update: hand over cleanly from updates older than 2026-10-19

013acac's update (in use 2026-08-14 to 2026-10-19) copies the new update
over itself with sudo cp while bash is still reading it, so bash reads on
from byte 1484 of the new file: today, the middle of the logo, and the
update dies with a syntax error. Put a line at exactly that byte that
execs the new update, in a here-document a normal run skips. Found by
30-upgrade-from-baseline at ca658dc; the test replays 013acac's update.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

tests/update.bats

@@ -166,3 +166,20 @@ ran() {
   [ "$status" -eq 1 ]
   [ ! -e "$RAN" ]
 }
+
+@test "an update from before 2026-10-19 that copies this one over itself hands over to it" {
+  # 013acac's update: sudo cp overwrites the file bash is still reading, and
+  # bash reads on in the new one from where it was
+  [ "$(/usr/bin/git -C "$REPO" rev-parse --is-shallow-repository)" = false ] \
+    || skip "needs update's history"
+  /usr/bin/git -C "$REPO" show 013acac:update > "$HOME/.local/bin/update"
+  chmod +x "$HOME/.local/bin/update"
+  stub sudo '[ "$1" = cp ] && exec "$@"; exit 0'
+  hook 10-a 'echo a >> "$RAN"'
+
+  run "$HOME/.local/bin/update"
+  [ "$status" -eq 0 ]
+  [[ "$output" != *"command not found"* ]]
+  [[ "$output" == *"Done."* ]]
+  ran a
+}