ci: run mutation tests with Infection

Infection is installed in the workflow rather than from the phar or require-dev: the phar's Testo adapter calls the unscoped IncludeInterceptor and fails every mutant, and Infection needs PHP 8.3+ while the package supports 8.2.

Assisted-By: Claude Opus 5.5

Author: roxblnfk

.gitattributes

@@ -6,3 +6,4 @@
 .travis.yml export-ignore
 testo.php export-ignore
 monorepo-builder.php export-ignore
+infection.json5 export-ignore

.github/workflows/mutation.yml

@@ -0,0 +1,52 @@
+---
+
+name: Mutation Tests
+
+on:  # yamllint disable-line rule:truthy
+  pull_request:
+  push:
+    branches: [2.x]
+
+permissions:
+  contents: read
+
+concurrency:
+  group: ${{ github.workflow }}-${{ github.head_ref || github.ref }}
+  cancel-in-progress: ${{ github.event_name == 'pull_request' }}
+
+jobs:
+  mutation:
+    name: Infection
+    runs-on: ubuntu-latest
+    timeout-minutes: 15
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v5
+        with:
+          persist-credentials: false
+
+      - name: Setup PHP
+        uses: shivammathur/setup-php@v2
+        with:
+          php-version: '8.4'
+          extensions: sockets
+          coverage: xdebug
+          ini-values: memory_limit=-1
+
+      - name: Install Composer dependencies
+        uses: ramsey/composer-install@v3
+        with:
+          dependency-versions: highest
+
+      # The Infection phar is unusable with Testo: its bundled adapter calls the
+      # unscoped \Infection\StreamWrapper\IncludeInterceptor. Infection requires
+      # PHP 8.3+, so it is installed here instead of in require-dev.
+      - name: Install Infection
+        run: |
+          composer config allow-plugins.infection/extension-installer true
+          composer require --dev --no-interaction --no-progress -W infection/infection testo/bridge-infection
+
+      - name: Run Infection
+        run: vendor/bin/infection --threads=max --logger-github --show-mutations=0 --min-msi=85 --min-covered-msi=85
+        env:
+          STRYKER_DASHBOARD_API_KEY: ${{ github.event_name == 'push' && secrets.STRYKER_DASHBOARD_API_KEY || '' }}

README.md

@@ -15,6 +15,7 @@
 [![Psalm Level](https://shepherd.dev/github/roadrunner-php/services/level.svg)](https://shepherd.dev/github/roadrunner-php/services)
 [![Type Coverage](https://shepherd.dev/github/roadrunner-php/services/coverage.svg)](https://shepherd.dev/github/roadrunner-php/services)
 [![Codecov](https://codecov.io/gh/roadrunner-php/services/branch/2.x/graph/badge.svg)](https://codecov.io/gh/roadrunner-php/services/branch/2.x)
+[![Mutation testing badge](https://img.shields.io/endpoint?style=flat&url=https%3A%2F%2Fbadge-api.stryker-mutator.io%2Fgithub.com%2Froadrunner-php%2Fservices%2F2.x)](https://dashboard.stryker-mutator.io/reports/github.com/roadrunner-php/services/2.x)
 
 </div>
 

infection.json5

@@ -0,0 +1,16 @@
+{
+    "$schema": "https://raw.githubusercontent.com/infection/infection/0.35.6/resources/schema.json",
+    "source": {
+        "directories": ["src"]
+    },
+    "testFramework": "testo",
+    "tmpDir": "runtime",
+    "timeout": 10,
+    "logs": {
+        "text": "runtime/infection.log",
+        "github": true,
+        "stryker": {
+            "report": "2.x"
+        }
+    }
+}