I recently deployed a new log for mtc_worker (#141) and forgot to create the corresponding secret (SIGNING_KEY_shard2). This is the error that I got:

POST https://bootstrap-mtca.cloudflareresearch.com/logs/shard2/add-entry - Ok @ 10/23/2025, 1:55:33 PM
POST http://fake_url.com/add_batch - Exception Thrown @ 10/23/2025, 1:55:34 PM
✘ [ERROR]   Error: unreachable

That's not very helpful. Instead of panicking, we should handle this gracefully as a 5xx error.