feat(chat): free-form GRUPPE channels with mutable participants

- ChatChannelType.GRUPPE: created by Leitungsteam (any KC) or a Gemeinde
  Verantwortliche/r (own KC), mixing team users and guests/Konfis as
  explicit ChatParticipant rows (unlike GEMEINDE_GRUPPE, membership is
  not derived from Gemeinde)
- POST /chat/:kcId/gruppen to create, GET participant-candidates, and
  POST/DELETE /chat/gruppen/:channelId/participants to manage membership
  (creator, LT, or Verantwortliche/r of that KC)
- ChatGateway broadcasts chat:participants-changed on membership change
- PushService updated for nullable ChatParticipant.userId + new
  guestAccountId column
- SyncService now replicates ChatParticipant
- Prisma migration + 14 new unit tests (75/75 passing), tsc clean
- CI: add .gitea/workflows/cybedefend-scan.yml + .cybedefend project config

.cybedefend/config.json

@@ -0,0 +1,3 @@
+{
+  "projectId": "5fe999f9-fbff-4a09-a987-48c4e7540b38"
+}

.gitea/workflows/cybedefend-scan.yml

@@ -0,0 +1,51 @@
+name: CybeDefend Security Scan
+
+on:
+  push:
+    branches:
+      - main
+      - master
+      - 'feat/**'
+  pull_request:
+    branches:
+      - main
+      - master
+
+jobs:
+  cybedefend_scan:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout code
+        uses: actions/checkout@v4
+
+      - name: Run CybeDefend Security Scan
+        env:
+          CYBEDEFEND_PAT: ${{ secrets.CYBEDEFEND_PAT }}
+          CYBEDEFEND_PROJECT_ID: ${{ secrets.CYBEDEFEND_PROJECT_ID }}
+        run: |
+          docker run --rm \
+            -v "${{ gitea.workspace }}":/app -w /app \
+            -e CYBEDEFEND_PAT="$CYBEDEFEND_PAT" \
+            -e CYBEDEFEND_PROJECT_ID="$CYBEDEFEND_PROJECT_ID" \
+            ghcr.io/cybedefend/cybedefend-cli:latest \
+            scan --dir . --region eu --ci --break-on-severity critical
+
+      - name: Fetch detailed SARIF results
+        if: always()
+        env:
+          CYBEDEFEND_PAT: ${{ secrets.CYBEDEFEND_PAT }}
+          CYBEDEFEND_PROJECT_ID: ${{ secrets.CYBEDEFEND_PROJECT_ID }}
+        run: |
+          docker run --rm \
+            -v "${{ gitea.workspace }}":/app -w /app \
+            -e CYBEDEFEND_PAT="$CYBEDEFEND_PAT" \
+            -e CYBEDEFEND_PROJECT_ID="$CYBEDEFEND_PROJECT_ID" \
+            ghcr.io/cybedefend/cybedefend-cli:latest \
+            results --project-id "$CYBEDEFEND_PROJECT_ID" --all --output sarif --filename results.sarif --ci
+
+      - name: Upload scan results as artifact
+        if: always()
+        uses: actions/upload-artifact@v4
+        with:
+          name: cybedefend-results
+          path: results.sarif

README.md

@@ -103,13 +103,28 @@ client's host - no separate web server is needed.
   (`WEBDAV_*` env vars), switchable to S3-compatible storage with
   `STORAGE_PROVIDER=s3` (`S3_*` env vars).
 - `chat/` — Gemeinde-Gruppenchat, 1:1 Direktnachrichten, Leitungsteam-über-
-  greifende Kanäle und Broadcast (Konfis lesen nur). Channel administration
-  and message history are plain REST (`ChatController`); real-time send/
-  receive is a raw `ws` gateway (`ChatGateway`, path `/chat`) since passport
-  guards don't apply to WS upgrades — auth happens once via `?token=` at
-  connect time (`TokenVerificationService` tries Authentik JWKS, then falls
-  back to a guest token). Access rules live in `ChatService` and are shared
-  between the REST and WS entry points.
+  greifende Kanäle, Broadcast (Konfis lesen nur), and free-form `GRUPPE`
+  chats. Channel administration and message history are plain REST
+  (`ChatController`); real-time send/receive is a raw `ws` gateway
+  (`ChatGateway`, path `/chat`) since passport guards don't apply to WS
+  upgrades — auth happens once via `?token=` at connect time
+  (`TokenVerificationService` tries Authentik JWKS, then falls back to a
+  guest token). Access rules live in `ChatService` and are shared between
+  the REST and WS entry points.
+  - `POST /chat/:kcId/gruppen` lets a Leitungsteam member (any KC) or a
+    Gemeinde Verantwortliche/r (their own KC — `RolesGuard`'s kcId scoping)
+    create a `GRUPPE` channel with any mix of team users and Konfis (guests)
+    from that KC as initial participants (`participantUserIds`,
+    `participantGuestIds`); the creator is always included. Unlike
+    `GEMEINDE_GRUPPE`, membership isn't derived from `Gemeinde` — every
+    participant is an explicit `ChatParticipant` row, so a Konfi (who always
+    belongs to exactly one Gemeinde) can be added regardless of which
+    Gemeinde the chat's creator manages.
+  - `POST` / `DELETE /chat/gruppen/:channelId/participants` (body
+    `{ userId }` or `{ guestId }`) add/remove a participant afterwards.
+    Allowed for the channel's creator, any Leitungsteam member, or a
+    Verantwortliche/r of that KC — not the participants themselves, and not
+    guests.
 - `sync/` — replicates mutations between the local (on-site) and cloud
   server. `SyncService.capture()` is called by feature services right after
   a write, appending an entry to the append-only `SyncLogEntry` log tagged

