docs(extensions): document custom file previews

[benvinegar]

Summary

• add a dedicated public guide for building custom file previews with hunk.registerFileView()
• document exact-source reads, symbolic rows, hunk geometry, source bindings, inline notes, constrained JSX painters, command controls, validation, and raw-diff fallback
• update the Extension API reference for API version 2 and ctx.fileViews
• link file previews from the docs sidebar, Extensions guide, and docs homepage
• cover the new documentation route in the browser smoke suite

Validation

• bun run typecheck
• bun run lint
• cd website && bun run check
• cd website && bun run build
• website Playwright suite: 34 passed across desktop and mobile Chromium
• bun test scripts/generate-docs.test.ts scripts/check-pack.ts
• formatting and git diff --check

This PR description was generated by Pi using OpenAI GPT-5.2

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Project	Deployment	Actions	Updated (UTC)
hunk-web	Ready	Preview	Jul 30, 2026 1:34am

[greptile-apps]

Example inputs are absent

The copyable launch command references before.md and after.md, but those files are not included or identified as user-provided placeholders, so running it from a repository checkout ends with a missing-file error instead of launching the example.

Knowledge Base Used: Extension System: API, Loading, and Host Integration

Prompt To Fix With AI

This is a comment left during a code review.
Path: website/src/content/docs/docs/extend/file-previews.md
Line: 199

Comment:
**Example inputs are absent**

The copyable launch command references `before.md` and `after.md`, but those files are not included or identified as user-provided placeholders, so running it from a repository checkout ends with a missing-file error instead of launching the example.

**Knowledge Base Used:** [Extension System: API, Loading, and Host Integration](https://app.greptile.com/modem/-/custom-context/knowledge-base/modem-dev/hunk/-/docs/extension-system.md)

---

For each issue above, determine whether it is valid and should be fixed. If so, fix it directly.

[greptile-apps]

Greptile Summary

This PR adds public documentation for extension API v2 custom file previews.

• Documents registration, layout geometry, source bindings, inline-note fallback, JSX painters, command controls, and validation limits.
• Adds navigation links from the sidebar, extension guide, API reference, and documentation homepage.
• Adds the new documentation route to the browser smoke suite.

Confidence Score: 4/5

The PR appears safe to merge, with one non-blocking documentation issue in the example launch command.

The documented feature contract aligns with the implementation, but the copyable quick-start command references input files that are neither included nor identified as placeholders.

Files Needing Attention: website/src/content/docs/docs/extend/file-previews.md

Important Files Changed

Filename	Overview
website/src/content/docs/docs/extend/file-previews.md	Adds the comprehensive file-preview guide; the try-it command depends on unexplained, absent input files.
website/src/content/docs/docs/extend/extension-api.md	Updates the documented API version and adds file-view registration and command-control references consistent with the public contract.
website/astro.config.mjs	Adds the new guide to the Extensions sidebar.
website/tests/docs-smoke.spec.ts	Adds the new documentation route to the existing route smoke test.

Prompt To Fix All With AI

### Issue 1
website/src/content/docs/docs/extend/file-previews.md:199
**Example inputs are absent**

The copyable launch command references `before.md` and `after.md`, but those files are not included or identified as user-provided placeholders, so running it from a repository checkout ends with a missing-file error instead of launching the example.

---

For each issue above, determine whether it is valid and should be fixed. If so, fix it directly.

_{Reviews (1): Last reviewed commit: "docs(extensions): document custom file p..." | Re-trigger Greptile}