issue with XYZTVector

Author: tomeichlersmith

src/developing/compatibility.md

@@ -42,6 +42,7 @@ sanitizers | enable one or more of the sanitizers, cmake: `-DENABLE_SANITIZER_*=
 detector id bindings | enable detector ID python bindings, cmake: `-DBUILD_DETECTORID_BINDINGS=ON`
 patch cmake | need to do both `no testing` and `force legacy onnx`
 header patch | transitioning to a newer compiler then required a few more headers to be included[^3]
+include lorentz vector | add `Math/GenVector/LorentzVector.h` and `Math/Vector4Dfwd.h` to inclusions in `Ecal/IntermediateCluster.h`
 
 [^1]: Currently in ldmx-sw, there isn't a command-line option to disable the
       testing so one must comment out the `build_test()` line in `ldmx-sw/CMakeLists.txt`.
@@ -124,7 +125,7 @@ patches to be included as well.
 It is encouraged to rebase and/or merge ldmx-sw:v4.3.0 into your branch in
 order for the main CI tests to work now that they use ldmx/dev:5.0.0.
 
-### >= v4.3.0
+### = v4.3.0
 Patches for the newer compiler have been included and so the default build
 configuration can be handled by the new image version.
 Not all of the _warnings_ from the newer compiler have been patched,
@@ -134,3 +135,26 @@ and runs as expected.
 build config | image version
 ---|---
 default | >= v4.0.0
+
+### >= 4.3.1
+One release after getting development to function with ldmx/dev:v5,
+I (Tom) accidentally introduced a change that breaks compatibility with ldmx/dev:4.2.2
+which uses an older version of ROOT.
+
+The error you see is with using `XYZTVector` which is not present in the `ROOT::Math` namespace
+without including a couple more headers.
+
+~~~admonish example title="Example Compile Error Message", collapsible=true
+I've removed the other errors generated by the compiler, mainly focused on how the `centroid` function
+is not defined anymore since its return type is not defined.
+```
+/home/tom/code/ldmx/ldmx-sw/Ecal/include/Ecal/IntermediateCluster.h:24:21: error: 'XYZTVector' in namespace 'ROOT::Math' does not name a type
+   24 |   const ROOT::Math::XYZTVector& centroid() const { return centroid_; }
+      |                     ^~~~~~~~~~
+```
+~~~
+
+build config | image version
+---|---
+default | >= v5.0.0
+include lorentz vector | >= v4.0.0