Pin the wiki's can() rules, quirks and all

The wiki's permission check predates every policy doc. Support macros quote its quirks back to customers.

Your task

Pin what can() does today. Not what the policy says. What the code does.

• fill REGRESSION_TESTS with cases: the arguments in, the value it returns today
• a test that expects the RIGHT answer instead of the CURRENT one fails the clean run
• at submit each test runs again against versions of the function with one line changed
• a change your tests do not notice is behavior you left unpinned
• the walk-through is read by the critique, not by the suite. Write it for the next engineer

The suite runs your tests against the untouched code, then against mutations you have not seen.