Merge pull request 'Version Bump' (#20) from dev into main

Reviewed-on: #20

.claude/settings.local.json

@@ -0,0 +1,8 @@
+{
+  "permissions": {
+    "allow": [
+      "Bash(git add *)",
+      "Bash(git commit *)"
+    ]
+  }
+}

.gitea/workflows/build.yml

@@ -7,48 +7,51 @@ on:
 
 jobs:
   build:
-    runs-on: ubuntu-latest
+    runs-on: ubuntu-java17
 
     steps:
       # 1. Checkout the code
       - name: Checkout code
-        uses: actions/checkout@v2
+        uses: actions/checkout@v4
 
-      # 2. Set up Java and Maven
+      # 2. Build the Spring Boot application using the Maven wrapper (Java 17 pre-installed in runner image)
-      - name: Set up JDK (Eclipse Temurin)
-        uses: actions/setup-java@v3
-        with:
-          distribution: "temurin"
-          java-version: "17"
-          cache: maven
-
-      # 3. Verify Maven installation
-      - name: Install Maven
-        run: |
-          sudo apt-get update
-          sudo apt-get install -y maven
-          mvn -version
-
-      # 4. Build the Spring Boot application
       - name: Build Spring Boot Application
-        run: |
+        run: ./mvnw clean package -DskipTests
-          mvn clean package -DskipTests
 
-      # 5. Set up Docker
+      # 4. Set up Docker Buildx (enables layer caching)
-      - name: Set up Docker
+      - name: Set up Docker Buildx
-        run: |
+        uses: docker/setup-buildx-action@v3
-          docker --version
 
-      # 6. Build the Docker image
+      # 5. Login to Docker Hub to avoid pull rate limits
-      - name: Build and Package Docker Image
+      - name: Login to Docker Hub
-        run: |
+        uses: docker/login-action@v3
-          docker build -t tea.zendric.de/cedric/xpensely-server:latest .
+        with:
+          username: ${{ secrets.DOCKERHUB_USER }}
+          password: ${{ secrets.DOCKERHUB_TOKEN }}
 
-      # 7. Docker login
+      # 6. Docker login to Gitea registry
       - name: Login to Docker Registry
+        uses: docker/login-action@v3
+        with:
+          registry: tea.zendric.de
+          username: ${{ secrets.TEAUSER }}
+          password: ${{ secrets.TEAPASSWORD }}
+
+      # 7. Build and push Docker image with layer caching
+      - name: Build and Push Docker Image
+        uses: docker/build-push-action@v5
+        with:
+          context: .
+          push: true
+          tags: tea.zendric.de/cedric/xpensely-server:latest
+          cache-from: type=registry,ref=tea.zendric.de/cedric/xpensely-server:buildcache
+          cache-to: type=registry,ref=tea.zendric.de/cedric/xpensely-server:buildcache,mode=max
+
+      # 8. Trigger Dokploy to redeploy the dev server automatically via API
+      - name: Trigger Dokploy Redeploy
         run: |
-          echo "${{ secrets.TEAPASSWORD }}" | docker login tea.zendric.de -u ${{ secrets.TEAUSER }} --password-stdin
+          curl -X POST "https://dokploy.zendric.de/api/compose.deploy" \
-      # 8. Push Docker image
+            -H "Content-Type: application/json" \
-      - name: Push the Docker Image to registry
+            -H "x-api-key: ${{ secrets.DOKPLOY_API_TOKEN }}" \
-        run: |
+            -d "{\"composeId\": \"${{ secrets.DOKPLOY_COMPOSE_ID }}\"}" \
-          docker push tea.zendric.de/cedric/xpensely-server:latest
+            --fail

.gitea/workflows/tag_release.yml

@@ -7,78 +7,65 @@ on:
 
 jobs:
   build:
-    runs-on: ubuntu-latest
+    runs-on: ubuntu-java17
 
     steps:
       # 1. Checkout the code
       - name: Checkout code
-        uses: actions/checkout@v2
+        uses: actions/checkout@v4
 
-      # 2. Set up Java and Maven
+      # 2. Build the Spring Boot application using the Maven wrapper
-      - name: Set up JDK (Eclipse Temurin)
+      #    (Java 17 is pre-installed in the runner image)
-        uses: actions/setup-java@v3
-        with:
-          distribution: "temurin"
-          java-version: "17"
-          cache: maven
-
-      # 3. Verify Maven installation
-      - name: Install Maven
-        run: |
-          sudo apt-get update
-          sudo apt-get install -y maven
-          mvn -version
-
-      # 4. Build the Spring Boot application
       - name: Build Spring Boot Application
-        run: |
+        run: ./mvnw clean package -DskipTests
-          mvn clean package -DskipTests
 
-      # 5. Set up Docker
+      # 3. Derive version tags from the pushed git tag
-      - name: Set up Docker
+      #    e.g. 1.1.0 -> tag_version=1.1.0, minor=1.1, major=1
+      - name: Extract version tags
+        id: ver
         run: |
-          docker --version
+          TAG_VERSION="${{ github.ref_name }}"
-
-      # 6. Extract the tag name
-      - name: Extract Tag Version
-        id: extract_version
-        run: |
-          TAG_VERSION=$(echo "${GITHUB_REF}" | sed 's#refs/tags/##')
           if [ -z "$TAG_VERSION" ]; then
             echo "Error: TAG_VERSION is empty."
             exit 1
           fi
-          echo "TAG_VERSION=$TAG_VERSION" >> $GITHUB_ENV
+          MINOR_VERSION=$(echo "$TAG_VERSION" | cut -d. -f1,2)
+          MAJOR_VERSION=$(echo "$TAG_VERSION" | cut -d. -f1)
+          echo "tag_version=$TAG_VERSION" >> "$GITHUB_OUTPUT"
+          echo "minor=$MINOR_VERSION"     >> "$GITHUB_OUTPUT"
+          echo "major=$MAJOR_VERSION"     >> "$GITHUB_OUTPUT"
 
-          # Extract major and minor versions
+      # 4. Set up Docker Buildx (enables layer caching)
-          MAJOR_VERSION=$(echo "${TAG_VERSION}" | cut -d. -f1)
+      - name: Set up Docker Buildx
-          MINOR_VERSION=$(echo "${TAG_VERSION}" | cut -d. -f1,2)
+        uses: docker/setup-buildx-action@v3
-          echo "MAJOR_VERSION=$MAJOR_VERSION" >> $GITHUB_ENV
-          echo "MINOR_VERSION=$MINOR_VERSION" >> $GITHUB_ENV
 
-      # 7. Build the Docker image with the tag
+      # 5. Login to Docker Hub to avoid base-image pull rate limits
-      - name: Build and Package Docker Image
+      - name: Login to Docker Hub
-        run: |
+        uses: docker/login-action@v3
-          docker build -t tea.zendric.de/cedric/xpensely-server:${{ env.TAG_VERSION }} .
+        with:
+          username: ${{ secrets.DOCKERHUB_USER }}
+          password: ${{ secrets.DOCKERHUB_TOKEN }}
 
-      # 8. Tag the image with Major Version (e.g., 0)
+      # 6. Login to the Gitea registry
-      - name: Tag with Major Version
-        run: |
-          docker tag tea.zendric.de/cedric/xpensely-server:${{ env.TAG_VERSION }} tea.zendric.de/cedric/xpensely-server:${{ env.MAJOR_VERSION }}
-
-      # 9. Tag the image with Minor Version (e.g., 0.1)
-      - name: Tag with Minor Version
-        run: |
-          docker tag tea.zendric.de/cedric/xpensely-server:${{ env.TAG_VERSION }} tea.zendric.de/cedric/xpensely-server:${{ env.MINOR_VERSION }}
-
-      # 10. Docker login
       - name: Login to Docker Registry
-        run: |
+        uses: docker/login-action@v3
-          echo "${{ secrets.TEAPASSWORD }}" | docker login tea.zendric.de -u ${{ secrets.TEAUSER }} --password-stdin
+        with:
+          registry: tea.zendric.de
+          username: ${{ secrets.TEAUSER }}
+          password: ${{ secrets.TEAPASSWORD }}
 
-      # 11. Push the Docker images with the tags
+      # 7. Build and push the versioned Docker images with layer caching.
-      - name: Push the Docker Image to registry
+      #    Pushes exact, minor, and major tags. The prod compose references
-        run: |
+      #    the major tag (":1"), so pushing here makes the new build available
-          docker push tea.zendric.de/cedric/xpensely-server:${{ env.TAG_VERSION }}
+      #    to pull in Dockge — deploy is triggered MANUALLY after the DB migration.
-          docker push tea.zendric.de/cedric/xpensely-server:${{ env.MAJOR_VERSION }}
+      - name: Build and Push Docker Image
-          docker push tea.zendric.de/cedric/xpensely-server:${{ env.MINOR_VERSION }}
+        uses: docker/build-push-action@v5
+        with:
+          context: .
+          push: true
+          tags: |
+            tea.zendric.de/cedric/xpensely-server:${{ steps.ver.outputs.tag_version }}
+            tea.zendric.de/cedric/xpensely-server:${{ steps.ver.outputs.minor }}
+            tea.zendric.de/cedric/xpensely-server:${{ steps.ver.outputs.major }}
+          cache-from: type=registry,ref=tea.zendric.de/cedric/xpensely-server:buildcache
+          cache-to: type=registry,ref=tea.zendric.de/cedric/xpensely-server:buildcache,mode=max

.gitignore

@@ -6,6 +6,11 @@ target/
 !**/src/test/**/target/
 .env
 
+# Local debugging (not for CI/prod)
+.env.local
+Dockerfile.local
+compose.local.yml
+
 ### STS ###
 .apt_generated
 .classpath

README.md

@@ -0,0 +1,7 @@
+Run it locally:
+
+1. build the current state:
+   mvn clean install or mvn clean install -DskipTests
+
+2. docker it up and run it
+   docker-compose -f dev-docker-compose.yml up --build

apiDesign.drawio

@@ -1,6 +1,6 @@
 <mxfile host="65bd71144e">
     <diagram id="TZX9Tq6sZIlTxQ58HocZ" name="Page-1">
-        <mxGraphModel dx="826" dy="472" grid="1" gridSize="10" guides="1" tooltips="1" connect="1" arrows="1" fold="1" page="1" pageScale="1" pageWidth="850" pageHeight="1100" math="0" shadow="0">
+        <mxGraphModel dx="989" dy="570" grid="1" gridSize="10" guides="1" tooltips="1" connect="1" arrows="1" fold="1" page="1" pageScale="1" pageWidth="850" pageHeight="1100" math="0" shadow="0">
             <root>
                 <mxCell id="0"/>
                 <mxCell id="1" parent="0"/>
@@ -193,6 +193,90 @@
                 <mxCell id="73" value="&lt;span style=&quot;font-size: 8px;&quot;&gt;24.12.24 ; Expense ; 24,12 €&lt;/span&gt;" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#76608a;fontColor=#ffffff;strokeColor=#432D57;" parent="1" vertex="1">
                     <mxGeometry x="1399" y="226" width="120" height="20" as="geometry"/>
                 </mxCell>
+                <mxCell id="86" style="edgeStyle=none;html=1;entryX=0;entryY=0.5;entryDx=0;entryDy=0;" edge="1" parent="1" source="74" target="79">
+                    <mxGeometry relative="1" as="geometry"/>
+                </mxCell>
+                <mxCell id="74" value="List" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#60a917;fontColor=#ffffff;strokeColor=#2D7600;" vertex="1" parent="1">
+                    <mxGeometry x="1880" y="160" width="120" height="60" as="geometry"/>
+                </mxCell>
+                <mxCell id="75" value="DB-Structure for Categories" style="text;html=1;strokeColor=none;fillColor=none;align=center;verticalAlign=middle;whiteSpace=wrap;rounded=0;" vertex="1" parent="1">
+                    <mxGeometry x="1930" y="35" width="100" height="30" as="geometry"/>
+                </mxCell>
+                <mxCell id="78" style="edgeStyle=none;html=1;entryX=0;entryY=0.5;entryDx=0;entryDy=0;" edge="1" parent="1" source="76" target="77">
+                    <mxGeometry relative="1" as="geometry"/>
+                </mxCell>
+                <mxCell id="76" value="List Entry" style="rounded=0;whiteSpace=wrap;html=1;" vertex="1" parent="1">
+                    <mxGeometry x="1920" y="220" width="120" height="60" as="geometry"/>
+                </mxCell>
+                <mxCell id="79" value="Available Categories" style="ellipse;whiteSpace=wrap;html=1;" vertex="1" parent="1">
+                    <mxGeometry x="2160" y="150" width="120" height="80" as="geometry"/>
+                </mxCell>
+                <mxCell id="83" style="edgeStyle=none;html=1;entryX=0.5;entryY=0;entryDx=0;entryDy=0;" edge="1" parent="1" source="81" target="79">
+                    <mxGeometry relative="1" as="geometry"/>
+                </mxCell>
+                <mxCell id="81" value="Standard Categories" style="ellipse;whiteSpace=wrap;html=1;" vertex="1" parent="1">
+                    <mxGeometry x="2060" y="35" width="120" height="80" as="geometry"/>
+                </mxCell>
+                <mxCell id="84" style="edgeStyle=none;html=1;entryX=0.5;entryY=0;entryDx=0;entryDy=0;" edge="1" parent="1" source="82" target="79">
+                    <mxGeometry relative="1" as="geometry"/>
+                </mxCell>
+                <mxCell id="82" value="Custom Categories" style="ellipse;whiteSpace=wrap;html=1;" vertex="1" parent="1">
+                    <mxGeometry x="2270" y="35" width="120" height="80" as="geometry"/>
+                </mxCell>
+                <mxCell id="91" style="edgeStyle=none;html=1;entryX=0;entryY=0.5;entryDx=0;entryDy=0;" edge="1" parent="1" source="87" target="90">
+                    <mxGeometry relative="1" as="geometry"/>
+                </mxCell>
+                <mxCell id="87" value="List Entry" style="rounded=0;whiteSpace=wrap;html=1;" vertex="1" parent="1">
+                    <mxGeometry x="1920" y="280" width="120" height="60" as="geometry"/>
+                </mxCell>
+                <mxCell id="92" style="edgeStyle=none;html=1;entryX=0;entryY=0.5;entryDx=0;entryDy=0;" edge="1" parent="1" source="88" target="89">
+                    <mxGeometry relative="1" as="geometry"/>
+                </mxCell>
+                <mxCell id="88" value="List Entry" style="rounded=0;whiteSpace=wrap;html=1;" vertex="1" parent="1">
+                    <mxGeometry x="1920" y="340" width="120" height="60" as="geometry"/>
+                </mxCell>
+                <mxCell id="89" value="Category" style="ellipse;whiteSpace=wrap;html=1;" vertex="1" parent="1">
+                    <mxGeometry x="2150" y="370" width="120" height="80" as="geometry"/>
+                </mxCell>
+                <mxCell id="90" value="Category" style="ellipse;whiteSpace=wrap;html=1;" vertex="1" parent="1">
+                    <mxGeometry x="2150" y="315" width="120" height="80" as="geometry"/>
+                </mxCell>
+                <mxCell id="94" value="&lt;h1 style=&quot;font-size: 18px;&quot;&gt;- list id&lt;/h1&gt;&lt;div&gt;- List &amp;lt;String&amp;gt;&lt;/div&gt;" style="text;html=1;strokeColor=none;fillColor=none;spacing=5;spacingTop=-20;whiteSpace=wrap;overflow=hidden;rounded=0;fontSize=18;" vertex="1" parent="1">
+                    <mxGeometry x="2410" y="50" width="130" height="70" as="geometry"/>
+                </mxCell>
+                <mxCell id="77" value="Category" style="ellipse;whiteSpace=wrap;html=1;" vertex="1" parent="1">
+                    <mxGeometry x="2150" y="260" width="120" height="80" as="geometry"/>
+                </mxCell>
+                <mxCell id="97" value="" style="rounded=0;whiteSpace=wrap;html=1;" vertex="1" parent="1">
+                    <mxGeometry x="1730" y="510" width="200" height="320" as="geometry"/>
+                </mxCell>
+                <mxCell id="98" value="ExpenseList" style="rounded=1;whiteSpace=wrap;html=1;" vertex="1" parent="1">
+                    <mxGeometry x="1770" y="520" width="120" height="20" as="geometry"/>
+                </mxCell>
+                <mxCell id="100" value="+" style="rounded=1;whiteSpace=wrap;html=1;" vertex="1" parent="1">
+                    <mxGeometry x="1880" y="790" width="30" height="30" as="geometry"/>
+                </mxCell>
+                <mxCell id="101" value="Categorie" style="text;html=1;strokeColor=none;fillColor=none;align=center;verticalAlign=middle;whiteSpace=wrap;rounded=0;" vertex="1" parent="1">
+                    <mxGeometry x="1770" y="480" width="120" height="30" as="geometry"/>
+                </mxCell>
+                <mxCell id="102" value="&lt;span style=&quot;font-size: 8px;&quot;&gt;Amount : 24,12 €&lt;br&gt;Title: Expense&lt;br&gt;Date: 24.12.24&lt;br&gt;From: Jessi&lt;br&gt;Deviation: 0 €&lt;/span&gt;" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#76608a;fontColor=#ffffff;strokeColor=#432D57;align=left;spacingLeft=12;" vertex="1" parent="1">
+                    <mxGeometry x="1745" y="550" width="170" height="170" as="geometry"/>
+                </mxCell>
+                <mxCell id="105" value="&lt;span style=&quot;font-size: 8px;&quot;&gt;Essen&lt;/span&gt;" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#1ba1e2;fontColor=#ffffff;strokeColor=#006EAF;align=left;spacingLeft=12;" vertex="1" parent="1">
+                    <mxGeometry x="1760" y="680" width="40" height="10" as="geometry"/>
+                </mxCell>
+                <mxCell id="106" value="&lt;span style=&quot;font-size: 8px;&quot;&gt;Trinken&lt;/span&gt;" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#a20025;fontColor=#ffffff;strokeColor=#6F0000;align=left;spacingLeft=12;" vertex="1" parent="1">
+                    <mxGeometry x="1800" y="680" width="40" height="10" as="geometry"/>
+                </mxCell>
+                <mxCell id="107" value="&lt;span style=&quot;font-size: 8px;&quot;&gt;Auto&lt;/span&gt;" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#d80073;fontColor=#ffffff;strokeColor=#A50040;align=left;spacingLeft=12;" vertex="1" parent="1">
+                    <mxGeometry x="1840" y="680" width="40" height="10" as="geometry"/>
+                </mxCell>
+                <mxCell id="111" style="edgeStyle=none;html=1;entryX=0;entryY=0.5;entryDx=0;entryDy=0;fontSize=18;" edge="1" parent="1" source="108" target="74">
+                    <mxGeometry relative="1" as="geometry"/>
+                </mxCell>
+                <mxCell id="108" value="Actor" style="shape=umlActor;verticalLabelPosition=bottom;verticalAlign=top;html=1;outlineConnect=0;fontSize=18;" vertex="1" parent="1">
+                    <mxGeometry x="1715" y="150" width="30" height="60" as="geometry"/>
+                </mxCell>
             </root>
         </mxGraphModel>
     </diagram>

