fix(lifecycle): preserve mixed shutdown error identity

README.md

@@ -35,6 +35,11 @@ an injected signal cancels work before teardown. One shared shutdown deadline
 abandons shutdown. Callbacks must cooperate: abandonment cannot kill goroutines,
 and the caller owns process exit and any unreleased resources.
 
+During App-initiated shutdown, callback errors containing only the callback's
+context cancellation are omitted. Mixed cancellation and independent failures
+are retained intact to preserve wrapper types, identity and custom matching;
+these errors may still match cancellation through `errors.Is`.
+
 The caller owns signal subscription, SIGINT/SIGTERM filtering, a channel buffered
 for at least two signals, and subscription cleanup. Nil signals disable reception.
 There are no signal subscriptions, process exits, external dependencies or CLI