diff --git a/backend/app/flows/api.py b/backend/app/flows/api.py
index a18d4a9..aa155b9 100644
--- a/backend/app/flows/api.py
+++ b/backend/app/flows/api.py
@@ -34,6 +34,8 @@ from .lfx_client import (
 from .schemas import (
     ApprovalCreate,
     ApprovalRead,
+    DecisionRead,
+    DecisionRequest,
     FlowDefinitionCreate,
     FlowDefinitionRead,
     FlowImportRead,
@@ -290,9 +292,13 @@ async def _run_stream(session: Session, lfx: LfxClient, version, data: RunReques
 
 
 @flows_router.get("/{flow_id}/runs", response_model=list[RunRead])
-def list_runs(flow_id: UUID, session: Session = Depends(get_db)):
+def list_runs(
+    flow_id: UUID,
+    tenant_id: str | None = Query(default=None),
+    session: Session = Depends(get_db),
+):
     try:
-        return [_read_run(r) for r in store.list_runs(session, flow_id)]
+        return [_read_run(r) for r in store.list_runs(session, flow_id, tenant_id)]
     except store.NotFoundError as exc:
         raise HTTPException(status_code=404, detail=str(exc)) from exc
 
@@ -350,11 +356,19 @@ async def import_flow(
 
 
 @flows_router.get("/runs/{run_id}", response_model=RunRead)
-def get_run(run_id: UUID, session: Session = Depends(get_db)):
+def get_run(
+    run_id: UUID,
+    tenant_id: str | None = Query(default=None),
+    session: Session = Depends(get_db),
+):
+    """Read a run. With tenant_id, cross-tenant reads 404 (v1 scoping)."""
     try:
-        return _read_run(store.get_run(session, run_id))
+        run = store.get_run(session, run_id)
     except store.NotFoundError as exc:
         raise HTTPException(status_code=404, detail=str(exc)) from exc
+    if tenant_id is not None and run.tenant_id != tenant_id:
+        raise HTTPException(status_code=404, detail=f"run {run_id} not found")
+    return _read_run(run)
 
 
 @approvals_router.post("", response_model=ApprovalRead, status_code=201)
@@ -376,3 +390,66 @@ def list_approvals(
     session: Session = Depends(get_db),
 ):
     return [_read_task(t) for t in store.list_approval_tasks(session, tenant_id)]
+
+
+@approvals_router.post("/{task_id}/decision", response_model=DecisionRead)
+async def decide_approval(
+    task_id: UUID,
+    data: DecisionRequest,
+    session: Session = Depends(get_db),
+    lfx: LfxClient = Depends(get_lfx),
+):
+    """Decide an open task. Approve starts the continuation flow (if any)."""
+    try:
+        task = store.get_task(session, task_id)
+    except store.NotFoundError as exc:
+        raise HTTPException(status_code=404, detail=str(exc)) from exc
+
+    # Resolve the continuation first: bad references fail before any state change.
+    continuation_version = None
+    if data.decision == "approve" and task.continuation_flow_id is not None:
+        try:
+            continuation_version = store.get_latest_deployed_version(
+                session, task.continuation_flow_id
+            )
+        except (store.NotFoundError, store.InvalidError) as exc:
+            raise HTTPException(status_code=422, detail=str(exc)) from exc
+    try:
+        task = store.decide_task(
+            session,
+            task,
+            decision="approved" if data.decision == "approve" else "rejected",
+            approver=data.approver,
+            note=data.note,
+        )
+    except store.ConflictError as exc:
+        raise HTTPException(status_code=409, detail=str(exc)) from exc
+
+    # Note: the decision is committed before the continuation runs. If LFX is
+    # down, the task stays decided and the continuation can be started
+    # manually from the preserved task payload.
