From 86ad8bc914ff4e6483352791aa7d283e1504cb7f Mon Sep 17 00:00:00 2001
From: atlas <atlas@pr1ma.darkest.space>
Date: Sun, 21 Jun 2026 14:47:15 +0200
Subject: [PATCH] hive-ci: build locally when a remote builder is unreachable

The CI container set `nix.settings.sandbox-fallback` but never
`nix.settings.fallback`, so a cache-miss build with an unreachable
remote build machine had no local fallback and hard-failed. A single
down or DNS-unresolvable `nix.buildMachines` host therefore turned every
fresh `nix flake check` red hive-wide, in ~30s, even for diffs that
can't affect the nix build (pure JS/markdown). Add
`nix.settings.fallback = true` so CI degrades to a slower local build
instead of failing.
---
 nix/modules/hive-ci.nix | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/nix/modules/hive-ci.nix b/nix/modules/hive-ci.nix
index a4168136..a8f0012c 100644
--- a/nix/modules/hive-ci.nix
+++ b/nix/modules/hive-ci.nix
@@ -393,6 +393,13 @@ in
           # sandboxing always fails. Fall back to unsandboxed builds.
           # See docs/gotchas.md.
           nix.settings.sandbox-fallback = lib.mkForce true;
+          # Build locally when a configured remote builder is unreachable
+          # instead of hard-failing. Without this a single down/unresolvable
+          # build machine (e.g. a DNS blip on a `nix.buildMachines` host)
+          # turns every cache-miss `nix flake check` red hive-wide — CI must
+          # degrade to a slower local build, not fail. (`sandbox-fallback`
+          # above is unrelated: it only governs the sandbox, not builders.)
+          nix.settings.fallback = lib.mkForce true;
           nix.settings.experimental-features = [
             "nix-command"
             "flakes"