothing, save_path=nothing,
                   is_save=false, is_show=false,
                   view_elevation=15, view_azimuth=-120, use_tex=false)
 
-Plot wing geometry from different viewpoints using Makie.
+Makie backend implementation of [`plot_geometry`](@ref).
 
 # Arguments:
 - `body_aero`: the BodyAerodynamics to plot
@@ -522,11 +522,11 @@ function VortexStepMethod.plot_geometry(body_aero::BodyAerodynamics, title,
 end
 
 """
-    plot_distribution(y_coordinates_list, results_list, label_list;
+    plot_distribution(y_coordinates_list, results_list, label_list, ::MakieBackend;
                       title="spanwise_distribution", data_type=nothing,
                       save_path=nothing, is_save=false, is_show=true, use_tex=false)
 
-Plot spanwise distributions of aerodynamic properties using Makie.
+Makie backend implementation of [`plot_distribution`](@ref).
 
 # Arguments
 - `y_coordinates_list`: List of spanwise coordinates
@@ -675,14 +675,14 @@ Generate polar data for aerodynamic analysis over a range of angles.
 """
 
 """
-    plot_polars(solver_list, body_aero_list, label_list;
+    plot_polars(solver_list, body_aero_list, label_list, ::MakieBackend;
                 literature_path_list=String[],
                 angle_range=range(0, 20, 2), angle_type="angle_of_attack",
                 angle_of_attack=0.0, side_slip=0.0, v_a=10.0,
                 title="polar", data_type=nothing, save_path=nothing,
                 is_save=true, is_show=true, use_tex=false)
 
-Plot polar data comparing different solvers using Makie.
+Makie backend implementation of [`plot_polars`](@ref).
 
 # Arguments
 - `solver_list`: List of aerodynamic solvers
@@ -874,12 +874,12 @@ function VortexStepMethod.plot_polars(
 end
 
 """
-    plot_polar_data(body_aero::BodyAerodynamics;
+    plot_polar_data(body_aero::BodyAerodynamics, ::MakieBackend;
                     alphas=collect(deg2rad.(-5:0.3:25)),
                     delta_tes=collect(deg2rad.(-5:0.3:25)),
                     is_show=true, use_tex=false)
 
-Plot polar data (Cl, Cd, Cm) as 3D surfaces using Makie.
+Makie backend implementation of [`plot_polar_data`](@ref).
 
 # Arguments
 - `body_aero`: Wing aerodynamics struct
@@ -938,7 +938,7 @@ function VortexStepMethod.plot_polar_data(body_aero::BodyAerodynamics,
 end
 
 """
-    plot_combined_analysis(solver, body_aero, results;
+    plot_combined_analysis(solver, body_aero, results, ::MakieBackend;
                           solver_label="VSM",
                           angle_range=range(0,20,length=20),
                           angle_type="angle_of_attack",
@@ -949,7 +949,7 @@ end
                           literature_path_list=String[],
                           data_type=".png", save_path=nothing, is_save=false)
 
-Create combined multi-panel figure with geometry, polar data, distributions, and polars.
+Makie backend implementation of [`plot_combined_analysis`](@ref).
 
 # Arguments
 - `solver`: Aerodynamic solver
diff --git a/src/VortexStepMethod.jl b/src/VortexStepMethod.jl
index 2466f878..62d96c72 100644
--- a/src/VortexStepMethod.jl
+++ b/src/VortexStepMethod.jl
@@ -91,22 +91,131 @@ function _active_backend()
     b
 end
 
+"""
+    plot_geometry(body_aero::BodyAerodynamics, title; kwargs...)
+
+Plot wing geometry from different viewpoints and optionally save/show plots.
+Routes to the active plotting backend (Makie or ControlPlots).
+
+# Arguments
+- `body_aero`: the [`BodyAerodynamics`](@ref) to plot
+- `title`: plot title
+
+# Keyword arguments
+- `data_type`: file extension for saving (default depends on backend)
+- `save_path`: path for saving the graphic (default: `nothing`)
+- `is_save`: whether to save the graphic (default: `false`)
+- `is_show`: whether to display the graphic (default: `false`)
+- `view_elevation`: initial view elevation angle in degrees (default: `15`)
+- `view_azimuth`: initial view azimuth angle in degrees (default: `-120`)
+- `use_tex`: use external `pdflatex` for rendering (default: `false`; ignored by Makie)
+"""
 function plot_geometry(body_aero, title; kwargs...)
     plot_geometry(body_aero, title, _active_backend(); kwargs...)
 end
 
+"""
+    plot_distribution(y_coordinates_list, results_list, label_list; kwargs...)
+
+Plot spanwise distributions of aerodynamic properties.
+Routes to the active plotting backend (Makie or ControlPlots).
+
+# Arguments
+- `y_coordinates_list`: list of spanwise coordinate arrays
+- `results_list`: list of result dictionaries from [`solve!`](@ref)
+- `label_list`: list of labels for each result
+
+# Keyword arguments
+- `title`: plot title (default: `"spanwise_distribution"`)
+- `data_type`: file extension for saving (default depends on backend)
+- `save_path`: path to save plots (default: `nothing`)
+- `is_save`: whether to save (default: `false`)
+- `is_show`: whether to display (default: `true`)
+- `use_tex`: use external `pdflatex` for rendering (default: `false`; ignored by Makie)
+"""
 function plot_distribution(y_coordinates_list, results_list, label_list; kwargs...)
     plot_distribution(y_coordinates_list, results_list, label_list, _active_backend(); kwargs...)
 end
 
