Record the behavior to preserve
For duplicated pricing logic, record inputs, rounding, discount order and displayed currency. Use confirmed examples or a specification rather than treating current code as the only authority. If a defect already exists, decide explicitly whether this task preserves or fixes it. Refactoring and behavior changes should not merge accidentally.
Request analysis before edits
Ask for callers, state changes and external access before proposing extraction. Identify genuine shared behavior and exceptions. Similar-looking functions can have different outputs or error semantics; combining them may create an abstraction that is harder to maintain. Require the proposed shared responsibility to be stated in plain language.
Keep each patch focused
Do not combine renaming, extraction and a dependency replacement in one patch. Validate an extraction with one caller, then extend it to the others. Preserve a diff and verification record at each stage. If behavior changes unexpectedly, this sequence provides a specific step to inspect or reject.
Check expected outputs independently
Review whether generated tests simply encode the new implementation’s output. Include empty input, limits, invalid values and known exceptions. For a UI change, inspect initial state and persistence after interaction. The meaningful measure is coverage of the behavior you need to preserve, not the number of generated assertions.
Example: extracting one shared calculation
If three screens repeat a calculation, replace it with a shared function in only one screen first. Verify the agreed input examples and inspect the patch before updating the others. This makes the point of any behavior change attributable and lets you accept a useful part of the work without committing to a simultaneous rewrite of every caller.
Select a reviewable workflow
Pilot the same small extraction in candidate tools such as Claude Code, Aider and Cursor. Judge whether the patch is explainable, unnecessary edits can be removed and another developer can continue it. Preserving a maintainable codebase through incremental improvement matters more than quickly generating a complete rewrite.
Official sources
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- Claude Code overviewInformation checked: 2026-10-27
- Aider usageInformation checked: 2026-10-27
- Cursor Agent overviewInformation checked: 2026-10-26
- Claude Code costsInformation checked: 2026-10-27
- Claude Code permissionsInformation checked: 2026-10-27
- Aider chat modesInformation checked: 2026-10-27
- Aider models and keysInformation checked: 2026-10-27
- Cursor pricingInformation checked: 2026-10-26
- Cursor models and pricingInformation checked: 2026-10-26