Update Stagehand docs to v4

[dprevoznik]

Updates the Stagehand documentation for Stagehand SDK v4 while keeping the v3 examples available. The prior guide was v3-only and no longer matched the shipped stagehand CLI template (migrated to v4).

Changes

integrations/stagehand.mdx

• Quick start with the CLI template (v4) — kernel create --template stagehand, set MODEL + MODEL_API_KEY, deploy, invoke.
• Adding Kernel to an existing Stagehand project — a <Tabs> block with a Stagehand v4 tab and a Stagehand v3 tab, each showing the full setup for that version:
  • v4: install the SDK, load the Stagehand extension onto the running browser, localBrowser.connect({ cdpUrl }) (no extensionId) + Stagehand.create({ browser }), async activePage(), { data } from extract, nested cleanup.
  • v3: the original flow (new Stagehand({ localBrowserLaunchOptions }) + init(), context.pages()[0], cleanup).
• Version note explains the extension model and points at the migration guide.

browsers/file-io.mdx — the Stagehand download example is now a <CodeGroup> with Stagehand v4 and Stagehand v3 variants. v4 reads from the default download directory /home/kernel/Downloads and skips in-progress .crdownload files; v3 keeps the localBrowserLaunchOptions (downloadsPath + acceptDownloads) approach.

reference/cli/create.mdx — template description updated from "v3 SDK integration" to "v4".

Testing

The v4 snippets were run end-to-end against a real Kernel browser (Stagehand 4.0.0, @onkernel/sdk 0.23.0, anthropic/claude-sonnet-4-5):

• The "existing v4 project" flow returns {"teamSize":"6"}.
• The v4 file I/O flow triggers a download, waits past the .crdownload temp file, and reads the completed file from /home/kernel/Downloads (6.1 MB). The .crdownload skip was added after an initial run read a partial file.

The v3 snippets are the previously-shipped v3 examples, restored unchanged.

Notes

• The CLI template is v4-only; this PR does not change the template, only the docs.
• Stagehand examples are TypeScript-only, matching the prior version of these pages (Stagehand is TS-first).

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[cursor]

Risk assessment: Very Low

Decision: Approve.

This PR touches only three Mintlify documentation pages (integrations/stagehand.mdx, browsers/file-io.mdx, reference/cli/create.mdx). The diff rewrites Stagehand examples from the v3 constructor/init() API to the v4 localBrowser.connect + Stagehand.create flow, updates the file I/O download snippet (default /home/kernel/Downloads, skip .crdownload), and changes one CLI template label from v3 to v4.

Why Very Low

• Documentation-only MDX. No application code, CI, config (docs.json), redirects, or infrastructure.
• No auth, billing, permissions, or production logic changes.
• No CODEOWNERS file and branch rules do not require code-owner review.
• Blast radius is limited to published docs copy and example snippets.

These files are product docs, not model-instruction / prompt files, so the prompt-change override does not apply.

  

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