+    continuation_run = None
+    if continuation_version is not None:
+        payload = task.payload
+        if isinstance(payload.get("facts"), dict):
+            payload = payload["facts"]
+        try:
+            continuation_run = await runner.execute_run(
+                session,
+                lfx,
+                continuation_version,
+                payload=payload,
+                tenant_id=task.tenant_id,
+                session_id=f"continuation-of-{task.run_id}",
+                callback_base_url=data.callback_base_url or settings.callback_base_url,
+            )
+        except LfxNotFound as exc:
+            raise HTTPException(status_code=502, detail=f"LFX drift: {exc}") from exc
+        except LfxUnavailable as exc:
+            raise HTTPException(status_code=503, detail=str(exc)) from exc
+        except LfxError as exc:
+            raise HTTPException(status_code=502, detail=str(exc)) from exc
+    return DecisionRead(
+        task=_read_task(task),
+        continuation_run=_read_run(continuation_run) if continuation_run else None,
+    )
diff --git a/backend/app/flows/schemas.py b/backend/app/flows/schemas.py
index 84270b5..c024c34 100644
--- a/backend/app/flows/schemas.py
+++ b/backend/app/flows/schemas.py
@@ -98,3 +98,15 @@ class FlowImportRequest(BaseModel):
 class FlowImportRead(BaseModel):
     definition: FlowDefinitionRead
     version: FlowVersionRead
+
+
+class DecisionRequest(BaseModel):
+    decision: str = Field(pattern="^(approve|reject)$")
+    approver: str = Field(default="", max_length=200)
+    note: str = Field(default="", max_length=2000)
+    callback_base_url: str | None = None
+
+
+class DecisionRead(BaseModel):
+    task: ApprovalRead
+    continuation_run: RunRead | None
diff --git a/backend/app/flows/store.py b/backend/app/flows/store.py
index ac9527c..c5039f0 100644
--- a/backend/app/flows/store.py
+++ b/backend/app/flows/store.py
@@ -174,16 +174,19 @@ def get_run(session: Session, run_id: UUID) -> FlowRun:
     return run
 
 
-def list_runs(session: Session, flow_id: UUID) -> list[FlowRun]:
+def list_runs(
+    session: Session, flow_id: UUID, tenant_id: str | None = None
+) -> list[FlowRun]:
     get_definition(session, flow_id)
-    return list(
-        session.exec(
-            select(FlowRun)
-            .join(FlowVersion, FlowVersion.id == FlowRun.version_id)
-            .where(FlowVersion.flow_id == flow_id)
-            .order_by(FlowRun.created_at.desc())
-        ).all()
+    query = (
+        select(FlowRun)
+        .join(FlowVersion, FlowVersion.id == FlowRun.version_id)
+        .where(FlowVersion.flow_id == flow_id)
+        .order_by(FlowRun.created_at.desc())
     )
+    if tenant_id is not None:
+        query = query.where(FlowRun.tenant_id == tenant_id)
+    return list(session.exec(query).all())
 
 
 def create_approval_task(session: Session, data: ApprovalCreate) -> ApprovalTask:
@@ -223,3 +226,33 @@ def list_approval_tasks(session: Session, tenant_id: str | None = None) -> list[
     if tenant_id is not None:
         query = query.where(ApprovalTask.tenant_id == tenant_id)
     return list(session.exec(query).all())
+
+
+def get_task(session: Session, task_id: UUID) -> ApprovalTask:
+    task = session.get(ApprovalTask, task_id)
+    if task is None:
+        raise NotFoundError(f"approval task {task_id} not found")
+    return task
+
+
+def decide_task(
+    session: Session,
+    task: ApprovalTask,
+    *,
+    decision: str,
+    approver: str = "",
+    note: str = "",
+) -> ApprovalTask:
+    """Approve or reject an open task. Decided tasks are immutable (409)."""
+    if task.status != "open":
+        raise ConflictError(f"task {task.id} is already {task.status}")
+    if decision not in ("approved", "rejected"):
+        raise InvalidError(f"unknown decision {decision!r}")
+    task.status = decision
+    task.approver = approver
+    task.decision_note = note
+    task.decided_at = datetime.now(timezone.utc)
+    session.add(task)
+    session.commit()
+    session.refresh(task)
+    return task
diff --git a/backend/tests/test_approvals.py b/backend/tests/test_approvals.py
new file mode 100644
index 0000000..bc8729d
--- /dev/null
+++ b/backend/tests/test_approvals.py
@@ -0,0 +1,255 @@
+"""Step 5 tests: decisions + continuations, tenant isolation, error paths."""
+
+import json
+from pathlib import Path
+from uuid import UUID, uuid4
+
+from app.flows.schemas import ApprovalCreate
+
+FIXTURES = Path(__file__).parent / "fixtures" / "flows"
+
+
+def load_fixture(name: str) -> dict:
+    return json.loads((FIXTURES / name).read_text())
+
+
+async def _create_flow(client, name):
+    response = await client.post("/api/flows", json={"name": name})
+    assert response.status_code == 201, response.text
+    return response.json()
+
+
+async def _version_and_deploy(client, flow_id, fixture="simple_rule.json"):
+    response = await client.post(
+        f"/api/flows/{flow_id}/versions",
+        json={"langflow_json": load_fixture(fixture)},
+    )
+    assert response.status_code == 201, response.text
+    response = await client.post(f"/api/flows/{flow_id}/versions/1/deploy")
+    assert response.status_code == 200, response.text
+    return response.json()
+
+
+async def _handoff_task(client, live_server, continuation_flow_id=None):
+    """Run approval_handoff over threshold; returns (run, task)."""
