diff --git a/.github/dependabot.yml b/.github/dependabot.yml
index f33af423..17b20623 100644
--- a/.github/dependabot.yml
+++ b/.github/dependabot.yml
@@ -1,8 +1,12 @@
 version: 2
 
 # Maintenance mode: ViTransfer takes security patches weekly and little else.
-# Everything targets dev; the weekly-security-release workflow promotes dev to
-# main.
+# Version updates target dev; the weekly-security-release workflow promotes dev
+# to main.
+#
+# Security updates do NOT follow target-branch — Dependabot raises those against
+# the default branch, main. sync-main-to-dev.yml carries them back to dev so the
+# release train does not keep shipping a lockfile the advisory already covers.
 #
 # Major version updates are ignored everywhere: in maintenance mode a runtime
 # or framework major is not worth the churn. The release run's
@@ -21,16 +25,17 @@ updates:
       prefix: deps
       prefix-development: deps-dev
     groups:
-      # One PR a week for routine churn, one for advisories.
+      # One PR a week for routine churn. There is deliberately no
+      # security-updates group here: `target-branch` applies to version updates
+      # only, so Dependabot opens security PRs against the default branch and
+      # ignores this file's groups and commit prefix entirely. A group here
+      # would read as if advisories arrive on dev, and they do not.
       npm:
         applies-to: version-updates
         patterns: ["*"]
         update-types:
           - patch
           - minor
-      npm-security:
-        applies-to: security-updates
-        patterns: ["*"]
     ignore:
       - dependency-name: "*"
         update-types:
diff --git a/.github/workflows/docker-integration-tests.yml b/.github/workflows/docker-integration-tests.yml
index c30f1ee3..4ea262f9 100644
--- a/.github/workflows/docker-integration-tests.yml
+++ b/.github/workflows/docker-integration-tests.yml
@@ -6,6 +6,12 @@ name: Docker Integration Tests
 #
 # No paths filter on PRs: "Test Summary" is a required check on dev, and a
 # required check that never runs leaves auto-merge pending forever.
+#
+# PRs to main are tested too. Setting `target-branch` in dependabot.yml turns
+# off security updates from that config, so GitHub opens them against the
+# default branch instead — main. Those PRs used to get CodeQL and nothing else,
+# which is how a browserslist advisory sat on main untested while the release
+# train kept building the vulnerable lockfile from dev.
 on:
   push:
     branches: [dev]
@@ -18,7 +24,7 @@ on:
       - '.github/workflows/docker-*.yml'
       - '.github/workflows/test-dev-*.yml'
   pull_request:
-    branches: [dev]
+    branches: [dev, main]
   workflow_dispatch:
 
 permissions:
diff --git a/.github/workflows/sync-main-to-dev.yml b/.github/workflows/sync-main-to-dev.yml
new file mode 100644
index 00000000..319088a0
--- /dev/null
+++ b/.github/workflows/sync-main-to-dev.yml
@@ -0,0 +1,84 @@
+name: Sync main to dev
+
+# main moves without dev twice, and only one of them matters. The release train
+# pushing the version bump and changelog is by design — dev never carries
+# VERSION, so it lags every week and that is fine. A Dependabot security PR
+# landing is not: those target the default branch (see dependabot.yml), so dev —
+# the branch every release is cut from — keeps a lockfile the advisory already
+# covers while main looks patched. That is how v1.3.5 built a vulnerable tree
+# after the fix was already sitting on main, and how the release then hit a
+# lockfile conflict waiting to happen the next time dev touched the same file.
+#
+# So this reports on what is stranded, not on how far behind dev is. Counting
+# commits would file an issue after every release, weekly, for the state that is
+# supposed to be true.
+#
+# It opens an issue rather than a PR: dev requires the "Test Summary" check, and
+# a PR opened with GITHUB_TOKEN does not trigger `pull_request` workflows, so
+# the check would never run and the PR would block forever. There is no PAT.
+
+on:
+  push:
+    branches: [main]
+  workflow_dispatch:
+
+permissions:
+  contents: read
+  issues: write
+
+jobs:
+  sync:
+    name: Check dev is in step
+    runs-on: ubuntu-latest
+
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v5
+        with:
+          fetch-depth: 0
+
+      - name: Report anything stranded on main
+        env:
+          GH_TOKEN: ${{ secrets.GITHUB_TOKEN }}
+        run: |
+          git fetch origin main dev --quiet
+
+          # Release commits are authored by github-actions[bot] and dev is meant
+          # to lag them. Everything else on main is a patch that never reached
+          # the branch the next release builds from.
+          stranded=$(git log --format='%an %h %s' origin/dev..origin/main \
+            | grep -v '^github-actions\[bot\] ' || true)
+
+          # One open issue at a time, closed again once dev catches up, so a
+          # stale one can never mask the next strand.
+          open_issue=$(gh issue list --label sync --state open --json number -q '.[0].number')
+
+          if [ -z "$stranded" ]; then
+            echo "Nothing stranded: dev has every patch main does."
+            if [ -n "$open_issue" ]; then
+              gh issue close "$open_issue" --comment "dev has caught up with main."
+            fi
+            exit 0
+          fi
+
+          echo "Stranded on main:"
+          echo "$stranded"
+
+          if [ -n "$open_issue" ]; then
+            echo "Issue #$open_issue is already tracking this."
+            exit 0
+          fi
+
+          # Its own label, not `ci`: that one is the release-failure report's,
+          # and sharing it would make either issue suppress the other.
+          gh label create sync \
+            --description "A patch on main has not reached dev" \
+            --color 1d76db --force
+
+          gh issue create \
+            --title "Patches on main have not reached dev" \
+            --label sync \
+            --body "$(printf '%s\n\n```\n%s\n```\n\n%s\n' \
+              "These commits are on main but not on dev. The weekly release is cut from dev, so until they are carried back it keeps building without them — and the release's own merge will conflict as soon as dev touches the same files." \
+              "$stranded" \
+              "Carry them over with \`git checkout dev && git merge origin/main && git push origin dev\`.")"
diff --git a/.github/workflows/weekly-security-release.yml b/.github/workflows/weekly-security-release.yml
index ec25e1b1..c3b45a96 100644
--- a/.github/workflows/weekly-security-release.yml
+++ b/.github/workflows/weekly-security-release.yml
@@ -112,8 +112,13 @@ jobs:
         run: |
           npm ci --legacy-peer-deps --ignore-scripts
           # Majors and unfixable advisories never reach auto-merge, so this is
-          # the backstop that makes them visible rather than silently skipped.
-          npm audit --audit-level=high || echo "::warning::npm audit reports unresolved advisories — review before approving"
+          # the backstop that catches them rather than silently skipping them.
+          #
+          # It fails rather than warns: the Dockerfile runs the same gate during
+          # `build`, which is after `publish` has merged dev and pushed the
+          # version bump. A warning here bought nothing and left main carrying
+          # release commits for a version that never tagged or shipped.
+          npm audit --audit-level=high
 
   # Individual PRs are tested against dev as it was when they opened, not
   # against the final merged state. With no human approving the release, this