fix(tui): preserve shell preview boundaries

packages/tui/test/cli/tui/collapse-tool-output.test.ts

@@ -1,5 +1,5 @@
 import { expect, test } from "bun:test"
-import { collapseToolOutput } from "../../../src/util/collapse-tool-output"
+import { collapseToolOutput, collapseToolOutputParts } from "../../../src/util/collapse-tool-output"
 
 test("limits command input and output to the same line budget", () => {
   const command = Array.from({ length: 8 }, (_, index) => `command ${index + 1}`).join("\n")
@@ -12,3 +12,33 @@ test("limits command input and output to the same line budget", () => {
   expect(collapsed.output).toContain("command 8\n\noutput 1…")
   expect(collapsed.output).not.toContain("output 2")
 })
+
+test.each([
+  {
+    name: "inside the command",
+    maxChars: 5,
+    expected: { input: "$ co…", output: "", overflow: true },
+  },
+  {
+    name: "after the command",
+    maxChars: 10,
+    expected: { input: "$ command…", output: "", overflow: true },
+  },
+  {
+    name: "on the first separator newline",
+    maxChars: 11,
+    expected: { input: "$ command…", output: "", overflow: true },
+  },
+  {
+    name: "on the second separator newline",
+    maxChars: 12,
+    expected: { input: "$ command…", output: "", overflow: true },
+  },
+  {
+    name: "inside the output",
+    maxChars: 15,
+    expected: { input: "$ command", output: "out…", overflow: true },
+  },
+])("keeps the ellipsis with the visible $name", ({ maxChars, expected }) => {
+  expect(collapseToolOutputParts("$ command", "output", 10, maxChars)).toEqual(expected)
+})