Add _atomic_swap_db helper that removes stale WAL files before and after
moving the temp DuckDB into place. Apply CHECKPOINT before close in both
orchestrator and Keboola extractor so DuckDB flushes WAL before the swap.
- Legacy extractor now uses read_csv(all_varchar=true) to avoid type
inference errors (e.g. seniority column typed as DOUBLE with string values)
- DEPLOYMENT.md rewritten based on actual dev VM deployment experience:
deploy key setup, DuckDB write locking, env reload gotchas, bootstrap flow
Extractors with remote tables now write a _remote_attach table into
extract.duckdb so the orchestrator can re-ATTACH external extensions
at query time. The mechanism is source-agnostic — any connector can use it.
- Keboola extractor writes _remote_attach + creates views on kbc.*
- Orchestrator reads _remote_attach, installs extension, reads token from env
- Graceful degradation: missing token → warning, local tables still work
Three-pronged fix for DuckDB lock conflicts:
1. WAL mode on system.duckdb — enables concurrent readers + writer
2. Sync trigger runs extractor as subprocess (not background task) —
separate process = separate DuckDB connections, no lock conflict
3. Both extractor and orchestrator write to .tmp then atomic rename —
avoids lock conflict with API reads on extract.duckdb/analytics.duckdb
Fixes#9 permanently.