docker-compose.yml

@@ -1,11 +1,9 @@
 services:
   xpensely-server:
     image: tea.zendric.de/cedric/xpensely-server:latest
+    pull_policy: always
     restart: always
     environment:
-      GOOGLE_CLIENT_ID: ${GOOGLE_CLIENT_ID}
-      GOOGLE_CLIENT_SECRET: ${GOOGLE_CLIENT_SECRET}
-
       DB_PORT: 5432
       DB_P_NAME: ${POSTGRES_DB}
       DB_USERNAME: ${POSTGRES_USER}

dockerfile

@@ -1,4 +1,4 @@
-FROM eclipse-temurin:17-jdk
+FROM eclipse-temurin:21-jdk
 
 COPY ./target/*.jar app.jar
 

docs/API.md

@@ -1,6 +1,6 @@
 # Xpensely Server — API Reference
 
-> Last updated: 2026-05-09 · Branch: `feature/security-hardening`
+> Last updated: 2026-05-14 · Branch: `dev`
 
 ## Table of Contents
 1. [Overview](#1-overview)
@@ -28,6 +28,7 @@ Xpensely Server is a Spring Boot REST API that manages shared expense lists for
 | Method | Path | Description |
 |--------|------|-------------|
 | GET | `/` | Health check — returns `"Welcome"` |
+| GET | `/api/version` | Returns build version and timestamp |
 | POST | `/api/users/createUser` | Register a new user |
 | GET | `/api/users/byName` | Look up a user by username |
 
@@ -98,6 +99,25 @@ Welcome
 
 ---
 
+#### `GET /api/version`
+
+Returns the application version and build timestamp. No authentication required.
+
+**Response:** `200 OK`
+```json
+{
+  "version": "0.0.1-SNAPSHOT",
+  "builtAt": "2026-05-09T10:00:00Z"
+}
+```
+
+| Field | Type | Notes |
+|-------|------|-------|
+| `version` | String | Maven project version |
+| `builtAt` | String (ISO-8601) | UTC timestamp of the build |
+
+---
+
 ### 4.2 Users
 
 Base path: `/api/users`
@@ -121,7 +141,7 @@ Base path: `/api/users`
 | `username` | String | Required. 3–30 chars. Pattern: `^[a-zA-Z0-9_.\-]+$` |
 | `googleId` | String | Required. Non-blank. Must match the JWT `sub` from Google. |
 
-**Success response:** `200 OK` — returns the created [AppUser](#appuser) object.
+**Success response:** `201 Created` — returns the created [AppUser](#appuser) object.
 
 **Error responses:**
 | Status | Condition |
@@ -145,6 +165,7 @@ Base path: `/api/users`
 **Error responses:**
 | Status | Condition |
 |--------|-----------|
+| 403 | Authenticated user's ID does not match the requested `id` |
 | 404 | No user found for `id` |
 
 ---
@@ -181,6 +202,7 @@ Base path: `/api/users`
 **Error responses:**
 | Status | Condition |
 |--------|-----------|
+| 403 | Requested Google ID does not match the authenticated user's Google ID |
 | 404 | No user found for that Google ID |
 
 ---
@@ -194,11 +216,12 @@ Base path: `/api/users`
 |-------|------|----------|-------------|
 | `id` | Long | Yes | Database ID of the user to delete |
 
-**Success response:** `200 OK` — returns the deleted [AppUser](#appuser).
+**Success response:** `200 OK` — returns a plain string: `"User deleted: <username>"`.
 
 **Error responses:**
 | Status | Condition |
 |--------|-----------|
+| 403 | Authenticated user's ID does not match the requested `id` |
 | 404 | No user found for `id` |
 
 ---
@@ -219,7 +242,11 @@ Returns all expense lists where the caller is the owner **or** has been shared t
 
