feat: flow engine data layer with tests

- SQLModel tables: flow_definitions/versions/runs, approval_tasks
- Alembic setup with autogenerate (sqlmodel types fixed via script.py.mako)
- Settings extended (shared root .env), db engine/session helpers
- pytest suite: conftest with isolated test DB, 5 model tests green

backend/alembic.ini

@@ -0,0 +1,149 @@
+# A generic, single database configuration.
+
+[alembic]
+# path to migration scripts.
+# this is typically a path given in POSIX (e.g. forward slashes)
+# format, relative to the token %(here)s which refers to the location of this
+# ini file
+script_location = %(here)s/migrations
+
+# template used to generate migration file names; The default value is %%(rev)s_%%(slug)s
+# Uncomment the line below if you want the files to be prepended with date and time
+# see https://alembic.sqlalchemy.org/en/latest/tutorial.html#editing-the-ini-file
+# for all available tokens
+# file_template = %%(year)d_%%(month).2d_%%(day).2d_%%(hour).2d%%(minute).2d-%%(rev)s_%%(slug)s
+# Or organize into date-based subdirectories (requires recursive_version_locations = true)
+# file_template = %%(year)d/%%(month).2d/%%(day).2d_%%(hour).2d%%(minute).2d_%%(second).2d_%%(rev)s_%%(slug)s
+
+# sys.path path, will be prepended to sys.path if present.
+# defaults to the current working directory.  for multiple paths, the path separator
+# is defined by "path_separator" below.
+prepend_sys_path = .
+
+
+# timezone to use when rendering the date within the migration file
+# as well as the filename.
+# If specified, requires the tzdata library which can be installed by adding
+# `alembic[tz]` to the pip requirements.
+# string value is passed to ZoneInfo()
+# leave blank for localtime
+# timezone =
+
+# max length of characters to apply to the "slug" field
+# truncate_slug_length = 40
+
+# set to 'true' to run the environment during
+# the 'revision' command, regardless of autogenerate
+# revision_environment = false
+
+# set to 'true' to allow .pyc and .pyo files without
+# a source .py file to be detected as revisions in the
+# versions/ directory
+# sourceless = false
+
+# version location specification; This defaults
+# to <script_location>/versions.  When using multiple version
+# directories, initial revisions must be specified with --version-path.
+# The path separator used here should be the separator specified by "path_separator"
+# below.
+# version_locations = %(here)s/bar:%(here)s/bat:%(here)s/alembic/versions
+
+# path_separator; This indicates what character is used to split lists of file
+# paths, including version_locations and prepend_sys_path within configparser
+# files such as alembic.ini.
+# The default rendered in new alembic.ini files is "os", which uses os.pathsep
+# to provide os-dependent path splitting.
+#
+# Note that in order to support legacy alembic.ini files, this default does NOT
+# take place if path_separator is not present in alembic.ini.  If this
+# option is omitted entirely, fallback logic is as follows:
+#
+# 1. Parsing of the version_locations option falls back to using the legacy
+#    "version_path_separator" key, which if absent then falls back to the legacy
+#    behavior of splitting on spaces and/or commas.
+# 2. Parsing of the prepend_sys_path option falls back to the legacy
+#    behavior of splitting on spaces, commas, or colons.
+#
+# Valid values for path_separator are:
+#
+# path_separator = :
+# path_separator = ;
+# path_separator = space
+# path_separator = newline
+#
+# Use os.pathsep. Default configuration used for new projects.
+path_separator = os
+
+# set to 'true' to search source files recursively
+# in each "version_locations" directory
+# new in Alembic version 1.10
+# recursive_version_locations = false
+
+# the output encoding used when revision files
+# are written from script.py.mako
+# output_encoding = utf-8
+
+# database URL.  This is consumed by the user-maintained env.py script only.
+# other means of configuring database URLs may be customized within the env.py
+# file.
+sqlalchemy.url = driver://user:pass@localhost/dbname
+
+
+[post_write_hooks]
+# post_write_hooks defines scripts or Python functions that are run
+# on newly generated revision scripts.  See the documentation for further
+# detail and examples
+
+# format using "black" - use the console_scripts runner, against the "black" entrypoint
+# hooks = black
+# black.type = console_scripts
+# black.entrypoint = black
+# black.options = -l 79 REVISION_SCRIPT_FILENAME
+
+# lint with attempts to fix using "ruff" - use the module runner, against the "ruff" module
+# hooks = ruff
+# ruff.type = module
+# ruff.module = ruff
+# ruff.options = check --fix REVISION_SCRIPT_FILENAME
+
+# Alternatively, use the exec runner to execute a binary found on your PATH
+# hooks = ruff
+# ruff.type = exec
+# ruff.executable = ruff
+# ruff.options = check --fix REVISION_SCRIPT_FILENAME
+
+# Logging configuration.  This is also consumed by the user-maintained
+# env.py script only.
+[loggers]
+keys = root,sqlalchemy,alembic
+
+[handlers]
+keys = console
+
+[formatters]
+keys = generic
+
+[logger_root]
+level = WARNING
+handlers = console
+qualname =
+
+[logger_sqlalchemy]
+level = WARNING
+handlers =
+qualname = sqlalchemy.engine
+
+[logger_alembic]
+level = INFO
+handlers =
+qualname = alembic
+
+[handler_console]
+class = StreamHandler
+args = (sys.stderr,)
+level = NOTSET
+formatter = generic
+
+[formatter_generic]
+format = %(levelname)-5.5s [%(name)s] %(message)s
+datefmt = %H:%M:%S

