M41: harden trust boundaries and delivery

backend/app/api/routers/knowledge.py

@@ -1,20 +1,32 @@
 from __future__ import annotations
 
+import hashlib
 import uuid
 from typing import Literal
 
-from fastapi import APIRouter, Depends, HTTPException
+from fastapi import APIRouter, Depends, HTTPException, Request, status
 from pydantic import BaseModel, Field
 from sqlalchemy import select
 from sqlalchemy.orm import Session
 
 from app.api.deps import get_current_user, get_db
+from app.core.config import get_settings
+from app.core.ratelimit import SlidingWindowLimiter
 from app.models.audit import AuditEvent
 from app.schemas import CurrentUser
 from app.services.audit import record_audit_event
 from app.services.knowledge import GroundedAnswer, KnowledgeHealth, get_knowledge_provider
 
 router = APIRouter(prefix="/api/v1/knowledge", tags=["knowledge"])
+settings = get_settings()
+_question_limiter = (
+    SlidingWindowLimiter(
+        max_requests=settings.knowledge_max_requests,
+        window_seconds=settings.knowledge_rate_limit_window_seconds,
+    )
+    if settings.knowledge_max_requests > 0
+    else None
+)
 
 SupportedLanguage = Literal["nl-BE", "en-GB", "fr-BE"]
 
@@ -32,9 +44,29 @@ class KnowledgeFeedbackRequest(BaseModel):
 @router.post("/questions", response_model=GroundedAnswer)
 def ask_question(
     body: AskQuestionRequest,
+    request: Request,
     db: Session = Depends(get_db),
     user: CurrentUser = Depends(get_current_user),
 ) -> GroundedAnswer:
+    if _question_limiter is not None:
+        forwarded = request.headers.get("x-forwarded-for", "")
+        client_ip = (
+            forwarded.split(",")[-1].strip()
+            if forwarded
+            else request.client.host if request.client else "unknown"
+        )
+        token = request.cookies.get(settings.session_cookie_name, "")
+        session_key = hashlib.sha256(token.encode("utf-8")).hexdigest()
+        retry_after = max(
+            _question_limiter.consume(f"ip:{client_ip}"),
+            _question_limiter.consume(f"session:{session_key}"),
+        )
+        if retry_after:
+            raise HTTPException(
+                status_code=status.HTTP_429_TOO_MANY_REQUESTS,
+                detail="Too many knowledge questions. Try again later.",
+                headers={"Retry-After": str(retry_after)},
+            )
     correlation_id = str(uuid.uuid4())
     provider = get_knowledge_provider()
     answer = provider.ask(body.question, correlation_id, body.language)