Experiment: pattern kitchen sink (experiments/syntax/)

[logbie]

Tracking issue for the experiments/syntax/ experiment created by the repository hygiene migration (see REPOSITORY_HYGIENE.md).

syntax_test/pattern.wfl was an exploratory pattern-matching kitchen-sink program. It now lives at experiments/syntax/pattern_kitchen_sink.wfl with the required experiment metadata.

Exit criteria: fold any coverage not already provided by TestPrograms/patterns_comprehensive.wfl / patterns_working_comprehensive.wfl into asserted tests, then archive or delete the prototype. Decision due by the experiment's Review-by date (the hygiene checker fails CI once it expires).

[logbie]

Confirmed present and correctly registered on current main (4178714a): experiments/syntax/pattern_kitchen_sink.wfl with experiments/syntax/README.md carrying Review-by: 2026-10-30.

Two things worth having on the record here, since this issue is the thing that will be read when the deadline bites:

The deadline is enforced, and it fails CI hard. scripts/check_repo_hygiene.py:341-350 parses Review-by and raises experiment-expired the moment review_by < today. That gate is blocking, so on 2026-10-31 this stops being a tracking issue and becomes a red build for everyone. That is 77 days from today (2026-08-14) — no action needed now, but it is a real dated commitment rather than an aspiration, and it is cheaper to fold the coverage in deliberately than to archive under CI pressure the morning it expires.

The exit criterion is a diff, and it can be done before the deadline at any time. The question is narrow: which pattern constructs does pattern_kitchen_sink.wfl exercise that TestPrograms/patterns_comprehensive.wfl and patterns_working_comprehensive.wfl do not? That is a mechanical comparison of construct coverage, not a design decision — and once the answer is "nothing", deletion is uncontroversial. If it turns out the kitchen sink covers constructs the asserted tests miss, that gap is itself worth knowing about independently of this issue's disposition, because it means pattern matching has untested surface.

Same shape as #668; both come due on the same date, so they are naturally one sitting.

Suggested labels: experiment, testing, tech-debt.

Posted by the WFL repo warden (automated triage pass).