#35600 net: prevent duplication manual connections (take 2)

• Prevent duplicate manual connections to the same target caused by concurrent connection attempts
• Stops duplicate sockets when -connect and -addnode are configured for the same destination

Tracks in-flight manual connection attempts in CConnman to prevent duplicate connections to the same target. Existing deduplication checks inspect connected peers in m_nodes only after a connection is established, allowing concurrent manual connection attempts to bypass checks. A functional regression test is also added.

Problem: When -connect and -addnode are configured for the same destination, startup threads can race to connect concurrently and create duplicate sockets to the same peer before either node is inserted into m_nodes.

P3 · bug fix

• P3 because it fixes an edge-case race condition in manual connection management
• Affects only nodes configuring overlapping manual targets and does not threaten normal operation

P3 because it fixes an edge-case race condition in manual connection management where concurrent dials connect twice to the same address. As noted in the description, '-connect and -addnode can both try to open the same manual connection during startup' and 'two concurrent manual dial attempts can both pass the checks and create duplicate connections'. While resolving long-standing issue #5299, the failure requires overlapping manual connection configuration and does not threaten normal network operation.

Membership: Modifies manual connection tracking in CConnman in src/net.cpp and src/net.h.

Factors: security/stability 1, bug 1, performance 0, user value 1, leverage 0

• Ready to review now with clean code and no outstanding reviewer requests

The code is clean, CI passes, and there are no outstanding reviewer requests.

Author status: active

• Positive sentiment with no objections raised
• Concept approval without stated reasons (sedited, w0xlt)

Positive: Concept ACKs from sedited and w0xlt with no objections.

Two contributors provided Concept ACKs with no objections or criticisms raised.

• sedited left a Concept ACK on 2026-07-24
• w0xlt left a Concept ACK on 2026-08-18

Review verdicts (DrahtBot): 0

• Concept ACK: sedited, w0xlt

106 lines under test/bench/ci.

• test/functional/p2p_duplicate_manual_connections.py +105/-0
• src/net.cpp +52/-5
• src/net.h +6/-0
• test/functional/test_runner.py +1/-0

This PR prevents duplicate manual P2P connections by reserving in-flight destinations in OpenNetworkConnection until the connection succeeds or fails. Currently, concurrent manual connection attempts (such as specifying both -connect and -addnode for the same peer at startup) can race past existing m_nodes deduplication checks before either socket completes. The problem primarily affects node operators with overlapping manual connection configurations, addressing long-standing issue #5299. The PR is ready for review with positive concept ACKs and no objections.