nixos-module: fix caddy Host-header matching for 127.0.0.1/[::1]

Caddy strictly matches vhosts on the exact Host header, unlike nginx
where a single vhost acts as the default regardless of Host. With
hostname = "localhost" (the local-dev default), visiting the VM via
http://127.0.0.1:PORT instead of http://localhost:PORT sent a Host
header matching no vhost, and Caddy silently returned an empty 200 OK
- a genuine white screen with no error anywhere (not in the console,
not in the network tab).

Adds serverAliases for 127.0.0.1:80 and [::1]:80 to the caddy vhost
when hostname is "localhost", so all three ways of reaching the local
VM resolve to the same site block. Verified directly: before this
fix, curl with `Host: 127.0.0.1` got an empty response while `Host:
localhost` got the full app shell; after, all three (localhost,
127.0.0.1, [::1]) return the same 200 response.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

CLAUDE.md

@@ -112,6 +112,10 @@ expect Nix to report the correct hash on a failed build (or use `nix-prefetch`/`
     earlier version of this module additionally set a second, static set of `Access-Control-*` headers at the
     proxy level, which browsers reject as conflicting duplicates (server-to-server/curl checks don't notice,
     since only browsers enforce CORS header validation).
+  - Caddy matches vhosts on the exact `Host` header, unlike nginx (where a single vhost acts as the default
+    regardless of `Host`). When `hostname == "localhost"`, the caddy vhost adds `serverAliases` for
+    `127.0.0.1:80`/`[::1]:80` too — otherwise visiting the VM via the IP literal instead of `localhost` matches no
+    vhost and Caddy silently returns an empty `200 OK` (a blank page with no error anywhere).
   - Chromium is required at runtime for PDF generation (`PDF_GENERATOR=snappdf`, `SNAPPDF_CHROMIUM_PATH`) and is
     added to the PHP-FPM and data-setup services' `path`.
 

nixos-module/invoiceninja.nix

@@ -557,6 +557,14 @@ in
           cfg.proxy.caddyConfig
           {
             hostName = lib.mkForce proto_hostname;
+            # Caddy matches vhosts on the exact Host header, unlike nginx's single-vhost-is-default
+            # behavior. For local dev, accept requests to 127.0.0.1/[::1] too - otherwise visiting
+            # via the IP literal instead of "localhost" hits no vhost and gets an empty 200 response
+            # (a silent white screen, no error anywhere).
+            serverAliases = lib.mkIf (cfg.hostname == "localhost") [
+              "127.0.0.1:80"
+              "[::1]:80"
+            ];
             extraConfig = ''
               encode zstd gzip
               root ${invoiceninja}/public