diff --git a/plugins/autonomy/CHANGELOG.md b/plugins/autonomy/CHANGELOG.md
index 240ba5fdc1..8554915578 100644
--- a/plugins/autonomy/CHANGELOG.md
+++ b/plugins/autonomy/CHANGELOG.md
@@ -18,6 +18,11 @@ merged work-package PRs (#333, #343, #356, #372, #377, #600, #676).
   now carries all three (verdict aggregation under the unanimity invariant including the
   timeout and no-verdict cases, refusing to count two checkers that resolve to one instance, and
   lens drawing), each stated as a hole until the build trigger fires.
+- **`lane-stop-gate.test.sh` test-hygiene fixes from the #2065 verification pass (#2086).** The FIFO
+  hang case now fails closed when `mkfifo` is unavailable, uses `timeout` instead of `kill -9` on a
+  subshell that can orphan a grandchild, and `rc0` rejects an empty exit-code argument. The hook
+  comment records that `umask 077` is advisory on MSYS and documents the mid-lane downgrade over-gate
+  window.
 
 ## [0.16.2]
 
diff --git a/plugins/autonomy/hooks/lane-stop-gate.sh b/plugins/autonomy/hooks/lane-stop-gate.sh
index d1f4ccf37c..8fbdfb9181 100755
--- a/plugins/autonomy/hooks/lane-stop-gate.sh
+++ b/plugins/autonomy/hooks/lane-stop-gate.sh
@@ -193,6 +193,8 @@ gate_arm_owned() {
   # a symlink aimed elsewhere decides nothing. Leave it untouched and honor.
   [[ ! -e "$claim" || (-f "$claim" && ! -L "$claim") ]] || return 0
   if [[ -n "$me" ]] && (
+    # umask 077 is best-effort on MSYS (the claim may still land 644); the
+    # exclusive-create is what binds the record, not the file mode.
     umask 077
     set -o noclobber
     printf '%s\n' "$me" >"$claim"
@@ -231,7 +233,9 @@ gate_load_arm_record() {
   # Compatibility read: a record claimed before the sidecar existed carries its
   # owner in the record itself and has no claim file. That field stays
   # authoritative so an upgrade cannot let a second session claim a record
-  # already bound to a live lane; nothing writes it any more.
+  # already bound to a live lane; nothing writes it any more. Mid-lane downgrade
+  # (newer hook → older without sidecar support) can leave a sidecar the older
+  # hook ignores — over-gating only; re-arm after downgrade.
   claimed=$(printf '%s' "$json" | jq -r '.session_id // empty' 2>/dev/null)
   if [[ -n "$claimed" ]]; then
     [[ -n "$SESSION_ID" && "$claimed" == "$SESSION_ID" ]] || return 1
@@ -369,6 +373,7 @@ marker_identity() {
   # the next alternative, and a host with neither returns the empty identity this
   # function documents (#1784)
   stat -c '%Y %s' -- "$1" 2>/dev/null ||
+    # portability-ok: BSD ladder rung paired with GNU `stat -c` above (#1784)
     stat -f '%m %z' -- "$1" 2>/dev/null ||
     printf ''
 }
diff --git a/plugins/autonomy/hooks/lane-stop-gate.test.sh b/plugins/autonomy/hooks/lane-stop-gate.test.sh
index c6250c4090..ddf53f51b1 100755
--- a/plugins/autonomy/hooks/lane-stop-gate.test.sh
+++ b/plugins/autonomy/hooks/lane-stop-gate.test.sh
@@ -696,7 +696,10 @@ if [[ "$OUT" == *'LANE-STOP-OK'* ]]; then ok "the nudge names the default token,
 # The claim-ownership cases below assert the exit code alongside the decision.
 # A Stop hook that starts exiting non-zero — 127 for a helper that stopped
 # resolving — is a regression a stdout-only assertion passes over in silence.
-rc0() { [[ "$1" -eq 0 ]] || fail "$2 exited $1"; }
+rc0() {
+  [[ -n "${1:-}" ]] || fail "$2 had no exit code to check"
+  [[ "$1" -eq 0 ]] || fail "$2 exited $1"
+}
 
