[kahrendt]

Summary

TransportTest.HeldBackConnectionsResumeInTheOrderTheyWereHeld was flaky. It failed on the Linux TSan job of #100 with order holding only the five "first" messages. The test raced the network thread in two places. This PR changes only the test.

Change

• The first connection's close. The first connection's close is raised outside the inbound ring's room, so it can reach core while later connections are still parked. The test then closed them and their messages never arrived. It now also waits until every expected message has been delivered before closing the later connections.
• The last later message. wait_taken() shows the kernel bytes were read, not that the push was refused. The last later message could therefore be pushed once core freed room, ahead of the parked ones (order showed "later 8" before the first's held message). A probe connection that core closes after that message is taken now ends only after the network thread has pushed it. The test waits for that before core runs.

Tests

• No new tests.
• Swapping two entries of the expected order still fails the assertion.
• Known gap: the stress runs were on macOS; the original failure was on Linux.

[Copilot]

🟡 Changes recommended

The synchronization probe is declared const, but its completion handler later modifies non-mutable members, causing undefined behavior in the new synchronization path.

1 open issue

• Avoid const for Peer probe captured by completion handler · New

What changed in this PR

This test-only PR addresses two races in the transport resume-order test that caused intermittent failures during Linux ThreadSanitizer testing.

Changes:

• Adds a probe connection to synchronize the final held-message push before core drains the inbound ring.
• Waits for every expected message before closing the remaining connections.
• Checks probe completion and errors alongside the existing peers.

File	Description
tests/​test_transport.cpp	Strengthens synchronization and shutdown conditions in the held-message resume-order test.

_{Review effort: Balanced}