feat: dialect aware sketch decomposition

[betodealmeida]

Summary

Rebase of #2559, since I feel bad that GitHub messed up @robinld's PRs. 😆

Test Plan

• PR has an associated issue: #
• make check passes
• make test shows 100% unit test coverage

Deployment Plan

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[shangyian]

It looks like the new family-decomposition lookup doesn't check which aggregate call it's being asked about?

1. get_decomposition() applies a metric's sketch family to every aggregate in the formula
2. then _attach_reaggregate_params broadcasts sketch tuning params onto every component

I think that means it adds reaggregate.params onto every component with aggregation and merge set... so AVG which decomposes into SUM + COUNT will both get the sketch's params attached.

Separately should we add merge_args/serialize etc to MetricComponent so that GraphQL is equivalent with REST?

[greptile-apps]

Confidence Score: 3/5

[High risk] Adds dialect-aware sketch decomposition to metric building.

The PR is not safe to merge until Druid cube expressions use the destination's combiner shape and existing parameterized multi-component metrics remain usable.

Findings

1.  Druid cube gets Spark combiner ▶
2.  Multi-component metrics now fail ▶

Summary

This PR adds family-selected, dialect-aware metric decomposition, target-specific sketch serialization, merge arguments, and sketch metadata in REST, GraphQL, and the edit form.

• Druid cube materialization still decomposes metrics for Spark, leaving dialect-specific cube expressions incorrect.
• A new parameter guard rejects previously supported multi-component metrics.

Diagram

%%{init: {'theme': 'neutral'}}%%
flowchart LR
  A[Metric with sketch family] --> B[Decompose using build dialect]
  B --> C[Build Spark measures SQL]
  C --> D[Serialize sketches for Druid target]
  B --> E[Store metric combiner for Druid cube]

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_{Reviews (1) · Last reviewed commit: "Fix sketch decomposition review findings"}