Coverage Said 69%, Mutation Testing Said 25%

Sunday 2026-06-28. intent-mail repo, fresh Stryker baseline run. The coverage gate reported green: 69.09% line coverage. Three seconds later, mutation testing reported 24.88%. The rules engine—the code that actually mutates user email—reported 0.00%. That zero is the story. The Gap Coverage counts lines. Mutation testing counts assertions. When a 535-line end-to-end suite exercises a piece of code but doesn't assert on its internal logic, coverage sees a line executed and calls it a