Fix duplicate key error in FetchedJobs when job has multiple queue entries

[nicolaj-hartmann]

Problem

When a job has multiple entries in the jobqueue table (e.g., due to re-queuing or race conditions), the Hangfire dashboard crashes with:

System.ArgumentException: An item with the same key has already been added. Key: 185

This occurs in PostgreSqlMonitoringApi.FetchedJobs because the SQL query returns duplicate job IDs which are then passed to ToDictionary().

Solution

• Add DISTINCT to GetQueuedOrFetchedJobIds to ensure unique job IDs are returned
• Add DISTINCT ON (j."id") to FetchedJobs and EnqueuedJobs SQL queries as a safeguard

Testing

Added integration test FetchedJobs_WithDuplicateJobQueueEntries_DoesNotThrow that:

1. Creates a job with two jobqueue entries (same jobId)
2. Calls FetchedJobs via the monitoring API
3. Verifies no exception is thrown and only one job is returned