Phase A: Extract Compaction Taxonomy to ADR 0007

Context Per Discussion #11419 (AGENTS.md Progressive Disclosure), the Compaction Taxonomy currently sitting at the top of AGENTS.md and AGENTS_ATLAS.md occupies ~3.5KB of the 24KB byte budget. Extracting this framework out of the L1 anchor file and into a standalone file is Phase A of the migration.

The Problem While awaiting Discussion #11419 graduation, the operator challenged the extraction format: "should 'Compaction Taxonomy (3-Axis Slot Rule)' become an ADR => decision record?" Per ADR 0005, any proposal that introduces/retires a primitive or defines durable path/layout must be classified as ADR_REQUIRED. The Compaction Taxonomy is a fundamental architectural primitive for substrate management.

The Architectural Reality

• The taxonomy must move out of AGENTS.md and AGENTS_ATLAS.md to free up budget.
• The extracted taxonomy must take the shape of an Architectural Decision Record, becoming ADR 0007.

The Fix

1. Author learn/agentos/decisions/0007-compaction-taxonomy.md using the ADR template format.
2. Replace the taxonomy blocks in AGENTS.md and AGENTS_ATLAS.md with a 1-line top-of-file pointer.

Discussion Criteria Mapping

• Maps to Discussion #11419, Phase A.
• Unanimous swarm approval achieved ([PHASE_A_APPROVED] by GPT).

Acceptance Criteria

• Create 0007-compaction-taxonomy.md in learn/agentos/decisions/.
• Transfer the taxonomy rules (keep, move, compress-to-trigger, rewrite, retire) into the ADR body.
• Remove taxonomy table from AGENTS_ATLAS.md.
• Update AGENTS.md to use the 1-line pointer text specified in OQ5.
• Post-merge validation: AGENTS.md size drops by ~3.5KB.

Out of Scope

• Phase B (description-router refactoring) and Phase C (§21 removal) are excluded from this ticket.

Origin Session ID 188acb85-b41e-435c-94ee-0cc9944d4c97