contract test: keep the loaded run's passes, discard only its failure

The javadoc threw away the whole loaded run as "not clean evidence". The
fixed cell order makes that too strong in one direction. A cell that runs
last on a climbing load has a free explanation for FAILING. It has no free
explanation for PASSING: surviving a worse condition than a fair order
would have given it is evidence in the safe direction. So the old version's
0 of 3 is still discarded, and the three passes are kept with the load each
one ran at.

Also names the cell that tests the swallow explanation head-on, which the
old text left as "nobody has managed that yet". SHELL_READY_TIMEOUT_MS at 0
types input at once — the worst case for "typed before the prompt" — and it
passed 3 of 3 at load 18.42 to 23.65. The wider read window cannot explain
that away, because a swallowed keystroke is lost, not late: the command
never runs, so no amount of polling makes its output appear.

And a warning not to carry the raw load average to another host. Load
average counts differently per core and per operating system, so only load
per core compares. I broke that rule myself when comparing this run with
another host's numbers.

Both points came from the fleet01 lead reviewing 2af13ab.

fleetd/src/test/java/dev/ltms/fleet/herdr/AgentControlContractTest.java

@@ -36,16 +36,28 @@ import static org.junit.jupiter.api.Assumptions.assumeTrue;
  * typing at 1000ms, and it is not.
  *
  * <p><strong>Where this was measured.</strong> A 12-core macOS host, load average 2.6 to 5.9,
- * on commit 20c1094. The same four cells were also run under load and gave the same answer, but
- * that run is not clean evidence: the load average climbed from 7 to 50 while the cells ran, and
- * the old version ran last, at the top of that climb. Above about load 20 everything here is
- * slow for reasons that have nothing to do with this seam. So read the claim as "measured near
- * idle on a 12-core host", and nothing stronger. If this test fails on a smaller or busier
- * machine, raise {@link #OUTPUT_TIMEOUT_MS} before you suspect the seam.
+ * on commit 20c1094. The same four cells were also run under load, with 8 spinners on 12 cores.
+ * The failure and the passes from that run are not worth the same. The cells ran in a fixed
+ * order while the load climbed from 7 to 50. The old version ran last, at the top of that climb,
+ * so it has a free explanation for failing and its 0 of 3 is discarded. A pass has no such free
+ * explanation: a cell that survives a worse condition than a fair order would have given it is
+ * evidence in the safe direction. So keep the three passes, each with the load it ran at: the
+ * fixed version 3 of 3 at load 7.42 to 18.42, the 0ms-write cell 3 of 3 at 18.42 to 23.65, the
+ * 1000ms-write cell 3 of 3 at 23.65 to 46.40. Above about load 20 everything here is slow for
+ * reasons that have nothing to do with this seam, so read the positive claim — that the read
+ * deadline was the whole cause — as "measured near idle on a 12-core host", and nothing
+ * stronger. Do not carry that raw load average to another host either: load average counts
+ * differently per core and per operating system, so only load per core compares. If this test
+ * fails on a smaller or busier machine, raise {@link #OUTPUT_TIMEOUT_MS} before you suspect the
+ * seam.
  *
  * <p>{@link #waitUntilSettled} is kept as cheap insurance against that swallow case, not because
- * anyone showed it was needed. If you want to delete it, the honest test is whether you can make
- * this test fail by typing early. Nobody has managed that yet.
+ * anyone showed it was needed. The cell that tests the swallow case head-on is the one with
+ * {@link #SHELL_READY_TIMEOUT_MS} at 0: input is typed at once, which is the worst case for
+ * "typed before the prompt is ready". It passed 3 of 3 at load 18.42 to 23.65. The wider read
+ * window cannot explain that pass away, because a swallowed keystroke is LOST, not late — the
+ * command never runs, so no amount of polling makes its output appear. So the swallow mechanism
+ * was tested and did not show up. If you want to delete this call, that is the cell to re-run.
  *
  * <p>Tagged {@code contract}; run with {@code mvn test -Pcontract}.
  */