fix: resolve real visitor IP via CF-Connecting-IP for per-IP limiting

websocket.client.host is always the Cloudflare Tunnel machine's LAN IP for
every internet-facing connection (the tunnel runs on a separate machine and
terminates TLS there), which collapsed per-IP rate limiting into a single
shared bucket for all remote visitors — the exact gap flagged in review.

Cloudflare's edge sets CF-Connecting-IP itself, overwriting any
client-supplied value, so it's safe to trust when present. Falls back to
the raw socket peer for direct LAN/local access.

backend/app/rate_limit.py

@@ -1,5 +1,24 @@
 import time
 from collections import defaultdict
+from typing import Mapping
+
+
+def resolve_client_ip(headers: Mapping[str, str], direct_host: str | None) -> str:
+    """Resolves the real visitor IP for per-IP rate limiting.
+
+    The App CT sits behind a Cloudflare Tunnel that runs on a separate
+    machine (see README Architecture) — every internet-facing connection's
+    raw TCP peer is that tunnel machine, not the visitor, which would
+    collapse per-IP limiting to a single shared bucket for all remote
+    traffic. Cloudflare's edge sets `CF-Connecting-IP` itself, stripping any
+    client-supplied value first, so it's safe to trust here. Direct
+    LAN/local access (no Cloudflare in front, e.g. local dev) has no such
+    header and falls back to the raw socket peer.
+    """
+    forwarded = headers.get("cf-connecting-ip")
+    if forwarded:
+        return forwarded
+    return direct_host or "unknown"
 
 
 class RateLimiter:

backend/app/ws.py

@@ -36,7 +36,7 @@ from app.models.contact_session import ContactSession
 from app.models.entity import Entity
 from app.models.entity_sighting import EntitySighting
 from app.models.event import Event
-from app.rate_limit import RateLimiter
+from app.rate_limit import RateLimiter, resolve_client_ip
 from app.telemetry import detect_wire_spike, sample_network
 from app.tts.piper import synthesize_spirit_voice
 from app.tts.voices import pick_voice
@@ -103,7 +103,8 @@ def serialize_entity(entity: Entity) -> dict:
 
 
 def _client_ip(websocket: WebSocket) -> str:
-    return websocket.client.host if websocket.client else "unknown"
+    host = websocket.client.host if websocket.client else None
+    return resolve_client_ip(websocket.headers, host)
 
 
 async def _authenticate(websocket: WebSocket) -> uuid.UUID | None:

backend/tests/test_rate_limit.py

@@ -1,6 +1,6 @@
 from unittest.mock import patch
 
-from app.rate_limit import RateLimiter
+from app.rate_limit import RateLimiter, resolve_client_ip
 
 
 def test_allows_up_to_limit_then_blocks():
@@ -29,3 +29,20 @@ def test_hits_expire_after_window_elapses():
     with patch("app.rate_limit.time.monotonic", return_value=111.0):
         # 11 seconds later, both prior hits (at t=100) are older than window_start (111 - 10 = 101)
         assert limiter.allow("user-1") is True
+
+
+def test_resolve_client_ip_prefers_cf_connecting_ip_over_socket_peer():
+    # The App CT sits behind a Cloudflare Tunnel on a separate machine — the
+    # raw socket peer is always the tunnel, never the visitor, for every
+    # internet-facing request.
+    headers = {"cf-connecting-ip": "203.0.113.7"}
+    assert resolve_client_ip(headers, "10.30.20.1") == "203.0.113.7"
+
+
+def test_resolve_client_ip_falls_back_to_socket_peer_without_header():
+    # Direct LAN/local access (no Cloudflare in front) has no such header.
+    assert resolve_client_ip({}, "10.30.20.1") == "10.30.20.1"
+
+
+def test_resolve_client_ip_falls_back_to_unknown_with_no_peer_or_header():
+    assert resolve_client_ip({}, None) == "unknown"

backend/tests/test_ws_session.py

@@ -232,3 +232,36 @@ async def test_summon_rate_limited_per_ip_even_with_fresh_account(
         assert rejection["message"] == (
             "The veil is crowded. The spirits need a moment before another summoning."
         )
+
+
+@pytest.mark.asyncio
+async def test_summon_per_ip_bucket_follows_cf_connecting_ip_not_socket_peer(
+    sync_client, monkeypatch
+):
+    # Every connection in this test suite shares the same simulated socket
+    # peer (TestClient has no real network). Without preferring
+    # CF-Connecting-IP, distinct visitors behind the Cloudflare Tunnel would
+    # collapse into one shared per-IP bucket — this proves they don't.
+    monkeypatch.setattr(
+        app.ws, "summon_ip_limiter", RateLimiter(max_requests=1, window_seconds=60)
+    )
+
+    token_a = _login(sync_client, "cf-ip-a")
+    with sync_client.websocket_connect(
+        "/ws/session",
+        headers={"cookie": f"qm_session={token_a}", "cf-connecting-ip": "203.0.113.1"},
+    ) as ws:
+        _read_until(ws, "session")
+        ws.send_json({"type": "summon"})
+        _read_until(ws, "entity")  # spends visitor A's per-IP slot only
+
+    token_b = _login(sync_client, "cf-ip-b")
+    with sync_client.websocket_connect(
+        "/ws/session",
+        headers={"cookie": f"qm_session={token_b}", "cf-connecting-ip": "203.0.113.2"},
+    ) as ws:
+        _read_until(ws, "session")
+        ws.send_json({"type": "summon"})
+        # A different visitor IP behind the same tunnel — must not be
+        # rejected by visitor A's already-spent bucket.
+        _read_until(ws, "entity")