Prices_transform nulls valid MarketPrice for SavingsPlan

[tkalc]

🐛 Problem

When ingesting Azure Cost Management MCA price sheet (pricelist) exports into FinOps hubs (v1_2), the transform logic in Prices_transform_v1_2 sets ListUnitPrice to null for SavingsPlan-related rows.

However, for MCA price sheet exports, the MarketPrice provided by Azure Cost Management is accurate and represents the authoritative list/unit price. Nulling this value causes loss of correct pricing data and breaks downstream enrichment and savings calculations.

Problematic logic:

| extend ListUnitPrice = iff(
    x_SkuPriceType != 'SavingsPlan',
    MarketPrice,
    real(null)
) // MarketPrice for savings plan is not the list price


## 👣 Repro steps
Deploy a FinOps hub using schema version v1_2 (ADX or Fabric).
Configure Azure Cost Management MCA price sheet (pricelist) export ingestion.
Allow the price sheet export to be ingested into the hub.
Query Prices_final_v1_2 or call Prices_transform_v1_2().
Observe SavingsPlan-related rows where:

MarketPrice exists in the raw export
ListUnitPrice is null after transform

## 🤔 Expected
For MCA price sheet exports:
The export-provided MarketPrice should be preserved and available for SavingsPlan rows.
Either:
ListUnitPrice should retain MarketPrice, or
The export MarketPrice should be retained in a dedicated column for downstream use.
Savings and enrichment calculations should be able to reference the correct MCA list price.

## 📷 Screenshots
N/A 

## 🔧 Environment
FinOps hub version: v1_2 (current)
Billing account type: MCA (Microsoft Customer Agreement)
Power BI report type: ADX (Azure Data Explorer)
Cost Management export: Azure Cost Management price sheet / pricelist (FOCUS-based)

## ℹ️ Additional context
In our environment, the MCA price sheet MarketPrice consistently matches the authoritative list pricing from Azure Cost Management. Dropping this value for SavingsPlan rows prevents accurate reporting and validation.
A backward-compatible approach could include retaining the raw export MarketPrice (e.g., as x_MarketPrice) even if existing ListUnitPrice behavior is preserved.

## 🙋‍♀️ Ask for the community
We could use your help:
Please vote this issue up (👍) to prioritize it.
Leave comments if you’ve observed similar issues with MCA price sheets or SavingsPlan pricing.

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[tkalc]

Reviewing implications of this on all fields

[RolandKrummenacher]

Thanks for filing this @tkalc. Related prior discussion: PR #2037 attempted to address this exact behavior (along with the broader per-batch issue tracked in #1625) by removing the SP price-nulling and the cross-row consumption-price lookup in Prices_transform_v1_2. It includes data validation against EA and MCA price sheets confirming that UnitPrice/MarketPrice on SavingsPlan rows do represent the SP contracted and retail rates respectively — consistent with what you're observing on MCA.

The PR was closed without merging because the right final shape of the fix isn't clear yet. The core trade-off is what semantics ListUnitPrice and ContractedUnitPrice should carry on SP rows:

• Preserve SP's own rates (what Fix: Prices transform cross-row operations broken by per-batch execution #2037 does, and what your issue suggests): ListUnitPrice = SP retail (MarketPrice), ContractedUnitPrice = SP contracted (UnitPrice). Each row reflects its own price type. Cross-price-type comparisons (SP vs. on-demand savings) move to query time.
• Keep on-demand reference prices on SP rows (the original intent of the existing logic): SP rows carry the matching Consumption row's prices to enable "SP vs. on-demand" savings analysis directly. This is what's broken today by per-batch ingestion (Prices_transform_v1_0 function does not work as intended #1625) and was the reason for the SP nulling — it was meant to be replaced by a consumption-price lookup, but that lookup doesn't work reliably.
• Add a separate column (x_MarketPrice as you suggest, or similar): preserve MarketPrice independently regardless of which semantics the existing columns end up with. Backward-compatible.

We're not committing to a fix yet — flagging this so the discussion is consolidated. Comments on the preferred shape (especially from anyone using ListUnitPrice on SP rows for savings calculations today) welcome here or on #2037 / #1625.