diff --git a/.CI/Jenkinsfile b/.CI/Jenkinsfile
index c7d2092..3323fb3 100644
--- a/.CI/Jenkinsfile
+++ b/.CI/Jenkinsfile
@@ -385,8 +385,7 @@ pipeline {
         }
         steps {
           runRegressiontest('master', 'wasm-jit', 'setCommandLineOptions("--simCodeTarget=wasm-jit")', '', false, '', '--wasmjitrunner=sim,me,cs', false, false, 0, 'configs/conf.json',
-                            '-DOM_OMC_ENABLE_RUST=ON -DRUST_OMC_CI=ON -DRUST_OMC_THREADS=4 -DCMAKE_C_COMPILER_LAUNCHER=sccache -DCMAKE_CXX_COMPILER_LAUNCHER=sccache',
-                            '.CI/wasm-jit')
+                            '-DOM_OMC_ENABLE_RUST=ON -DRUST_OMC_CI=ON -DRUST_OMC_THREADS=4 -DCMAKE_C_COMPILER_LAUNCHER=sccache -DCMAKE_CXX_COMPILER_LAUNCHER=sccache')
         }
       }
       stage('generateSymbolicJacobian') {
@@ -702,7 +701,12 @@ def numLogicalCPU() {
 def omsimulatorHash() {
   return 'master'
 }
-def installLibraries(boolean removePackageOrder, boolean conversionScript, name, String omhomeTestedOMC) {
+/**
+  * Installs the libraries a run tests, with the node's own omc, and returns the home directory
+  * holding them. `runSh` is how the conversion script is run: that one uses the omc that was just
+  * built, which is a binary of the image when the job has one.
+  */
+def installLibraries(boolean removePackageOrder, boolean conversionScript, name, String omhomeTestedOMC, Closure runSh) {
   sh "rm -rf '${env.HOME}/saved_omc/libraries/.openmodelica/libraries'"
   sh "mkdir -p '${env.HOME}/saved_omc/libraries/'"
   sh "HOME='${env.HOME}/saved_omc/libraries/' /usr/bin/omc OpenModelicaLibraryTesting/.CI/installLibraries.mos"
@@ -714,11 +718,11 @@ def installLibraries(boolean removePackageOrder, boolean conversionScript, name,
   sh "cp -ai /mnt/ReferenceFiles/ExtraLibs/packaged/* '${env.HOME}/saved_omc/libraries/'"
   echo "installLibraries removePackageOrder: ${removePackageOrder} conversionScript: ${conversionScript} name: ${name}"
   if (conversionScript) {
-    sh """
+    runSh("""
     cd '${WORKSPACE}/OpenModelicaLibraryTesting'
     OPENMODELICAHOME="${omhomeTestedOMC}" ./conversionscript.py --diff --allowErrorsInDiff '${env.HOME}/saved_omc/libraries/.openmodelica/libraries'
     scp converted-libraries/.openmodelica/libraries/*.diff 'libraries.openmodelica.org:/var/www/libraries.openmodelica.org/branches/${name}'
-    """
+    """)
     return "${WORKSPACE}/OpenModelicaLibraryTesting/converted-libraries"
   } else {
     return "${env.HOME}/saved_omc/libraries"
@@ -808,9 +812,10 @@ def sccachePreamble() {
   *                             This file specifies which libraries to test and what options to use for them.
   * @param cmakeFlags:          Target-specific cmake flags, e.g. `-DOM_OMC_ENABLE_RUST=ON`. If non-empty, omc is
   *                             built with cmake instead of autotools; the shared release flags are added here.
-  * @param dockerfile:          Directory with a Dockerfile, relative to the testing repository, e.g.
-  *                             `.CI/wasm-jit`. If non-empty, the omc build and test.py run in that image
-  *                             instead of on the node; everything using the node's own omc stays outside.
+  * @param dockerfile:          Directory with a Dockerfile, relative to the testing repository. Defaults to
+  *                             `.CI/testing`, the image every job runs in: the omc build, the OMSimulator
+  *                             build and test.py happen inside it, and only the steps using the node's own
+  *                             omc stay outside. Passing `''` runs the job on the node itself.
   */
 /* The FMI simulators a job runs, from the parameters that used to start one job each.
  * Both ticked is one job that builds every FMU once and simulates it with both,
@@ -822,7 +827,7 @@ def fmiSimulators(boolean omsimulator, boolean fmpy) {
   return simulators
 }
 
