diff --git a/src/renderer/components/WorkbenchControls.tsx b/src/renderer/components/WorkbenchControls.tsx
index 7624781..db4e0b2 100644
--- a/src/renderer/components/WorkbenchControls.tsx
+++ b/src/renderer/components/WorkbenchControls.tsx
@@ -396,17 +396,20 @@ function ToolDiffSection({
 }) {
   const [showAll, setShowAll] = useState(false);
   const rows = diffLines(oldText, newText);
-  const isLong = text.length > TOOL_TEXT_PREVIEW_LIMIT;
+  const isLong =
+    rows.reduce((length, row) => length + row.text.length + 1, 0) >
+    TOOL_TEXT_PREVIEW_LIMIT;
   let visible = rows;
   if (isLong && !showAll) {
     visible = [];
-    let used = 0;
+    let remaining = TOOL_TEXT_PREVIEW_LIMIT;
     for (const row of rows) {
-      used += row.text.length + 1;
-      if (used > TOOL_TEXT_PREVIEW_LIMIT) break;
-      visible.push(row);
+      if (remaining <= 0) break;
+      // Include the diff marker in the budget and clip even a single long row.
+      const clipped = row.text.slice(0, remaining - 1);
+      visible.push({ ...row, text: clipped });
+      remaining -= clipped.length + 1;
     }
-    if (visible.length === 0 && rows.length > 0) visible = [rows[0]];
   }
   return (
     <ToolSection title="Input" text={text} stateKey={stateKey} expanded={expanded}>
@@ -422,6 +425,11 @@ function ToolDiffSection({
         ))}
         {visible.length === 0 && <div className="wb-tool-diff-line">No changes.</div>}
       </div>
+      {isLong && !showAll && (
+        <p className="wb-tool-notice wb-muted">
+          Input preview shortened. Show more or copy the full input.
+        </p>
+      )}
       {isLong && (
         <button
           type="button"
diff --git a/tests/e2e/tool-preview.test.ts b/tests/e2e/tool-preview.test.ts
new file mode 100644
index 0000000..0a0672a
--- /dev/null
+++ b/tests/e2e/tool-preview.test.ts
@@ -0,0 +1,119 @@
+import { afterAll, beforeAll, describe, expect, inject, it } from 'vitest';
+import { _electron as electron, type ElectronApplication, type Page } from 'playwright-core';
+import fs from 'node:fs/promises';
+import os from 'node:os';
+import path from 'node:path';
+
+const root = path.resolve(__dirname, '../..');
+const oldText = `const settings = {${'enabled: false, '.repeat(400)}}; // old-end`;
+const newText = `const settings = {${'enabled: true, '.repeat(400)}}; // new-end`;
+const shots = path.join(root, 'test-results/tool-preview');
+let app: ElectronApplication;
+let page: Page;
+let fixture: string;
+const errors: string[] = [];
+
+describe('bounded tool previews in Electron', () => {
+  beforeAll(async () => {
+    fixture = await fs.mkdtemp(path.join(os.tmpdir(), 'pidex-tool-preview-'));
+    const project = path.join(fixture, 'project');
+    const archives = path.join(fixture, 'sessions/workspace');
+    await Promise.all([
+      fs.mkdir(project),
+      fs.mkdir(archives, { recursive: true }),
+      fs.mkdir(path.join(fixture, 'user-data')),
+      fs.mkdir(path.join(root, '.tmp/proof'), { recursive: true }),
+      fs.mkdir(shots, { recursive: true }),
+    ]);
+    for (const tool of ['write', 'edit']) {
+      const records = [
+        { type: 'session', version: 3, id: tool, cwd: project, timestamp: new Date().toISOString() },
+        { type: 'message', id: 'task', parentId: null, message: {
+          role: 'user', content: [{ type: 'text', text: `Inspect long ${tool} input` }],
+        } },
+        { type: 'message', id: 'call', parentId: 'task', message: {
+          role: 'assistant', content: [{ type: 'toolCall', id: tool, name: tool, arguments: {
+            path: 'settings.js',
+            ...(tool === 'write' ? { content: newText } : { oldText, newText }),
+          } }],
+        } },
+        { type: 'message', id: 'result', parentId: 'call', message: {
+          role: 'toolResult', toolCallId: tool, toolName: tool,
+          content: [{ type: 'text', text: 'Updated settings.js' }],
+        } },
+      ];
+      await fs.writeFile(path.join(archives, `${tool}.jsonl`), records.map((r) => JSON.stringify(r)).join('\n'));
+    }
+    app = await electron.launch({
+      executablePath: require('electron'),
+      args: ['.'],
+      cwd: root,
+      env: {
