diff --git a/.config/dotnet-tools.json b/.config/dotnet-tools.json
new file mode 100644
index 00000000..010a8c12
--- /dev/null
+++ b/.config/dotnet-tools.json
@@ -0,0 +1,13 @@
+{
+  "version": 1,
+  "isRoot": true,
+  "tools": {
+    "dotnet-stryker": {
+      "version": "4.16.0",
+      "commands": [
+        "dotnet-stryker"
+      ],
+      "rollForward": false
+    }
+  }
+}
\ No newline at end of file
diff --git a/.github/workflows/mutation.yml b/.github/workflows/mutation.yml
new file mode 100644
index 00000000..055ace1a
--- /dev/null
+++ b/.github/workflows/mutation.yml
@@ -0,0 +1,60 @@
+name: Mutation Testing
+
+on:
+  pull_request:
+    branches: [main]
+  schedule:
+    - cron: "0 6 * * *"
+
+env:
+  DOTNET_ROLL_FORWARD: Major
+
+permissions:
+  contents: read
+
+jobs:
+  mutation:
+    name: Mutation (${{ matrix.project }})
+    runs-on: ubuntu-latest
+    timeout-minutes: 45
+
+    strategy:
+      fail-fast: false
+      matrix:
+        project: [domain, application, infrastructure]
+
+    steps:
+      - uses: actions/checkout@v7
+        with:
+          fetch-depth: 0
+
+      - name: Setup .NET
+        uses: actions/setup-dotnet@v5
+        with:
+          dotnet-version: "10.0.x"
+
+      - name: Restore
+        run: dotnet restore
+
+      - name: Restore local tools
+        run: dotnet tool restore
+
+      - name: Run Stryker (PR — changed in-scope files only)
+        if: github.event_name == 'pull_request'
+        run: |
+          git fetch origin main
+          dotnet stryker -f stryker-config.${{ matrix.project }}.json --since:origin/main
+
+      - name: Run Stryker (nightly — full in-scope)
+        if: github.event_name == 'schedule'
+        run: dotnet stryker -f stryker-config.${{ matrix.project }}.json --concurrency 2
+
+      - name: Upload mutation report
+        if: always()
+        uses: actions/upload-artifact@v7
+        with:
+          name: mutation-report-${{ github.event_name }}-${{ matrix.project }}
+          path: |
+            StrykerOutput/**/reports/*.html
+            StrykerOutput/**/reports/*.json
+          if-no-files-found: ignore
diff --git a/.gitignore b/.gitignore
index bdfc8909..ca82231a 100644
--- a/.gitignore
+++ b/.gitignore
@@ -2,7 +2,8 @@
 ## Build Results
 [Bb]in/
 [Oo]bj/
-.config/
+.config/*
+!.config/dotnet-tools.json
 .fake/
 
 ## JetBrains / Rider
@@ -31,6 +32,9 @@
 TestResults/
 *.trhx
 
+## Mutation testing (Stryker)
+StrykerOutput/
+
 ## Environment Variables & Secrets (CRÍTICO PARA SEU PROJETO)
 .env
 appsettings.Development.json
@@ -49,7 +53,7 @@ Desktop.ini
 
 ## Docker / Caddy
 caddy_data/
-caddy_config/.claude/worktrees/
+caddy_config/
 
 ## Claude Code worktrees
 .claude/worktrees/
diff --git a/stryker-config.application.json b/stryker-config.application.json
new file mode 100644
index 00000000..23187e00
--- /dev/null
+++ b/stryker-config.application.json
@@ -0,0 +1,22 @@
+{
+  "stryker-config": {
+    "project": "Orbit.Application.csproj",
+    "test-projects": ["tests/Orbit.Application.Tests/Orbit.Application.Tests.csproj"],
+    "mutate": [
+      "**/Subscriptions/Commands/VerifyPlayPurchaseCommand.cs",
+      "**/Subscriptions/Commands/HandlePlayNotificationCommand.cs",
+      "**/Subscriptions/Services/PlayReferralCouponConsumer.cs",
+      "**/Common/PlaySubscriptionStateExtensions.cs",
+      "**/Common/SubscriptionSourceExtensions.cs",
+      "**/Auth/Commands/*.cs",
+      "**/Habits/Services/HabitScheduleService.cs"
+    ],
+    "mutation-level": "Standard",
+    "reporters": ["cleartext", "html", "json"],
+    "thresholds": {
+      "high": 80,
+      "low": 60,
+      "break": 0
+    }
+  }
+}
diff --git a/stryker-config.domain.json b/stryker-config.domain.json
new file mode 100644
index 00000000..4452190d
--- /dev/null
+++ b/stryker-config.domain.json
@@ -0,0 +1,19 @@
+{
+  "stryker-config": {
+    "project": "Orbit.Domain.csproj",
+    "test-projects": ["tests/Orbit.Domain.Tests/Orbit.Domain.Tests.csproj"],
+    "mutate": [
+      "**/Entities/Habit.cs",
+      "**/Entities/HabitInvariants.cs",
+      "**/Entities/User.cs",
+      "**/Entities/StreakFreeze.cs"
+    ],
+    "mutation-level": "Standard",
+    "reporters": ["cleartext", "html", "json"],
+    "thresholds": {
+      "high": 80,
+      "low": 60,
+      "break": 0
+    }
+  }
+}
diff --git a/stryker-config.infrastructure.json b/stryker-config.infrastructure.json
new file mode 100644
index 00000000..bc3bd5c6
--- /dev/null
+++ b/stryker-config.infrastructure.json
@@ -0,0 +1,24 @@
+{
+  "stryker-config": {
+    "project": "Orbit.Infrastructure.csproj",
+    "test-projects": ["tests/Orbit.Infrastructure.Tests/Orbit.Infrastructure.Tests.csproj"],
+    "mutate": [
+      "**/Services/JwtTokenService.cs",
+      "**/Services/AuthSessionService.cs",
+      "**/Services/UserStreakService.cs",
+      "**/Services/HabitDueDateAdvancementService.cs",
+      "!**/Services/GooglePlayBillingService.cs",
+      "!**/Services/GoogleTokenService.cs",
+      "!**/Services/GooglePlayPushTokenValidator.cs",
+      "!**/Services/UserDateService.cs",
+      "!**/Services/StreakFreezeAutoActivationService.cs"
+    ],
+    "mutation-level": "Standard",
+    "reporters": ["cleartext", "html", "json"],
+    "thresholds": {
+      "high": 80,
+      "low": 60,
+      "break": 0
+    }
+  }
+}
diff --git a/tests/Orbit.Application.Tests/Commands/Auth/LogoutAndRefreshSessionTests.cs b/tests/Orbit.Application.Tests/Commands/Auth/LogoutAndRefreshSessionTests.cs
deleted file mode 100644
index e69de29b..00000000