0667 — Every _config table carries created_at and updated_at

Context

The table-name and column review found the six _config tables disagreeing on their timestamp columns: system_config and topic_config carried both created_at and updated_at, consumer_group_config only created_at, and worker_config, schedule_config, and binding_config neither. No rule had produced the split; each table got whatever its first writer needed. Two of the four UPDATE paths on config rows (topic rename and replace) set updated_at; the schedule and worker paths had no column to set.

The alternative was the narrower rule: created_at everywhere, updated_at only on mutable rows with no _config_log trail, since the newest trail row’s declared_at already says when a config row last changed. That saves two columns and avoids a redundant fact on topic_config and worker_config.

Decision

Every _config table carries created_at and updated_at, both TIMESTAMPTZ NOT NULL DEFAULT NOW(), as the last two columns before any table constraint. Consistency across the kind outranks the redundancy with the _config_log trail.

• Every UPDATE on a config row sets updated_at = NOW(): topic rename and replace, schedule replace, suspend, and unsuspend, the schedule producer’s missed-run suspend, and the worker metadata replace.
• A config row that is never updated (system_config, and binding_config, whose rows are replaced by delete and insert) keeps updated_at equal to created_at.
• Read models are unchanged: a field still needs a production reader. System exposes both, Consumer exposes created_at, the rest expose neither.
• tools/conventions walks the baseline DDL and fails on a _config table missing either column.

Consequences

Four tables gain columns and five UPDATE statements gain a SET clause; no Row struct, literal select list, or lab changes, since every insert names its columns. _config_log tables are untouched: they are append-only and their instant is declared_at. schedule_config now records when it last changed even though it has no trail yet; the trail stays a roadmap item.