+        ...process.env,
+        PIDEX_E2E_CWD: project,
+        PIDEX_E2E_RENDERER_URL: inject('rendererUrl'),
+        PIDEX_E2E_USER_DATA: path.join(fixture, 'user-data'),
+        PIDEX_SESSIONS_ROOT: path.join(fixture, 'sessions'),
+        PIDEX_PI: path.join(root, 'tests/fixtures/pi-rpc.cjs'),
+      },
+    });
+    page = await app.firstWindow();
+    page.setDefaultTimeout(10_000);
+    page.on('pageerror', (error) => errors.push(error.message));
+    await page.getByRole('heading', { name: 'Start a session', exact: true }).waitFor();
+    await page.setViewportSize({ width: 1280, height: 1100 });
+    await page.evaluate(() => document.fonts.ready);
+    await page.getByRole('button', { name: /^Sessions/ }).click();
+  });
+
+  afterAll(async () => {
+    await app?.close();
+    if (fixture) await fs.rm(fixture, { recursive: true, force: true });
+  });
+
+  it.each(['write', 'edit'])('bounds a long %s line, copies the full input and expands on request', async (tool) => {
+    await page.getByRole('tree', { name: 'Session archives', exact: true })
+      .getByRole('treeitem', { name: new RegExp(`Inspect long ${tool} input`) }).click();
+    const card = page.locator('.wb-tool');
+    await card.locator('summary').click();
+    await card.getByRole('button', { name: 'Output details' }).click();
+    await card.getByRole('button', { name: 'Input details' }).click();
+    const diff = card.locator('.wb-tool-diff');
+    await expect.poll(async () => (await diff.textContent())?.length).toBe(2000);
+    expect(await diff.textContent()).not.toContain('new-end');
+    await card.getByText('Input preview shortened. Show more or copy the full input.').waitFor();
+    await card.getByRole('button', { name: 'Copy input' }).click();
+    await card.getByText('Copied', { exact: true }).waitFor();
+    expect(await app.evaluate(({ clipboard }) => clipboard.readText())).toBe(
+      tool === 'write' ? `settings.js\n\n${newText}` : `settings.js\n\nOld:\n${oldText}\n\nNew:\n${newText}`,
+    );
+    await card.getByRole('button', { name: 'Show more' }).focus();
+    await page.keyboard.press('Enter');
+    expect(await diff.textContent()).toContain(newText);
+    if (tool === 'edit') expect(await diff.textContent()).toContain(oldText);
+    await card.getByRole('button', { name: 'Show less' }).click();
+    expect((await diff.textContent())?.length).toBe(2000);
+    await card.locator('summary').scrollIntoViewIfNeeded();
+    // Expansion changes the virtual row height. Wait for measurement before
+    // capturing so the history footer has moved below the resized card.
+    await page.evaluate(() => new Promise<void>((resolve) => {
+      requestAnimationFrame(() => requestAnimationFrame(() => resolve()));
+    }));
+    await expect.poll(async () => {
+      const outputBounds = await card.getByRole('button', { name: 'Output details' }).boundingBox();
+      const footerBounds = await page.getByRole('button', { name: 'Fork from here', exact: true }).boundingBox();
+      return !!outputBounds && !!footerBounds && footerBounds.y >= outputBounds.y + outputBounds.height;
+    }).toBe(true);
+    const screenshot = `${tool}-bounded-preview.png`;
+    await page.screenshot({ path: path.join(root, '.tmp/proof', screenshot) });
+    await page.screenshot({ path: path.join(shots, screenshot) });
+
+    await page.setViewportSize({ width: 900, height: 600 });
+    await card.getByRole('button', { name: 'Show more' }).scrollIntoViewIfNeeded();
+    expect(await page.evaluate(() => document.body.scrollWidth <= window.innerWidth)).toBe(true);
+    await page.screenshot({ path: path.join(root, '.tmp/proof', `${tool}-bounded-narrow.png`) });
+    await page.screenshot({ path: path.join(shots, `${tool}-bounded-narrow.png`) });
+    await page.setViewportSize({ width: 1280, height: 1100 });
+    expect(errors).toEqual([]);
+  });
+});
diff --git a/tests/integration/ToolCard.test.tsx b/tests/integration/ToolCard.test.tsx
index 2881fcd..8402373 100644
--- a/tests/integration/ToolCard.test.tsx
+++ b/tests/integration/ToolCard.test.tsx
@@ -1,6 +1,6 @@
 import { describe, expect, it, beforeEach, vi } from 'vitest';
