`PolarisDiagnostics` leaks internal information

### Describe the bug

(Related to #759) `PolarisDiagnostics` can expose raw contents of an entity, including internal information.
The contents of those entities then ends in exception messages, which leak all the way down to users via HTTP responses and gets exposed to potentially external systems (logging / tracing).

### To Reproduce

_No response_

### Actual Behavior

_No response_

### Expected Behavior

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### Additional context

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### System information

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Start by locating PolarisDiagnostics and tracing how entity contents enter exception messages and then HTTP responses. Review the related issue #759 for context. Done means internal entity information is no longer exposed through exception messages, HTTP responses, logging, or tracing.

Written by the indexing model from the issue text.