 **Request body:** None
 
-**Success response:** `200 OK` — array of [ExpenseList](#expenselist).
+**Success responses:**
+| Status | Condition |
+|--------|-----------|
+| 200 OK | Returns array of [ExpenseList](#expenselist) |
+| 204 No Content | Caller has no expense lists |
 
 ```json
 [
@@ -337,7 +364,7 @@ Only the **owner** may delete a list. Deleting a list cascades to all its expens
 | `date` | String (ISO-8601) | Required. Format: `YYYY-MM-DD`. |
 | `category` | String | Required. Non-blank category name. |
 
-**Success response:** `200 OK` — returns the created [Expense](#expense).
+**Success response:** `201 Created` — returns the created [Expense](#expense).
 
 **Error responses:**
 | Status | Condition |
@@ -411,7 +438,7 @@ Caller must be a member of the list. Expense must belong to the specified list.
 
 Caller must be a member of the list.
 
-**Success response:** `200 OK` — returns the deleted [Expense](#expense).
+**Success response:** `204 No Content`
 
 **Error responses:**
 | Status | Condition |
@@ -465,13 +492,14 @@ Joins the caller to a shared expense list using an invite code.
 |-------|------|-------------|
 | `inviteCode` | String | Required. Exactly 6 characters. |
 
-**Success response:** `200 OK` — returns the [ExpenseList](#expenselist) the caller joined.
+**Success response:** `200 OK` — returns a plain string: `"User added to the list"`.
 
 **Error responses:**
 | Status | Condition |
 |--------|-----------|
-| 400 | Validation failure or invite code not found / expired |
+| 400 | Validation failure or caller is already the owner of the list |
-| 403 | Caller is already the owner of this list |
+| 404 | Invite code not found or expired |
+| 226 IM Used | List already has a second member (`sharedWith` is not null) |
 
 ---
 

docs/xpensely-api.http

@@ -0,0 +1,148 @@
+# Xpensely API — Manual test file (IntelliJ HTTP Client / VS Code REST Client)
+#
+# HOW TO GET A TOKEN:
+#   1. Run the Flutter dev app and sign in with Google
+#   2. Add a breakpoint or log in auth_interceptor.dart after _storage.read(key: 'id_token')
+#   3. Paste the token value below (valid for ~1 hour)
+#
+# Switch between dev and prod by changing @baseUrl.
+
+@devBaseUrl  = https://dev-xpensely.zendric.de/api
+@prodBaseUrl = https://xpensely.zendric.de/api
+@baseUrl     = {{devBaseUrl}}
+
+# Paste your Google ID token here:
+@token = PASTE_ID_TOKEN_HERE
+
+# Your Google sub (from the JWT payload — decode at jwt.io):
+@googleId = PASTE_GOOGLE_SUB_HERE
+
+
+### ─── Health ────────────────────────────────────────────────────────────────
+
+### Version (no auth required — should always return 200)
+GET {{baseUrl}}/version
+
+### ─── Auth probe ─────────────────────────────────────────────────────────────
+
+### Any protected endpoint without a token — expect 401
+GET {{baseUrl}}/users/byGoogleId?id={{googleId}}
+
+### ─── Users ──────────────────────────────────────────────────────────────────
+
+### Look up your account by Google ID — expect 200 if account exists, 403 if not
+GET {{baseUrl}}/users/byGoogleId?id={{googleId}}
+Authorization: Bearer {{token}}
+
+###
+
+### Get your account by DB id — replace {id} with your numeric user id
+GET {{baseUrl}}/users?id=1
+Authorization: Bearer {{token}}
+
+###
+
+### Get any user by username (no auth required)
+GET {{baseUrl}}/users/byName?username=testuser
+
+###
+
+### Create a new account (requires valid JWT — account must not exist yet)
+POST {{baseUrl}}/users/createUser
+Content-Type: application/json
+Authorization: Bearer {{token}}
+
+{
+  "username": "myusername",
+  "googleId": "{{googleId}}"
+}
+
+###
+
+### Delete your account — replace {id} with your numeric user id
+DELETE {{baseUrl}}/users?id=1
+Authorization: Bearer {{token}}
+
+### ─── Expense Lists ───────────────────────────────────────────────────────────
+
+### Get all your expense lists — expect 200 (with data) or 204 (empty)
+GET {{baseUrl}}/expenselist/mine
+Authorization: Bearer {{token}}
+
+###
+
+### Get a specific expense list by id
+GET {{baseUrl}}/expenselist/byId?id=1
+Authorization: Bearer {{token}}
+
+###
+
+### Create a new expense list
+POST {{baseUrl}}/expenselist/create
+Content-Type: application/json
+Authorization: Bearer {{token}}
+
+{
+  "name": "Groceries"
+}
+
+###
+
+### Add an expense to a list — replace {listId} in the URL
+POST {{baseUrl}}/expenselist/1/add
+Content-Type: application/json
+Authorization: Bearer {{token}}
+
+{
+  "title": "Coffee",
+  "owner": "myusername",
+  "amount": 4.50,
+  "date": "2026-05-15",
+  "category": "Food"
+}
+
+###
+
+### Update an expense in a list
+PUT {{baseUrl}}/expenselist/1/update
+Content-Type: application/json
+Authorization: Bearer {{token}}
+
+{
+  "id": 1,
+  "title": "Coffee (updated)",
+  "ownerName": "myusername",
+  "amount": 5.00,
+  "date": "2026-05-15",
+  "category": "Food",
+  "expenseListId": 1
+}
+
+###
+
+### Delete an expense from a list
+DELETE {{baseUrl}}/expenselist/1/delete?expenseId=1
+Authorization: Bearer {{token}}
+
+###
+
+### Generate an invite code for a list (you must be the owner)
+POST {{baseUrl}}/expenselist/1/invite
+Authorization: Bearer {{token}}
+
+###
+
+### Accept an invite
+POST {{baseUrl}}/expenselist/accept-invite
+Content-Type: application/json
+Authorization: Bearer {{token}}
+
+{
+  "inviteCode": "PASTE_6_CHAR_CODE_HERE"
+}
+
+###
+
+### Delete an expense list (you must be the owner)
+DELETE {{baseUrl}}/expenselist/1
+Authorization: Bearer {{token}}

pom.xml

@@ -6,11 +6,11 @@
         <groupId>org.springframework.boot</groupId>
         <artifactId>spring-boot-starter-parent</artifactId>
         <version>4.0.6</version>
-        <relativePath/> <!-- lookup parent from repository -->
+        <relativePath/>
     </parent>
     <groupId>de.zendric.app</groupId>
     <artifactId>XpenselyServer</artifactId>
-    <version>1.0.0</version>
+    <version>1.2.2</version>
     <name>XpenselyServer</name>
     <description>XpenselyServer used to handle the Xpensely App</description>
     <url/>
@@ -52,10 +52,6 @@
             <groupId>org.springframework.boot</groupId>
             <artifactId>spring-boot-starter-oauth2-resource-server</artifactId>
         </dependency>
-        <dependency>
-            <groupId>org.springframework.boot</groupId>
-            <artifactId>spring-boot-starter-oauth2-client</artifactId>
-        </dependency>
         <dependency>
             <groupId>org.springframework.boot</groupId>
             <artifactId>spring-boot-starter-web</artifactId>
@@ -128,6 +124,13 @@
                         </exclude>
                     </excludes>
                 </configuration>
+                <executions>
+                    <execution>
+                        <goals>
+                            <goal>build-info</goal>
+                        </goals>
+                    </execution>
+                </executions>
             </plugin>
         </plugins>
     </build>

src/main/java/de/zendric/app/xpensely_server/controller/AppUserController.java

@@ -9,6 +9,7 @@ import org.springframework.web.server.ResponseStatusException;
 
 import de.zendric.app.xpensely_server.model.AppUser;
 import de.zendric.app.xpensely_server.model.AppUserCreateRequest;
+import de.zendric.app.xpensely_server.model.UsernameUpdateRequest;
 import de.zendric.app.xpensely_server.security.AuthenticatedUserResolver;
 import de.zendric.app.xpensely_server.services.UserService;
 
@@ -31,11 +32,6 @@ public class AppUserController {
         return ResponseEntity.ok(userService.getUser(id));
     }
 
-    @GetMapping("/byName")
-    public AppUser getUserByName(@RequestParam String username) {
-        return userService.getUserByName(username);
-    }
-
     @GetMapping("/byGoogleId")
     public ResponseEntity<AppUser> getUserByGoogleId(@RequestParam String id, Authentication authentication) {
         AppUser self = authenticatedUserResolver.resolveCurrentUser(authentication);
@@ -51,6 +47,14 @@ public class AppUserController {
         return new ResponseEntity<>(nUser, HttpStatus.CREATED);
     }
 
+    @PutMapping("/username")
+    public ResponseEntity<AppUser> updateUsername(@RequestBody @Valid UsernameUpdateRequest request,
+            Authentication authentication) {
+        AppUser self = authenticatedUserResolver.resolveCurrentUser(authentication);
+        AppUser updated = userService.updateUsername(self.getId(), request.getUsername());
+        return ResponseEntity.ok(updated);
+    }
+
     @DeleteMapping
     public ResponseEntity<String> deleteUser(@RequestParam Long id, Authentication authentication) {
         AppUser self = authenticatedUserResolver.resolveCurrentUser(authentication);

src/main/java/de/zendric/app/xpensely_server/controller/ExpenseListController.java

@@ -14,10 +14,12 @@ import org.springframework.web.bind.annotation.*;
 import org.springframework.web.server.ResponseStatusException;
 
 import de.zendric.app.xpensely_server.model.*;
+import de.zendric.app.xpensely_server.model.DTO.HistoryPageDto;
+import de.zendric.app.xpensely_server.model.DTO.RecentHistoryEntryDto;
 import de.zendric.app.xpensely_server.security.AuthenticatedUserResolver;
 import de.zendric.app.xpensely_server.services.CategoryService;
 import de.zendric.app.xpensely_server.services.ExpenseListService;
-import de.zendric.app.xpensely_server.services.UserService;
+import de.zendric.app.xpensely_server.services.HistoryService;
 
 @RestController
 @RequestMapping("/api/expenselist")
@@ -26,16 +28,17 @@ public class ExpenseListController {
     private static final Logger log = LoggerFactory.getLogger(ExpenseListController.class);
 
     private final ExpenseListService expenseListService;
-    private final UserService userService;
     private final CategoryService categoryService;
     private final AuthenticatedUserResolver authenticatedUserResolver;
+    private final HistoryService historyService;
 
-    public ExpenseListController(ExpenseListService expenseListService, UserService userService,
+    public ExpenseListController(ExpenseListService expenseListService,
-            CategoryService categoryService, AuthenticatedUserResolver authenticatedUserResolver) {
+            CategoryService categoryService, AuthenticatedUserResolver authenticatedUserResolver,
+            HistoryService historyService) {
         this.expenseListService = expenseListService;
-        this.userService = userService;
         this.categoryService = categoryService;
         this.authenticatedUserResolver = authenticatedUserResolver;
+        this.historyService = historyService;
     }
 
     @GetMapping("/mine")
@@ -83,6 +86,30 @@ public class ExpenseListController {
         return new ResponseEntity<>(HttpStatus.NO_CONTENT);
     }
 
+    @PutMapping("/{id}/rename")
+    public ResponseEntity<ExpenseList> rename(@PathVariable("id") Long id,
+            @RequestBody @Valid CreateExpenseListRequest request, Authentication authentication) {
+        AppUser user = authenticatedUserResolver.resolveCurrentUser(authentication);
+        Optional<ExpenseList> listOpt = expenseListService.findById(id);
+        if (listOpt.isEmpty())
+            return new ResponseEntity<>(HttpStatus.NOT_FOUND);
+        assertOwner(user, listOpt.get());
+        ExpenseList renamed = expenseListService.renameList(id, request.getName());
+        return new ResponseEntity<>(renamed, HttpStatus.OK);
+    }
+
+    @PutMapping("/{id}/default-split")
+    public ResponseEntity<ExpenseList> updateDefaultSplit(@PathVariable("id") Long id,
+            @RequestBody @Valid DefaultSplitRequest request, Authentication authentication) {
+        AppUser user = authenticatedUserResolver.resolveCurrentUser(authentication);
+        Optional<ExpenseList> listOpt = expenseListService.findById(id);
+        if (listOpt.isEmpty())
+            return new ResponseEntity<>(HttpStatus.NOT_FOUND);
+        assertMember(user, listOpt.get());
+        ExpenseList updated = expenseListService.updateDefaultSplit(id, request.getPercentage());
+        return new ResponseEntity<>(updated, HttpStatus.OK);
+    }
+
     @PostMapping("/{id}/add")
     public ResponseEntity<Expense> addExpenseToList(
             @PathVariable("id") Long expenseListId,
@@ -93,9 +120,9 @@ public class ExpenseListController {
         if (listOpt.isEmpty())
             return new ResponseEntity<>(HttpStatus.NOT_FOUND);
         assertMember(user, listOpt.get());
-        AppUser expenseOwner = userService.getUserByName(expenseInput.getOwner());
+        AppUser expenseOwner = resolveListMember(listOpt.get(), expenseInput.getOwner());
         Expense expense = expenseInput.convertToExpense(expenseOwner.getId());
-        Expense addedExpense = expenseListService.addExpenseToList(expenseListId, expense);
+        Expense addedExpense = expenseListService.addExpenseToList(expenseListId, expense, user);
         return new ResponseEntity<>(addedExpense, HttpStatus.CREATED);
     }
 
@@ -109,9 +136,9 @@ public class ExpenseListController {
         if (expenseListOpt.isEmpty())
             return new ResponseEntity<>(HttpStatus.NOT_FOUND);
         assertMember(user, expenseListOpt.get());
-        AppUser expenseOwner = userService.getUserByName(expenseChangeRequest.getOwnerName());
+        AppUser expenseOwner = resolveListMember(expenseListOpt.get(), expenseChangeRequest.getOwnerName());
         Expense expense = expenseChangeRequest.convertToExpense(expenseOwner.getId(), expenseListOpt.get());
-        Expense updatedExpense = expenseListService.updateExpense(expenseListId, expense);
+        Expense updatedExpense = expenseListService.updateExpense(expenseListId, expense, user);
         return new ResponseEntity<>(updatedExpense, HttpStatus.OK);
     }
 
@@ -125,7 +152,7 @@ public class ExpenseListController {
         if (listOpt.isEmpty())
             return new ResponseEntity<>(HttpStatus.NOT_FOUND);
         assertMember(user, listOpt.get());
-        expenseListService.deleteExpenseFromList(expenseListId, expenseId);
+        expenseListService.deleteExpenseFromList(expenseListId, expenseId, user);
         return new ResponseEntity<>(HttpStatus.NO_CONTENT);
     }
 
@@ -156,11 +183,38 @@ public class ExpenseListController {
         if (list.getOwner().getId().equals(authenticatedUser.getId())) {
             return ResponseEntity.status(HttpStatus.BAD_REQUEST).body("You cannot join your own list");
         }
+        if (list.getOwner().getUsername().equals(authenticatedUser.getUsername())) {
+            return ResponseEntity.status(HttpStatus.CONFLICT).body(
+                    "You and the list owner both use the username \"" + authenticatedUser.getUsername()
+                            + "\". Please change your username before joining this list.");
+        }
         list.setSharedWith(authenticatedUser);
         expenseListService.save(list);
         return ResponseEntity.ok("User added to the list");
     }
 
+    @GetMapping("/{id}/history")
+    public ResponseEntity<HistoryPageDto> getHistory(
+            @PathVariable("id") Long id,
+            @RequestParam(defaultValue = "0") int page,
+            @RequestParam(defaultValue = "30") int size,
+            Authentication authentication) {
+        AppUser user = authenticatedUserResolver.resolveCurrentUser(authentication);
+        Optional<ExpenseList> listOpt = expenseListService.findById(id);
+        if (listOpt.isEmpty())
+            return new ResponseEntity<>(HttpStatus.NOT_FOUND);
+        assertMember(user, listOpt.get());
+        return ResponseEntity.ok(historyService.getHistory(id, page, size));
+    }
+
+    @GetMapping("/history/recent")
+    public ResponseEntity<List<RecentHistoryEntryDto>> getRecentHistory(
+            @RequestParam(defaultValue = "4") int limit,
+            Authentication authentication) {
+        AppUser user = authenticatedUserResolver.resolveCurrentUser(authentication);
+        return ResponseEntity.ok(historyService.getRecentForUser(user, limit));
+    }
+
     private void assertOwner(AppUser authenticated, ExpenseList list) {
         if (!list.getOwner().getId().equals(authenticated.getId()))
             throw new ResponseStatusException(HttpStatus.FORBIDDEN);
@@ -173,4 +227,20 @@ public class ExpenseListController {
         if (!isOwner && !isShared)
             throw new ResponseStatusException(HttpStatus.FORBIDDEN);
     }
+
+    /**
+     * Resolves an expense owner by username among the list's members. Usernames are
+     * not globally unique, so the owner must be one of this list's (at most two)
+     * members — never a global lookup.
+     */
+    private AppUser resolveListMember(ExpenseList list, String username) {
+        if (list.getOwner() != null && list.getOwner().getUsername().equals(username)) {
+            return list.getOwner();
+        }
+        if (list.getSharedWith() != null && list.getSharedWith().getUsername().equals(username)) {
+            return list.getSharedWith();
+        }
+        throw new ResponseStatusException(HttpStatus.BAD_REQUEST,
