diff --git a/crates/benilla-app/assets/ui/CompatTemplates.xml b/crates/benilla-app/assets/ui/CompatTemplates.xml
new file mode 100644
index 00000000..49406a70
--- /dev/null
+++ b/crates/benilla-app/assets/ui/CompatTemplates.xml
@@ -0,0 +1,93 @@
+<Ui>
+    <!--
+        The ClassicAPI-era FrameXML templates addons on this install inherit by name. Not windows:
+        there is nothing to migrate, because 1.12 does not have these templates at all — they are
+        the same kind of surface as `script/compat/`'s verbs, declared here because `inherits=` is
+        resolved by the XML loader and cannot be answered from Lua.
+
+        Both are used **unguarded inside Ace3 itself**, so this is not one addon's problem:
+        `AceGUIContainer-Frame.lua:179` and `:206` and `AceGUIContainer-DropDownGroup.lua:128`
+        name `BackdropTemplate`, and `AceConfigDialog-3.0.lua:573` names
+        `DialogBorderOpaqueTemplate`. A missing template makes `CreateFrame` raise
+        ("Couldn't find inherited node"), which is where OpenMapClassic stopped — on its first
+        file, in a library, before a line of its own code ran.
+    -->
+
+    <!--
+        9.0 moved the backdrop off the C side and gave addons `BackdropTemplateMixin` to put it
+        back; 1.12 has `SetBackdrop`/`GetBackdrop`/`SetBackdropColor`/`SetBackdropBorderColor` as
+        real frame methods, so the template is correctly **empty** — a frame inheriting it already
+        answers all four. The global the mixin idiom tests for
+        (`BackdropTemplateMixin and "BackdropTemplate" or nil`) is set beside it, its methods
+        forwarding to those stock ones so `Mixin(f, BackdropTemplateMixin)` is a no-op rather than
+        a shadow. `OnBackdropLoaded`/`OnBackdropSizeChanged` are the hooks 9.0's own template
+        fires; ours have nothing to recompute, and an addon that calls one gets a function rather
+        than a nil.
+    -->
+    <Frame name="BackdropTemplate" virtual="true"/>
+
+    <!--
+        A dialog border frame, which is all Ace3 wants of it: `local border = CreateFrame("Frame",
+        nil, frame, "DialogBorderOpaqueTemplate")` then `border:SetAllPoints(frame)`. Era's own is
+        nine textures out of `SharedUIPanelTemplates.xml`; the same shape in 1.12's vocabulary is
+        one `<Backdrop>` over this client's dialog art, which is what every stock 1.12 dialog
+        draws and what our `GameMenuFrame.xml` already uses. The opaque variant differs only in
+        its background alpha, hence the two rows.
+
+        `enableMouse` stays off: it is a decoration over a frame that handles its own input, and a
+        border that ate clicks would make an Ace options window unusable.
+    -->
+    <Frame name="DialogBorderTemplate" virtual="true">
+        <Backdrop bgFile="Interface\DialogFrame\UI-DialogBox-Background" edgeFile="Interface\DialogFrame\UI-DialogBox-Border" tile="true">
+            <BackgroundInsets><AbsInset left="11" right="12" top="12" bottom="11"/></BackgroundInsets>
+            <TileSize><AbsValue val="32"/></TileSize>
+            <EdgeSize><AbsValue val="32"/></EdgeSize>
+            <Color r="1" g="1" b="1" a="0.85"/>
+        </Backdrop>
+    </Frame>
+
+    <Frame name="DialogBorderOpaqueTemplate" virtual="true">
+        <Backdrop bgFile="Interface\DialogFrame\UI-DialogBox-Background" edgeFile="Interface\DialogFrame\UI-DialogBox-Border" tile="true">
+            <BackgroundInsets><AbsInset left="11" right="12" top="12" bottom="11"/></BackgroundInsets>
+            <TileSize><AbsValue val="32"/></TileSize>
+            <EdgeSize><AbsValue val="32"/></EdgeSize>
+            <Color r="1" g="1" b="1" a="1"/>
+        </Backdrop>
+    </Frame>
+
+    <Script><![CDATA[
+        -- The mixin 9.0 shipped so addons could call the backdrop methods it had removed. Here
+        -- the stock methods are the real ones, so each row forwards; the table exists for the
+        -- `BackdropTemplateMixin and "BackdropTemplate"` test and for `Mixin()`.
