Crate rx4 

rx4 — the agent harness engine.

Models write. rx4 gives them tools, memory, loops, permissions, sessions, and control planes. Hosts (CLIs, TUIs, IDEs) embed rx4.

Safety

This crate is #![forbid(unsafe_code)] — no unsafe code is allowed anywhere.

use rx4::Agent;

let mut agent = Agent::new();
agent.set_scope(rx4::Scope::Coding);
agent.prompt("fix the failing test").await?;

Re-exports

pub use agent::is_planning_content;

pub use agent::normalize_tool_name;

pub use agent::wipe_planning_tokens;

pub use agent::Agent;

pub use agent::AgentBudget;

pub use agent::CacheAudit;

pub use agent::CacheDivergence;

pub use agent::Event;

pub use agent::GateResult;

pub use agent::MemoryRecall;

pub use agent::PatchHunkNotice;

pub use agent::PermissionAsk;

pub use agent::QualityGateConfig;

pub use agent::RecoveryKind;

pub use agent::SemanticEmbedder;

pub use agent::SemanticRecallConfig;

pub use agent::ToolCall;

pub use agent::ToolContext;

pub use agent::ToolDefinition;

pub use agent::ToolEffect;

pub use agent::ToolErrorKind;

pub use agent::ToolExecuteBox;

pub use agent::ToolExecuteFn;

pub use agent::ToolExecutor;

pub use agent::ToolFuture;

pub use agent::ToolRegistry;

pub use agent::ToolResult;

pub use agent::TurnEndMetadata;

pub use avo::commit_if_better;

pub use avo::is_protected_branch;

pub use avo::lineage_p_t;

pub use avo::objective_f;

pub use avo::CommitDecision;

pub use avo::LineageScore;

pub use avo::StallDetector;

pub use capsule::ContextCapsule;

pub use cassette::detect_divergence;

pub use cassette::detect_tool_divergence;

pub use cassette::simulate_tool;

pub use cassette::CassetteTurn;

pub use cassette::Divergence;

pub use cassette::ReplayProvider;

pub use compaction::apply_compaction;

pub use compaction::compact_messages;

pub use compaction::compact_messages_semantically;

pub use compaction::project_compact;

pub use compaction::prune_messages;

pub use compaction::CompactionConfig;

pub use compaction::CompactionMarker;

pub use compaction::CompactionResult;

pub use compaction::PrefixShape;

pub use compaction::ProjectionResult;

pub use compaction::ProjectionStep;

pub use compaction::RavenArchive;

pub use context::compose_system_prompt;

pub use context::load_project_instructions;

pub use context::ProjectInstructions;

pub use cost::CostEntry;

pub use cost::ModelPricing;

pub use cost::PricingRegistry;

pub use cost::SessionCost;

pub use cost::TokenUsage;

pub use guardrails::classify_tool;

pub use guardrails::reclassify_effect;

pub use guardrails::recover_empty_turn;

pub use guardrails::recover_stuck_tool;

pub use guardrails::schedule_tool_calls;

pub use guardrails::GuardrailConfig;

pub use guardrails::GuardrailDecision;

pub use guardrails::RecoveryAction;

pub use guardrails::SelfHealingRetry;

pub use guardrails::ToolClass;

pub use guardrails::ToolGuardrails;

pub use hashline::apply as apply_hashline;

pub use hashline::format_read as format_hashline_read;

pub use hashline::tag_for as hashline_tag_for;

pub use hashline::HashlineError;

pub use hashline::HashlineSight;

pub use hashline::HunkCheckpoint;

pub use hashline::HunkLog;

pub use hashline::ModelFamily as HashlineModelFamily;

pub use hashline::ParseMode as HashlineParseMode;

pub use hashline::ReadOptions as HashlineReadOptions;

pub use hashline::RewindError;

pub use hashline::RewindMode;

pub use hashline::TaggedRead;

pub use hashline::VisibleSet;

pub use hooks::HookDecision;

pub use hooks::HookEvent;

pub use hooks::HookFn;

pub use hooks::HookRegistry;

pub use mode::Profile;

pub use mode::Scope;

pub use models::CompatConfig;

pub use models::ModelBinding;

pub use models::ModelInfo;

pub use models::ModelRegistry;

pub use permissions::authorize;

pub use permissions::authorize_with_workspace;

pub use permissions::command_from_args;

pub use permissions::is_dangerous_shell_command;

pub use permissions::is_process_tool;

pub use permissions::is_read_only_tool;

pub use permissions::is_write_tool;

pub use permissions::path_outside_workspace;

pub use permissions::shell_argv;

pub use permissions::shell_ast;

pub use permissions::shell_command_allowed;

pub use permissions::shell_command_matches_all;

pub use permissions::shell_command_matches_any;

pub use permissions::shell_rule_matches;

pub use permissions::shell_segments;

pub use permissions::shell_simples;

pub use permissions::AlwaysAllow;

pub use permissions::AlwaysApprovePlan;

pub use permissions::AlwaysDeny;

pub use permissions::ApprovalRequest;

pub use permissions::Approver;

pub use permissions::AsyncApprover;

pub use permissions::Authorizer;

pub use permissions::ChannelApprover;

pub use permissions::ChannelAsyncApprover;

pub use permissions::ChannelPlanApprover;

pub use permissions::Decision;

pub use permissions::ExecPrefixRule;

pub use permissions::GuardianAuthorizer;

pub use permissions::GuardianReview;

pub use permissions::PermissionMode;

pub use permissions::PlanApprover;

pub use permissions::PlanDecision;

pub use permissions::PlanProposal;

pub use permissions::Policy;

pub use permissions::PolicyAuthorizer;

