fix(api): 未改动任何字段的 PATCH 返回空 patched 数组而非 null

internal/api/handlers_user.go

@@ -683,7 +683,9 @@ func (a *API) handlePatchServer(w http.ResponseWriter, r *http.Request) {
 	// the SAME helpers the create form uses. `changed` records what actually moves
 	// so the response and audit name the real mutation.
 	var patch ServerSpecPatch
-	var changed []string
+	// Non-nil so a patch that moves nothing (re-picking the image a server is
+	// already pinned to) still answers "patched": [], as the API documents.
+	changed := []string{}
 	// imageFrom is the image a confirmed image change replaced, for the audit row.
 	var imageFrom string
 

internal/api/images_pin_test.go

@@ -6,6 +6,7 @@ import (
 	"errors"
 	"fmt"
 	"net/http"
+	"strings"
 	"testing"
 
 	"felis.lolicon.best/internal/imagepin"
@@ -136,6 +137,9 @@ func TestPatchServerImageSamePinIsNoChange(t *testing.T) {
 	if p := cl.patched["survival"]; p.Image != nil {
 		t.Errorf("patched image = %q, want no image change", *p.Image)
 	}
+	if !strings.Contains(w.Body.String(), `"patched":[]`) {
+		t.Errorf("body = %s, want an empty patched list", w.Body.String())
+	}
 	if len(repo.audits) != 1 || repo.audits[0].Payload != nil {
 		t.Errorf("audits = %+v, want a plain server.patch", repo.audits)
 	}