# ADR-008: Common columns pattern

## Status

Accepted

## Context

All tables need auditability (creation/modification timestamps) and extensibility (metadata). Without a common pattern, each table defines these differently.

## Decision

All tables share `id` (text PK, consumer-generated), `metadata` (JSON text defaulting to `{}`), `createdAt`, and `updatedAt` (integer timestamps in SQLite, timestamptz in PG). The `metadata` column is an extension namespace following `_subsystem.key` namespacing — it's for opaque key-value pairs that subsystems add without schema changes, not for queryable data.

## Consequences

- Every row has auditability and extensibility
- Subsystems add metadata without schema changes
- Columns that appear in WHERE/JOIN conditions should be proper columns, not metadata
- SQLite uses `integer` timestamps; PG will use `timestamptz`

## References

- [sqlite-host.md](../sqlite-host.md)