scripts/mutation-check reads a JSON list of breaks, applies each to the tree
one at a time, restores the file byte for byte, and reports CAUGHT, MISSED,
WRONG-MESSAGE, NOT-FOUND, SKIPPED or CONTROL-FAILED for each.
New tests: TestApplyAndRestoreAreByteExact, TestOldTextMustOccurOnce,
TestSidePicksPatternAndMessage, TestARecordWithASideRunsOnlyThere,
TestOutcomes, TestStatelessListStopsOnAFailingControl,
TestControlRunsOncePerDistinctTest,
TestStatefulListPreparesAndControlsEachBreak,
TestStatefulControlFailureMarksOnlyThatBreak, TestPrepareFailureStopsTheList,
TestCommandRecordsAreClassifiedByExitAndText,
TestCommandRecordReadsTheInspectedFileAndNeverAStaleOne,
TestCommandControlFailsWhenTheTextIsAlreadyThere,
TestSummarizeExitsOneUnlessEveryBreakIsCaught.