cybedefend-test-vuln.js

@@ -0,0 +1,21 @@
+// TEMPORARY TEST FILE — intentionally vulnerable code to trigger CybeDefend scan
+// Safe to delete after the scan demo.
+
+const AWS_ACCESS_KEY = "AKIAABCDEFGHIJKLMNOP"; // hardcoded secret (should trigger secret scanner)
+const DB_PASSWORD = "SuperSecret123!";          // hardcoded credential
+
+const mysql = require('mysql');
+
+function getUser(db, userId) {
+  // SQL injection: string concatenation of user input directly into query
+  const query = "SELECT * FROM users WHERE id = '" + userId + "'";
+  return db.query(query);
+}
+
+function runCommand(userInput) {
+  const { exec } = require('child_process');
+  // command injection: unsanitized user input passed to shell
+  exec("echo " + userInput);
+}
+
+module.exports = { getUser, runCommand, AWS_ACCESS_KEY, DB_PASSWORD };

docker-compose.yml

@@ -8,7 +8,7 @@ services:
     volumes:
       - pgdata:/var/lib/postgresql/data
     ports:
-      - "5432:5432"
+      - "5433:5432"
     healthcheck:
       test: ["CMD-SHELL", "pg_isready -U postgres -d kcapp"]
       interval: 5s

prisma/migrations/20260912130000_chat_gruppe/migration.sql

@@ -0,0 +1,17 @@
+-- AlterEnum
+ALTER TYPE "ChatChannelType" ADD VALUE 'GRUPPE';
+
+-- AlterTable
+ALTER TABLE "ChatChannel" ADD COLUMN     "createdByUserId" TEXT,
+ADD COLUMN     "name" TEXT;
+
+-- AlterTable
+ALTER TABLE "ChatParticipant" ADD COLUMN     "guestAccountId" TEXT,
+ALTER COLUMN "userId" DROP NOT NULL;
+
+-- CreateIndex
+CREATE UNIQUE INDEX "ChatParticipant_channelId_guestAccountId_key" ON "ChatParticipant"("channelId", "guestAccountId");
+
+-- AddForeignKey
+ALTER TABLE "ChatParticipant" ADD CONSTRAINT "ChatParticipant_guestAccountId_fkey" FOREIGN KEY ("guestAccountId") REFERENCES "GuestAccount"("id") ON DELETE CASCADE ON UPDATE CASCADE;
+

prisma/schema.prisma

@@ -16,14 +16,14 @@ model Kc {
   createdAt  DateTime @default(now())
   updatedAt  DateTime @updatedAt
 
-  gemeinden     Gemeinde[]
-  memberships   Membership[]
-  wahlen        Wahl[]
-  files         File[]
-  channels      ChatChannel[]
-  guests        GuestAccount[]
-  localUsers    User[]
-  teamerInvites TeamerInvite[]
+  gemeinden              Gemeinde[]
+  memberships            Membership[]
+  wahlen                 Wahl[]
+  files                  File[]
+  channels               ChatChannel[]
+  guests                 GuestAccount[]
+  localUsers             User[]
+  teamerInvites          TeamerInvite[]
   verantwortlicheInvites VerantwortlicheInvite[]
 }
 
@@ -34,10 +34,10 @@ model Gemeinde {
   kcId      String
   createdAt DateTime @default(now())
 
-  kc            Kc             @relation(fields: [kcId], references: [id], onDelete: Cascade)
-  memberships   Membership[]
-  guests        GuestAccount[]
-  teamerInvites TeamerInvite[]
+  kc                     Kc                      @relation(fields: [kcId], references: [id], onDelete: Cascade)
+  memberships            Membership[]
+  guests                 GuestAccount[]
+  teamerInvites          TeamerInvite[]
   verantwortlicheInvites VerantwortlicheInvite[]
 
   @@unique([kcId, name])
@@ -110,11 +110,12 @@ model GuestAccount {
   lastName   String
   createdAt  DateTime @default(now())
 
-  kc           Kc            @relation(fields: [kcId], references: [id], onDelete: Cascade)
-  gemeinde     Gemeinde?     @relation(fields: [gemeindeId], references: [id], onDelete: Cascade)
-  messages     ChatMessage[]
-  teilnehmer   Teilnehmer[]
-  deviceTokens DeviceToken[]
+  kc                 Kc                @relation(fields: [kcId], references: [id], onDelete: Cascade)
+  gemeinde           Gemeinde?         @relation(fields: [gemeindeId], references: [id], onDelete: Cascade)
+  messages           ChatMessage[]
+  teilnehmer         Teilnehmer[]
+  deviceTokens       DeviceToken[]
+  chatParticipations ChatParticipant[]
 }
 
 /// A push-notification target (FCM registration token) bound to whoever
@@ -202,13 +203,13 @@ model Wahl {
 /// A workshop offered in one phase of a Wahl. `phase` is 1-based and must be
 /// <= the owning Wahl's `phasenAnzahl`.
 model Workshop {
-  id            String @id @default(cuid())
+  id            String  @id @default(cuid())
   wahlId        String
-  phase         Int    @default(1)
+  phase         Int     @default(1)
   name          String
   beschreibung  String?
   kapazitaet    Int
-  minTeilnehmer Int    @default(0)
+  minTeilnehmer Int     @default(0)
 
   wahl             Wahl             @relation(fields: [wahlId], references: [id], onDelete: Cascade)
   zuteilungen      Zuteilung[]
@@ -282,32 +283,47 @@ enum ChatChannelType {
   DIREKT
   LT_UEBERGREIFEND
   BROADCAST
+  /// Freely composed group chat: created by a Leitungsteam member or a
+  /// Gemeinde Verantwortliche/r (for their own KC), with an explicit,
+  /// mutable participant list (team users and/or guests) via ChatParticipant
+  /// - unlike GEMEINDE_GRUPPE, membership is not derived from Gemeinde.
+  GRUPPE
 }
 
 model ChatChannel {
-  id         String          @id @default(cuid())
-  kcId       String
-  type       ChatChannelType
-  gemeindeId String?
-  createdAt  DateTime        @default(now())
+  id              String          @id @default(cuid())
+  kcId            String
+  type            ChatChannelType
+  gemeindeId      String?
+  /// Display name; used by GRUPPE channels (optional for other types).
+  name            String?
+  /// Who created the channel; only set for GRUPPE so far. Used to let the
+  /// creator manage participants alongside Leitungsteam/Verantwortliche.
+  createdByUserId String?
+
+  createdAt DateTime @default(now())
 
   kc           Kc                @relation(fields: [kcId], references: [id], onDelete: Cascade)
   messages     ChatMessage[]
   participants ChatParticipant[]
 }
 
