# Cobalt release review — unknown route produces a blank page

**Observed:** October 19, 2026, 14:10 UTC.  
**System:** Cobalt's public website.  
**Status:** failure reproduced in a browser; minimal repair passes local regression cases; live deployment unchanged.

## Buyer-visible outcome

Opening an unknown URL ending in `/` produces an empty page instead of the site's existing home fallback. A missing or mistyped link can therefore strand a visitor with no visible navigation.

Reproduction URL: <https://cobalt.build/route-probe-does-not-exist/>

The browser rendered no page content and reported:

```text
TypeError: Cannot read properties of undefined (reading 'variant')
```

The observed script was <https://cobalt.build/assets/index-Bqw4c_id.js>. The failing render was recorded at line 9, column 64027 of that deployed bundle. Minified locations may change on the next deployment.

## Root cause

The route-selection function has two paths. With a trailing slash it immediately returns the trimmed path. Only the other path checks whether a matching page exists. An unknown trailing-slash URL therefore reaches the renderer as an unrecognized key; the renderer reads `variant` from an undefined page.

The local demonstration preserves that branch order in `legacyResolve`. The repair first normalizes the path, then checks membership in the configured page map. This keeps the existing home fallback and does not invent a new 404 policy.

## Reproduce the evidence

With Node.js 18 or later, from this directory:

```sh
node verify.mjs
```

No package installation, account, API key, or network request is required for the local check. It runs the same 15 inputs against the before and after functions. Valid routes with and without a trailing slash remain valid; unknown trailing-slash paths fall back safely after the patch.

| Version | Passing cases | Failing cases |
| --- | ---: | ---: |
| Original branch order | 12 | 3 |
| Patched branch order | 15 | 0 |

The regression also explicitly verifies that the failing input throws a `TypeError` before the change and renders the `home` variant after it.

## Handoff

Apply the normalization-then-validation change to the source router, run the project's existing build and checks, and verify the reproduction URL in a preview deployment. Verify known routes still render, the missing route uses the agreed fallback, and the console no longer reports the error. Reverting the small resolver change is the rollback.

This sample contains a minimal behavioral fixture rather than the full application. It does not establish production deployment, whole-site accessibility, performance improvement, customer conversion impact, or revenue. The observed live failure and the local passing regression are distinct evidence. There is no customer or testimonial claim.