diff --git a/.editorconfig b/.editorconfig
index a3f5ca8f69e3..8afd0dd3dd1a 100644
--- a/.editorconfig
+++ b/.editorconfig
@@ -287,21 +287,25 @@ dotnet_diagnostic.IDE0200.severity = none
 # Remove redundant nullable directive
 dotnet_diagnostic.IDE0240.severity = warning
 # MSBuildTask0001-0005 (Microsoft.Build.TaskAuthoring.Analyzer). MSBuildTask0001 is Error severity by
-# default; the rest are warnings. All are downgraded to 'suggestion' here for report-only onboarding while
-# task migration to the multithreaded model (IMultiThreadableTask / TaskEnvironment) is pending. At
-# suggestion level they are info diagnostics, so they never fail the build (not even under Arcade's
-# MSBuild-engine warn-as-error) without needing any WarningsNotAsErrors exemptions.
+# default; the rest are warnings. These were all initially downgraded to 'suggestion' for report-only
+# onboarding while task migration to the multithreaded model (IMultiThreadableTask / TaskEnvironment) is
+# pending. At suggestion level they are info diagnostics, so they never fail the build (not even under
+# Arcade's MSBuild-engine warn-as-error) without needing any WarningsNotAsErrors exemptions.
 #
-# Incremental re-enablement: a follow-up PR can raise a single rule globally (edit a line below to
-# 'warning'/'error' -- a "category" at a time), or raise severity for one task class by adding an
-# .editorconfig in that task's source directory that overrides these codes.
+# Incremental re-enablement (ratcheting): MSBuildTask0004 ('API may cause issues in multithreaded tasks')
+# is enabled at 'error' below. Its concerns (Assembly.Load* / Activator.CreateInstance* / AppDomain.* in a
+# shared task host) do NOT depend on the IMultiThreadableTask / TaskEnvironment migration, so it can be
+# enforced today, and the codebase already has zero violations. MSBuildTask0001/0002/0003/0005 remain at
+# 'suggestion' pending that migration (0002/0003 need TaskEnvironment; 0005 is transitive on the others).
+# A follow-up PR can raise a single rule globally (edit a line below), or raise severity for one task class
+# by adding an .editorconfig in that task's source directory that overrides these codes.
 #
 # NOTE: src/StaticWebAssetsSdk/.editorconfig sets `root = true`, so it does not inherit these lines and
 # carries its own copy of this block. Keep the two in sync.
 dotnet_diagnostic.MSBuildTask0001.severity = suggestion
 dotnet_diagnostic.MSBuildTask0002.severity = suggestion
 dotnet_diagnostic.MSBuildTask0003.severity = suggestion
-dotnet_diagnostic.MSBuildTask0004.severity = suggestion
+dotnet_diagnostic.MSBuildTask0004.severity = error
 dotnet_diagnostic.MSBuildTask0005.severity = suggestion
 
 # Additional rules for template engine source code
diff --git a/src/StaticWebAssetsSdk/.editorconfig b/src/StaticWebAssetsSdk/.editorconfig
index 97131d5fdf35..1e99d37ecc44 100644
--- a/src/StaticWebAssetsSdk/.editorconfig
+++ b/src/StaticWebAssetsSdk/.editorconfig
@@ -94,15 +94,18 @@ charset = utf-8-bom
 
 [*.{cs,vb}]
 
-# MSBuildTask0001-0005 (Microsoft.Build.TaskAuthoring.Analyzer) downgraded to 'suggestion' for report-only
-# onboarding while task migration to the multithreaded model (IMultiThreadableTask / TaskEnvironment) is
-# pending. This must be duplicated from the repo-root .editorconfig because this file sets `root = true`,
-# which severs inheritance from the root. Raise these to 'warning'/'error' (here or in a more specific
-# nested .editorconfig) as task classes are migrated.
+# MSBuildTask0001-0005 (Microsoft.Build.TaskAuthoring.Analyzer) were initially downgraded to 'suggestion'
+# for report-only onboarding while task migration to the multithreaded model (IMultiThreadableTask /
+# TaskEnvironment) is pending. This must be duplicated from the repo-root .editorconfig because this file
+# sets `root = true`, which severs inheritance from the root. MSBuildTask0004 ('API may cause issues in
+# multithreaded tasks') is enabled at 'error' below: its concerns do NOT depend on the TaskEnvironment
+# migration, so it can be enforced today, and the codebase already has zero violations. The remaining rules
+# stay at 'suggestion' pending that migration. Raise these (here or in a more specific nested .editorconfig)
+# as task classes are migrated. Keep this block in sync with the repo-root .editorconfig.
 dotnet_diagnostic.MSBuildTask0001.severity = suggestion
 dotnet_diagnostic.MSBuildTask0002.severity = suggestion
 dotnet_diagnostic.MSBuildTask0003.severity = suggestion
-dotnet_diagnostic.MSBuildTask0004.severity = suggestion
+dotnet_diagnostic.MSBuildTask0004.severity = error
 dotnet_diagnostic.MSBuildTask0005.severity = suggestion
 
 # SYSLIB1054: Use 'LibraryImportAttribute' instead of 'DllImportAttribute' to generate P/Invoke marshalling code at compile time