-/// Explicit membership for DIREKT (1:1) channels; other channel types derive
-/// access from Membership/Gemeinde instead of this table.
+/// Explicit membership for DIREKT (1:1) and GRUPPE channels; other channel
+/// types derive access from Membership/Gemeinde instead of this table.
+/// Exactly one of userId/guestAccountId is set per row.
 model ChatParticipant {
-  id        String   @id @default(cuid())
-  channelId String
-  userId    String
-  createdAt DateTime @default(now())
+  id             String   @id @default(cuid())
+  channelId      String
+  userId         String?
+  guestAccountId String?
+  createdAt      DateTime @default(now())
 
-  channel ChatChannel @relation(fields: [channelId], references: [id], onDelete: Cascade)
-  user    User        @relation(fields: [userId], references: [id], onDelete: Cascade)
+  channel      ChatChannel   @relation(fields: [channelId], references: [id], onDelete: Cascade)
+  user         User?         @relation(fields: [userId], references: [id], onDelete: Cascade)
+  guestAccount GuestAccount? @relation(fields: [guestAccountId], references: [id], onDelete: Cascade)
 
   @@unique([channelId, userId])
+  @@unique([channelId, guestAccountId])
 }
 
 model ChatMessage {

src/chat/chat.controller.ts

@@ -1,8 +1,10 @@
-import { Body, Controller, Get, Param, Post, Req, UseGuards } from '@nestjs/common';
+import { Body, Controller, Delete, Get, Param, Post, Req, UseGuards } from '@nestjs/common';
 import { AuthGuard } from '@nestjs/passport';
 import { ChatService } from './chat.service';
+import { ChatGateway } from './chat.gateway';
 import { CreateChannelDto } from './dto/create-channel.dto';
 import { CreateDirectChannelDto } from './dto/create-direct-channel.dto';
+import { AddParticipantDto } from './dto/add-participant.dto';
 import { Roles } from '../common/roles.decorator';
 import { RolesGuard } from '../common/roles.guard';
 import { Role } from '../common/role.enum';
@@ -14,7 +16,10 @@ type ChatRequest = AuthenticatedRequest & { user?: AuthenticatedRequest['user']
 
 @Controller('chat')
 export class ChatController {
-  constructor(private readonly chat: ChatService) {}
+  constructor(
+    private readonly chat: ChatService,
+    private readonly gateway: ChatGateway,
+  ) {}
 
   /// Channel administration (Gemeinde-Gruppen, LT-Kanäle, Broadcasts) is Leitungsteam-only.
   @Post(':kcId/channels')
@@ -24,6 +29,73 @@ export class ChatController {
     return this.chat.createChannel(kcId, dto.type, dto.gemeindeId);
   }
 
+  /// Free-form group chat ("Gruppenchat"): a Leitungsteam member (any KC) or
+  /// a Gemeinde Verantwortliche/r (their own KC, enforced by RolesGuard's
+  /// kcId scoping) can create one and pick any mix of team users and Konfis
+  /// (guests) from this KC as initial participants.
+  @Post(':kcId/gruppen')
+  @UseGuards(AuthGuard(['authentik', 'team']), RolesGuard)
+  @Roles(Role.LEITUNGSTEAM, Role.GEMEINDE_VERANTWORTLICHER)
+  createGruppe(
+    @Param('kcId') kcId: string,
+    @Body() dto: CreateChannelDto,
+    @Req() req: AuthenticatedRequest,
+  ) {
+    return this.chat.createGruppe(kcId, dto.name, req.user!.userId, {
+      userIds: dto.participantUserIds,
+      guestIds: dto.participantGuestIds,
+    });
+  }
+
+  /// Candidates (team users + Konfis) a caller may add to a Gruppenchat in
+  /// this KC. Allowed for LT or a Verantwortliche/r of this KC.
+  @Get(':kcId/gruppen/participant-candidates')
+  @UseGuards(AuthGuard(['authentik', 'team']))
+  listPossibleParticipants(@Param('kcId') kcId: string, @Req() req: AuthenticatedRequest) {
+    return this.chat.listPossibleParticipants(kcId, req.user!);
+  }
+
+  /// Add a team user or Konfi to a Gruppenchat. Allowed for the channel's
+  /// creator, any Leitungsteam member, or a Verantwortliche/r of that KC.
+  @Post('gruppen/:channelId/participants')
+  @UseGuards(AuthGuard(['authentik', 'team']))
+  addParticipant(
+    @Param('channelId') channelId: string,
+    @Body() dto: AddParticipantDto,
+    @Req() req: AuthenticatedRequest,
+  ) {
+    return this.chat
+      .addParticipant(
+        channelId,
+        { kind: 'user', user: req.user! },
+        { userId: dto.userId, guestId: dto.guestId },
+      )
+      .then((result) => {
+        this.gateway.notifyParticipantsChanged(channelId);
+        return result;
+      });
+  }
+
+  /// Remove a team user or Konfi from a Gruppenchat. Same authorization as add.
+  @Delete('gruppen/:channelId/participants')
+  @UseGuards(AuthGuard(['authentik', 'team']))
+  removeParticipant(
+    @Param('channelId') channelId: string,
+    @Body() dto: AddParticipantDto,
+    @Req() req: AuthenticatedRequest,
+  ) {
+    return this.chat
+      .removeParticipant(
+        channelId,
+        { kind: 'user', user: req.user! },
+        { userId: dto.userId, guestId: dto.guestId },
+      )
+      .then((result) => {
+        this.gateway.notifyParticipantsChanged(channelId);
+        return result;
+      });
+  }
+
   /// Any two team members of the same KC can start a direct conversation
   /// (Authentik-backed members and local Gemeinde Teamer alike).
   @Post('direct')

