Rename Core\Reducer to Composite and expose it as a public validator

[henriquemoody]

The term "Reducer" is widely used in functional programming to describe a specific pattern: a function that takes an accumulator and a value, returning a new accumulator (e.g., array_reduce, Redux reducers). This class does not perform that operation. Instead, it consolidates multiple validators into a single one, which is the definition of composition.

The new name "Composite" accurately reflects what this validator does: it composes zero or more validators into a unified validation unit. This aligns with the Composite design pattern terminology and avoids semantic confusion with functional programming concepts.

The class has also been moved from the internal Core namespace to the public Validators namespace. This change acknowledges that composing validators dynamically is a legitimate use case for library consumers, not just an internal implementation detail. The library itself uses this pattern in Attributes and KeySet validators, demonstrating its practical value.

The signature has been extended to accept zero or more validators:

• Zero validators: Returns AlwaysValid (useful for conditional chains)
• One validator: Pass-through without wrapping (avoids unnecessary nesting)
• Multiple validators: Combines using AllOf (all must pass)

This flexibility is particularly useful when building validation chains dynamically, where the number of validators may vary at runtime based on configuration or user input.

Assisted-by: Claude Code (Claude Opus 4.5)

[Copilot]

Pull request overview

This PR renames the internal Core\Reducer class to Composite and promotes it to a public validator in the Validators namespace. The change addresses semantic confusion with functional programming's "reducer" concept and better reflects the class's purpose of composing multiple validators into a unified validation unit. The signature has been enhanced to accept zero or more validators, with intelligent behavior: zero validators returns AlwaysValid, one validator acts as pass-through, and multiple validators are combined using AllOf.

Changes:

• Renamed Core\Reducer to Validators\Composite with enhanced variadic parameter support (zero or more validators)
• Updated all internal usages in Attributes and KeySet validators to use the new class
• Added comprehensive mixin interfaces for the new public validator across all builder patterns

Reviewed changes

Copilot reviewed 22 out of 22 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
src/Validators/Composite.php	New public validator that composes zero or more validators using AlwaysValid, pass-through, or AllOf patterns
src/Validators/Core/Reducer.php	Removed - replaced by the new Composite validator
src/Validators/Attributes.php	Updated to use new Composite class, simplified logic by removing empty validator check
src/Validators/KeySet.php	Updated to use new Composite class instead of Reducer
tests/unit/Validators/CompositeTest.php	Renamed test class and added test for zero-validator case
tests/src/SmokeTestProvider.php	Added smoke test for the new Composite validator
src/Mixins/*.php	Added method signatures for Composite across all mixin interfaces (Chain, Builder, and various decorators)
docs/validators/Composite.md	Comprehensive documentation with usage examples and use cases
docs/validators.md	Added Composite to the validator list in appropriate categories

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 99.20%. Comparing base (ec16b3d) to head (8df357c).
⚠️ Report is 3 commits behind head on main.

Additional details and impacted files

@@             Coverage Diff              @@
##               main    #1650      +/-   ##
============================================
+ Coverage     99.19%   99.20%   +0.01%     
- Complexity      908      919      +11     
============================================
  Files           190      191       +1     
  Lines          2117     2150      +33     
============================================
+ Hits           2100     2133      +33     
  Misses           17       17              

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