OxygenFlow (flow) — Deterministic Execution & Provenance Pipeline Specification

The key words MUST, MUST NOT, SHOULD, SHOULD NOT, and MAY are to be interpreted as described in RFC 2119.

1. Overview and Core Invariants

OxygenFlow (flow) is a content-addressed, hermetic execution engine, runner system, and pipeline language designed natively for the Oxygen (oxy) version control system.

Existing runner engines (GitHub Actions, GitLab CI, Forgejo Runner) suffer from structural flaws:

1. Workspace Bloat: Full clones, index unpacks, and checkout scans dominate I/O.
2. String Injection: Shell interpolation within untyped YAML files produces expression injection and command execution exploits.
3. Decoupled Supply Chain: Attestations (SLSA, in-toto, Cosign) exist outside the VCS, relying on external registries rather than native repository trust.
4. Coarse Caching: Opaque tarballs keyed by arbitrary string hashes fail to leverage commutative history or granular dependency graphs.

OxygenFlow solves these liabilities through direct integration with Oxygen:

• Zero-Copy Workspaces: Jobs mount workspaces directly from Oxygen's FastCDC- chunked, BLAKE3-addressed Content-Addressable Store (CAS) using Copy-on-Write (COW) overlays.
• Commutative History & Impact Trees: Pipelines evaluate over change closures rather than linear snapshot sequences. Commuting changes automatically reuse cached execution receipts without redundant re-execution.
• Micro-Engine Sandboxing: Jobs run inside isolated environments (WASM, gVisor, or MicroVMs) with strict, deny-by-default capabilities and no ambient network egress.
• Native Cryptographic Provenance: Provenance and execution receipts are generated outside the untrusted guest, encoded as deterministic CBOR, and signed using composite Ed25519 + ML-DSA-65 keys as native Oxygen Attest objects governed by in-repository Policy rules.

2. Threat Model and Security Architecture

2.1 Adversaries

• Untrusted Proposal Author: Submits code to an open repository containing malicious build configurations intended to escape the runner, exfiltrate secrets, or corrupt shared worker caches.
• Malicious Dependency / Upstream: Third-party dependencies invoked during build time attempting out-of-band network calls or host file modification.
• Compromised Runner / Malicious Worker: An execution node attempting to forge successful build receipts or inject backdoors into published artifacts.

2.2 Security Invariants

• I1 Deny-by-Default Execution: Sandboxes possess no network interfaces (excluding loopback when requested) and no host filesystem access unless explicitly granted in policy-signed configuration.
• I2 Injection-Free Invocation: Configuration parsing directly yields an argv string vector executed via execve(). Shell interpretation (/bin/sh -c) does not exist.
• I3 Host-Enforced Provenance: The running payload cannot author, inspect, or alter its own provenance statement. Provenance is emitted solely by the isolation hypervisor boundary.
• I4 Cryptographic Identity & Authorization: Runners execute using an Oxygen Identity whose KeyId is enrolled as a delegate in the repository's Policy. Unenrolled runners cannot publish recognized attestations or advance gates.

3. The OxygenFlow Configuration Language (.flow)

Pipelines are declared in KDL syntax within .flow/pipeline.kdl at the repository root. KDL provides strict typing, structured nesting, and rejects arbitrary text macro expansion.

3.1 Pipeline Specification Schema

schema-version 1

// Define the hermetic execution boundary
sandbox "rust-builder" {
    runtime "microvm"       // Options: "wasm" | "gvisor" | "microvm"
    rootfs "cas://blob/9b5c2a1e8f3d4e7a6b8c9d0e1f2a3b4c5d6e7f8a9b0c1d2e3f4a5b6c7d8e9f0a"
    memory-limit "4GiB"
    cpu-limit 4
    network "isolated"      // Options: "isolated" | "loopback" | "egress"
}

// Job evaluated based on Oxygen change closure
job "compile-core" {
    sandbox "rust-builder"

    // Commutation boundary: runs only if change closure touches these paths
    scope "crates/oxy-core/**" "crates/oxy-server/**" "Cargo.*"

    // Zero-copy workspace mount backed by Oxygen CAS
    mount {
        source "oxy://workspace"
        target "/src"
        include "crates/oxy-core" "crates/oxy-server" "Cargo.toml" "Cargo.lock"
        readonly #true
    }

    // Ephemeral scratch space
    mount {
        source "ephemeral://tmpfs"
        target "/src/target"
        size "8GiB"
    }

    env {
        RUSTFLAGS "-Dwarnings"
        CARGO_INCREMENTAL "0"
    }

    // Direct argv execution vector (no subshell)
    exec "cargo" "build" "--release" "--package" "oxy-core"

    output {
        artifact "oxy-core-lib" {
            path "/src/target/release/liboxy_core.rlib"
            format "blob"
        }
    }
}

job "unit-tests" {
    sandbox "rust-builder"
    depends-on "compile-core"

    mount {
        source "oxy://workspace"
        target "/src"
        readonly #true
    }

    mount {
        source "artifact://compile-core/oxy-core-lib"
        target "/src/target/release/liboxy_core.rlib"
    }

    exec "cargo" "test" "--release" "--package" "oxy-core"
}

publish "release-provenance" {
    depends-on "unit-tests"

    attest {
        kind "provenance"
        bind-ref "bookmarks/main"
        include-artifacts "compile-core/oxy-core-lib"
    }
}


### 3.2 Canonical Compilation
Upon commit, .flow/pipeline.kdl is validated and compiled into a deterministic
CBOR job-graph blob. Runners evaluate the canonical CBOR to prevent syntax or
parser ambiguities across varying client platforms.

