bcx

bcx is the Rust crate for Bifrost Causal Exchange: a no-std-first protocol foundation for signed causal meaning, proof composition, native bindings, checkpoints, and bounded explanations across multiple underlying systems.

BCX is not an HTTP replacement, an Ethereum protocol, or a Cardano protocol. It is a semantic overlay layer. BCX defines what an operation means, why it was authorized, what it caused, who attested to it, what evidence exists, and what remains unknown. HTTP, QUIC, Ethereum, Cardano, Fluxheim, Skrifheim, offline bundles, and future systems can carry, observe, store, or settle BCX objects through explicit profiles and integrations.

Current Status

bcx is at repository foundation stage. The crate is not production-ready.

Implemented now:

no_std default build.
zero third-party runtime dependencies.
root publishable crate named bcx.
focused no-std subcrates for core IDs, model types, crypto envelope metadata, policy profiles, and wire limits.
local check script, modularity guard, release metadata guard, and GitHub CI.
implementation, version, protocol-family, threat-model, toolchain, and modularity docs.
repository families for future profiles, integrations, proofs, domain profiles, and services.

Trust Dashboard

Area	Status
License	`EUPL-1.2`
MSRV	Rust `1.90.0`
Preferred toolchain	Rust `1.96.0`
Default target	`no_std`
Runtime dependencies	zero third-party crates
Unsafe policy	`unsafe_code = "forbid"`
Main crate	`bcx`
First serious target	`1.0.0` production-ready protocol crate
High-security position	trust canonical signed BCX objects, not one carrier or chain

Rust Version Support

The minimum supported Rust version is Rust 1.90.0. New deployments should prefer the latest stable Rust validated by the project.

Compatibility evidence:

Rust	Local Evidence
`1.90.0`	planned full check gate
`1.91.0`	planned `cargo check --all-features`
`1.92.0`	planned `cargo check --all-features`
`1.93.0`	planned `cargo check --all-features`
`1.94.0`	planned `cargo check --all-features`
`1.95.0`	planned `cargo check --all-features`
`1.96.0`	current pinned toolchain

Workspace Shape

Crate	Purpose
`bcx`	Published facade crate and stable user entry point.
`bcx-core`	Identifiers, nonces, replay sequence primitives, validation errors.
`bcx-model`	Statements, causal edges, admissions, effects, truth, and assurance model types.
`bcx-crypto`	Crypto-agile signature envelope metadata and verifier traits.
`bcx-policy`	Protocol profiles, proof levels, and disclosure levels.
`bcx-wire`	Wire version and bounded-message limit primitives.

Future crates are organized by family:

Family	Purpose
`profiles/`	Normative mappings such as HTTP, QUIC, Ethereum, Cardano, offline, SCITT, or future Bitcoin/XRP profiles.
`integrations/`	Concrete adapters such as Hyper, Axum, Alloy, Pallas, Fluxheim, or Skrifheim.
`proofs/`	Concrete proof suites such as COSE, threshold proofs, or ZK proof integrations.
`domains/`	Business and operational semantics such as banking or AI-agent profiles.
`services/`	Optional applications such as CLI, witness, prover, query, or node services.

The root bcx crate and foundation crates must remain independent of these future families unless a release explicitly admits a new dependency boundary. Package versions are tracked in Crate Version Matrix so future releases can publish only the crates that changed instead of republishing the whole ecosystem.

Verification

Run the local gate:

scripts/checks.sh

The gate checks formatting, tests, no-default-feature builds, all-feature builds, clippy, docs, package metadata, file-size policy, release metadata, and installed target triples.

Security Position

BCX must distinguish:

what was observed,
what was declared,
what was cryptographically verified,
what policy enforced,
what another participant acknowledged,
what remains unknown.

The protocol must not claim to prove a participant's internal motive. A signed purpose is an attributable declaration, not proof that the declared purpose was truthful.

Read Security Policy, Threat Model, and Implementation Plan before using BCX in any security-sensitive system. The broader architecture is documented in BCX Protocol Family, and the preserved idea draft is kept as Original Idea.