diff --git a/.github/workflows/fogproject-tests.yml b/.github/workflows/fogproject-tests.yml
index 7d49fcd..1deafef 100644
--- a/.github/workflows/fogproject-tests.yml
+++ b/.github/workflows/fogproject-tests.yml
@@ -104,7 +104,36 @@ jobs:
       - name: Check out the pull request
         uses: actions/checkout@v4
 
+      - name: Is there a Composer tree to check?
+        id: manifest
+        # dev-branch has no packages/web/composer.json at all, and neither does
+        # any branch cut before the dependency manager landed on working-1.6.
+        # Every step below assumes one: `composer validate` answers
+        # "./composer.json not found." and exits 3, so the whole check goes red
+        # on a branch that was never expected to have it and cannot be fixed
+        # without porting the dependency manager to it. That turned every
+        # dev-branch pull request red the moment this job was added.
+        #
+        # Skip loudly rather than fail, which is what the generated-files sweep
+        # already does for update-language.sh on branches that predate it: a
+        # visible ::warning::, not a silent pass, and not a failure for an
+        # absence that is correct on that branch. If the 1.5.x line ever gets a
+        # composer.json this starts checking it with no change here.
+        run: |
+          if [ -f packages/web/composer.json ]; then
+            echo "present=true" >> "$GITHUB_OUTPUT"
+          else
+            echo "present=false" >> "$GITHUB_OUTPUT"
+            echo "::warning::packages/web/composer.json is not on this branch; skipping the vendor checks."
+            {
+              echo '### vendor/'
+              echo ''
+              echo 'Skipped — this branch carries no `packages/web/composer.json`.'
+            } >> "$GITHUB_STEP_SUMMARY"
+          fi
+
       - name: Set up PHP 7.4 and Composer
+        if: steps.manifest.outputs.present == 'true'
         uses: shivammathur/setup-php@v2
         with:
           # 7.4 because composer.json pins config.platform.php to 7.4.0. The
@@ -122,10 +151,12 @@ jobs:
         # and the installer reads its own version from the tree. Plain
         # validate still catches a malformed manifest and, more usefully, a
         # lock that has fallen out of step with the requirements.
+        if: steps.manifest.outputs.present == 'true'
         run: composer validate
         working-directory: packages/web
 
       - name: Reinstall from the lock
+        if: steps.manifest.outputs.present == 'true'
         run: composer install --no-interaction --no-progress
         working-directory: packages/web
 
@@ -141,6 +172,7 @@ jobs:
         # elsewhere. The dependency's own files carry no such dependency and
         # are where a hand-edit or a stale package would show, so those fail
         # hard.
+        if: steps.manifest.outputs.present == 'true'
         run: |
           git diff --exit-code -- packages/web/vendor \
             ':!packages/web/vendor/composer' \
@@ -151,7 +183,11 @@ jobs:
         # worth seeing: a change here means the tree was last regenerated by a
         # different Composer, which is the thing to know before believing a
         # vendor diff in some later pull request.
-        if: always()
+        #
+        # Still `always()` so it reports after a failed content comparison --
+        # but not when the manifest is absent, since composer was never
+        # installed and the summary line has already been written above.
+        if: always() && steps.manifest.outputs.present == 'true'
         run: |
           {
             echo '### vendor/'