fix(frontend): stop swallowing Vite preload errors into router crashes

[posthog-eu]

Summary

• Who's hurt: users mid-session during a deploy hit a dead page instead of the auto-reload built for exactly this case. Every deploy that lands while a stale index.html is open can trigger it — any lazy route, not just the device page.
• Root cause: the vite:preloadError handler in src/main.ts called event.preventDefault(). Vite's preload helper only rethrows the import failure when !e.defaultPrevented, so preventing the default makes __vitePreload resolve with undefined. The lazy route then resolves to a falsy component and vue-router throws Couldn't resolve component "default" at ... — a hard crash.
• Extra sting: that router error text matches none of STALE_ASSET_ERROR_PATTERNS, so the PostHog suppression this code was written to provide never applied to the error it created. The real Failed to fetch dynamically imported module cause was swallowed; only the downstream router error escaped.

Changes

• Drop event.preventDefault() (and the now-pointless stopImmediatePropagation()) from the vite:preloadError handler so Vite rethrows. The rejection surfaces as Failed to fetch dynamically imported module, which the existing patterns in src/services/staleAssetErrors.ts already match — restoring both the auto-reload and the PostHog suppression that were intended.
• Add a router.onError fallback that treats Couldn't resolve component as a chunk error too, so a navigation that races the async window.location.reload() still recovers instead of leaving a blank route.
• New isComponentResolutionErrorMessage helper + unit coverage.

Note

Adding the Couldn't resolve component pattern to the PostHog suppression list on its own would only hide the symptom — the root-cause fix is removing preventDefault(). The router.onError handler catches the error before it propagates, so it no longer reaches PostHog's exception autocapture.

Test plan

• vitest run tests/stale-asset-errors.unit.test.ts — 6 passing (includes new component-resolution matcher cases).
• Manual: deploy invalidating chunk URLs while an old index.html is open → navigating to a lazy route now auto-reloads to the latest version instead of crashing on Couldn't resolve component.

Screenshots

Checklist

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• My change has adequate E2E test coverage.
• I have tested my code manually, and I have provided steps how to reproduce my tests.

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Created with PostHog Desktop from this inbox report.

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[codspeed-hq]

Merging this PR will not alter performance

✅ 43 untouched benchmarks
⏩ 2 skipped benchmarks¹

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_{Comparing posthog-self-driving/fixfrontend-stop-swallowing-vite-319f87 (3e2f827) with main (60a641e)}

Footnotes

1. 2 benchmarks were skipped, so the baseline results were used instead. If they were deleted from the codebase, click here and archive them to remove them from the performance reports. ↩

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud