Hang up the original leg after a successful blind transfer

[calebtt]

Summary

Closes #14.

SipClient.BlindTransferAsync is documented as "The original call leg is hung up on success", but it never hung up. Against a VitalPBX (Asterisk 20.14) lab PBX, the PBX completed the transfer and took the transferor's channel out of the bridge without hanging it up. The client stayed in the call:

• IsCallActive stayed true, and CallEnded was not raised.
• sipbot serve emitted no ended after transfer.
• The next dial failed with already handling a call.

This was seen on v0.1.2 and master.

When the REFER is accepted, BlindTransferAsync now calls Hangup() after raising TransferSucceeded. That sends BYE and raises CallEnded through the usual path, so sipbot serve emits ended. A declined, failed, or cancelled transfer leaves the call up, as before. AGENTS.md now describes this.

Tests

New BlindTransferTests: a SipClient calls a plain SIPUserAgent over loopback, with no PBX needed.

• Accepted REFER (202): the caller's CallEnded fires, IsCallActive becomes false, and the transferee receives a BYE. This test fails on current master.
• Declined REFER: BlindTransferAsync returns false and the call stays up.

dotnet test: 62 passed (60 existing + 2 new). The new tests passed 5 of 5 repeated runs. Build warnings unchanged (17).

Compatibility

SipBotOpen and homeline call BlindTransferAsync and never hang up afterwards, so their leg currently stays up after a transfer. With this change it ends, raising CallEnded, which matches the documented behavior. JSONL event and field names are unchanged. transfer is now followed by ended.

🤖 Generated with Claude Code

[calebtt]

The first CI run failed in Accepted_transfer_hangs_up_the_original_leg on its last assertion ("the transferee never received a BYE"). The caller-side checks had passed: CallEnded fired and IsCallActive was false.

The cause was a race in the test's callee. After accepting the REFER, SIPSorcery's SIPUserAgent starts its own call to the transfer target, and on the runner that replaced its dialog before the caller's BYE arrived, so OnCallHungup never fired. Commit 30fb331 now checks for the BYE on the callee's transport instead. It passed 8 of 8 local runs, and CI is green.

🤖 Generated with Claude Code