diff --git a/src/browser/features/Tools/Shared/NestedToolsContainer.tsx b/src/browser/features/Tools/Shared/NestedToolsContainer.tsx
index df5f6b73fc..e1f94048b1 100644
--- a/src/browser/features/Tools/Shared/NestedToolsContainer.tsx
+++ b/src/browser/features/Tools/Shared/NestedToolsContainer.tsx
@@ -13,7 +13,9 @@ interface NestedToolsContainerProps {
 
 /**
  * Renders nested tool calls as a list.
- * Parent component provides the container styling (dashed border).
+ * The parent owns the border and padding. Preserve that inset for every nested
+ * tool: cancelling it with negative margins makes bordered cards touch the frame
+ * and forces each new tool renderer to work around the nesting layout.
  */
 export const NestedToolsContainer: React.FC<NestedToolsContainerProps> = ({
   calls,
@@ -24,7 +26,7 @@ export const NestedToolsContainer: React.FC<NestedToolsContainerProps> = ({
   if (calls.length === 0) return null;
 
   return (
-    <div className="-mx-3 space-y-3">
+    <div className="space-y-3">
       {calls.map((call) => {
         const status = getNestedToolStatus(
           call.state,
diff --git a/src/browser/stories/App.codeExecution.stories.tsx b/src/browser/stories/App.codeExecution.stories.tsx
new file mode 100644
index 0000000000..5a5d7a5012
--- /dev/null
+++ b/src/browser/stories/App.codeExecution.stories.tsx
@@ -0,0 +1,143 @@
+import { expect, userEvent, within } from "@storybook/test";
+import { getAutoExpandPrefsKey } from "@/common/constants/storage";
+import { updatePersistedState } from "@/browser/hooks/usePersistedState";
+import { appMeta, AppWithMocks, type AppStory } from "./meta.js";
+import { setupSimpleChatStory } from "./helpers/chatSetup";
+import { PhoneSubagentReportDecorator } from "./helpers/subagentReportStory";
+import { collapseLeftSidebar, collapseRightSidebar } from "./helpers/uiState";
+import { createAssistantMessage } from "./mocks/messages";
+import { createWorkspace, STABLE_TIMESTAMP } from "./mocks/workspaces";
+
+const WORKSPACE_ID = "ws-code-execution-spacing";
+const REVIEWER_ID = "code-execution-reviewer";
+
+function setupNestedToolsStory() {
+  collapseLeftSidebar();
+  collapseRightSidebar();
+  updatePersistedState(getAutoExpandPrefsKey(WORKSPACE_ID), {});
+  return setupSimpleChatStory({
+    workspaceId: WORKSPACE_ID,
+    workspaceName: "nested-tool-spacing",
+    projectName: "mux",
+    messages: [
+      createAssistantMessage("nested-tools", "", {
+        historySequence: 1,
+        timestamp: STABLE_TIMESTAMP,
+        toolCalls: [
+          {
+            type: "dynamic-tool",
+            toolCallId: "code-execution",
+            toolName: "code_execution",
+            state: "output-available",
+            input: { code: "mux.file_read({ path: 'src/config.ts' });" },
+            output: { success: true, toolCalls: [], consoleOutput: [] },
+            nestedCalls: [
+              {
+                toolCallId: "nested-report",
+                toolName: "agent_report",
+                state: "output-available",
+                input: {
+                  title: "Layout review",
+                  reportMarkdown: "The tool cards should stay inside the code execution border.",
+                },
+                output: { success: true },
+              },
+              {
+                toolCallId: "nested-read",
+                toolName: "file_read",
+                state: "output-available",
+                input: { path: "src/config.ts" },
+                output: {
+                  success: true,
+                  lines_read: 1,
+                  file_size: 24,
+                  content: "1\tconst debug = false;",
+                },
+              },
+              {
+                toolCallId: "nested-message",
+                toolName: "task_send_message",
+                state: "output-available",
+                input: {
+                  task_id: REVIEWER_ID,
+                  message:
+                    "Check both collapsed and expanded cards at phone widths.\n\nInspect src/browser/features/Tools/Shared/NestedToolsContainer.tsx for spacing shared by all nested tools.",
+                },
+                output: { status: "reactivated", taskId: REVIEWER_ID },
+              },
+            ],
+          },
+        ],
+      }),
+    ],
+    additionalWorkspaces: [
+      createWorkspace({
+        id: REVIEWER_ID,
+        name: "reviewer",
+        title: "Reviewer",
+        projectName: "mux",
+        parentWorkspaceId: WORKSPACE_ID,
+        taskStatus: "running",
+      }),
+    ],
+  });
+}
+
+export default {
+  ...appMeta,
+  title: "App/CodeExecution",
+};
+
+export const NestedTools: AppStory = {
+  render: () => <AppWithMocks setup={setupNestedToolsStory} />,
+  globals: { viewport: { value: "desktop", isRotated: false } },
+  parameters: { pixel: { matrix: { viewports: ["laptop"] } } },
+  play: async ({ canvasElement }) => {
+    const canvas = within(canvasElement);
+    const toggle = await canvas.findByRole("button", { name: "Message to Reviewer" });
+    const frame = canvas.getByRole("group", { name: "Code Execution" });
+    const legend = frame.querySelector("legend")!;
+    const tools = frame.querySelector(":scope > div")!;
+    await expect(tools.children).toHaveLength(3);
+
+    const checkSpacing = async () => {
+      const bounds = frame.getBoundingClientRect();
+      let previousBottom = legend.getBoundingClientRect().bottom;
+      // Assert rendered geometry, not utility classes: every tool (including an
+      // unbordered file read) needs its own clearance from the shared border.
+      for (const card of tools.children) {
+        const rect = card.getBoundingClientRect();
+        await expect(rect.left - bounds.left).toBeGreaterThanOrEqual(8);
+        await expect(bounds.right - rect.right).toBeGreaterThanOrEqual(8);
+        await expect(rect.top - previousBottom).toBeGreaterThanOrEqual(8);
+        await expect(card.scrollWidth).toBeLessThanOrEqual(card.clientWidth);
+        previousBottom = rect.bottom;
+      }
+      await expect(bounds.bottom - previousBottom).toBeGreaterThanOrEqual(8);
+      await expect(frame.scrollWidth).toBeLessThanOrEqual(frame.clientWidth);
+    };
+
+    await expect(toggle).toHaveAttribute("aria-expanded", "false");
+    await checkSpacing();
+    await userEvent.click(toggle);
+    await expect(toggle).toHaveAttribute("aria-expanded", "true");
+    await new Promise<void>((resolve) =>
+      requestAnimationFrame(() => requestAnimationFrame(() => resolve()))
+    );
+    await checkSpacing();
+  },
+};
+
+export const NestedToolsPhone: AppStory = {
+  ...NestedTools,
+  globals: { viewport: { value: "mobile1", isRotated: false } },
+  // Keep the narrow-container regression active in the desktop-sized test-runner too.
+  decorators: [PhoneSubagentReportDecorator],
+  parameters: { pixel: { matrix: { viewports: ["phone"] } } },
+  play: async (context) => {
+    await expect(context.parameters.pixel).toMatchObject({ matrix: { viewports: ["phone"] } });
+    await NestedTools.play?.(context);
+    const frame = within(context.canvasElement).getByRole("group", { name: "Code Execution" });
+    await expect(frame.getBoundingClientRect().width).toBeLessThan(390);
+  },
+};