matrix: registration token mode 0644 so tuwunel (dynamic user) can read it (#644)

hive-c0re/src/matrix.rs

@@ -123,7 +123,13 @@ pub fn ensure_register_token() -> Result<String> {
     }
     std::fs::write(path, format!("{token}\n"))
         .with_context(|| format!("write registration token to {}", path.display()))?;
-    let _ = std::fs::set_permissions(path, std::fs::Permissions::from_mode(0o600));
+    // Mode 0644: tuwunel inside the hive-matrix container runs as its
+    // own dynamic user (not root), so the bind-mounted file needs to
+    // be world-readable for tuwunel to load it. 0600 root-owned would
+    // block tuwunel with `Permission denied (os error 13)` (#644). On
+    // a single-tenant host the trade-off is acceptable; multi-tenant
+    // would need group-readable with explicit gid matching.
+    let _ = std::fs::set_permissions(path, std::fs::Permissions::from_mode(0o644));
     tracing::info!(path = %path.display(), "matrix: generated registration token");
     Ok(token)
 }

nix/modules/hive-matrix.nix

@@ -249,15 +249,27 @@ in
     # until the next restart). Idempotent: only writes when the file
     # doesn't exist. 32-byte hex = 64 chars, same shape hive-c0re's
     # `matrix::ensure_register_token` would produce.
+    #
+    # Mode 0644 (world-readable): tuwunel inside the hive-matrix
+    # container runs as its own dynamic user, which doesn't match the
+    # host's root UID, so a 0600 root-owned bind mount blocks tuwunel
+    # from reading the file (`Permission denied (os error 13)` —
+    # observed on #644). 0644 trades "any user on the host can read
+    # the token" for "tuwunel can actually start". On a single-tenant
+    # host that's an acceptable trade; tightening to a group-readable
+    # mode with explicit gid matching is a follow-up if multi-tenant
+    # hosts need it.
     system.activationScripts.hive-matrix-register-token = lib.stringAfter [ "var" ] ''
       tokenFile=${lib.escapeShellArg (toString cfg.registrationTokenFile)}
       if [ ! -s "$tokenFile" ]; then
         mkdir -p "$(dirname "$tokenFile")"
         head -c 32 /dev/urandom | od -An -tx1 | tr -d ' \n' > "$tokenFile"
         echo >> "$tokenFile"
-        chmod 600 "$tokenFile"
         echo "hive-matrix: generated registration token at $tokenFile"
       fi
+      # Always re-apply the mode (covers existing 0600 files from
+      # before #644 — `chmod` is idempotent).
+      chmod 644 "$tokenFile"
     '';
 
     containers.hive-matrix = {