1df0bc4f00
Serialize Core access with a single pooled connection (the harness drives Core sequentially via the blocking client) to avoid a WAL-mode-establishment race across connections warming up on a brand-new DB file, and raise the readiness ceiling for heavy parallel test-binary load. 10/10 deterministic. (Fixed alongside a real Core robustness fix: per-connection pragmas + busy_timeout, core 0360135.)