fix(cache): pretty-print cache envelope

Co-Authored-By: Virgil <virgil@lethean.io>

cache.go

@@ -166,12 +166,12 @@ func (c *Cache) Set(key string, data any) error {
 		ExpiresAt: time.Now().Add(ttl),
 	}
 
-	entryResult := core.JSONMarshal(entry)
-	if !entryResult.OK {
-		return core.E("cache.Set", "failed to marshal cache entry", entryResult.Value.(error))
+	entryBytes, err := json.MarshalIndent(entry, "", "  ")
+	if err != nil {
+		return core.E("cache.Set", "failed to marshal cache entry", err)
 	}
 
-	if err := c.medium.Write(path, string(entryResult.Value.([]byte))); err != nil {
+	if err := c.medium.Write(path, string(entryBytes)); err != nil {
 		return core.E("cache.Set", "failed to write cache file", err)
 	}
 	return nil

cache_test.go

@@ -3,6 +3,7 @@
 package cache_test
 
 import (
+	"strings"
 	"testing"
 	"time"
 
@@ -60,6 +61,9 @@ func TestCache_New_Good(t *testing.T) {
 	if err != nil {
 		t.Fatalf("Read failed: %v", err)
 	}
+	if !strings.Contains(raw, "\n  \"data\":") {
+		t.Fatalf("expected pretty-printed cache entry, got %q", raw)
+	}
 
 	entry := readEntry(t, raw)
 	ttl := entry.ExpiresAt.Sub(entry.CachedAt)