fix: --stall-after Budget der Rettungsstation client-kumulativ zählen

Der Testschalter zählte bisher pro Anfrage, sodass eine Lampe nach ihrem
Empfangs-Timeout einfach per Range neu verband und ein frisches Budget bekam
– am EVK reichten fünf Reconnects, um trotz --stall-after das komplette
Image zu übertragen. Station verfolgt die ausgelieferten Bytes jetzt pro
Client-IP über alle Anfragen hinweg (Station.reserve_stall_bytes, unter dem
bestehenden Lock), sodass kein erneutes Verbinden das Budget auffüllt.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

tools/station/tests/test_server.py

@@ -278,6 +278,62 @@ def test_stall_after_stops_sending_but_keeps_the_connection(tmp_path):
         s.stop()
 
 
+def test_stall_after_budget_survives_a_resumed_request(tmp_path):
+    """--stall-after must stop a client for good, not just for one request.
+
+    On real hardware, a lamp whose download stalls hits its own receive timeout, gives up
+    on the connection, and opens a new one with a Range header picking up right where it
+    left off - exactly what test_stall_after_stops_sending_but_keeps_the_connection above
+    exercises for a single request. A per-request byte counter would hand that resumed
+    request a brand-new --stall-after allowance, so the "stall" would only ever delay
+    delivery instead of actually stopping it - which is what was observed on the EVK: the
+    server stalled at 65536 bytes each time, but the lamp reconnected five times and walked
+    away with the complete image. This test reproduces that reconnect and checks that the
+    second, resumed request gets no further bytes at all.
+    """
+    s = Station(tmp_path, "--stall-after", "1000")
+    try:
+        make_image(s.image_dir / "ninlight_evk_ota.img", "evk", "1.0.0", b"y" * 200000)
+
+        # First request: burns through the whole --stall-after budget, then the server
+        # holds the connection open and sends nothing further.
+        sock = socket.create_connection(("127.0.0.1", s.port), timeout=5)
+        sock.sendall(b"GET /ninlight_evk_ota.img HTTP/1.1\r\nHost: x\r\n\r\n")
+        got = b""
+        sock.settimeout(2)
+        try:
+            while len(got) < 200000:
+                chunk = sock.recv(65536)
+                if not chunk:
+                    break
+                got += chunk
+        except socket.timeout:
+            pass
+        assert len(got) < 20000  # far less than the full image, same bound as above
+        sock.close()  # the lamp's watchdog gives up and reconnects, like on real hardware
+
+        # Second request, resuming with Range exactly like a real lamp would. This
+        # client's cumulative budget is already spent, so it must get zero more bytes of
+        # body - not a fresh --stall-after allowance just because it's a new connection.
+        sock2 = socket.create_connection(("127.0.0.1", s.port), timeout=5)
+        sock2.sendall(b"GET /ninlight_evk_ota.img HTTP/1.1\r\nHost: x\r\nRange: bytes=1000-\r\n\r\n")
+        sock2.settimeout(2)
+        header = b""
+        while b"\r\n\r\n" not in header:
+            header += sock2.recv(4096)
+        assert b" 206 " in header.split(b"\r\n", 1)[0]
+        body_after_header = header.split(b"\r\n\r\n", 1)[1]
+        assert body_after_header == b"", "resumed request must not receive any body bytes"
+        try:
+            more = sock2.recv(1)
+        except socket.timeout:
+            more = None
+        assert more in (None, b""), "server sent data after the client's stall budget was spent"
+        sock2.close()
+    finally:
+        s.stop()
+
+
 def test_concurrent_downloads_are_all_recorded(station):
     """Several lamps hitting the station at once must not lose or corrupt status.json.