+"""
+    plot_polars(solver_list, body_aero_list, label_list; kwargs...)
+
+Plot polar data comparing different solvers and configurations.
+Routes to the active plotting backend (Makie or ControlPlots).
+
+# Arguments
+- `solver_list`: list of aerodynamic solvers
+- `body_aero_list`: list of [`BodyAerodynamics`](@ref) objects
+- `label_list`: list of labels for each configuration
+
+# Keyword arguments
+- `literature_path_list`: optional paths to literature data CSV files (default: `String[]`)
+- `angle_range`: range of angles to analyze in degrees (default: `range(0, 20, 2)`)
+- `angle_type`: `"angle_of_attack"` or `"side_slip"` (default: `"angle_of_attack"`)
+- `angle_of_attack`: AoA for the polar sweep (default: `0.0`) [°]
+- `side_slip`: side slip angle (default: `0.0`) [°]
+- `v_a`: apparent wind speed magnitude (default: `10.0`) [m/s]
+- `title`: plot title (default: `"polar"`)
+- `data_type`: file extension for saving (default depends on backend)
+- `save_path`: path to save plots (default: `nothing`)
+- `is_save`: whether to save (default: `true`)
+- `is_show`: whether to display (default: `true`)
+- `use_tex`: use external `pdflatex` for rendering (default: `false`; ignored by Makie)
+- `cl_over_cd`: plot CL/CD vs angle instead of CL vs CD (default: `true`)
+"""
 function plot_polars(solver_list, body_aero_list, label_list; kwargs...)
     plot_polars(solver_list, body_aero_list, label_list, _active_backend(); kwargs...)
 end
 
+"""
+    plot_polar_data(body_aero::BodyAerodynamics; kwargs...)
+
+Plot polar data (Cl, Cd, Cm) as 3-D surfaces against angle of attack and trailing edge deflection.
+Routes to the active plotting backend (Makie or ControlPlots).
+
+# Arguments
+- `body_aero`: the [`BodyAerodynamics`](@ref) to plot (must use `POLAR_MATRICES` aero model)
+
+# Keyword arguments
+- `alphas`: AoA values in radians (default: `deg2rad.(-5:0.3:25)`)
+- `delta_tes`: trailing edge deflection angles in radians (default: `deg2rad.(-5:0.3:25)`)
+- `is_show`: whether to display (default: `true`)
+- `use_tex`: use external `pdflatex` for rendering (default: `false`; ignored by Makie)
+"""
 function plot_polar_data(body_aero; kwargs...)
     plot_polar_data(body_aero, _active_backend(); kwargs...)
 end
 
+"""
+    plot_combined_analysis(solver, body_aero, results; kwargs...)
+
+Create a combined analysis by calling `plot_geometry`, `plot_distribution`, and `plot_polars`
+in sequence. Routes to the active plotting backend (Makie or ControlPlots).
+
+# Arguments
+- `solver`: solver or vector of solvers
+- `body_aero`: [`BodyAerodynamics`](@ref) object or vector thereof
+- `results`: results dictionary (or vector) from [`solve!`](@ref)
+
+# Keyword arguments
+- `solver_label`: label string for the solver (backward-compatible alias for `labels`)
+- `labels`: optional label string or vector
+- `angle_range`: range of angles for polar plots (default: `range(0, 20, length=20)`)
+- `angle_type`: `"angle_of_attack"` or `"side_slip"` (default: `"angle_of_attack"`)
+- `angle_of_attack`: AoA in degrees (default: `0.0`)
+- `side_slip`: side slip angle in degrees (default: `0.0`)
+- `v_a`: wind speed in m/s (default: `10.0`)
+- `title`: overall figure title (default: `"Combined Analysis"`)
+- `view_elevation`: geometry view elevation in degrees (default: `15`)
+- `view_azimuth`: geometry view azimuth in degrees (default: `-120`)
+- `is_show`: whether to display (default: `true`)
+- `use_tex`: use external `pdflatex` for rendering (default: `false`; ignored by Makie)
+- `literature_path_list`: paths to literature CSV files (default: `String[]`)
+- `data_type`: file extension for saving (default depends on backend)
+- `save_path`: directory to save files (default: `nothing`)
+- `is_save`: whether to save (default: `false`)
+- `cl_over_cd`: plot CL/CD vs angle (default: `true`)
+"""
 function plot_combined_analysis(solver, body_aero, results; kwargs...)
     plot_combined_analysis(solver, body_aero, results, _active_backend(); kwargs...)
 end

From 38c31f898d8f7d0f7eea5e0ca5006d664cda19eb Mon Sep 17 00:00:00 2001
From: Uwe Fechner <u.fechner-1@tudelft.nl>
Date: Thu, 21 May 2026 18:25:11 +0200
Subject: [PATCH 04/16] Fix copilot remarks

---
 ext/VortexStepMethodControlPlotsExt.jl | 16 ++++++++++------
 ext/VortexStepMethodMakieExt.jl        |  5 +++--
 2 files changed, 13 insertions(+), 8 deletions(-)

diff --git a/ext/VortexStepMethodControlPlotsExt.jl b/ext/VortexStepMethodControlPlotsExt.jl
index c34af63f..2f15562a 100644
--- a/ext/VortexStepMethodControlPlotsExt.jl
+++ b/ext/VortexStepMethodControlPlotsExt.jl
@@ -6,9 +6,10 @@ import VortexStepMethod: calculate_filaments_for_plotting
 export plot_wing, plot_circulation_distribution, plot_geometry, plot_distribution,
        plot_polars, save_plot, show_plot, plot_polar_data, plot_combined_analysis
 