+                "Expense owner must be a member of this list");
+    }
 }

src/main/java/de/zendric/app/xpensely_server/controller/GlobalExceptionHandler.java

@@ -1,5 +1,6 @@
 package de.zendric.app.xpensely_server.controller;
 
+import de.zendric.app.xpensely_server.model.Exception.GoogleAccountAlreadyRegisteredException;
 import de.zendric.app.xpensely_server.model.Exception.ResourceNotFoundException;
 import de.zendric.app.xpensely_server.model.Exception.UsernameAlreadyExistsException;
 import org.slf4j.Logger;
@@ -47,6 +48,13 @@ public class GlobalExceptionHandler {
                 .body(Map.of("error", ex.getMessage()));
     }
 
+    @ExceptionHandler(GoogleAccountAlreadyRegisteredException.class)
+    public ResponseEntity<Map<String, String>> handleGoogleAccountConflict(
+            GoogleAccountAlreadyRegisteredException ex) {
+        return ResponseEntity.status(HttpStatus.CONFLICT)
+                .body(Map.of("error", ex.getMessage()));
+    }
+
     @ExceptionHandler(ResponseStatusException.class)
     public ResponseEntity<Map<String, String>> handleResponseStatus(ResponseStatusException ex) {
         return ResponseEntity.status(ex.getStatusCode())

src/main/java/de/zendric/app/xpensely_server/controller/HomeController.java

@@ -1,13 +1,30 @@
 package de.zendric.app.xpensely_server.controller;
 
+import org.springframework.boot.info.BuildProperties;
 import org.springframework.web.bind.annotation.GetMapping;
 import org.springframework.web.bind.annotation.RestController;
 
+import java.util.Map;
+
 @RestController
 class HomeController {
 
+    private final BuildProperties buildProperties;
+
+    HomeController(BuildProperties buildProperties) {
+        this.buildProperties = buildProperties;
+    }
+
     @GetMapping("/")
     public String getAll() {
         return "Welcome";
     }
+
+    @GetMapping("/api/version")
+    public Map<String, String> version() {
+        return Map.of(
+                "version", buildProperties.getVersion(),
+                "builtAt", buildProperties.getTime().toString()
+        );
+    }
 }

src/main/java/de/zendric/app/xpensely_server/model/AppUser.java

@@ -26,9 +26,10 @@ public class AppUser {
     @GeneratedValue(strategy = GenerationType.IDENTITY)
     private Long id;
 
-    @Column(name = "username", nullable = false, unique = true)
+    @Column(name = "username", nullable = false)
     private String username;
 
+    @Column(name = "google_id", unique = true)
     @JsonIgnore
     private String googleId;
 

src/main/java/de/zendric/app/xpensely_server/model/DTO/HistoryEntryDto.java

@@ -0,0 +1,14 @@
+package de.zendric.app.xpensely_server.model.DTO;
+
+import java.time.LocalDateTime;
+import java.util.List;
+
+import de.zendric.app.xpensely_server.model.FieldChange;
+
+public record HistoryEntryDto(
+        String type,
+        String actorUsername,
+        String expenseTitle,
+        LocalDateTime timestamp,
+        List<FieldChange> changes) {
+}

src/main/java/de/zendric/app/xpensely_server/model/DTO/HistoryPageDto.java

@@ -0,0 +1,6 @@
+package de.zendric.app.xpensely_server.model.DTO;
+
+import java.util.List;
+
+public record HistoryPageDto(List<HistoryEntryDto> entries, boolean hasMore) {
+}

src/main/java/de/zendric/app/xpensely_server/model/DTO/RecentHistoryEntryDto.java

@@ -0,0 +1,12 @@
+package de.zendric.app.xpensely_server.model.DTO;
+
+import java.time.LocalDateTime;
+
+public record RecentHistoryEntryDto(
+        String type,
+        String actorUsername,
+        String expenseTitle,
+        LocalDateTime timestamp,
+        Long listId,
+        String listName) {
+}

src/main/java/de/zendric/app/xpensely_server/model/DefaultSplitRequest.java

@@ -0,0 +1,17 @@
+package de.zendric.app.xpensely_server.model;
+
+import jakarta.validation.constraints.Max;
+import jakarta.validation.constraints.Min;
+import jakarta.validation.constraints.NotNull;
+import lombok.Data;
+import lombok.NoArgsConstructor;
+
+@Data
+@NoArgsConstructor
+public class DefaultSplitRequest {
+
+    @NotNull(message = "Percentage is required")
+    @Min(value = 0, message = "Percentage must be between 0 and 100")
+    @Max(value = 100, message = "Percentage must be between 0 and 100")
+    private Integer percentage;
+}

src/main/java/de/zendric/app/xpensely_server/model/Exception/GoogleAccountAlreadyRegisteredException.java

@@ -0,0 +1,11 @@
+package de.zendric.app.xpensely_server.model.Exception;
+
+import org.springframework.http.HttpStatus;
+import org.springframework.web.bind.annotation.ResponseStatus;
+
+@ResponseStatus(HttpStatus.CONFLICT)
+public class GoogleAccountAlreadyRegisteredException extends RuntimeException {
+    public GoogleAccountAlreadyRegisteredException(String message) {
+        super(message);
+    }
+}

src/main/java/de/zendric/app/xpensely_server/model/Expense.java

@@ -1,10 +1,13 @@
 package de.zendric.app.xpensely_server.model;
 
 import java.time.LocalDate;
+import java.time.LocalDateTime;
 
 import com.fasterxml.jackson.annotation.JsonBackReference;
 
 import jakarta.persistence.Entity;
+import jakarta.persistence.EnumType;
+import jakarta.persistence.Enumerated;
 import jakarta.persistence.GeneratedValue;
 import jakarta.persistence.GenerationType;
 import jakarta.persistence.Id;
@@ -35,7 +38,14 @@ public class Expense {
     private Double personalUseAmount;
     private Double otherPersonAmount;
     private String category;
+
+    @Enumerated(EnumType.STRING)
+    private SplitMode splitMode;
+
+    private Integer splitPercentage;
+
     private LocalDate date;
+    private LocalDateTime lastModified;
 
     @ManyToOne
     @JoinColumn(name = "expense_list_id", nullable = false)

src/main/java/de/zendric/app/xpensely_server/model/ExpenseChangeRequest.java

@@ -3,6 +3,8 @@ package de.zendric.app.xpensely_server.model;
 import java.time.LocalDate;
 
 import jakarta.validation.constraints.DecimalMin;
+import jakarta.validation.constraints.Max;
+import jakarta.validation.constraints.Min;
 import jakarta.validation.constraints.NotBlank;
 import jakarta.validation.constraints.NotNull;
 import jakarta.validation.constraints.Size;
@@ -24,17 +26,24 @@ public class ExpenseChangeRequest {
     @NotBlank(message = "Owner name is required")
     private String ownerName;
 
+    // Same bounds as ExpenseInput: Quick Add creates stub expenses with amount 0
+    // and no category, and those stubs must remain editable.
     @NotNull(message = "Amount is required")
-    @DecimalMin(value = "0.01", message = "Amount must be greater than zero")
+    @DecimalMin(value = "0.00", message = "Amount must not be negative")
     private Double amount;
 
     private Double personalUseAmount;
     private Double otherPersonAmount;
 
+    private SplitMode splitMode;
+
+    @Min(0)
+    @Max(100)
+    private Integer splitPercentage;
+
     @NotNull(message = "Date is required")
     private LocalDate date;
 
-    @NotBlank(message = "Category is required")
     private String category;
 
     public Expense convertToExpense(Long userId, ExpenseList expenseList) {
@@ -51,7 +60,11 @@ public class ExpenseChangeRequest {
         expense.setId(id);
         expense.setOwner(appUser);
         expense.setTitle(title);
-        expense.setCategory(category);
+        // The edit dialog sends "" for a missing category; store null so the
+        // stub state stays uniform and history diffs don't report null -> "".
+        expense.setCategory(category == null || category.isBlank() ? null : category);
+        expense.setSplitMode(splitMode == null ? SplitMode.DETAILED : splitMode);
+        expense.setSplitPercentage(splitPercentage);
 
         return expense;
     }

src/main/java/de/zendric/app/xpensely_server/model/ExpenseHistoryEntry.java

@@ -0,0 +1,52 @@
+package de.zendric.app.xpensely_server.model;
+
+import java.time.LocalDateTime;
+
+import jakarta.persistence.Column;
+import jakarta.persistence.Entity;
+import jakarta.persistence.EnumType;
+import jakarta.persistence.Enumerated;
+import jakarta.persistence.GeneratedValue;
+import jakarta.persistence.GenerationType;
+import jakarta.persistence.Id;
+import jakarta.persistence.Index;
+import jakarta.persistence.JoinColumn;
+import jakarta.persistence.ManyToOne;
+import jakarta.persistence.Table;
+import lombok.Getter;
+import lombok.NoArgsConstructor;
+import lombok.Setter;
+
+@Getter
+@Setter
+@NoArgsConstructor
+@Entity
+@Table(name = "expense_history_entry", indexes = @Index(name = "idx_history_list_timestamp", columnList = "expense_list_id, timestamp DESC"))
+public class ExpenseHistoryEntry {
+
+    @Id
+    @GeneratedValue(strategy = GenerationType.IDENTITY)
+    private Long id;
+
+    @ManyToOne
+    @JoinColumn(name = "expense_list_id", nullable = false)
+    private ExpenseList expenseList;
+
+    /** Plain column on purpose — no FK, so history survives expense deletion. */
+    private Long expenseId;
+
+    /** Denormalized so entries for deleted expenses still render. */
+    private String expenseTitle;
+
+    @ManyToOne
+    private AppUser actor;
+
+    @Enumerated(EnumType.STRING)
+    private HistoryEntryType type;
+
+    private LocalDateTime timestamp;
+
+    /** JSON array of FieldChange; null for CREATED/DELETED. */
+    @Column(columnDefinition = "TEXT")
+    private String changes;
+}

src/main/java/de/zendric/app/xpensely_server/model/ExpenseInput.java

@@ -3,6 +3,8 @@ package de.zendric.app.xpensely_server.model;
 import java.time.LocalDate;
 
 import jakarta.validation.constraints.DecimalMin;
+import jakarta.validation.constraints.Max;
+import jakarta.validation.constraints.Min;
 import jakarta.validation.constraints.NotBlank;
 import jakarta.validation.constraints.NotNull;
 import jakarta.validation.constraints.Size;
@@ -27,16 +29,22 @@ public class ExpenseInput {
     private String owner;
 
     @NotNull(message = "Amount is required")
-    @DecimalMin(value = "0.01", message = "Amount must be greater than zero")
+    @DecimalMin(value = "0.00", message = "Amount must not be negative")
     private Double amount;
 
     private Double personalUseAmount;
     private Double otherPersonAmount;
 
+    private SplitMode splitMode;
+
+    @Min(0)
+    @Max(100)
+    private Integer splitPercentage;
+
     @NotNull(message = "Date is required")
     private LocalDate date;
 
-    @NotBlank(message = "Category is required")
+    // Optional: Quick Add creates stub expenses without a category, to be filled in later.
     private String category;
 
     private ExpenseList expenseList;
@@ -56,6 +64,8 @@ public class ExpenseInput {
         expense.setOwner(appUser);
         expense.setTitle(title);
         expense.setCategory(category);
+        expense.setSplitMode(splitMode == null ? SplitMode.DETAILED : splitMode);
+        expense.setSplitPercentage(splitPercentage);
 
         return expense;
     }

src/main/java/de/zendric/app/xpensely_server/model/ExpenseList.java

@@ -31,6 +31,8 @@ public class ExpenseList {
 
     private String name;
 
+    private Integer defaultSplitPercentage = 50;
+
     private String inviteCode;
     @JsonIgnore
     private LocalDateTime inviteCodeExpiration;

src/main/java/de/zendric/app/xpensely_server/model/FieldChange.java

@@ -0,0 +1,9 @@
+package de.zendric.app.xpensely_server.model;
+
+import com.fasterxml.jackson.annotation.JsonProperty;
+
+public record FieldChange(
+        String field,
+        @JsonProperty("old") String oldValue,
+        @JsonProperty("new") String newValue) {
+}

src/main/java/de/zendric/app/xpensely_server/model/HistoryEntryType.java

@@ -0,0 +1,5 @@
+package de.zendric.app.xpensely_server.model;
+
+public enum HistoryEntryType {
+    CREATED, UPDATED, DELETED
+}

src/main/java/de/zendric/app/xpensely_server/model/SplitMode.java

@@ -0,0 +1,6 @@
+package de.zendric.app.xpensely_server.model;
+
+public enum SplitMode {
+    DETAILED,
+    PERCENTAGE
+}

src/main/java/de/zendric/app/xpensely_server/model/UsernameUpdateRequest.java

@@ -0,0 +1,15 @@
+package de.zendric.app.xpensely_server.model;
+
+import jakarta.validation.constraints.NotBlank;
+import jakarta.validation.constraints.Pattern;
+import jakarta.validation.constraints.Size;
+import lombok.Data;
+
+@Data
+public class UsernameUpdateRequest {
+
+    @NotBlank(message = "Username is required")
+    @Size(min = 3, max = 30, message = "Username must be between 3 and 30 characters")
+    @Pattern(regexp = "^[a-zA-Z0-9_.\\-]+$", message = "Username may only contain letters, digits, underscores, dots, and hyphens")
+    private String username;
+}

src/main/java/de/zendric/app/xpensely_server/preparation/HistoryBackfillRunner.java

@@ -0,0 +1,61 @@
+package de.zendric.app.xpensely_server.preparation;
+
+import java.time.LocalDateTime;
+import java.util.HashSet;
+import java.util.Set;
+
+import org.springframework.boot.CommandLineRunner;
+import org.springframework.stereotype.Component;
+import org.springframework.transaction.annotation.Transactional;
+
+import de.zendric.app.xpensely_server.model.Expense;
+import de.zendric.app.xpensely_server.model.ExpenseHistoryEntry;
+import de.zendric.app.xpensely_server.model.HistoryEntryType;
+import de.zendric.app.xpensely_server.repo.ExpenseHistoryRepository;
+import de.zendric.app.xpensely_server.repo.ExpenseRepository;
+
+/**
+ * One-time (idempotent) backfill for the history feature: fills
+ * Expense.lastModified from the expense date and creates a synthetic CREATED
+ * history entry for every expense that predates change logging. Both steps
+ * are no-ops on every startup after the first.
+ */
+@Component
+public class HistoryBackfillRunner implements CommandLineRunner {
+
+    private final ExpenseRepository expenseRepository;
+    private final ExpenseHistoryRepository historyRepository;
+
+    public HistoryBackfillRunner(ExpenseRepository expenseRepository,
+            ExpenseHistoryRepository historyRepository) {
+        this.expenseRepository = expenseRepository;
+        this.historyRepository = historyRepository;
+    }
+
+    @Override
+    @Transactional
+    public void run(String... args) {
+        for (Expense expense : expenseRepository.findByLastModifiedIsNull()) {
+            expense.setLastModified(startOfDayOrNow(expense));
+            expenseRepository.save(expense);
+        }
+
+        Set<Long> loggedExpenseIds = new HashSet<>(historyRepository.findAllExpenseIds());
+        for (Expense expense : expenseRepository.findAll()) {
+            if (loggedExpenseIds.contains(expense.getId()))
+                continue;
+            ExpenseHistoryEntry entry = new ExpenseHistoryEntry();
+            entry.setExpenseList(expense.getExpenseList());
+            entry.setExpenseId(expense.getId());
+            entry.setExpenseTitle(expense.getTitle());
+            entry.setActor(expense.getOwner());
+            entry.setType(HistoryEntryType.CREATED);
+            entry.setTimestamp(startOfDayOrNow(expense));
+            historyRepository.save(entry);
+        }
+    }
+
+    private LocalDateTime startOfDayOrNow(Expense expense) {
+        return expense.getDate() == null ? LocalDateTime.now() : expense.getDate().atStartOfDay();
+    }
+}

src/main/java/de/zendric/app/xpensely_server/repo/ExpenseHistoryRepository.java

@@ -0,0 +1,23 @@
+package de.zendric.app.xpensely_server.repo;
+
+import java.util.List;
+
+import org.springframework.data.domain.Page;
+import org.springframework.data.domain.Pageable;
+import org.springframework.data.jpa.repository.JpaRepository;
+import org.springframework.data.jpa.repository.Query;
+
+import de.zendric.app.xpensely_server.model.ExpenseHistoryEntry;
+
+public interface ExpenseHistoryRepository extends JpaRepository<ExpenseHistoryEntry, Long> {
+
+    Page<ExpenseHistoryEntry> findByExpenseListIdOrderByTimestampDescIdDesc(Long expenseListId, Pageable pageable);
+
+    Page<ExpenseHistoryEntry> findByExpenseListOwnerIdOrExpenseListSharedWithIdOrderByTimestampDescIdDesc(
+            Long ownerId, Long sharedWithId, Pageable pageable);
+
+    @Query("select h.expenseId from ExpenseHistoryEntry h")
+    List<Long> findAllExpenseIds();
+
+    void deleteByExpenseListId(Long expenseListId);
+}

src/main/java/de/zendric/app/xpensely_server/repo/ExpenseRepository.java

@@ -10,4 +10,6 @@ import de.zendric.app.xpensely_server.model.Expense;
 @Repository
 public interface ExpenseRepository extends JpaRepository<Expense, Long> {
     List<Expense> findAllByOrderByDateAsc();
+
+    List<Expense> findByLastModifiedIsNull();
 }

src/main/java/de/zendric/app/xpensely_server/repo/UserRepository.java

@@ -14,4 +14,6 @@ public interface UserRepository extends JpaRepository<AppUser, Long> {
     Optional<AppUser> findByGoogleId(String id);
 
     Boolean existsByUsername(String username);
+
+    Boolean existsByGoogleId(String googleId);
 }

src/main/java/de/zendric/app/xpensely_server/security/AuthenticatedUserResolver.java

@@ -1,6 +1,7 @@
 package de.zendric.app.xpensely_server.security;
 
 import de.zendric.app.xpensely_server.model.AppUser;