src/chat/chat.gateway.ts

@@ -106,4 +106,12 @@ export class ChatGateway implements OnGatewayConnection, OnGatewayDisconnect {
       }
     }
   }
+
+  /// Called by ChatController after add/removeParticipant so anyone with the
+  /// channel already open (e.g. the creator's participant-management UI)
+  /// gets a live update. Newly added participants join the room themselves
+  /// via `chat:join` once they open the chat.
+  notifyParticipantsChanged(channelId: string) {
+    this.broadcast(channelId, { event: 'chat:participants-changed', data: { channelId } });
+  }
 }

src/chat/chat.service.spec.ts

@@ -0,0 +1,280 @@
+import { BadRequestException, ForbiddenException, NotFoundException } from '@nestjs/common';
+import { ChatChannelType, Role } from '@prisma/client';
+import { ChatService } from './chat.service';
+import { AuthenticatedUser } from '../auth/authenticated-request';
+import { GuestJwtPayload } from '../auth/guest-auth.service';
+
+/// Focus: GRUPPE channel creation + participant management authorization
+/// (creator / Leitungsteam / Verantwortliche/r of that KC), and read/write
+/// access for team users and guests. Prisma + Sync + Push faked in memory.
+
+function userCaller(userId: string, memberships: AuthenticatedUser['memberships']) {
+  return {
+    kind: 'user' as const,
+    user: { userId, authentikSub: `sub-${userId}`, email: `${userId}@example.org`, memberships },
+  };
+}
+function guestCaller(guestId: string, kcId: string, gemeindeId: string | null = null) {
+  const guest: GuestJwtPayload = { guestId, kcId, gemeindeId };
+  return { kind: 'guest' as const, guest };
+}
+
+const LT = userCaller('lt-1', [{ kcId: 'kc-1', gemeindeId: null, role: Role.LEITUNGSTEAM }]);
+const VERANTW = userCaller('ver-1', [
+  { kcId: 'kc-1', gemeindeId: 'gem-1', role: Role.GEMEINDE_VERANTWORTLICHER },
+]);
+const TEAMER = userCaller('teamer-1', [
+  { kcId: 'kc-1', gemeindeId: 'gem-1', role: Role.GEMEINDE_TEAMER },
+]);
+
+function makeService(
+  opts: {
+    channels?: Record<string, any>;
+    memberships?: { kcId: string; userId: string }[];
+    guests?: { id: string; kcId: string }[];
+  } = {},
+) {
+  const channels: Record<string, any> = opts.channels ?? {};
+  const memberships = opts.memberships ?? [];
+  const guests = opts.guests ?? [];
+  const participants: any[] = [];
+  let participantSeq = 0;
+
+  const prisma = {
+    chatChannel: {
+      create: jest.fn(({ data, include }: any) => {
+        const id = `chan-${Object.keys(channels).length + 1}`;
+        const created = { id, ...data, participants: [] };
+        if (data.participants?.create) {
+          for (const p of data.participants.create) {
+            const row = { id: `part-${++participantSeq}`, channelId: id, userId: null, guestAccountId: null, ...p };
+            participants.push(row);
+            created.participants.push(row);
+          }
+        }
+        channels[id] = created;
+        return Promise.resolve(include ? created : { id, ...data });
+      }),
+      findUnique: jest.fn(({ where, include }: any) => {
+        const channel = channels[where.id];
+        if (!channel) return Promise.resolve(null);
+        if (include?.participants) {
+          const seeded = participants.filter((p) => p.channelId === channel.id);
+          const fallback = Array.isArray(channel.participants) ? channel.participants : [];
+          return Promise.resolve({
+            ...channel,
+            participants: seeded.length ? seeded : fallback,
+          });
+        }
+        return Promise.resolve(channel);
+      }),
+      findMany: jest.fn().mockResolvedValue([]),
+    },
+    membership: {
+      findMany: jest.fn(({ where }: any) => {
+        const ids: string[] = where.userId.in;
+        const rows = memberships.filter((m) => m.kcId === where.kcId && ids.includes(m.userId));
+        const seen = new Set<string>();
+        const distinct = rows.filter((r) => (seen.has(r.userId) ? false : (seen.add(r.userId), true)));
+        return Promise.resolve(distinct);
+      }),
+      findFirst: jest.fn(({ where }: any) =>
+        Promise.resolve(memberships.find((m) => m.kcId === where.kcId && m.userId === where.userId) ?? null),
+      ),
+      count: jest.fn().mockResolvedValue(0),
+    },
+    guestAccount: {
+      count: jest.fn(({ where }: any) =>
+        Promise.resolve(guests.filter((g) => where.id.in.includes(g.id) && g.kcId === where.kcId).length),
+      ),
+      findFirst: jest.fn(({ where }: any) =>
+        Promise.resolve(guests.find((g) => g.id === where.id && g.kcId === where.kcId) ?? null),
+      ),
+    },
+    chatParticipant: {
+      upsert: jest.fn(({ create }: any) => {
+        const existing = participants.find(
+          (p) =>
+            p.channelId === create.channelId &&
+            p.userId === (create.userId ?? null) &&
+            p.guestAccountId === (create.guestAccountId ?? null),
+        );
+        if (existing) return Promise.resolve(existing);
+        const row = { id: `part-${++participantSeq}`, userId: null, guestAccountId: null, ...create };
+        participants.push(row);
+        return Promise.resolve(row);
+      }),
+      findFirst: jest.fn(({ where }: any) =>
+        Promise.resolve(
+          participants.find(
+            (p) =>
+              p.channelId === where.channelId &&
+              (where.userId === undefined || p.userId === where.userId) &&
+              (where.guestAccountId === undefined || p.guestAccountId === where.guestAccountId),
+          ) ?? null,
+        ),
+      ),
+      delete: jest.fn(({ where }: any) => {
+        const idx = participants.findIndex((p) => p.id === where.id);
+        const [removed] = participants.splice(idx, 1);
+        return Promise.resolve(removed);
+      }),
+    },
+    chatMessage: { create: jest.fn(), findMany: jest.fn() },
+  };
+  const sync = { capture: jest.fn().mockResolvedValue(undefined) };
+  const push = { notifyChannel: jest.fn().mockResolvedValue(undefined) };
+  const service = new ChatService(prisma as never, sync as never, push as never);
+  return { service, prisma, sync, push, channels, participants };
+}
+
+describe('ChatService.createGruppe', () => {
