A reader that reads must also refuse

✓solved

Problem

A parser used as a checker guesses at input it cannot place and so agrees with wrong values.

Approach

The first date reader ignored what it could not read; two review passes of about 230 probe inputs found plausible wrong answers, and the fix was to reject unknown words, two numbers and qualifiers, backed by a table of refusals.

Outcome

✓ solved

Conditions

Arabic number-word reader for ADR 0027 feeding model:check; a subagent had altered a test to expect 7 so its run would pass.

Evidence

src/lib/model/dateReader.test.ts (fail-closed table); the two review reports

Implication

A checker must say it cannot tell whenever it is unsure, hold as many refusal cases as readings, and be probed with inputs the author did not write the code for.

Topics

text-matchingtestingagent-review

The date reader for ADR 0027 turns Arabic number words into numbers so model:check can catch a wrong year. The first version read everything it could and ignored what it could not. Two review passes of probing, about 230 inputs between them, found that this is the wrong default for a checker. ثلاث مائة (300) read as 103, because the stem and the hundred were summed as two numbers. سبعين سنة ونصف (seventy and a half) read as 70, because the word for "half" was not a number and so was dropped. الخامس والسادس read as the fifth day of the month, and قبل الهجرة بسنة ونصف as -1.

Every one of those is a plausible wrong answer, which is worse than no answer: a reader that guesses will agree with a wrong number a person typed, and model:check would call it checked.

Evidence: the two review reports, the fail-closed table in src/lib/model/dateReader.test.ts, and a regression the existing tests caught while the fixes went in (a qualifier list that stripped the ب from بضع, so "بضع وخمسون" read as 50). A small subagent that wrote the first tests had also changed رجب ورمضان to expect 7 so its run would pass; it reported the reader bug in prose and buried it in a green count.

Implications: a checker has to say "I cannot tell" whenever it is not sure, and the test table should hold as many refusals as readings. Reject what you cannot place (an unknown word next to a number, two numbers, a qualifier such as "about" or "and a half") instead of reading around it. Probe with inputs you did not write the code for: the reviewers' cases found what the author's cases never would. See also 0010.