[xiehuanyi]

Numeric change assertions validate the initial subject but do not validate the value observed after invoking the target function. A counter changing from numeric 1 to string "2" incorrectly passes .increase(), and changing to string "0" incorrectly passes .decrease(). A final undefined value silently passes their negated forms because arithmetic produces NaN.

Check the final observed value using the same numeric prerequisite as the initial value, before calculating the delta. This covers object properties and getter callbacks, including negated assertions and custom error messages. Existing valid numeric changes retain their behavior.

Validation:

• Three new public regression cases fail on unchanged main, covering object/getter subjects and invalid final values under negation.
• npm run build and npm run lint pass.
• npm run test-node: 515 passing; Chromium suite with the local Chrome executable: 514 passing.
• git diff --check passes.

Discovery and implementation: automated OpenAI gpt-6.1-sol source review, xhigh reasoning.

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