+    flow = await _create_flow(client, f"handoff-{uuid4().hex[:8]}")
+    await _version_and_deploy(client, flow["id"], fixture="approval_handoff.json")
+    body = {
+        "input": {"betrag": 250000, "schwelle": 200000},
+        "callback_base_url": live_server,
+    }
+    if continuation_flow_id is not None:
+        body["continuation_flow_id"] = continuation_flow_id
+    run = (
+        await client.post(f"/api/flows/{flow['id']}/run", json=body)
+    ).json()
+    assert run["status"] == "pending_approval"
+    tasks = (await client.get("/api/approvals")).json()
+    task = next(t for t in tasks if t["run_id"] == run["id"])
+    return run, task
+
+
+async def test_approve_without_continuation(client, lfx_server, live_server):
+    _, task = await _handoff_task(client, live_server)
+    response = await client.post(
+        f"/api/approvals/{task['id']}/decision",
+        json={"decision": "approve", "approver": "sachbearbeiter", "note": "ok"},
+    )
+    assert response.status_code == 200, response.text
+    body = response.json()
+    assert body["task"]["status"] == "approved"
+    assert body["task"]["approver"] == "sachbearbeiter"
+    assert body["task"]["decided_at"] is not None
+    assert body["continuation_run"] is None
+
+
+async def test_approve_with_continuation_runs_facts(client, lfx_server, live_server):
+    cont = await _create_flow(client, f"cont-{uuid4().hex[:8]}")
+    await _version_and_deploy(client, cont["id"], fixture="simple_rule.json")
+
+    _, task = await _handoff_task(
+        client, live_server, continuation_flow_id=cont["id"]
+    )
+    assert task["continuation_flow_id"] == cont["id"]
+
+    response = await client.post(
+        f"/api/approvals/{task['id']}/decision",
+        json={"decision": "approve", "approver": "chef"},
+    )
+    assert response.status_code == 200, response.text
+    body = response.json()
+    assert body["task"]["status"] == "approved"
+    cont_run = body["continuation_run"]
+    assert cont_run is not None
+    assert cont_run["status"] == "completed"
+    assert cont_run["tenant_id"] == task["tenant_id"]
+    # Facts (betrag 250000 > Schwelle) flowed into the continuation.
+    assert "Sonderfall" in cont_run["output"]["result"]
+
+
+async def test_reject_task(client, lfx_server, live_server):
+    _, task = await _handoff_task(client, live_server)
+    response = await client.post(
+        f"/api/approvals/{task['id']}/decision",
+        json={"decision": "reject", "approver": "chef", "note": "zu teuer"},
+    )
+    assert response.status_code == 200, response.text
+    body = response.json()
+    assert body["task"]["status"] == "rejected"
+    assert body["task"]["decision_note"] == "zu teuer"
+    assert body["continuation_run"] is None
+
+
+async def test_decision_guards(client, lfx_server, live_server):
+    _, task = await _handoff_task(client, live_server)
+    url = f"/api/approvals/{task['id']}/decision"
+
+    response = await client.post(url, json={"decision": "approve"})
+    assert response.status_code == 200
+    response = await client.post(url, json={"decision": "reject"})
+    assert response.status_code == 409
+
+    response = await client.post(
+        f"/api/approvals/{uuid4()}/decision", json={"decision": "approve"}
+    )
+    assert response.status_code == 404
+
+    _, task2 = await _handoff_task(client, live_server)
+    response = await client.post(
+        f"/api/approvals/{task2['id']}/decision", json={"decision": "maybe"}
+    )
+    assert response.status_code == 422
+
+    response = await client.post(
+        f"/api/approvals/{task2['id']}/decision",
+        json={"decision": "approve", "note": "x"},
+    )
+    # continuation unset -> fine, resolves to no continuation run
+    assert response.status_code == 200
+
+
+async def test_decision_bad_continuation_reference(client, session):
+    from app.flows import store as flow_store
+
+    flow = await _create_flow(client, f"badcont-{uuid4().hex[:8]}")
+    version = (
+        await client.post(
+            f"/api/flows/{flow['id']}/versions",
+            json={"langflow_json": load_fixture("simple_rule.json")},
+        )
+    ).json()