+  it('creates a GRUPPE channel with the creator plus given team/guest participants', async () => {
+    const { service, sync } = makeService({
+      memberships: [{ kcId: 'kc-1', userId: 'ver-1' }, { kcId: 'kc-1', userId: 'teamer-1' }],
+      guests: [{ id: 'guest-1', kcId: 'kc-1' }],
+    });
+    const channel = await service.createGruppe('kc-1', 'Ausflugsplanung', 'ver-1', {
+      userIds: ['teamer-1'],
+      guestIds: ['guest-1'],
+    });
+    expect(channel.type).toBe(ChatChannelType.GRUPPE);
+    expect(channel.createdByUserId).toBe('ver-1');
+    const userIds = channel.participants.map((p: any) => p.userId).filter(Boolean);
+    const guestIds = channel.participants.map((p: any) => p.guestAccountId).filter(Boolean);
+    expect(userIds.sort()).toEqual(['teamer-1', 'ver-1']);
+    expect(guestIds).toEqual(['guest-1']);
+    expect(sync.capture).toHaveBeenCalledWith('ChatChannel', 'CREATE', channel.id, expect.anything());
+  });
+
+  it('does not duplicate the creator if already listed as a participant', async () => {
+    const { service } = makeService({ memberships: [{ kcId: 'kc-1', userId: 'ver-1' }] });
+    const channel = await service.createGruppe('kc-1', 'X', 'ver-1', { userIds: ['ver-1'] });
+    const userIds = channel.participants.map((p: any) => p.userId).filter(Boolean);
+    expect(userIds).toEqual(['ver-1']);
+  });
+
+  it('rejects a participant who is not a member of the KC', async () => {
+    const { service } = makeService({ memberships: [] });
+    await expect(
+      service.createGruppe('kc-1', 'X', 'ver-1', { userIds: ['ghost'] }),
+    ).rejects.toBeInstanceOf(BadRequestException);
+  });
+
+  it('rejects a guest who is not part of the KC', async () => {
+    const { service } = makeService({ guests: [{ id: 'guest-1', kcId: 'kc-2' }] });
+    await expect(
+      service.createGruppe('kc-1', 'X', 'ver-1', { guestIds: ['guest-1'] }),
+    ).rejects.toBeInstanceOf(BadRequestException);
+  });
+});
+
+describe('ChatService participant management', () => {
+  function seedGruppe() {
+    const channels = {
+      'chan-1': { id: 'chan-1', kcId: 'kc-1', type: ChatChannelType.GRUPPE, createdByUserId: 'ver-1', gemeindeId: null },
+    };
+    return channels;
+  }
+
+  it('lets the creator add a team user', async () => {
+    const { service } = makeService({
+      channels: seedGruppe(),
+      memberships: [{ kcId: 'kc-1', userId: 'teamer-1' }],
+    });
+    const p = await service.addParticipant('chan-1', VERANTW, { userId: 'teamer-1' });
+    expect(p.userId).toBe('teamer-1');
+  });
+
+  it('lets a Leitungsteam member add a guest even if not the creator', async () => {
+    const { service } = makeService({
+      channels: seedGruppe(),
+      guests: [{ id: 'guest-1', kcId: 'kc-1' }],
+    });
+    const p = await service.addParticipant('chan-1', LT, { guestId: 'guest-1' });
+    expect(p.guestAccountId).toBe('guest-1');
+  });
+
+  it('forbids a plain Teamer (not creator, not LT, not Verantwortliche/r) from managing participants', async () => {
+    const { service } = makeService({ channels: seedGruppe() });
+    await expect(
+      service.addParticipant('chan-1', TEAMER, { userId: 'teamer-1' }),
+    ).rejects.toBeInstanceOf(ForbiddenException);
+  });
+
+  it('forbids guests from managing participants', async () => {
+    const { service } = makeService({ channels: seedGruppe() });
+    await expect(
+      service.addParticipant('chan-1', guestCaller('g-1', 'kc-1') as never, { userId: 'x' }),
+    ).rejects.toBeInstanceOf(ForbiddenException);
+  });
+
+  it('404s for a non-GRUPPE channel', async () => {
+    const channels = {
+      'chan-2': { id: 'chan-2', kcId: 'kc-1', type: ChatChannelType.GEMEINDE_GRUPPE, createdByUserId: null },
+    };
+    const { service } = makeService({ channels });
+    await expect(
+      service.addParticipant('chan-2', LT, { userId: 'teamer-1' }),
+    ).rejects.toBeInstanceOf(NotFoundException);
+  });
+
+  it('rejects adding a user not in the KC', async () => {
+    const { service } = makeService({ channels: seedGruppe(), memberships: [] });
+    await expect(
+      service.addParticipant('chan-1', LT, { userId: 'ghost' }),
+    ).rejects.toBeInstanceOf(BadRequestException);
+  });
+
+  it('removes a participant and is a no-op if already absent', async () => {
+    const { service } = makeService({
+      channels: seedGruppe(),
+      memberships: [{ kcId: 'kc-1', userId: 'teamer-1' }],
+    });
+    await service.addParticipant('chan-1', VERANTW, { userId: 'teamer-1' });
+    const res = await service.removeParticipant('chan-1', VERANTW, { userId: 'teamer-1' });
+    expect(res).toEqual({ ok: true });
+    const res2 = await service.removeParticipant('chan-1', VERANTW, { userId: 'teamer-1' });
+    expect(res2).toEqual({ ok: true });
+  });
+});
+
+describe('ChatService GRUPPE read/write access', () => {
+  function seedGruppeWithParticipants(participants: any[]) {
+    return {
+      'chan-1': {
+        id: 'chan-1',
+        kcId: 'kc-1',
+        type: ChatChannelType.GRUPPE,
+        createdByUserId: 'ver-1',
+        gemeindeId: null,
+        participants,
+      },
+    };
+  }
+
+  it('lets a listed guest read messages', async () => {
+    const { service } = makeService({
+      channels: seedGruppeWithParticipants([{ userId: null, guestAccountId: 'guest-1' }]),
+    });
+    await expect(
+      service.assertCanRead('chan-1', guestCaller('guest-1', 'kc-1') as never),
+    ).resolves.toBeDefined();
+  });
+
+  it('forbids a guest not in the participant list', async () => {
+    const { service } = makeService({
+      channels: seedGruppeWithParticipants([{ userId: null, guestAccountId: 'guest-1' }]),
+    });
+    await expect(
+      service.assertCanRead('chan-1', guestCaller('guest-2', 'kc-1') as never),
+    ).rejects.toBeInstanceOf(ForbiddenException);
+  });
+
+  it('forbids a team user not in the participant list', async () => {
+    const { service } = makeService({
+      channels: seedGruppeWithParticipants([{ userId: 'someone-else', guestAccountId: null }]),
+    });
+    await expect(service.assertCanRead('chan-1', TEAMER)).rejects.toBeInstanceOf(ForbiddenException);
+  });
+});

