# Spec: Validate custom-router parity and apply fixes

## Overview
Verify parity between `custom-router/updated-custom-router` and `src/` using the migration checklist. Implement only minimal fixes required to close any gaps found, add tests for changes, and update documentation if behavior changes.

## In Scope
- Engines: confirm `getCurrentPoolState()` and `setPool()` presence/behavior where applicable.
- BaseRouter: verify fallback behavior and caching logic.
- Factory: validate protocol routing and legacy compatibility paths.

## Out of Scope
- Large refactors or architecture changes.
- New protocol additions or feature expansions beyond parity.
- Performance optimizations unrelated to parity gaps.

## Functional Requirements
1. Audit all engines for `getCurrentPoolState()` and `setPool()` parity with expected behavior.
2. Validate BaseRouter fallback behavior and caching consistency with documented intent.
3. Validate factory protocol routing behavior and legacy compatibility.
4. Implement minimal fixes only when concrete gaps are identified.
5. Add or adjust tests for any code changes.
6. Update documentation if a behavior change is introduced.

## Non-Functional Requirements
- Preserve existing public API compatibility.
- Keep changes minimal and focused on parity gaps.

## Acceptance Criteria
- Verified parity checklist completed for engines, BaseRouter, and factory.
- Any identified gaps are fixed with minimal changes.
- Tests added/updated for all changes.
- Documentation updated only when behavior changes.