+    run = flow_store.create_run(
+        session,
+        flow_store.get_version(session, UUID(version["id"])),
+        input={},
+    )
+    task = flow_store.create_approval_task(
+        session, ApprovalCreate(run_id=run.id, title="t")
+    )
+    # plant unknown continuation directly (store allows it pre-validation)
+    task.continuation_flow_id = uuid4()
+    session.add(task)
+    session.commit()
+
+    response = await client.post(
+        f"/api/approvals/{task.id}/decision", json={"decision": "approve"}
+    )
+    assert response.status_code == 422
+
+
+async def test_tenant_isolation(client, lfx_server):
+    flow = await _create_flow(client, f"tenant-{uuid4().hex[:8]}")
+    await _version_and_deploy(client, flow["id"])
+
+    for tenant in ("pfarramt-a", "pfarramt-b"):
+        response = await client.post(
+            f"/api/flows/{flow['id']}/run",
+            json={"input": {"betrag": 1}, "tenant_id": tenant},
+        )
+        assert response.status_code == 200
+
+    response = await client.get(
+        f"/api/flows/{flow['id']}/runs", params={"tenant_id": "pfarramt-a"}
+    )
+    runs_a = response.json()
+    assert len(runs_a) == 1
+    assert runs_a[0]["tenant_id"] == "pfarramt-a"
+
+    response = await client.get(f"/api/flows/{flow['id']}/runs")
+    assert len(response.json()) == 2
+
+    # Cross-tenant read with scoping 404s.
+    response = await client.get(
+        f"/api/flows/runs/{runs_a[0]['id']}", params={"tenant_id": "pfarramt-b"}
+    )
+    assert response.status_code == 404
+    response = await client.get(
+        f"/api/flows/runs/{runs_a[0]['id']}", params={"tenant_id": "pfarramt-a"}
+    )
+    assert response.status_code == 200
+
+
+async def test_lfx_down_maps_to_503(client, lfx_server, monkeypatch):
+    from app.settings import settings
+
+    flow = await _create_flow(client, f"down-{uuid4().hex[:8]}")
+    await client.post(
+        f"/api/flows/{flow['id']}/versions",
+        json={"langflow_json": load_fixture("simple_rule.json")},
+    )
+    monkeypatch.setattr(settings, "lfx_url", "http://127.0.0.1:9")
+    response = await client.post(f"/api/flows/{flow['id']}/versions/1/deploy")
+    assert response.status_code == 503
+
+    # Deploy for real, then break the URL again for the run call.
+    monkeypatch.setattr(settings, "lfx_url", lfx_server)
+    deployed = await client.post(f"/api/flows/{flow['id']}/versions/1/deploy")
+    assert deployed.status_code == 200
+    monkeypatch.setattr(settings, "lfx_url", "http://127.0.0.1:9")
+    response = await client.post(
+        f"/api/flows/{flow['id']}/run", json={"input": {"betrag": 1}}
+    )
+    assert response.status_code == 503
+
+
+async def test_lfx_drift_maps_to_502(client, lfx_server):
+    from app.flows.lfx_client import LfxClient
+    from app.settings import settings
+
+    flow = await _create_flow(client, f"drift-{uuid4().hex[:8]}")
+    deployed = await _version_and_deploy(client, flow["id"])
+    await LfxClient(settings.lfx_url, api_key=settings.lfx_api_key or None).delete_flow(
+        deployed["lfx_flow_id"]
+    )
+    response = await client.post(
+        f"/api/flows/{flow['id']}/run", json={"input": {"betrag": 1}}
+    )
+    assert response.status_code == 502
+
+
+async def test_corrupt_flow_json_deploy_maps_to_422(client, lfx_server):
+    flow = await _create_flow(client, f"corrupt-{uuid4().hex[:8]}")
+    bogus = {
+        "name": "bogus",
+        "data": {
+            "nodes": [
+                {
+                    "id": "Nope-x1",
+                    "data": {
+                        "id": "Nope-x1",
+                        "type": "Nope",
+                        "showNode": True,
+                        "node": {"template": {}, "outputs": []},
+                    },
+                    "type": "genericNode",
+                }
+            ],
+            "edges": [],
+        },
+    }
+    response = await client.post(
+        f"/api/flows/{flow['id']}/versions", json={"langflow_json": bogus}
+    )
+    assert response.status_code == 201, response.text
+    response = await client.post(f"/api/flows/{flow['id']}/versions/1/deploy")
+    assert response.status_code == 422