@@ -188,8 +188,10 @@ jobs:
         if: matrix.test_commit_records
         run: yarn test-upsert-comment
 
+      # The format check gives the same result everywhere; it runs on Linux
+      # only, where it is fastest.
       - name: Run tests
-        run: node scripts/test.js -all
+        run: node scripts/test.js ${{ runner.os == 'Linux' && '-all' || '-ounit -mocha -build -docstrings' }}
 
       - name: Check for diffs in tests folder
         run: git diff --ignore-cr-at-eol --exit-code tests
@@ -393,50 +395,80 @@ jobs:
 
       # Checks that the website builds with the generated API docs. These
       # steps stay in this job rather than in one that needs build-compiler,
-      # which would wait for the slowest platform before starting.
-      - name: Checkout rescript-lang.org
+      # which would wait for the slowest platform before starting. The build
+      # depends only on the docs and the website commit, so an empty cache
+      # entry keyed on both records each pair that built, and a pull request
+      # whose docs match an earlier build skips it.
+      - name: Website build key
+        id: website-build-key
         if: ${{ matrix.generate_api_docs }}
+        env:
+          WEBSITE_BRANCH: ${{ steps.api-docs-plan.outputs.website-branch }}
+        run: |
+          sha=$(git ls-remote https://github.com/rescript-lang/rescript-lang.org.git "refs/heads/$WEBSITE_BRANCH" | cut -f1)
+          if [ -z "$sha" ]; then
+            echo "::error::The website has no branch $WEBSITE_BRANCH"
+            exit 1
+          fi
+          echo "sha=$sha" >> "$GITHUB_OUTPUT"
+          echo "value=website-build-v1-$sha-${{ hashFiles('scripts/res/apiDocs/**') }}" >> "$GITHUB_OUTPUT"
+        shell: bash
+
+      - name: Look up website build
+        id: website-build
+        if: ${{ matrix.generate_api_docs }}
+        uses: actions/cache/restore@v6
+        with:
+          path: tmp/website-build
+          key: ${{ steps.website-build-key.outputs.value }}
+          lookup-only: true
+
+      - name: Checkout rescript-lang.org
+        if: ${{ matrix.generate_api_docs && steps.website-build.outputs.cache-hit != 'true' }}
         uses: actions/checkout@v7
         with:
           repository: rescript-lang/rescript-lang.org
-          ref: ${{ steps.api-docs-plan.outputs.website-branch }}
+          ref: ${{ steps.website-build-key.outputs.sha }}
           path: rescript-lang.org
 
-      - name: Check for API docs changes
-        id: api-docs-diff
-        if: ${{ matrix.generate_api_docs }}
-        run: |
-          cp -R scripts/res/apiDocs/. rescript-lang.org/data/api/
-          git -C rescript-lang.org status
-          if [[ -z "$(git -C rescript-lang.org status --porcelain)" ]]; then
-            echo "changed=false" >> "$GITHUB_OUTPUT"
-          else
-            echo "changed=true" >> "$GITHUB_OUTPUT"
-          fi
-        shell: bash
-
       # The website is checked out inside this repository, so its Yarn also
       # reads this repository's .yarnrc.yml and rejects the settings it does
       # not know yet. The steps that need this config are done.
       - name: Hide the compiler's Yarn config from the website
-        if: ${{ matrix.generate_api_docs && steps.api-docs-diff.outputs.changed == 'true' }}
+        if: ${{ matrix.generate_api_docs && steps.website-build.outputs.cache-hit != 'true' }}
         run: mv .yarnrc.yml "$RUNNER_TEMP/rescript.yarnrc.yml"
         shell: bash
 
       - name: Use Node.js for website
-        if: ${{ matrix.generate_api_docs && steps.api-docs-diff.outputs.changed == 'true' }}
+        if: ${{ matrix.generate_api_docs && steps.website-build.outputs.cache-hit != 'true' }}
         uses: actions/setup-node@v7
         with:
           cache: yarn
           cache-dependency-path: rescript-lang.org/yarn.lock
           node-version-file: rescript-lang.org/.node-version
 
       - name: Build website with the API docs
-        if: ${{ matrix.generate_api_docs && steps.api-docs-diff.outputs.changed == 'true' }}
+        if: ${{ matrix.generate_api_docs && steps.website-build.outputs.cache-hit != 'true' }}
         run: |
+          cp -R ../scripts/res/apiDocs/. data/api/
           yarn
           yarn build
         working-directory: rescript-lang.org
+        shell: bash
+
+      - name: Record website build
+        if: ${{ matrix.generate_api_docs && steps.website-build.outputs.cache-hit != 'true' }}
+        run: mkdir -p tmp/website-build && echo "$KEY" > tmp/website-build/key
+        env:
+          KEY: ${{ steps.website-build-key.outputs.value }}
+        shell: bash
+
+      - name: Save website build record
+        if: ${{ matrix.generate_api_docs && steps.website-build.outputs.cache-hit != 'true' }}
+        uses: actions/cache/save@v6
+        with:
+          path: tmp/website-build
+          key: ${{ steps.website-build-key.outputs.value }}
 
