Made the tolerance trait separable from the integrator itself

roadmap/README.md

@@ -58,6 +58,23 @@ Each feature below links to a detailed implementation plan in the `features/` di
   - **Dependencies**: None
   - **Effort**: Small
 
+### API Ergonomics
+
+- [x] **[Tolerances Trait](features/40-tolerances-trait.md)** ✅ COMPLETED
+  - Move `a_tol` / `a_tol_full` / `r_tol` off the inherent impls into a trait, and
+    add getters, so a generic `S` can set and read them
+  - Raised by `astrokit`, which declared its own copy as a workaround
+  - **Dependencies**: None
+  - **Effort**: Small
+  - **Status**: All four integrators implement `Tolerances`; no call site changed
+
+- [ ] **[Runtime Integrator Selection](features/41-runtime-integrator-selection.md)**
+  - Structural facts move from associated constants to `&self` methods, so an
+    enum can dispatch and an integrator can be chosen at runtime or named in a
+    config file
+  - **Dependencies**: None (pairs with Tolerances Trait)
+  - **Effort**: Medium
+
 ### Callbacks
 
 - [ ] **[Discrete Callbacks](features/05-discrete-callbacks.md)**
@@ -336,17 +353,18 @@ Each algorithm implementation should include:
 
 ## Progress Tracking
 
-Total Features: 38
-- Tier 1: 8 features (4/8 complete) ✅
-- Tier 2: 12 features (0/12 complete)
-- Tier 3: 18 features (0/18 complete)
+Total Features: 41
+- Tier 1: 10 features (5/10 complete) ✅
+- Tier 2: 11 features (0/11 complete)
+- Tier 3: 20 features (0/20 complete)
 
-**Overall Progress: 10.5% (4/38 features complete)**
+**Overall Progress: 12.2% (5/41 features complete)**
 
 ### Completed Features
 1. ✅ BS3 (Bogacki-Shampine 3/2) - Tier 1 (2025-10-23)
 2. ✅ Vern7 (Verner 7th order) - Tier 1 (2025-10-24)
 3. ✅ PID Controller - Tier 1 (2025-10-24)
 4. ✅ Rosenbrock23 - Tier 1 (2025-10-24)
+5. ✅ Tolerances Trait - Tier 1 (2026-09-30)
 
-Last updated: 2025-10-24
+Last updated: 2026-09-30