ADR-0004: Structured predicates only for rules

• Status: Accepted
• Date: 2026-07-25
• Deciders: El

Context

Rules must be safe, portable, reviewable, and must not be executable code running inside the shared brain.

Decision

Rules are structured data — {fact, operator, value} predicates over a published catalog of facts and actions, combined with AND/OR. No expression language, no eval, no lambda, no embedded scripting. New facts or actions are added to the catalog in code (available to all tenants), then referenced as config. A rule = on when then with .

Consequences

Safe; portable (pure data on exit); inspectable and versionable; some exotic rules require a catalog extension — a feature, since it forces genuinely new logic through code review; the catalog defines the ceiling of expressibility.

Alternatives considered

• A DSL or scripting layer in tenant config — rejected: security hole, un-reviewable, breaks portability and the config-as-data line.