 import { render, cleanup, fireEvent } from '@testing-library/react';
-import { TranscriptRow } from '../../src/renderer/components/WorkbenchControls';
+import { TOOL_TEXT_PREVIEW_LIMIT, TranscriptRow } from '../../src/renderer/components/WorkbenchControls';
 import type { Entry } from '../../src/renderer/timeline';
 
 const toolEntry: Extract<Entry, { kind: 'tool' }> = {
@@ -115,6 +115,68 @@ describe('<TranscriptRow> tool card', () => {
     expect(container.querySelector('.wb-tool-diff-line--del')).toBeNull();
   });
 
+  it.each(['edit', 'write'])('bounds a single long %s line and preserves full inspection and copying', async (tool) => {
+    const oldText = tool === 'edit' ? `before-${'x'.repeat(5000)}-old-end` : '';
+    const newText = `after-${'y'.repeat(5000)}-new-end`;
+    const input = tool === 'edit'
+      ? `${toolEntry.args}\n\nOld:\n${oldText}\n\nNew:\n${newText}`
+      : `${toolEntry.args}\n\n${newText}`;
+    const writeText = vi.fn().mockResolvedValue(undefined);
+    Object.defineProperty(navigator, 'clipboard', {
+      value: { writeText },
+      configurable: true,
+    });
+    const entry = { ...toolEntry, tool, input, oldText, newText };
+    const { container, getByRole, queryByText } = render(
+      <TranscriptRow entry={entry} expanded={new Map([[entry.key, true]])} />,
+    );
+    fireEvent.click(getByRole('button', { name: 'Input details' }));
+    const diff = container.querySelector('.wb-tool-diff')!;
+    expect(diff.textContent?.length).toBe(TOOL_TEXT_PREVIEW_LIMIT);
+    expect(diff.textContent).not.toContain('-new-end');
+    expect(diff.textContent).not.toContain('-old-end');
+    expect(queryByText('Input preview shortened. Show more or copy the full input.')).toBeTruthy();
+
+    fireEvent.click(getByRole('button', { name: 'Copy input' }));
+    await vi.waitFor(() => expect(writeText).toHaveBeenCalledWith(input));
+    fireEvent.click(getByRole('button', { name: 'Show more' }));
+    expect(diff.textContent).toContain(newText);
+    if (oldText) expect(diff.textContent).toContain(oldText);
+    expect(queryByText('Input preview shortened. Show more or copy the full input.')).toBeNull();
+    fireEvent.click(getByRole('button', { name: 'Show less' }));
+    expect(diff.textContent?.length).toBe(TOOL_TEXT_PREVIEW_LIMIT);
+  });
+
+  it('bounds multiple diff rows including the final partial row', () => {
+    const lines = Array.from({ length: 4 }, (_, index) => `${index}-${'x'.repeat(700)}`);
+    const entry = { ...toolEntry, oldText: '', newText: lines.join('\n') };
+    const { container, getByRole } = render(
+      <TranscriptRow entry={entry} expanded={new Map([[entry.key, true]])} />,
+    );
+    fireEvent.click(getByRole('button', { name: 'Input details' }));
+    const diff = container.querySelector('.wb-tool-diff')!;
+    expect(diff.textContent?.length).toBe(TOOL_TEXT_PREVIEW_LIMIT);
+    const rows = diff.querySelectorAll('.wb-tool-diff-line');
+    expect(rows).toHaveLength(3);
+    expect(rows[0].textContent).toBe(`+${lines[0]}`);
+    expect(rows[2].textContent).toMatch(/^\+2-x+$/);
+    expect(rows[2].textContent?.length).toBeLessThan(lines[2].length);
+    fireEvent.click(getByRole('button', { name: 'Show more' }));
+    expect(diff.querySelectorAll('.wb-tool-diff-line')).toHaveLength(4);
+    expect(diff.textContent).toContain(lines[3]);
+  });
+
+  it.each([TOOL_TEXT_PREVIEW_LIMIT - 1, TOOL_TEXT_PREVIEW_LIMIT])('does not shorten a %i-character diff because of input path or labels', (length) => {
+    const newText = 'x'.repeat(length - 1);
+    const entry = { ...toolEntry, input: `${toolEntry.args}\n\n${newText}`, oldText: '', newText };
+    const { container, getByRole, queryByRole } = render(
+      <TranscriptRow entry={entry} expanded={new Map([[entry.key, true]])} />,
+    );
+    fireEvent.click(getByRole('button', { name: 'Input details' }));
+    expect(container.querySelector('.wb-tool-diff')?.textContent).toBe(`+${newText}`);
+    expect(queryByRole('button', { name: 'Show more' })).toBeNull();
+  });
+
   it('copies the exact plain input text from a diff card', async () => {
     const writeText = vi.fn().mockResolvedValue(undefined);
     Object.defineProperty(navigator, 'clipboard', {