fix(hubs): never lower retention on redeploy

src/powershell/Tests/Unit/HubsRetentionGuard.Tests.ps1

@@ -0,0 +1,61 @@
+# Copyright (c) Microsoft Corporation.
+# Licensed under the MIT License.
+
+<#
+    Regression coverage for the settings.json retention guard (#2206):
+    Copy-FileToAzureBlob.ps1 unconditionally overwrote retention.ingestion.months / retention.final.months
+    with whatever the deploymentScript's Bicep parameters passed in. Bicep always resolves a value for an
+    optional parameter (defaulting to 13 if the caller didn't specify one), so the script cannot tell an
+    explicit redeploy value from a silently-defaulted one. A redeploy that omitted a previously-customized
+    retention value therefore silently reset it to the toolkit default, and the next purge pipeline run
+    aged out historical data older than the new (lower) cutoff -- oldest data first.
+
+    The fix: never lower stored retention on redeploy. Growing retention is always safe; shrinking it has a
+    destructive, hard-to-reverse consequence (data purge), so the script now takes the max of the stored
+    value and the incoming one instead of overwriting unconditionally.
+#>
+
+Describe 'HubsRetentionGuard' {
+
+    BeforeAll {
+        $repoRoot = (Resolve-Path "$PSScriptRoot/../../../..").Path
+        $scriptPath = Join-Path $repoRoot 'src/templates/finops-hub/modules/Microsoft.FinOpsHubs/Core/Copy-FileToAzureBlob.ps1'
+        $content = Get-Content -Path $scriptPath -Raw
+    }
+
+    Context 'Never-shrink guard' {
+
+        It 'Should take the max of stored and incoming ingestion retention' {
+            $content | Should -Match '\$json\.retention\.ingestion\.months\s*=\s*\[Math\]::Max\(\$json\.retention\.ingestion\.months,\s*\[Int32\]::Parse\(\$env:ingestionRetentionInMonths\)\)' `
+                -Because 'a redeploy that omits an explicit retention value must not silently shrink stored retention and purge historical data (#2206)'
+        }
+
+        It 'Should take the max of stored and incoming final retention' {
+            $content | Should -Match '\$json\.retention\.final\.months\s*=\s*\[Math\]::Max\(\$json\.retention\.final\.months,\s*\[Int32\]::Parse\(\$env:finalRetentionInMonths\)\)' `
+                -Because 'a redeploy that omits an explicit retention value must not silently shrink stored retention and purge historical data (#2206)'
+        }
+
+        It 'Should not unconditionally overwrite ingestion retention' {
+            $content | Should -Not -Match '\$json\.retention\.ingestion\.months\s*=\s*\[Int32\]::Parse\(\$env:ingestionRetentionInMonths\)\s*$' `
+                -Because 'a direct assignment (rather than a max guard) was the source of the #2206 regression'
+        }
+
+        It 'Should not unconditionally overwrite final retention' {
+            $content | Should -Not -Match '\$json\.retention\.final\.months\s*=\s*\[Int32\]::Parse\(\$env:finalRetentionInMonths\)\s*$' `
+                -Because 'a direct assignment (rather than a max guard) was the source of the #2206 regression'
+        }
+    }
+
+    Context 'First-run behavior unchanged' {
+
+        It 'Should still seed ingestion retention from the parameter when no retention object exists yet' {
+            $content | Should -Match 'Add-Member -Name ingestion -Value \(ConvertFrom-Json "\{""months"":\$\(\$env:ingestionRetentionInMonths\)\}"\)' `
+                -Because 'a brand-new settings.json has no stored value to protect, so the first deploy must still honor the requested retention'
+        }
+
+        It 'Should still seed final retention from the parameter when no retention object exists yet' {
+            $content | Should -Match 'Add-Member -Name final -Value \(ConvertFrom-Json "\{""months"":\$\(\$env:finalRetentionInMonths\)\}"\)' `
+                -Because 'a brand-new settings.json has no stored value to protect, so the first deploy must still honor the requested retention'
+        }
+    }
+}

src/templates/finops-hub/modules/Microsoft.FinOpsHubs/Core/Copy-FileToAzureBlob.ps1

@@ -125,13 +125,16 @@ else
 }
 
 # Set or update ingestion retention
+# NOTE: Bicep always passes a value here (defaulting to 13 if the caller didn't specify one), so this script
+# cannot tell an explicit redeploy value from a silently-defaulted one. Never lower retention on redeploy --
+# shrinking silently ages out historical data the next time the purge pipeline runs (#2206); growing is safe.
 if (!($json.retention.ingestion))
 {
     $json.retention | Add-Member -Name ingestion -Value (ConvertFrom-Json "{""months"":$($env:ingestionRetentionInMonths)}") -MemberType NoteProperty
 }
 else
 {
-    $json.retention.ingestion.months = [Int32]::Parse($env:ingestionRetentionInMonths)
+    $json.retention.ingestion.months = [Math]::Max($json.retention.ingestion.months, [Int32]::Parse($env:ingestionRetentionInMonths))
 }
 
 # Set or update raw retention
@@ -144,14 +147,14 @@ else
     $json.retention.raw.days = [Int32]::Parse($env:rawRetentionInDays)
 }
 
-# Set or update final retention
+# Set or update final retention (never lower on redeploy -- see note above)
 if (!($json.retention.final))
 {
     $json.retention | Add-Member -Name final -Value (ConvertFrom-Json "{""months"":$($env:finalRetentionInMonths)}") -MemberType NoteProperty
 }
 else
 {
-    $json.retention.final.months = [Int32]::Parse($env:finalRetentionInMonths)
+    $json.retention.final.months = [Math]::Max($json.retention.final.months, [Int32]::Parse($env:finalRetentionInMonths))
 }
 
 # Updating settings