docs: update unreleased changelog entries

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: rasheedja

ChangeLog.md

@@ -2,23 +2,48 @@
 
 ## Unreleased changes
 
-- **BREAKING CHANGE**: Restructured `VarDomain` type to support upper bounds
-  - Replaced `NonNegative`, `LowerBound SimplexNum`, and `Unbounded` constructors with 
+### Breaking changes
+
+- **`twoPhaseSimplex` signature changed**:
+  - Old: `ObjectiveFunction -> [PolyConstraint] -> m (Maybe Result)`
+  - New: `VarDomainMap -> [ObjectiveFunction] -> [PolyConstraint] -> m SimplexResult`
+  - The first argument is now a `VarDomainMap` specifying variable domains
+  - The second argument is now a **list** of `ObjectiveFunction`; pass an empty list to check
+    feasibility only (Phase 1) without optimising
+  - The return type is now `SimplexResult` (see below)
+- **`VarDomain` type restructured** to support upper bounds:
+  - Replaced `NonNegative`, `LowerBound SimplexNum`, and `Unbounded` constructors with
     a single `Bounded { lowerBound :: Maybe SimplexNum, upperBound :: Maybe SimplexNum }` record
-  - Added smart constructors for convenience: `unbounded`, `nonNegative`, `lowerBoundOnly`, 
-    `upperBoundOnly`, and `boundedRange`
-  - `Bounded Nothing Nothing` is equivalent to `Unbounded`
-  - `Bounded (Just 0) Nothing` is equivalent to `NonNegative`
-  - Upper bounds are now supported and automatically added as LEQ constraints
-- Added `AddUpperBound` constructor to `VarTransform` for upper bound constraint generation
-- Updated `getTransform` to return a list of transforms (can now generate both lower and upper bound transforms)
-- Use Hspec for tests
-- Add nix flake
-- twoPhaseSimplex now takes a VarDomainMap (as the first param)
-  - You can specify each Var's domain using smart constructors: `nonNegative`, `unbounded`, 
-    `lowerBoundOnly`, `upperBoundOnly`, or `boundedRange`
-  - If a VarDomain for a Var is undefined, it's assumed to be `unbounded`
-  - If you want to keep the same behaviour as before (all vars non-negative), use `nonNegative` for all Vars
+  - `Bounded Nothing Nothing` is equivalent to the old `Unbounded`
+  - `Bounded (Just 0) Nothing` is equivalent to the old `NonNegative`
+  - Added smart constructors: `unbounded`, `nonNegative`, `lowerBoundOnly`, `upperBoundOnly`,
+    and `boundedRange`
+- **`Result` and `SimplexMeta` types removed**; replaced by:
+  - `SimplexResult { feasibleSystem :: Maybe FeasibleSystem, objectiveResults :: [ObjectiveResult] }`
+    — the top-level return from `twoPhaseSimplex`
+  - `ObjectiveResult { objectiveFunction :: ObjectiveFunction, outcome :: OptimisationOutcome }`
+    — the result for each objective function
+  - `OptimisationOutcome` — describes the outcome of optimising a single objective (optimal
+    value found, unbounded, or infeasible)
+
+### New features
+
+- Upper bounds on variables are now supported: use `upperBoundOnly` or `boundedRange` in the
+  `VarDomainMap`; upper bounds are automatically added as LEQ constraints
+- `twoPhaseSimplex` can optimise multiple objective functions in a single call against one
+  constraint set; results are returned in the same order as the input list
+- Added `VarDomainMap` type for mapping variables to their domains; variables not present are
+  assumed `unbounded`
+
+### Infrastructure
+
+- Added Nix flake (`flake.nix`) for a reproducible dev environment via `nix develop` (GHC 9.6,
+  cabal, stack, fourmolu, hlint, HLS)
+- Added `Makefile` with `make build`, `make test`, `make ci`, etc.; supports both cabal and
+  stack via `BUILD_TOOL=cabal|stack` (default: cabal)
+- CI now tests GHC 9.2–9.12 across ubuntu, macos, and windows (cabal); Stack LTS 22.44 on
+  ubuntu and macos; and a Nix-based job running both cabal and stack
+- Replaced HUnit golden tests with HSpec (`hspec-discover`)
 
 ## [v0.2.0.0](https://github.com/rasheedja/LPPaver/tree/v0.2.0.0)