Document destination_route_unavailable proxy error code

[aylee855]

Summary

The metro egress proxy emits destination_route_unavailable on the X-Kernel-Proxy-Error header when a destination matches a per-host proxy route whose proxy can't be resolved (e.g. it was deleted). The request fails closed rather than falling back to the session proxy or a direct connection. The code was missing from the proxy errors table.

Adds a row to proxies/errors.mdx matching the proxy's own error page copy. It is intentionally not added to the retryable set in the example, since retrying won't help until the route is fixed.

🤖 Generated with Claude Code

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Note

Low Risk
Documentation-only change to the proxy errors table with no runtime or API behavior changes.

Overview
Documents the destination_route_unavailable X-Kernel-Proxy-Error code in the proxy errors reference table.

The new row explains that traffic matched a per-host proxy route whose assigned proxy cannot be used (e.g. deleted), that Kernel does not fall back to the session proxy or a direct connection, and that callers should fix the route rather than retry.

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