Re-validate `mixed_2_charon_2_pluto` smoke scenario without the `sched` alert exclusion

[emlautarom1-agent]

Summary

The mixed_2_charon_2_pluto smoke scenario exempts the sched log topic from the Warn Log Rate alert, on the stated grounds that Pluto does not serve /charon/priority/2.0.0. That rationale no longer holds: priority + infosync wiring landed in #574 (3c031a6e, 31 July). The exclusion may now be hiding a real regression, or may simply be dead weight — nobody has re-run the scenario without it.

Evidence

The exclusion and its rationale: smoke_test.go#L239-L244

The same claim is repeated on the knob's doc comment: config.go#L166-L171

Pluto serves the protocol:

• prioritiser.rs#L46 — PROTOCOL_ID = "charon/priority/2.0.0", cross-checked against the Charon wire token in interop_protocol_id.rs.
• pluto_priority::protocols() is included in the node's advertised protocol set in node/behaviour.rs.
• run_node starts the priority component and wire_core_workflow registers the per-epoch infosync trigger as a slot subscriber.

The remaining TODO(#402 part B) in node/mod.rs covers routing the decided priority result into ConsensusController, which is a no-op while QBFTv2 is the only protocol. It does not affect the serving side, so it does not justify suppressing the alert.

Work

• Run the mixed_2_charon_2_pluto scenario with conf.AlertWarnExcludeTopics unset and inspect app_log_warn_total{topic="sched"} on the Charon nodes.
• If clean: drop the exclusion from the scenario.
• If not clean: capture the actual Charon-side warning and open a follow-up against the serving path. Keep the exclusion only with a comment describing the real, current cause.
• Either way, rewrite the AlertWarnExcludeTopics doc comment in config.go — its worked example is this scenario.
• Decide whether the knob stays. mixed_2_charon_2_pluto is its only user; if the exclusion is dropped, the knob has none. TestWriteAlertRules covers the mechanism, so removing it means removing that case too.

Acceptance

• No smoke scenario suppresses a log topic with a rationale that is not true of the current code.
• mixed_2_charon_2_pluto passes with whatever alert configuration it ends up with.