+import de.zendric.app.xpensely_server.model.Exception.ResourceNotFoundException;
 import de.zendric.app.xpensely_server.services.UserService;
 import org.springframework.http.HttpStatus;
 import org.springframework.security.core.Authentication;
@@ -24,12 +25,8 @@ public class AuthenticatedUserResolver {
         Jwt jwt = (Jwt) authentication.getPrincipal();
         String googleId = jwt.getSubject();
         try {
-            AppUser user = userService.getUserByGoogleId(googleId);
+            return userService.getUserByGoogleId(googleId);
-            if (user == null) {
+        } catch (IllegalArgumentException | ResourceNotFoundException e) {
-                throw new ResponseStatusException(HttpStatus.FORBIDDEN, "User not registered");
-            }
-            return user;
-        } catch (IllegalArgumentException e) {
             throw new ResponseStatusException(HttpStatus.FORBIDDEN, "User not registered");
         }
     }

src/main/java/de/zendric/app/xpensely_server/security/SecurityConfig.java

@@ -28,10 +28,10 @@ public class SecurityConfig {
         public SecurityFilterChain securityFilterChain(HttpSecurity http) throws Exception {
                 http
                                 .authorizeHttpRequests(auth -> auth
+                                                .requestMatchers("/api/version").permitAll()
                                                 .anyRequest().authenticated())
                                 .oauth2ResourceServer(oauth2 -> oauth2
                                                 .jwt(Customizer.withDefaults()))
-                                .oauth2Login(Customizer.withDefaults())
                                 .addFilterAfter(new RateLimitFilter(), BearerTokenAuthenticationFilter.class)
                                 .csrf(csrf -> csrf.disable());
 

src/main/java/de/zendric/app/xpensely_server/services/ExpenseListService.java

@@ -8,6 +8,7 @@ import java.util.UUID;
 import org.springframework.stereotype.Service;
 import org.springframework.transaction.annotation.Transactional;
 
+import de.zendric.app.xpensely_server.model.AppUser;
 import de.zendric.app.xpensely_server.model.Expense;
 import de.zendric.app.xpensely_server.model.ExpenseList;
 import de.zendric.app.xpensely_server.model.Exception.ResourceNotFoundException;
@@ -23,12 +24,14 @@ public class ExpenseListService {
     private final ExpenseListRepository repository;
     private final ExpenseRepository expenseRepository;
     private final XpenselyCustomCategoryRepository customCategoryRepository;
+    private final HistoryService historyService;
 
     public ExpenseListService(ExpenseListRepository repository, ExpenseRepository expenseRepository,
-            XpenselyCustomCategoryRepository customCategoryRepository) {
+            XpenselyCustomCategoryRepository customCategoryRepository, HistoryService historyService) {
         this.repository = repository;
         this.expenseRepository = expenseRepository;
         this.customCategoryRepository = customCategoryRepository;
+        this.historyService = historyService;
     }
 
     public ExpenseList createList(ExpenseList list) {
@@ -36,9 +39,24 @@ public class ExpenseListService {
     }
 
     public void deleteById(Long id) {
+        historyService.deleteForList(id);
         repository.deleteById(id);
     }
 
+    public ExpenseList renameList(Long id, String newName) {
+        ExpenseList list = repository.findById(id)
+                .orElseThrow(() -> new ResourceNotFoundException("ExpenseList not found with id: " + id));
+        list.setName(newName);
+        return repository.save(list);
+    }
+
+    public ExpenseList updateDefaultSplit(Long id, int percentage) {
+        ExpenseList list = repository.findById(id)
+                .orElseThrow(() -> new ResourceNotFoundException("ExpenseList not found with id: " + id));
+        list.setDefaultSplitPercentage(percentage);
+        return repository.save(list);
+    }
+
     public Optional<ExpenseList> findById(Long id) {
         return repository.findById(id);
     }
@@ -55,15 +73,17 @@ public class ExpenseListService {
         return repository.findByOwnerUsernameOrSharedWithUsername(username);
     }
 
-    public Expense addExpenseToList(Long expenseListId, Expense expense) {
+    public Expense addExpenseToList(Long expenseListId, Expense expense, AppUser actor) {
         ExpenseList expenseList = repository.findById(expenseListId)
                 .orElseThrow(() -> new ResourceNotFoundException("ExpenseList not found with id: " + expenseListId));
+        expense.setLastModified(LocalDateTime.now());
         expenseList.addExpense(expense);
         repository.save(expenseList);
+        historyService.recordCreated(expenseList, expense, actor);
         return expense;
     }
 
-    public void deleteExpenseFromList(Long expenseListId, Long expenseId) {
+    public void deleteExpenseFromList(Long expenseListId, Long expenseId, AppUser actor) {
         ExpenseList expenseList = repository.findById(expenseListId)
                 .orElseThrow(() -> new ResourceNotFoundException("ExpenseList not found with id: " + expenseListId));
         Expense expenseToRemove = null;
@@ -73,11 +93,11 @@ public class ExpenseListService {
                 break;
             }
         }
-        if (expenseToRemove != null) {
+        if (expenseToRemove == null) {
-            expenseList.removeExpense(expenseToRemove);
-        } else {
             throw new ResourceNotFoundException("Expense not found with id: " + expenseId);
         }
+        historyService.recordDeleted(expenseList, expenseToRemove, actor);
+        expenseList.removeExpense(expenseToRemove);
         repository.save(expenseList);
     }
 
@@ -103,7 +123,7 @@ public class ExpenseListService {
         return repository.findByInviteCode(inviteCode);
     }
 
-    public Expense updateExpense(Long expenseListId, Expense updatedExpense) {
+    public Expense updateExpense(Long expenseListId, Expense updatedExpense, AppUser actor) {
         ExpenseList expenseList = repository.findById(expenseListId)
                 .orElseThrow(() -> new ResourceNotFoundException("ExpenseList not found with id: " + expenseListId));
 
@@ -114,6 +134,9 @@ public class ExpenseListService {
 
         Expense existingExpense = expenseRepository.findById(updatedExpense.getId())
                 .orElseThrow(() -> new ResourceNotFoundException("Expense not found with id: " + updatedExpense.getId()));
+
+        Expense before = snapshot(existingExpense);
+
         existingExpense.setTitle(updatedExpense.getTitle());
         existingExpense.setAmount(updatedExpense.getAmount());
         existingExpense.setPersonalUseAmount(updatedExpense.getPersonalUseAmount());
@@ -121,8 +144,29 @@ public class ExpenseListService {
         existingExpense.setDate(updatedExpense.getDate());
         existingExpense.setOwner(updatedExpense.getOwner());
         existingExpense.setCategory(updatedExpense.getCategory());
+        existingExpense.setSplitMode(updatedExpense.getSplitMode());
+        existingExpense.setSplitPercentage(updatedExpense.getSplitPercentage());
+        existingExpense.setLastModified(LocalDateTime.now());
 
-        return expenseRepository.save(existingExpense);
+        Expense saved = expenseRepository.save(existingExpense);
+        historyService.recordUpdated(expenseList, before, saved, actor);
+        return saved;
+    }
+
+    /** Detached copy of the mutable fields, taken before applying an update. */
+    private Expense snapshot(Expense e) {
+        Expense copy = new Expense();
+        copy.setId(e.getId());
+        copy.setTitle(e.getTitle());
+        copy.setAmount(e.getAmount());
+        copy.setPersonalUseAmount(e.getPersonalUseAmount());
+        copy.setOtherPersonAmount(e.getOtherPersonAmount());
+        copy.setCategory(e.getCategory());
+        copy.setSplitMode(e.getSplitMode());
+        copy.setSplitPercentage(e.getSplitPercentage());
+        copy.setDate(e.getDate());
+        copy.setOwner(e.getOwner());
+        return copy;
     }
 
     // TODO implement API for this

src/main/java/de/zendric/app/xpensely_server/services/HistoryService.java

@@ -0,0 +1,147 @@
+package de.zendric.app.xpensely_server.services;
+
+import java.time.LocalDateTime;
+import java.util.ArrayList;
+import java.util.List;
+import java.util.Objects;
+
+import org.springframework.data.domain.Page;
+import org.springframework.data.domain.PageRequest;
+import org.springframework.stereotype.Service;
+import org.springframework.transaction.annotation.Transactional;
+
+import tools.jackson.core.JacksonException;
+import tools.jackson.core.type.TypeReference;
+import tools.jackson.databind.ObjectMapper;
+
+import de.zendric.app.xpensely_server.model.AppUser;
+import de.zendric.app.xpensely_server.model.DTO.HistoryEntryDto;
+import de.zendric.app.xpensely_server.model.DTO.HistoryPageDto;
+import de.zendric.app.xpensely_server.model.DTO.RecentHistoryEntryDto;
+import de.zendric.app.xpensely_server.model.Expense;
+import de.zendric.app.xpensely_server.model.ExpenseHistoryEntry;
+import de.zendric.app.xpensely_server.model.ExpenseList;
+import de.zendric.app.xpensely_server.model.FieldChange;
+import de.zendric.app.xpensely_server.model.HistoryEntryType;
+import de.zendric.app.xpensely_server.repo.ExpenseHistoryRepository;
+
+@Service
+@Transactional
+public class HistoryService {
+
+    private final ExpenseHistoryRepository historyRepository;
+    private final ObjectMapper objectMapper;
+
+    public HistoryService(ExpenseHistoryRepository historyRepository, ObjectMapper objectMapper) {
+        this.historyRepository = historyRepository;
+        this.objectMapper = objectMapper;
+    }
+
+    public void recordCreated(ExpenseList list, Expense expense, AppUser actor) {
+        historyRepository.save(baseEntry(list, expense, actor, HistoryEntryType.CREATED));
+    }
+
+    public void recordUpdated(ExpenseList list, Expense before, Expense after, AppUser actor) {
+        List<FieldChange> changes = diff(before, after);
+        if (changes.isEmpty())
+            return;
+        ExpenseHistoryEntry entry = baseEntry(list, after, actor, HistoryEntryType.UPDATED);
+        try {
+            entry.setChanges(objectMapper.writeValueAsString(changes));
+        } catch (JacksonException e) {
+            throw new IllegalStateException("Failed to serialize history changes", e);
+        }
+        historyRepository.save(entry);
+    }
+
+    public void recordDeleted(ExpenseList list, Expense expense, AppUser actor) {
+        historyRepository.save(baseEntry(list, expense, actor, HistoryEntryType.DELETED));
+    }
+
+    public void deleteForList(Long listId) {
+        historyRepository.deleteByExpenseListId(listId);
+    }
+
+    public List<FieldChange> diff(Expense before, Expense after) {
+        List<FieldChange> changes = new ArrayList<>();
+        addIfChanged(changes, "title", before.getTitle(), after.getTitle());
+        addIfChanged(changes, "amount", before.getAmount(), after.getAmount());
+        addIfChanged(changes, "personalUseAmount", before.getPersonalUseAmount(), after.getPersonalUseAmount());
+        addIfChanged(changes, "otherPersonAmount", before.getOtherPersonAmount(), after.getOtherPersonAmount());
+        addIfChanged(changes, "category", before.getCategory(), after.getCategory());
+        addIfChanged(changes, "splitMode",
+                before.getSplitMode() == null ? null : before.getSplitMode().name(),
+                after.getSplitMode() == null ? null : after.getSplitMode().name());
+        addIfChanged(changes, "splitPercentage", before.getSplitPercentage(), after.getSplitPercentage());
+        addIfChanged(changes, "date", before.getDate(), after.getDate());
+        addIfChanged(changes, "owner",
+                before.getOwner() == null ? null : before.getOwner().getUsername(),
+                after.getOwner() == null ? null : after.getOwner().getUsername());
+        return changes;
+    }
+
+    private ExpenseHistoryEntry baseEntry(ExpenseList list, Expense expense, AppUser actor, HistoryEntryType type) {
+        ExpenseHistoryEntry entry = new ExpenseHistoryEntry();
+        entry.setExpenseList(list);
+        entry.setExpenseId(expense.getId());
+        entry.setExpenseTitle(expense.getTitle());
+        entry.setActor(actor);
+        entry.setType(type);
+        entry.setTimestamp(LocalDateTime.now());
+        return entry;
+    }
+
+    private void addIfChanged(List<FieldChange> changes, String field, Object oldVal, Object newVal) {
+        if (!Objects.equals(oldVal, newVal)) {
+            changes.add(new FieldChange(field,
+                    oldVal == null ? null : String.valueOf(oldVal),
+                    newVal == null ? null : String.valueOf(newVal)));
+        }
+    }
+
+    @Transactional(readOnly = true)
+    public HistoryPageDto getHistory(Long listId, int page, int size) {
+        int cappedSize = Math.min(Math.max(size, 1), 100);
+        Page<ExpenseHistoryEntry> result = historyRepository
+                .findByExpenseListIdOrderByTimestampDescIdDesc(listId,
+                        PageRequest.of(Math.max(page, 0), cappedSize));
+        List<HistoryEntryDto> entries = result.getContent().stream().map(this::toDto).toList();
+        return new HistoryPageDto(entries, result.hasNext());
+    }
+
+    @Transactional(readOnly = true)
+    public List<RecentHistoryEntryDto> getRecentForUser(AppUser user, int limit) {
+        int cappedLimit = Math.min(Math.max(limit, 1), 20);
+        Page<ExpenseHistoryEntry> result = historyRepository
+                .findByExpenseListOwnerIdOrExpenseListSharedWithIdOrderByTimestampDescIdDesc(
+                        user.getId(), user.getId(), PageRequest.of(0, cappedLimit));
+        return result.getContent().stream()
+                .map(e -> new RecentHistoryEntryDto(
+                        e.getType().name(),
+                        e.getActor() == null ? null : e.getActor().getUsername(),
+                        e.getExpenseTitle(),
+                        e.getTimestamp(),
+                        e.getExpenseList().getId(),
+                        e.getExpenseList().getName()))
+                .toList();
+    }
+
+    private HistoryEntryDto toDto(ExpenseHistoryEntry entry) {
+        List<FieldChange> changes = List.of();
+        if (entry.getChanges() != null) {
+            try {
+                changes = objectMapper.readValue(entry.getChanges(),
+                        new TypeReference<List<FieldChange>>() {
+                        });
+            } catch (JacksonException e) {
+                throw new IllegalStateException("Corrupt history changes for entry " + entry.getId(), e);
+            }
+        }
+        return new HistoryEntryDto(
+                entry.getType().name(),
+                entry.getActor() == null ? null : entry.getActor().getUsername(),
+                entry.getExpenseTitle(),
+                entry.getTimestamp(),
+                changes);
+    }
+}

src/main/java/de/zendric/app/xpensely_server/services/UserService.java

@@ -5,8 +5,8 @@ import java.util.List;
 import org.springframework.stereotype.Service;
 
 import de.zendric.app.xpensely_server.model.AppUser;
+import de.zendric.app.xpensely_server.model.Exception.GoogleAccountAlreadyRegisteredException;
 import de.zendric.app.xpensely_server.model.Exception.ResourceNotFoundException;
-import de.zendric.app.xpensely_server.model.Exception.UsernameAlreadyExistsException;
 import de.zendric.app.xpensely_server.repo.UserRepository;
 
 @Service
@@ -22,9 +22,18 @@ public class UserService {
     }
 
     public AppUser createUser(AppUser user) {
-        if (Boolean.TRUE.equals(userRepository.existsByUsername(user.getUsername()))) {
+        if (Boolean.TRUE.equals(userRepository.existsByGoogleId(user.getGoogleId()))) {
-            throw new UsernameAlreadyExistsException("Username already exists");
+            throw new GoogleAccountAlreadyRegisteredException(
+                    "An account already exists for this Google account");
         }
+        // Usernames are not unique — identity is the Google account (googleId).
+        return userRepository.save(user);
+    }
+
+    public AppUser updateUsername(Long userId, String newUsername) {
+        AppUser user = userRepository.findById(userId)
+                .orElseThrow(() -> new ResourceNotFoundException("User not found with id: " + userId));
+        user.setUsername(newUsername);
         return userRepository.save(user);
     }
 

src/main/resources/application.properties

@@ -3,8 +3,6 @@ spring.application.name=XpenselyServer
 
 #Security
 spring.security.enabled=false
-spring.security.oauth2.client.registration.google.client-id=${GOOGLE_CLIENT_ID}
-spring.security.oauth2.client.registration.google.client-secret=${GOOGLE_CLIENT_SECRET}
 spring.security.oauth2.resourceserver.jwt.issuer-uri=https://accounts.google.com
 