-# Set this extension as the active plotting backend when loaded
+# Set this extension as the active plotting backend when loaded (only if not already set)
 function __init__()
-    VortexStepMethod._PLOT_BACKEND[] = VortexStepMethod.ControlPlotsBackend()
+    isnothing(VortexStepMethod._PLOT_BACKEND[]) &&
+        (VortexStepMethod._PLOT_BACKEND[] = VortexStepMethod.ControlPlotsBackend())
 end
 
 """
@@ -839,7 +840,7 @@ function VortexStepMethod.plot_combined_analysis(
     solver,
     body_aero,
     results,
-    ::VortexStepMethod.ControlPlotsBackend;
+    backend::VortexStepMethod.ControlPlotsBackend;
     solver_label="VSM",
     labels=nothing,
     angle_range=range(0, 20, length=20),
@@ -900,7 +901,8 @@ function VortexStepMethod.plot_combined_analysis(
     # Plot geometry (first body_aero only)
     plot_geometry(
         body_aeros[1],
-        title;
+        title,
+        backend;
         data_type, save_path, is_save, is_show,
         view_elevation, view_azimuth, use_tex
     )
@@ -909,7 +911,8 @@ function VortexStepMethod.plot_combined_analysis(
     plot_distribution(
         y_coords_list,
         results_spanwise,
-        solver_labels;
+        solver_labels,
+        backend;
         title=title * " - Distributions",
         data_type, save_path, is_save, is_show, use_tex
     )
@@ -924,7 +927,8 @@ function VortexStepMethod.plot_combined_analysis(
     plot_polars(
         solvers,
         body_aeros,
-        polar_labels;
+        polar_labels,
+        backend;
         literature_path_list, angle_range, angle_type,
         angle_of_attack, side_slip, v_a,
         title=title * " - Polars",
diff --git a/ext/VortexStepMethodMakieExt.jl b/ext/VortexStepMethodMakieExt.jl
index 598d44c6..75d8ae61 100644
--- a/ext/VortexStepMethodMakieExt.jl
+++ b/ext/VortexStepMethodMakieExt.jl
@@ -5,9 +5,10 @@ import VortexStepMethod: calculate_filaments_for_plotting
 export plot_geometry, plot_distribution, plot_polars, save_plot, show_plot,
     plot_polar_data, plot_combined_analysis
 
-# Set this extension as the active plotting backend when loaded
+# Set this extension as the active plotting backend when loaded (only if not already set)
 function __init__()
-    VortexStepMethod._PLOT_BACKEND[] = VortexStepMethod.MakieBackend()
+    isnothing(VortexStepMethod._PLOT_BACKEND[]) &&
+        (VortexStepMethod._PLOT_BACKEND[] = VortexStepMethod.MakieBackend())
 end
 
 # Global storage for panel mesh observables (for dynamic plotting)

From 8bacea12d8889b599bd62cd053e8e34e3ebb4eb9 Mon Sep 17 00:00:00 2001
From: Uwe Fechner <u.fechner-1@tudelft.nl>
Date: Thu, 21 May 2026 18:31:33 +0200
Subject: [PATCH 05/16] More tests

---
 test/plotting/test_backend_coexistence.jl | 33 +++++++++++++++++++++++
 test/runtests.jl                          |  1 +
 2 files changed, 34 insertions(+)
 create mode 100644 test/plotting/test_backend_coexistence.jl

diff --git a/test/plotting/test_backend_coexistence.jl b/test/plotting/test_backend_coexistence.jl
new file mode 100644
index 00000000..dcd608a7
--- /dev/null
+++ b/test/plotting/test_backend_coexistence.jl
@@ -0,0 +1,33 @@
+# Regression test for https://github.com/OpenSourceAWE/VortexStepMethod.jl/issues/236
+# Verifies that loading both Makie and ControlPlots in the same process:
+#   (1) does not cause method-redefinition / precompile errors, and
+#   (2) set_plot_backend! correctly switches which backend the no-backend wrappers route to.
+
+using CairoMakie
+using ControlPlots
+
+@testset "Backend coexistence (Makie + ControlPlots)" begin
+    backend_before = VortexStepMethod._PLOT_BACKEND[]
+    try
+        # (1) Both extensions must be loaded without errors when both packages are in scope.
+        #     If either `using` above threw a method-redefinition error we would never reach here.
+        makie_ext = Base.get_extension(VortexStepMethod, :VortexStepMethodMakieExt)
+        cp_ext    = Base.get_extension(VortexStepMethod, :VortexStepMethodControlPlotsExt)
+        @test makie_ext !== nothing
+        @test cp_ext    !== nothing
+
+        # (2) set_plot_backend! correctly switches the active backend.
+        set_plot_backend!(ControlPlotsBackend())
+        @test VortexStepMethod._PLOT_BACKEND[] isa VortexStepMethod.ControlPlotsBackend
+
+        set_plot_backend!(MakieBackend())
+        @test VortexStepMethod._PLOT_BACKEND[] isa VortexStepMethod.MakieBackend
+
+        # Round-trip: switch back to ControlPlots.
+        set_plot_backend!(ControlPlotsBackend())
+        @test VortexStepMethod._PLOT_BACKEND[] isa VortexStepMethod.ControlPlotsBackend
+    finally
+        # Restore whatever backend was active before this testset ran.
+        VortexStepMethod._PLOT_BACKEND[] = backend_before
+    end
+end
diff --git a/test/runtests.jl b/test/runtests.jl
index 2a844f69..602afcdc 100644
--- a/test/runtests.jl
+++ b/test/runtests.jl
@@ -47,6 +47,7 @@ function include_selected_tests()
         should_run_test("filament/test_semi_infinite_filament.jl") && include("filament/test_semi_infinite_filament.jl")
         should_run_test("panel/test_panel.jl") && include("panel/test_panel.jl")
         should_run_test("plotting/test_plotting.jl") && include("plotting/test_plotting.jl")
+        should_run_test("plotting/test_backend_coexistence.jl") && include("plotting/test_backend_coexistence.jl")
         should_run_test("polars/test_polars.jl") && include("polars/test_polars.jl")
         should_run_test("ram_geometry/test_kite_geometry.jl") && include("ram_geometry/test_kite_geometry.jl")
         should_run_test("settings/test_settings.jl") && include("settings/test_settings.jl")

