Cleanup after the reference loader (scripts/site_imports/wjf/) proved out.
Removed the drifted direct-SQL migrators - migrate_assets/communications/
notifications/usb.py, run_migration.py, verify_migration.py, and
scripts/import_from_mysql.py. They targeted a nonexistent equipment table, the
retired Machine model, and columns that no longer exist; nothing imported them.
scripts/migration/README.md now points at the import API + the site loader.
Kept the one-time SQL fixups (fix_legacy_schema.sql, one-offs/).
Added docs/IMPORT-ADOPTION.md: the two-layer import story (stable IMPORT-API
contract + per-site loader), stage-ordering + crosswalk guidance, the
agent-assisted mapping path, and what the WJ loader demonstrates. Updated the
loader README to complete status (all 15 stages, final counts).
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
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