 # PostgreSQL Configuration

src/test/java/de/zendric/app/xpensely_Server/config/TestJwtDecoderConfig.java

@@ -0,0 +1,24 @@
+package de.zendric.app.xpensely_Server.config;
+
+import org.springframework.boot.test.context.TestConfiguration;
+import org.springframework.context.annotation.Bean;
+import org.springframework.context.annotation.Primary;
+import org.springframework.security.oauth2.jwt.JwtDecoder;
+import org.springframework.security.oauth2.jwt.JwtException;
+
+/**
+ * Provides a no-op JwtDecoder so the application context starts without
+ * fetching Google's JWKS endpoint. Tests use SecurityMockMvcRequestPostProcessors.jwt()
+ * which populates the SecurityContext directly and never calls this decoder.
+ */
+@TestConfiguration
+public class TestJwtDecoderConfig {
+
+    @Bean
+    @Primary
+    public JwtDecoder jwtDecoder() {
+        return token -> {
+            throw new JwtException("Real JWT validation is disabled in integration tests — use jwt() post-processor");
+        };
+    }
+}

src/test/java/de/zendric/app/xpensely_Server/controller/AppUserControllerTest.java

@@ -6,8 +6,6 @@ import de.zendric.app.xpensely_server.security.AuthenticatedUserResolver;
 import de.zendric.app.xpensely_server.services.UserService;
 import org.junit.jupiter.api.Test;
 import org.springframework.beans.factory.annotation.Autowired;
-import org.springframework.boot.security.oauth2.client.autoconfigure.OAuth2ClientAutoConfiguration;
-import org.springframework.boot.security.oauth2.client.autoconfigure.servlet.OAuth2ClientWebSecurityAutoConfiguration;
 import org.springframework.boot.security.oauth2.server.resource.autoconfigure.servlet.OAuth2ResourceServerAutoConfiguration;
 import org.springframework.boot.webmvc.test.autoconfigure.AutoConfigureMockMvc;
 import org.springframework.boot.webmvc.test.autoconfigure.WebMvcTest;
@@ -22,8 +20,6 @@ import static org.springframework.test.web.servlet.request.MockMvcRequestBuilder
 import static org.springframework.test.web.servlet.result.MockMvcResultMatchers.*;
 
 @WebMvcTest(value = AppUserController.class, excludeAutoConfiguration = {
-        OAuth2ClientAutoConfiguration.class,
-        OAuth2ClientWebSecurityAutoConfiguration.class,
         OAuth2ResourceServerAutoConfiguration.class
 })
 @AutoConfigureMockMvc(addFilters = false)
@@ -99,4 +95,38 @@ class AppUserControllerTest {
         mockMvc.perform(delete("/api/users").param("id", "99"))
                 .andExpect(status().isForbidden());
     }
+
+    // --- Rename username ---
+
+    @Test
+    void updateUsername_valid_returns200WithUpdatedUser() throws Exception {
+        AppUser self = new AppUser(); self.setId(1L); self.setUsername("old");
+        AppUser updated = new AppUser(); updated.setId(1L); updated.setUsername("newname");
+        when(authenticatedUserResolver.resolveCurrentUser(any())).thenReturn(self);
+        when(userService.updateUsername(1L, "newname")).thenReturn(updated);
+
+        mockMvc.perform(put("/api/users/username")
+                .contentType(MediaType.APPLICATION_JSON)
+                .content("{\"username\":\"newname\"}"))
+                .andExpect(status().isOk())
+                .andExpect(jsonPath("$.username").value("newname"));
+    }
+
+    @Test
+    void updateUsername_invalidPattern_returns400() throws Exception {
+        mockMvc.perform(put("/api/users/username")
+                .contentType(MediaType.APPLICATION_JSON)
+                .content("{\"username\":\"bad name!\"}"))
+                .andExpect(status().isBadRequest())
+                .andExpect(jsonPath("$.username").exists());
+    }
+
+    @Test
+    void updateUsername_tooShort_returns400() throws Exception {
+        mockMvc.perform(put("/api/users/username")
+                .contentType(MediaType.APPLICATION_JSON)
+                .content("{\"username\":\"ab\"}"))
+                .andExpect(status().isBadRequest())
+                .andExpect(jsonPath("$.username").exists());
+    }
 }

src/test/java/de/zendric/app/xpensely_Server/controller/ExpenseListControllerTest.java

@@ -2,15 +2,16 @@ package de.zendric.app.xpensely_Server.controller;
 
 import de.zendric.app.xpensely_server.controller.ExpenseListController;
 import de.zendric.app.xpensely_server.model.AppUser;
+import de.zendric.app.xpensely_server.model.DTO.HistoryPageDto;
+import de.zendric.app.xpensely_server.model.DTO.RecentHistoryEntryDto;
+import de.zendric.app.xpensely_server.model.Expense;
 import de.zendric.app.xpensely_server.model.ExpenseList;
 import de.zendric.app.xpensely_server.security.AuthenticatedUserResolver;
 import de.zendric.app.xpensely_server.services.CategoryService;
 import de.zendric.app.xpensely_server.services.ExpenseListService;
-import de.zendric.app.xpensely_server.services.UserService;
+import de.zendric.app.xpensely_server.services.HistoryService;
 import org.junit.jupiter.api.Test;
 import org.springframework.beans.factory.annotation.Autowired;
-import org.springframework.boot.security.oauth2.client.autoconfigure.OAuth2ClientAutoConfiguration;
-import org.springframework.boot.security.oauth2.client.autoconfigure.servlet.OAuth2ClientWebSecurityAutoConfiguration;
 import org.springframework.boot.security.oauth2.server.resource.autoconfigure.servlet.OAuth2ResourceServerAutoConfiguration;
 import org.springframework.boot.webmvc.test.autoconfigure.AutoConfigureMockMvc;
 import org.springframework.boot.webmvc.test.autoconfigure.WebMvcTest;
@@ -19,17 +20,17 @@ import org.springframework.test.context.ActiveProfiles;
 import org.springframework.test.context.bean.override.mockito.MockitoBean;
 import org.springframework.test.web.servlet.MockMvc;
 
+import java.time.LocalDateTime;
 import java.util.List;
 import java.util.Optional;
 
 import static org.mockito.ArgumentMatchers.any;
+import static org.mockito.ArgumentMatchers.eq;
 import static org.mockito.Mockito.when;
 import static org.springframework.test.web.servlet.request.MockMvcRequestBuilders.*;
 import static org.springframework.test.web.servlet.result.MockMvcResultMatchers.*;
 
 @WebMvcTest(value = ExpenseListController.class, excludeAutoConfiguration = {
-        OAuth2ClientAutoConfiguration.class,
-        OAuth2ClientWebSecurityAutoConfiguration.class,
         OAuth2ResourceServerAutoConfiguration.class
 })
 @AutoConfigureMockMvc(addFilters = false)
@@ -38,9 +39,9 @@ class ExpenseListControllerTest {
 
     @Autowired MockMvc mockMvc;
     @MockitoBean ExpenseListService expenseListService;
-    @MockitoBean UserService userService;
     @MockitoBean CategoryService categoryService;
     @MockitoBean AuthenticatedUserResolver authenticatedUserResolver;
+    @MockitoBean HistoryService historyService;
 
     // --- Validation tests ---
 
@@ -53,6 +54,54 @@ class ExpenseListControllerTest {
                 .andExpect(jsonPath("$.title").exists());
     }
 
+    // Quick Add creates stub expenses (amount 0, no category); updating such a
+    // stub must be allowed so the user can fill in the details afterwards.
+    @Test
+    void updateExpense_quickAddStub_zeroAmountAndNoCategory_returns200() throws Exception {
+        AppUser owner = new AppUser(); owner.setId(1L); owner.setUsername("alice");
+        ExpenseList list = new ExpenseList(); list.setId(1L); list.setOwner(owner);
+        when(expenseListService.findById(1L)).thenReturn(Optional.of(list));
+        when(authenticatedUserResolver.resolveCurrentUser(any())).thenReturn(owner);
+        when(expenseListService.updateExpense(eq(1L), any(Expense.class), eq(owner)))
+                .thenAnswer(inv -> inv.getArgument(1));
+
+        mockMvc.perform(put("/api/expenselist/1/update")
+                .contentType(MediaType.APPLICATION_JSON)
+                .content("{\"id\":42,\"title\":\"Groceries\",\"ownerName\":\"alice\",\"amount\":0.0,"
+                        + "\"personalUseAmount\":0.0,\"otherPersonAmount\":0.0,\"date\":\"2026-07-06\"}"))
+                .andExpect(status().isOk());
+    }
+
+    @Test
+    void updateExpense_blankCategory_isStoredAsNull() throws Exception {
+        AppUser owner = new AppUser(); owner.setId(1L); owner.setUsername("alice");
+        ExpenseList list = new ExpenseList(); list.setId(1L); list.setOwner(owner);
+        when(expenseListService.findById(1L)).thenReturn(Optional.of(list));
+        when(authenticatedUserResolver.resolveCurrentUser(any())).thenReturn(owner);
+        when(expenseListService.updateExpense(eq(1L), any(Expense.class), eq(owner)))
+                .thenAnswer(inv -> inv.getArgument(1));
+
+        mockMvc.perform(put("/api/expenselist/1/update")
+                .contentType(MediaType.APPLICATION_JSON)
+                .content("{\"id\":42,\"title\":\"Groceries\",\"ownerName\":\"alice\",\"amount\":0.0,"
+                        + "\"personalUseAmount\":0.0,\"otherPersonAmount\":0.0,\"date\":\"2026-07-06\",\"category\":\"\"}"))
+                .andExpect(status().isOk());
+
+        org.mockito.ArgumentCaptor<Expense> captor = org.mockito.ArgumentCaptor.forClass(Expense.class);
+        org.mockito.Mockito.verify(expenseListService).updateExpense(eq(1L), captor.capture(), eq(owner));
+        org.assertj.core.api.Assertions.assertThat(captor.getValue().getCategory()).isNull();
+    }
+
+    @Test
+    void updateExpense_negativeAmount_returns400() throws Exception {
+        mockMvc.perform(put("/api/expenselist/1/update")
+                .contentType(MediaType.APPLICATION_JSON)
+                .content("{\"id\":42,\"title\":\"Groceries\",\"ownerName\":\"alice\",\"amount\":-5.0,"
+                        + "\"personalUseAmount\":0.0,\"otherPersonAmount\":0.0,\"date\":\"2026-07-06\",\"category\":\"Food\"}"))
+                .andExpect(status().isBadRequest())
+                .andExpect(jsonPath("$.amount").exists());
+    }
+
     @Test
     void addExpense_negativeAmount_returns400() throws Exception {
         mockMvc.perform(post("/api/expenselist/1/add")
@@ -178,4 +227,227 @@ class ExpenseListControllerTest {
                 .andExpect(status().isBadRequest())
                 .andExpect(jsonPath("$.name").exists());
     }
+
+    // --- Owner resolution within list members ---
+
+    @Test
+    void addExpense_ownerNotAListMember_returns400() throws Exception {
+        AppUser member = new AppUser(); member.setId(1L); member.setUsername("alice");
+        ExpenseList list = new ExpenseList(); list.setId(1L); list.setOwner(member);
+
+        when(expenseListService.findById(1L)).thenReturn(Optional.of(list));
+        when(authenticatedUserResolver.resolveCurrentUser(any())).thenReturn(member);
+
+        mockMvc.perform(post("/api/expenselist/1/add")
+                .contentType(MediaType.APPLICATION_JSON)
+                .content("{\"title\":\"Lunch\",\"owner\":\"ghost\",\"amount\":10.0,\"date\":\"2026-05-04\",\"category\":\"Food\"}"))
+                .andExpect(status().isBadRequest());
+    }
+
+    @Test
+    void addExpense_ownerIsAListMember_returns201() throws Exception {
+        AppUser member = new AppUser(); member.setId(1L); member.setUsername("alice");
+        ExpenseList list = new ExpenseList(); list.setId(1L); list.setOwner(member);
+
+        when(expenseListService.findById(1L)).thenReturn(Optional.of(list));
+        when(authenticatedUserResolver.resolveCurrentUser(any())).thenReturn(member);
+        when(expenseListService.addExpenseToList(eq(1L), any(), any())).thenReturn(new Expense());
+
+        mockMvc.perform(post("/api/expenselist/1/add")
+                .contentType(MediaType.APPLICATION_JSON)
+                .content("{\"title\":\"Lunch\",\"owner\":\"alice\",\"amount\":10.0,\"date\":\"2026-05-04\",\"category\":\"Food\"}"))
+                .andExpect(status().isCreated());
+    }
+
+    // --- Rename list ---
+
+    @Test
+    void renameList_owner_returns200WithRenamedList() throws Exception {
+        AppUser owner = new AppUser(); owner.setId(1L);
+        ExpenseList list = new ExpenseList(); list.setId(5L); list.setOwner(owner);
+        ExpenseList renamed = new ExpenseList(); renamed.setId(5L); renamed.setName("Groceries");
+
+        when(expenseListService.findById(5L)).thenReturn(Optional.of(list));
+        when(authenticatedUserResolver.resolveCurrentUser(any())).thenReturn(owner);
+        when(expenseListService.renameList(5L, "Groceries")).thenReturn(renamed);
+
+        mockMvc.perform(put("/api/expenselist/5/rename")
+                .contentType(MediaType.APPLICATION_JSON)
+                .content("{\"name\":\"Groceries\"}"))
+                .andExpect(status().isOk())
+                .andExpect(jsonPath("$.name").value("Groceries"));
+    }
+
+    @Test
+    void renameList_nonOwner_returns403() throws Exception {
+        AppUser owner = new AppUser(); owner.setId(1L);
+        AppUser nonOwner = new AppUser(); nonOwner.setId(2L);
+        ExpenseList list = new ExpenseList(); list.setId(5L); list.setOwner(owner);
+
+        when(expenseListService.findById(5L)).thenReturn(Optional.of(list));
+        when(authenticatedUserResolver.resolveCurrentUser(any())).thenReturn(nonOwner);
+
+        mockMvc.perform(put("/api/expenselist/5/rename")
+                .contentType(MediaType.APPLICATION_JSON)
+                .content("{\"name\":\"Groceries\"}"))
+                .andExpect(status().isForbidden());
+    }
+
+    @Test
+    void renameList_blankName_returns400() throws Exception {
+        mockMvc.perform(put("/api/expenselist/5/rename")
+                .contentType(MediaType.APPLICATION_JSON)
+                .content("{\"name\":\"\"}"))
+                .andExpect(status().isBadRequest())
+                .andExpect(jsonPath("$.name").exists());
+    }
+
+    @Test
+    void renameList_notFound_returns404() throws Exception {
+        AppUser owner = new AppUser(); owner.setId(1L);
+        when(expenseListService.findById(9L)).thenReturn(Optional.empty());
+        when(authenticatedUserResolver.resolveCurrentUser(any())).thenReturn(owner);
+
+        mockMvc.perform(put("/api/expenselist/9/rename")
+                .contentType(MediaType.APPLICATION_JSON)
+                .content("{\"name\":\"Groceries\"}"))
+                .andExpect(status().isNotFound());
+    }
+
+    // --- Default split ---
+
+    @Test
+    void updateDefaultSplit_setsPercentageForMember() throws Exception {
+        AppUser owner = new AppUser(); owner.setId(1L);
+        ExpenseList list = new ExpenseList(); list.setId(5L); list.setOwner(owner);
+
+        when(expenseListService.findById(5L)).thenReturn(Optional.of(list));
+        when(authenticatedUserResolver.resolveCurrentUser(any())).thenReturn(owner);
+        when(expenseListService.updateDefaultSplit(5L, 60)).thenReturn(list);
+
+        mockMvc.perform(put("/api/expenselist/5/default-split")
+                .contentType(MediaType.APPLICATION_JSON)
+                .content("{\"percentage\":60}"))
+                .andExpect(status().isOk());
+
+        org.mockito.Mockito.verify(expenseListService).updateDefaultSplit(5L, 60);
+    }
+
+    @Test
+    void updateDefaultSplit_nonMember_returns403() throws Exception {
+        AppUser owner = new AppUser(); owner.setId(1L);
+        AppUser stranger = new AppUser(); stranger.setId(2L);
+        ExpenseList list = new ExpenseList(); list.setId(5L); list.setOwner(owner);
+
+        when(expenseListService.findById(5L)).thenReturn(Optional.of(list));
+        when(authenticatedUserResolver.resolveCurrentUser(any())).thenReturn(stranger);
+
+        mockMvc.perform(put("/api/expenselist/5/default-split")
+                .contentType(MediaType.APPLICATION_JSON)
+                .content("{\"percentage\":60}"))
+                .andExpect(status().isForbidden());
+    }
+
+    // --- Duplicate-username invite guard ---
+
+    @Test
+    void acceptInvite_sameUsernameAsOwner_returns409() throws Exception {
+        AppUser owner = new AppUser(); owner.setId(1L); owner.setUsername("cedric");
+        AppUser joiner = new AppUser(); joiner.setId(2L); joiner.setUsername("cedric");
+        ExpenseList list = new ExpenseList();
+        list.setId(1L);
+        list.setOwner(owner);
+        list.setInviteCodeExpiration(LocalDateTime.now().plusHours(1));
+
+        when(expenseListService.findByInviteCode("ABC123")).thenReturn(list);
+        when(authenticatedUserResolver.resolveCurrentUser(any())).thenReturn(joiner);
+
+        mockMvc.perform(post("/api/expenselist/accept-invite")
+                .contentType(MediaType.APPLICATION_JSON)
+                .content("{\"inviteCode\":\"ABC123\"}"))
+                .andExpect(status().isConflict());
+    }
+
+    // --- History endpoint ---
+
+    @Test
+    void getHistory_member_returns200WithPage() throws Exception {
+        AppUser owner = new AppUser(); owner.setId(1L); owner.setUsername("alice");
+        ExpenseList list = new ExpenseList(); list.setId(1L); list.setOwner(owner);
+        when(expenseListService.findById(1L)).thenReturn(Optional.of(list));
+        when(authenticatedUserResolver.resolveCurrentUser(any())).thenReturn(owner);
