diff --git a/.xum/skills/verify-xum/SKILL.md b/.xum/skills/verify-xum/SKILL.md
index ffaa533adc4..2542533221f 100644
--- a/.xum/skills/verify-xum/SKILL.md
+++ b/.xum/skills/verify-xum/SKILL.md
@@ -45,8 +45,9 @@ newest-run link live there. Use a checkout of your own, not a shared repository.
 (the default on Debian and Ubuntu, which give each user a private group), git makes a clone's
 folder, `.git` and `.git/worktrees/<name>` 0775, so every command refuses. Run
 `chmod g-w,o-w` on the folder the message names (it names one at a time), or use a checkout made
-under umask 022. Bun on PATH must be the version in `package.json` `packageManager`. Launch
-refuses another Bun.
+under umask 022. A writable folder you do not own (root's, for example) cannot be fixed that way:
+the message then says to use a checkout under folders you own. Bun on PATH must be the version in
+`package.json` `packageManager`. Launch refuses another Bun.
 
 ```bash
 .xum/skills/verify-xum/scripts/verify-xum.sh launch
diff --git a/.xum/skills/verify-xum/scripts/verify-xum.sh b/.xum/skills/verify-xum/scripts/verify-xum.sh
index 9364fe55fff..1828d936c58 100755
--- a/.xum/skills/verify-xum/scripts/verify-xum.sh
+++ b/.xum/skills/verify-xum/scripts/verify-xum.sh
@@ -91,7 +91,7 @@ group_is_ours() {
 # replacement again and undoes the quoting.
 refusal_fix() { # refusal_fix <fix> <folder>
   [[ -n $1 ]] || return 0
-  printf ': %s%q%s' "${1%%@DIR@*}" "$2" "${1#*@DIR@}"
+  if [[ $1 == *@DIR@* ]]; then printf ': %s%q%s' "${1%%@DIR@*}" "$2" "${1#*@DIR@}"; else printf ': %s' "$1"; fi
 }
 
 # A run's state.env is sourced, so the run folder and the home above it must be real folders (no
@@ -114,8 +114,12 @@ require_safe_ancestors() { # require_safe_ancestors <path> [<what it is, for mes
     owner=$(stat -c %u "$dir")
     mode=$(stat -c %a "$dir")
     [[ $owner == 0 || $owner == "$(id -u)" ]] || die "$dir, above $what, is owned by user $owner"
-    (((8#$mode & 8#022) == 0 || (8#$mode & 8#1000) != 0)) \
-      || die "$dir, above $what, is writable by group or others and not sticky (mode $mode)$(refusal_fix "$fix" "$dir")"
+    if ! (((8#$mode & 8#022) == 0 || (8#$mode & 8#1000) != 0)); then
+      # Only the owner can chmod it: for a root-owned folder (a group-writable /usr/local, for
+      # example) the fix is to move the checkout.
+      [[ $owner == "$(id -u)" || -z $fix ]] || fix="use a checkout under folders you own"
+      die "$dir, above $what, is writable by group or others and not sticky (mode $mode)$(refusal_fix "$fix" "$dir")"
+    fi
   done
 }
 
@@ -469,8 +473,10 @@ cmd_launch() {
   mkdir -m 700 "$VERIFY_XUM_RUN/tmp"
   require_private_dir "$VERIFY_XUM_RUN/tmp"
   log="$VERIFY_XUM_RUN/server.log"
-  # Milliseconds: a stamp from earlier in the launch's own second is a stale build.
-  t0=$(date +%s%3N)
+  # Milliseconds: a stamp from earlier in the launch's own second is a stale build. From node,
+  # like the stamp itself (scripts/build-main-watch.js writes Date.now()): uutils date 0.8 ignores
+  # the width in %3N and prints nanoseconds, so no stamp would ever be newer.
+  t0=$(node -p 'Date.now()')
 
   local env_without_live_xum=(env -i PATH="$PATH" HOME="$HOME" USER="${USER:-}" LANG="${LANG:-C.UTF-8}"
     TERM=dumb TMPDIR="$VERIFY_XUM_RUN/tmp" XUM_MOCK_AI=1 XUM_DISABLE_TELEMETRY=1