--- a/internal/ledger/apply.go	2026-03-02 09:14:03.000000000 +0000
+++ b/internal/ledger/apply.go	2026-03-02 10:41:55.000000000 +0000
@@ -1,14 +1,21 @@
 package ledger
 
-import "errors"
+import (
+	"errors"
+	"fmt"
+)
 
 // ErrShortBalance is returned when a posting would drive the balance negative.
 var ErrShortBalance = errors.New("ledger: insufficient balance")
 
 // Apply posts one delta against the running balance and returns the new total.
+// A zero delta is a no-op and never reports an error.
 func Apply(balance, delta int64) (int64, error) {
+	if delta == 0 {
+		return balance, nil
+	}
 	if balance+delta < 0 {
-		return balance, ErrShortBalance
+		return balance, fmt.Errorf("%w: balance %d, requested %d", ErrShortBalance, balance, delta)
 	}
 	return balance + delta, nil
 }