+        when(historyService.getHistory(1L, 0, 30))
+                .thenReturn(new HistoryPageDto(List.of(), false));
+
+        mockMvc.perform(get("/api/expenselist/1/history"))
+                .andExpect(status().isOk())
+                .andExpect(jsonPath("$.entries").isArray())
+                .andExpect(jsonPath("$.hasMore").value(false));
+    }
+
+    @Test
+    void getHistory_nonMember_returns403() throws Exception {
+        AppUser owner = new AppUser(); owner.setId(1L);
+        AppUser stranger = new AppUser(); stranger.setId(2L);
+        ExpenseList list = new ExpenseList(); list.setId(1L); list.setOwner(owner);
+        when(expenseListService.findById(1L)).thenReturn(Optional.of(list));
+        when(authenticatedUserResolver.resolveCurrentUser(any())).thenReturn(stranger);
+
+        mockMvc.perform(get("/api/expenselist/1/history"))
+                .andExpect(status().isForbidden());
+    }
+
+    @Test
+    void getHistory_unknownList_returns404() throws Exception {
+        when(expenseListService.findById(99L)).thenReturn(Optional.empty());
+        when(authenticatedUserResolver.resolveCurrentUser(any())).thenReturn(new AppUser());
+
+        mockMvc.perform(get("/api/expenselist/99/history"))
+                .andExpect(status().isNotFound());
+    }
+
+    // --- Recent history endpoint ---
+
+    @Test
+    void getRecentHistory_returnsArrayWithListInfo() throws Exception {
+        AppUser user = new AppUser(); user.setId(1L); user.setUsername("alice");
+        when(authenticatedUserResolver.resolveCurrentUser(any())).thenReturn(user);
+        when(historyService.getRecentForUser(user, 4)).thenReturn(List.of(
+                new RecentHistoryEntryDto("UPDATED", "alice", "Groceries",
+                        LocalDateTime.of(2026, 7, 6, 12, 0), 10L, "Trip to Rome")));
+
+        mockMvc.perform(get("/api/expenselist/history/recent"))
+                .andExpect(status().isOk())
+                .andExpect(jsonPath("$[0].type").value("UPDATED"))
+                .andExpect(jsonPath("$[0].actorUsername").value("alice"))
+                .andExpect(jsonPath("$[0].expenseTitle").value("Groceries"))
+                .andExpect(jsonPath("$[0].listId").value(10))
+                .andExpect(jsonPath("$[0].listName").value("Trip to Rome"));
+    }
+
+    @Test
+    void getRecentHistory_passesLimitParam() throws Exception {
+        AppUser user = new AppUser(); user.setId(1L);
+        when(authenticatedUserResolver.resolveCurrentUser(any())).thenReturn(user);
+        when(historyService.getRecentForUser(user, 10)).thenReturn(List.of());
+
+        mockMvc.perform(get("/api/expenselist/history/recent").param("limit", "10"))
+                .andExpect(status().isOk())
+                .andExpect(jsonPath("$").isEmpty());
+    }
+
+    @Test
+    void getRecentHistory_doesNotClashWithPerListHistoryRoute() throws Exception {
+        // /api/expenselist/1/history must still hit the per-list handler.
+        AppUser owner = new AppUser(); owner.setId(1L); owner.setUsername("alice");
+        ExpenseList list = new ExpenseList(); list.setId(1L); list.setOwner(owner);
+        when(expenseListService.findById(1L)).thenReturn(Optional.of(list));
+        when(authenticatedUserResolver.resolveCurrentUser(any())).thenReturn(owner);
+        when(historyService.getHistory(1L, 0, 30))
+                .thenReturn(new HistoryPageDto(List.of(), false));
+
+        mockMvc.perform(get("/api/expenselist/1/history"))
+                .andExpect(status().isOk())
+                .andExpect(jsonPath("$.entries").isArray());
+    }
 }

src/test/java/de/zendric/app/xpensely_Server/preparation/HistoryBackfillRunnerTest.java

@@ -0,0 +1,92 @@
+package de.zendric.app.xpensely_Server.preparation;
+
+import java.time.LocalDate;
+import java.util.List;
+
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.api.extension.ExtendWith;
+import org.mockito.ArgumentCaptor;
+import org.mockito.InjectMocks;
+import org.mockito.Mock;
+import org.mockito.junit.jupiter.MockitoExtension;
+
+import de.zendric.app.xpensely_server.model.AppUser;
+import de.zendric.app.xpensely_server.model.Expense;
+import de.zendric.app.xpensely_server.model.ExpenseHistoryEntry;
+import de.zendric.app.xpensely_server.model.ExpenseList;
+import de.zendric.app.xpensely_server.model.HistoryEntryType;
+import de.zendric.app.xpensely_server.preparation.HistoryBackfillRunner;
+import de.zendric.app.xpensely_server.repo.ExpenseHistoryRepository;
+import de.zendric.app.xpensely_server.repo.ExpenseRepository;
+
+import static org.assertj.core.api.Assertions.assertThat;
+import static org.mockito.ArgumentMatchers.any;
+import static org.mockito.Mockito.never;
+import static org.mockito.Mockito.verify;
+import static org.mockito.Mockito.when;
+
+@ExtendWith(MockitoExtension.class)
+class HistoryBackfillRunnerTest {
+
+    @Mock ExpenseRepository expenseRepository;
+    @Mock ExpenseHistoryRepository historyRepository;
+
+    @InjectMocks
+    HistoryBackfillRunner runner;
+
+    private Expense expense(long id, LocalDate date) {
+        AppUser owner = new AppUser(); owner.setId(1L); owner.setUsername("alice");
+        ExpenseList list = new ExpenseList(); list.setId(10L);
+        Expense e = new Expense();
+        e.setId(id);
+        e.setTitle("Groceries");
+        e.setDate(date);
+        e.setOwner(owner);
+        e.setExpenseList(list);
+        return e;
+    }
+
+    @Test
+    void fillsLastModifiedFromDate_forExpensesMissingIt() throws Exception {
+        Expense e = expense(42L, LocalDate.of(2026, 6, 1));
+        when(expenseRepository.findByLastModifiedIsNull()).thenReturn(List.of(e));
+        when(expenseRepository.findAll()).thenReturn(List.of(e));
+        when(historyRepository.findAllExpenseIds()).thenReturn(List.of(42L));
+
+        runner.run();
+
+        assertThat(e.getLastModified()).isEqualTo(LocalDate.of(2026, 6, 1).atStartOfDay());
+        verify(expenseRepository).save(e);
+    }
+
+    @Test
+    void createsSyntheticCreatedEntry_forExpensesWithoutHistory() throws Exception {
+        Expense e = expense(42L, LocalDate.of(2026, 6, 1));
+        when(expenseRepository.findByLastModifiedIsNull()).thenReturn(List.of());
+        when(expenseRepository.findAll()).thenReturn(List.of(e));
+        when(historyRepository.findAllExpenseIds()).thenReturn(List.of());
+
+        runner.run();
+
+        ArgumentCaptor<ExpenseHistoryEntry> captor = ArgumentCaptor.forClass(ExpenseHistoryEntry.class);
+        verify(historyRepository).save(captor.capture());
+        ExpenseHistoryEntry entry = captor.getValue();
+        assertThat(entry.getType()).isEqualTo(HistoryEntryType.CREATED);
+        assertThat(entry.getExpenseId()).isEqualTo(42L);
+        assertThat(entry.getExpenseTitle()).isEqualTo("Groceries");
+        assertThat(entry.getActor().getUsername()).isEqualTo("alice");
+        assertThat(entry.getTimestamp()).isEqualTo(LocalDate.of(2026, 6, 1).atStartOfDay());
+    }
+
+    @Test
+    void isIdempotent_skipsExpensesThatAlreadyHaveHistory() throws Exception {
+        Expense e = expense(42L, LocalDate.of(2026, 6, 1));
+        when(expenseRepository.findByLastModifiedIsNull()).thenReturn(List.of());
+        when(expenseRepository.findAll()).thenReturn(List.of(e));
+        when(historyRepository.findAllExpenseIds()).thenReturn(List.of(42L));
+
+        runner.run();
+
+        verify(historyRepository, never()).save(any());
+    }
+}

src/test/java/de/zendric/app/xpensely_Server/security/AuthenticatedUserResolverTest.java

@@ -1,6 +1,7 @@
 package de.zendric.app.xpensely_Server.security;
 
 import de.zendric.app.xpensely_server.model.AppUser;
+import de.zendric.app.xpensely_server.model.Exception.ResourceNotFoundException;
 import de.zendric.app.xpensely_server.security.AuthenticatedUserResolver;
 import de.zendric.app.xpensely_server.services.UserService;
 import org.junit.jupiter.api.BeforeEach;
@@ -48,7 +49,8 @@ class AuthenticatedUserResolverTest {
                 .subject("unknown-id")
                 .build();
         JwtAuthenticationToken auth = new JwtAuthenticationToken(jwt);
-        when(userService.getUserByGoogleId("unknown-id")).thenReturn(null);
+        when(userService.getUserByGoogleId("unknown-id"))
+                .thenThrow(new ResourceNotFoundException("User not found with Google ID: unknown-id"));
 
         ResponseStatusException ex = assertThrows(ResponseStatusException.class,
                 () -> resolver.resolveCurrentUser(auth));

src/test/java/de/zendric/app/xpensely_Server/security/SecurityFilterChainIntegrationTest.java

@@ -0,0 +1,153 @@
+package de.zendric.app.xpensely_Server.security;
+
+import de.zendric.app.xpensely_Server.config.TestJwtDecoderConfig;
+import de.zendric.app.xpensely_server.model.AppUser;
+import de.zendric.app.xpensely_server.repo.ExpenseListRepository;
+import de.zendric.app.xpensely_server.repo.UserRepository;
+import org.junit.jupiter.api.AfterEach;
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
+import org.springframework.beans.factory.annotation.Autowired;
+import org.springframework.boot.webmvc.test.autoconfigure.AutoConfigureMockMvc;
+import org.springframework.boot.test.context.SpringBootTest;
+import org.springframework.context.annotation.Import;
+import org.springframework.http.MediaType;
+import org.springframework.test.context.ActiveProfiles;
+import org.springframework.test.web.servlet.MockMvc;
+
+import static org.springframework.security.test.web.servlet.request.SecurityMockMvcRequestPostProcessors.jwt;
+import static org.springframework.test.web.servlet.request.MockMvcRequestBuilders.*;
+import static org.springframework.test.web.servlet.result.MockMvcResultMatchers.*;
+
+/**
+ * Full-stack integration tests for the security filter chain.
+ * Runs with the real securityFilterChain (not the test permit-all chain).
+ * Uses an H2 in-memory database (see application-integration.properties).
+ * JWT validation is bypassed via jwt() post-processor — no real Google token needed.
+ */
+@SpringBootTest(webEnvironment = SpringBootTest.WebEnvironment.MOCK)
+@AutoConfigureMockMvc
+@ActiveProfiles("integration")
+@Import(TestJwtDecoderConfig.class)
+class SecurityFilterChainIntegrationTest {
+
+    @Autowired MockMvc mockMvc;
+    @Autowired UserRepository userRepository;
+    @Autowired ExpenseListRepository expenseListRepository;
+
+    private static final String KNOWN_GOOGLE_ID = "google-integration-test-123";
+    private static final String UNKNOWN_GOOGLE_ID = "google-unknown-999";
+
+    @BeforeEach
+    void setUp() {
+        expenseListRepository.deleteAll();
+        userRepository.deleteAll();
+
+        AppUser user = new AppUser();
+        user.setGoogleId(KNOWN_GOOGLE_ID);
+        user.setUsername("integrationtestuser");
+        userRepository.save(user);
+    }
+
+    @AfterEach
+    void tearDown() {
+        expenseListRepository.deleteAll();
+        userRepository.deleteAll();
+    }
+
+    // --- Public endpoints ---
+
+    @Test
+    void versionEndpoint_noAuth_returns200() throws Exception {
+        mockMvc.perform(get("/api/version"))
+                .andExpect(status().isOk())
+                .andExpect(jsonPath("$.version").exists());
+    }
+
+    // --- Unauthenticated access (no JWT) → 401 ---
+
+    @Test
+    void byGoogleId_noJwt_returns401() throws Exception {
+        mockMvc.perform(get("/api/users/byGoogleId").param("id", KNOWN_GOOGLE_ID))
+                .andExpect(status().isUnauthorized());
+    }
+
+    @Test
+    void createUser_noJwt_returns401() throws Exception {
+        mockMvc.perform(post("/api/users/createUser")
+                        .contentType(MediaType.APPLICATION_JSON)
+                        .content("{\"username\":\"newuser\",\"googleId\":\"new-google-id\"}"))
+                .andExpect(status().isUnauthorized());
+    }
+
+    @Test
+    void expenseListMine_noJwt_returns401() throws Exception {
+        mockMvc.perform(get("/api/expenselist/mine"))
+                .andExpect(status().isUnauthorized());
+    }
+
+    // --- Authenticated, user exists in DB → success ---
+
+    @Test
+    void byGoogleId_withJwt_userInDb_returns200() throws Exception {
+        mockMvc.perform(get("/api/users/byGoogleId")
+                        .param("id", KNOWN_GOOGLE_ID)
+                        .with(jwt().jwt(j -> j.subject(KNOWN_GOOGLE_ID))))
+                .andExpect(status().isOk());
+    }
+
+    @Test
+    void expenseListMine_withJwt_userInDb_emptyList_returns204() throws Exception {
+        mockMvc.perform(get("/api/expenselist/mine")
+                        .with(jwt().jwt(j -> j.subject(KNOWN_GOOGLE_ID))))
+                .andExpect(status().isNoContent());
+    }
+
+    @Test
+    void createUser_withJwt_validBody_returns201() throws Exception {
+        mockMvc.perform(post("/api/users/createUser")
+                        .contentType(MediaType.APPLICATION_JSON)
+                        .content("{\"username\":\"newuser123\",\"googleId\":\"brand-new-google-id\"}")
+                        .with(jwt().jwt(j -> j.subject("brand-new-google-id"))))
+                .andExpect(status().isCreated());
+    }
+
+    // --- Authenticated, user NOT in DB → 403 ---
+
+    @Test
+    void byGoogleId_withJwt_userNotInDb_returns403() throws Exception {
+        mockMvc.perform(get("/api/users/byGoogleId")
+                        .param("id", UNKNOWN_GOOGLE_ID)
+                        .with(jwt().jwt(j -> j.subject(UNKNOWN_GOOGLE_ID))))
+                .andExpect(status().isForbidden());
+    }
+
+    @Test
+    void expenseListMine_withJwt_userNotInDb_returns403() throws Exception {
+        mockMvc.perform(get("/api/expenselist/mine")
+                        .with(jwt().jwt(j -> j.subject(UNKNOWN_GOOGLE_ID))))
+                .andExpect(status().isForbidden());
+    }
+
+    // --- Authenticated, accessing another user's resource → 403 ---
+
+    @Test
+    void byGoogleId_withJwt_differentId_returns403() throws Exception {
+        mockMvc.perform(get("/api/users/byGoogleId")
+                        .param("id", UNKNOWN_GOOGLE_ID)
+                        .with(jwt().jwt(j -> j.subject(KNOWN_GOOGLE_ID))))
+                .andExpect(status().isForbidden());
+    }
+
+    // --- Validation errors still return 400 with JWT ---
+
+    @Test
+    void createUser_withJwt_blankUsername_returns400() throws Exception {
+        mockMvc.perform(post("/api/users/createUser")
+                        .contentType(MediaType.APPLICATION_JSON)
+                        .content("{\"username\":\"\",\"googleId\":\"some-id\"}")
+                        .with(jwt().jwt(j -> j.subject("some-id"))))
+                .andExpect(status().isBadRequest())
+                .andExpect(jsonPath("$.username").exists());
+    }
+}

src/test/java/de/zendric/app/xpensely_Server/services/ExpenseListServiceTest.java

@@ -1,20 +1,28 @@
 package de.zendric.app.xpensely_Server.services;
 
 import de.zendric.app.xpensely_server.model.AppUser;
+import de.zendric.app.xpensely_server.model.Expense;
 import de.zendric.app.xpensely_server.model.ExpenseList;
+import de.zendric.app.xpensely_server.model.SplitMode;
 import de.zendric.app.xpensely_server.repo.ExpenseListRepository;
 import de.zendric.app.xpensely_server.repo.ExpenseRepository;
 import de.zendric.app.xpensely_server.repo.XpenselyCustomCategoryRepository;
 import de.zendric.app.xpensely_server.services.ExpenseListService;
+import de.zendric.app.xpensely_server.services.HistoryService;
 import org.junit.jupiter.api.Test;
 import org.junit.jupiter.api.extension.ExtendWith;
 import org.mockito.InjectMocks;
 import org.mockito.Mock;
 import org.mockito.junit.jupiter.MockitoExtension;
 
+import java.time.LocalDate;
+import java.util.ArrayList;
 import java.util.List;
+import java.util.Optional;
 
 import static org.assertj.core.api.Assertions.assertThat;
+import static org.mockito.Mockito.any;
+import static org.mockito.Mockito.eq;
 import static org.mockito.Mockito.verify;
 import static org.mockito.Mockito.when;
 import static org.mockito.Mockito.never;
@@ -25,6 +33,7 @@ class ExpenseListServiceTest {
     @Mock ExpenseListRepository repository;
     @Mock ExpenseRepository expenseRepository;
     @Mock XpenselyCustomCategoryRepository customCategoryRepository;
+    @Mock HistoryService historyService;
 
     @InjectMocks
     ExpenseListService service;
@@ -54,4 +63,95 @@ class ExpenseListServiceTest {
         verify(repository).findByOwnerUsernameOrSharedWithUsername("alice");
         verify(repository, never()).findAll();
     }
+
+    private Expense makeExpense(Long id, String title, double amount) {
+        Expense e = new Expense();
+        e.setId(id);
+        e.setTitle(title);
+        e.setAmount(amount);
+        e.setPersonalUseAmount(0.0);
+        e.setOtherPersonAmount(0.0);
+        e.setDate(LocalDate.of(2026, 7, 1));
+        return e;
+    }
+
+    @Test
+    void addExpenseToList_setsLastModified_andRecordsCreated() {
