brief: T27 row 251 records the monotonic-boundary check, 8 of 80 adds lost the key (mos-1185 item 2)

docs/plans/2026-10-21_t27-ssh-add-lifetime.md

@@ -22,6 +22,12 @@ The cause is not known yet. One lead, unverified (Mos, mos-1185): ssh-agent may
 seconds of CLOCK_MONOTONIC, so a key added just before a monotonic second boundary expires within
 milliseconds. A test aligned to wall-clock seconds did not test that idea.
 
+Sage checked the lead on dragon-lin, OpenSSH 10.5p1, 2026-10-21T17:19Z (`/mnt/storage/scratch/sage-r64/t27-mono.mjs`,
+outside any gate). It made 80 adds of `ssh-add -t 1`, each at a chosen fraction of a CLOCK_MONOTONIC second
+(`process.hrtime`), and listed at once. 8 of 80 missed. Every miss was an add made at 0.9947-0.9973 of a
+monotonic second that finished at 0.998-0.0008. No add earlier in the second missed. So a 1-second lifetime
+can end within milliseconds of the add. Step 2 still confirms this against the T27 failure itself.
+
 ## Steps, in order
 
 1. Make the failure name its cause. When the first assertion fails, print the time from addKey's start