diff --git a/.gitea/workflows/update-badges.yml b/.gitea/workflows/update-badges.yml
index 7db0341..34b9871 100644
--- a/.gitea/workflows/update-badges.yml
+++ b/.gitea/workflows/update-badges.yml
@@ -54,11 +54,23 @@ jobs:
           echo "percent=$PERCENT" >> $GITHUB_OUTPUT
           echo "Coverage: $PERCENT%"
 
+      - name: Extract core (critical-module) coverage percentage
+        id: core_coverage
+        run: |
+          # Reuses the .coverage data from the previous step. The core list is
+          # the single source of truth in scripts/critical-modules.txt; every
+          # core module is unit-tested, so the unit-only run is accurate for it.
+          INCLUDE=$(grep -vE '^[[:space:]]*(#|$)' scripts/critical-modules.txt | paste -sd, -)
+          PERCENT=$(python -m coverage report --include="$INCLUDE" 2>/dev/null | grep '^TOTAL' | grep -oP '\d+(?=%)' | tail -1)
+          echo "percent=$PERCENT" >> $GITHUB_OUTPUT
+          echo "Core coverage: $PERCENT%"
+
       - name: Update badges in README
         run: |
           PYLINT_SCORE="${{ steps.pylint.outputs.score }}"
           PYRIGHT_ERRORS="${{ steps.pyright.outputs.errors }}"
           COVERAGE_PERCENT="${{ steps.coverage.outputs.percent }}"
+          CORE_COVERAGE_PERCENT="${{ steps.core_coverage.outputs.percent }}"
 
           PYLINT_SCORE_ENCODED=$(echo "$PYLINT_SCORE" | sed 's|/|%2F|g')
 
@@ -71,9 +83,12 @@ jobs:
           if [ -n "$COVERAGE_PERCENT" ]; then
             sed -i "s|/badge/coverage-[^)]*|/badge/coverage-${COVERAGE_PERCENT}%25-brightgreen|" README.md
           fi
+          if [ -n "$CORE_COVERAGE_PERCENT" ]; then
+            sed -i "s|/badge/core%20coverage-[^)]*|/badge/core%20coverage-${CORE_COVERAGE_PERCENT}%25-brightgreen|" README.md
+          fi
 
           echo "Updated badges:"
-          grep -E "pylint|pyright|coverage" README.md | head -3
+          grep -E "pylint|pyright|coverage" README.md | head -4
 
       - name: Commit and push badge updates
         run: |
@@ -86,7 +101,7 @@ jobs:
           else
             echo "Badge changes detected, committing..."
             git add README.md
-            MSG="chore: update quality badges"$'\n\n'"- Pylint: ${{ steps.pylint.outputs.score }}"$'\n'"- Pyright: ${{ steps.pyright.outputs.errors }} errors"$'\n'"- Coverage: ${{ steps.coverage.outputs.percent }}%"$'\n\n'"[skip ci]"
+            MSG="chore: update quality badges"$'\n\n'"- Pylint: ${{ steps.pylint.outputs.score }}"$'\n'"- Pyright: ${{ steps.pyright.outputs.errors }} errors"$'\n'"- Coverage: ${{ steps.coverage.outputs.percent }}%"$'\n'"- Core coverage: ${{ steps.core_coverage.outputs.percent }}%"$'\n\n'"[skip ci]"
             git commit -m "$MSG"
             git push
           fi
diff --git a/README.md b/README.md
index 876a95f..8e8e86d 100644
--- a/README.md
+++ b/README.md
@@ -8,6 +8,7 @@
 [![pylint](https://img.shields.io/badge/pylint-9.93%2F10-brightgreen)](https://github.com/PyCQA/pylint)
 [![pyright](https://img.shields.io/badge/pyright-0%20errors-brightgreen)](https://github.com/microsoft/pyright)
 [![coverage](https://img.shields.io/badge/coverage-79%25-brightgreen)](https://coverage.readthedocs.io/)
+[![core coverage](https://img.shields.io/badge/core%20coverage-95%25-brightgreen)](https://gitea.dideric.is/didericis/bot-bottle/src/branch/main/docs/decisions/0004-coverage-policy.md)
 
