# OxygenFlow (flow) — Deterministic Execution & Provenance Pipeline Specification

| | |
|---|---|
| **Format version** | 1 |
| **Date** | 2026-09-28 |
| **Status** | Draft 0.1 |
| **Target VCS** | Oxygen (oxy) Draft 0.8i |
| **Audience** | Implementers, Security Architects, and Systems Engineers |


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

```kdl
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

```json
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):

```cbor
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.

```json
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.
## 11. Runner Capabilities and Placement (proposed 2026-10-04)

A runner MUST never take a job it cannot run or cannot finish well: the
wrong architecture, no hardware virtualisation for the MicroVM tier, too
little memory, an image it does not hold, or a machine too slow for the
job's time limit. Today a runner reports its architecture, OS, labels,
job slots, memory and vCPUs when it registers and on each claim, and a
claim carries the tiers it can run, the memory and vCPUs free now, and
the images it holds; the hub matches tier, room, labels, scope and image.
What is missing: architecture is reported but never matched (an image's
architecture is implicit in its bytes), a pipeline cannot say which
architecture it needs or offer a rootfs per architecture, speed and load
play no part, and a runner cannot decline a job it was handed.

### 11.1 Capability Profile

At registration and on every claim a runner sends its profile:

| Field | Meaning |
|---|---|
| `arch`, `os`, `kernel` | `x86_64`, `aarch64`, `riscv64`, …; the kernel release |
| `tiers` | The sandbox tiers it can honour: `microvm` only with `/dev/kvm` usable (a board without KVM, such as an OrangePi RV2, offers `syscall`, §4.2, and `wasm`) |
| `memory_mib`, `cpus`, `max_jobs` | What its jobs share |
| `images` | The rootfs images it holds, each with the architecture its manifest records (§11.2) |
| `labels` | As §3.1 |
| `speed` | A class from 1 (slow) to 5 (fast), measured at `flow runner register` and `flow runner bench` by a fixed workload (BLAKE3 over 256 MiB and the compilation of a fixed C file), bucketed so that two machines of the same class finish a job within a factor of two of each other |
| `load` | The 1-minute load average divided by `cpus`, memory free now, jobs running |

### 11.2 Image Manifests Carry the Architecture

`flow rootfs import` reads the ELF header of the image's `/bin/sh` and
records its architecture in the CAS manifest beside the hash. A runner
refuses to import an image for another architecture (there is no
emulation tier). An image imported before this section has no recorded
architecture and is treated as the importing runner's.

### 11.3 Job Requirements

Hard requirements, all of which a runner MUST satisfy to be offered the
job: the sandbox's tier, its rootfs (hence the image's architecture),
`memory-limit`, `cpus`, every `runs-on` label of the job and its sandbox,
and the runner's scope (OxygenHub spec §13.2). Two additions to the
language:

- `arch "riscv64"` on a sandbox pins the architecture; without it the
  architecture is the rootfs image's.
- A rootfs per architecture: `rootfs { x86_64 "cas://blob/…"; riscv64 "cas://blob/…" }`.
  The job runs on whichever architecture takes it; the receipt and the
  provenance record the architecture and image used, and a check's
  description names them.

Soft requirements guide placement but never block it: a job's `timeout`
against the runner's speed class. The hub keeps, per job hash and speed
class, the median duration of past runs; a runner whose class predicts a
duration over the limit is offered the job only when no better runner
is free.

### 11.4 Placement

The hub filters by the hard requirements, then ranks the runners that
remain: idle before busy (`load`), a higher speed class first, a runner
already holding the image before one that must fetch it (§5), fewer jobs
waiting on it first. A job no runner can satisfy waits and the queue
says what it waits for: tier, architecture, image, memory, labels or
scope, so the gap is visible rather than a silent stall.

### 11.5 Declining

A runner double-checks a claim before it starts: the architecture, that
`/dev/kvm` opens for the MicroVM tier, that the image's blob is present
and verifies, that the memory is free. If any check fails it answers the
hub with `declined` and a reason instead of running and failing; the hub
re-queues the job, never offers it to that runner again until its
profile changes, records the decline on the runner's page, and after
three declines by different runners marks the job `unplaceable` with the
reasons. A decline is never a failed check on the state.

### 11.6 Conformance

1. Architecture Safety: a job whose image is `x86_64` MUST never be
   offered to a `riscv64` runner, with or without the image copied there.
2. Tier Safety: a runner without `/dev/kvm` MUST NOT be offered a
   MicroVM job, and MUST decline one if handed it.
3. Room: a job whose `memory-limit` exceeds the runner's free memory
   MUST wait, not be killed.
4. Visibility: a job nobody can take MUST say why on the queue within
   one scheduling pass.
5. Preference: with two idle runners that both satisfy a job, the hub
   MUST offer it to the higher speed class, and to the one holding the
   image when classes tie.