It said it stopped, and three lanes were still writing
A bulk save ran four writers at once and said it stopped on the first refusal. Three lanes kept going, so the count was wrong and the sentence false.
The till has a morning sheet that asks whether yesterday's sold-out dishes are still out, and a second sheet beside it for anything that has come back in. The first had been given four parallel lanes by hand earlier the same day, with a comment reasoning about why four. Its sibling makes the same call over the same list, its button says "All back in stock", and it was still one round trip per dish. A list of siblings with one missing, and the missing one sat behind the button that means all of them.
Lifting the hand-rolled version found a flaw in it
The four lanes had been started with the standard combinator that rejects on the first failure. Rejecting is not stopping. The other three lanes carry on writing, nobody is watching them, and the counter they share keeps climbing. So the sheet's sentence, N of M switched back on, then it stopped, was not true. It had not stopped, and N was read off a number three detached lanes were still incrementing.
That matters because four of the seven places that needed this print a sentence per row: N saved, M refused. A group that looks done and is not is how a VAT return goes out wrong. The combinator abandons the rest in flight on the first refusal, so that sentence could not be written honestly on top of it.
One pool, and it never rejects
The replacement is one shared helper. Four lanes drain a queue. It never rejects. Every failure is collected against its own row, and results come back in input order although completion order varies. It is wired at seven sites: both sold-out sheets on the till, and in the back office the bulk VAT change over a category, the timesheets week save, both par-level saves and the receipt-printout save. One behaviour change, stated: the three sites that used to abandon the remaining writes after a refusal now attempt them all and report the first. For independent settings writes that is strictly more saved for the same sentence on screen.
Ten other loops that wait row by row were judged and left alone, each with an assertion saying why. The kitchen screen's outbox re-reads and rewrites a file per step, and lanes would interleave that and resurrect an action already sent. The photo copies decode an image per row, where the cost is the processor, not the network. The label printer sends chunks over a cable. The supplier run sends a real order to a real supplier per step. A scan that finds a loop with a wait in it is not a finding, and the next person to run that scan now hits a test instead of a silence.
The test is behavioural rather than a text search, because the properties that matter, bounded, never rejects, finishes the list after a failure, are invisible to a matcher. Nothing was timed on the live site, because timing a bulk VAT change there means writing to it. The claim is a count: seven places went from N round trips to a quarter of N.