Replace synthetic id INTEGER PRIMARY KEY with composite PRIMARY KEY (fk1, fk2)
on the eight pure-junction tables: dashboard_roles, dashboard_slices,
dashboard_user, report_schedule_user, rls_filter_roles, rls_filter_tables,
slice_user, sqlatable_user. The redundant UNIQUE(fk1, fk2) on dashboard_slices
and report_schedule_user is dropped (subsumed by the new PK).
Migration handles dialect quirks: copy_from for tables with pre-existing
UNIQUE (so SQLite's anonymous-constraint reflection doesn't matter), wrapped-
subquery dedupe for MySQL (ERROR 1093), sa.Identity(always=False) on downgrade
to backfill the restored id column without NOT NULL violations, and distinct
PK names per direction (pk_<table> on upgrade, <table>_pkey on downgrade) to
avoid round-trip index-name collisions on Postgres.
ORM Table() definitions updated to match. UPDATING.md entry added with
operator runbook (BI-tool impact, pre-flight inventory queries, dedupe-row-
loss notice, pg_dump workaround, FK-NOT-NULL downgrade asymmetry note).
Tests: 8 schema-shape assertions (post-upgrade), 8 duplicate-rejection unit
tests, 8 distinct-pair sanity tests, 1 round-trip + idempotency test
(in-memory SQLite via Alembic MigrationContext).
Continuum-restore verification against the new shape is out of scope for this
PR; it is the responsibility of the versioning epic (sc-103156).
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
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