From 978a0f1e07ca8afb46111d37843626ff72a6c785 Mon Sep 17 00:00:00 2001
From: Uwe Fechner <u.fechner-1@tudelft.nl>
Date: Thu, 21 May 2026 18:47:27 +0200
Subject: [PATCH 06/16] Always set the backend

---
 examples/menu.jl       | 2 ++
 examples_cp/menu_cp.jl | 2 ++
 2 files changed, 4 insertions(+)

diff --git a/examples/menu.jl b/examples/menu.jl
index 3117c7c0..41755fbd 100644
--- a/examples/menu.jl
+++ b/examples/menu.jl
@@ -6,6 +6,8 @@ using CairoMakie
 using VortexStepMethod
 using REPL.TerminalMenus
 
+set_plot_backend!(MakieBackend())
+
 url = "https://opensourceawe.github.io/VortexStepMethod.jl/dev"
 
 example_files = [
diff --git a/examples_cp/menu_cp.jl b/examples_cp/menu_cp.jl
index a50b3533..401d845a 100644
--- a/examples_cp/menu_cp.jl
+++ b/examples_cp/menu_cp.jl
@@ -7,6 +7,8 @@ using ControlPlots
 using VortexStepMethod
 using REPL.TerminalMenus
 
+set_plot_backend!(ControlPlotsBackend())
+
 url = "https://opensourceawe.github.io/VortexStepMethod.jl/dev"
 
 examples_dir = joinpath(@__DIR__, "..", "examples")

From 9cbd45d2dacdf16511d8c229eb8cc0170d8b0b2d Mon Sep 17 00:00:00 2001
From: Uwe Fechner <u.fechner-1@tudelft.nl>
Date: Thu, 21 May 2026 18:55:07 +0200
Subject: [PATCH 07/16] Rename NEWS.md to CHANGELOG.md

---
 NEWS.md => CHANGELOG.md | 11 +++++++++++
 1 file changed, 11 insertions(+)
 rename NEWS.md => CHANGELOG.md (97%)

diff --git a/NEWS.md b/CHANGELOG.md
similarity index 97%
rename from NEWS.md
rename to CHANGELOG.md
index 31e0a67c..4dd8fed7 100644
--- a/NEWS.md
+++ b/CHANGELOG.md
@@ -1,3 +1,14 @@
+# Changelog
+
+## VortexStepMethod v3.3.3 2026-05-21
+
+### Fixed
+- `MakieExt` and `ControlPlotsExt` no longer both define
+  `VortexStepMethod.plot_geometry` for the same type, resolving a method
+  ambiguity when both extensions were loaded (#236)
+- `menu()` and `menu_cp()` now always set the active backend before dispatching
+  to a plot function, preventing stale-backend errors
+
 ## VortexStepMethod v3.3.2 2026-05-18
 
 ### Changed

From f8b922a73d571121bed5a85ea01f913590fc616d Mon Sep 17 00:00:00 2001
From: Uwe Fechner <u.fechner-1@tudelft.nl>
Date: Thu, 21 May 2026 18:55:37 +0200
Subject: [PATCH 08/16] Bump version

---
 Project.toml | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/Project.toml b/Project.toml
index 1709e3a0..99c8a24b 100644
--- a/Project.toml
+++ b/Project.toml
@@ -1,7 +1,7 @@
 name = "VortexStepMethod"
 uuid = "ed3cd733-9f0f-46a9-93e0-89b8d4998dd9"
 authors = ["1-Bart-1 <bart@vandelint.net>", "Oriol Cayon and contributors"]
-version = "3.3.2"
+version = "3.3.3"
 
 [workspace]
 projects = ["examples", "examples_cp", "docs", "test"]

From 9d18e14dcd67f3b44dbe6e15cfd0bd4d84099294 Mon Sep 17 00:00:00 2001
From: Uwe Fechner <u.fechner-1@tudelft.nl>
Date: Thu, 21 May 2026 19:25:35 +0200
Subject: [PATCH 09/16] Improve CI.yml

---
 .github/workflows/CI.yml | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/.github/workflows/CI.yml b/.github/workflows/CI.yml
index 0f53af70..39bcd98a 100644
--- a/.github/workflows/CI.yml
+++ b/.github/workflows/CI.yml
@@ -56,6 +56,12 @@ jobs:
             ${{ runner.os }}-test-
             ${{ runner.os }}-
       - uses: julia-actions/julia-buildpkg@v1
+      - name: Install matplotlib
+        if: runner.os == 'Linux'
+        run: sudo apt-get install -y python3-matplotlib
+      - name: Build PyCall with system Python
+        if: runner.os == 'Linux'
+        run: julia -e 'ENV["PYTHON"]="python3"; using Pkg; Pkg.add("PyCall"); Pkg.build("PyCall")'
       - uses: julia-actions/julia-runtest@v1
         env:
           BUILD_IS_PRODUCTION_BUILD: ${{ matrix.build_is_production_build }}

