Safe Refactoring Rules

Purpose

Ensure all refactoring is deterministic, non-breaking, and behavior-preserving.

This skill enforces how changes are made, not how the system is structured.

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1. Behavior Preservation

• Never change runtime behavior unless explicitly instructed.
• Any refactoring must preserve observable outputs.
• Moving code between layers must not alter execution results.

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2. Existing Code Respect

• Never overwrite an existing method if it already satisfies part of the requirement.
• Extend existing implementations instead of replacing them.
• Do not delete or rewrite working logic unless required for a fix.

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3. Dependency Integrity

• Always preserve constructor injection.
• Never replace dependency injection with service locators (app(), resolve()).
• Do not introduce new dependencies when existing ones suffice.
• Do not change dependency graphs without explicit intent.

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4. Public API Stability

• Never change public method signatures unless all call sites are updated in the same change.
• Avoid breaking changes at all costs.
• Prefer internal adaptation over external contract modification.

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5. Idempotency Requirement

• Refactoring must be idempotent.
• Running the same change twice must produce no further diff.
• No duplicate logic, imports, traits, or methods may be introduced.

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6. Uncertainty Handling

If any of the following is unclear:

• intended behavior
• service contract
• domain rule
• expected output

Then:

• Stop immediately
• Do not guess
• Report ambiguity explicitly
• Request clarification

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7. Abstraction Reuse Rule (Local Scope Only)

This skill only enforces reuse during refactoring operations.

Global abstraction policy is defined in application-architecture-standard.

Before introducing:

• Trait
• Service
• DTO
• Transformer
• Base class

Search for an existing implementation.

Reuse existing abstractions whenever practical.

Duplicate abstractions are architectural defects.

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8. Scope Discipline

This skill does NOT define:

• architecture layering (handled by application-architecture-standard)
• testing strategy (handled by data-layer-contracts / filament-resource-testing)
• security rules (handled separately if present)

It ONLY defines safe transformation rules.

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9. Enforcement Priority

If this skill conflicts with others:

1. application-architecture-standard
2. domain-specific skills
3. execution workflows
4. this skill (always subordinate to architecture)