feat: mail service

mail/internal/adapters/redisstate/errors.go

@@ -0,0 +1,12 @@
+// Package redisstate defines the frozen Redis keyspace, strict JSON records,
+// and low-level mutation helpers used by future Mail Service Redis adapters.
+package redisstate
+
+import "errors"
+
+var (
+	// ErrConflict reports that a Redis mutation could not be applied because
+	// one of the watched or newly created keys already existed or changed
+	// concurrently.
+	ErrConflict = errors.New("redis state conflict")
+)