backend/app/db.py

@@ -0,0 +1,36 @@
+"""Database engine, sessions, and FastAPI dependency."""
+
+from collections.abc import Iterator
+
+from sqlalchemy import Engine
+from sqlmodel import Session, SQLModel, create_engine
+
+from .settings import settings
+
+_engine: Engine | None = None
+
+
+def get_engine(url: str | None = None) -> Engine:
+    """Process-wide engine singleton (override URL in tests via settings)."""
+    global _engine
+    if _engine is None:
+        _engine = create_engine(url or settings.database_url)
+    return _engine
+
+
+def reset_engine() -> None:
+    """Drop the cached engine (used by the test suite between DB targets)."""
+    global _engine
+    if _engine is not None:
+        _engine.dispose()
+        _engine = None
+
+
+def get_session() -> Iterator[Session]:
+    with Session(get_engine()) as session:
+        yield session
+
+
+def create_all(url: str | None = None) -> None:
+    """Create tables directly (dev convenience; migrations own prod schema)."""
+    SQLModel.metadata.create_all(get_engine(url))

backend/app/models/__init__.py

@@ -0,0 +1,3 @@
+from .flow import ApprovalTask, FlowDefinition, FlowRun, FlowVersion
+
+__all__ = ["ApprovalTask", "FlowDefinition", "FlowRun", "FlowVersion"]

