The host gate's model controls run only the tests their verdicts name, and refuse a run that selected none

issues/build/a-clean-cannot-land-inside-a-build-judges-a-flat-700-ms-window.md

@@ -0,0 +1,23 @@
+---
+status: open
+kind: tooling
+opened: 2026-10-01
+---
+
+# `a_clean_cannot_land_inside_a_build` judges a flat 700 ms window
+
+`src/buildlock.rs`'s `clean_racing_a_build` touches `builder-mid` and then
+reads whether the cleaner child wrote `cleaner-done` within a flat 700 ms
+(`appeared(&root.join("cleaner-done"), Duration::from_millis(700))`).
+
+- Unlocked, it asserts the clean finished inside the window: a cleaner the
+  host does not schedule for 700 ms reds the test with the lock working.
+- Locked, it asserts the clean did not finish inside the window: that shows
+  the lock held only if an unheld clean would have finished in 700 ms, which
+  this run does not measure.
+
+Not seen red.
+
+**Exit condition**: the unlocked arm waits on `cleaner-done` under a ceiling
+that fails loudly, and the locked arm reads an order of events (the clean
+after the build's lock is let go), not the absence of one inside a window.