You can use a well known template like ARC42 and insist on the maintenance of suitable indexes for agent access and review for coherence on a regular basis.

Ultimately any useful documentation needs active curation.

Getting devs to do this well is hard. Agents can be driven to do a fair job through suitable prompt frameworks and repetition eg as PR reviewers.

I’ve had reasonable success with a combination of space dimensions structured requirements and component based indexes and time dimensions of decision records and commits.

Also a strong design model to give common structure - hex arch with ports and adapters and pure business logic.

YMMV