+        AppUser actor = new AppUser(); actor.setId(1L);
+        ExpenseList list = new ExpenseList(); list.setId(10L);
+        list.setExpenses(new ArrayList<>());
+        when(repository.findById(10L)).thenReturn(Optional.of(list));
+
+        Expense expense = makeExpense(null, "Lunch", 10.0);
+        service.addExpenseToList(10L, expense, actor);
+
+        assertThat(expense.getLastModified()).isNotNull();
+        verify(historyService).recordCreated(list, expense, actor);
+    }
+
+    @Test
+    void updateExpense_setsLastModified_andRecordsUpdatedWithBeforeSnapshot() {
+        AppUser actor = new AppUser(); actor.setId(1L);
+        ExpenseList list = new ExpenseList(); list.setId(10L);
+        Expense existing = makeExpense(42L, "Old title", 12.0);
+        list.setExpenses(new ArrayList<>(List.of(existing)));
+        when(repository.findById(10L)).thenReturn(Optional.of(list));
+        when(expenseRepository.findById(42L)).thenReturn(Optional.of(existing));
+        when(expenseRepository.save(any(Expense.class))).thenAnswer(inv -> inv.getArgument(0));
+
+        Expense updated = makeExpense(42L, "New title", 15.0);
+        service.updateExpense(10L, updated, actor);
+
+        assertThat(existing.getLastModified()).isNotNull();
+        org.mockito.ArgumentCaptor<Expense> beforeCaptor =
+                org.mockito.ArgumentCaptor.forClass(Expense.class);
+        verify(historyService).recordUpdated(eq(list), beforeCaptor.capture(), eq(existing), eq(actor));
+        assertThat(beforeCaptor.getValue().getTitle()).isEqualTo("Old title");
+        assertThat(beforeCaptor.getValue().getAmount()).isEqualTo(12.0);
+    }
+
+    @Test
+    void updateExpense_persistsSplitModeAndPercentage() {
+        AppUser actor = new AppUser(); actor.setId(1L);
+        ExpenseList list = new ExpenseList(); list.setId(10L); list.setOwner(actor);
+        Expense existing = makeExpense(5L, "Groceries", 100.0);
+        list.setExpenses(new ArrayList<>(List.of(existing)));
+
+        Expense incoming = makeExpense(5L, "Groceries", 100.0);
+        incoming.setDate(LocalDate.now());
+        incoming.setOwner(list.getOwner());
+        incoming.setSplitMode(SplitMode.PERCENTAGE);
+        incoming.setSplitPercentage(70);
+
+        when(repository.findById(10L)).thenReturn(Optional.of(list));
+        when(expenseRepository.findById(5L)).thenReturn(Optional.of(existing));
+        when(expenseRepository.save(any(Expense.class))).thenAnswer(inv -> inv.getArgument(0));
+
+        Expense saved = service.updateExpense(10L, incoming, actor);
+
+        assertThat(saved.getSplitMode()).isEqualTo(SplitMode.PERCENTAGE);
+        assertThat(saved.getSplitPercentage()).isEqualTo(70);
+    }
+
+    @Test
+    void deleteById_deletesHistoryEntriesBeforeDeletingList() {
+        service.deleteById(10L);
+
+        org.mockito.InOrder inOrder = org.mockito.Mockito.inOrder(historyService, repository);
+        inOrder.verify(historyService).deleteForList(10L);
+        inOrder.verify(repository).deleteById(10L);
+    }
+
+    @Test
+    void deleteExpenseFromList_recordsDeleted() {
+        AppUser actor = new AppUser(); actor.setId(1L);
+        ExpenseList list = new ExpenseList(); list.setId(10L);
+        Expense existing = makeExpense(42L, "Taxi", 9.0);
+        list.setExpenses(new ArrayList<>(List.of(existing)));
+        when(repository.findById(10L)).thenReturn(Optional.of(list));
+
+        service.deleteExpenseFromList(10L, 42L, actor);
+
+        verify(historyService).recordDeleted(eq(list), any(Expense.class), eq(actor));
+    }
 }

src/test/java/de/zendric/app/xpensely_Server/services/HistoryServiceTest.java

@@ -0,0 +1,298 @@
+package de.zendric.app.xpensely_Server.services;
+
+import java.time.LocalDate;
+import java.util.List;
+
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.api.extension.ExtendWith;
+import org.mockito.ArgumentCaptor;
+import org.mockito.InjectMocks;
+import org.mockito.Mock;
+import org.mockito.Spy;
+import org.mockito.junit.jupiter.MockitoExtension;
+import org.springframework.data.domain.PageImpl;
+import org.springframework.data.domain.PageRequest;
+import org.springframework.data.domain.Pageable;
+
+import tools.jackson.databind.ObjectMapper;
+
+import de.zendric.app.xpensely_server.model.AppUser;
+import de.zendric.app.xpensely_server.model.DTO.HistoryPageDto;
+import de.zendric.app.xpensely_server.model.DTO.RecentHistoryEntryDto;
+import de.zendric.app.xpensely_server.model.Expense;
+import de.zendric.app.xpensely_server.model.ExpenseHistoryEntry;
+import de.zendric.app.xpensely_server.model.ExpenseList;
+import de.zendric.app.xpensely_server.model.FieldChange;
+import de.zendric.app.xpensely_server.model.HistoryEntryType;
+import de.zendric.app.xpensely_server.model.SplitMode;
+import de.zendric.app.xpensely_server.repo.ExpenseHistoryRepository;
+import de.zendric.app.xpensely_server.services.HistoryService;
+
+import static org.assertj.core.api.Assertions.assertThat;
+import static org.mockito.ArgumentMatchers.any;
+import static org.mockito.ArgumentMatchers.eq;
+import static org.mockito.Mockito.never;
+import static org.mockito.Mockito.verify;
+import static org.mockito.Mockito.when;
+
+@ExtendWith(MockitoExtension.class)
+class HistoryServiceTest {
+
+    @Mock ExpenseHistoryRepository historyRepository;
+    @Spy ObjectMapper objectMapper = new ObjectMapper();
+
+    @InjectMocks
+    HistoryService service;
+
+    private AppUser user(long id, String name) {
+        AppUser u = new AppUser();
+        u.setId(id);
+        u.setUsername(name);
+        return u;
+    }
+
+    private Expense expense(String title, double amount, String category, LocalDate date, AppUser owner) {
+        Expense e = new Expense();
+        e.setId(42L);
+        e.setTitle(title);
+        e.setAmount(amount);
+        e.setPersonalUseAmount(0.0);
+        e.setOtherPersonAmount(0.0);
+        e.setCategory(category);
+        e.setDate(date);
+        e.setOwner(owner);
+        return e;
+    }
+
+    @Test
+    void diff_detectsChangedFields_withOldAndNewValues() {
+        AppUser alice = user(1L, "alice");
+        Expense before = expense("Groceries", 12.0, "Food", LocalDate.of(2026, 7, 1), alice);
+        Expense after = expense("Groceries", 15.5, "Household", LocalDate.of(2026, 7, 1), alice);
+
+        List<FieldChange> changes = service.diff(before, after);
+
+        assertThat(changes).containsExactlyInAnyOrder(
+                new FieldChange("amount", "12.0", "15.5"),
+                new FieldChange("category", "Food", "Household"));
+    }
+
+    @Test
+    void diff_ownerChange_isReportedByUsername() {
+        Expense before = expense("Taxi", 9.0, null, LocalDate.of(2026, 7, 1), user(1L, "alice"));
+        Expense after = expense("Taxi", 9.0, null, LocalDate.of(2026, 7, 1), user(2L, "ben"));
+
+        List<FieldChange> changes = service.diff(before, after);
+
+        assertThat(changes).containsExactly(new FieldChange("owner", "alice", "ben"));
+    }
+
+    @Test
+    void diff_reportsSplitModeAndPercentageChanges() {
+        Expense before = new Expense();
+        before.setSplitMode(SplitMode.DETAILED);
+        before.setSplitPercentage(null);
+
+        Expense after = new Expense();
+        after.setSplitMode(SplitMode.PERCENTAGE);
+        after.setSplitPercentage(70);
+
+        List<FieldChange> changes = service.diff(before, after);
+
+        assertThat(changes).contains(new FieldChange("splitMode", "DETAILED", "PERCENTAGE"));
+        assertThat(changes).contains(new FieldChange("splitPercentage", null, "70"));
+    }
+
+    @Test
+    void diff_nullToValue_isReported() {
+        Expense before = expense("Taxi", 9.0, null, LocalDate.of(2026, 7, 1), user(1L, "alice"));
+        Expense after = expense("Taxi", 9.0, "Transportation", LocalDate.of(2026, 7, 1), user(1L, "alice"));
+
+        assertThat(service.diff(before, after))
+                .containsExactly(new FieldChange("category", null, "Transportation"));
+    }
+
+    @Test
+    void recordUpdated_noChanges_writesNothing() {
+        AppUser alice = user(1L, "alice");
+        Expense same = expense("Groceries", 12.0, "Food", LocalDate.of(2026, 7, 1), alice);
+        ExpenseList list = new ExpenseList();
+        list.setId(5L);
+
+        service.recordUpdated(list, same, same, alice);
+
+        verify(historyRepository, never()).save(any());
+    }
+
+    @Test
+    void recordUpdated_savesEntryWithJsonChanges() {
+        AppUser alice = user(1L, "alice");
+        ExpenseList list = new ExpenseList();
+        list.setId(5L);
+        Expense before = expense("Groceries", 12.0, "Food", LocalDate.of(2026, 7, 1), alice);
+        Expense after = expense("Groceries", 15.5, "Food", LocalDate.of(2026, 7, 1), alice);
+
+        service.recordUpdated(list, before, after, alice);
+
+        ArgumentCaptor<ExpenseHistoryEntry> captor = ArgumentCaptor.forClass(ExpenseHistoryEntry.class);
+        verify(historyRepository).save(captor.capture());
+        ExpenseHistoryEntry entry = captor.getValue();
+        assertThat(entry.getType()).isEqualTo(HistoryEntryType.UPDATED);
+        assertThat(entry.getExpenseId()).isEqualTo(42L);
+        assertThat(entry.getExpenseTitle()).isEqualTo("Groceries");
+        assertThat(entry.getActor()).isEqualTo(alice);
+        assertThat(entry.getExpenseList()).isEqualTo(list);
+        assertThat(entry.getTimestamp()).isNotNull();
+        assertThat(entry.getChanges())
+                .isEqualTo("[{\"field\":\"amount\",\"old\":\"12.0\",\"new\":\"15.5\"}]");
+    }
+
+    @Test
+    void recordCreated_savesEntryWithoutChanges() {
+        AppUser alice = user(1L, "alice");
+        ExpenseList list = new ExpenseList();
+        list.setId(5L);
+        Expense e = expense("Groceries", 12.0, "Food", LocalDate.of(2026, 7, 1), alice);
+
+        service.recordCreated(list, e, alice);
+
+        ArgumentCaptor<ExpenseHistoryEntry> captor = ArgumentCaptor.forClass(ExpenseHistoryEntry.class);
+        verify(historyRepository).save(captor.capture());
+        assertThat(captor.getValue().getType()).isEqualTo(HistoryEntryType.CREATED);
+        assertThat(captor.getValue().getChanges()).isNull();
+    }
+
+    @Test
+    void recordDeleted_savesEntry() {
+        AppUser alice = user(1L, "alice");
+        ExpenseList list = new ExpenseList();
+        list.setId(5L);
+        Expense e = expense("Taxi", 9.0, null, LocalDate.of(2026, 7, 1), alice);
+
+        service.recordDeleted(list, e, alice);
+
+        ArgumentCaptor<ExpenseHistoryEntry> captor = ArgumentCaptor.forClass(ExpenseHistoryEntry.class);
+        verify(historyRepository).save(captor.capture());
+        assertThat(captor.getValue().getType()).isEqualTo(HistoryEntryType.DELETED);
+        assertThat(captor.getValue().getExpenseTitle()).isEqualTo("Taxi");
+    }
+
+    @Test
+    void getHistory_mapsEntriesToDto_andParsesChangesJson() {
+        ExpenseHistoryEntry entry = new ExpenseHistoryEntry();
+        entry.setType(HistoryEntryType.UPDATED);
+        entry.setActor(user(1L, "alice"));
+        entry.setExpenseTitle("Groceries");
+        entry.setTimestamp(java.time.LocalDateTime.of(2026, 7, 6, 14, 31));
+        entry.setChanges("[{\"field\":\"amount\",\"old\":\"12.0\",\"new\":\"15.5\"}]");
+        when(historyRepository.findByExpenseListIdOrderByTimestampDescIdDesc(eq(5L), any(Pageable.class)))
+                .thenReturn(new PageImpl<>(List.of(entry), PageRequest.of(0, 30), 31));
+
+        HistoryPageDto page = service.getHistory(5L, 0, 30);
+
+        assertThat(page.hasMore()).isTrue();
+        assertThat(page.entries()).hasSize(1);
+        assertThat(page.entries().get(0).type()).isEqualTo("UPDATED");
+        assertThat(page.entries().get(0).actorUsername()).isEqualTo("alice");
+        assertThat(page.entries().get(0).changes())
+                .containsExactly(new FieldChange("amount", "12.0", "15.5"));
+    }
+
+    @Test
+    void getHistory_capsPageSizeAt100() {
+        when(historyRepository.findByExpenseListIdOrderByTimestampDescIdDesc(eq(5L), any(Pageable.class)))
+                .thenReturn(new PageImpl<>(List.of()));
+
+        service.getHistory(5L, 0, 5000);
+
+        ArgumentCaptor<Pageable> captor = ArgumentCaptor.forClass(Pageable.class);
+        verify(historyRepository).findByExpenseListIdOrderByTimestampDescIdDesc(eq(5L), captor.capture());
+        assertThat(captor.getValue().getPageSize()).isEqualTo(100);
+    }
+
+    @Test
+    void getHistory_nullChanges_yieldsEmptyList() {
+        ExpenseHistoryEntry entry = new ExpenseHistoryEntry();
+        entry.setType(HistoryEntryType.CREATED);
+        entry.setActor(user(1L, "alice"));
+        entry.setExpenseTitle("Groceries");
+        entry.setTimestamp(java.time.LocalDateTime.of(2026, 7, 6, 14, 31));
+        when(historyRepository.findByExpenseListIdOrderByTimestampDescIdDesc(eq(5L), any(Pageable.class)))
+                .thenReturn(new PageImpl<>(List.of(entry)));
+
+        HistoryPageDto page = service.getHistory(5L, 0, 30);
+
+        assertThat(page.entries().get(0).changes()).isEmpty();
+    }
+
+    private ExpenseHistoryEntry historyEntry(Long id, ExpenseList list, AppUser actor,
+            HistoryEntryType type, String title, java.time.LocalDateTime timestamp) {
+        ExpenseHistoryEntry e = new ExpenseHistoryEntry();
+        e.setId(id);
+        e.setExpenseList(list);
+        e.setActor(actor);
+        e.setType(type);
+        e.setExpenseTitle(title);
+        e.setTimestamp(timestamp);
+        return e;
+    }
+
+    @Test
+    void getRecentForUser_mapsEntriesWithListIdAndName() {
+        AppUser alice = user(1L, "alice");
+        ExpenseList list = new ExpenseList();
+        list.setId(10L);
+        list.setName("Trip to Rome");
+        ExpenseHistoryEntry entry = historyEntry(100L, list, alice,
+                HistoryEntryType.UPDATED, "Groceries", java.time.LocalDateTime.of(2026, 7, 6, 12, 0));
+
+        when(historyRepository
+                .findByExpenseListOwnerIdOrExpenseListSharedWithIdOrderByTimestampDescIdDesc(
+                        eq(1L), eq(1L), any(Pageable.class)))
+                .thenReturn(new PageImpl<>(List.of(entry)));
+
+        List<RecentHistoryEntryDto> result = service.getRecentForUser(alice, 4);
+
+        assertThat(result).containsExactly(new RecentHistoryEntryDto(
+                "UPDATED", "alice", "Groceries",
+                java.time.LocalDateTime.of(2026, 7, 6, 12, 0), 10L, "Trip to Rome"));
+    }
+
+    @Test
+    void getRecentForUser_nullActor_mapsToNullUsername() {
+        AppUser alice = user(1L, "alice");
+        ExpenseList list = new ExpenseList();
+        list.setId(10L);
+        list.setName("Trip to Rome");
+        ExpenseHistoryEntry entry = historyEntry(100L, list, null,
+                HistoryEntryType.CREATED, "Taxi", java.time.LocalDateTime.of(2026, 7, 6, 12, 0));
+
+        when(historyRepository
+                .findByExpenseListOwnerIdOrExpenseListSharedWithIdOrderByTimestampDescIdDesc(
+                        eq(1L), eq(1L), any(Pageable.class)))
+                .thenReturn(new PageImpl<>(List.of(entry)));
+
+        List<RecentHistoryEntryDto> result = service.getRecentForUser(alice, 4);
+
+        assertThat(result.get(0).actorUsername()).isNull();
+    }
+
+    @Test
+    void getRecentForUser_clampsLimitBetween1And20() {
+        AppUser alice = user(1L, "alice");
+        when(historyRepository
+                .findByExpenseListOwnerIdOrExpenseListSharedWithIdOrderByTimestampDescIdDesc(
+                        eq(1L), eq(1L), any(Pageable.class)))
+                .thenReturn(new PageImpl<>(List.of()));
+
+        service.getRecentForUser(alice, 500);
+        verify(historyRepository)
+                .findByExpenseListOwnerIdOrExpenseListSharedWithIdOrderByTimestampDescIdDesc(
+                        1L, 1L, PageRequest.of(0, 20));
+
+        service.getRecentForUser(alice, 0);
+        verify(historyRepository)
+                .findByExpenseListOwnerIdOrExpenseListSharedWithIdOrderByTimestampDescIdDesc(
+                        1L, 1L, PageRequest.of(0, 1));
+    }
+}

src/test/resources/META-INF/build-info.properties

@@ -0,0 +1,5 @@
+build.artifact=xpensely-server
+build.group=de.zendric.app
+build.name=XpenselyServer
+build.time=2026-01-01T00\:00\:00.000Z
+build.version=test

src/test/resources/application-integration.properties

@@ -0,0 +1,10 @@
+# H2 in-memory database replaces PostgreSQL for integration tests
+spring.datasource.url=jdbc:h2:mem:testdb;DB_CLOSE_DELAY=-1;MODE=PostgreSQL
+spring.datasource.driver-class-name=org.h2.Driver
+spring.datasource.username=sa
+spring.datasource.password=
+spring.jpa.database-platform=org.hibernate.dialect.H2Dialect
+spring.jpa.hibernate.ddl-auto=create-drop
+
+# Placeholder URI — TestJwtDecoderConfig overrides the decoder bean so this URI is never fetched
+spring.security.oauth2.resourceserver.jwt.jwk-set-uri=https://placeholder.invalid/jwks