backend/app/models/flow.py

@@ -0,0 +1,90 @@
+"""Flow engine domain models (SQLModel tables)."""
+
+from datetime import datetime, timezone
+from uuid import UUID, uuid4
+
+from sqlalchemy import JSON, Column, DateTime, UniqueConstraint
+from sqlmodel import Field, SQLModel
+
+
+def utcnow() -> datetime:
+    return datetime.now(timezone.utc)
+
+
+def _ts_column() -> Column:
+    return Column(DateTime(timezone=True))
+
+
+def _json_column() -> Column:
+    # Generic JSON: JSONB on Postgres, JSON/TEXT elsewhere.
+    return Column(JSON)
+
+
+class FlowDefinition(SQLModel, table=True):
+    """A named decision flow (e.g. 'Bauvorhaben pruefen'). Versions live separately."""
+
+    __tablename__ = "flow_definitions"
+
+    id: UUID = Field(default_factory=uuid4, primary_key=True)
+    name: str = Field(index=True, unique=True, max_length=200)
+    description: str = Field(default="", max_length=2000)
+    status: str = Field(default="active", max_length=20)  # active | archived
+    # Flow to run after a human approval on this flow's runs (nullable).
+    continuation_flow_id: UUID | None = Field(
+        default=None, foreign_key="flow_definitions.id"
+    )
+    created_at: datetime = Field(default_factory=utcnow, sa_column=_ts_column())
+
+
+class FlowVersion(SQLModel, table=True):
+    """An immutable version of a flow: the exact Langflow JSON that runs."""
+
+    __tablename__ = "flow_versions"
+    __table_args__ = (UniqueConstraint("flow_id", "version_no"),)
+
+    id: UUID = Field(default_factory=uuid4, primary_key=True)
+    flow_id: UUID = Field(foreign_key="flow_definitions.id", index=True)
+    version_no: int = Field(index=True)
+    langflow_json: dict = Field(default_factory=dict, sa_column=_json_column())
+    # Flow id under which LFX serves this version (set on deploy).
+    lfx_flow_id: str | None = Field(default=None, max_length=200)
+    deployed_at: datetime | None = Field(default=None, sa_column=_ts_column())
+    author: str = Field(default="", max_length=200)
+    created_at: datetime = Field(default_factory=utcnow, sa_column=_ts_column())
+
+
+class FlowRun(SQLModel, table=True):
+    """One execution of a flow version."""
+
+    __tablename__ = "flow_runs"
+
+    id: UUID = Field(default_factory=uuid4, primary_key=True)
+    version_id: UUID = Field(foreign_key="flow_versions.id", index=True)
+    tenant_id: str = Field(default="default", index=True, max_length=200)
+    # running | completed | pending_approval | failed
+    status: str = Field(default="running", index=True, max_length=30)
+    input: dict | None = Field(default=None, sa_column=_json_column())
+    output: dict | None = Field(default=None, sa_column=_json_column())
+    session_id: str | None = Field(default=None, max_length=200)
+    created_at: datetime = Field(default_factory=utcnow, sa_column=_ts_column())
+    finished_at: datetime | None = Field(default=None, sa_column=_ts_column())
+
+
+class ApprovalTask(SQLModel, table=True):
+    """Human task created by a flow that reached a terminal approval state."""
+
+    __tablename__ = "approval_tasks"
+
+    id: UUID = Field(default_factory=uuid4, primary_key=True)
+    run_id: UUID = Field(foreign_key="flow_runs.id", index=True)
+    version_id: UUID = Field(foreign_key="flow_versions.id", index=True)
+    tenant_id: str = Field(default="default", index=True, max_length=200)
+    title: str = Field(default="", max_length=500)
+    payload: dict = Field(default_factory=dict, sa_column=_json_column())
+    continuation_flow_id: UUID | None = Field(default=None)
+    approver: str | None = Field(default=None, max_length=200)
+    # open | approved | rejected
+    status: str = Field(default="open", index=True, max_length=20)
+    decision_note: str = Field(default="", max_length=2000)
+    created_at: datetime = Field(default_factory=utcnow, sa_column=_ts_column())
+    decided_at: datetime | None = Field(default=None, sa_column=_ts_column())

backend/app/settings.py

@@ -1,11 +1,27 @@
-from pydantic_settings import BaseSettings
+from pathlib import Path
+
+from pydantic_settings import BaseSettings, SettingsConfigDict
+
+# Repo-root .env (shared with the compose stack). Real environment variables
+# always take precedence over .env values.
+REPO_ROOT = Path(__file__).resolve().parent.parent.parent
 
 
 class Settings(BaseSettings):
+    model_config = SettingsConfigDict(env_file=REPO_ROOT / ".env", extra="ignore")
+
     version: str = "0.1.0"
     debug: bool = False
 
-    model_config = {"env_prefix": "KIRCHE_"}
+    database_url: str = "postgresql+psycopg://kirche:kirche@localhost:5432/kirche_einfach"
+    test_database_url: str = (
+        "postgresql+psycopg://kirche:kirche@localhost:5432/kirche_einfach_test"
+    )
+
+    langflow_url: str = "http://localhost:7860"
+    langflow_api_key: str = ""
+    lfx_url: str = "http://localhost:6004"
+    llm_api_key: str = ""
 
 
 settings = Settings()

backend/migrations/README

@@ -0,0 +1 @@
+Generic single-database configuration.

