DEV-1788: unify aggregated slot-type and display-format inference

[ZmeiGorynych]

Follow-up to DEV-1784 (PR #286 review G2, item 8). Reconciles the two parallel inference functions that disagreed on stat/parametric aggregations.

Problem

aggregated_type (slot DataType) and _infer_aggregated_format (display NumberFormat) diverged on the stat/parametric family: type said DOUBLE while format fell through to inherit the source column's format, so revenue:stddev_samp was typed DOUBLE yet displayed as currency.

Fix

Both functions now read a single classify_aggregation (core/enums.py) returning one of four AggregationValueClass buckets; each maps the bucket to its own output, so no per-name branching survives and the two axes cannot drift. The four builtin frozensets partition BUILTIN_AGGREGATIONS (pinned by a completeness test). Custom/model-defined aggregations hit the PRESERVING fallback (inherit type & format), unchanged.

category	aggregations	slot type	display format
COUNT	count(_distinct/_approx), *	INT	INTEGER
PRESERVING	sum, min, max, first, last	source type (None if absent)	source format (None if absent)
FLOAT_SOURCE_UNITS	avg, median, weighted_avg, percentile, stddev_samp, stddev_pop	DOUBLE	source format, else FLOAT
FLOAT_PLAIN	corr, var_samp, var_pop, covar_samp, covar_pop	DOUBLE	FLOAT

Behavioral change (format only; aggregated_type unchanged)

• avg/median/weighted_avg of a formatted measure now inherit that format (was FLOAT); of an unformatted measure stay FLOAT.
• corr/var*/covar* → FLOAT (were inherit).
• stddev*/percentile unchanged (already inherited).

Tests

Drift-guard matrix extended to the full four-bucket set and routed through the public callers (measure_key_type / measure_key_format_description); partition-completeness test; missing-source-column and custom-aggregation cases; response-metadata assertions for the stat/parametric family. Full non-integration suite green; ruff clean.

Base: this PR targets the umbrella branch egor/dev-1742-... per the issue, not main.

Summary by CodeRabbit

• Improvements

  • Improved aggregation result types and number formatting for averages, counts, correlations, variance, covariance, percentiles, and standard deviations.
  • Average-based results now preserve source units such as currency where applicable.
  • Added consistent fallback formatting for fractional results without a source format.
  • Custom aggregations continue to preserve existing behavior.

• Documentation

  • Expanded documentation describing aggregation type and format inference behavior.

[linear]

DEV-1788

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• DECISIONS.md
• docs/architecture/sql-generation.md
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📝 Walkthrough

Walkthrough

The change adds a shared aggregation classifier. Prebound result types and response metadata formats now use four aggregation classes. Tests cover source-format inheritance, float fallbacks, custom aggregations, star counts, missing columns, and caller consistency.

Changes

Aggregation inference

Layer / File(s)	Summary
Aggregation result classification slayer/core/enums.py	Adds four aggregation classes and classify_aggregation for built-in, wildcard, custom, and unknown aggregations.
Type and format inference integration slayer/engine/prebound.py, slayer/engine/response_meta.py, docs/architecture/sql-generation.md, DECISIONS.md	Uses shared classification for result types and formats. Count operations use integer results. Plain-float operations use FLOAT. Source-unit and preserving operations inherit source formats where applicable.
Propagation and metadata validation tests/test_format_propagation.py, tests/test_response_meta.py	Adds coverage for all classification buckets, source formats, fallbacks, missing columns, custom aggregations, star counts, and public caller consistency.

Estimated code review effort: 3 (Moderate) | ~20 minutes

Merge Risk: ⚪ Minimal · up to 03d89

The PR unifies aggregated type and display-format inference with focused tests and no actionable merge-blocking risk remains beyond normal checks and review.

Possibly related PRs

• MotleyAI/slayer#258: Shares aggregation classification and result type/format inference changes.
• MotleyAI/slayer#302: Introduces related shared integer-aggregation logic extended by this change.

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 3.33% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly and concisely describes the main change: unifying aggregated slot-type and display-format inference.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

✨ Finishing Touches 💡 1

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• Create stacked PR
• Commit on current branch

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch egor/dev-1788-aggregated-slot-format-inference-diverges-from-slot-type-for

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Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

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