Two more from Macroscope review:

- `ORDER BY COALESCE(...)` throws on a source down to one recency
  column. SQLite requires at least two arguments, so the pre-017 schema
  the column filter exists to support was exactly the case that aborted.
  Emit the column directly when only one survives the filter.
- `seedDevDatabase` accepted non-positive limits. Both are bound into
  `LIMIT ?`, where SQLite reads a negative as "no limit" — a caller
  bypassing the CLI flags silently got a full-table copy instead of the
  bounded one the options contract promises. Rejected before the target
  is touched, alongside the existing upper-bound check.

Both regression tests confirmed failing without their fix.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>