Architecture

Anvil captures source contracts, combines them with reviewed policy, and compiles AIR into CLI, MCP, SDK, and supporting artifacts. This page maps those stages to packages and explains where validation and execution occur.

Start with the product boundary to distinguish contract compilation, offline legacy evidence, and runnable bridge support.

Design invariants

The architecture protects seven invariants:

1. One semantic model. CLI, MCP, skill, client SDKs, hooks, mocks, and deployment inputs are projections of AIR, not separate sources of truth.
2. Captured inputs. Compilation reads a content-addressed source snapshot, not a mutable remote contract.
3. Conservative safety. Unknown mutation semantics cannot become callable by default.
4. Approval controls exposure. Only approved operations enter callable projections.
5. Runtime enforcement remains authoritative. A missing harness hook cannot remove a safety requirement.
6. Evidence binds to bytes. Assurance records identify the bundle hash they tested and become stale after change.
7. Legacy discovery is not execution authority. A technical candidate or approved binding cannot imply that a runtime bridge exists.

System flow

Stage	Input	Responsibility	Output
Source capture	Files or a source directory	Detect entrypoints, follow permitted local references, reject path escape, store verbatim bytes	Immutable source snapshot
Protocol adaptation	One locked entrypoint	Lower OpenAPI, Swagger, GraphQL, proto3, WSDL, Discovery, OData, Postman, or a HAR capture into the shared HTTP-shaped compiler input	Normalized source document
Semantic compilation	Adapted document plus optional manifest	Normalize operations, classify effects, apply reviewed facts, validate safety, discover capabilities	AIR document
Projection	AIR	Generate CLI, MCP, skill, client SDKs, hooks, mocks, evals, runtime documents, targets, and deploy inputs	Bundle directory
Review	Bundle	Inspect diagnostics, enrich missing facts, review capabilities, approve operations	Reviewed bundle
Assurance	One immutable bundle	Check static identity, exercise transport, compare surfaces, simulate safety behavior	Hash-bound evidence records
Release planning	Assured bundle plus target inputs	Verify required evidence and emit an operator plan	Publication plan; no deployment

anvil agentify orchestrates the first four discovery activities—capture, compile, assess, and capability proposal—then stops for review.

Legacy inventory and refinement flow

Legacy mode does not pass deployment descriptors or broker configuration through the API protocol adapters. It uses a separate evidence model:

Stage	Input	Responsibility	Output
Offline acquisition	Caller-supplied file or hardened-expanded directory	Bound filesystem reads and preserve provenance	Relative member paths and bytes
Collection	Java EE, .NET, or messaging members	Parse only declared configuration; hash opaque binaries	Artifacts, evidence, observations, diagnostics
Reconciliation	Verified inventory snapshot	Group exact coordinate and invocation matches; retain every assertion	Technical candidates and explicit conflicts
Task creation	One exact candidate	Freeze required decisions and non-negotiable policy	Content-addressed harness task
Harness proposal	Task plus external evidence access	Propose business schema, errors, transport, and operational semantics	Untrusted submission bound to the task
Assessment and review	Inventory, task, proposal, human decision	Verify lineage and completeness; keep approval separate	Assessment, receipt, and reviewed binding

Candidates are reconciliation products, not AIR operations. The approved binding records runtime.placement = deployment_local_bridge and runtime.status = not_implemented. No generator or runtime currently consumes it as executable input.

This deliberate gap prevents the compiler architecture from implying that configuration parsing also solved vendor client compatibility, field mapping, transactions, identity, network placement, or completion semantics.

Layer 0: source capture

Source capture is intentionally separate from parsing. The store records:

• verbatim file bytes;
• discovered entrypoints and formats;
• the role of each file in the graph;
• external references that were observed but not fetched;
• structured diagnostics;
• a content-derived snapshot id and source hash; and
• optional origin metadata such as a gateway vendor.

Local references must remain inside the import root. Remote references are not fetched. A malformed input can be preserved as an invalid snapshot for diagnosis, but only a valid snapshot can enter the compiler.

This separation answers a foundational question: which exact bytes did the compiler read? Later evidence can bind to that identity rather than to a path or URL that may have changed.

