diff --git a/apps/desktop/src/components/codeSnapshot/CodeSnapshotDialog.vue b/apps/desktop/src/components/codeSnapshot/CodeSnapshotDialog.vue
index 0a389ea300..a953ecc048 100644
--- a/apps/desktop/src/components/codeSnapshot/CodeSnapshotDialog.vue
+++ b/apps/desktop/src/components/codeSnapshot/CodeSnapshotDialog.vue
@@ -156,7 +156,9 @@ const previewVisible = computed(() => open.value && !!props.source);
 
 <template>
   <Dialog v-model:open="open">
-    <DialogContent class="max-h-[86vh] overflow-y-auto border border-border !bg-background text-foreground shadow-2xl !backdrop-blur-none sm:max-w-[860px]">
+    <!-- 对话框整体限高：高度上限跟随 --dbx-viewport-height（兼容旧版 WebView 中 vh 不准的情况）；
+         内部采用纵向 flex 布局，header/footer 固定，只有中间预览区滚动，保证底部按钮始终可见 -->
+    <DialogContent class="flex max-h-[calc(var(--dbx-viewport-height)-2rem)] flex-col overflow-hidden border border-border !bg-background text-foreground shadow-2xl !backdrop-blur-none sm:max-w-[860px]">
       <DialogHeader>
         <DialogTitle class="flex items-center gap-2">
           <Camera class="h-5 w-5 text-primary" />
@@ -164,11 +166,14 @@ const previewVisible = computed(() => open.value && !!props.source);
         </DialogTitle>
       </DialogHeader>
 
-      <div v-if="previewVisible" class="flex flex-col gap-4 md:flex-row">
+      <!-- min-h-0 flex-1：让内容区占满剩余高度并允许收缩，超高时由预览区内部滚动而不是撑破对话框 -->
+      <div v-if="previewVisible" class="flex min-h-0 flex-1 flex-col gap-4 md:flex-row">
         <!-- Snapshot preview -->
-        <div class="min-w-0 flex-1">
-          <div ref="previewWrapRef" class="max-h-[56vh] overflow-auto rounded-md border bg-muted/30 p-3">
-            <div v-html="snapshotHtml" class="inline-block min-w-[320px]" />
+        <div class="flex min-h-0 min-w-0 flex-1 flex-col">
+          <!-- 预览容器随父级伸缩（flex-1 + min-h-0），代码/图片过长时仅此处出现滚动条 -->
+          <div ref="previewWrapRef" class="min-h-0 flex-1 overflow-auto rounded-md border bg-muted/30 p-3">
+            <!-- 截图内容按代码的固有宽度展开，不跟随外层 flex 容器收缩；外层预览容器负责横向滚动 -->
+            <div v-html="snapshotHtml" class="flex w-max min-w-[320px] flex-none" />
           </div>
         </div>
 
diff --git a/apps/desktop/src/components/codeSnapshot/__tests__/CodeSnapshotDialogLayout.spec.ts b/apps/desktop/src/components/codeSnapshot/__tests__/CodeSnapshotDialogLayout.spec.ts
new file mode 100644
index 0000000000..a3b5bed288
--- /dev/null
+++ b/apps/desktop/src/components/codeSnapshot/__tests__/CodeSnapshotDialogLayout.spec.ts
@@ -0,0 +1,11 @@
+import { readFileSync } from "node:fs";
+import { describe, expect, it } from "vitest";
+
+const dialogSource = readFileSync(new URL("../CodeSnapshotDialog.vue", import.meta.url), "utf8");
+
+describe("CodeSnapshotDialog layout", () => {
+  it("keeps the exported snapshot at its intrinsic width inside the scrollable preview", () => {
+    // 截图节点不能被外层 flex 布局压缩，否则长代码导出时会被裁切或错误换行。
+    expect(dialogSource).toContain('v-html="snapshotHtml" class="flex w-max min-w-[320px] flex-none"');
+  });
+});
diff --git a/apps/desktop/src/lib/codeSnapshot/__tests__/codeSnapshot.spec.ts b/apps/desktop/src/lib/codeSnapshot/__tests__/codeSnapshot.spec.ts
index 36ae3ce5ac..5bb884f4cd 100644
--- a/apps/desktop/src/lib/codeSnapshot/__tests__/codeSnapshot.spec.ts
+++ b/apps/desktop/src/lib/codeSnapshot/__tests__/codeSnapshot.spec.ts
@@ -32,6 +32,9 @@ describe("renderCodeSnapshotHtml", () => {
     expect(html).toContain('class="dbx-code-snapshot"');
     expect(html).toContain('data-snapshot-appearance="dark"');
     expect(html).toContain('class="dbx-code-snapshot__pre dbx-code-snapshot__pre--numbered"');
+    expect(html).toContain(".dbx-code-snapshot *");
+    expect(html).toContain("border: 0");
+    expect(html).toContain("outline: 0");
   });
 