backend/migrations/env.py

@@ -0,0 +1,84 @@
+from logging.config import fileConfig
+
+from sqlalchemy import engine_from_config
+from sqlalchemy import pool
+
+from alembic import context
+
+# this is the Alembic Config object, which provides
+# access to the values within the .ini file in use.
+config = context.config
+
+# Interpret the config file for Python logging.
+# This line sets up loggers basically.
+if config.config_file_name is not None:
+    fileConfig(config.config_file_name)
+
+# add your model's MetaData object here
+# for 'autogenerate' support
+from app.models import *  # noqa: F401,F403 - register all tables
+from app.settings import settings
+from sqlmodel import SQLModel
+
+target_metadata = SQLModel.metadata
+
+# The URL always comes from settings (repo-root .env or environment),
+# alembic.ini's sqlalchemy.url is only a fallback placeholder.
+config.set_main_option("sqlalchemy.url", settings.database_url)
+
+# other values from the config, defined by the needs of env.py,
+# can be acquired:
+# my_important_option = config.get_main_option("my_important_option")
+# ... etc.
+
+
+def run_migrations_offline() -> None:
+    """Run migrations in 'offline' mode.
+
+    This configures the context with just a URL
+    and not an Engine, though an Engine is acceptable
+    here as well.  By skipping the Engine creation
+    we don't even need a DBAPI to be available.
+
+    Calls to context.execute() here emit the given string to the
+    script output.
+
+    """
+    url = config.get_main_option("sqlalchemy.url")
+    context.configure(
+        url=url,
+        target_metadata=target_metadata,
+        literal_binds=True,
+        dialect_opts={"paramstyle": "named"},
+    )
+
+    with context.begin_transaction():
+        context.run_migrations()
+
+
+def run_migrations_online() -> None:
+    """Run migrations in 'online' mode.
+
+    In this scenario we need to create an Engine
+    and associate a connection with the context.
+
+    """
+    connectable = engine_from_config(
+        config.get_section(config.config_ini_section, {}),
+        prefix="sqlalchemy.",
+        poolclass=pool.NullPool,
+    )
+
+    with connectable.connect() as connection:
+        context.configure(
+            connection=connection, target_metadata=target_metadata
+        )
+
+        with context.begin_transaction():
+            context.run_migrations()
+
+
+if context.is_offline_mode():
+    run_migrations_offline()
+else:
+    run_migrations_online()

backend/migrations/script.py.mako

@@ -0,0 +1,29 @@
+"""${message}
+
+Revision ID: ${up_revision}
+Revises: ${down_revision | comma,n}
+Create Date: ${create_date}
+
+"""
+from typing import Sequence, Union
+
+from alembic import op
+import sqlalchemy as sa
+import sqlmodel  # noqa: F401 - autogenerate renders sqlmodel.* column types
+${imports if imports else ""}
+
+# revision identifiers, used by Alembic.
+revision: str = ${repr(up_revision)}
+down_revision: Union[str, Sequence[str], None] = ${repr(down_revision)}
+branch_labels: Union[str, Sequence[str], None] = ${repr(branch_labels)}
+depends_on: Union[str, Sequence[str], None] = ${repr(depends_on)}
+
+
+def upgrade() -> None:
+    """Upgrade schema."""
+    ${upgrades if upgrades else "pass"}
+
+
+def downgrade() -> None:
+    """Downgrade schema."""
+    ${downgrades if downgrades else "pass"}

