startNewRun read flows.execution_count from a cached row and wrote
`cached + 1`. Two concurrent webhooks starting runs on the same flow
for different contacts both read N and both write N+1 — one count
permanently lost.
Mirrors the automations engine's solution (migration 007): a tiny
SECURITY DEFINER function that does the increment server-side, locked
to the service role. The engine's call becomes a single RPC.
The counter is best-effort: if the RPC fails we log + continue rather
than failing the run for a stat error.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
