Fixed event handling to properly keep the state changes, plus a few other fixes

roadmap/README.md

@@ -8,7 +8,8 @@ The library currently has:
 - ✅ Dormand-Prince 4(5) adaptive explicit RK method with dense output
 - ✅ Tsit5 explicit RK method with dense output
 - ✅ PI step size controller
-- ✅ Basic continuous callbacks with zero-crossing detection
+- ✅ Continuous callbacks with zero-crossing detection, whose effects can change
+  the state, the parameters, or end the solution
 - ✅ Solution interpolation interface
 - ✅ Generic over array dimensions at compile-time
 - ✅ Support for ordinary and second-order ODE problems
@@ -79,6 +80,18 @@ Each feature below links to a detailed implementation plan in the `features/` di
 
 ### Callbacks
 
+- [x] **[Callback Effects That Can Change the State](features/42-callback-effects.md)** ✅ COMPLETED
+  - An effect's write to the state was overwritten by the step it was located in,
+    so a callback could stop a solution but not change one
+  - `effect(&mut self)`, termination at the crossing, both sides of a jump
+    recorded, the controller reset across one, and a defined order for two events
+    in one step
+  - Raised by `astrokit`, which needs a Modified Rodrigues Parameter shadow set
+    swap mid-propagation
+  - **Dependencies**: None
+  - **Effort**: Medium
+  - **Status**: All success criteria met; benches unchanged within run-to-run drift
+
 - [ ] **[Discrete Callbacks](features/05-discrete-callbacks.md)**
   - Event detection based on conditions (not zero-crossings)
   - Useful for time-based events, iteration counts, etc.
@@ -93,13 +106,13 @@ Each feature below links to a detailed implementation plan in the `features/` di
 
 ### Solution Interface
 
-- [ ] **[Saveat Functionality](features/07-saveat.md)**
+- [ ] **[Saveat Functionality](features/07-saveat-functionality.md)**
   - Save solution at specific timepoints
   - Dense vs sparse saving strategies
   - **Dependencies**: None
   - **Effort**: Medium
 
-- [ ] **[Solution Derivatives](features/08-solution-derivatives.md)**
+- [ ] **Solution Derivatives** (no plan written yet)
   - Access derivatives at any time point via interpolation
   - `solution.derivative(t)` interface
   - **Dependencies**: None
@@ -111,7 +124,7 @@ Each feature below links to a detailed implementation plan in the `features/` di
 
 ### Algorithms
 
-- [ ] **[DP8 (Dormand-Prince 8th order)](features/09-dp8-method.md)**
+- [ ] **DP8 (Dormand-Prince 8th order)** (no plan written yet)
   - 8th order explicit RK for very high accuracy
   - Complements Vern7 for algorithm selection
   - **Dependencies**: None
@@ -123,7 +136,7 @@ Each feature below links to a detailed implementation plan in the `features/` di
   - **Dependencies**: Linear solver infrastructure, Nordsieck representation
   - **Effort**: Large
 
-- [ ] **[Rodas4/Rodas5P](features/11-rodas-methods.md)**
+- [ ] **[Rodas4/Rodas5P](features/11-rodas4-rodas5p-methods.md)**
   - Higher-order Rosenbrock methods (4th/5th order)
   - Better accuracy for stiff problems
   - **Dependencies**: Rosenbrock23
@@ -138,7 +151,7 @@ Each feature below links to a detailed implementation plan in the `features/` di
   - **Dependencies**: At least one stiff solver (Rosenbrock23 or FBDF)
   - **Effort**: Large
 
-- [ ] **[Default Algorithm Selection](features/13-default-algorithm.md)**
+- [ ] **[Default Algorithm Selection](features/13-default-algorithm-selection.md)**
   - Smart defaults based on problem characteristics
   - `solve(problem)` without specifying algorithm
   - **Dependencies**: Auto-switching, multiple algorithms
@@ -146,7 +159,7 @@ Each feature below links to a detailed implementation plan in the `features/` di
 
 ### Initialization
 
-- [ ] **[Automatic Initial Step Size](features/14-initial-stepsize.md)**
+- [ ] **[Automatic Initial Step Size](features/14-automatic-initial-step-size.md)**
   - Algorithm to determine good initial dt
   - Based on local Lipschitz estimate
   - **Dependencies**: None
@@ -154,19 +167,19 @@ Each feature below links to a detailed implementation plan in the `features/` di
 
 ### Callbacks
 
-- [ ] **[PresetTimeCallback](features/15-preset-time-callback.md)**
+- [ ] **[PresetTimeCallback](features/15-presettimecallback.md)**
   - Trigger callbacks at specific predetermined times
   - Important for time-varying forcing functions
   - **Dependencies**: Discrete callbacks
   - **Effort**: Small
 
