diff --git a/tools/ci/merge-to-master.sh b/tools/ci/merge-to-master.sh
index 1e7bd890..842cc10a 100755
--- a/tools/ci/merge-to-master.sh
+++ b/tools/ci/merge-to-master.sh
@@ -55,6 +55,19 @@ master_gate() {
   esac
 }
 
+# After a landing, master goes to the box mirrors too (7 October 2026, 18:25 UTC: build-2's /srv/igneum.git master sat at 15:27's
+# a4bca198 while GitHub's carried cf7d6ccb, and three branches were cut from the stale tip; the mirrors only ever received what a
+# build happened to push). One push per mirror in IGNEUM_MIRRORS (default: both box files), fast-forward only, best effort: a mirror
+# that is down prints a line and never fails the landing.
+mirror_master() {   # <sha>
+  local sha="$1" m host key="${BS_KEY:-$HOME/.ssh/igneum_ed25519}" list="${IGNEUM_MIRRORS:-}"
+  if [ -z "$list" ]; then for f in "$HOME/.config/igneum/build-server" "$HOME/.config/igneum/build-server-2"; do [ -s "$f" ] && list="$list $(head -1 "$f" | tr -d '[:space:]'):/srv/igneum.git"; done; fi
+  for m in $list; do
+    if GIT_SSH_COMMAND="ssh -i $key -o BatchMode=yes -o ConnectTimeout=10" git push -q "$m" "$sha:refs/heads/master" 2>/dev/null; then echo "merge-to-master: mirror $m master -> ${sha:0:8}"
+    else echo "merge-to-master: mirror $m did not take master ${sha:0:8} (down, or not a fast-forward); the next landing tries again"; fi
+  done
+}
+
 if [ "$SELF_TEST" = 1 ]; then
   fails=0; d=$(mktemp -d); fake="$d/ci-state.sh"
   # the fake answers from $d/answer-<sha> (one line per call, consumed top to bottom; the last line repeats) and $d/answer-master
@@ -102,8 +115,18 @@ success 4 u push run
   FIXES_MASTER=0 master_gate >/dev/null || { echo "self-test failed: an unknown master read that turned green refused a merge"; fails=1; }
   printf 'unknown - - gh: exit 1\n' > "$d/answer-master"; rm -f "$d/i-master"
   FIXES_MASTER=0 master_gate >/dev/null 2>&1 && { echo "self-test failed: a lasting unknown master read let a merge through"; fails=1; }
+  # the mirror push: a bare repository behind master is fast-forwarded; one that is not a fast-forward is left alone with a line
+  mkdir -p "$d/src" && ( cd "$d/src" && git init -q -b master . && git -c user.name=t -c user.email=t@t commit -q --allow-empty -m one && git -c user.name=t -c user.email=t@t commit -q --allow-empty -m two ) 2>/dev/null
+  git clone -q --bare "$d/src" "$d/mirror.git" && ( cd "$d/mirror.git" && git update-ref refs/heads/master "$(git rev-parse master~1)" )
+  tip=$(git -C "$d/src" rev-parse master)
+  out=$( cd "$d/src" && IGNEUM_MIRRORS="$d/mirror.git" mirror_master "$tip" )
+  [ "$(git -C "$d/mirror.git" rev-parse master)" = "$tip" ] || { echo "self-test failed: the mirror was not fast-forwarded to the landed master: $out"; fails=1; }
+  ( cd "$d/src" && git checkout -q -b other master~1 && git -c user.name=t -c user.email=t@t commit -q --allow-empty -m fork ); fork=$(git -C "$d/src" rev-parse other)
+  out=$( cd "$d/src" && IGNEUM_MIRRORS="$d/mirror.git" mirror_master "$fork" )
+  [ "$(git -C "$d/mirror.git" rev-parse master)" = "$tip" ] || { echo "self-test failed: a non-fast-forward push moved the mirror's master"; fails=1; }
+  case "$out" in *"did not take master"*) ;; *) echo "self-test failed: the refused mirror push was not reported: $out"; fails=1 ;; esac
   rm -rf "$d"
-  [ "$fails" = 0 ] && echo "self-test passed: a green branch run merges; a red one is refused; an unknown read is waited through and refused only at the deadline; a queued run is waited for with the clock; an unrun branch is pushed once and then waited for; a red master refuses every merge but the declared fix"
+  [ "$fails" = 0 ] && echo "self-test passed: a landed master is fast-forwarded to every mirror and a refused mirror push is a line, not a failure; a green branch run merges; a red one is refused; an unknown read is waited through and refused only at the deadline; a queued run is waited for with the clock; an unrun branch is pushed once and then waited for; a red master refuses every merge but the declared fix"
   exit $fails
 fi
 [ -z "$(git status --porcelain --untracked-files=no)" ] || { echo "merge-to-master: the tree has uncommitted tracked changes; commit first" >&2; exit 1; }
@@ -125,7 +148,8 @@ for i in $(seq 1 "$TRIES"); do
   if ( cd "$W" && git "${AUTHOR[@]}" merge -q --no-ff -m "Merge $BRANCH ${SHA:0:8} into master (gate: green on ${SHA:0:8}, recorded by tools/ci/pre-push.sh; the full gate runs in CI on this merge)" "$SHA" ); then
     if ( cd "$W" && git push -q origin HEAD:master ); then   # the hook asks ci-state about ${SHA:0:8} once more on this push
       git worktree remove --force "$W"; git fetch -q origin master
-      echo "merge-to-master: pushed on try $i: origin/master $(git log -1 --format='%h %ci' origin/master) $(TZ=Europe/London date '+%H:%M %Z')"; exit 0
+      echo "merge-to-master: pushed on try $i: origin/master $(git log -1 --format='%h %ci' origin/master) $(TZ=Europe/London date '+%H:%M %Z')"
+      mirror_master "$(git rev-parse origin/master)"; exit 0
     fi
     echo "merge-to-master: try $i: the push was rejected (master moved or the hook was red); again"
   else