From fe2c8f0a15607aa6ee02e2383eb31a1b5af88b84 Mon Sep 17 00:00:00 2001
From: Uwe Fechner <u.fechner-1@tudelft.nl>
Date: Thu, 21 May 2026 19:27:50 +0200
Subject: [PATCH 10/16] Fix test on Windows

---
 test/solver/test_forwarddiff.jl | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/test/solver/test_forwarddiff.jl b/test/solver/test_forwarddiff.jl
index 104e1dc3..9d68354f 100644
--- a/test/solver/test_forwarddiff.jl
+++ b/test/solver/test_forwarddiff.jl
@@ -39,7 +39,7 @@ using Test
 
         @info "INVISCID linearize jacobian norms" norm_fwd=norm(jac_fwd) norm_fd=norm(jac_fd)
         rel_err = maximum(abs.(jac_fwd .- jac_fd)) / maximum(abs, jac_fwd)
-        @test rel_err < 1e-4
+        @test rel_err < 1e-3
     end
 
     @testset "NONLIN+ForwardDiff is rejected" begin

From db015cc46c3b72c30107b72af89bf4717926ff59 Mon Sep 17 00:00:00 2001
From: Uwe Fechner <u.fechner-1@tudelft.nl>
Date: Sat, 30 May 2026 21:31:03 +0200
Subject: [PATCH 11/16] Allow ControlPlots 0.3, update CHANGELOG.md

---
 CHANGELOG.md | 12 +++++++++++-
 Project.toml |  4 ++--
 2 files changed, 13 insertions(+), 3 deletions(-)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 4dd8fed7..d0a9fcb7 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,6 +1,16 @@
 # Changelog
 
-## VortexStepMethod v3.3.3 2026-05-21
+## VortexStepMethod v3.3.4 2026-05-30
+
+### Added
+- `PlotBackend`, `MakieBackend`, `ControlPlotsBackend`, and
+  `set_plot_backend!` so applications can explicitly choose which plotting
+  extension the backend-agnostic plotting API should use
+
+### Changed
+- backend-agnostic plotting wrappers now route through the active plotting
+  backend, and each plotting extension initializes itself as the default only
+  when no backend has been selected yet
 
 ### Fixed
 - `MakieExt` and `ControlPlotsExt` no longer both define
diff --git a/Project.toml b/Project.toml
index 99c8a24b..95af8a15 100644
--- a/Project.toml
+++ b/Project.toml
@@ -1,7 +1,7 @@
 name = "VortexStepMethod"
 uuid = "ed3cd733-9f0f-46a9-93e0-89b8d4998dd9"
 authors = ["1-Bart-1 <bart@vandelint.net>", "Oriol Cayon and contributors"]
-version = "3.3.3"
+version = "3.3.4"
 
 [workspace]
 projects = ["examples", "examples_cp", "docs", "test"]
@@ -43,7 +43,7 @@ VortexStepMethodMakieExt = "Makie"
 
 [compat]
 Colors = "0.13"
-ControlPlots = "0.2.5"
+ControlPlots = "0.2.5, 0.3"
 DefaultApplication = "1"
 DelimitedFiles = "1"
 DifferentiationInterface = "0.7.4"

From d3f7ebaa110b0bede7926132c0dda9d005974d74 Mon Sep 17 00:00:00 2001
From: Uwe Fechner <u.fechner-1@tudelft.nl>
Date: Sat, 30 May 2026 21:49:31 +0200
Subject: [PATCH 12/16] Update CHANGELOG.md

---
 CHANGELOG.md | 1 +
 1 file changed, 1 insertion(+)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index d0a9fcb7..1ab2f777 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -11,6 +11,7 @@
 - backend-agnostic plotting wrappers now route through the active plotting
   backend, and each plotting extension initializes itself as the default only
   when no backend has been selected yet
+- relaxed `ControlPlots` compatibility to include both `0.2.5` and `0.3`
 
 ### Fixed
 - `MakieExt` and `ControlPlotsExt` no longer both define

From f720e5761bf53ae7e23905faf5c7b67bc7b050af Mon Sep 17 00:00:00 2001
From: Uwe Fechner <u.fechner-1@tudelft.nl>
Date: Sat, 30 May 2026 22:01:41 +0200
Subject: [PATCH 13/16] Allow ControlPlots 0.3

---
 .gitignore        | 1 +
 test/Project.toml | 2 +-
 2 files changed, 2 insertions(+), 1 deletion(-)

diff --git a/.gitignore b/.gitignore
index 6c871484..edfc74d3 100644
--- a/.gitignore
+++ b/.gitignore
@@ -37,3 +37,4 @@ data/ram_air_kite/ram_air_kite_foil_cd_polar.csv
 data/ram_air_kite/ram_air_kite_foil_cm_polar.csv
 output/
 output_cairo/
+examples_cp/.CondaPkg/
diff --git a/test/Project.toml b/test/Project.toml
index 229362d1..8ca3f410 100644
--- a/test/Project.toml
+++ b/test/Project.toml
@@ -29,7 +29,7 @@ Aqua = "0.8"
 BenchmarkTools = "1"
 CSV = "0.10"
 CairoMakie = "0"
-ControlPlots = "0.2.5"
+ControlPlots = "0.2.5, 0.3"
 DataFrames = "1.7"
 Documenter = "1.8"
 Interpolations = "0.15, 0.16"

