diff --git a/Directory.Build.props b/Directory.Build.props
new file mode 100644
index 0000000..c8a3c67
--- /dev/null
+++ b/Directory.Build.props
@@ -0,0 +1,10 @@
+<Project>
+  <PropertyGroup>
+    <CultLibRoot Condition="'$(CultLibRoot)' == '' and '$(CULTLIB_ROOT)' != ''">$(CULTLIB_ROOT)</CultLibRoot>
+    <CultLibRoot Condition="'$(CultLibRoot)' == ''">$(MSBuildThisFileDirectory)..\CultLib</CultLibRoot>
+    <!-- CultLib 2.0.0: tag cultlib-unity-v2.0.0. -->
+    <CultLibRevision>42dce3611a81adc5c5fac54cadbaa5637d6022d3</CultLibRevision>
+    <GitExecutable Condition="'$(GitExecutable)' == '' and Exists('C:\Program Files\Git\cmd\git.exe')">C:\Program Files\Git\cmd\git.exe</GitExecutable>
+    <GitExecutable Condition="'$(GitExecutable)' == ''">git</GitExecutable>
+  </PropertyGroup>
+</Project>
diff --git a/Directory.Build.targets b/Directory.Build.targets
new file mode 100644
index 0000000..46d436a
--- /dev/null
+++ b/Directory.Build.targets
@@ -0,0 +1,30 @@
+<Project>
+  <!-- Builds consume CultLib at one admitted revision. Point CultLibRoot (or CULTLIB_ROOT) at a clean
+       worktree of that revision: git worktree add <path> cultlib-unity-v2.0.0 (detached) (in CultLib). -->
+  <Target Name="VerifyCultLibRevision"
+          BeforeTargets="ResolveProjectReferences"
+          Condition="'$(SkipCultLibRevisionCheck)' != 'true'">
+    <ItemGroup>
+      <_CultLibReference Include="@(ProjectReference)"
+                         Condition="$([System.String]::Copy('%(Filename)').StartsWith('GameCult.')) or '%(Filename)' == 'CultMath'" />
+    </ItemGroup>
+    <Error Condition="'@(_CultLibReference)' != '' and !Exists('$(CultLibRoot)\src\GameCult.Caching\GameCult.Caching.csproj')"
+           Text="CultLibRoot '$(CultLibRoot)' is not a CultLib checkout." />
+    <Exec Condition="'@(_CultLibReference)' != ''"
+          Command="&quot;$(GitExecutable)&quot; -C &quot;$(CultLibRoot)&quot; rev-parse HEAD"
+          ConsoleToMSBuild="true"
+          StandardOutputImportance="Low">
+      <Output TaskParameter="ConsoleOutput" PropertyName="ActualCultLibRevision" />
+    </Exec>
+    <Error Condition="'@(_CultLibReference)' != '' and '$([System.String]::Copy($(ActualCultLibRevision)).Trim())' != '$(CultLibRevision)'"
+           Text="CultLib must be revision $(CultLibRevision) (cultlib-unity-v2.0.0); found $([System.String]::Copy($(ActualCultLibRevision)).Trim()). Set CultLibRoot to a clean worktree of that tag." />
+    <Exec Condition="'@(_CultLibReference)' != ''"
+          Command="&quot;$(GitExecutable)&quot; -C &quot;$(CultLibRoot)&quot; status --porcelain --untracked-files=normal"
+          ConsoleToMSBuild="true"
+          StandardOutputImportance="Low">
+      <Output TaskParameter="ConsoleOutput" PropertyName="CultLibStatus" />
+    </Exec>
+    <Error Condition="'@(_CultLibReference)' != '' and '$([System.String]::Copy($(CultLibStatus)).Trim())' != ''"
+           Text="CultLibRoot '$(CultLibRoot)' must be clean before this repo consumes it." />
+  </Target>
+</Project>
diff --git a/README.md b/README.md
index 9392c11..5d56c7f 100644
--- a/README.md
+++ b/README.md
@@ -135,3 +135,14 @@ and contact facts come from Box3D through an explicitly owned Ymir session.
 Manual Unity callbacks and Aetheria geometry tests must be structurally unable
 to decide the result. Snapshot compatibility calls may use isolated sessions;
 they are not allowed to infer or share retained-world identity.
+
+## Building against CultLib
+
+Builds are pinned to CultLib 2.0.0 (tag `cultlib-unity-v2.0.0`, revision `42dce3611a81adc5c5fac54cadbaa5637d6022d3`); the build fails if the CultLib checkout differs or is dirty. Create a pinned worktree and point the build at it:
+
+```powershell
+git -C <CultLib> worktree add --detach <path> cultlib-unity-v2.0.0
+dotnet build -p:CultLibRoot=<path>   # or set CULTLIB_ROOT=<path>
+```
+
+Without an override the sibling `..\CultLib` checkout is used and must itself be at that tag.
diff --git a/src/Ymir.Core/Ymir.Core.csproj b/src/Ymir.Core/Ymir.Core.csproj
index 6518910..29683f8 100644
--- a/src/Ymir.Core/Ymir.Core.csproj
+++ b/src/Ymir.Core/Ymir.Core.csproj
@@ -1,7 +1,6 @@
 <Project Sdk="Microsoft.NET.Sdk">
 
   <PropertyGroup>
-    <CultLibRoot Condition="'$(CultLibRoot)' == ''">$(MSBuildThisFileDirectory)..\..\..\CultLib</CultLibRoot>
     <EveRoot Condition="'$(EveRoot)' == ''">$(MSBuildThisFileDirectory)..\..\..\Eve</EveRoot>
   </PropertyGroup>