src/chat/chat.service.ts

@@ -1,4 +1,4 @@
-import { ForbiddenException, Injectable, NotFoundException } from '@nestjs/common';
+import { BadRequestException, ForbiddenException, Injectable, NotFoundException } from '@nestjs/common';
 import { ChatChannelType, Role, SyncOperation } from '@prisma/client';
 import { PrismaClient } from '../prisma/prisma.module';
 import { AuthenticatedUser } from '../auth/authenticated-request';
@@ -15,8 +15,14 @@ const CHANNEL_TITLES: Record<ChatChannelType, string> = {
   [ChatChannelType.DIREKT]: 'Direktnachricht',
   [ChatChannelType.LT_UEBERGREIFEND]: 'Leitungsteam',
   [ChatChannelType.BROADCAST]: 'Ankündigung',
+  [ChatChannelType.GRUPPE]: 'Gruppenchat',
 };
 
+export interface CreateGruppeParticipants {
+  userIds?: string[];
+  guestIds?: string[];
+}
+
 @Injectable()
 export class ChatService {
   constructor(
@@ -31,6 +37,206 @@ export class ChatService {
     return channel;
   }
 
+  /// Free-form group chat: created by a Leitungsteam member (any KC) or a
+  /// Gemeinde Verantwortliche/r (their own KC — enforced by the RolesGuard's
+  /// kcId scoping at the controller level). Konfis (guests) may be included
+  /// directly, unlike DIREKT/GEMEINDE_GRUPPE channels which are team-only.
+  async createGruppe(
+    kcId: string,
+    name: string | undefined,
+    createdByUserId: string,
+    participants: CreateGruppeParticipants,
+  ) {
+    const userIds = [...new Set(participants.userIds ?? [])];
+    const guestIds = [...new Set(participants.guestIds ?? [])];
+
+    if (userIds.length) {
+      // A user may show up under more than one Gemeinde membership; just
+      // make sure every requested id resolves to at least one row for this KC.
+      const distinctUsers = await this.prisma.membership.findMany({
+        where: { kcId, userId: { in: userIds } },
+        select: { userId: true },
+        distinct: ['userId'],
+      });
+      if (distinctUsers.length !== userIds.length) {
+        throw new BadRequestException('One or more users are not part of this KC');
+      }
+    }
+    if (guestIds.length) {
+      const guestCount = await this.prisma.guestAccount.count({
+        where: { id: { in: guestIds }, kcId },
+      });
+      if (guestCount !== guestIds.length) {
+        throw new BadRequestException('One or more guests are not part of this KC');
+      }
+    }
+
+    const channel = await this.prisma.chatChannel.create({
+      data: {
+        kcId,
+        type: ChatChannelType.GRUPPE,
+        name,
+        createdByUserId,
+        participants: {
+          create: [
+            ...(userIds.includes(createdByUserId) ? [] : [{ userId: createdByUserId }]),
+            ...userIds.map((userId) => ({ userId })),
+            ...guestIds.map((guestAccountId) => ({ guestAccountId })),
+          ],
+        },
+      },
+      include: { participants: true },
+    });
+    await this.sync.capture('ChatChannel', SyncOperation.CREATE, channel.id, channel);
+    return channel;
+  }
+
+  /// Candidates a caller may add to a GRUPPE channel in this KC: every team
+  /// member (any Gemeinde) plus every Konfi/guest, so a Verantwortliche/r can
+  /// pick across Gemeinde boundaries as intended. Same authorization as
+  /// creating a Gruppenchat (LT or Verantwortliche/r of this KC).
+  async listPossibleParticipants(kcId: string, caller: AuthenticatedUser) {
+    const isLt = caller.memberships.some((m) => m.role === Role.LEITUNGSTEAM);
+    const isVerantwortlicherHere = caller.memberships.some(
+      (m) => m.kcId === kcId && m.role === Role.GEMEINDE_VERANTWORTLICHER,
+    );
+    if (!isLt && !isVerantwortlicherHere) {
+      throw new ForbiddenException('Not allowed to list participants for this KC');
+    }
+
+    const [memberships, guests] = await Promise.all([
+      this.prisma.membership.findMany({
+        where: { kcId, status: 'ACTIVE' },
+        include: { user: { select: { id: true, firstName: true, lastName: true, email: true } } },
+        orderBy: { user: { lastName: 'asc' } },
+      }),
+      this.prisma.guestAccount.findMany({
+        where: { kcId },
+        select: { id: true, firstName: true, lastName: true, gemeindeId: true },
+        orderBy: { lastName: 'asc' },
+      }),
+    ]);
+
+    const seenUsers = new Set<string>();
+    const users = [];
+    for (const m of memberships) {
+      if (seenUsers.has(m.userId)) continue;
+      seenUsers.add(m.userId);
+      users.push({
+        userId: m.user.id,
+        firstName: m.user.firstName,
+        lastName: m.user.lastName,
+        email: m.user.email,
+        role: m.role,
+        gemeindeId: m.gemeindeId,
+      });
+    }
+
+    return {
+      users,
+      guests: guests.map((g) => ({
+        guestId: g.id,
+        firstName: g.firstName,
+        lastName: g.lastName,
+        gemeindeId: g.gemeindeId,
+      })),
+    };
+  }
+
