fix(shell): remove runtime early-exit pipe hazards (#1105)

Co-authored-by: f10-coder <[email protected]>

packages/mosaic/framework/tools/git/mutate-push-guard.sh

@@ -84,7 +84,7 @@ cp "$TARGET" "$BAK"
 export MOSAIC_TEST_WORK_DIR="$WORK/.work"
 
 # --- where the prose lives: usage() { ... EOF ---------------------------------
-PROSE_LO="$(grep -n '^usage() {' "$BAK" | head -1 | cut -d: -f1)"
+PROSE_LO="$(grep -n -m1 '^usage() {' "$BAK" | cut -d: -f1)"
 PROSE_HI="$(awk -v lo="$PROSE_LO" 'NR > lo && /^EOF$/ { print NR; exit }' "$BAK")"
 if [[ -z "$PROSE_LO" || -z "$PROSE_HI" ]]; then
     echo "!! cannot locate the usage() heredoc -- the prose guard would be inert; refusing" >&2