CI fix windows integration test failures (#435)

Fix ShrinkRootPartition to reliably free space on stemcell 2019.99

On stemcell 2019.99 the gap between SizeMin (~29.05 GB) and the
partition size (~30 GB) is only ~950 MB. The previous approach used
SizeMin + 1 GB as the target, which exceeded SizeMax (= CurrentSize)
and caused Resize-Partition to fail with "Size Not Supported". A later
attempt used SizeMax - 10 GB, which fell below SizeMin and caused
Resize-Partition to silently return exit code 0 without making any
change (LargestFreeExtent remained 0).

Fix by shrinking 200 MB from the current partition size:
- Uses (Get-Partition).Size (current size) instead of SizeMax, so we
  always shrink even when there is adjacent unallocated space.
- 200 MB is well within the achievable range (~950 MB gap) and well
  above the agent's 1 MB minimum for creating an ephemeral partition.
- Small amount means minimal data movement and fast completion.

Also remove the agent-windows-large-root-disk.yml ops file added as a
workaround: the AWS CPI ignores root_disk in instance-group-level
cloud_properties, so the disk remained at 30 GB regardless. The ops
file is no longer needed with the corrected shrink strategy.

Co-authored-by: Cursor <cursoragent@cursor.com>

Author: julian-hj

ci/pipeline.yml

@@ -464,8 +464,6 @@ jobs:
             stemcells:
               - "aws-stemcell/*.tgz"
               - "aws-windows-stemcell/*.tgz"
-            ops_files:
-              - "bosh-agent/integration/assets/agent-windows-large-root-disk.yml"
             vars:
               deployment_name: bosh-agent-integration-windows-main
         - task: get-agent-info
@@ -510,7 +508,6 @@ jobs:
               - "aws-stemcell/*.tgz"
               - "aws-windows-stemcell/*.tgz"
             ops_files:
-              - "bosh-agent/integration/assets/agent-windows-large-root-disk.yml"
               - "bosh-agent/integration/assets/agent-windows-nats-blobstore.yml"
             releases:
               - bosh-bosh-release/release.tgz
@@ -570,6 +567,7 @@ jobs:
                 delete:
                   enabled: true
                   force: true
+
   - name: bosh-integration-tests
     serial: true
     plan:

integration/assets/agent-windows-large-root-disk.yml

@@ -28,17 +28,24 @@ type WindowsEnvironment struct {
 }
 
 func (e *WindowsEnvironment) ShrinkRootPartition() {
-	// Shrink C: by a fixed amount from its current maximum rather than trying
-	// to reach the theoretical SizeMin. Shrinking to SizeMin requires Windows
-	// to move almost all data to the start of the disk, which fails with
-	// "Size Not Supported" when NTFS unmovable files (MFT mirror, NTFS log,
-	// VSS snapshots) are scattered throughout the partition. Shrinking by a
-	// modest fixed amount only requires the last N GB to be free contiguous
-	// space, which is reliably true on a freshly provisioned VM.
-	// 10 GB is more than enough for the ephemeral partition the tests create.
-	const shrinkBy = 10 * GB
+	// Shrink C: by a small fixed amount from its current size rather than
+	// trying to reach the theoretical SizeMin.
+	//
+	// On stemcell 2019.99 the gap between SizeMin and the partition size is
+	// only ~950 MB, so a large shrink (e.g. 10 GB) would request a target
+	// below SizeMin and silently fail (Resize-Partition returns exit code 0
+	// but leaves the partition unchanged). Using a small amount (200 MB)
+	// keeps the target safely above SizeMin while giving the agent more than
+	// enough room to create an ephemeral partition (minimum is 1 MB).
+	//
+	// Using (Get-Partition -DriveLetter C).Size (current size) rather than
+	// (Get-PartitionSupportedSize -DriveLetter C).SizeMax ensures we are
+	// always shrinking: SizeMax includes adjacent unallocated space and can
+	// be larger than the current partition size.
+	const MB = 1024 * 1024
+	const shrinkBy = 200 * MB
 	cmd := fmt.Sprintf(
-		"Get-Partition -DriveLetter C | Resize-Partition -Size $((Get-PartitionSupportedSize -DriveLetter C).SizeMax - %d)",
+		"$currentSize = (Get-Partition -DriveLetter C).Size; Get-Partition -DriveLetter C | Resize-Partition -Size ($currentSize - %d)",
 		shrinkBy,
 	)