DuckDB 1.5 enforces a strict per-process exclusive file lock on
system.duckdb. The uvicorn --reload master process was importing
app.main, which called create_app() at module load — and create_app()
was opening system.duckdb via three seed/warning blocks (seed_admin,
scheduler_user, no-password warning). The forked worker then could
not acquire the lock and every request 500'd with "Could not set lock
on file system.duckdb".
Move the three blocks into the existing lifespan (worker-only). The
master/reloader no longer touches system.duckdb. _resolve_error_user
stays in create_app() — it only runs at request time inside a closure,
which is worker-context already.
Co-authored-by: Minas Arustamyan <arustamyan.minas@gmail.com>
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