-def runRegressiontest(branch, name, extraFlags, omsHash, omcompiler, extrasimflags, testFlags, boolean removePackageOrder, boolean conversionScript, int jobs=0, libs_config_file = 'configs/conf.json', cmakeFlags = '', dockerfile = '', fmiSimulators = null) {
+def runRegressiontest(branch, name, extraFlags, omsHash, omcompiler, extrasimflags, testFlags, boolean removePackageOrder, boolean conversionScript, int jobs=0, libs_config_file = 'configs/conf.json', cmakeFlags = '', dockerfile = '.CI/testing', fmiSimulators = null) {
   sh '''
   find /tmp  -name "*openmodelica.hudson*" -exec rm {} ";" || true
 
@@ -846,7 +851,10 @@ def runRegressiontest(branch, name, extraFlags, omsHash, omcompiler, extrasimfla
   if (dockerfile) {
     // Build context is the Dockerfile directory; the workspace has a directory per tested model.
     sh "cp OpenModelicaLibraryTesting/requirements.txt OpenModelicaLibraryTesting/${dockerfile}/"
-    image = docker.build("openmodelica-library-testing:${name}", "--pull OpenModelicaLibraryTesting/${dockerfile}")
+    // Tagged after the Dockerfile rather than after the job, so that jobs sharing an image share
+    // its tag as well and a node keeps one of them instead of one per job it has ever run.
+    image = docker.build("openmodelica-library-testing:${dockerfile.tokenize('/').last()}",
+                         "--pull OpenModelicaLibraryTesting/${dockerfile}")
   }
   // --init reaps the omc processes test.py orphans. ssh refuses to run for a uid it cannot look
   // up, so the node's passwd entry is needed to publish the results. The home holds the cached omc
@@ -885,7 +893,9 @@ def runRegressiontest(branch, name, extraFlags, omsHash, omcompiler, extrasimfla
   }
   FMI_TESTING_FLAG = ""
   if (simulators.contains('OMSimulator') && omsHash) {
-    sh """
+    // In the image rather than on the node: test.py runs this binary from inside it, and one built
+    // against the node's libraries need not load there.
+    runSh("""
     if ! test -d OMSimulator; then
       git clone --recursive https://openmodelica.org/git-readonly/OMSimulator.git || exit 1
     fi
@@ -916,16 +926,14 @@ def runRegressiontest(branch, name, extraFlags, omsHash, omcompiler, extrasimfla
     fi
     echo OMSimulator version:
     ${env.HOME}/saved_omc/OMSimulator/install/bin/OMSimulator --version
-    """
+    """)
     FMI_TESTING_FLAG = " --fmisimulator=${env.HOME}/saved_omc/OMSimulator/install/bin/OMSimulator"
   }
 
   if (simulators.contains('fmpy')) {
-    sh """
-    # update fmpy
-    pip install FMPy || true
-    python3 -m fmpy -h || exit 1
-    """
+    // The version is the image's; check it in the interpreter test.py will reach rather than
+    // installing one over it, which in a container would be thrown away with the container.
+    runSh('python3 -m fmpy -h > /dev/null || exit 1')
     FMI_TESTING_FLAG += " --fmisimulator='python3 -m fmpy'"
   }
 
@@ -1117,7 +1125,7 @@ def runRegressiontest(branch, name, extraFlags, omsHash, omcompiler, extrasimfla
   mkdir -p "/var/www/libraries.openmodelica.org/branches/${name}/"
   """
 
-  def libraryPath = installLibraries(removePackageOrder, conversionScript, name, "${WORKSPACE}/OpenModelica/${OMCPATH}/build")
+  def libraryPath = installLibraries(removePackageOrder, conversionScript, name, "${WORKSPACE}/OpenModelica/${OMCPATH}/build", runSh)
 
   sh "test -d '${libraryPath}/.openmodelica/libraries/Modelica trunk'"
 
diff --git a/.CI/wasm-jit/Dockerfile b/.CI/testing/Dockerfile
similarity index 59%
rename from .CI/wasm-jit/Dockerfile
rename to .CI/testing/Dockerfile
index 30ab938..95dff69 100644
--- a/.CI/wasm-jit/Dockerfile
+++ b/.CI/testing/Dockerfile
@@ -1,17 +1,28 @@
-# Image for the targets needing the Rust omc (wasm-jit); the nodes run an Ubuntu
-# too old to build it. Built by .CI/Jenkinsfile, with this directory as the
-# context (the job copies requirements.txt into it).
+# The image every library testing job runs in: it builds omc, OMSimulator and runs test.py.
+# Built by .CI/Jenkinsfile, with this directory as the context (the job copies requirements.txt
+# into it).
+#
+# One image for all of them rather than one per target: what a node then needs is docker, git and
+# an ssh key instead of a set of packages kept up to date by hand, and a job moved to another
+# machine tests what it tested before. The base is the one the wasm-jit target needs - the OMDev
+# image the OpenModelica repository builds against, in the variant carrying the Rust toolchain,
+# since a Rust omc cannot be built on the Ubuntu the nodes run, and its sccache keys only hit for
+# the toolchain that job used.
 FROM docker.openmodelica.org/build-deps:ubuntu-26.04-rust
 
