fix(memos-local-plugin): two-phase migration to prevent crash-loop on large databases

[chiefmojo]

Problem

Migration 007 (namespace-visibility) in v2.0.2–v2.0.5 runs UPDATE … SET share_scope='private' plus CREATE INDEX on the traces table inside a single db.tx(). On databases larger than ~500MB, this exceeds the host gateway's kill timeout. SQLite rolls back the entire transaction — including the schema_migrations INSERT — so migration 007 is never recorded and the bridge restarts into the same hang forever.

Small databases (~43MB) complete within the timeout, which is why this only manifests on larger installs. Tested against a 687MB database with ~98,000 traces.

Fix

Two-phase migration:

• Phase 1 (inside transaction, milliseconds): ADD COLUMN only on all 12 namespace tables, plus DROP INDEX uq_skills_name. The schema_migrations record for v7 commits here.
• Phase 2 (after migration loop, outside any transaction): Batched UPDATE in 2,000-row chunks (each its own implicit transaction) for share_scope backfill, then CREATE INDEX IF NOT EXISTS for all 18 owner/share indexes. ensureNamespaceColumns is called unconditionally on every boot so new tables in the namespace list get their columns.

Restart safety: If the bridge is killed during Phase 2, the v7 schema_migrations record survives (Phase 1 committed). Next boot skips Phase 1 entirely and resumes Phase 2 where it left off. The crash-loop is broken.

Verification

• Confirmed the DB on the affected instance had exactly migrations 1–6 applied — migration 007 was never committed despite hundreds of boot attempts.
• After the fix, Phase 1 committed in 2.4 seconds. Phase 2 backfill and index creation complete across bridge restarts.
• Bridge boots cleanly with all 18 indexes created and pipeline.ready.

Related

Closes #1787