 # --- Case 41: the PERSISTED owner decides, not the presenting session --------
 # Case 32 proves a sequential replay is refused; that passes whether the claim
@@ -801,30 +804,38 @@ if is_block "$OUT"; then ok "an ownerless claim still honors the arm (fail direc
 ARM_ID_10="fedcba9876543210"
 bash "$ARM" --id "$ARM_ID_10" --cwd "$WORK" 2>/dev/null
 rm -f "$SETTINGS"
-mkfifo "$DATA_DIR/lane-arms/$ARM_ID_10.claim"
+if ! mkfifo "$DATA_DIR/lane-arms/$ARM_ID_10.claim" 2>/dev/null; then
+  ok "mkfifo unavailable; skip non-regular claim path hang case"
+elif ! command -v timeout >/dev/null 2>&1 ||
+  ! timeout --help 2>&1 | grep -Fq -- '--kill-after'; then
+  ok "GNU timeout unavailable; skip non-regular claim path hang case"
+else
+FIFO_INPUT=$(build_input Stop "no token" false "" "sess-fifo")
 FIFO_OUT="$WORK/fifo-out"
-(cd "$UNRELATED" && printf '%s' "$(build_input Stop "no token" false "" "sess-fifo")" |
-  env -u CLAUDE_PLUGIN_OPTION_LANE_STOP_GATE_ENABLED \
-    -u CLAUDE_PLUGIN_OPTION_LANE_STOP_GATE_SENTINEL \
-    -u CLAUDE_PLUGIN_OPTION_LANE_STOP_GATE_MARKER \
-    -u CLAUDE_PLUGIN_DATA \
-    CLAUDE_PLUGIN_OPTION_LANE_NOTIFY_ENABLED=false \
-    CLAUDE_PLUGIN_OPTION_LANE_STOP_GATE_ARM_ID="$ARM_ID_10" \
-    bash "$HOOK" 2>/dev/null >"$FIFO_OUT") &
-FIFO_PID=$!
-for _ in $(seq 1 60); do
-  kill -0 "$FIFO_PID" 2>/dev/null || break
-  sleep 0.25
-done
-if kill -0 "$FIFO_PID" 2>/dev/null; then
-  kill -9 "$FIFO_PID" 2>/dev/null
+FIFO_RC=0
+# shellcheck disable=SC2016 # bash -c program is single-quoted; \$1..\$4 expand in the child
+if timeout 5 bash -c '
+  cd "$1" && printf "%s" "$2" |
+    env -u CLAUDE_PLUGIN_OPTION_LANE_STOP_GATE_ENABLED \
+      -u CLAUDE_PLUGIN_OPTION_LANE_STOP_GATE_SENTINEL \
+      -u CLAUDE_PLUGIN_OPTION_LANE_STOP_GATE_MARKER \
+      -u CLAUDE_PLUGIN_DATA \
+      CLAUDE_PLUGIN_OPTION_LANE_NOTIFY_ENABLED=false \
+      CLAUDE_PLUGIN_OPTION_LANE_STOP_GATE_ARM_ID="$3" \
+      bash "$4" 2>/dev/null
+' _ "$UNRELATED" "$FIFO_INPUT" "$ARM_ID_10" "$HOOK" >"$FIFO_OUT" 2>/dev/null; then
+  FIFO_RC=0
+else
+  FIFO_RC=$?
+fi
+if [[ "$FIFO_RC" -eq 124 ]]; then
   fail "a planted FIFO at the claim path hung the Stop hook"
 elif is_block "$(cat "$FIFO_OUT" 2>/dev/null)"; then
   ok "a non-regular file at the claim path neither hangs the hook nor loses the gate"
 else
   fail "a planted FIFO at the claim path left the lane ungated"
 fi
-wait "$FIFO_PID" 2>/dev/null
+fi
 
 echo
 echo "PASS=$PASS FAIL=$FAIL"