feat(dispatch): wire hostmetrics through embed via EmbedConsumers (PIPE-1023)

[Dylan-M]

Proposed Change

Refactor dispatch.ForEmbed to take an EmbedConsumers struct (with LogConsumer, MetricConsumer, and TraceConsumer fields) instead of a single embed.LogConsumer. Each per-signal nil check is hoisted into a requireLog/requireMetric/requireTrace helper method on EmbedConsumers, so the per-case boilerplate stays a single line and the error messages all live in one place.

New GeneratorTypeHostMetrics case constructs hostmetrics.New(...) with consumers.MetricConsumer, returning the helper's typed error if it's nil.

config.EmbedOpts grows a MetricConsumer embed.MetricConsumer field; config.LoadModules passes both consumers through to dispatch.ForEmbed. The old "EmbedOpts.LogConsumer is required" early check goes away — the error now surfaces from ForEmbed per-generator-type with the relevant signal in the message.

cmd/blitz/main.go no longer hand-constructs hostmetrics: it delegates to dispatch.ForEmbed after asserting the configured output implements output.MetricWriter and wrapping it via output.WriterAsMetricConsumer. This kills the per-generator-type duplication between cmd/blitz and dispatch that #228 already partially cleaned up for logs.

New yamlSeedDefault helper translates YAML zero-value Seed into -1 (randomize per worker) for hostmetrics. Programmatic Go callers bypass the translation. See PIPE-1036 for the follow-up that routes identity-level determinism through environment.seed_config.

Conflict-point note: this PR shares internal/dispatch/embed.go and config/loader.go with #235. Conflicts: EmbedConsumers struct (each PR adds its consumer field), EmbedOpts struct (each PR adds its consumer field), one case per generator type, and the yamlSeedDefault helper (both PRs define it identically). Whichever lands second rebases mechanically — the helper resolution is "keep one, drop the duplicate."

Tests

Existing TestForEmbed* updated to use EmbedConsumers{LogConsumer: ...}; new TestForEmbedHostMetricsReturnsProducerModule, TestForEmbedHostMetricsRejectsMissingMetricConsumer, TestForEmbedRejectsMissingLogConsumerForLogType. TestLoadModules_NilConsumer updated to feed a valid config so the error surfaces from ForEmbed.

Part of PIPE-1023. Stacked on #230.

[Dylan-M]

• test(embed): add hostmetrics integration test + docs update for MetricConsumer (PIPE-1023) #232
• feat(dispatch): wire hostmetrics through embed via EmbedConsumers (PIPE-1023) #231 👈 (View in Graphite)
• feat(hostmetrics): migrate to embed.MetricConsumer + ProducerModule (PIPE-1023) #230
• feat(output): add WriterAsMetricConsumer adapter (PIPE-1023) #229
• main

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[graphite-app]

Merge activity

• Jun 3, 1:29 PM UTC: Graphite rebased this pull request, because this pull request is set to merge when ready.