Add validation helpers and refactor constraint validations

[Copilot]

Eliminates duplicated validation code across port, max-file-size, max-file-count, and retention-days constraints by introducing a reusable helper.

Changes

New validation helper (pkg/workflow/validation_helpers.go)

• validateIntRange(value, min, max int, fieldName string) error - Single source of truth for range validation
• Consistent error message format across all constraints

Refactored validations

• Port (gateway.go): 1-65535
• Max-file-size (repo_memory.go): 1-104857600 bytes
• Max-file-count (repo_memory.go): 1-1000 files
• Retention-days (cache.go): 1-90 days

Before:

if entry.MaxFileSize < 1 || entry.MaxFileSize > 104857600 {
    return nil, fmt.Errorf("max-file-size must be between 1 and 104857600 bytes, got %d", entry.MaxFileSize)
}

After:

if err := validateIntRange(entry.MaxFileSize, 1, 104857600, "max-file-size"); err != nil {
    return nil, err
}

Test coverage

• 28 new test cases for validation helper (boundary conditions + real-world constraints)
• Existing test suites verified: 39 tests covering all 4 fields with min/max/zero/negative/overflow cases

Original prompt

---

This section details on the original issue you should resolve

<issue_title>[plan] Create validation helpers and boundary tests</issue_title>
<issue_description>## Objective

Create reusable validation helper functions and comprehensive boundary value tests for the 4 newly validated constraint fields.

Context

After fixing the 4 specific constraint validations, we need:

1. Reusable validation helpers to prevent code duplication
2. Comprehensive tests to ensure boundary conditions are properly handled
3. Documentation of validation patterns for future development

Approach

Part 1: Validation Helpers

Create validation utility functions in appropriate location (e.g., pkg/workflow/validation.go or new pkg/workflow/validation_helpers.go):

func validateIntRange(value, min, max int, fieldName string) error {
    if value < min || value > max {
        return fmt.Errorf("%s must be between %d and %d, got %d",
                          fieldName, min, max, value)
    }
    return nil
}

Part 2: Unit Tests

Create or update test files to cover boundary conditions for each field:

• pkg/workflow/gateway_test.go - Port validation tests
• pkg/workflow/repo_memory_test.go - File size/count/retention tests

Test cases for each field:

• Minimum valid value (should pass)
• Maximum valid value (should pass)
• Below minimum (should fail with clear error)
• Above maximum (should fail with clear error)
• Zero value (should fail if minimum > 0)
• Negative value (should fail)

Files to Create/Modify

• Create or update: pkg/workflow/validation_helpers.go - Reusable validation functions
• Update: pkg/workflow/gateway_test.go - Port boundary tests
• Update: pkg/workflow/repo_memory_test.go - File size/count/retention boundary tests

Acceptance Criteria

• Validation helper function created and documented
• Port field has 6+ test cases (min, max, below, above, zero, negative)
• Max-file-size field has 6+ test cases
• Max-file-count field has 6+ test cases
• Retention-days field has 6+ test cases
• All tests pass with make test-unit
• Code coverage maintained or improved
  Related to [plan] Fix missing constraint validations in parser/compiler #7524

AI generated by Plan Command for discussion #7454

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

• Fixes [plan] Create validation helpers and boundary tests #7529

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