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Concepts

The Concepts quadrant is understanding-oriented. Each page explains what a subsystem is, why it exists, how it fits with the others, and the handful of named types you'll encounter when reading Zeroth source code. Pair every Concept with its sibling Usage Guide once you're ready to pick up the API.

Zeroth follows the Diátaxis model: Concepts for understanding, Usage Guides for task-oriented instructions, Tutorials for guided learning, and Reference for look-up.

Primary product

  • Economic debugger service — attribute cost and outcomes, analyze timelines/cohorts/breakage, backtest candidates, and define the free-versus-paid boundary. The sections below document preserved platform capabilities that supply or govern its evidence.

Execution

The nodes, edges, and runners that move a payload through a graph.

  • Graph — the top-level workflow model: nodes, edges, mappings, conditions, and the repository that persists them.
  • Orchestrator — the runtime that drives a graph, dispatches nodes, and terminates runs.
  • Agents — agent_runtime: AgentRunner, provider adapters, prompt assembly, and tool attachment.
  • Execution units — sandboxed tool runners, manifests, admission control, and environment preparation.
  • Conditions — edge-bound expressions, BranchResolver, and safe AST evaluation.
  • Parallel execution — concurrent fan-out/fan-in with isolated branch state and deterministic merging.
  • Subgraph composition — nested published graphs with inherited governance and approval propagation.
  • Context window management — token tracking and automatic compaction strategies for long-running agents.

Data and state

The models, contracts, and stores that carry run state between steps.

  • Mappings — edge-level payload transformations between nodes.
  • Memory — MemoryConnector protocol, ephemeral and persistent backends (memory-pg, memory-chroma, memory-es).
  • Storage — async database abstraction, SQLite + Postgres backends, and Alembic migrations.
  • Contracts — Pydantic-model-backed input/output schemas resolved through ContractRegistry.
  • Runs — Run, RunStatus, failure state, threads, and the repository that persists every transition.
  • Templates — versioned, sandbox-rendered prompt content.
  • Artifacts — external storage for large node outputs.

Governance

The gates, audits, and identities that make Zeroth auditable.

  • Policy — capability-based access control with PolicyGuard and PolicyDefinition.
  • Approvals — human-in-the-loop gates via HumanApprovalNode and ApprovalService.
  • Audit — NodeAuditRecord, hash-chained integrity, and AuditRepository queries.
  • Guardrails — rate limits, quotas, and token-bucket enforcement.
  • Identity — ActorIdentity, AuthenticatedPrincipal, ServiceRole, and tenant scoping.

Platform

The cross-cutting infrastructure: secrets, dispatch, cost, service, webhooks.

  • Secrets — SecretProvider, SecretResolver, and SecretRedactor.
  • Dispatch — RunWorker, LeaseManager, and the arq wakeup channel.
  • Economics — CostEstimator, InstrumentedProviderAdapter, and BudgetEnforcer against Regulus.
  • Service — bootstrap_service, FastAPI app factory, and the uvicorn entrypoint.
  • Webhooks — WebhookService, delivery worker, and HMAC-SHA256 signing.
  • Resilient HTTP client — retries, circuit breaking, rate limiting, and pooled outbound HTTP.