Retransmit state transfers before the first progress ACK - #12
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…its first ACK The sender's ACK-timeout path (rewind to peer_ack, resend the window) only armed once an ACK had made progress. Before that there was no timer at all, so a first burst that lost chunk 0, or whose chunks overtook BEGIN through reordering, left peer_ack at 0 with nothing ever resent: the receiver sat in receive at 0/N, the sender logged "0 acked" every half second, and the app gave up on the stall timeout. Reproduced with the link simulator at RNET_SIM_LATENCY_MS=35 RNET_SIM_JITTER_MS=15 (the guest memory-card upload never got past 0/131076) and with RNET_SIM_LOSS_PCT=5. The timer now runs from the transfer's start until the first progress ACK takes over; both runs complete. Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_012YnTp36AZz1iswG9X2fadT
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A state transfer can stall forever at
0/N ackedwhen the first chunk is lost or chunks overtake the initial BEGIN. The retransmit timeout was armed only after a progress ACK, so those transfers never resent their first window.Start the timeout from the transfer start until a progress ACK arrives. Keep the existing rewind-to-contiguous-ACK and timeout pacing behavior.
Validation: reproduced in the Forbidden Memories loopback harness with 35 ms latency and 15 ms jitter. A deterministic local test against current upstream 46ef6ed drops either the first STATE_CHUNK or BEGIN, uses clocks starting at 0 and 1000 ms, and requires both peers to receive the identical 100000-byte payload. It fails without this change and passes with it. That additional test is committed locally but is not included in this PR because this work is under a no-push constraint.
The existing upstream rollback_episode_test has four failures both with and without this fix; the other 15 local CTest cases, including the new loss test, pass.