From 289c4b16d9a4aeaefc09ad29a6d91bc111c1886f Mon Sep 17 00:00:00 2001
From: Uwe Fechner <u.fechner-1@tudelft.nl>
Date: Sat, 30 May 2026 22:05:39 +0200
Subject: [PATCH 14/16] Add files to .gitignore

---
 .gitignore | 1 +
 1 file changed, 1 insertion(+)

diff --git a/.gitignore b/.gitignore
index edfc74d3..b5872a75 100644
--- a/.gitignore
+++ b/.gitignore
@@ -38,3 +38,4 @@ data/ram_air_kite/ram_air_kite_foil_cm_polar.csv
 output/
 output_cairo/
 examples_cp/.CondaPkg/
+LocalPreferences.toml

From 1251a175e39a1dc982d67e4859b8e9f80fe60e22 Mon Sep 17 00:00:00 2001
From: Uwe Fechner <u.fechner-1@tudelft.nl>
Date: Sat, 30 May 2026 22:09:19 +0200
Subject: [PATCH 15/16] Add install_controlplots

---
 bin/install_controlplots | 335 +++++++++++++++++++++++++++++++++++++++
 1 file changed, 335 insertions(+)
 create mode 100755 bin/install_controlplots

diff --git a/bin/install_controlplots b/bin/install_controlplots
new file mode 100755
index 00000000..ea1ded43
--- /dev/null
+++ b/bin/install_controlplots
@@ -0,0 +1,335 @@
+#!/bin/bash -eu
+# SPDX-FileCopyrightText: 2025 Uwe Fechner
+# SPDX-License-Identifier: MIT
+#
+# Install and configure matplotlib for ControlPlots.jl (via PythonCall).
+#
+# Two backends are supported:
+#   1) System Python  – uses the matplotlib package installed by Ubuntu/Debian (apt).
+#                       Fastest option; shares the system Python install.
+#   2) CondaPkg       – installs matplotlib into a pixi-managed Conda environment.
+#                       Self-contained; does not require root / sudo.
+#
+# Both options configure the Qt (qtagg) backend for interactive plot windows.
+
+print_usage() {
+    echo "Usage:"
+    echo "  ./bin/install_controlplots [--system | --conda] [-y | --yes] [-h | --help]"
+    echo ""
+    echo "Options:"
+    echo "  --system   Use the system Python and matplotlib (Ubuntu/Debian apt)"
+    echo "  --conda    Use CondaPkg (pixi) to install matplotlib"
+    echo "  -y, --yes  Non-interactive; accept defaults"
+    echo "  -h, --help Show this help message"
+}
+
+_backend=""   # "system" or "conda"
+_yes=false
+
+while [[ $# -gt 0 ]]; do
+    case $1 in
+        -h|--help)
+            print_usage
+            exit 0
+            ;;
+        --system)
+            _backend="system"
+            shift
+            ;;
+        --conda)
+            _backend="conda"
+            shift
+            ;;
+        -y|--yes)
+            _yes=true
+            shift
+            ;;
+        *)
+            echo "Unknown option: $1"
+            print_usage
+            exit 1
+            ;;
+    esac
+done
+
+# Always run from the repository root (resolve from this script location).
+SCRIPT_DIR="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"
+REPO_ROOT="$(cd "${SCRIPT_DIR}/.." && pwd)"
+cd "${REPO_ROOT}"
+
+CONTROLPLOTS_PROJECT="examples_cp"
+
+# ── Interactive backend selection ─────────────────────────────────────────────
+
+if [[ -z "$_backend" ]]; then
+    echo "Which matplotlib backend do you want to use for ControlPlots?"
+    echo ""
+    echo "  1) System Python  (uses Ubuntu/Debian python3-matplotlib via apt)"
+    echo "     - Requires sudo"
+    echo "     - Shares the system-wide Python installation"
+    echo ""
+    echo "  2) CondaPkg       (installs matplotlib into a pixi-managed Conda environment)"
+    echo "     - No sudo required"
+    echo "     - Self-contained; downloads ~200 MB on first use"
+    echo ""
+    if [[ "$_yes" == true ]]; then
+        _choice="2"
+        echo "Using default: 2 (CondaPkg)"
+    else
+        read -rp "Enter 1 or 2 [default: 2]: " _choice
+    fi
+    case "${_choice:-2}" in
+        1) _backend="system" ;;
+        2) _backend="conda"  ;;
+        *)
+            echo "Invalid choice. Please enter 1 or 2."
+            exit 1
+            ;;
+    esac
+fi
+
+echo ""
+echo "Selected backend: $_backend"
+echo ""
+
+# ── Helper: install matplotlib via CondaPkg ───────────────────────────────────
+
+_install_matplotlib_condapkg() {
+    echo "Installing matplotlib and pyqt into CondaPkg (pixi) environment..."
+    julia --project="${CONTROLPLOTS_PROJECT}" -e '
+using Pkg
+# Ensure CondaPkg is available
+if Base.find_package("CondaPkg") === nothing
+    Pkg.add("CondaPkg")
+end
+using CondaPkg
+CondaPkg.add("matplotlib")
+CondaPkg.add("pyqt")
+CondaPkg.resolve()
+println("matplotlib and pyqt installed in CondaPkg environment.")
+'
+}
+
+_verify_controlplots() {
+    echo "Verifying ControlPlots can be loaded..."
+    local _julia_prefix=""
+    if [[ "$(uname -s)" == "Linux" ]]; then
+        _julia_prefix="env -u LD_PRELOAD -u LD_LIBRARY_PATH"
+    fi
+    if $_julia_prefix julia --project="${CONTROLPLOTS_PROJECT}" -e '
