row 251: BUILD.md predicts part A's reds on e5e4b2e5a and records no rebase onto 6096b051b (sage-2084)

agents/darkwing/work/queue-251/BUILD.md

@@ -55,6 +55,35 @@ I considered `-t 3` with a 4.5 s sleep for a 2 s floor. One second of floor is f
 first list has needed (31.9 ms in proof 5), and the concurrent-suite run below tests it under load, so I
 took the smaller change.
 
+## Base
+
+The branch stays on 3b0aef995. By 19:15Z origin/refactor was at 6096b051b, after rows 66 and 243
+landed. `git diff 3b0aef995 6096b051b` touches neither `packages/bus/src/host-run.mjs` nor
+`packages/bus/tests/host-run.test.mjs`, so there's no rebase (sage-2084). Row 243 did change
+`packages/bus/tests/process.test.mjs`. My slot's bus suites run that file as it was at 3b0aef995, and the
+gate rerun on Sage's slot runs it as landed.
+
+## Prediction for part A on e5e4b2e5a (written before the slot)
+
+The hook starts `ssh-add -t 1` at the given fraction of a monotonic second. From the brief's probe, the
+agent stores the key about 3 ms later. The first list reaches the agent a few ms after addKey resolves:
+Node's exit event, the mark, and `ssh-add -l`'s own start. A red needs the add to land before the second
+boundary and the list to land after it.
+
+- 0.990: green. The add and the list both land before the boundary.
+- 0.993, 0.995, 0.996, 0.997: red expected. The add lands before the boundary, the list after. At 0.993
+  and 0.997 I'm less sure, because the list (at 0.993) or the add (at 0.997) can land right at the
+  boundary. A green at either is in line with the cause, and so is a red.
+- 0.998: green. The add lands after the boundary, so the key gets almost a full second.
+
+Every red should show "first list got" an answer with no SHA256 line. It should also show addKey
+resolving before a second boundary and the first list starting after it or within a few ms of it, with
+the agent alive and its socket present.
+
+Under sage-2084's rule, on e5e4b2e5a only a red at 0.990 or 0.998 counts toward the stop, and two such
+reds stop the run. On the fix commit any red counts, and two stop it. In parts B to D, the first red stops
+the run.
+
 ## Slot plan
 
 All scripts are in `/mnt/storage/scratch/darkwing-251-out/`, launched from `/`, each behind the busy