backend/migrations/versions/62ea9a5d8f9d_flow_engine_tables.py

@@ -0,0 +1,108 @@
+"""flow engine tables
+
+Revision ID: 62ea9a5d8f9d
+Revises: 
+Create Date: 2026-09-06 22:27:07.129788
+
+"""
+from typing import Sequence, Union
+
+from alembic import op
+import sqlalchemy as sa
+import sqlmodel
+
+
+# revision identifiers, used by Alembic.
+revision: str = '62ea9a5d8f9d'
+down_revision: Union[str, Sequence[str], None] = None
+branch_labels: Union[str, Sequence[str], None] = None
+depends_on: Union[str, Sequence[str], None] = None
+
+
+def upgrade() -> None:
+    """Upgrade schema."""
+    # ### commands auto generated by Alembic - please adjust! ###
+    op.create_table('flow_definitions',
+    sa.Column('id', sa.Uuid(), nullable=False),
+    sa.Column('name', sqlmodel.sql.sqltypes.AutoString(length=200), nullable=False),
+    sa.Column('description', sqlmodel.sql.sqltypes.AutoString(length=2000), nullable=False),
+    sa.Column('status', sqlmodel.sql.sqltypes.AutoString(length=20), nullable=False),
+    sa.Column('continuation_flow_id', sa.Uuid(), nullable=True),
+    sa.Column('created_at', sa.DateTime(timezone=True), nullable=True),
+    sa.ForeignKeyConstraint(['continuation_flow_id'], ['flow_definitions.id'], ),
+    sa.PrimaryKeyConstraint('id')
+    )
+    op.create_index(op.f('ix_flow_definitions_name'), 'flow_definitions', ['name'], unique=True)
+    op.create_table('flow_versions',
+    sa.Column('id', sa.Uuid(), nullable=False),
+    sa.Column('flow_id', sa.Uuid(), nullable=False),
+    sa.Column('version_no', sa.Integer(), nullable=False),
+    sa.Column('langflow_json', sa.JSON(), nullable=True),
+    sa.Column('lfx_flow_id', sqlmodel.sql.sqltypes.AutoString(length=200), nullable=True),
+    sa.Column('deployed_at', sa.DateTime(timezone=True), nullable=True),
+    sa.Column('author', sqlmodel.sql.sqltypes.AutoString(length=200), nullable=False),
+    sa.Column('created_at', sa.DateTime(timezone=True), nullable=True),
+    sa.ForeignKeyConstraint(['flow_id'], ['flow_definitions.id'], ),
+    sa.PrimaryKeyConstraint('id'),
+    sa.UniqueConstraint('flow_id', 'version_no')
+    )
+    op.create_index(op.f('ix_flow_versions_flow_id'), 'flow_versions', ['flow_id'], unique=False)
+    op.create_index(op.f('ix_flow_versions_version_no'), 'flow_versions', ['version_no'], unique=False)
+    op.create_table('flow_runs',
+    sa.Column('id', sa.Uuid(), nullable=False),
+    sa.Column('version_id', sa.Uuid(), nullable=False),
+    sa.Column('tenant_id', sqlmodel.sql.sqltypes.AutoString(length=200), nullable=False),
+    sa.Column('status', sqlmodel.sql.sqltypes.AutoString(length=30), nullable=False),
+    sa.Column('input', sa.JSON(), nullable=True),
+    sa.Column('output', sa.JSON(), nullable=True),
+    sa.Column('session_id', sqlmodel.sql.sqltypes.AutoString(length=200), nullable=True),
+    sa.Column('created_at', sa.DateTime(timezone=True), nullable=True),
+    sa.Column('finished_at', sa.DateTime(timezone=True), nullable=True),