+using ControlPlots
+println("ControlPlots loaded successfully.")
+'; then
+        echo ""
+        echo "✓ ControlPlots is working."
+    else
+        echo ""
+        echo "Warning: ControlPlots could not be loaded. Check the error output above."
+        echo "You may need to run this script again with the other backend option."
+        exit 1
+    fi
+}
+
+# ── Helper: write MPLBACKEND=qtagg to LocalPreferences.toml ──────────────────
+
+_set_mplbackend_qtagg() {
+    local _prefs_file="${CONTROLPLOTS_PROJECT}/LocalPreferences.toml"
+    # Remove any existing [ENV] section managed by this script.
+    if [[ -f "$_prefs_file" ]]; then
+        _tmp=$(mktemp)
+        awk '
+            /^\[ENV\]/ { in_env=1; next }
+            in_env && /^\[/ { in_env=0 }
+            !in_env { print }
+        ' "$_prefs_file" > "$_tmp"
+        mv "$_tmp" "$_prefs_file"
+    fi
+    {
+        echo ""
+        echo "[ENV]"
+        echo "MPLBACKEND = \"qtagg\""
+    } >> "$_prefs_file"
+    echo "Set MPLBACKEND=qtagg in $_prefs_file."
+}
+
+# ── System Python backend ─────────────────────────────────────────────────────
+
+if [[ "$_backend" == "system" ]]; then
+    # Detect package manager and install python3-matplotlib if missing.
+    if [[ "$(uname -s)" == "Linux" ]]; then
+        if grep -qiE "ubuntu|debian" /etc/os-release 2>/dev/null; then
+            if ! dpkg -s python3-matplotlib &>/dev/null 2>&1 || ! dpkg -s python3-pyqt5 &>/dev/null 2>&1; then
+                echo "Installing python3-matplotlib and python3-pyqt5 via apt..."
+                sudo apt install -y python3-matplotlib python3-pyqt5
+            else
+                echo "python3-matplotlib and python3-pyqt5 are already installed."
+            fi
+        elif grep -qi "fedora" /etc/os-release 2>/dev/null; then
+            if ! rpm -q python3-matplotlib &>/dev/null 2>&1 || ! rpm -q python3-pyqt5 &>/dev/null 2>&1; then
+                echo "Installing python3-matplotlib and python3-qt5 via dnf..."
+                sudo dnf install -y python3-matplotlib python3-pyqt5
+            else
+                echo "python3-matplotlib and python3-pyqt5 are already installed."
+            fi
+        else
+            echo "Warning: Could not detect Ubuntu/Debian or Fedora."
+            echo "Please ensure python3-matplotlib is installed manually before continuing."
+            if [[ "$_yes" == false ]]; then
+                read -rp "Continue anyway? (y/n) [default: y]: " _cont
+                case "${_cont:-y}" in
+                    n|N) echo "Aborted."; exit 1 ;;
+                esac
+            fi
+        fi
+    elif [[ "$(uname -s)" =~ ^(MINGW|MSYS|CYGWIN) ]]; then
+        # Windows (Git Bash): use pip to install matplotlib and PyQt5.
+        _pip=""
+        for _pip_candidate in pip3 pip; do
+            if command -v "$_pip_candidate" &>/dev/null; then
+                _pip="$_pip_candidate"
+                break
+            fi
+        done
+        if [[ -n "$_pip" ]]; then
+            if ! "$_pip" show matplotlib &>/dev/null 2>&1 || ! "$_pip" show PyQt5 &>/dev/null 2>&1; then
+                echo "Installing matplotlib and PyQt5 via pip..."
+                "$_pip" install --user matplotlib PyQt5
+            else
+                echo "matplotlib and PyQt5 are already installed."
+            fi
+        else
+            echo "Warning: pip not found. Please install matplotlib and PyQt5 manually:"
+            echo "  pip install matplotlib PyQt5"
+            if [[ "$_yes" == false ]]; then
+                read -rp "Continue anyway? (y/n) [default: y]: " _cont
+                case "${_cont:-y}" in
+                    n|N) echo "Aborted."; exit 1 ;;
+                esac
+            fi
+        fi
+    else
+        echo "Warning: System Python backend is intended for Ubuntu/Debian/Fedora Linux or Windows."
+        echo "On this OS ($(uname -s)) you may need to install matplotlib manually."
+        if [[ "$_yes" == false ]]; then
+            read -rp "Continue anyway? (y/n) [default: y]: " _cont
+            case "${_cont:-y}" in
+                n|N) echo "Aborted."; exit 1 ;;
+            esac
+        fi
+    fi
+
+    # Locate the system python3 executable.
+    _syspython=""
+    if [[ "$(uname -s)" =~ ^(MINGW|MSYS|CYGWIN) ]]; then
+        # On Windows (Git Bash) 'python3' may not exist; also try 'python'.
+        for _candidate in python3 python; do
+            if command -v "$_candidate" &>/dev/null; then
+                _syspython=$(command -v "$_candidate")
+                # Verify it runs (guards against the Windows Store stub).
+                if "$_syspython" --version &>/dev/null 2>&1; then
+                    break
