nix: allow archive relay URL affinity override

evolution/proposals/ECP-0073-archive-relay-affinity-override.md

@@ -0,0 +1,33 @@
+# ECP-0073: Archive Relay Affinity Override
+
+## Context
+
+`wt-archive` workers discover streams from `/api/public-streams` and subscribe to the listed `relay_url`. In practice, `cdn.moq.dev` resolves to region-local relay IPs, and broadcasts published from one region are not consistently visible from another region endpoint.
+
+For archive nodes running in a different region than publishers, this causes workers to connect successfully but wait indefinitely for broadcast announcements.
+
+## Decision
+
+Add an explicit Nix module option:
+
+- `services.every-channel.ec-node.archive.relayUrlOverride` (nullable string)
+
+When set, archive workers ignore per-entry `relay_url` from directory listings and always subscribe through the configured override URL.
+
+This allows operators to pin archive ingestion to the same relay endpoint used by publishers without changing public directory payloads.
+
+## Why
+
+- Restores deterministic archival ingestion across regions.
+- Keeps deployment-level control in Nix (no app-level migration needed).
+- Reversible with a single config change.
+
+## Rollout
+
+1. Set `archive.relayUrlOverride` on archive hosts that need relay affinity.
+2. If override uses an IP literal, enable `archive.tlsDisableVerify = true` until SNI-preserving IP overrides are implemented.
+3. Rebuild host and verify manifest growth.
+
+## Reversibility
+
+Unset `archive.relayUrlOverride` to return to directory-provided `relay_url` behavior.

nix/modules/ec-node.nix

@@ -222,6 +222,12 @@ in
         description = "Discovery poll interval for public streams.";
       };
 
+      relayUrlOverride = lib.mkOption {
+        type = lib.types.nullOr lib.types.str;
+        default = null;
+        description = "Optional fixed relay URL override for archive workers (bypasses per-stream relay_url from directory entries).";
+      };
+
       streamPrefix = lib.mkOption {
         type = lib.types.nullOr lib.types.str;
         default = null;
@@ -669,6 +675,7 @@ in
               output_dir=${lib.escapeShellArg cfg.archive.outputDir}
               manifest_dir=${lib.escapeShellArg cfg.archive.manifestDir}
               relay_fallback=${lib.escapeShellArg cfg.relayUrl}
+              relay_override=${lib.escapeShellArg (if cfg.archive.relayUrlOverride == null then "" else cfg.archive.relayUrlOverride)}
               stream_prefix=${lib.escapeShellArg archivePrefix}
               state_dir="/run/every-channel/archive"
               pids_dir="$state_dir/pids"
@@ -705,7 +712,9 @@ in
                   if [[ -n "$stream_prefix" && "$name" != "$stream_prefix"* ]]; then
                     continue
                   fi
-                  if [[ -z "$relay" ]]; then
+                  if [[ -n "$relay_override" ]]; then
+                    relay="$relay_override"
+                  elif [[ -z "$relay" ]]; then
                     relay="$relay_fallback"
                   fi