🐛 [rum-nuxt] Fix Nuxt post-hydration error handling

[BeltranBulbarellaDD]

Motivation

Issue.

Nuxt installs its default vueApp.config.errorHandler during initial rendering and removes it after hydration on app:suspense:resolve, as long as the handler was not overridden.

The Nuxt RUM plugin wraps that handler before hydration, which prevents Nuxt’s identity check from removing it. As a result, client-side Vue errors triggered after hydration keep delegating to Nuxt’s default error handler and render the full-page error.vue, even though Nuxt would normally only log them to the console.

Changes

• Stop delegating to Nuxt’s default error handler after app:suspense:resolve.
• Continue reporting Vue errors to RUM after hydration.
• Preserve the original behavior before hydration so initial render/startup errors can still trigger Nuxt’s error page.
• Keep delegating to custom original Vue error handlers after hydration.
• Add unit coverage for Nuxt default handler gating and custom handler preservation.
• Added e2e test.

Test instructions

1. Checkout main.
2. Start the Nuxt test app.
3. Open the Nuxt error test page without RUM.
4. Click Trigger Error.
5. Confirm the error is only logged to the console and the app does not render the Nuxt error page.
6. Open the same page with: ?rum-config={"applicationId":"test","clientToken":"test","site":"datadoghq.com"}
7. Click Trigger Error.
8. On main, confirm the app renders the Nuxt 500 Internal Server Error page.
9. With this fix, confirm the error is reported to RUM but the app stays on the page and only logs the error to the console.

Checklist

• Tested locally
• Tested on staging
• Added unit tests for this change.
• Added e2e/integration tests for this change.
• Updated documentation and/or relevant AGENTS.md file

[cit-pr-commenter-54b7da]

Bundles Sizes Evolution

📦 Bundle Name	Base Size	Local Size	𝚫	𝚫%	Status
Rum	178.53 KiB	178.53 KiB	0 B	0.00%	✅
Rum Profiler	8.22 KiB	8.22 KiB	0 B	0.00%	✅
Rum Recorder	21.12 KiB	21.12 KiB	0 B	0.00%	✅
Logs	55.59 KiB	55.59 KiB	0 B	0.00%	✅
Rum Salesforce	N/A	136.60 KiB	N/A	N/A	N/A
Rum Slim	136.60 KiB	136.60 KiB	0 B	0.00%	✅
Worker	22.96 KiB	22.96 KiB	0 B	0.00%	✅

[datadog-datadog-prod-us1-2]

🎉 All green!

🧪 All tests passed
❄️ No new flaky tests detected

🎯 Code Coverage (details)
• Patch Coverage: 57.14%
• Overall Coverage: 77.19% (-0.01%)

_{This comment will be updated automatically if new data arrives.
🔗 Commit SHA: 9b5cc2e | Docs | Datadog PR Page | Give us feedback!}

[BeltranBulbarellaDD]

@codex review

[chatgpt-codex-connector]

Codex Review: Didn't find any major issues. You're on a roll.

Reviewed commit: bf131bfd1c

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[chatgpt-codex-connector]

💡 Codex Review

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Reviewed commit: bf131bfd1c

ℹ️ About Codex in GitHub

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[chatgpt-codex-connector]

Support untagged Nuxt 3 default handlers

issue: This only disables delegation when Nuxt marks its default handler with __nuxt_default, but supported Nuxt 3 releases such as 3.11.2 install handleVueError without that marker and clear it after mount via an identity check instead (Nuxt 3.11.2 source). Because this wrapper has already replaced vueApp.config.errorHandler, Nuxt cannot clear its default handler, and this condition never flips shouldCallOriginal, so post-hydration client errors in those Nuxt 3 apps still delegate to Nuxt's default handler and render the full-page error.

Useful? React with 👍 / 👎.

[bdibon]

Good job! A couple of suggestions to improve tests readability.