diff --git a/docs/superpowers/specs/2026-07-31-xy-start-on-login-design.md b/docs/superpowers/specs/2026-07-31-xy-start-on-login-design.md
index deed339..9fe4461 100644
--- a/docs/superpowers/specs/2026-07-31-xy-start-on-login-design.md
+++ b/docs/superpowers/specs/2026-07-31-xy-start-on-login-design.md
@@ -154,8 +154,11 @@ which is too late to open a log file for the logger itself.
 For the `Cmd::Daemon` arm only, the subscriber writes to `stderr.and(file)` via
 `MakeWriterExt`, where the file half is `log_dir/xy.log` backed by the existing
 `xy_supervisor::logs::RotatingLogWriter` (10 MB × 5, the same rotation used for
-per-server logs). A small `MakeWriter` newtype wrapping
-`Arc<Mutex<RotatingLogWriter>>` bridges the two.
+per-server logs). No adapter type is needed: `tracing-subscriber` 0.3 already
+implements `MakeWriter` for `Mutex<W> where W: io::Write` (`fmt/writer.rs:808`)
+and for `Arc<W> where W: MakeWriter` (`fmt/writer.rs:694`), so
+`Arc<Mutex<RotatingLogWriter>>` satisfies the bound once Task 1 lands the
+`io::Write` impl.
 
 Every other subcommand keeps stderr-only logging; CLI output does not belong in
 the daemon's log.