fix(ui): per-key 编辑器画布画错容器、保存成功却不关弹窗

CDP 实测发现两个真 bug，都是复用画布时引入的。

一、画布画进了后台标签页。sortCanvasEl() 原本按文档顺序找，先命中
#scr-canvas（全局优先级页的画布）。而弹窗是挂在设置页之上的，两个画布
同时存在于 DOM —— 于是 per-key 的 36 条泳道被画进隐藏的全局画布，弹窗
里空空如也，回���全局页还会发现自己的链被覆盖了。

改为按 sortState.scope 解析：有 scope 就用 #key-auto-canvas，否则用
#scr-canvas。

二、保存成功却弹窗不关。!j.slots 分支里我写了 return，跳过了
keyAutoClose。写确实成功了（服务端已存），但用户看到弹窗还开着、按钮
还是禁用状态，会反复点保存。而且那条 toast 文案写成"保存后 AUTO 请求
会失败"，读起来像保存失败了 —— 一并改成"已保存，但槽位无法解析…"。

判据两条，变异验证：恢复按文档顺序查找 → 第一条判红；!slots 分支加
return → 第二条判红。第二条最初只查 keyAutoClose() 是否存在，变异加了
return 仍然通过，属于判据漏放，已改为扫描 try 块内 close 调用之前的
所有 return 语句。

CDP 复测（先开全局页制造干扰，再开 per-key 弹窗）：
- 弹窗画布 36 泳道，全局画布保持 4 泳道未被污染
- 保存 gpt-5.2@xinjianya 后弹窗关闭、服务端存储正确、scope 清空
- 重开弹窗读回 [["gpt-5.2@xinjianya"]]

Co-Authored-By: ModelRouter <noreply@modelrouter.dev>

internal/gateway/ui_key_auto_test.go

@@ -124,4 +124,83 @@ func TestUIStatsShowsPeriodWindow(t *testing.T) {
 	if n := strings.Count(src, "periodRange"); n < 2 {
 		t.Fatalf("i18n key periodRange appears %d time(s), want both zh and en", n)
 	}
-}
+}
+// Both canvases can exist in the DOM at once: the modal is mounted on top of
+// the settings tab, whose #scr-canvas stays alive behind it. Resolving the
+// canvas by document order (whichever comes first) painted the per-key chain
+// into the hidden background tab and left the dialog empty — and worse,
+// overwrote the global chain the user returns to. The lookup must follow
+// sortState.scope instead.
+func TestUISortCanvasResolvesByScope(t *testing.T) {
+	src := uiSource(t)
+	el := readFuncBody(t, src, "sortCanvasEl")
+	if !strings.Contains(el, "if (sortState.scope)") {
+		t.Fatal("sortCanvasEl must branch on sortState.scope, not document order")
+	}
+	if strings.Contains(el, `getElementById("scr-canvas")`) &&
+		strings.Index(el, `getElementById("scr-canvas")`) < strings.Index(el, "sortState.scope") {
+		t.Fatal("sortCanvasEl returns #scr-canvas before checking scope — the " +
+			"per-key editor paints into the global canvas")
+	}
+}
+
+// A successful save must close the dialog even when the slots do not resolve.
+// The write DID succeed; leaving the modal open makes the user click Save
+// again and again. This regressed once: the !slots branch returned early.
+func TestUIKeyAutoSaveClosesOnSuccess(t *testing.T) {
+	src := uiSource(t)
+	body := readFuncBody(t, src, "keyAutoSave")
+	// keyAutoClose() must be reached on every success path, not only in the
+	// happy branch.
+	iClose := strings.Index(body, "keyAutoClose()")
+	if iClose < 0 {
+		t.Fatal("keyAutoSave never calls keyAutoClose — the dialog would stay open")
+	}
+	iToast := strings.Index(body, "toast(")
+	if iToast >= 0 && iClose < iToast {
+		t.Fatal("keyAutoClose is called before the toast; the warning must be " +
+			"shown first or it is lost with the modal")
+	}
+	// An early `return` inside a branch bypasses keyAutoClose entirely, so
+	// merely finding the call is not enough: every `return` that sits between
+	// entering the try block and the close call is a path that leaves the
+	// dialog open after a successful write.
+	tryStart := strings.Index(body, "try {")
+	seg := body[tryStart:iClose]
+	for _, line := range strings.Split(seg, "\n") {
+		trimmed := strings.TrimSpace(line)
+		if trimmed == "return;" || strings.HasPrefix(trimmed, "return ") {
+			t.Fatal("a `return` before keyAutoClose leaves the dialog open after " +
+				"a successful save: " + trimmed)
+		}
+	}
+}
+
+// readFuncBody returns the source of a top-level function by name, using
+// brace matching so nested blocks do not truncate it.
+func readFuncBody(t *testing.T, src, name string) string {
+	t.Helper()
+	idx := strings.Index(src, "function "+name+"(")
+	if idx < 0 {
+		t.Fatalf("function %s not found", name)
+	}
+	start := strings.Index(src[idx:], "{")
+	if start < 0 {
+		t.Fatalf("function %s has no body", name)
+	}
+	i := idx + start
+	depth := 0
+	for j := i; j < len(src); j++ {
+		switch src[j] {
+		case '{':
+			depth++
+		case '}':
+			depth--
+			if depth == 0 {
+				return src[i : j+1]
+			}
+		}
+	}
+	t.Fatalf("function %s body is unterminated", name)
+	return ""
+}