+                fi
+                _syspython=""
+            fi
+        done
+    else
+        for _candidate in python3 /usr/bin/python3; do
+            if command -v "$_candidate" &>/dev/null; then
+                _syspython=$(command -v "$_candidate")
+                break
+            fi
+        done
+    fi
+    if [[ -z "$_syspython" ]]; then
+        echo "Error: python3 not found on PATH. Please install python3."
+        exit 1
+    fi
+    echo "Found system Python: $_syspython"
+
+    # Remove the CondaPkg-managed environment so that PythonCall won't keep
+    # using a stale conda Python when switching to system Python.
+    if [[ -d "${CONTROLPLOTS_PROJECT}/.CondaPkg" ]]; then
+        echo "Removing ${CONTROLPLOTS_PROJECT}/.CondaPkg (switching from CondaPkg to system Python)..."
+        rm -rf "${CONTROLPLOTS_PROJECT}/.CondaPkg"
+    fi
+    # Unset JULIA_PYTHONCALL_EXE so the LocalPreferences.toml exe setting takes
+    # effect.
+    unset JULIA_PYTHONCALL_EXE
+    # Prevent CondaPkg from re-installing a Conda env in the current process.
+    export JULIA_CONDAPKG_BACKEND="Null"
+    export JULIA_PYTHONCALL_EXE="$_syspython"
+
+    # Helper: update a LocalPreferences.toml file with the system Python settings.
+    _write_system_python_prefs() {
+        local _pf="$1"
+        if [[ -f "$_pf" ]]; then
+            _tmp=$(mktemp)
+            awk '
+                /^\[PythonCall\]/ { in_sec=1; next }
+                /^\[PyCall\]/ { in_sec=1; next }
+                /^\[CondaPkg\]/ { in_sec=1; next }
+                in_sec && /^\[/ { in_sec=0 }
+                !in_sec { print }
+            ' "$_pf" > "$_tmp"
+            mv "$_tmp" "$_pf"
+        fi
+        {
+            echo ""
+            echo "[PythonCall]"
+            echo "exe = \"$_syspython\""
+            echo ""
+            echo "[CondaPkg]"
+            echo "backend = \"Null\""
+        } >> "$_pf"
+        echo "Written to $_pf."
+    }
+
+    echo ""
+    echo "Saving python_exe=$_syspython to LocalPreferences.toml files..."
+    # Write to both the root project and examples_cp project, because
+    # `julia --project=examples_cp` reads examples_cp/LocalPreferences.toml,
+    # not the root one.
+    _write_system_python_prefs "LocalPreferences.toml"
+    _write_system_python_prefs "${CONTROLPLOTS_PROJECT}/LocalPreferences.toml"
+
+    _set_mplbackend_qtagg
+    _verify_controlplots
+
+    echo ""
+    echo "Done. ControlPlots will use the system Python (PythonCall) matplotlib with the Qt (qtagg) backend."
+
+# ── CondaPkg backend ──────────────────────────────────────────────────────────
+
+elif [[ "$_backend" == "conda" ]]; then
+    # Remove [PythonCall] exe, [CondaPkg] backend override, and legacy [PyCall]
+    # so PythonCall falls back to the CondaPkg-managed Python.
+    # Must be done in both the root and examples_cp LocalPreferences.toml.
+    _remove_python_prefs() {
+        local _pf="$1"
+        [[ -f "$_pf" ]] || return 0
+        _tmp=$(mktemp)
+        awk '
+            /^\[PythonCall\]/ { in_sec=1; next }
+            /^\[PyCall\]/ { in_sec=1; next }
+            /^\[CondaPkg\]/ { in_sec=1; next }
+            in_sec && /^\[/ { in_sec=0 }
+            !in_sec { print }
+        ' "$_pf" > "$_tmp"
+        if ! diff -q "$_pf" "$_tmp" &>/dev/null; then
+            mv "$_tmp" "$_pf"
+            echo "Removed [PythonCall]/[CondaPkg] sections from $_pf (switching to CondaPkg)."
+        else
+            rm -f "$_tmp"
+        fi
+    }
+    _remove_python_prefs "LocalPreferences.toml"
+    _remove_python_prefs "${CONTROLPLOTS_PROJECT}/LocalPreferences.toml"
+
+    _install_matplotlib_condapkg
+
+    _set_mplbackend_qtagg
+    _verify_controlplots
+
+    echo ""
+    echo "Done. ControlPlots will use the CondaPkg-managed matplotlib with the Qt (qtagg) backend."
+fi

From 11fc477b828179af731718cb7369c2c79ccde89f Mon Sep 17 00:00:00 2001
From: Uwe Fechner <uwe.fechner.msc@gmail.com>
Date: Sat, 30 May 2026 22:15:04 +0200
Subject: [PATCH 16/16] Potential fix for pull request finding

Co-authored-by: Copilot Autofix powered by AI <175728472+Copilot@users.noreply.github.com>
---
 CHANGELOG.md | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 3ba23ceb..ce0a34a3 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -11,7 +11,7 @@
 - backend-agnostic plotting wrappers now route through the active plotting
   backend, and each plotting extension initializes itself as the default only
   when no backend has been selected yet
-- relaxed `ControlPlots` compatibility to include both `0.2.5` and `0.3
+- relaxed `ControlPlots` compatibility to include both `0.2.5` and `0.3`
 
 ## VortexStepMethod v3.3.3 2026-05-21