core-logic-executor

name	core-logic-executor
description	Domain guidance for implementing core logic and algorithm phases. Loaded when phase category is CORE.

Core Logic Implementation Guidance

TDD order for logic

1. Edge cases + invalid inputs
2. Boundary conditions (off-by-one zones)
3. Happy path
4. Scale/performance sanity (if plan specifies)

Pure function rules (when plan says PURE)

• No mutation of input arguments — return new objects.
• No I/O, logging, time, randomness, or environment reads.
• No module-level globals for shared state; inject explicitly.

State machine discipline

• Implement transition function as single source of truth.
• Test every valid transition AND every illegal transition.
• If plan requires immutability: return NEW state object, do not mutate input.

Algorithm correctness checklist

Before finalizing, verify:

• Index math at boundaries (0, len-1, empty).
• Inclusive vs exclusive ranges.
• Stable behavior on duplicates/ties if relevant.
• Big-O target from plan met (don't brute-force unless allowed).

Avoid over-engineering

• Implement minimum that satisfies pass_criteria.
• No extra layers, no new frameworks, no "future-proofing."
• If tempted to refactor: stop and re-read plan constraints.

Do NOT weaken assertions

If tests fail, fix the root cause. Do not "fix" by loosening assertions unless plan explicitly allows it.