fix(docs): prevent custom components from being shadowed inside Aside (v2)

[Ryan-Amirthan]

Fixes custom React components not rendering inside <Aside> components.

Short description of the changes made

When the rehypeExtractAsides plugin extracts Aside content, it generates a component that destructures JSX elements from useMDXComponents(). This was causing imported custom components to be shadowed by undefined values, resulting in "Something went wrong!" errors.

The fix extracts module-level ESM bindings from the full AST and filters them out from the list of components to destructure, preventing the shadowing of imported custom components.

What was the motivation & context behind this PR?

Custom React components (e.g., CustomCard) work correctly in the main content but fail inside <Aside> components. This was reported in Slack - see the test case at https://plantman-preview-4ed7e531-1b9f-402c-9f0f-a2e2b811e9ed.docs.buildwithfern.com/concepts

The root cause: the generated AsideComponent function creates const { CustomCard } = MdxJsReact.useMDXComponents(), which shadows any CustomCard imported at module scope. Since the MDXProvider doesn't have CustomCard, it becomes undefined.

How has this PR been tested?

• Lint checks pass (pnpm lint:biome)

Human review checklist:

• Verify the fix works against the failing preview URL
• Confirm extractJsx(ast).esmElements correctly captures imported component names
• Check for edge cases where a component might need to come from both import and MDXProvider
• Consider if extractJsx call should be moved after the asides.length === 0 check for performance

---

Link to Devin run: https://app.devin.ai/sessions/48f55436d7304e6fbf43694fbaf910a7
Requested by: [email protected] (@Ryan-Amirthan)

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Project	Deployment	Review	Updated (UTC)
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[github-actions]

🌱 Smoke Test Preview

Run at: 2025-12-23 02:46:52 UTC

Testing branch changes with smoke test content:

• Smoke Test Content (from FDR): https://smoke-test-preview-e680e257-6822-4485-ae14-f1d6aa76e4c4.docs.buildwithfern.com
• Branch's Docs Platform (Vercel): https://prodferndocscom-git-devin-1766456645-fix-c-61837d-buildwithfern.vercel.app/api/fern-docs/preview?host=smoke-test-preview-e680e257-6822-4485-ae14-f1d6aa76e4c4.docs.buildwithfern.com

🕷️ Smoke Test Crawler Results

Pages crawled: 49
Successful: 44
With errors: 5 ❌

❌ Pages with Errors

https://smoke-test-preview-e680e257-6822-4485-ae14-f1d6aa76e4c4.docs.buildwithfern.com/home/rest-api/rest-api/user/get-auth-token

• Network errors (1):
  • Failed to load https://api.github.com/repos/fern-api/fern: net::ERR_ABORTED

https://smoke-test-preview-e680e257-6822-4485-ae14-f1d6aa76e4c4.docs.buildwithfern.com/home/rest-api/rest-api/user/get-user-by-name

• Network errors (1):
  • Failed to load https://api.github.com/repos/fern-api/fern: net::ERR_ABORTED

https://smoke-test-preview-e680e257-6822-4485-ae14-f1d6aa76e4c4.docs.buildwithfern.com/home/rest-api/rest-api/one-of-examples/one-of-example

• Network errors (1):
  • Failed to load https://api.github.com/repos/fern-api/fern: net::ERR_ABORTED

https://smoke-test-preview-e680e257-6822-4485-ae14-f1d6aa76e4c4.docs.buildwithfern.com/home/rest-api/rest-api/one-of-examples/one-of-example-no-discriminator

• Network errors (1):
  • Failed to load https://api.github.com/repos/fern-api/fern: net::ERR_ABORTED

https://smoke-test-preview-e680e257-6822-4485-ae14-f1d6aa76e4c4.docs.buildwithfern.com/home/rest-api/rest-api/one-of-examples/one-of-example-titled

• Network errors (1):
  • Failed to load https://api.github.com/repos/fern-api/fern: net::ERR_ABORTED

📊 Full error breakdown

• Console errors: 0
• Network errors: 5
• Page errors: 0

See full details in the workflow logs.