 # rsync/ssh publish the results; time and killall are used around test.py.
 # libcomedi-dev libx11-dev is used by Modelica_DeviceDrivers
 # Python 3.8 and 3.12 are used by Buildings
+# autoconf/automake/libtool and omniORB build the targets that do not ask for a cmake omc: those
+# still go through `autoreconf && ./configure --with-omniORB`. The base image carries what the
+# cmake build needs, which is not quite the same set.
 RUN export DEBIAN_FRONTEND=noninteractive \
   && apt-get update \
   && apt-get install -qy software-properties-common \
   && add-apt-repository -y ppa:deadsnakes/ppa \
   && apt-get install -qy --no-install-recommends openssh-client psmisc rsync time \
   && apt-get install -qy --no-install-recommends libcomedi-dev libx11-dev \
+  && apt-get install -qy --no-install-recommends autoconf automake libtool omniidl libomniorb4-dev \
   && apt-get install -qy python3.8 python3.12 libpython3.8-dev libpython3.12-dev \
   && apt-get clean \
   && rm -rf /var/lib/apt/lists/*
@@ -23,6 +34,9 @@ RUN python3 -m venv /opt/libtest-venv \
   && /opt/libtest-venv/bin/pip install --no-cache-dir -r /tmp/requirements.txt \
   # Python dependencies of library install scripts (e.g. Buildings EnergyPlus)
   && /opt/libtest-venv/bin/pip install --no-cache-dir jinja2 \
+  # The simulator of the -fmi-fmpy targets, which test.py runs as `python3 -m fmpy`. Its version
+  # is the image's: a job cannot pip install one over it that outlives the container.
+  && /opt/libtest-venv/bin/pip install --no-cache-dir FMPy \
   && rm /tmp/requirements.txt
 ENV PATH=/opt/libtest-venv/bin:$PATH
 
diff --git a/.gitignore b/.gitignore
index 409402b..388d96d 100644
--- a/.gitignore
+++ b/.gitignore
@@ -1,5 +1,5 @@
 __pycache__
-/.CI/wasm-jit/requirements.txt
+/.CI/testing/requirements.txt
 !HelloWorld.mo
 !HelloWorld.mos
 /.venv/
diff --git a/README.md b/README.md
index a2997d6..fd5284b 100644
--- a/README.md
+++ b/README.md
@@ -42,6 +42,35 @@ OpenModelica
 [issue tracker](https://github.com/OpenModelica/OpenModelica/issues/new/choose)
 and ask us to do it for you.
 
+### The image the OSMC jobs run in
+
+Every job of [.CI/Jenkinsfile](.CI/Jenkinsfile) runs in one docker image, built
+from [.CI/testing/Dockerfile](.CI/testing/Dockerfile) at the start of the job
+and with `--pull`, so a rebuilt base is picked up on its own. What a node needs
+is then docker, git and an ssh key to publish the results with; the compilers,
+the python environment, the `omc` that generates the mos files, FMPy and the
+packages the tested libraries need are the image's, not the machine's, and a job
+moved to another machine tests what it tested before.
+
+The omc build, the OMSimulator build and `test.py` run inside the image; the
+steps that use the node's own `omc` - installing the libraries and preparing the
+reference files - stay outside it. The node's home directory is mounted, so the
+cached omc build in `~/saved_omc`, the installed libraries and the ssh key are
+the files they always were, and so is `/mnt/ReferenceFiles`, where the
+maintenance job installs the reference results: the container reads the same
+directory the node does, and writes the hash `test.py` keeps next to a reference
+file back into it. The container is capped at 85% of the node's memory, which a
+job running on the node itself was not.
+
+A dependency a library needs is therefore a line in the Dockerfile rather than
+an `apt-get install` repeated on every machine:
+
+```bash
+cp requirements.txt .CI/testing/          # the build context has to carry it
+docker build -t openmodelica-library-testing:testing .CI/testing
+docker run --rm -it openmodelica-library-testing:testing bash
+```
+
 ## Running the library testing infrastructure on your own server
 
 The scripts from this repository can be used to run regression tests for public,