crowdsim 1.40.2

Three defects in probe, in one neighbourhood, found by asking why the ci workflow went red on a tree
where make test was green (#94).

Fixed

• A preflight against a target that does not answer cost 2 minutes 7 seconds. 1.33.0 made probe
  sample five URLs per pool instead of checking one — paced and bounded in count, and nothing bounded
  the time. Each sample used the preflight's own curl options: --max-time 10 --retry 1 --retry-connrefused. The CLI suite makes thirteen probe calls, so a 90-second job became a 46-minute
  one and the runner killed it. It never showed locally, because a resolver that answers NXDOMAIN
  instantly makes every one of those requests free.

  Now: nothing is sampled when the target did not answer the first request — that request already
  settled reachability, and asking about every pool sends thirty more to learn the same thing. A sample
  request is bounded by CROWDSIM_SAMPLE_MAX_TIME (default 3s) and never retried: it answers does
  this path exist, and a path that did not answer inside the budget has answered that. The first request
  keeps the longer timeout and the retry, because reachability is the one thing worth waiting for.
  Measured on the same blackholed address: 2m07s → 21s, and the 21 seconds are that first request.

• A target that never answered exited 0. probe documents exit 4 if the target answers ≥400 and the
  exit-code contract says 4 = target not reachable. A failed curl leaves the status as 000, and
  "000" -ge 400 is false, so an address nothing listens on reported a preflight that passed — to a
  person, and to a scheduler reading the exit code.

• The documented exit 4 was dead code. Everything that reads the status runs inside
  { … } | tee "$log", which is a subshell, so the variable the parent tested was always empty. A 404 on
  the first pool entry printed target does not answer 2xx/3xx and exited 0 — true for as long as the
  log has been teed. The only exit-4 paths that worked were the marker files added later for the pool and
  premise checks, and the status now crosses the same boundary the same way.

  The two shapes are told apart in words, because they send you to different places: the target never
  answered is connectivity, and it answered 404 on the first pool entry is a pool or a route.

Added

• Tests asserting each exit code against a real socket rather than trusting the variable: a refused port,
  and a first pool entry that answers 404.

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Container image

docker pull ghcr.io/hiway-media/crowdsim:1.40.2

Install and usage: docs/docker.md