+  /// Adds a team user or a guest/Konfi to an existing GRUPPE channel. Only
+  /// the channel's creator or a Leitungsteam member may manage participants.
+  async addParticipant(
+    channelId: string,
+    caller: ChatCaller,
+    target: { userId?: string; guestId?: string },
+  ) {
+    const channel = await this.getGruppeForManagementOrThrow(channelId, caller);
+
+    if (!target.userId && !target.guestId) {
+      throw new BadRequestException('userId or guestId is required');
+    }
+    if (target.userId && target.guestId) {
+      throw new BadRequestException('Provide either userId or guestId, not both');
+    }
+
+    if (target.userId) {
+      const isMember = await this.prisma.membership.findFirst({
+        where: { kcId: channel.kcId, userId: target.userId },
+      });
+      if (!isMember) {
+        throw new BadRequestException('User is not part of this KC');
+      }
+      const participant = await this.prisma.chatParticipant.upsert({
+        where: { channelId_userId: { channelId, userId: target.userId } },
+        create: { channelId, userId: target.userId },
+        update: {},
+      });
+      await this.sync.capture('ChatParticipant', SyncOperation.CREATE, participant.id, participant);
+      return participant;
+    }
+
+    const guest = await this.prisma.guestAccount.findFirst({
+      where: { id: target.guestId, kcId: channel.kcId },
+    });
+    if (!guest) {
+      throw new BadRequestException('Guest is not part of this KC');
+    }
+    const participant = await this.prisma.chatParticipant.upsert({
+      where: { channelId_guestAccountId: { channelId, guestAccountId: target.guestId! } },
+      create: { channelId, guestAccountId: target.guestId },
+      update: {},
+    });
+    await this.sync.capture('ChatParticipant', SyncOperation.CREATE, participant.id, participant);
+    return participant;
+  }
+
+  /// Removes a team user or a guest/Konfi from a GRUPPE channel. Same
+  /// authorization as addParticipant.
+  async removeParticipant(
+    channelId: string,
+    caller: ChatCaller,
+    target: { userId?: string; guestId?: string },
+  ) {
+    await this.getGruppeForManagementOrThrow(channelId, caller);
+
+    if (!target.userId && !target.guestId) {
+      throw new BadRequestException('userId or guestId is required');
+    }
+
+    const existing = await this.prisma.chatParticipant.findFirst({
+      where: {
+        channelId,
+        userId: target.userId ?? undefined,
+        guestAccountId: target.guestId ?? undefined,
+      },
+    });
+    if (!existing) return { ok: true };
+
+    await this.prisma.chatParticipant.delete({ where: { id: existing.id } });
+    await this.sync.capture('ChatParticipant', SyncOperation.DELETE, existing.id, { id: existing.id });
+    return { ok: true };
+  }
+
+  private async getGruppeForManagementOrThrow(channelId: string, caller: ChatCaller) {
+    if (caller.kind !== 'user') {
+      throw new ForbiddenException('Guests may not manage channel participants');
+    }
+    const channel = await this.prisma.chatChannel.findUnique({ where: { id: channelId } });
+    if (!channel || channel.type !== ChatChannelType.GRUPPE) {
+      throw new NotFoundException('Gruppenchat not found');
+    }
+    const { user } = caller;
+    const isLt = user.memberships.some((m) => m.role === Role.LEITUNGSTEAM);
+    const isCreator = channel.createdByUserId === user.userId;
+    const isVerantwortlicherHere = user.memberships.some(
+      (m) => m.kcId === channel.kcId && m.role === Role.GEMEINDE_VERANTWORTLICHER,
+    );
+    if (!isLt && !isCreator && !isVerantwortlicherHere) {
+      throw new ForbiddenException('Not allowed to manage this Gruppenchat');
+    }
+    return channel;
+  }
+
   async getOrCreateDirectChannel(kcId: string, userAId: string, userBId: string) {
     const existing = await this.prisma.chatChannel.findFirst({
       where: {
@@ -57,7 +263,13 @@ export class ChatService {
   async listChannelsForCaller(kcId: string, caller: ChatCaller) {
     if (caller.kind === 'guest') {
       return this.prisma.chatChannel.findMany({
-        where: { kcId, type: ChatChannelType.BROADCAST },
+        where: {
+          kcId,
+          OR: [
+            { type: ChatChannelType.BROADCAST },
+            { type: ChatChannelType.GRUPPE, participants: { some: { guestAccountId: caller.guest.guestId } } },
+          ],
+        },
       });
     }
     const { user } = caller;
@@ -75,6 +287,7 @@ export class ChatService {
           { type: ChatChannelType.BROADCAST },
           { type: ChatChannelType.GEMEINDE_GRUPPE, gemeindeId: { in: gemeindeIds } },
           { type: ChatChannelType.DIREKT, participants: { some: { userId: user.userId } } },
+          { type: ChatChannelType.GRUPPE, participants: { some: { userId: user.userId } } },
         ],
       },
     });
@@ -102,14 +315,22 @@ export class ChatService {
     }
 
