fix(open-data): parse and write ISF ratios with the invariant culture

Ratios were parsed and written with the current culture. On a comma-decimal
machine that corrupts the dataset in both directions:

- de-DE parses "2.1" as 21, so a ratio is silently ten times too large.
- fr-CH fails the parse outright, so the row is dropped.
- Export-Csv writes the value back as "2,1", which breaks every consumer:
  the Optimization Engine's externaldata(... Ratio:double) and the Power BI
  partitions typed as number.

CI runs on ubuntu-latest and is unaffected, but the README documents running
the generator by hand, so a contributor in a comma-decimal locale would
publish a corrupt file. Both parse sites and the write path now pin
InvariantCulture, with a regression test that drives the generator under
de-DE and asserts the round trip.

Also corrects the SKU count in the changelog: it still said 2,574 from
before the zero-ratio row was dropped, against 2,573 actually published.

Reported by Copilot review on #2308 (the parse side; the write side turned
up while verifying it).

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

Author: Roland Krummenacher

docs-mslearn/toolkit/changelog.md

@@ -79,7 +79,7 @@ The following section lists features and enhancements that are currently in deve
 - **Added**
   - Added a new [Instance size flexibility](open-data.md#instance-size-flexibility) dataset that maps each ARM SKU to its instance size flexibility group and ratio, sourced from the Azure Reservations Catalogs API. It replaces the deprecated ISF ratio files hosted on `ccmstorageprod.blob.core.windows.net` ([#2090](https://github.com/microsoft/finops-toolkit/issues/2090)).
 - **Fixed**
-  - Fixed the instance size flexibility dataset omitting SKUs that are no longer available to purchase. The Catalogs API only returns purchasable SKUs, so retired series that reservations still cover (Av2, D, DS, Dv2, Dv3, Ev3, F, G, H, LS, NC, NV, and others) were missing. The dataset is now additive and backfilled from the retired ratio file, growing from 211 to 318 flexibility groups and from 1,353 to 2,574 SKUs ([#2300](https://github.com/microsoft/finops-toolkit/issues/2300)).
+  - Fixed the instance size flexibility dataset omitting SKUs that are no longer available to purchase. The Catalogs API only returns purchasable SKUs, so retired series that reservations still cover (Av2, D, DS, Dv2, Dv3, Ev3, F, G, H, LS, NC, NV, and others) were missing. The dataset is now additive and backfilled from the retired ratio file, growing from 211 to 318 flexibility groups and from 1,353 to 2,573 SKUs ([#2300](https://github.com/microsoft/finops-toolkit/issues/2300)).
   - Fixed the generator sweeping a hardcoded list of 26 regions, which silently omitted SKUs that launch only in regions outside the list. It now enumerates every physical region from the ARM locations API, 63 at the time of the change ([#2300](https://github.com/microsoft/finops-toolkit/issues/2300)).
   - Fixed the dataset publishing a SKU whose ratio is `0`, which the Optimization Engine's benefits simulation divides by. Non-positive ratios are now dropped ([#2300](https://github.com/microsoft/finops-toolkit/issues/2300)).
   - Fixed ratios from the retired files sitting on a different scale than the Catalogs API. The retired files normalized each group so its smallest SKU was `1`; the API returns them unnormalized, so a group's smallest SKU usually isn't `1`. Because Azure retires individual sizes rather than whole families, the API covers only part of many groups, so combining the two left single groups holding both units. The backfilled rows were converted onto the API scale, and the generator now fails rather than publishing a group in two units ([#2300](https://github.com/microsoft/finops-toolkit/issues/2300)).

src/powershell/Tests/Unit/Update-InstanceSizeFlexibility.Tests.ps1

@@ -167,6 +167,32 @@ Describe 'Update-InstanceSizeFlexibility' {
             @(Import-Csv $outFile).ArmSkuName | Should -Be 'Standard_D2'
         }
 
