feat(dispatch): wire traces through embed via EmbedConsumers (PIPE-1024)

[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.

New GeneratorTypeTraces case constructs traces.New(...) with consumers.TraceConsumer, returning the helper's typed error if it's nil.

config.EmbedOpts grows a TraceConsumer embed.TraceConsumer field; config.LoadModules passes all three consumers through to dispatch.ForEmbed. The old "EmbedOpts.LogConsumer is required" early check goes away — the error now surfaces from ForEmbed per-generator-type.

cmd/blitz/main.go no longer hand-constructs traces: it delegates to dispatch.ForEmbed after asserting the configured output implements output.TraceWriter and wrapping it via output.WriterAsTraceConsumer. Kills the per-generator-type duplication between cmd/blitz and dispatch.

New yamlSeedDefault helper translates YAML zero-value Seed into -1 (randomize per worker) for traces. 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 #231. Conflicts: EmbedConsumers struct (each PR adds its consumer field), EmbedOpts struct, one case per generator type, and the yamlSeedDefault helper (both PRs define it identically). Whichever lands second rebases mechanically.

Tests

Existing TestForEmbed* updated to use EmbedConsumers{LogConsumer: ...}; new TestForEmbedTracesReturnsProducerModule, TestForEmbedTracesRejectsMissingTraceConsumer, TestForEmbedRejectsMissingLogConsumerForLogType. TestLoadModules_NilConsumer updated to feed a valid config.

Part of PIPE-1024. Stacked on #234.

[Dylan-M]

• test(embed): add traces integration test + docs update for TraceConsumer (PIPE-1024) #236
• feat(dispatch): wire traces through embed via EmbedConsumers (PIPE-1024) #235 👈 (View in Graphite)
• feat(traces): migrate to embed.TraceConsumer + ProducerModule with realistic per-span emission timing (PIPE-1024) #234
• feat(output): add WriterAsTraceConsumer adapter (PIPE-1024) #233
• main

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Merge activity

• Jun 3, 2:24 PM UTC: Graphite rebased this pull request, because this pull request is set to merge when ready.