   # Compares the words the compiler allocates on fixed inputs, and the
   # instructions it executes on some of them, with the base branch
 
@@ -60,14 +60,21 @@ replace() {
   fi
 }
 
-wait_for_pid_gone() {
-  local pid="$1"; local timeout
-  timeout=${2:-20}
-  while process_is_running "$pid" && [ "$timeout" -gt 0 ]; do
-    sleep 1
-    timeout=$((timeout - 1))
+# Runs a command every 0.1 seconds until it succeeds or the timeout in
+# seconds (the first argument) has passed. A one-second interval made every
+# wait in the suite take up to a second longer than needed.
+poll() {
+  local deadline=$((SECONDS + $1)); shift
+  until "$@"; do
+    [ "$SECONDS" -lt "$deadline" ] || return 1
+    sleep 0.1
   done
-  ! process_is_running "$pid"
+}
+
+process_is_gone() { ! process_is_running "$1"; }
+
+wait_for_pid_gone() {
+  poll "${2:-20}" process_is_gone "$1"
 }
 
 exit_watcher() {
@@ -116,62 +123,25 @@ clear_locks() {
   rm -f lib/rescript/watch.lock lib/rescript/build.lock
 }
 
-wait_for_file() {
-  local file="$1"; local timeout
-  timeout=${2:-60}
-  while [ "$timeout" -gt 0 ]; do
-    [ -f "$file" ] && return 0
-    sleep 1
-    timeout=$((timeout - 1))
-  done
-  return 1
-}
+file_exists() { [ -f "$1" ]; }
+file_is_gone() { [ ! -f "$1" ]; }
+file_has_pattern() { grep -q "$2" "$1" 2>/dev/null; }
 
-wait_for_pattern() {
-  local file="$1"; local pattern="$2"; local timeout
-  timeout=${3:-60}
-  while [ "$timeout" -gt 0 ]; do
-    grep -q "$pattern" "$file" 2>/dev/null && return 0
-    sleep 1
-    timeout=$((timeout - 1))
-  done
-  return 1
+file_lacks_pattern() {
+  [ -f "$1" ] && ! grep -q "$2" "$1" 2>/dev/null
 }
 
-wait_for_pattern_count() {
-  local file="$1"; local pattern="$2"; local expected="$3"; local timeout
-  timeout=${4:-60}
-  while [ "$timeout" -gt 0 ]; do
-    local current_count
-    current_count=$(grep -c "$pattern" "$file" 2>/dev/null || true)
-    current_count=${current_count:-0}
-    [ "$current_count" -ge "$expected" ] && return 0
-    sleep 1
-    timeout=$((timeout - 1))
-  done
-  return 1
+file_has_pattern_count() {
+  local current_count
+  current_count=$(grep -c "$2" "$1" 2>/dev/null || true)
+  [ "${current_count:-0}" -ge "$3" ]
 }
 
-wait_for_pattern_gone() {
-  local file="$1"; local pattern="$2"; local timeout
-  timeout=${3:-60}
-  while [ "$timeout" -gt 0 ]; do
-    if [ -f "$file" ] && ! grep -q "$pattern" "$file" 2>/dev/null; then
-      return 0
-    fi
-    sleep 1
-    timeout=$((timeout - 1))
-  done
-  return 1
-}
+wait_for_file() { poll "${2:-60}" file_exists "$1"; }
+wait_for_file_gone() { poll "${2:-60}" file_is_gone "$1"; }
+wait_for_pattern() { poll "${3:-60}" file_has_pattern "$1" "$2"; }
+wait_for_pattern_gone() { poll "${3:-60}" file_lacks_pattern "$1" "$2"; }
 
-wait_for_file_gone() {
-  local file="$1"; local timeout
-  timeout=${2:-60}
-  while [ "$timeout" -gt 0 ]; do
-    [ ! -f "$file" ] && return 0
-    sleep 1
-    timeout=$((timeout - 1))
-  done
-  return 1
+wait_for_pattern_count() {
+  poll "${4:-60}" file_has_pattern_count "$1" "$2" "$3"
 }
@@ -15,17 +15,12 @@ else
   exit 1
 fi
 
