Worker Error 1101: your script threw, and how to see it

# Worker Error 1101

Error class `1101`: the Worker threw a JavaScript exception. (Sibling: `1102` means the Worker exceeded its CPU time limit, which is a performance problem, not a bug.)

## See the actual error

The public error page is deliberately uninformative. Run `wrangler tail` in the Worker project directory and reproduce the request: you get a live feed of console and exception logs with the real stack trace.

## "The script will never generate a response"

A special 1101 variant: the runtime detected that all code for the request executed and the event loop is empty, but no Response was ever returned. Typical causes:

- An async code path that never resolves or never returns (missing `return` in a branch).
- `event.waitUntil` misuse or a promise chain that drops the response.
- A fetch handler that conditionally responds and the condition missed every branch.

Fix by ensuring every code path through the handler returns a Response (or throws, which becomes a 1101 with a visible stack).

## Checklist

- `wrangler tail` first, always: the edge page hides the stack on purpose.
- Distinguish 1101 (exception: fix the bug) from 1102 (CPU limit: make it faster or split the work).
- Add a catch-all at the handler top level that logs and returns a 500, so the next 1101 comes with context.