Refactor: Extract engine validation methods to dedicated file

[Copilot]

Extracted validation methods from engine.go to improve code organization and follow the established *_validation.go pattern used throughout the codebase.

Changes

• Created pkg/workflow/engine_validation.go

  • Moved validateEngine method (validates engine ID support via registry)
  • Moved validateSingleEngineSpecification method (enforces single engine across imports)
  • Added documentation header consistent with docker_validation.go, npm_validation.go, etc.
  • Introduced engineValidationLog logger with namespace workflow:engine_validation

• Updated pkg/workflow/engine.go

  • Removed 76 lines (both validation methods)
  • No functional changes to remaining code

Context

This aligns with the validation file pattern where domain-specific validation lives in dedicated *_validation.go files rather than mixed with core logic. Improves discoverability and maintains architectural consistency.

Related to #3478

Original prompt

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This section details on the original issue you should resolve

<issue_title>[task] Extract validation methods from engine.go to engine_validation.go</issue_title>
<issue_description>## Objective
Extract validation methods from pkg/workflow/engine.go into a new dedicated validation file following the established *_validation.go pattern.

Context

The codebase follows a good pattern of having dedicated validation files (docker_validation.go, npm_validation.go, pip_validation.go), but validation methods in engine.go break this pattern, reducing discoverability. This is part of Issue #3 from the semantic function clustering analysis (Priority 2: Medium Impact, Medium Effort).

Related to #3478

Approach

1. Create new file pkg/workflow/engine_validation.go
2. Move validateEngine method from engine.go
3. Move validateSingleEngineSpecification method from engine.go
4. Ensure proper imports are in place
5. Update any internal references if needed
6. Verify all tests pass

Files to Modify

• Create: pkg/workflow/engine_validation.go
• Update: pkg/workflow/engine.go (remove validation methods)
• Update: Any test files that reference these methods

Acceptance Criteria

• New file engine_validation.go created
• validateEngine method moved to new file
• validateSingleEngineSpecification method moved to new file
• All imports correctly updated
• All existing tests pass
• No functionality broken
• File naming consistent with docker_validation.go, npm_validation.go pattern

Estimated Effort

1-2 hours

Benefits

• Improved discoverability of validation logic
• Consistent file organization across the codebase
• Follows established architectural patterns
• Easier to locate and maintain validation logic
  Related to [refactor] 🔧 Semantic Function Clustering Analysis - Refactoring Opportunities #3478

AI generated by Plan Command for #3478</issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes [task] Extract validation methods from engine.go to engine_validation.go #3486

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[Copilot]

Pull Request Overview

This PR refactors the engine validation code by extracting validation functions from engine.go into a new dedicated file engine_validation.go. This follows the project's code organization guidelines for domain-specific validation.

• Moves validateEngine() and validateSingleEngineSpecification() functions to a new file dedicated to engine validation
• Adds comprehensive documentation explaining when to add validation to this file
• Maintains identical functionality - this is purely a code organization improvement

Reviewed Changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
pkg/workflow/engine_validation.go	New file containing engine validation functions with comprehensive documentation following the validation architecture pattern
pkg/workflow/engine.go	Removes engine validation functions (moved to engine_validation.go) - keeps engine configuration extraction logic

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