 **Problem:** Developer wants to run a coding agent without supervision, but they don't want a prompt injected or misbehaving agent wrecking their environment or exfiltrating sensitive data.
 
diff --git a/docs/decisions/0004-coverage-policy.md b/docs/decisions/0004-coverage-policy.md
index 6141e5b..acaaa4e 100644
--- a/docs/decisions/0004-coverage-policy.md
+++ b/docs/decisions/0004-coverage-policy.md
@@ -88,3 +88,9 @@ omit list.
 - PRs #290 (cover the egress adapter), and the coverage-policy PR that
   introduces this record.
 - `.coveragerc`, `scripts/coverage.sh`, `scripts/diff_coverage.py`.
+- `scripts/critical-modules.txt` — the single source of truth for the
+  core-module list; read by both `scripts/coverage.sh` and the
+  `update-badges.yml` "core coverage" badge so they cannot drift.
+- The README carries a `core coverage` badge (auto-updated from that
+  list) — the headline number, distinct from the informational global
+  `coverage` badge.
diff --git a/scripts/coverage.sh b/scripts/coverage.sh
index db9556c..0dae61b 100755
--- a/scripts/coverage.sh
+++ b/scripts/coverage.sh
@@ -16,13 +16,10 @@ cd "$(dirname "$0")/.."
 
 PY="${PYTHON:-python3}"
 
-# Critical security/logic core held to the high bar by ADR 0004.
-CRITICAL="bot_bottle/egress_addon.py,bot_bottle/egress_addon_core.py,\
-bot_bottle/dlp_detectors.py,bot_bottle/egress.py,bot_bottle/manifest.py,\
-bot_bottle/manifest_egress.py,bot_bottle/manifest_agent.py,\
-bot_bottle/manifest_schema.py,bot_bottle/git_gate.py,\
-bot_bottle/git_http_backend.py,bot_bottle/supervise.py,\
-bot_bottle/yaml_subset.py,bot_bottle/bottle_state.py"
+# Critical security/logic core held to the high bar by ADR 0004. The list
+# lives in one place (scripts/critical-modules.txt) so this report and the
+# README "core coverage" badge can't drift; comma-join it for --include.
+CRITICAL=$(grep -vE '^[[:space:]]*(#|$)' scripts/critical-modules.txt | paste -sd, -)
 
 rm -f .coverage
 
diff --git a/scripts/critical-modules.txt b/scripts/critical-modules.txt
new file mode 100644
index 0000000..8f23b04
--- /dev/null
+++ b/scripts/critical-modules.txt
@@ -0,0 +1,23 @@
+# Critical security/logic core held to the >=90% coverage bar by
+# docs/decisions/0004-coverage-policy.md.
+#
+# SINGLE SOURCE OF TRUTH: scripts/coverage.sh (the `critical` report) and
+# .gitea/workflows/update-badges.yml (the "core coverage" badge) both read
+# this file. Add a module here when it becomes part of the core; a coverage
+# number that silently stops measuring a module is worse than no badge.
+#
+# One module path per line, relative to the repo root. Blank lines and
+# `#` comments are ignored.
+bot_bottle/egress_addon.py
+bot_bottle/egress_addon_core.py
+bot_bottle/dlp_detectors.py
+bot_bottle/egress.py
+bot_bottle/manifest.py
+bot_bottle/manifest_egress.py
+bot_bottle/manifest_agent.py
+bot_bottle/manifest_schema.py
+bot_bottle/git_gate.py
+bot_bottle/git_http_backend.py
+bot_bottle/supervise.py
+bot_bottle/yaml_subset.py
+bot_bottle/bottle_state.py