RFC 0012 — Behavior as a content-addressed package resource

Document status: proposed, with executable experimental profile. Canonical source.

nuif-behavior-package-resource-0. This RFC chooses the first transport for the bounded behavior experiment. It does not add behavior to the canonical semantic Document, standardize a media type, or authorize execution when a package is opened.

Motivation

The independent Rust/Node behavior traces and the three-engine web lowering show that one finite state-machine subset is executable. Keeping it only as an out-of-band JSON fixture, however, cannot test offline delivery, package identity, corruption handling or document-reference validation after a package round trip. Moving it directly into the canonical document would make a much larger and less-tested compatibility commitment.

The narrow requirement is therefore: transport one exact behavior program with one exact document using the current deterministic package, while keeping behavior modular and inert until an explicit capability-aware runtime accepts it.

Prior art and evidence

• nuif:research:behavior-portability-state-machines defines the finite trace contract and its current exclusions.
• nuif:research:behavior-package-resource-binding compares OCI descriptors, EPUB container processing and KHR_interactivity, then records the executable package decision.
• RFC 0010 already defines deterministic package manifests, digest-addressed blobs, resource roles, explicit resolution and the rule that resources do not execute merely because they are present.

Profile

nuif-behavior-package-resource-0 uses nuif-package-0 unchanged. A conforming attachment has all of these properties:

• exactly one resource descriptor has media type application/nuif-behavior+cbor;
• that media type is provisional and is not an IANA-registration claim;
• the descriptor role is source, its locator is embedded, and it has no derivation record;
• the embedded path is the normal blobs/sha256/<digest> path;
• the resource bytes are canonical nuif-cbor-0 encoding of exactly one nuif-behavior-state-machine-0 BehaviorProgram;
• required_capabilities contains nuif-behavior-state-machine-0;
• the complete program validates against document.cbor before attachment and after package decode.

Zero behavior resources with no behavior capability is a valid package without behavior. A capability with no resource, a resource without its capability, more than one behavior resource, a linked behavior resource, non-canonical bytes or invalid document references fail the attachment profile.

Identity and binding

The behavior resource digest identifies its exact canonical program bytes. The document canonical hash identifies exact semantic document bytes. Neither is redefined to include the other.

manifest.cbor carries both descriptors, and the deterministic complete package hash binds their delivered pairing. Consequently:

• attaching behavior changes the package hash but not the document hash;
• changing the document changes both its hash and the complete package hash;
• the same behavior resource can be deduplicated by digest without claiming it is valid for every document;
• every explicit load revalidates stable entity references against the actual package document.

Processing and authority

Package processing is layered:

1. NuifPackage::decode validates the deterministic ZIP, canonical manifest, document, descriptors, sizes, hashes and embedded bytes.
2. capability_report or require_capabilities compares every package requirement with a caller-declared host capability set without executing it.
3. attached_behavior opts into this RFC, checks descriptor/capability agreement, decodes canonical behavior bytes and validates the program against the document.
4. A caller creates a behavior runtime only with an explicit set of available abstract-effect capabilities.
5. A host adapter separately maps admitted effects under its own profile and security policy.

Step 1 never implies steps 2–5. Generic tools may inspect, copy and deterministically re-encode the package without executing the resource. Tools that claim full behavioral conformance must understand the required behavior capability; a structural package decode alone is not such a claim.

Security and limits

The package verifies declared byte length and SHA-256 before canonical CBOR or behavior validation. Existing package byte/resource/member limits and behavior state/transition/action/string limits both apply. Linked behavior is rejected so the profile neither invokes a resolver nor grants network authority.

The program remains data. It contains no scripts, dynamic imports, filesystem paths, URLs, timers or host calls. Runtime creation and every host lowering are separate authorization decisions.

Conformance

nuif:experiment:behavior-package-resource requires:

• canonical program bytes and exact attach/decode/encode fixpoint;
• unchanged document hash and changed package hash after attachment;
• exact required capability, source role, media type and digest-derived path;
• refusal of missing/duplicate/linked/malformed/rebound resources;
• rejection of package-byte corruption before behavior decoding;
• an independent standard-library ZIP reader checking exact package bytes, member order/metadata, CRC and the content-addressed behavior resource.

cargo xtask gate-behavior includes this gate before the independent behavior trace gate. CI archives all generated package and report artifacts.

Rejected alternatives

• Canonical Document.behavior in the first experiment: premature semantic commitment and forced support in all readers.
• A special behavior.cbor ZIP path: duplicates the resource manifest and requires a new container path profile.
• An opaque extension inside an arbitrary entity: gives behavior no unique package-level discovery or cardinality rule and couples it to one visual node.
• JSON attachment: creates a competing canonical encoding and larger parsing surface.
• Automatic execution on package open: violates RFC 0010’s inert-resource boundary and prevents safe inspection tools.

Unresolved questions

• Which next event/effect types remain finite and portable across web, native and presentation hosts.
• When independently implemented adapters provide enough evidence to propose a canonical behavior model.
• Final media-type naming and registration timing.