Small changes to facilitate fuzzing

[andyleiserson]

My fuzzing setup is still WIP and not in a condition to merge, but these changes are small and can stand alone.

• Avoid a crash if deserializing a zero ID from a trace
• Make some crash messages more distinctive so it's easier to catch and identify them.

Testing
Not a lot to test here but I have exercised it locally.

Squash or Rebase? Squash

Checklist

• Run cargo fmt.
• Run taplo format.
• Run cargo clippy --tests. If applicable, add:
  • --target wasm32-unknown-unknown
• Run cargo xtask test to run tests.
• If this contains user-facing changes, add a CHANGELOG.md entry.