Fix the error handling

Audit the error handling in this: <paste>

Find:
- Empty catch blocks, and catches that only log then continue as if
  nothing happened.
- Errors caught too broadly, hiding ones I'd want to know about.
- Promises with no rejection handling.
- Failures that leave things half-done — a record created but not
  linked, a file written but not registered.
- Errors shown to users with internal detail in them.

For each: what actually happens today, what should happen, and whether
this failure should be retried, reported, or shown to the user.