node: deterministic tie-breaker for cross-init NAT traversal adoption

When both peers' Nostr-mediated UDP punches complete within the
same scheduling window, each side's `BootstrapEvent::Established`
event arrives with `is_connecting_to_peer` already true: each side
received an inbound msg1 from the peer's pre-punch outbound
attempt, which created a connecting-state record. The deduplication
skip then fires on both sides, neither installs the fresh
traversal socket as canonical, and the peer-adoption budget
(45 s) expires. Cross-node wall-clock alignment of the skip log
line in observed failures was within ~1 ms — simultaneous dual-
fire under contention, the dual-initiation pattern.

Apply the deterministic NodeAddr tie-breaker already used at
`handlers/handshake.rs:269` for rekey dual-initiation and in
`peer::cross_connection_winner` for cross-connection resolution.
Smaller NodeAddr wins as adopter: enumerate the in-flight
connections whose `expected_identity` points at this peer, tear
them down via the canonical `cleanup_stale_connection` helper, and
fall through to `adopt_established_traversal`. Larger NodeAddr
loses and keeps the existing `continue` semantics; the loser's
in-flight outbound is reconciled by `handle_msg1`'s cross-
connection logic when the winner's fresh msg1 arrives over the
adopted socket.

`cleanup_stale_connection` visibility bumped from module-private
to `pub(in crate::node)` so it is callable from `lifecycle.rs`.
The defensive re-check inside `adopt_established_traversal`
itself is left as-is — after the outer cleanup the winner reaches
it with `is_connecting_to_peer == false`, so the inner skip
won't trip. The `BootstrapEvent::Failed` arm is unchanged: there
is no winning outcome on dual failure, and the existing skip +
retry-schedule semantics are correct.

CHANGELOG.md

@@ -60,6 +60,25 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ### Fixed
 
+- NAT-traversal cross-init adoption is now deterministic under
+  simultaneous dual-initiation. Previously, when two peers'
+  Nostr-mediated UDP punches completed within the same scheduling
+  window, each side's bootstrap-completion event arrived with an
+  in-flight handshake already recorded against the other peer (each
+  side had received an inbound msg1 from the other's pre-punch
+  outbound attempt). The deduplication skip then fired on both
+  sides, neither installed the fresh traversal socket as canonical,
+  and the 45-second peer-adoption budget expired with both nodes
+  stuck waiting for an adoption that never happened. The handler now
+  applies the same deterministic NodeAddr tie-breaker the codebase
+  already uses for rekey dual-initiation and cross-connection
+  resolution: the smaller NodeAddr wins as adopter, tears down its
+  in-flight handshake state, and proceeds with adoption; the larger
+  NodeAddr keeps the skip semantics, and its in-flight outbound is
+  reconciled by the cross-connection logic when the winner's fresh
+  msg1 arrives over the adopted socket. The dual cross-init stall is
+  eliminated; cross-init NAT-traversal completes in well under a
+  second even under host CPU contention.
 - FSP session rekey is now hitless under packet loss and reordering.
   Previously, a rekey could leave the two endpoints holding different
   key sets for a brief window — if a handshake message was lost in