   it("renders macOS traffic lights and an optional title by default", async () => {
@@ -93,25 +96,72 @@ describe("renderCodeSnapshotHtml", () => {
     toPng.mockResolvedValue("data:image/png;base64,test");
     vi.stubGlobal("window", { devicePixelRatio: 3 });
     try {
-      await snapshotElementToPng({ offsetWidth: 320, offsetHeight: 160 } as HTMLElement);
+      await snapshotElementToPng({ offsetWidth: 320, offsetHeight: 160, scrollWidth: 640, scrollHeight: 240 } as HTMLElement);
 
       expect(toPng).toHaveBeenLastCalledWith(
         expect.anything(),
         expect.objectContaining({
-          width: 320,
-          height: 160,
-          pixelRatio: 2,
+          width: 640,
+          height: 240,
+          scale: 2,
+          style: {
+            width: "640px",
+            height: "240px",
+          },
         }),
       );
 
       vi.stubGlobal("window", { devicePixelRatio: 0 });
-      await snapshotElementToPng({ offsetWidth: 320, offsetHeight: 160 } as HTMLElement);
-      expect(toPng).toHaveBeenLastCalledWith(expect.anything(), expect.objectContaining({ pixelRatio: 1 }));
+      await snapshotElementToPng({ offsetWidth: 320, offsetHeight: 160, scrollWidth: 320, scrollHeight: 160 } as HTMLElement);
+      expect(toPng).toHaveBeenLastCalledWith(expect.anything(), expect.objectContaining({ scale: 1 }));
     } finally {
       vi.unstubAllGlobals();
     }
   });
 
+  it("reduces the export scale when a wide snapshot reaches the canvas edge limit", async () => {
+    toPng.mockResolvedValue("data:image/png;base64,test");
+    vi.stubGlobal("window", { devicePixelRatio: 2 });
+    try {
+      await snapshotElementToPng({ offsetWidth: 10_000, offsetHeight: 100, scrollWidth: 10_000, scrollHeight: 100 } as HTMLElement);
+
+      expect(toPng).toHaveBeenLastCalledWith(expect.anything(), expect.objectContaining({ scale: 16_384 / 10_000 }));
+    } finally {
+      vi.unstubAllGlobals();
+    }
+  });
+
+  it("reduces the export scale when a tall snapshot reaches the canvas edge limit", async () => {
+    toPng.mockResolvedValue("data:image/png;base64,test");
+    vi.stubGlobal("window", { devicePixelRatio: 2 });
+    try {
+      await snapshotElementToPng({ offsetWidth: 100, offsetHeight: 10_000, scrollWidth: 100, scrollHeight: 10_000 } as HTMLElement);
+
+      expect(toPng).toHaveBeenLastCalledWith(expect.anything(), expect.objectContaining({ scale: 16_384 / 10_000 }));
+    } finally {
+      vi.unstubAllGlobals();
+    }
+  });
+
+  it("reduces the export scale when a dense snapshot reaches the total pixel limit", async () => {
+    toPng.mockResolvedValue("data:image/png;base64,test");
+    vi.stubGlobal("window", { devicePixelRatio: 2 });
+    try {
+      await snapshotElementToPng({ offsetWidth: 6_000, offsetHeight: 6_000, scrollWidth: 6_000, scrollHeight: 6_000 } as HTMLElement);
+
+      expect(toPng).toHaveBeenLastCalledWith(expect.anything(), expect.objectContaining({ scale: Math.sqrt((64 * 1024 * 1024) / (6_000 * 6_000)) }));
+    } finally {
+      vi.unstubAllGlobals();
+    }
+  });
+
+  it("rejects snapshots that exceed the safe rendering budget at 1x", async () => {
+    toPng.mockClear();
+
+    await expect(snapshotElementToPng({ offsetWidth: 20_000, offsetHeight: 100, scrollWidth: 20_000, scrollHeight: 100 } as HTMLElement)).rejects.toThrow("Snapshot is too large to export safely (20000 × 100px)");
+    expect(toPng).not.toHaveBeenCalled();
+  });
+
   it("propagates a failed native save instead of reporting a browser download", async () => {
     isTauriRuntime.mockReturnValue(true);
     save.mockResolvedValue("C:\\Users\\example\\snapshot.png");
diff --git a/apps/desktop/src/lib/codeSnapshot/codeSnapshot.ts b/apps/desktop/src/lib/codeSnapshot/codeSnapshot.ts
index a5b87211e7..89cf5414c1 100644
--- a/apps/desktop/src/lib/codeSnapshot/codeSnapshot.ts
+++ b/apps/desktop/src/lib/codeSnapshot/codeSnapshot.ts
@@ -57,12 +57,19 @@ const SNAPSHOT_LINE_NUMBER: Record<AppThemeAppearance, string> = {
 