+    sa.ForeignKeyConstraint(['version_id'], ['flow_versions.id'], ),
+    sa.PrimaryKeyConstraint('id')
+    )
+    op.create_index(op.f('ix_flow_runs_status'), 'flow_runs', ['status'], unique=False)
+    op.create_index(op.f('ix_flow_runs_tenant_id'), 'flow_runs', ['tenant_id'], unique=False)
+    op.create_index(op.f('ix_flow_runs_version_id'), 'flow_runs', ['version_id'], unique=False)
+    op.create_table('approval_tasks',
+    sa.Column('id', sa.Uuid(), nullable=False),
+    sa.Column('run_id', sa.Uuid(), nullable=False),
+    sa.Column('version_id', sa.Uuid(), nullable=False),
+    sa.Column('tenant_id', sqlmodel.sql.sqltypes.AutoString(length=200), nullable=False),
+    sa.Column('title', sqlmodel.sql.sqltypes.AutoString(length=500), nullable=False),
+    sa.Column('payload', sa.JSON(), nullable=True),
+    sa.Column('continuation_flow_id', sa.Uuid(), nullable=True),
+    sa.Column('approver', sqlmodel.sql.sqltypes.AutoString(length=200), nullable=True),
+    sa.Column('status', sqlmodel.sql.sqltypes.AutoString(length=20), nullable=False),
+    sa.Column('decision_note', sqlmodel.sql.sqltypes.AutoString(length=2000), nullable=False),
+    sa.Column('created_at', sa.DateTime(timezone=True), nullable=True),
+    sa.Column('decided_at', sa.DateTime(timezone=True), nullable=True),
+    sa.ForeignKeyConstraint(['run_id'], ['flow_runs.id'], ),
+    sa.ForeignKeyConstraint(['version_id'], ['flow_versions.id'], ),
+    sa.PrimaryKeyConstraint('id')
+    )
+    op.create_index(op.f('ix_approval_tasks_run_id'), 'approval_tasks', ['run_id'], unique=False)
+    op.create_index(op.f('ix_approval_tasks_status'), 'approval_tasks', ['status'], unique=False)
+    op.create_index(op.f('ix_approval_tasks_tenant_id'), 'approval_tasks', ['tenant_id'], unique=False)
+    op.create_index(op.f('ix_approval_tasks_version_id'), 'approval_tasks', ['version_id'], unique=False)
+    # ### end Alembic commands ###
+
+
+def downgrade() -> None:
+    """Downgrade schema."""
+    # ### commands auto generated by Alembic - please adjust! ###
+    op.drop_index(op.f('ix_approval_tasks_version_id'), table_name='approval_tasks')
+    op.drop_index(op.f('ix_approval_tasks_tenant_id'), table_name='approval_tasks')
+    op.drop_index(op.f('ix_approval_tasks_status'), table_name='approval_tasks')
+    op.drop_index(op.f('ix_approval_tasks_run_id'), table_name='approval_tasks')
+    op.drop_table('approval_tasks')
+    op.drop_index(op.f('ix_flow_runs_version_id'), table_name='flow_runs')
+    op.drop_index(op.f('ix_flow_runs_tenant_id'), table_name='flow_runs')
+    op.drop_index(op.f('ix_flow_runs_status'), table_name='flow_runs')
+    op.drop_table('flow_runs')
+    op.drop_index(op.f('ix_flow_versions_version_no'), table_name='flow_versions')
+    op.drop_index(op.f('ix_flow_versions_flow_id'), table_name='flow_versions')
+    op.drop_table('flow_versions')
+    op.drop_index(op.f('ix_flow_definitions_name'), table_name='flow_definitions')
+    op.drop_table('flow_definitions')
+    # ### end Alembic commands ###