+        It 'Parses and writes ratios independently of the current culture' {
+            # On a comma-decimal culture, culture-aware parsing turns "2.1" into 21 (de-DE) or
+            # drops the row outright (fr-CH), and Export-Csv writes "2,1" back out, which breaks
+            # every consumer of the published file.
+            $originalCulture = [System.Threading.Thread]::CurrentThread.CurrentCulture
+            try
+            {
+                [System.Threading.Thread]::CurrentThread.CurrentCulture = [System.Globalization.CultureInfo]::new('de-DE')
+                @([PSCustomObject]@{ InstanceSizeFlexibilityGroup = 'Av2 Series'; ArmSkuName = 'Standard_A2_v2'; Ratio = '2.1' }) `
+                | Export-Csv $outFile -NoTypeInformation
+                Mock Invoke-AzRestMethod {
+                    New-CatalogResponse -Items @((New-CatalogItem -Sku 'Standard_D2' -Group 'DSeries' -Ratio '4.5'))
+                }
+
+                Invoke-Generator $baseParams
+
+                $raw = Get-Content $outFile -Raw
+                $raw | Should -BeLike '*"Standard_A2_v2","2.1"*'   # carried forward, not 21
+                $raw | Should -BeLike '*"Standard_D2","4.5"*'      # from the API, not 45
+            }
+            finally
+            {
+                [System.Threading.Thread]::CurrentThread.CurrentCulture = $originalCulture
+            }
+        }
+
         It 'Skips items without ISF group or ratio properties' {
             Mock Invoke-AzRestMethod {
                 New-CatalogResponse -Items @(

src/scripts/Update-InstanceSizeFlexibility.ps1

@@ -268,7 +268,8 @@ function Get-IsfRecords
         # Optimization Engine's benefits simulation does exactly that -- so drop it rather than
         # publish a division by zero. The API returns one today (Azure Redis Cache Isolated).
         $parsedRatio = 0.0
-        if ($flexGroup -and $armSkuName -and [double]::TryParse($ratio, [ref]$parsedRatio) -and $parsedRatio -gt 0)
+        $parsed = [double]::TryParse($ratio, [Globalization.NumberStyles]::Float, [Globalization.CultureInfo]::InvariantCulture, [ref]$parsedRatio)
+        if ($flexGroup -and $armSkuName -and $parsed -and $parsedRatio -gt 0)
         {
             $null = $records.Add([PSCustomObject]@{
                     InstanceSizeFlexibilityGroup = [string]$flexGroup
@@ -333,7 +334,7 @@ function Import-IsfCsv
     foreach ($row in $rows)
     {
         $ratio = 0.0
-        if (-not [double]::TryParse($row.Ratio, [ref]$ratio)) { continue }
+        if (-not [double]::TryParse($row.Ratio, [Globalization.NumberStyles]::Float, [Globalization.CultureInfo]::InvariantCulture, [ref]$ratio)) { continue }
         if ($ratio -le 0) { continue }
         if (-not $groupsPerSku.ContainsKey($row.ArmSkuName)) { $groupsPerSku[$row.ArmSkuName] = @{} }
         $groupsPerSku[$row.ArmSkuName][$row.InstanceSizeFlexibilityGroup] = $true
@@ -342,7 +343,7 @@ function Import-IsfCsv
     foreach ($row in $rows)
     {
         $ratio = 0.0
-        if (-not [double]::TryParse($row.Ratio, [ref]$ratio)) { continue }
+        if (-not [double]::TryParse($row.Ratio, [Globalization.NumberStyles]::Float, [Globalization.CultureInfo]::InvariantCulture, [ref]$ratio)) { continue }
         if ($ratio -le 0) { continue }
         if ($groupsPerSku[$row.ArmSkuName].Count -gt 1) { continue }
         # Same placeholder filter the API path applies, so a retired file's placeholder rows
@@ -513,7 +514,12 @@ if ($Normalize)
     $allRecords = Get-NormalizedRecords -Records $allRecords
 }
 
-$rows = $allRecords | Sort-Object InstanceSizeFlexibilityGroup, ArmSkuName
+# Ratio is formatted invariantly rather than left to Export-Csv, which uses the current culture:
+# on a comma-decimal machine it would publish "2,1" and break every consumer of the file.
+$rows = $allRecords |
+    Sort-Object InstanceSizeFlexibilityGroup, ArmSkuName |
+    Select-Object InstanceSizeFlexibilityGroup, ArmSkuName,
+        @{ Name = 'Ratio'; Expression = { $_.Ratio.ToString([Globalization.CultureInfo]::InvariantCulture) } }
 
 $rows | Export-Csv -Path $OutputPath -UseQuotes Always -NoTypeInformation -Encoding utf8
 Write-Host "Wrote $($rows.Count) SKUs to $OutputPath"