qa: Intermittent failure in `p2p_eviction.py` #36533

https://github.com/bitcoin/bitcoin/actions/runs/38678030191/job/116235980574:

367/497 - p2p_eviction.py failed (exit code 1), Duration: 1 s

stdout:
2026-10-15T03:57:38.655914Z TestFramework (INFO): PRNG seed is: 7665210796316295926
2026-10-15T03:57:38.706216Z TestFramework (INFO): Initializing test directory /tmp/test_runner_₿_🏃_20261015_035617/p2p_eviction_126
2026-10-15T03:57:38.989690Z TestFramework (INFO): Create 4 peers and protect them from eviction by sending us a block
2026-10-15T03:57:39.416125Z TestFramework (INFO): Create 5 slow-pinging peers, making them eviction candidates
2026-10-15T03:57:39.930086Z TestFramework (INFO): Create 4 peers and protect them from eviction by sending us a tx
2026-10-15T03:57:40.344877Z TestFramework (INFO): Create 8 peers and protect them from eviction by having faster pings
2026-10-15T03:57:40.361164Z TestFramework (INFO): Create peer that triggers the eviction mechanism
2026-10-15T03:57:40.474285Z TestFramework (INFO): Test that one peer was evicted
2026-10-15T03:57:40.475103Z TestFramework (ERROR): Unexpected exception:
Traceback (most recent call last):
  File "/home/runner/work/bitcoin/bitcoin/test/functional/test_framework/test_framework.py", line 146, in main
    self.run_test()
  File "/home/runner/work/bitcoin/bitcoin/ci_build/test/functional/p2p_eviction.py", line 120, in run_test
    assert_equal(len(evicted_peers), 1)
  File "/home/runner/work/bitcoin/bitcoin/test/functional/test_framework/util.py", line 95, in assert_equal
    raise AssertionError("not(%s)" % " == ".join(str(arg) for arg in (thing1, thing2) + args))
AssertionError: not(0 == 1)
2026-10-15T03:57:40.526095Z TestFramework (INFO): Not stopping nodes as test failed. The dangling processes will be cleaned up later.
2026-10-15T03:57:40.526190Z TestFramework (WARNING): Not cleaning up dir /tmp/test_runner_₿_🏃_20261015_035617/p2p_eviction_126
2026-10-15T03:57:40.526218Z TestFramework (ERROR): Test failed. Test logging available at /tmp/test_runner_₿_🏃_20261015_035617/p2p_eviction_126/test_framework.log
2026-10-15T03:57:40.526288Z TestFramework (ERROR): 
2026-10-15T03:57:40.526345Z TestFramework (ERROR): Hint: Call /home/runner/work/bitcoin/bitcoin/test/functional/combine_logs.py '/tmp/test_runner_₿_🏃_20261015_035617/p2p_eviction_126' to consolidate all logs
2026-10-15T03:57:40.526364Z TestFramework (ERROR): 
2026-10-15T03:57:40.526379Z TestFramework (ERROR): If this failure happened unexpectedly or intermittently, please file a bug and provide a link or upload of the combined log.
2026-10-15T03:57:40.526412Z TestFramework (ERROR): https://github.com/bitcoin/bitcoin/issues
2026-10-15T03:57:40.526428Z TestFramework (ERROR): 


stderr:
[node 0] Cleaning up leftover process

Interesting. I would have assumed that the disconnect from the eviction is synchronised from the connection's double-ping. However, those are different sockets, so the Python asyncio thread can learn about the closed socket later than the successful connection 🤷‍♂️

repro diff:

diff --git a/test/functional/p2p_eviction.py b/test/functional/p2p_eviction.py
index f297b8f39f..e4789887eb 100755
--- a/test/functional/p2p_eviction.py
+++ b/test/functional/p2p_eviction.py
@@ -14,2 +14,3 @@ Therefore, this test is limited to the remaining protection criteria.
 """
+import threading
 import time
@@ -59,2 +60,15 @@ class P2PEvict(BitcoinTestFramework):
         self.wallet = MiniWallet(node)
+        disconnect_started = threading.Event()
+        allow_disconnect = threading.Event()
+
+        def gate_connection_lost(peer):
+            connection_lost = peer.connection_lost
+
+            def delayed_connection_lost(exc):
+                disconnect_started.set()
+                assert allow_disconnect.wait(timeout=10)
+                connection_lost(exc)
+
+            peer.connection_lost = delayed_connection_lost
+            return peer
 
@@ -62,3 +76,3 @@ class P2PEvict(BitcoinTestFramework):
         for _ in range(4):
-            block_peer = node.add_p2p_connection(SlowP2PDataStore())
+            block_peer = node.add_p2p_connection(gate_connection_lost(SlowP2PDataStore()))
             current_peer += 1
@@ -75,3 +89,3 @@ class P2PEvict(BitcoinTestFramework):
         for _ in range(5):
-            node.add_p2p_connection(SlowP2PInterface())
+            node.add_p2p_connection(gate_connection_lost(SlowP2PInterface()))
             current_peer += 1
@@ -80,3 +94,3 @@ class P2PEvict(BitcoinTestFramework):
         for i in range(4):
-            txpeer = node.add_p2p_connection(SlowP2PInterface())
+            txpeer = node.add_p2p_connection(gate_connection_lost(SlowP2PInterface()))
             current_peer += 1
@@ -90,3 +104,3 @@ class P2PEvict(BitcoinTestFramework):
         for _ in range(8):
-            fastpeer = node.add_p2p_connection(P2PInterface())
+            fastpeer = node.add_p2p_connection(gate_connection_lost(P2PInterface()))
             current_peer += 1
@@ -107,3 +121,6 @@ class P2PEvict(BitcoinTestFramework):
         self.log.info("Create peer that triggers the eviction mechanism")
-        node.add_p2p_connection(SlowP2PInterface())
+        node.add_p2p_connection(SlowP2PInterface(), wait_for_verack=False)
+        assert disconnect_started.wait(timeout=10)
+        allow_disconnect.set()
+
 
@@ -112,2 +129,3 @@ class P2PEvict(BitcoinTestFramework):
         # and the eviction mechanism doesn't preserve the order of identical elements.
+        # This is the fix: self.wait_until(lambda: sum(not peer.is_connected for peer in node.p2ps) == 1)
         evicted_peers = []
@@ -116,2 +134,3 @@ class P2PEvict(BitcoinTestFramework):
                 evicted_peers.append(i)
+        allow_disconnect.set()