Protocol adapters

The downstream compiler consumes one internal document shape. Protocol adapters perform deterministic lowering before semantic normalization:

Adapter	Mapping
OpenAPI 3.x	Parsed and dereferenced directly
Swagger 2.0	Upgraded with swagger2openapi, then parsed as OpenAPI
GraphQL SDL	Root fields become POST-shaped operations; GraphQL kind carries read/mutation meaning
gRPC/proto3	RPCs become operations; messages and enums become JSON schemas
SOAP/WSDL 1.1	portType operations become POST-shaped operations; WSDL/XSD types become schemas
Google Discovery	Resource methods and schemas become paths, operations, and components
OData v2/v4	Entity sets become permitted CRUD operations based on metadata
Postman v2.x	Saved requests, folders, examples, and auth shapes become an API document
HAR 1.2 capture	Recorded requests become templated operations; every operation is capped review_required — a capture is evidence, never a declared contract

Adapters own syntax and mechanical fidelity. They do not grant business authority. A method named TransferFunds remains a mutation whose idempotency must be established by evidence or a reviewed manifest.

See Source format support for exact boundaries.

AIR: the canonical contract

AIR—the Anvil Intermediate Representation—is defined with Zod in @anvil/air. One document contains the service, operations, capabilities, workflows, shared schemas, evidence, and diagnostics.

Each operation carries:

Axis	Examples
Identity	stable id, source reference, canonical name
Effect	read or mutation, action, risk, reversibility
Repeatability	idempotency mode, key location, retry eligibility
Intent gate	confirmation requirement, human-approval tier, reason
Access	auth type, principal, scopes, credential profile, carrier
Interface	input/output schemas, parameters, errors, pagination
Projection	CLI command, MCP tool name, skill intents
Lifecycle	generated, review required, approved, blocked, deprecated
Ownership	capability and workflow relationships
Evidence	claim-scoped provenance, confidence, reliability, review state

Claims and confidence

Evidence is recorded per semantic claim. A strong claim that an endpoint exists must not increase confidence that it is idempotent. The reconciler evaluates confidence by predicate and uses asymmetric trust:

• loosening safety requires strong evidence;
• tightening safety can proceed on weaker warning evidence; and
• conflicting safety-sensitive claims choose the safer posture and require review.

The aggregate confidence shown for an operation is descriptive. Safety gates use the relevant claim, not a blended score.

Capabilities and workflows

A capability groups related operations. Discovery uses source structure such as tags and resource names and records provenance for the grouping. A capability has its own review lifecycle and disclosure budget.

Workflows are authored, not guessed. Each step references an existing operation; an unresolved reference or unapproved mutation blocks the workflow. A workflow cannot grant authority that its steps do not have.

Compiler passes

The semantic compiler applies ordered passes:

1. Normalize source operations into stable AIR identities and schemas.
2. Classify effect, action, risk, idempotency, retry, confirmation, auth, and pagination conservatively.
3. Apply manifest facts and reviewed decisions.
4. Recompute derived policy so idempotency, retries, confirmation, and effect remain coherent after overrides.
5. Validate invariants and force unsafe or uncertain operations into review_required or blocked.
6. Discover capabilities and attach authored workflows.
7. Generate diagnostics and evidence for every material decision.

The manifest wins where it explicitly supplies a value. Unset fields are recomputed; stale derived values are not retained merely because a nearby field changed.

Generated projections

@anvil/generators treats AIR as read-only input and emits independent views:

• operation catalog and compiled runtime documents;
• typed CLI;
• MCP server and resource index;
• skill package and operation references;
• shared hook core plus harness adapters;
• mock server, evals, and conformance assets;
• target-specific connector kits;
• Cloud Run and infrastructure inputs; and
• certification metadata.

The bundle installer stages generated output, verifies surface agreement, and swaps the complete candidate into place. Partial projection updates are not a supported state.

Runtime architecture

The deployed unit is the generated MCP server backed by @anvil/mcp-runtime and @anvil/runtime. It does not parse source specifications or run enrichment. anvil serve mcp <dir> serves one bundle per process; anvil serve mcp <workspace-root> --fleet mounts every bundle beneath a workspace root onto one MCP surface instead, each under a stable per-bundle tool-name prefix, composed from independently-built single-bundle servers rather than a second serving path — see fleet.md.

Before an upstream call, the executor evaluates the following controls in a deterministic order:

Control	Purpose
Input validation	Reject arguments outside the generated schema
Confirmation	Require explicit intent for gated effects
Idempotency	Require and fingerprint deduplication keys where configured
Principal scope	Refuse a caller missing a scope auth.scopes requires (fleet runtime; anonymous/every-scope by default)
Rate/spend limits	Refuse a caller over its configured per-principal rate or spend budget (fleet runtime; unlimited by default)
Dry run	Return a redacted request plan after preconditions pass
Host pinning	Restrict upstream egress to reviewed hosts
Auth resolution	Resolve named credential profiles without placing secrets in AIR
Ledger durability	Fail closed when a required durable write ledger is unavailable
Retry policy	Retry only bounded transient conditions when repetition is safe
Response normalization	Produce structured outputs and stable error envelopes
Observation	Emit an OpenTelemetry-shaped execution record, including the calling principal’s id (never its credential)

Runtime policy hooks can deny at defined pre/post phases. They are not the same as harness hooks: runtime hooks execute inside the authority boundary, while harness hooks improve the caller experience before transport.

