Crate car_engine 

Core runtime engine for Common Agent Runtime.

The runtime loop:

1. Receive a proposal (batch of actions from a model)
2. Build a DAG from state_dependencies
3. Execute each level (concurrent if no ABORT actions, sequential otherwise)
4. Validate, execute with idempotency + timeout + retry, commit
5. On abort: rollback state to pre-proposal snapshot

Re-exports

pub use agent_basics::entries as agent_basic_entries;

pub use agent_capability::AgentCapabilityRegistry;

pub use authz::AllowAllPermissions;

pub use authz::AuthzDecision;

pub use authz::AuthzPipeline;

pub use authz::AuthzResult;

pub use authz::AuthzStage;

pub use authz::PermissionHandler;

pub use authz::Restriction;

pub use builtin_agents::agent_metadata;

pub use builtin_agents::format_capability_payload;

pub use builtin_agents::register_builtins;

pub use builtin_agents::BuiltinAgent;

pub use builtin_agents::CapabilityPayloadError;

pub use builtin_agents::BUILTIN_AGENTS;

pub use cache::ResultCache;

pub use capabilities::CapabilitySet;

pub use checkpoint::Checkpoint;

pub use mcp::McpServer;

pub use mcp::McpServerConfig;

pub use mcp::McpToolExecutor;

pub use mcp::McpToolInfo;

pub use rate_limit::RateLimit;

pub use rate_limit::RateLimiter;

pub use registry::ToolEntry;

pub use registry::ToolPermission;

pub use registry::ToolRegistry;

pub use registry::ToolSource;

pub use scope::RuntimeScope;

pub use subprocess::SubprocessTool;

pub use subprocess::SubprocessToolExecutor;

pub use voice_turn::dispatch_voice_turn;

pub use voice_turn::dispatch_voice_turn_sidecar_only;

pub use voice_turn::dispatch_voice_turn_sidecar_only_with_classifier;

pub use voice_turn::dispatch_voice_turn_sidecar_only_with_telemetry;

pub use voice_turn::dispatch_voice_turn_with_telemetry;

pub use voice_turn::DirectDataFetcher;

pub use voice_turn::SidecarResult;

pub use voice_turn::VoiceTelemetry;

pub use voice_turn::VoiceTurnControl;

pub use voice_turn::VoiceTurnError;

pub use voice_turn::VoiceTurnHandle;

Modules

agent_basics

agent_capability

Agent capability registry — maps capability id → agents that implement it.

authz

Authorization pipeline for tool execution.

builtin_agents

Built-in agent vocabulary — single source of truth across FFI surfaces.

cache

Cross-proposal result cache for tool call results.

capabilities

Per-agent capability permissions for the Common Agent Runtime.

checkpoint

Checkpoint and resume support for the Common Agent Runtime.

mcp

MCP (Model Context Protocol) server integration.

rate_limit

Token bucket rate limiter for tool calls with backpressure support.

registry

Canonical tool registry — single source of truth for tool identity.

scope

RuntimeScope — per-execution caller identity surface for the multi-tenant work tracked in Parslee-ai/car#187.

subprocess

Subprocess tool executor — runs tools as external processes via stdin/stdout JSON-RPC.

voice_turn

Two-track voice turn orchestration.

Structs

Action

A single unit of agent intent compiled into IR.

ActionProposal

A batch of actions proposed by a model for runtime validation and execution.

AgentOutcome

The outcome of an agent execution loop.

CostBudget

Budget constraints for proposal execution.

EventLog

Append-only event log with optional JSONL journal.

Evidence

Evidence supporting an outcome classification.

FailedActionSummary

Summary of a failed action, included in ReplanContext.

OutcomeMetrics

Execution metrics associated with an outcome.

Planner

Proposal scorer and ranker.

PlannerConfig

Configuration for proposal scoring.

PolicyEngine

Evaluates actions against registered policies.

ProposalResult

The complete result of processing a proposal through the runtime.

ReplanConfig

Configuration for the replan loop.

ReplanContext

Context provided to the replan callback so the model can generate an alternative.

Runtime

Common Agent Runtime — deterministic execution layer.

StateStore

Thread-safe state store with transition logging.

ToolFeedback

Historical tool success rates computed from the trajectory store. Pass to rank_with_feedback() to bias scoring based on past outcomes.

ToolSchema

Rich schema describing a tool’s interface and runtime configuration.

VerifyIssue

A single verification finding.

Enums

ActionType

What kind of action this is.

EventKind

Event kinds matching the Python EventKind enum.

EvidenceKind

Types of evidence that can support an outcome.

FailureBehavior

What to do when an action fails.

OutcomeStatus

Outcome classification for an agent execution.

SpanStatus

Status of a trace span.

Constants

CANCELED_PREFIX

Prefix on the error field of an ActionResult that distinguishes “the user pulled the plug” from “earlier abort cascaded.” The ActionStatus itself is Skipped in both cases (introducing a new variant ripples through every IR consumer + FFI binding); the prefix lets callers like the A2A bridge tell the cases apart without string-matching a magic literal.

Traits

ReplanCallback

Callback trait for replanning failed proposals. Implement this to let the runtime ask the model for an alternative plan when a proposal aborts.

ToolExecutor

Trait for tool execution. Implement this to provide tools to the runtime.

Functions

format_tool_result

Format a tool result for feeding back to a model.

Type Aliases

PolicyCheck

Policy check function: (action, state) -> Option<violation_reason>