AGENTS.md

Protobuf Guidelines

Also see root AGENTS.md for cross-language standards.

Compatibility

• All changes must be backwards compatible. Never re-use or change field numbers of existing fields.

Schema Design

• Use optional when you need to distinguish "not set" from "zero value" — optional enables presence tracking (has_* methods) and maps to Option<T> in Rust. Bare proto3 fields have no presence semantics: they always hold a value (defaulting to zero), so you cannot tell if the sender explicitly set them.
• Use structured message types (e.g., BasePath) instead of plain scalars, and scope fields to operation-specific messages (e.g., InsertTransaction) rather than generic top-level ones.
• Don't duplicate data across messages — store each fact once and derive relationships. Prefer parallel sequences over maps when keys already exist in another field.

Documentation

• Document the semantic meaning of both present and absent states for optional fields — explain when each case applies.
• Use precise domain terminology in field descriptions — avoid ambiguous abbreviations or terms that collide with domain concepts.