 const TRAFFIC_LIGHT_COLORS = ["#ff5f57", "#febc2e", "#28c840"] as const;
 const MAX_EXPORT_PIXEL_RATIO = 2;
+const MAX_EXPORT_CANVAS_EDGE = 16_384;
+const MAX_EXPORT_CANVAS_PIXELS = 64 * 1024 * 1024;
 
 /**
  * Self-contained stylesheet embedded in every snapshot DOM. Keep it prefix
  * namespaced (`dbx-code-snapshot`) so it never leaks into the app chrome.
  */
 export const CODE_SNAPSHOT_CSS = `
+.dbx-code-snapshot,
+.dbx-code-snapshot * {
+  border: 0;
+  outline: 0;
+}
 .dbx-code-snapshot {
   border-radius: 8px;
   overflow: hidden;
@@ -180,13 +187,26 @@ export async function renderCodeSnapshotHtml(source: CodeSnapshotSource, options
 /** Convert a snapshot DOM element into a PNG data URL. */
 export async function snapshotElementToPng(element: HTMLElement): Promise<string> {
   const domtoimage = (await import("dom-to-image-more")).default;
+  // 预览区允许滚动，因此导出尺寸必须覆盖完整内容，而不是只取当前可见宽度。
+  const width = Math.max(element.offsetWidth, element.scrollWidth);
+  const height = Math.max(element.offsetHeight, element.scrollHeight);
+  const basePixels = width * height;
+  if (width > MAX_EXPORT_CANVAS_EDGE || height > MAX_EXPORT_CANVAS_EDGE || basePixels > MAX_EXPORT_CANVAS_PIXELS) {
+    throw new Error(`Snapshot is too large to export safely (${width} × ${height}px). Reduce the code size and try again.`);
+  }
+
+  const targetScale = Math.min(MAX_EXPORT_PIXEL_RATIO, Math.max(1, typeof window === "undefined" ? 1 : window.devicePixelRatio || 1));
+  const scale = Math.min(targetScale, MAX_EXPORT_CANVAS_EDGE / width, MAX_EXPORT_CANVAS_EDGE / height, Math.sqrt(MAX_EXPORT_CANVAS_PIXELS / basePixels));
   return domtoimage.toPng(element, {
     quality: 1,
-    width: element.offsetWidth,
-    height: element.offsetHeight,
-    // Preserve text sharpness on high-DPI displays without letting a large
-    // selected block allocate an unbounded export canvas.
-    pixelRatio: Math.min(MAX_EXPORT_PIXEL_RATIO, Math.max(1, typeof window === "undefined" ? 1 : window.devicePixelRatio || 1)),
+    width,
+    height,
+    // dom-to-image-more 使用 scale 放大实际画布；pixelRatio 不是该库支持的参数。
+    scale,
+    style: {
+      width: `${width}px`,
+      height: `${height}px`,
+    },
   });
 }