     if (caller.kind === 'guest') {
-      const allowed = channel.type === ChatChannelType.BROADCAST && mode === 'read';
-      if (!allowed) {
-        throw new ForbiddenException('Guests may only read broadcast channels');
+      if (channel.type === ChatChannelType.BROADCAST && mode === 'read') {
+        if (caller.guest.kcId !== channel.kcId) {
+          throw new ForbiddenException('Guest does not belong to this KC');
+        }
+        return channel;
       }
-      if (caller.guest.kcId !== channel.kcId) {
-        throw new ForbiddenException('Guest does not belong to this KC');
+      if (channel.type === ChatChannelType.GRUPPE) {
+        const isParticipant = channel.participants.some(
+          (p) => p.guestAccountId === caller.guest.guestId,
+        );
+        if (!isParticipant) {
+          throw new ForbiddenException('Not a participant of this Gruppenchat');
+        }
+        return channel;
       }
-      return channel;
+      throw new ForbiddenException('Guests may only read broadcast channels or their Gruppenchats');
     }
 
     const { user } = caller;
@@ -145,6 +366,13 @@ export class ChatService {
         }
         return channel;
       }
+      case ChatChannelType.GRUPPE: {
+        const isParticipant = channel.participants.some((p) => p.userId === user.userId);
+        if (!isParticipant) {
+          throw new ForbiddenException('Not a participant of this Gruppenchat');
+        }
+        return channel;
+      }
       default:
         throw new ForbiddenException('Unknown channel type');
     }

src/chat/dto/add-participant.dto.ts

@@ -0,0 +1,13 @@
+import { IsOptional, IsString } from 'class-validator';
+
+/// Exactly one of userId/guestId must be set; validated in the service since
+/// class-validator doesn't express "exactly one of" declaratively.
+export class AddParticipantDto {
+  @IsOptional()
+  @IsString()
+  userId?: string;
+
+  @IsOptional()
+  @IsString()
+  guestId?: string;
+}

src/chat/dto/create-channel.dto.ts

@@ -1,4 +1,4 @@
-import { IsEnum, IsOptional, IsString } from 'class-validator';
+import { ArrayUnique, IsArray, IsEnum, IsOptional, IsString } from 'class-validator';
 import { ChatChannelType } from '@prisma/client';
 
 export class CreateChannelDto {
@@ -8,4 +8,24 @@ export class CreateChannelDto {
   @IsOptional()
   @IsString()
   gemeindeId?: string;
+
+  /// Display name; used for GRUPPE channels.
+  @IsOptional()
+  @IsString()
+  name?: string;
+
+  /// Initial participants for a GRUPPE channel (team users). More can be
+  /// added/removed later via the participants endpoints.
+  @IsOptional()
+  @IsArray()
+  @ArrayUnique()
+  @IsString({ each: true })
+  participantUserIds?: string[];
+
+  /// Initial guest/Konfi participants for a GRUPPE channel.
+  @IsOptional()
+  @IsArray()
+  @ArrayUnique()
+  @IsString({ each: true })
+  participantGuestIds?: string[];
 }

src/push/push.service.ts

@@ -50,7 +50,7 @@ export class PushService {
     try {
       const channel = await this.prisma.chatChannel.findUnique({
         where: { id: channelId },
-        include: { participants: { select: { userId: true } } },
+        include: { participants: { select: { userId: true, guestAccountId: true } } },
       });
       if (!channel) return;
 
@@ -90,10 +90,22 @@ export class PushService {
     kcId: string;
     type: ChatChannelType;
     gemeindeId: string | null;
-    participants: { userId: string }[];
+    participants: { userId: string | null; guestAccountId: string | null }[];
   }): Promise<{ userIds: string[]; guestIds: string[] }> {
     if (channel.type === ChatChannelType.DIREKT) {
-      return { userIds: channel.participants.map((p) => p.userId), guestIds: [] };
+      return {
+        userIds: channel.participants.map((p) => p.userId).filter((id): id is string => !!id),
+        guestIds: [],
+      };
+    }
+
+    if (channel.type === ChatChannelType.GRUPPE) {
+      return {
+        userIds: channel.participants.map((p) => p.userId).filter((id): id is string => !!id),
+        guestIds: channel.participants
+          .map((p) => p.guestAccountId)
+          .filter((id): id is string => !!id),
+      };
     }
 
     const ltUsers = await this.prisma.user.findMany({

src/sync/sync.service.ts

@@ -18,6 +18,7 @@ const SYNCED_MODELS = [
   'Zuteilung',
   'File',
   'ChatChannel',
+  'ChatParticipant',
   'ChatMessage',
   'DeviceToken',
 ] as const;