music_library/backlog/completed/ml-155 - Compact-collection-summary-format-statistical-preamble-for-chat-context.md

id, title, status, assignee, created_date, updated_date, labels, dependencies, priority

id	title	status	assignee	created_date	updated_date	labels	dependencies	priority
ML-155	Compact collection summary format + statistical preamble for chat context	Done		2026-05-01 21:43	2026-05-01 21:49			high

Description

Reduce the token count of collection_summary/0 by:

1. Compacting format_group/1 (year-only dates, remove type field, reduce max genres 3→2)
2. Adding statistical preamble (genre/formats/decade distribution) computed inline from fetched records
3. Updating tests for the new format

Final Summary

Compacted collection_summary format_group/1: year-only dates, removed type field, reduced max genres 3→2. Added statistical preamble (genre/formats/eras distribution + artist count) computed in-memory from already-fetched records. ~27% token reduction (~26.4k → ~19.4k for 1200 records). All 886 tests pass.