Fix PerfMon first-value spike that skews graphs

[erikdarlingdata]

Summary

• Fixes [BUG] Lite - PerfMon first values spike skews graph #482
• Added baselineOnly parameter to DeltaCalculator.CalculateDelta() — when true, the first read stores the baseline and returns 0 instead of the raw cumulative value
• Applied to all cumulative-counter collectors: PerfMon, WaitStats, FileIO, MemoryGrants
• Query/proc stats unchanged (single-execution queries still surface in top-N views)
• X-axis anchoring issue was a visual side effect of the spike dominating the Y scale

Test plan

• Start Lite, open Server > PerfMon tab
• Verify first data point does not create a spike for any counter group
• Verify chart scales normally after 2+ collections
• Verify WaitStats, FileIO, MemoryGrants tabs also have no first-value spike
• Verify Top Queries / Top Procs still show single-execution entries

🤖 Generated with Claude Code

[dphugo]

Hi @erikdarlingdata. Wow, what a rapid response! 🚀
Not sure if I should respond here or on the original Issue I raised (482) ?:

I noticed the scope was expanded to the following files, which is great:

However, I've picked up that _deltaCalculator.CalculateDelta is also used in:

• Services\RemoteCollectorService.ProdecureStats.cs
• Services\RemoteCollectorService.QueryStats.cs

These are currently not included in the commit and (for graphing) it does affect:

• "Server Tab -> Queries -> Performance Trends" as can be seen in this screenshot:

As the scope was expanded by this commit, I figured it would makes sense to include it on this branch?
Or, because it is closed/merged, should I raise a separate bug for the above increased scope?

Kind regards,
Daniel

[erikdarlingdata]

Totally fine here. I can pick it up. Thanks for letting me know, as always.

[erikdarlingdata]

@dphugo Good catch -- query stats and procedure stats collectors now also use baselineOnly: true in PR #491, merged to dev. Thanks for flagging it!