pub use permissions::ShellNode;

pub use permissions::ShellSimple;

pub use permissions::WorktreeAuthorizer;

pub use permissions::WorktreeClaim;

pub use permissions::WritePathSchedule;

pub use prewalk::is_mutating_call;

pub use prewalk::Prewalk;

pub use prompt_cache::apply_cache_control;

pub use prompt_cache::CachePoint;

pub use prompt_cache::CachePosition;

pub use prompt_cache::CacheProvider;

pub use prompt_cache::CacheStats;

pub use prompt_cache::CacheStatsTracker;

pub use prompt_cache::CacheTtl;

pub use prompt_cache::PromptCacheConfig;

pub use provider::Message;

pub use provider::Provider;

pub use provider::ProviderRegistry;

pub use provider::Role;

pub use provider::StreamEvent;

pub use repomap::RepoMap;

pub use repomap::RepoMapError;

pub use rollout::RolloutEntry;

pub use rollout::RolloutManager;

pub use rollout::TraceWriter;

pub use sandbox::detect_sandbox;

pub use sandbox::escalate_on_deny;

pub use sandbox::OsSandbox;

pub use sandbox::OsSandboxConfig;

pub use sandbox::OsSandboxRunner;

pub use sandbox::SandboxConfig;

pub use sandbox::SandboxError;

pub use sandbox::SandboxLayer;

pub use sandbox::SandboxManager;

pub use sandbox::SandboxProfile;

pub use sandbox::SandboxViolation;

pub use secrets::filter_env_vars;

pub use secrets::is_sensitive_env_var;

pub use secrets::RedactionConfig;

pub use secrets::Redactor;

pub use secrets::SecretMatch;

pub use secrets::SecretPattern;

pub use session::Session;

pub use session::SessionProjection;

pub use shadow_git::ShadowGit;

pub use shadow_git::ShadowGitError;

pub use slash::help_text as slash_help_text;

pub use slash::parse as parse_slash;

pub use slash::Command as SlashCommand;

pub use snapshot::FileSnapshot;

pub use snapshot::FileVersionGuard;

pub use snapshot::SnapshotStore;

pub use subagent::SubagentBudget;

pub use subagent::SubagentConfig;

pub use subagent::SubagentError;

pub use subagent::SubagentEvent;

pub use subagent::SubagentHandle;

pub use subagent::SubagentLimits;

pub use subagent::SubagentManager;

pub use subagent::SubagentResult;

pub use subagent::SubagentStatus;

pub use subagent::SubagentSubscriber;

pub use subtask::claim_complete;

pub use subtask::ClaimOutcome;

pub use subtask::Evidence;

pub use subtask::EvidenceLedger;

pub use subtask::HostAdjudication;

pub use subtask::Subtask;

pub use subtask::SubtaskClaim;

pub use subtask::SubtaskStatus;

pub use todo::TodoConfig;

pub use todo::TodoItem;

pub use todo::TodoState;

pub use todo::TodoStatus;

pub use tools::exec::ExecOutput;

pub use tools::exec::ExecProcess;

pub use tools::exec::ExecRegistry;

pub use tools::spill::SpillNotice;

pub use tools::spill::SpillStatus;

pub use tools::spill::SpilledResult;

pub use tools::register_apply_patch_tool;

pub use tools::register_builtin_tools;

pub use tools::register_complete_subtask_tool;

pub use tools::register_spawn_agent_tool;

Modules

agent

Agent loop: event-driven turn cycling with tool execution, permissions, scopes, cancellation, caching, and parallel tool dispatch.

avo

AVO helpers: scored lineage, two-part objective, commit-if-better, stall.

capsule

cassette

compaction

Semantic context compaction: token estimation, compaction markers, and oldest-first message removal that preserves the system prompt and a recent token window.

config

Configuration: load config from file + env.

context

Context: project instruction files (AGENTS.md), system prompt composition, compaction.

cost

Cost tracking per-model and per-session (Crush pattern).

guardrails

Guardrails: empty-turn detection, repeated tool failure, loop hygiene, bounded tool recursion, abort signaling, and tool effect batching.

hashline

Hashline edit protocol: tagged reads and fail-closed PUT/CUT/MV/REM.

hooks

Lifecycle hooks: real async dispatch with parking_lot (grok pattern).

mode

Work scopes (not named agents). Profiles shape tools, policy, and prompt tone.

models

Consumer-supplied model metadata and provider compatibility.

permissions

Permissions: policy modes, allow/deny lists, host Approver / Authorizer (pi beforeToolCall).

prewalk

Prewalk / plan-yolo: investigate on the big model, apply on smol.

prompt_cache

Prompt caching support for Anthropic and OpenAI providers.

provider

Provider abstraction with async streaming (pi_agent_rust pattern). Real SSE streaming via reqwest + eventsource-stream.

repomap

Repository map: structural summary of a codebase ranked by importance.

rollout

Rollout persistence: durable JSONL event logging with buffered I/O.

sandbox

Sandbox: userspace filesystem, command, and environment validation layer.

secrets

Secrets: detection and redaction of common credential patterns in text and environment variables.

session

Session: conversation tree with fork/merge/persist (JSONL).

shadow_git

Per-turn shadow-git checkpoints. The user’s .git is never touched.

slash

Slash command parser.

snapshot

Pre-edit file snapshots and observed-file version guards (not git).

subagent

Subagent: isolated agent execution contexts with optional git worktree isolation.

subtask

todo

Session-scoped task tracking with confidence-gated completion.

tools

Built-in coding tools: read, write, edit, bash, grep, find, ls + extended tools. Uses fff for fast indexed file search.

Constants

VERSION