diff --git a/.github/workflows/openstudio-server-tests.yml b/.github/workflows/openstudio-server-tests.yml
index 50aee4909..4c61a5a26 100644
--- a/.github/workflows/openstudio-server-tests.yml
+++ b/.github/workflows/openstudio-server-tests.yml
@@ -120,7 +120,21 @@ jobs:
           docker --version
           docker-compose --version
           docker-compose -f docker-compose.test.yml pull
-          docker-compose -f docker-compose.test.yml build --build-arg OPENSTUDIO_VERSION=$OPENSTUDIO_TAG
+          # Rebuild the rserve image only when its inputs changed. PR runs otherwise reuse
+          # the pulled nrel/openstudio-rserve:latest (kept fresh by docker-upload on
+          # develop/master pushes): rebuilding R packages on every run cost ~10 min and
+          # failed whenever CRAN had a transient outage or mid-day version drift.
+          # Push runs always build everything - docker-upload deploys those images.
+          # Two-commit tree diff (not A...B) so it works on the shallow PR merge-ref clone;
+          # any fetch/diff failure falls back to building everything.
+          BUILD_SERVICES="web rserve"
+          if [ "${GITHUB_EVENT_NAME}" = "pull_request" ] \
+             && git fetch --no-tags --quiet --depth=1 origin "${GITHUB_BASE_REF}" \
+             && git diff --quiet FETCH_HEAD HEAD -- docker/R; then
+            echo "docker/R is unchanged by this PR: reusing pulled nrel/openstudio-rserve:latest instead of rebuilding it"
+            BUILD_SERVICES="web"
+          fi
+          docker-compose -f docker-compose.test.yml build --build-arg OPENSTUDIO_VERSION=$OPENSTUDIO_TAG $BUILD_SERVICES
           docker-compose -f docker-compose.test.yml up -d
           #set SKIP_URBANOPT_ALGO=true to skip UrbanOpt algo tests
           docker-compose exec -e SKIP_URBANOPT_ALGO=true -T web /usr/local/bin/run-server-tests
diff --git a/docker-compose.test.yml b/docker-compose.test.yml
index 40c04a464..d3e075bf3 100644
--- a/docker-compose.test.yml
+++ b/docker-compose.test.yml
@@ -22,6 +22,11 @@ services:
       args:
         rails_env: docker
         bundle_args: ''
+        # embed layer-cache metadata so pushed images can seed later builds (BuildKit
+        # no longer uses pulled images as cache without it, unlike the classic builder)
+        BUILDKIT_INLINE_CACHE: '1'
+      cache_from:
+        - nrel/openstudio-server:latest
     environment:
       - CI
       - COVERALLS_REPO_TOKEN
@@ -53,6 +58,11 @@ services:
       args:
         rails_env: docker
         bundle_args: ''
+        # embed layer-cache metadata so pushed images can seed later builds (BuildKit
+        # no longer uses pulled images as cache without it, unlike the classic builder)
+        BUILDKIT_INLINE_CACHE: '1'
+      cache_from:
+        - nrel/openstudio-server:latest
     environment:
       - OS_SERVER_NUMBER_OF_WORKERS=1
       - QUEUES=background,analyses
@@ -75,6 +85,11 @@ services:
       args:
         rails_env: docker
         bundle_args: ''
+        # embed layer-cache metadata so pushed images can seed later builds (BuildKit
+        # no longer uses pulled images as cache without it, unlike the classic builder)
+        BUILDKIT_INLINE_CACHE: '1'
+      cache_from:
+        - nrel/openstudio-server:latest
     environment:
       - OS_SERVER_NUMBER_OF_WORKERS=1
       - QUEUES=requeued,simulations
@@ -92,7 +107,12 @@ services:
   rserve:
     image: nrel/openstudio-rserve:latest
     platform: ${DOCKER_PLATFORM:-linux/amd64}
-    build: ./docker/R
+    build:
+      context: ./docker/R
+      args:
+        BUILDKIT_INLINE_CACHE: '1'
+      cache_from:
+        - nrel/openstudio-rserve:latest
     environment:
       - OS_SERVER_NUMBER_OF_WORKERS=1
       - REDIS_URL=${REDIS_URL}
diff --git a/docker/R/install_packages.R b/docker/R/install_packages.R
index 03e492fe1..bdba072c4 100644
--- a/docker/R/install_packages.R
+++ b/docker/R/install_packages.R
@@ -7,8 +7,24 @@
 # OpenStudio-R image here:
 # https://raw.githubusercontent.com/NREL/docker-openstudio-r/master/base_packages.R
 
+# Install from a date-frozen CRAN snapshot (Posit Package Manager) so the UNPINNED
+# dependencies of the pinned packages below also resolve deterministically. On
+# 2026-07-16 a mid-day CRAN publish (ggrepel requiring ggplot2 >= 3.5.2/gtable >=
+# 0.3.6) broke image rebuilds that had passed hours earlier. The __linux__/jammy
+# path serves prebuilt binaries for the base image's Ubuntu 22.04 + R 4.4 (much
+# faster than source compiles); the plain snapshot path is the source fallback.
+# To take newer packages, bump the snapshot date deliberately.
+snapshot_repos = c(
+    'https://packagemanager.posit.co/cran/__linux__/jammy/2026-07-15',
+    'https://packagemanager.posit.co/cran/2026-07-15'
+)
+# Posit Package Manager only serves Linux binaries to clients whose User-Agent
+# announces the R version; set it explicitly so install.packages gets binaries.
+options(HTTPUserAgent = sprintf('R/%s R (%s)', getRversion(),
+    paste(getRversion(), R.version$platform, R.version$arch, R.version$os)))
+
 # Function for installing and verifying that the package was installed correctly (i.e. can be loaded)
-install_and_verify = function(package_name, version=NULL, configure.args=c(), repos=c('http://cloud.r-project.org', 'http://cran.r-project.org')){
+install_and_verify = function(package_name, version=NULL, configure.args=c(), repos=snapshot_repos){
     if (!is.null(version)) {
         print(paste("Installing package", package_name, "version", version))
         remotes::install_version(package_name, version=version, repos=repos)