**Issue:** 0031 migration failed on re-run due to duplicate index creation errors.
kartselldb_test partial schema state caused "relation already exists" (42P07).
**Fix:** Add IF NOT EXISTS clause to all 16 CREATE INDEX statements.
- Makes migration fully idempotent per DbUp design
- Allows safe re-execution on partially-initialized database
- No functional change; purely defensive
**Result:**
- Migration now succeeds on fresh database
- All 95 integration tests PASS on kartselldb_test
- Validated: test DB isolation restored, no production DB writes
Co-Authored-By: Claude Haiku 4.5 <noreply@anthropic.com>
kjh2064
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