## 4. Sandbox Execution Engine

OxygenFlow implements three distinct isolation tiers depending on the workload:

### 4.1 Level 0: WASM Component Sandbox
- Intended for static linters, formatters, doc generators, and policy checks.
- Runs on a standard WebAssembly System Interface (WASI) runtime.
- Startup latency: < 5 ms.
- Zero host I/O; virtualized file system presented in-memory.

### 4.2 Level 1: Intercepted Syscall Isolation (gVisor / Landlock + seccomp-bpf)
- Intended for standard compilation and hermetic test suites.
- Emulates or filters Linux system call interfaces in user space.
- Blocks access to raw network sockets, real-time hardware clocks, and device
  nodes.
- Memory and execution CPU quotas are strictly bounded via cgroups v2.

### 4.3 Level 2: MicroVM Isolation (Firecracker / Cloud-Hypervisor)
- Intended for kernel tests, multi-container integration, and untrusted code.
- Ephemeral Linux microVM booting in < 80 ms.
- The root filesystem is presented as a read-only virtio-block device mapped
  directly to FastCDC chunks stored in Oxygen's CAS.
- Guest VM memory is cleared upon termination.

## 5. Content-Addressable Storage (CAS) & Zero-Copy Mounting

OxygenFlow runners bypass traditional clone operations. Repositories are accessed
directly via the local object store (.oxy/objects/) or streamed on demand
using Oxygen's wire protocol.

### 5.1 FUSE Overlay Mounting (flow-casfs)
1. The runner receives a task targeting an Oxygen State ObjectRef (a sorted
   list of maximal heads).
2. The nearest Checkpoint is resolved. Uncommitted changes between the
   checkpoint and heads are replayed into a virtual tree in-memory.
3. The virtual tree is exposed to the sandbox via flow-casfs:
   - File reads resolve chunks using the FastCDC gear table (32 KiB to 256 KiB,
     mean 64 KiB) pinned in Oxygen Spec Section 13.2.
   - Missing chunks are fetched lazily using the POST /objects protocol.
   - To prevent FUSE context-switch bottlenecks on many small reads, flow-casfs aggressively mmaps chunk data and utilizes host page caching.
   - All guest mutations are diverted to a scratch tmpfs layer; base objects
     remain immutable.

### 5.2 Artifact Capture
1. At task completion, flow-casfs scans the paths declared in the output block.
2. Modified outputs are chunked with FastCDC, hashed via BLAKE3-256, and
   written as canonical Blob and Chunk objects.
3. Output ObjectRefs are stored directly in the Oxygen repository.

## 6. Commutative Execution & Change Caching

In Oxygen, changes that do not share scopes (referenced atoms, placements, or
nodes) commute. OxygenFlow exploits this invariant to provide granular caching.

