retest-floating: check what the bench brings (docker, python3), not what the sync puts there (R-749)

The check asked for /opt/upg/upgrade-test.py before sync_bench() copies it, so a bench freshly created by the
runbook was refused in one minute (2026-10-01). After the sync, the file is now required.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_0159rPz1ZhFKsS53msqPYxtS

scripts/retest-floating.py

@@ -95,9 +95,11 @@ def bench(script, timeout=3600):
 
 def prerequisites():
     missing = []
-    r = bench("test -f /opt/upg/upgrade-test.py && echo bench-ok", timeout=120)
+    # R-749: ask for what the bench must BRING (docker, python3) — /opt/upg is what sync_bench() puts there AFTER this
+    # check; asking for it here refused every freshly created bench.
+    r = bench("command -v docker >/dev/null && command -v python3 >/dev/null && docker info >/dev/null 2>&1 && echo bench-ok", timeout=120)
     if "bench-ok" not in (r.stdout or ""):
-        missing.append("the bench LXC %s on %s with /opt/upg (runbook §2)" % (BENCH_CT, BENCH_HOST))
+        missing.append("the bench LXC %s on %s with docker and python3 (runbook §2)" % (BENCH_CT, BENCH_HOST))
     if not os.path.isdir(os.path.join(DRILL, ".git")):
         missing.append("the drill checkout at %s (runbook §3)" % DRILL)
     if not os.path.isfile(os.path.join(os.environ.get("SC", os.path.expanduser("~/.felhom-retest")), ".ctlpw")):
@@ -202,7 +204,7 @@ def main(argv):
         print("CANNOT START — missing: " + "; ".join(missing))
         return 2
     s = sync_bench()
-    if "synced" not in (s.stdout or ""):
+    if "synced" not in (s.stdout or "") or "bench-ok" not in (bench("test -f /opt/upg/upgrade-test.py && echo bench-ok", timeout=120).stdout or ""):
         print("CANNOT START — the bench could not be synced: " + (s.stdout + s.stderr).strip()[-200:])
         return 2
     results = []