Crate layer0 

layer0 — Protocol traits for composable agentic AI systems

This crate defines the four protocol boundaries and two cross-cutting interfaces that compose to form any agentic AI system.

The Protocols

Protocol	Trait	What it does
① Operator	Operator	What one operator does per cycle
② Orchestration	Orchestrator	How operators compose + durability
③ State	StateStore	How data persists across turns
④ Environment	Environment	Isolation, credentials, resources

The Interfaces

Interface	Types	What it does
⑤ Middleware	DispatchMiddleware, StoreMiddleware, ExecMiddleware	Interception + policy
⑥ Lifecycle	BudgetEvent, CompactionEvent	Cross-layer coordination

Design Principle

Every protocol trait is operation-defined, not mechanism-defined. Operator::execute means “cause this agent to process one cycle” — not “make an API call” or “run a subprocess.” This is what makes implementations swappable: a Temporal workflow, a function call, and a future system that doesn’t exist yet all implement the same trait.

Companion Documents

• See ARCHITECTURE.md for design rationale

Dependency Notes

This crate depends on serde_json::Value for extension data fields (metadata, tool inputs, custom payloads). This is an intentional choice: JSON is the universal interchange format for agentic systems, and serde_json::Value is the de facto standard in the Rust ecosystem. The alternative (generic T: Serialize) would complicate trait object safety without practical benefit.

Future: Native Async Traits

Protocol traits currently use async-trait (heap-allocated futures). When Rust stabilizes async fn in dyn Trait with Send bounds, these traits will migrate to native async. This will be a breaking change in a minor version bump before v1.0.

Re-exports

pub use content::Content;

pub use content::ContentBlock;

pub use context::Context;

pub use context::ContextError;

pub use context::ContextMessage;

pub use context::ContextSnapshot;

pub use context::ContextWatcher;

pub use context::Message;

pub use context::MessageMeta;

pub use context::OperatorContext;

pub use context::Position;

pub use context::Role;

pub use context::WatcherVerdict;

pub use duration::DurationMs;

pub use effect::Effect;

pub use effect::Scope;

pub use effect::SignalPayload;

pub use environment::Environment;

pub use environment::EnvironmentSpec;

pub use error::EnvError;

pub use error::OperatorError;

pub use error::OrchError;

pub use error::StateError;

pub use id::OperatorId;

pub use id::ScopeId;

pub use id::SessionId;

pub use id::WorkflowId;

pub use lifecycle::BudgetEvent;

pub use lifecycle::CompactionEvent;

pub use lifecycle::CompactionPolicy;

pub use middleware::DispatchMiddleware;

pub use middleware::DispatchNext;

pub use middleware::DispatchStack;

pub use middleware::ExecMiddleware;

pub use middleware::ExecNext;

pub use middleware::ExecStack;

pub use middleware::StoreMiddleware;

pub use middleware::StoreReadNext;

pub use middleware::StoreStack;

pub use middleware::StoreWriteNext;

pub use operator::ExitReason;

pub use operator::Operator;

pub use operator::OperatorConfig;

pub use operator::OperatorInput;

pub use operator::OperatorMetadata;

pub use operator::OperatorOutput;

pub use operator::SubDispatchRecord;

pub use operator::ToolMetadata;

pub use orchestrator::Orchestrator;

pub use orchestrator::QueryPayload;

pub use secret::SecretAccessEvent;

pub use secret::SecretAccessOutcome;

pub use secret::SecretSource;

pub use state::ContentKind;

pub use state::Lifetime;

pub use state::MemoryLink;

pub use state::MemoryTier;

pub use state::SearchOptions;

pub use state::SearchResult;

pub use state::StateReader;

pub use state::StateStore;

pub use state::StoreOptions;

Modules

content

Universal content types that cross every protocol boundary.

context

Context management for operator message histories.

duration

Stable duration type for protocol wire format.

effect

Effect system — side-effects declared by operators for external execution.

environment

The Environment protocol — isolation, credentials, and resource constraints.

error

Error types for each protocol.

id

Typed ID wrappers for operator, session, workflow, and scope identifiers.

lifecycle

Lifecycle events — cross-protocol coordination vocabulary.

middleware

Per-boundary middleware traits using the continuation pattern.

operator

The Operator protocol — what one operator does per cycle.

orchestrator

The Orchestrator protocol — how operators from different agents compose.

secret

Secret management data types — the stability contract for credential resolution.

state

The State protocol — how data persists and is retrieved across turns.