+        BackdropTemplateMixin = {}
+
+        function BackdropTemplateMixin.OnBackdropLoaded(self) end
+        function BackdropTemplateMixin.OnBackdropSizeChanged(self) end
+
+        function BackdropTemplateMixin.SetupTextureCoordinates(self) end
+
+        function BackdropTemplateMixin.ApplyBackdrop(self)
+            -- 9.0's own ApplyBackdrop re-reads `self.backdropInfo`; ours hands it to the stock
+            -- setter, which is the same journey with the C side still present.
+            if self.backdropInfo then
+                self:SetBackdrop(self.backdropInfo)
+                if self.backdropColor then
+                    local c = self.backdropColor
+                    self:SetBackdropColor(c.r, c.g, c.b, self.backdropColorAlpha or 1)
+                end
+                if self.backdropBorderColor then
+                    local c = self.backdropBorderColor
+                    self:SetBackdropBorderColor(c.r, c.g, c.b, self.backdropBorderColorAlpha or 1)
+                end
+            end
+        end
+
+        function BackdropTemplateMixin.ClearBackdrop(self)
+            self:SetBackdrop(nil)
+        end
+
+        -- No getter rows: 1.12's own `GetBackdrop`/`GetBackdropColor`/`GetBackdropBorderColor`
+        -- already answer, and a forwarding copy would call *itself* once `Mixin()` had written it
+        -- onto the frame.
+    ]]></Script>
+</Ui>
diff --git a/crates/benilla-app/assets/ui/benilla.toc b/crates/benilla-app/assets/ui/benilla.toc
index 78dadbe8..6c060dd7 100644
--- a/crates/benilla-app/assets/ui/benilla.toc
+++ b/crates/benilla-app/assets/ui/benilla.toc
@@ -86,6 +86,10 @@ Interface\FrameXML\ComboFrame.xml
 # Ours: the scroll parts of our options window and script log.
 ScrollTemplates.xml
 
+# The ClassicAPI-era templates addons inherit by name (Ace3 names two of them unguarded).
+# Templates only, so anywhere above the addon load is correct; here, beside our other one.
+CompatTemplates.xml
+
 Interface\FrameXML\UIPanelTemplates.lua
 
 Interface\FrameXML\UIPanelTemplates.xml
diff --git a/crates/benilla-app/src/ui_script/shipped_xml_tests.rs b/crates/benilla-app/src/ui_script/shipped_xml_tests.rs
index 0ba149c8..f2324b7d 100644
--- a/crates/benilla-app/src/ui_script/shipped_xml_tests.rs
+++ b/crates/benilla-app/src/ui_script/shipped_xml_tests.rs
@@ -1974,6 +1974,13 @@ fn assets_ui_does_not_grow() {
         // falls through into `attempt to call local 'handledata'`. There is no stock file to
         // migrate — AIO is the realm's, not Blizzard's. The file's own header has the trace.
         "AIOHandlers.lua",
+        // Not a window either: the ClassicAPI-era FrameXML templates addons inherit by name,
+        // which have no stock 1.12 file to migrate from because 1.12 has no such templates. They
+        // live in XML rather than `script/compat/` only because `inherits=` is resolved by the
+        // loader and cannot be answered from Lua. Ace3 names two of them **unguarded**, so a
+        // missing one raises inside the library: `CreateFrame(): Couldn't find inherited node
+        // "DialogBorderOpaqueTemplate"` is where OpenMapClassic stopped, on its first file.
+        "CompatTemplates.xml",
         "ContainerFrameAdapters.xml",
         "GameMenuFrame.xml",
         "KeyBindingsPage.xml",