Fix interaction retention never running on large channels

[stphnlee]

Problem

RockCleanup's interaction retention silently stops working once a channel gets large, so InteractionChannel.RetentionDuration is never enforced.

CleanupOldInteractions accumulates every expiring InteractionSessionId into a List<int>, filtering each candidate with List<int>.Contains against the same list it is appending to:

var interactionSessionIdsOfDeletedInteractions = new List<int>();
...
    .Distinct()
    .ToList()
    .Where( i => !interactionSessionIdsOfDeletedInteractions.Contains( i ) );

interactionSessionIdsOfDeletedInteractions.AddRange( interactionSessionIdsForInteractionChannel );

Contains is a linear scan, so the accumulation is O(n²). It also sits before the BulkDeleteInChunks call, so when it doesn't finish, nothing is deleted at all. RunCleanupTask catches the resulting exception into the job result list rather than failing loudly, so the job reports as having run.

We hit this on a channel that reached 96M rows despite a 60 day retention — roughly 94M distinct expiring session ids, which is on the order of 4×10¹⁵ comparisons, plus a ~380MB List<int> materialized before any delete. The channel had been accumulating since an upgrade six months earlier with no visible failure.

CleanupUnusedInteractionSessions( List<int> ) has two further problems:

• for ( int x = 0; x < interactionSessionIds.Count / 1000; x++ ) — integer division drops the final partial chunk on every run, and skips the work entirely when there are fewer than 1000 ids.
• interactionSessionIds.Skip( x * 1000 ).Take( 1000 ) re-enumerates the list from the start on each iteration, giving the same O(n²) behaviour over the id list.

Changes

• Accumulator is a HashSet<int>, making the duplicate check O(1).
• UnionWith streams query results into the set instead of ToList()-ing every id and then filtering, dropping one full materialization of the id list.
• Chunk count rounds up, so the last partial chunk is processed.
• Chunks are taken with GetRange (indexed) rather than Skip.

No behavioural change to what gets deleted — the resulting set of session ids is the same, and the parameterless CleanupUnusedInteractionSessions() overload is untouched.

Testing

⚠️ Not compiled. Authored on macOS; this targets .NET Framework 4.7.2 with an old-style csproj and needs msbuild on Windows. Please build before merging.

Worth exercising CleanupOldInteractions against a channel with a retention duration and a non-multiple-of-1000 number of expiring sessions, which is the case the integer division was silently skipping.

Upstream

Both bugs are present in upstream Rock, not SECC customizations — they will return on each upgrade until fixed there. Worth reporting to Spark.

[Copilot]

Pull request overview

This PR fixes interaction retention cleanup becoming effectively non-functional on very large interaction channels by removing O(n²) accumulation patterns and correcting chunk-processing logic so deletions reliably run to completion.

Changes:

• Replaces the accumulating List<int> of expiring interaction session IDs with a HashSet<int> and streams IDs into it via UnionWith to avoid O(n²) Contains checks and extra materialization.
• Fixes session cleanup chunking to process the final partial chunk (and any <1000 remainder) by rounding up the chunk count.
• Improves chunk extraction performance by using indexed GetRange instead of repeated Skip(...).

Suppressed comments (1)

Rock/Jobs/RockCleanup.cs:1290

• Variable names interactionSessionsIdsToKeep / interactionSessionsIdsToRemove read like a pluralization typo ("SessionsIds"), which makes the intent harder to follow in this already performance-sensitive cleanup loop. Rename them to interactionSessionIdsToKeep / interactionSessionIdsToRemove for clarity and consistency with the surrounding interactionSessionIds* naming.

                var interactionSessionIdChunk = interactionSessionIds.GetRange( chunkStartIndex, chunkSize );

                // Find a list of session IDs in the delete list that are being used for other interactions
                var interactionSessionsIdsToKeep = new InteractionService( rockContext )
                    .Queryable()

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[stphnlee]

Superseded by #14, which applies the same fix against hotfix-1.16.12 where the v16 upgrade work lives. Reopen if we want this on develop / upstream later.