+completed_log_changed() {
+  [ -f "$1" ] && ! cmp -s "$1" "$2" && grep -q "#Done(" "$1" 2>/dev/null
+}
+
 wait_for_changed_completed_log() {
-  local file="$1"; local baseline="$2"; local timeout
-  timeout=${3:-60}
-  while [ "$timeout" -gt 0 ]; do
-    if [ -f "$file" ] && ! cmp -s "$file" "$baseline" && grep -q "#Done(" "$file" 2>/dev/null; then
-      return 0
-    fi
-    sleep 1
-    timeout=$((timeout - 1))
-  done
-  return 1
+  poll "${3:-60}" completed_log_changed "$1" "$2"
 }
 
 COMPILER_LOG="./packages/watch-warnings/lib/rescript/.compiler.log"
 
@@ -42,17 +42,12 @@ wait_for_next_build() {
     "$completed_builds" 30
 }
 
+tracked_outputs_exist() {
+  [ -z "$(git ls-files --deleted -- '*.mjs')" ]
+}
+
 wait_for_tracked_outputs() {
-  local timeout
-  timeout=60
-  while [ "$timeout" -gt 0 ]; do
-    if [ -z "$(git ls-files --deleted -- '*.mjs')" ]; then
-      return 0
-    fi
-    sleep 1
-    timeout=$((timeout - 1))
-  done
-  return 1
+  poll 60 tracked_outputs_exist
 }
 
 # Change the suffix in rescript.json (same approach as suffix test)
@@ -118,12 +113,10 @@ else
 fi
 
 # The rebuild after the restore also removes the outputs with the new suffix.
-timeout=30
-while [ "$timeout" -gt 0 ] && [ -n "$(find . -name '*.res.mjs' -print -quit)" ]; do
-  sleep 1
-  timeout=$((timeout - 1))
-done
-if [ -n "$(find . -name '*.res.mjs' -print -quit)" ]; then
+suffixed_outputs_gone() {
+  [ -z "$(find . -name '*.res.mjs' -print -quit)" ]
+}
+if ! poll 30 suffixed_outputs_gone; then
   error "Outputs with the restored configuration's previous suffix were not removed"
   find . -name '*.res.mjs'
   git restore --worktree -- ./src/Test.res
 
@@ -44,18 +44,13 @@ REWATCH_COMPILER_DOMAINS=1 "$REWATCH_EXECUTABLE" watch > rewatch.log 2>&1 &
 watch_pid=$!
 compiler_log=lib/rescript/.compiler.log
 
+compiler_log_changed() {
+  [ -f "$compiler_log" ] && ! cmp -s "$compiler_log" "$1" &&
+    grep -q '#Done(' "$compiler_log"
+}
+
 wait_for_changed_compiler_log() {
-  local baseline="$1"; local timeout
-  timeout=60
-  while [ "$timeout" -gt 0 ]; do
-    if [ -f "$compiler_log" ] && ! cmp -s "$compiler_log" "$baseline" &&
-      grep -q '#Done(' "$compiler_log"; then
-      return 0
-    fi
-    sleep 1
-    timeout=$((timeout - 1))
-  done
-  return 1
+  poll 60 compiler_log_changed "$1"
 }
 
 if ! wait_for_pattern_count rewatch.log "Finished .*compilation" 1 60; then
 
@@ -42,18 +42,13 @@ retained_output() {
 rewatch_bg watch > rewatch.log 2>&1 &
 success "Watcher Started"
 
+retained_output_has() {
+  output=$(retained_output)
+  [ -n "$output" ] && grep -q "$1" "$output"
+}
+
 wait_for_retained_value() {
-  local value=$1
-  local timeout=30
-  while [ "$timeout" -gt 0 ]; do
-    output=$(retained_output)
-    if [ -n "$output" ] && grep -q "$value" "$output"; then
-      return 0
-    fi
-    sleep 1
-    timeout=$((timeout - 1))
-  done
-  return 1
+  poll 30 retained_output_has "$1"
 }
 
 if ! wait_for_retained_value "= 1"; then
@@ -70,12 +65,10 @@ success "Initial build completed"
 # watched on its own
 mkdir "$RETAINED/nested"
 echo 'let value = 1' > "$RETAINED/nested/Nested.res"
-timeout=30
-until [ -n "$(find "$RETAINED/nested" -name 'Nested.*js')" ] || [ "$timeout" -le 0 ]; do
-  sleep 1
-  timeout=$((timeout - 1))
-done
-if [ -n "$(find "$RETAINED/nested" -name 'Nested.*js')" ]; then
+nested_output_exists() {
+  [ -n "$(find "$RETAINED/nested" -name 'Nested.*js')" ]
+}
+if poll 30 nested_output_exists; then
   success "A folder created inside the retained folder is watched"
 else
   error "A folder created inside the retained folder is not watched"