diff --git a/.coderabbit.yaml b/.coderabbit.yaml
new file mode 100644
index 00000000..a8e81637
--- /dev/null
+++ b/.coderabbit.yaml
@@ -0,0 +1,32 @@
+# SPDX-License-Identifier: MPL-2.0
+# Review-only. No AI-authored finishing-touch commits.
+# Canonical language policy:
+# https://github.com/metadatastician/standards/blob/main/3-practice/LANGUAGE-POLICY.adoc
+reviews:
+  auto_review:
+    enabled: true
+    drafts: false
+  path_instructions:
+    - path: "**/*"
+      instructions: >-
+        Estate policy prohibits NEW Python files, scripts, test code,
+        dependencies, and Python package manifests with no exceptions.
+        Do not recommend Python or generate Python fixes. The existing
+        upstream React and TypeScript frontend is temporarily permitted until
+        Marid is ready. Scientific code is Julia and R with pinned toolchains.
+        Flag additions of Python as a policy violation. Do not rewrite
+        unrelated upstream code for cosmetic compliance. Validate any
+        replacement through scientific result parity and tests.
+  finishing_touches:
+    docstrings:
+      enabled: false
+    unit_tests:
+      enabled: false
+    simplify:
+      enabled: false
+    autofix:
+      enabled: false
+    fix_ci:
+      enabled: false
+    resolve_merge_conflict:
+      enabled: false
diff --git a/.github/workflows/language-policy.yml b/.github/workflows/language-policy.yml
new file mode 100644
index 00000000..3b3effe6
--- /dev/null
+++ b/.github/workflows/language-policy.yml
@@ -0,0 +1,43 @@
+# SPDX-License-Identifier: MPL-2.0
+name: Language policy (no new Python)
+on:
+  pull_request:
+    branches: [main]
+  push:
+    branches: [main]
+  workflow_dispatch:
+permissions:
+  contents: read
+jobs:
+  no-new-python:
+    name: No new Python
+    runs-on: ubuntu-24.04
+    timeout-minutes: 5
+    steps:
+      - uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1 # v7.0.1
+        with:
+          persist-credentials: false
+          fetch-depth: 0
+          ref: ${{ github.event.pull_request.head.sha || github.sha }}
+      - name: Refuse Python additions and edits (allow deletion)
+        env:
+          PR_BASE_SHA: ${{ github.event.pull_request.base.sha }}
+          PUSH_BEFORE_SHA: ${{ github.event.before }}
+          EVENT_KIND: ${{ github.event_name }}
+        run: |
+          set -euo pipefail
+          if [[ "$EVENT_KIND" == pull_request ]]; then
+            base=$PR_BASE_SHA
+          elif [[ "$EVENT_KIND" == push ]]; then
+            base=$PUSH_BEFORE_SHA
+            if [[ "$base" == 0000000000000000000000000000000000000000 ]]; then
+              echo 'No push base available: refusing ambiguous evidence' >&2
+              exit 2
+            fi
+          else
+            echo 'Manual probe covers HEAD^..HEAD, not PR merge-base scope'
+            base=$(git rev-parse HEAD^)
+          fi
+          bash scripts/check-no-new-python.sh "$base"
+      - name: Planted-negative and positive controls
+        run: bash scripts/tests/test-no-new-python.sh
diff --git a/scripts/check-no-new-python.sh b/scripts/check-no-new-python.sh
new file mode 100644
index 00000000..65d32107
--- /dev/null
+++ b/scripts/check-no-new-python.sh
@@ -0,0 +1,34 @@
+#!/usr/bin/env bash
+# SPDX-License-Identifier: MPL-2.0
+# Refuse newly added/modified Python source and manifests. Untouched inherited
+# debt is not a blanket authorisation to add more. Deletion is allowed.
