docs: cite clean build 28d31e4 for F-02 bench-verification

F-02/P-17 SSH host certs re-verified on the rebuilt 28d31e4 image (not the
hand-fixed host): the auto-derived FQDN principal is baked, so by-FQDN no-TOFU
admin login survives a reboot with zero manual steps. Cite the digest in the
design-doc status + bench-outcome, SSP v0.4 status line + R-16 row, and Annex A
2.4 row + R-16 register row.

docs/ssh-host-certificate-design.md

@@ -1,6 +1,6 @@
 # SSH host-certificate design — killing per-boot TOFU (F-02 / P-17)
 
-> Status: **BENCH-VERIFIED end-to-end 2026-07-11** (`comet-beacon-54`, real TPM):
+> Status: **BENCH-VERIFIED end-to-end 2026-07-11 on clean build `28d31e4`** (`comet-beacon-54`, real TPM):
 > TPM-mTLS → broker → step-ca signing → cert install → admin login **by FQDN with
 > no TOFU**, and per-boot auto-re-sign across a reboot. Closes SAR finding **F-02**
 > / POA&M **P-17**. Signing is **broker-mediated** (host → enrol-broker host plane →
@@ -122,6 +122,13 @@ automatically. **SELinux confinement is clean** (no AVCs writing `/etc/ssh` +
 reloading sshd → **no local TE module needed**), and STIG crypto policy accepts the
 `ecdsa-sha2-nistp256-cert-v01` host cert.
 
+**Re-verified on the rebuilt `28d31e4` image (2026-07-11), not hand-patched:** the
+auto-derived FQDN principal (`<host>.<domain>`) is baked, so admin login by FQDN
+with no TOFU **survives a reboot with zero manual steps** — the exact case the
+hand-fixed host regressed on (its manual `SSH_HOSTCERT_PRINCIPALS` edit lived on the
+RAM overlay and evaporated). F-02/P-17 is closed on a real build, not just a
+hand-fixed host.
+
 Getting there surfaced defects, all fixed on `poam-hardening` (`28d31e4`):
 
 | # | Defect (as seen on the bench) | Fix |