every.channel/evolution/proposals/ECP-0070-relay-cas-archival.md

ECP-0070: Relay-Native CAS Archival + NixOS Auto-Archive Service

Status: Implemented

Summary

Add a first-party archival path for MoQ relay streams:

1. ec-node wt-archive:

• Subscribe to a relay broadcast over WebTransport/MoQ.
• Persist each received group payload as a content-addressed object (BLAKE3).
• Append per-track JSONL index records ("manifests") that reference CAS object hashes/paths.

2. Extend the NixOS services.every-channel.ec-node module with archive.* options:

• Poll every.channel public stream directory.
• Auto-start one wt-archive worker per discovered broadcast.
• Store large CAS blobs and manifest indices in separately configurable roots.

Motivation

We need durable, low-duplication TV archive storage on dedicated storage hosts.

• Relay ingestion makes archive nodes location-agnostic.
• CAS enables deduplication and integrity-friendly storage semantics.
• Separate manifest/index storage allows faster metadata operations and simpler backup policy.
• Nix-managed host config keeps archival behavior immutable and repeatable.

Decision

• Introduce ec-node wt-archive as the minimal relay subscriber for archival.
• Use BLAKE3 object IDs and a sharded filesystem layout (<cas-root>/objects/blake3/aa/<hash>.bin).
• Write append-only JSONL records per broadcast/track under a configurable manifest directory.
• Add services.every-channel.ec-node.archive.* in the Nix module to auto-discover and archive public streams.

Initial default archived tracks target current relay publisher output:

• catalog.json
• init.mp4
• video0.m4s
• audio0.m4s

Consequences

Pros:

• Immediate archival path without requiring browser components.
• Works with current Cloudflare relay + WebTransport deployment.
• Fully declarative deployment via existing Nix input wiring.

Tradeoffs:

• First version archives raw group payloads and does not yet normalize across track schema variants.
• Discovery source is the web public stream list (not full control-topic gossip ingestion).
• Per-broadcast workers are process-based and best-effort supervised.

Alternatives considered

• Rely on browser-side replay caches only. Rejected because it does not provide durable archival storage.
• Archive only manifests without CAS payloads. Rejected because replay/integrity requires retained object bytes.

Rollout

1. Ship wt-archive command in ec-node.
2. Extend Nix module with archive.*.
3. Enable on storage host(s) with:

• CAS root on large ZFS pool.
• manifest root on separate filesystem/dataset.

Reversibility

• Disable services.every-channel.ec-node.archive.enable.
• Existing CAS/manifests remain inert on disk and can be pruned independently.