diff --git a/.github/workflows/repo-contract.yml b/.github/workflows/repo-contract.yml
new file mode 100644
index 0000000..89d5597
--- /dev/null
+++ b/.github/workflows/repo-contract.yml
@@ -0,0 +1,25 @@
+name: repo-contract
+
+# The local pre-commit hook can be skipped (a fresh clone has no hooks), so the
+# contract is enforced on push too. Mirrors md-naming.yml.
+on:
+  push:
+    branches: [main]
+  pull_request:
+  workflow_dispatch:
+
+jobs:
+  repo-contract:
+    name: repo contract
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+
+      - name: Check out the shared gate
+        uses: actions/checkout@v4
+        with:
+          repository: kuhyx/utils
+          path: .utils
+
+      - name: Enforce the repo contract
+        run: bash .utils/scripts/check_repo_contract.sh
diff --git a/.pre-commit-config.yaml b/.pre-commit-config.yaml
index 3da0401..5dc0a09 100644
--- a/.pre-commit-config.yaml
+++ b/.pre-commit-config.yaml
@@ -249,3 +249,10 @@ repos:
         pass_filenames: false
         always_run: true
         stages: [pre-push]
+
+      - id: repo-contract
+        name: repo contract (CLAUDE.md Commands + test_changed)
+        entry: scripts/check_repo_contract.sh
+        language: system
+        pass_filenames: false
+        files: ^(CLAUDE\.md|AGENTS\.md|scripts/test_changed\.sh)$
diff --git a/AGENTS.md b/AGENTS.md
index 2a326ae..c5535c3 100644
--- a/AGENTS.md
+++ b/AGENTS.md
@@ -14,3 +14,12 @@ After running tests fix all coverage gaps and issues, do not ignore unless speci
 - cmd_done completion path can pick next game from snapshot-only hours; keep it aligned with HLTB cache/refresh before pick_next_game to avoid prologue-derived stale times (e.g., A Space 0.56h while cache has ~20h).
 - HLTB renames games (e.g., "Needy Streamer Overload" → "NEEDY GIRL OVERDOSE"). The old name lives in `game_alias`. Both `game_name` and `game_alias` must be checked when matching — fixed in `_pick_best_hltb_entry`.
 - **ALWAYS clear HLTB cache and re-run `run.sh` after changing the HLTB picking/matching algorithm.** Delete `~/.config/steam_backlog_enforcer/hltb_cache.json` (entire file, not just one entry) so all games get re-matched with the new logic. Then run `./run.sh` to verify correct results. Stale cache entries from the old algorithm will persist and hide bugs otherwise.
+
+## Commands
+
+- run: `./run.sh`
+- test: `python3 -m pytest -q`
+- test-changed: `scripts/test_changed.sh`
+- lint: `pre-commit run ruff --all-files`
+- coverage: `python3 -m pytest -q`
+- coverage-gaps: `coverage-gaps coverage.lcov`
diff --git a/scripts/check_repo_contract.sh b/scripts/check_repo_contract.sh
new file mode 100755
index 0000000..8488858
--- /dev/null
+++ b/scripts/check_repo_contract.sh
@@ -0,0 +1,26 @@
+#!/bin/bash
+
+# ============================================================================
+# Fail if this repo breaks the shared repo contract.
+#
+# Thin delegate to the shared gate in ~/src/utils, which owns the contract
+# text. Copy this file to scripts/check_repo_contract.sh in a repo; never copy
+# the shared gate itself, or the shim would exec itself forever.
+# ============================================================================
+
+set -euo pipefail
+
+readonly SHARED_GATE="${UTILS_ROOT:-$HOME/src/utils}/scripts/check_repo_contract.sh"
+
+main() {
+    if [[ ! -x "$SHARED_GATE" ]]; then
+        echo "Error: shared repo-contract gate not found at $SHARED_GATE" >&2
+        echo "       Clone github.com/kuhyx/utils to ~/src/utils, or set" >&2
+        echo "       UTILS_ROOT to where it lives." >&2
+        exit 1
+    fi
+
+    exec bash "$SHARED_GATE" "$@"
+}
+
+main "$@"
diff --git a/scripts/test_changed.sh b/scripts/test_changed.sh
new file mode 100755
index 0000000..65efb87
--- /dev/null
+++ b/scripts/test_changed.sh
@@ -0,0 +1,50 @@
+#!/bin/bash
+
+# ============================================================================
+# Run only the tests related to files changed vs HEAD (staged, unstaged and
+# untracked). Quiet: failures plus a one-line summary. Falls back to the full
+# suite when a change cannot be mapped to tests. Generated by repo_contract.
+# ============================================================================
+
+set -euo pipefail
+
+cd "$(git rev-parse --show-toplevel)"
+CHANGED=()
+while IFS= read -r f; do
+    [[ -n "$f" && -e "$f" ]] && CHANGED+=("$f")
+done < <({ git diff --name-only HEAD 2>/dev/null || true; git ls-files --others --exclude-standard; } | sort -u)
+
+pytest_run() {
+    if [[ -f uv.lock ]]; then uv run pytest "$@"
+    elif [[ -f poetry.lock ]]; then poetry run pytest "$@"
+    else python3 -m pytest "$@"; fi
+}
+
+if grep -qs testmon pyproject.toml requirements*.txt; then
+    pytest_run --testmon -q --tb=short; exit $?
+fi
+
+full=0
+tests=()
+for f in "${CHANGED[@]}"; do
+    case "$f" in
+        */conftest.py | conftest.py | pyproject.toml | requirements*.txt | pytest.ini | setup.cfg) full=1 ;;
+        *.py)
+            base="$(basename "$f" .py)"
+            if [[ "$base" == test_* || "$base" == *_test ]]; then
+                tests+=("$f")
+            else
+                while IFS= read -r t; do tests+=("$t"); done \
+                    < <(git ls-files "*test_${base}.py" "*${base}_test.py")
+            fi
+            ;;
+    esac
+done
+
+if [[ $full -eq 0 && ${#CHANGED[@]} -eq 0 ]]; then echo "no changes vs HEAD: nothing to test"; exit 0; fi
+if [[ $full -eq 0 && ${#tests[@]} -gt 0 ]]; then pytest_run -q --tb=short "${tests[@]}"; exit $?; fi
+if [[ $full -eq 0 ]] && ! printf '%s\n' "${CHANGED[@]}" | grep -q '\.py$'; then
+    echo "no python changes: nothing to test"; exit 0
+fi
+echo "no mapped tests: running full suite"
+pytest_run -q --tb=short