feat: Langflow authoring pipeline with tests

- LangflowClient (list/export, x-api-key auth, error mapping)
- import_from_langflow: export -> versioned definition -> LFX deploy
- POST /api/flows/import, GET /api/flows/langflow/available
- scripts/deploy_flow.py CLI
- 25 tests green (Langflow faked via dependency override + respx
  client tests; respx passthrough proven unreliable for LFX traffic)

backend/app/flows/api.py

@@ -15,6 +15,13 @@ from app.db import get_engine, get_session
 from app.settings import settings
 
 from . import runner, store
+from .deploy import import_from_langflow
+from .langflow_client import (
+    LangflowClient,
+    LangflowError,
+    LangflowNotFound,
+    LangflowUnavailable,
+)
 from .lfx_client import (
     LfxClient,
     LfxConflict,
@@ -29,6 +36,8 @@ from .schemas import (
     ApprovalRead,
     FlowDefinitionCreate,
     FlowDefinitionRead,
+    FlowImportRead,
+    FlowImportRequest,
     FlowVersionCreate,
     FlowVersionRead,
     RunRead,
@@ -47,6 +56,12 @@ def get_lfx() -> LfxClient:
     return LfxClient(settings.lfx_url, api_key=settings.lfx_api_key or None)
 
 
+def get_langflow() -> LangflowClient:
+    return LangflowClient(
+        settings.langflow_url, api_key=settings.langflow_api_key or ""
+    )
+
+
 def _read_definition(d) -> FlowDefinitionRead:
     return FlowDefinitionRead(
         id=d.id,
@@ -282,6 +297,58 @@ def list_runs(flow_id: UUID, session: Session = Depends(get_db)):
         raise HTTPException(status_code=404, detail=str(exc)) from exc
 
 
+@flows_router.get("/langflow/available")
+async def list_langflow_flows(langflow: LangflowClient = Depends(get_langflow)):
+    """Browse flows on the Langflow authoring server (admin import source)."""
+    try:
+        return await langflow.list_flows()
+    except LangflowUnavailable as exc:
+        raise HTTPException(status_code=503, detail=str(exc)) from exc
+    except LangflowError as exc:
+        raise HTTPException(status_code=502, detail=str(exc)) from exc
+
+
+@flows_router.post("/import", response_model=FlowImportRead, status_code=201)
+async def import_flow(
+    data: FlowImportRequest,
+    session: Session = Depends(get_db),
+    langflow: LangflowClient = Depends(get_langflow),
+    lfx: LfxClient = Depends(get_lfx),
+):
+    """Import a flow from Langflow: export -> version -> (deploy to LFX)."""
+    try:
+        definition, version = await import_from_langflow(
+            session,
+            langflow,
+            lfx,
+            data.langflow_flow_id,
+            name=data.name,
+            author=data.author,
+            deploy=data.deploy,
+        )
+    except LangflowNotFound as exc:
+        raise HTTPException(status_code=404, detail=str(exc)) from exc
+    except LangflowUnavailable as exc:
+        raise HTTPException(status_code=503, detail=str(exc)) from exc
+    except LangflowError as exc:
+        raise HTTPException(status_code=502, detail=str(exc)) from exc
+    except store.ConflictError as exc:
+        raise HTTPException(status_code=409, detail=str(exc)) from exc
+    except store.InvalidError as exc:
+        raise HTTPException(status_code=422, detail=str(exc)) from exc
+    except LfxInvalidFlow as exc:
+        raise HTTPException(status_code=422, detail=str(exc)) from exc
+    except LfxConflict as exc:
+        raise HTTPException(status_code=409, detail=str(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 FlowImportRead(
+        definition=_read_definition(definition), version=_read_version(version)
+    )
+
+
 @flows_router.get("/runs/{run_id}", response_model=RunRead)
 def get_run(run_id: UUID, session: Session = Depends(get_db)):
     try: