google/api/annotations.proto: File not found.

When I try and use polyglot, I get a missing import

`google/api/annotations.proto: File not found.`

Full error

```
WARNING: Use --illegal-access=warn to enable warnings of further illegal reflective access operations
WARNING: All illegal access operations will be denied in a future release
google/api/annotations.proto: File not found.
target/protoc-dependencies/c8d906d66905cf92bbd1cfbc0960871a/google/api/monitoring.proto: Import "google/api/annotations.proto" was not found or had errors.
```

This is my request

```
java -jar ~/Downloads/polyglot.jar \
--proto_discovery_root=/Users/bparks/myprotos/ \
list_services

```

Reproduce the reported `java -jar` invocation with `list_services` and `--proto_discovery_root`, then trace how the CLI resolves the `google/api/monitoring.proto` import. Done means the `google/api/annotations.proto` dependency is found and `list_services` completes without the missing-file error.

Written by the indexing model from the issue text.