Build and measurement lock for agents on the Mac; the standing rule in CLAUDE.md

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

tools/lock/with-lock.sh

@@ -0,0 +1,30 @@
+#!/usr/bin/env bash
+# Serialises the two things that must not overlap on this Mac: BUILDS (cargo, swiftc, zigbuild, large cross-compiles) and
+# MEASUREMENTS (test networks, hash-rate samples, simulators, anything whose numbers go in the bench log).
+#   tools/lock/with-lock.sh build   <command...>      one build at a time (builds also nice -n 19, 4 jobs)
+#   tools/lock/with-lock.sh measure <command...>      one measurement at a time, and no build may start meanwhile
+# Rule (4 October 2026): code and documents run in parallel; builds and measurements queue. Waits up to 2 hours.
+set -euo pipefail
+kind="$1"; shift
+dir=/tmp/igneum-locks; mkdir -p "$dir"
+case "$kind" in
+  build)   locks=("$dir/build");;
+  measure) locks=("$dir/measure" "$dir/build");;
+  *) echo "usage: with-lock.sh build|measure <command...>" >&2; exit 2;;
+esac
+fds=(); i=9
+for l in "${locks[@]}"; do
+  i=$((i+1)); eval "exec $i>\"$l\""
+  if ! python3 - "$i" "$l" <<'PY'
+import fcntl, sys, time, os
+fd=int(sys.argv[1]); name=sys.argv[2]; t=time.time()
+while True:
+    try: fcntl.flock(fd, fcntl.LOCK_EX | fcntl.LOCK_NB); break
+    except BlockingIOError:
+        if time.time()-t > 7200: print(f"with-lock: gave up waiting for {name} after 2 h", file=sys.stderr); sys.exit(1)
+        time.sleep(5)
+PY
+  then exit 1; fi
+done
+echo "with-lock: holding ${locks[*]##*/} for: $*" >&2
+exec "$@"