Durable idempotency

A horizontally scaled stateless runtime cannot keep deduplication state in process. Required-idempotency writes therefore use a pluggable durable ledger. Outside development, the runtime fails closed when the configured durable backend is unavailable.

The built-in Firestore path provides reservation, replay, conflict, and readiness behavior. It is bounded deduplication, not a claim of exactly-once execution: a crash after upstream success but before ledger completion remains an operator-reconciliation case.

Assurance architecture

Assurance is split so one green check cannot hide another class of failure:

• Certification checks static artifact identity and contract coherence.
• Self-test boots the generated servers and exercises approved tools over the real local MCP transport.
• Conformance compares the operations and policy described by each surface.
• Simulation crosses operations with applicable safety dimensions and injects mutations to prove regressions are detected.
• Benchmarking measures discovery and callability rather than safety.

Each record names the bundle hash it evaluated. status verifies freshness and selects the next required action. publish snapshots the required evidence into a plan but performs no provider mutation.

Build-time, deploy-time, and run-time boundary

Phase	Contains	Must not contain
Build	parsers, adapters, compiler, enrichment, generators, review, assurance	production credential values
Deploy	generated runtime, target configuration, IAM/network/secret references, ledger contract	source parsing or LLM enrichment
Run	validation, policy, auth resolution, ledger, upstream execution, telemetry	spec compilation, capability discovery, approval changes

This boundary keeps the hot path small and reviewable. The runtime consumes compiled documents; it does not reinterpret the source contract.

Package map

Package	Responsibility
@anvil/air	Canonical schemas, operation semantics, disclosure model
@anvil/compiler	Source store, protocol adapters, normalization, classification, manifest, validation, drift
@anvil/grammar	Bounded query grammar and template analysis
@anvil/refinement	Deficiency detection, readiness assessment, cases, review, enrichment plans
@anvil/generators	Bundle projections and static certification inputs
@anvil/runtime	Safety executor, auth, retries, idempotency, errors, observation
@anvil/mcp-runtime	MCP serving path, capability lanes, resource serving
@anvil/harness	Evidence-source orchestration and executable bundle drivers
@anvil/legacy-bridge	Deployment-local HTTP facade executing one reviewed legacy capability binding over one transport (queue request/reply), and its in-process conformance runner
@anvil/certification	Cross-artifact and async contract checks
@anvil/simulator	Scenario matrix and safety-regression mutation battery
@anvil/targets	Agent-platform connector profiles
@anvil/system-pack	Cross-bundle system packaging
@anvil/cli	Command tree and orchestration over the libraries above

The CLI is an adapter over library APIs. Core behavior belongs in packages that can be called and tested without parsing terminal output.

The legacy collectors, inventory model, reconciliation, and refinement workflow currently live behind the Node-only @anvil/compiler/legacy package export. This entrypoint accepts caller-supplied bytes and does not acquire files or network resources itself. @anvil/legacy-bridge depends only on @anvil/air and @anvil/compiler (see packages/cli/src/boundaries.test.ts’s ALLOWED_EDGES) and is not part of the deployed MCP server’s dependency closure — it is its own deployment-local process, run and reviewed separately from @anvil/mcp-runtime.

Extension seams

New behavior should enter through a narrow seam:

• new source syntax through a protocol adapter;
• new offline legacy evidence through a non-executing collector that emits the shared legacy artifact, evidence, observation, and diagnostic model;
• new executable legacy transport through a deployment-local adapter that consumes only reviewed bindings and cannot widen their target or semantics;
• new generated surface through a generator;
• new agent platform through a target profile;
• new durable store through the ledger interface;
• new evidence source through an MCP-published connector and structured claims;
• new harness through a thin adapter over shared hook decisions; and
• new assurance rule through a structured check and stable diagnostic code.

An extension may add evidence or a projection. It must not create a second semantic model or bypass approval and runtime enforcement.

Read next

• Product boundary
• Mechanisms
• Simulation and backtesting
• Hooks and plugins
• Certification authority