-- [ ] **[TerminateSteadyState](features/16-terminate-steady-state.md)**
+- [ ] **[TerminateSteadyState](features/16-terminatesteadystate.md)**
   - Auto-detect when solution reaches steady state
   - Stop integration early
   - **Dependencies**: Discrete callbacks
   - **Effort**: Small
 
-- [ ] **[SavingCallback](features/17-saving-callback.md)**
+- [ ] **[SavingCallback](features/17-savingcallback.md)**
   - Custom saving logic beyond default
   - For memory-efficient large-scale simulations
   - **Dependencies**: CallbackSet
@@ -194,7 +207,7 @@ Each feature below links to a detailed implementation plan in the `features/` di
 
 ### Algorithms
 
-- [ ] **[Low-Storage Runge-Kutta](features/20-low-storage-rk.md)**
+- [ ] **[Low-Storage Runge-Kutta](features/20-low-storage-runge-kutta.md)**
   - 2N, 3N, 4N storage variants
   - Critical for large-scale problems
   - **Dependencies**: None
@@ -212,7 +225,7 @@ Each feature below links to a detailed implementation plan in the `features/` di
   - **Dependencies**: Second-order ODE infrastructure (already exists)
   - **Effort**: Medium
 
-- [ ] **[Verner Methods Suite](features/23-verner-methods.md)**
+- [ ] **[Verner Methods Suite](features/23-verner-methods-suite.md)**
   - Vern6, Vern8, Vern9
   - Complete Verner family for different accuracy needs
   - **Dependencies**: Vern7
@@ -258,19 +271,19 @@ Each feature below links to a detailed implementation plan in the `features/` di
 
 ### Advanced Callbacks
 
-- [ ] **[VectorContinuousCallback](features/30-vector-continuous-callback.md)**
+- [ ] **[VectorContinuousCallback](features/30-vectorcontinuouscallback.md)**
   - Multiple simultaneous event detection
   - More efficient than multiple callbacks
   - **Dependencies**: CallbackSet
   - **Effort**: Medium
 
-- [ ] **[PositiveDomain](features/31-positive-domain.md)**
+- [ ] **[PositiveDomain](features/31-positivedomain.md)**
   - Enforce positivity constraints
   - Important for physical systems
   - **Dependencies**: CallbackSet
   - **Effort**: Small
 
-- [ ] **[ManifoldProjection](features/32-manifold-projection.md)**
+- [ ] **[ManifoldProjection](features/32-manifoldprojection.md)**
   - Project solution onto constraint manifolds
   - For constrained mechanical systems
   - **Dependencies**: CallbackSet
@@ -278,14 +291,14 @@ Each feature below links to a detailed implementation plan in the `features/` di
 
 ### Infrastructure
 
-- [ ] **[Nonlinear Solver Infrastructure](features/33-nonlinear-solver.md)**
+- [ ] **[Nonlinear Solver Infrastructure](features/33-nonlinear-solver-infrastructure.md)**
   - Newton's method
   - Quasi-Newton methods
   - Generic nonlinear solver interface
   - **Dependencies**: Linear solver infrastructure
   - **Effort**: Large
 
-- [ ] **[Krylov Linear Solvers](features/34-krylov-solvers.md)**
+- [ ] **[Krylov Linear Solvers](features/34-krylov-linear-solvers.md)**
   - GMRES, BiCGStab
   - For large sparse systems
   - **Dependencies**: Linear solver infrastructure
@@ -355,12 +368,12 @@ Each algorithm implementation should include:
 
 ## Progress Tracking
 
-Total Features: 41
-- Tier 1: 10 features (6/10 complete) ✅
+Total Features: 42
+- Tier 1: 11 features (7/11 complete) ✅
 - Tier 2: 11 features (0/11 complete)
 - Tier 3: 20 features (0/20 complete)
 
-**Overall Progress: 14.6% (6/41 features complete)**
+**Overall Progress: 16.7% (7/42 features complete)**
 
 ### Completed Features
 1. ✅ BS3 (Bogacki-Shampine 3/2) - Tier 1 (2025-10-23)
@@ -369,5 +382,6 @@ Total Features: 41
 4. ✅ Rosenbrock23 - Tier 1 (2025-10-24)
 5. ✅ Tolerances Trait - Tier 1 (2026-09-30)
 6. ✅ Runtime Integrator Selection - Tier 1 (2026-09-30)
+7. ✅ Callback Effects That Can Change the State - Tier 1 (2026-10-01)
 
-Last updated: 2026-09-30
+Last updated: 2026-10-01