backend/pyproject.toml

@@ -4,9 +4,12 @@ version = "0.1.0"
 description = "Kirche Einfach - KI-gestuetzte Verwaltungsplattform fuer Kirche"
 requires-python = ">=3.12"
 dependencies = [
+    "alembic>=1.14",
     "fastapi[standard]>=0.115.0",
-    "django>=5.1",
+    "httpx>=0.28",
+    "psycopg[binary]>=3.2",
     "pydantic-settings>=2.0",
+    "sqlmodel>=0.0.24",
     "uvicorn[standard]>=0.30.0",
 ]
 
@@ -17,3 +20,16 @@ build-backend = "uv_build"
 [tool.uv.build-backend]
 module-name = "app"
 module-root = ""
+
+[tool.pytest.ini_options]
+asyncio_mode = "auto"
+testpaths = ["tests"]
+
+[dependency-groups]
+dev = [
+    "lfx==1.12.0",
+    "pytest>=8",
+    "pytest-asyncio>=0.24",
+    "pytest-cov>=6",
+    "respx>=0.22",
+]

backend/tests/conftest.py

@@ -0,0 +1,69 @@
+"""Shared pytest fixtures.
+
+Requires TEST_DATABASE_URL (a dedicated Postgres database, e.g. the
+`kirche_einfach_test` database from the compose stack). The URL is mapped
+onto DATABASE_URL *before* any app module is imported, so settings and the
+alembic env both target the test database. Never point this at production.
+"""
+
+import os
+from pathlib import Path
+
+import pytest
+
+TEST_DB_URL = os.environ.get("TEST_DATABASE_URL")
+if not TEST_DB_URL:
+    raise RuntimeError(
+        "TEST_DATABASE_URL is not set. Refusing to run tests without "
+        "an explicit test database (see .env.example)."
+    )
+
+# Must precede all `app.*` imports: Settings is instantiated at import time.
+os.environ["DATABASE_URL"] = TEST_DB_URL
+
+BACKEND_DIR = Path(__file__).resolve().parent.parent
+
+
+@pytest.fixture(scope="session")
+def db_engine():
+    """Engine on the test DB, migrated to head once per session."""
+    from alembic import command as alembic_command
+    from alembic.config import Config
+
+    from app import db as app_db
+
+    app_db.reset_engine()
+    engine = app_db.get_engine()
+
+    cfg = Config()
+    cfg.set_main_option("script_location", str(BACKEND_DIR / "migrations"))
+    alembic_command.upgrade(cfg, "head")
+
+    yield engine
+
+    engine.dispose()
+    app_db.reset_engine()
+
+
+@pytest.fixture()
+def session(db_engine):
+    """Function-scoped session; tables are truncated after each test."""
+    from sqlmodel import Session, SQLModel
+
+    with Session(db_engine) as s:
+        yield s
+    with db_engine.begin() as conn:
+        for table in reversed(SQLModel.metadata.sorted_tables):
+            conn.execute(table.delete())
+
+
+@pytest.fixture()
+async def client():
+    """ASGI test client for the FastAPI app."""
+    from httpx import ASGITransport, AsyncClient
+
+    from app.main import app
+
+    transport = ASGITransport(app=app)
+    async with AsyncClient(transport=transport, base_url="http://test") as c:
+        yield c

backend/tests/test_models.py

@@ -0,0 +1,82 @@
+"""Model-level tests: defaults, constraints, JSON roundtrip, linkage."""
+
+import pytest
+from sqlalchemy.exc import IntegrityError
+from sqlmodel import select
+
+from app.models import ApprovalTask, FlowDefinition, FlowRun, FlowVersion
+
+
+def test_flow_definition_defaults(session):
+    d = FlowDefinition(name="bauvorhaben")
+    session.add(d)
+    session.commit()
+    session.refresh(d)
+    assert d.id is not None
+    assert d.status == "active"
+    assert d.continuation_flow_id is None
+    assert d.created_at is not None
+    assert d.created_at.tzinfo is not None
+
+
+def test_flow_definition_name_unique(session):
+    session.add(FlowDefinition(name="doppelt"))
+    session.commit()
+    session.add(FlowDefinition(name="doppelt"))
+    with pytest.raises(IntegrityError):
+        session.commit()
+    session.rollback()
+
+
+def test_flow_version_unique_per_flow(session):
+    d = FlowDefinition(name="v-flow")
+    session.add(d)
+    session.commit()
+    session.add(FlowVersion(flow_id=d.id, version_no=1, author="a"))
+    session.commit()
+    session.add(FlowVersion(flow_id=d.id, version_no=1, author="b"))
+    with pytest.raises(IntegrityError):
+        session.commit()
+    session.rollback()
+    session.add(FlowVersion(flow_id=d.id, version_no=2, author="b"))
+    session.commit()
+
+
+def test_flow_version_json_roundtrip(session):
+    payload = {"data": {"nodes": [{"id": "n1"}], "edges": []}, "name": "x"}
+    d = FlowDefinition(name="json-flow")
+    session.add(d)
+    session.commit()
+    v = FlowVersion(flow_id=d.id, version_no=1, langflow_json=payload)
+    session.add(v)
+    session.commit()
+    session.refresh(v)
+    assert v.langflow_json == payload
+    assert v.deployed_at is None
+    assert v.lfx_flow_id is None
+
+
+def test_run_and_task_linkage_with_tenant_default(session):
+    d = FlowDefinition(name="linked")
+    session.add(d)
+    session.commit()
+    v = FlowVersion(flow_id=d.id, version_no=1)
+    session.add(v)
+    session.commit()
+    run = FlowRun(version_id=v.id, input={"a": 1})
+    session.add(run)
+    session.commit()
+    task = ApprovalTask(run_id=run.id, version_id=v.id, title="bitte pruefen")
+    session.add(task)
+    session.commit()
+
+    assert run.tenant_id == "default"
+    assert run.status == "running"
+    assert task.tenant_id == "default"
+    assert task.status == "open"
+
+    runs = session.exec(select(FlowRun).where(FlowRun.version_id == v.id)).all()
+    assert len(runs) == 1
+    tasks = session.exec(select(ApprovalTask).where(ApprovalTask.run_id == run.id)).all()
+    assert len(tasks) == 1
+    assert tasks[0].payload == {}