+set -euo pipefail
+if [[ $# -ne 1 || ! "$1" =~ ^[0-9a-fA-F]{40}$ ]]; then
+  printf 'Usage: %s <base-commit-sha>\n' "$0" >&2
+  exit 2
+fi
+base=$1
+if ! git cat-file -e "${base}^{commit}"; then
+  echo 'Base commit unavailable; no language-policy evidence' >&2
+  exit 2
+fi
+changed=$(mktemp)
+trap 'rm -f "$changed"' EXIT
+if ! git diff --name-only --diff-filter=ACMR -z "${base}...HEAD" -- > "$changed"; then
+  echo 'Cannot determine changed files; refusing a false green' >&2
+  exit 2
+fi
+bad=0
+while IFS= read -r -d '' file; do
+  case "${file##*/}" in
+    *.py|*.pyi|pyproject.toml|Pipfile|Pipfile.lock|poetry.lock|uv.lock|.python-version|setup.cfg|tox.ini|pytest.ini|requirements*.txt|requirements*.in)
+      printf 'BANNED Python contribution: %q\n' "$file" >&2
+      bad=1 ;;
+  esac
+done < "$changed"
+if (( bad )); then
+  echo 'Python is banned for new work; migrate to approved languages. Removal-only cleanup is allowed.' >&2
+  echo 'Canon: metadatastician/standards/3-practice/LANGUAGE-POLICY.adoc section 3' >&2
+  exit 1
+fi
+echo 'Language policy PASS: no new or modified Python files/manifests in this diff; legacy untouched files are not certified.'
diff --git a/scripts/tests/test-no-new-python.sh b/scripts/tests/test-no-new-python.sh
new file mode 100644
index 00000000..db733e1c
--- /dev/null
+++ b/scripts/tests/test-no-new-python.sh
@@ -0,0 +1,46 @@
+#!/usr/bin/env bash
+# SPDX-License-Identifier: MPL-2.0
+# Both pass and planted-fail controls for the diff-based ban.
+set -euo pipefail
+script=$(cd "$(dirname "$0")/.." && pwd)/check-no-new-python.sh
+scratch=$(mktemp -d)
+trap 'rm -rf "$scratch"' EXIT
+cd "$scratch"
+git init -q
+git config user.name 'Language Gate Test'
+git config user.email 'language-gate@example.invalid'
+mkdir -p bench scripts
+printf 'print("legacy")\n' > scripts/legacy.py
+git add . && git commit -qm 'Pre-existing Python debt'
+base=$(git rev-parse HEAD)
+expect_failure() {
+  if bash "$script" "$base" > "$scratch/output.log" 2>&1; then
+    echo 'ERROR: planted Python violation passed' >&2; exit 1
+  fi
+  grep -q 'BANNED Python contribution:' "$scratch/output.log" || { cat "$scratch/output.log" >&2; exit 1; }
+}
+expect_pass() { bash "$script" "$base" > /dev/null; }
+printf 'cat("R allowed")\n' > bench/check.R
+git add . && git commit -qm 'Add R'
+expect_pass
+printf 'print("new")\n' > bench/new.py
+git add . && git commit -qm 'Add Python'
+expect_failure
+git rm -q bench/new.py && git commit -qm 'Remove Python'
+expect_pass
+printf 'print("changed")\n' >> scripts/legacy.py
+git add . && git commit -qm 'Edit legacy Python'
+expect_failure
+git restore --source="$base" scripts/legacy.py
+git add . && git commit -qm 'Restore legacy'
+expect_pass
+printf '[project]\nname = "wrong"\n' > pyproject.toml
+git add . && git commit -qm 'Add Python manifest'
+expect_failure
+git rm -q pyproject.toml && git commit -qm 'Remove manifest'
+expect_pass
+git rm -q scripts/legacy.py && git commit -qm 'Retire Python'
+expect_pass
+if bash "$script" not-a-sha >/dev/null 2>&1; then echo 'Malformed base passed' >&2; exit 1; fi
+if bash "$script" 0000000000000000000000000000000000000000 >/dev/null 2>&1; then echo 'Missing base passed' >&2; exit 1; fi
+echo 'no-new-python gate: planted-positive and planted-negative fixtures PASS'