### 6.1 Execution Receipt Object
Every successful or failed job run emits an immutable Receipt:

```cbor
Receipt {
  version        [0]: 1
  job_name       [1]: text
  pipeline_hash  [2]: ObjectRef
  scope_tree_hash [3]: ObjectRef     // BLAKE3 tree hash of the materialized scope
  inputs         [4]: [ObjectRef]   // Artifacts and input files consumed
  environment    [5]: ObjectRef     // Hash of rootfs, compiler flags, and argv
  outputs        [6]: [ObjectRef]   // Produced artifact blobs
  exit_code      [7]: u32
  duration_ms    [8]: u64
}

A Receipt is hashed as an Oxygen object with type name "receipt": ObjectRef = BLAKE3-256("oxy1 receipt " || decimal(len) || 0x00 || body)

6.2 Cache Re-use Invariant

Let Scope(J) be the file paths and tree nodes declared by job J. Because changes that do not share scopes commute, we do not need to track lists of ChangeHashes. Instead, we hash the materialized tree of Scope(J).

If an existing Receipt R exists such that: R.job_name == J.name && R.pipeline_hash == Hash(J) && R.scope_tree_hash == TreeHash(Scope(J)) && R.environment == CurrentEnvironmentHash

Then the job execution is bypassed. R.outputs are mapped into downstream dependents immediately as a cached-commuted hit.

7. Native Provenance Specification

OxygenFlow formalizes build provenance as a native, tamper-evident Oxygen Attest object (kind: "attest"). Provenance is generated exclusively by the runner hypervisor, not the guest payload.

7.1 Provenance Object Schema

Attest {
  version [0]: 1
  kind    [1]: "attest"
  repo    [2]: bytes(16)               // Oxygen Repository ID
  hlc     [3]: HLC                     // Hybrid Logical Clock
  body    [4]: {
    "type": "flow/provenance/v1",
    
    // Subject artifacts produced by the build
    "subjects": [
      {
        "name": text,
        "ref": ObjectRef,              // BLAKE3 hash of output blob
        "media_type": text
      }
    ],

    // Builder platform and execution identity
    "builder": {
      "runner_id": KeyId,              // ObjectRef of runner's Oxygen Identity
      "isolation_level": text,         // "wasm" | "gvisor" | "microvm"
      "hypervisor_image": ObjectRef    // Rootfs blob digest
    },

    // Exact input materials
    "materials": {
      "state_heads": [ChangeHash],     // Oxygen heads of the state built
      "scope_tree_hash": ObjectRef,        // Captures exact state without O(N) array bloat
      "inputs": [
        {
          "name": text,
          "ref": ObjectRef             // Content hash of locked dependencies
        }
      ]
    },

    // Structured execution arguments
    "invocation": {
      "job": text,
      "pipeline_spec": ObjectRef,      // ObjectRef of .flow/pipeline.kdl
      "argv": [text],                  // Unmodified execution vector
      "env": map<text, text>           // Explicitly whitelisted environment
    },

    // Environment observations
    "metadata": {
      "started_on": u64,               // Wallclock milliseconds
      "finished_on": u64,
      "hermetic": bool,                // Verified zero outbound network access
      "reproducible": bool
    }
  }
}

7.2 Composite Signatures

All provenance attestations are signed using Oxygen's composite signature construction (Ed25519 and ML-DSA-65):

Signature {
  key [0]: KeyId
  alg [1]: 1                           // 1 = Ed25519 + ML-DSA-65
  ed  [2]: bytes(64)                   // Classical signature
  ml  [3]: bytes(3309)                 // Post-quantum signature
}

Both signatures are computed over: "oxy1 sig attest\0" || KeyId || ObjectRef

8. Policy Integration & Bookmark Gates

Oxygen repositories enforce branch and bookmark protections via signed Policy objects (Oxygen Spec Section 14.5). OxygenFlow integrates provenance directly into policy evaluation during push validation.

8.1 Policy Gate Definition

A Policy rule governing a bookmark MAY demand valid OxygenFlow attestations. To mitigate a compromised authorized worker, high-security repositories can require Consensus Builds by setting the threshold > 1. This requires multiple independent runner identities to arrive at the exact same output hashes and both sign it.

PolicyRule {
  pattern: "bookmarks/production"
  keys: [ KeyId ]
  threshold: 1
  require: "signed"
  allow_conflicts: false
  require_attestations: [
    {
      type: "flow/provenance/v1",
      job: "release-provenance",
      require_hermetic: true,
      signer_roles: [ "official-worker" ]
    }
  ]
}

### 8.2 Push Verification Sequence (VCS Engine Enforcement)
When a push request arrives at an Oxygen server attempting to update a
protected bookmark:
1. Object Integrity: Validate that all changes, chunks, and blobs exist and match
   their BLAKE3 hashes.
2. Attestation Resolution: Verify that an Attest object of type
   "flow/provenance/v1" is present, referencing the exact heads of the new
   State.
3. Identity Verification: Validate that the attestation's composite signature
   resolves to a KeyId listed as an authorized delegate of the repository
   policy roots.
4. Invariant Checking: Confirm that the provenance statement records
   "hermetic: true" and exit code 0.
5. Atomic Update: If validation fails at any point, the entire push is refused
   with ok = false.

## 9. Zero-Environment Secret Brokering

OxygenFlow forbids the injection of raw secret strings into process environment
tables to eliminate accidental leaking via child process dumping, procfs
reads, and verbose compiler logging.

### 9.1 Ephemeral Secret Broker
1. If a job requires a credential (e.g., signing key, cloud deployment token),
   it declares a secret mount:
     secret "deploy-token" {
         vault-ref "infra/tokens/prod"
         mount-path "/run/secrets/token"
     }
2. The runner negotiates a short-lived token lease from the configured vault.
3. The secret is mounted onto an ephemeral, in-memory ramfs location inside
   the sandbox with access mode 0400, owned exclusively by the worker process.
4. Upon process termination, the memory pages are zeroized and the token is
   marked for immediate revocation at the vault.

## 10. Conformance and Verification Requirements

A conforming OxygenFlow implementation MUST pass the following tests:

1. Injection Immunity: Attempting to supply unescaped shell metacharacters
   (; && | ` $() \n) in any job field MUST pass those characters as literal
   bytes to argv; subshells MUST NOT be spawned.
2. FastCDC Determinism: Chunks produced by artifact extraction MUST match
   the gear table cuts and BLAKE3 hashes generated by Oxygen's core chunker.
3. Commutation Hit Invariance: For any two commuting changes A and B, running
   a pipeline on State(A, B) MUST reuse cached receipts generated on State(A)
   for any job whose scope does not intersect the touched paths of B.
4. Non-Downgrade Attestation: An attestation missing the ML-DSA-65 component
   MUST be rejected by policy verification.
5. Hermetic Network Isolation: Jobs configured with network "isolated" MUST
   have outgoing TCP SYN and UDP packets dropped at the hypervisor boundary.