Bump to v0.19.0-beta and document CTModels.Utils integration

- Version bump: 0.18.15-beta → 0.19.0-beta
- CHANGELOGS.md: Added comprehensive entry for Interpolation module and Core utilities
- BREAKINGS.md: Added non-breaking note documenting no breaking changes

Author: ocots

BREAKINGS.md

@@ -2,6 +2,21 @@
 
 This document outlines all breaking changes introduced in CTBase v0.18.0-beta compared to v0.17.4. Use this guide to migrate your code and understand the impact of these changes.
 
+## Non-breaking note (0.19.0-beta)
+
+- **Interpolation module**: Added new `Interpolation` module with interpolation utilities migrated from CTModels.Utils
+  - `ctinterpolate`: linear interpolation with flat extrapolation
+  - `ctinterpolate_constant`: piecewise-constant (steppost) interpolation
+  - `Interpolant{Linear}` and `Interpolant{Constant}` parametric types with type-stable call methods
+  - Custom `show` methods for interpolant display
+- **Core utilities**: Extended `Core` module with utilities from CTModels.Utils
+  - `matrix2vec`: public utility for matrix-to-vector conversion
+  - `to_out_of_place`: private utility for out-of-place function transformation
+  - `@ensure`: private macro for argument validation
+- **Documentation**: Updated `docs/api_reference.jl` to include new Interpolation module and Core utilities
+- **Tests**: Added comprehensive test suites for interpolation (56 tests), function_utils (18 tests), macros (14 tests), and matrix_utils (26 tests)
+- **No breaking changes**: All additions are new public API; existing CTBase API unchanged. No migration required.
+
 ## Non-breaking note (0.18.15-beta)
 
 - **Philosophy documentation**: Added comprehensive code philosophy documentation in `dev/philosophy/` covering modules, types/traits, exceptions, docstrings, testing, and documentation standards. No API changes; purely documentation additions.

CHANGELOGS.md

@@ -5,6 +5,49 @@ All notable changes to CTBase will be documented in this file.
 The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
 and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
+## [0.19.0-beta] - 2026-06-11
+
+### ✨ New Features
+
+#### **Interpolation Module**
+
+- **New module**: Added `Interpolation` module with interpolation utilities migrated from CTModels.Utils (issue #445)
+- **Linear interpolation**: `ctinterpolate(x, f)` creates a linear interpolant with flat extrapolation beyond bounds
+- **Constant interpolation**: `ctinterpolate_constant(x, f)` creates a right-continuous piecewise-constant (steppost) interpolant
+- **Typed interpolants**: `Interpolant{Linear}` and `Interpolant{Constant}` parametric types with type-stable call methods
+- **Custom display**: Added `show` methods for interpolants showing method type and node count
+- **Optimal control support**: Constant interpolation implements standard steppost behavior for control applications
+
+#### **Core Utilities**
+
+- **Matrix utilities**: Extended `Core` module with `matrix2vec` for matrix-to-vector conversion (public)
+- **Function utilities**: Added `to_out_of_place` for out-of-place function transformation (private)
+- **Validation macro**: Added `@ensure` macro for argument validation (private)
+
+### 📚 Documentation
+
+- **API reference**: Updated `docs/api_reference.jl` to include new Interpolation module with public and private documentation
+- **Core documentation**: Extended Core API reference to include matrix_utils, function_utils, and macros
+- **Docstrings**: Comprehensive docstrings with `$(TYPEDSIGNATURES)` and julia-repl examples
+
+### 🧪 Testing
+
+- **Interpolation tests**: 56 tests covering linear/constant interpolation, extrapolation, non-uniform grids, vector values, type stability, and display
+- **Function utils tests**: 18 tests for `to_out_of_place` function transformation
+- **Macro tests**: 14 tests for `@ensure` validation macro
+- **Matrix utils tests**: 26 tests for `matrix2vec` and related utilities
+- **All tests pass**: 1237/1237 tests pass (45.9s)
+
+### 🏗️ Architecture
+
+- **Modular design**: Split utilities by responsibility (Interpolation module + Core extensions) rather than monolithic Utils module
+- **Qualified imports**: All new code follows CTBase convention of qualified imports without top-level exports
+- **Type stability**: Interpolant call methods are type-stable with `@inferred` tests
+
+### 🧹 Maintenance
+
+- **Version bump**: Bumped to 0.19.0-beta for feature release.
+
 ## [0.18.15-beta] - 2026-06-06
 
 ### 📚 Documentation

Project.toml

@@ -1,6 +1,6 @@
 name = "CTBase"
 uuid = "54762871-cc72-4466-b8e8-f6c8b58076cd"
-version = "0.18.15-beta"
+version = "0.19.0-beta"
 authors = ["Olivier Cots <olivier.cots@irit.fr>", "Jean-Baptiste Caillau <caillau@univ-cotedazur.fr>"]
 
 [deps]