Thread safety: _allSessionPoints accessed from multiple threads without synchronization

[tylerkron]

Problem

DatabaseLogger._allSessionPoints (and its contained List<DataPoint> values) is written on a background thread during DisplayLoggingSession / LoadSampledData (Phase 2) while simultaneously being read on the UI thread by UpdateMainPlotViewport, UpdateSeriesFromMemory, ResetZoom, and FetchViewportDataFromDb.

This can cause InvalidOperationException (collection modified during enumeration), ArgumentOutOfRangeException (index into a list that was cleared), or corrupted data during pan/zoom while a session is loading.

Identified in

PR #467 double-check audit and Qodo review comment #2.4.

Suggested approaches (pick one)

1. Single-thread ownership: Build all point data in local structures on the background thread, then Dispatcher.Invoke once to swap _allSessionPoints references on the UI thread.
2. Locking: Add a lock(_sessionPointsLock) around all reads/writes/iterations of _allSessionPoints and contained lists.
3. Pause viewport timers: Stop _viewportThrottleTimer during Phase 2 loading and restart after data is stable.

Option 1 is cleanest — it eliminates the shared mutable state entirely.

Files involved

• Daqifi.Desktop/Loggers/DatabaseLogger.cs — DisplayLoggingSession, LoadSampledData, UpdateMainPlotViewport, UpdateSeriesFromMemory, ResetZoom, PrepareMinimapData