fix(transport): pin a compressed copy of the decrypted bundle on the import session, release the upload buffer early, document the footprint (review 2026-10-21 04/M2)

src/ZB.MOM.WW.ScadaBridge.Commons/Types/Transport/BundleSession.cs

@@ -16,7 +16,12 @@ public sealed class BundleSession
     public Guid SessionId { get; init; }
     /// <summary>Parsed manifest from the uploaded bundle.</summary>
     public BundleManifest Manifest { get; init; } = null!;
-    /// <summary>Decrypted bundle content bytes; empty until the bundle is successfully unlocked.</summary>
+    /// <summary>
+    /// The decrypted bundle content, held Brotli-compressed by the importer (review
+    /// 2026-10-21 04/M2) — still sensitive (it decompresses to the plaintext content,
+    /// secret values included), so every release path zeroes it before dropping the
+    /// session. Empty until the bundle is successfully unlocked.
+    /// </summary>
     public byte[] DecryptedContent { get; init; } = Array.Empty<byte>();
     /// <summary>UTC timestamp after which this session is considered expired and must be re-uploaded.</summary>
     public DateTimeOffset ExpiresAt { get; init; }