feat: add SAE last executed and last settled height metrics

[JonathanOppenheimer]

Why this should be merged

This PR adds two new SAE-specific metrics, last_executed_height and last_settled_height, registered under the sae namespace. Snowman already publishes last_accepted_height, but execution and settlement heights are SAE-only.

Once these guages are added, you can compute lag as shown below

avalanche_snowman_last_accepted_height - avalanche_<vm>_sae_last_executed_height
avalanche_snowman_last_accepted_height - avalanche_<vm>_sae_last_settled_height

This is the first PR in a planned series of PRs to add metrics, as outlined in the shared Notion document.

How this works

I tried to follow general Prometheus best practices here, and follow the AVM metrics pattern (as suggested to me by Stephen). We add a *saemetrics.Metrics field on the VM, and a separate *prometheus.Registry for registration.

How this was tested

I added three tests:

• TestMetrics: calls MarkBlockExecuted(6) and MarkBlockSettled(7) and asserts both gauges hold the expected heights.
• TestExecutionMetrics: asserts LastExecutedHeight advances.
• TestSettlementMetric: asserts LastSettledHeight advances.

Need to be documented in RELEASES.md?

Yes

[JonathanOppenheimer]

This is an intentional choice to have the metricRegistry as the *prometheus.Registry used for registration and /ext/metrics (and as already used for registerer for the bloom/gossip/p2p metrics) while metrics is used to record metrics updates.

[Copilot]

Pull request overview

Adds SAE-specific Prometheus gauges to expose the VM’s async execution and settlement frontiers, enabling operators to compute lag vs Snowman’s last accepted height.

Changes:

• Introduces sae_last_executed_height and sae_last_settled_height gauges (via a new vms/saevm/metrics package).
• Wires the new metrics into SAE VM initialization, block execution, and settlement paths.
• Adds unit/integration tests and updates Bazel deps and RELEASES.md.

Reviewed changes

Copilot reviewed 14 out of 14 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
vms/saevm/txgossip/txgossip_test.go	Updates executor construction in tests to provide SAE metrics.
vms/saevm/txgossip/BUILD.bazel	Adds metrics dependency for txgossip tests.
vms/saevm/saexec/saexec.go	Threads SAE metrics through the executor.
vms/saevm/saexec/saexec_test.go	Adds a test for last executed height metric (potentially timing-sensitive).
vms/saevm/saexec/execution.go	Updates last executed height metric after successful execution.
vms/saevm/saexec/BUILD.bazel	Adds metrics + Prometheus testutil deps.
vms/saevm/sae/vm.go	Registers an SAE-prefixed registry and instantiates SAE metrics; passes registry to other subsystems.
vms/saevm/sae/vm_test.go	Adds a settlement metric test.
vms/saevm/sae/consensus.go	Updates last settled height metric when blocks settle during acceptance.
vms/saevm/sae/BUILD.bazel	Adds deps for metrics + testutil.
vms/saevm/metrics/metrics.go	New SAE metrics collectors and update helpers.
vms/saevm/metrics/metrics_test.go	Unit test for the new metrics helpers.
vms/saevm/metrics/BUILD.bazel	New Bazel targets for metrics package + tests.
RELEASES.md	Documents the newly added gauges in pending release notes.

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[Copilot]

Pull request overview

Copilot reviewed 14 out of 14 changed files in this pull request and generated 2 comments.

[alarso16]

I don't think making a "metrics" package makes sense. This metrics struct IMO should be unexported in whatever package has access to each metric. Do you agree?

[JonathanOppenheimer]

I modeled this after avalanchego/avm/metrics. I don't think it's as simple as unexporting it in whatever package has access to each metric -- sae and saeexec -- we need host it, and then export it somewhere. This package will also grow over time as we add more metrics, all of which not be as tightly coupled to an individual package.

What do you think?

I could at least unexport the gauge fields so callers can only go through MarkBlockExecuted/MarkBlockSettled.

[JonathanOppenheimer]

We talked in the office about this.

[JonathanOppenheimer]

Does this look better?