Changes touching this path

• the readiness wait stops being a wall-clock BUDGET over a polled directory and waits on the child OWN first line instead - a strictly stronger condition, because the banner is printed AFTER the signal handler is armed while the temp tree appears EARLIER, in sandbox create. so the directory only ever proved the run had STARTED, and a 500ms sleep stood in for and-by-now-it-is-probably-armed: signalling inside that sliver tests the GAP rather than the fix, which is why the wait was load-bearing and is REPLACED here rather than deleted. the banner is a pub const so the test waits on the VALUE rather than on a copy of the sentence, and the ordering it depends on is PINNED - and that pin is shown load-bearing rather than decorative, because moving the banner above the arming leaves the very test it protects GREEN on an idle machine. the damage would have been an INTERMITTENTLY red test, not an obviously broken one. the measurement behind all of this was REDONE rather than relayed, because the tree it was supposedly taken on DID NOT COMPILE - probes whose definitions had been deleted and whose uses were left behind - so nothing about it had ever been built, let alone run. 534 loaded runs against 12 idle, the test binary invoked DIRECTLY rather than through cargo so no rebuild could contend, under up to three concurrent cold workspace builds at 100% CPU. the correction is MATERIAL: the worst whole-test reading goes from 22.75 to 61.4 seconds, 2.7 times worse, and signal-to-exit from 18.3 to 29.8, 1.6 times worse - while the IDLE column reconciles exactly, which is what says the earlier figures sampled a quieter machine rather than a different test. two findings come out better than the ones they replace. the old 30-second budget is not marginal but EXCEEDED OUTRIGHT: three of 534 readiness readings blew past it at 61.3, 60.4 and 50.7 seconds, a 0.6 percent outright loss, reproduced rather than inferred. and the sibling one assertion below it was 215 MILLISECONDS short of being the same bug, at 29.8 against its own 30. so both clocks are re-derived as BACKSTOPS rather than budgets, and deliberately to the SAME number, because the measurement shows a machine that intermittently stops scheduling this child for tens of seconds and which slice a given stall lands in is LUCK - sizing each against only its own sample understates both by exactly the amount that sample under-sampled. the budgets-versus-backstops distinction is stated once for both: a budget is sized to how long the work ought to take and is therefore a claim about the machine, while a backstop is sized to nothing, exists only for states where no progress will ever be made, and must be far enough out that crossing it says WEDGED and never BUSY. the sibling sweep is recorded in the file so it is not redone from zero, and it was READ rather than line-window grepped - the rust suite comes out clean, every other bounded wait being over an in-process thread already awaited on a condition, or a LOWER bound, or iteration-bounded, or slack over a kill rather than a cold start. and one loaded run of the 534 failed UNEXPLAINED, in 0.48 seconds so not a clock at all, before the harness captured panic text, never recurring in the 510 that followed with capture on. it is recorded as what it is: a SECOND load-sensitive failure mode in this test, which this change does not close and must not be read as having closed (#1693) 0d517bfe · dbf3dbe6…

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