The owner retested text editing twice and reported the same thing both times: still not working, and once you try to edit one run of text you cannot click any other until you leave Edit mode. Then the offer in the pull quote.
What the manager found
Driving the application itself, the manager found the gap. The Rust core answered an edit with the page’s text under one spelling of the field name; the interface looked for another; the mismatch raised an error that nothing surfaced. Three merged slices had shipped on top of this. The interface tests mocked the core and the core’s tests never ran the interface, so both suites had been green from the start.
The first attempt at a fix, a slice adding typing feedback, was built on the wrong diagnosis and did not touch the cause. The second corrects the field name, hardens the interface so a failed edit is reported rather than swallowed, and fixes the stuck Edit mode.
The rule
Every slice that touches a command crossing from the shell to the core is now smoke-tested in the real executable, driven through the embedded browser’s remote debugging, before it is called done. Mocked tests remain, but they no longer count as proof that the two halves agree.