fix(telemetry): keep the workload cluster on [ips], not [ips_fixed]

The previous commit switched the generated node config from [ips] to
[ips_fixed] on the grounds that the variable, the comment and the sibling cfg
template all named ips_fixed, and that ips_fixed is the section whose
documented meaning fits a private cluster. Both of those are still true. The
switch is reverted anyway, because it is a workload change rather than a
naming fix.

Measured on CI, parent commit against this branch's previous tip, one
functional config line apart:

  span.consensus.ledger_close.p95    0.57 ms -> 6.43 ms   (tripped the gate)
  span.consensus.ledger_close.p99    0.94 ms -> 9.50 ms
  span.consensus.accept.p50          0.97 ms -> 2.63 ms
  span.tx.process.p50                0.36 ms -> 0.18 ms   (faster)
  job.acceptLedger.running.p95      21157 us -> 10938 us  (faster)

Every consensus-path span rose and every transaction-path metric fell, which
is the shape a denser always-connected mesh produces and not the shape of
run-to-run variance. [ips_fixed] holds connections open to all four peers
instead of treating the list as a discovery hint, so each node processes
proposals and validations from the full mesh every round. Nothing else in that
commit touches the consensus path: the emitted config differed in exactly
three lines, of which one is a die message and one expands to an identical
string.

The committed baseline describes the [ips] topology. Adopting [ips_fixed]
therefore needs a refreshed baseline and re-derived bounds, which is the
process baselines/README.md already documents for a workload change. Left as
its own work item rather than smuggled in behind a section rename, and the
reason is now recorded beside the line so it is not repeated.

This also falsified a claim the previous commit had written into
baselines/README.md and regression-thresholds.json: that none of the six
weakly-guarded keys fires on any observed run. Corrected in both, and the
measurement above is cited in place of the absolute.

docker/telemetry/workload/baselines/README.md

@@ -136,8 +136,18 @@ The guarantee costs sensitivity where the ladder is coarse: the detection floor
 | `span.tx.process.p99`             | 0.9940 ms  | 5 ms      | 5.03x | 1 ms → 5 ms          |
 
 Four of the six are limited by the same `1 ms → 5 ms` step, which is where this ladder is coarsest
-relative to how the spans actually behave. None of the six fires on any observed run, so all six
-stay gated; the weak floor is recorded here so it is visible rather than surprising.
+relative to how the spans actually behave. All six stay gated; the weak floor is recorded here so it
+is visible rather than surprising.
+
+None of the six fires on an observed run **of this workload** — but the qualifier is load-bearing,
+and there is now a measurement behind it. Changing one line of the generated node config from
+`[ips]` to `[ips_fixed]`, which holds peer connections open instead of treating the list as a
+discovery hint, moved `span.consensus.ledger_close.p95` from 0.57 ms to 6.43 ms and tripped this
+gate, while every transaction-path metric fell. Nothing else in that commit touched the consensus
+path. So a weak floor is not the only way one of these keys reddens: a change to the cluster's
+topology is enough on its own, which is exactly why
+[Refreshing the baseline](#refreshing-the-baseline) treats a workload change as requiring a new
+baseline.
 
 The fix is a 2 ms edge (ideally 3 ms as well) in the collector's spanmetrics `buckets` list plus the
 matching entries in `kMillisecondBuckets`, and 2000 us plus 50000 us edges in `kMicrosecondBuckets`.

docker/telemetry/workload/run-full-validation.sh

@@ -351,7 +351,14 @@ for i in $(seq 1 "$NUM_NODES"); do
         "" | null) die "$NODE_PREFIX-$i has no seed in $WORKDIR/validator-keys.json — the file holds fewer than $NUM_NODES entries, or entry $((i - 1)) carries no seed" ;;
     esac
 
-    # Build ips_fixed.
+    # Peer list for the loopback mesh. Emitted as [ips], NOT [ips_fixed],
+    # even though [ips_fixed] is the section whose documented meaning fits a
+    # private cluster. [ips_fixed] holds the connections open to all peers, and
+    # measured against this same commit that moved consensus.ledger_close.p95
+    # from 0.57 ms to 6.43 ms and tripped the regression gate, while every
+    # transaction-path metric fell. The committed baseline describes the [ips]
+    # topology, so switching sections is a deliberate workload change that has
+    # to arrive with a refreshed baseline and re-derived bounds.
     IPS_FIXED=""
     for j in $(seq 1 "$NUM_NODES"); do
         if [ "$j" -ne "$i" ]; then
@@ -400,7 +407,7 @@ $SEED
 [validators_file]
 $WORKDIR/validators.txt
 
-[ips_fixed]
+[ips]
 ${IPS_FIXED}
 
 [telemetry]