[zzmark]

Tested-by: Xshell 5(1339),Xshell 7(0164), Xshell 8(0057)

#89

[boypt]

Also tested :

• Xshell 7 (Build 0170)
• Xshell 8 Beta (Build 0051)
• Xshell 8 (Build 0057)

[Zerek-Cheng]

LGTM

Also tested :
· Xshell 8 (Build 0063)

From : #92

[boypt]

XShell 8 build 0119 introduced an extended handshake layout for agent forwarding: the handshake frame now carries an extra field and a trailing key name after the cookie (e.g. desk-ed25519), producing a probe connection (a=28) that the old code rejected as invalid message length, causing XShell to close it and breaking forwarding (ssh_fetch_identitylist: communication with agent failed).

Fix: truncate initMsg.Cookie to initMsg.Length instead of erroring when extra trailing bytes are present. The reply already echoes initMsg.Flag (extra), which is what XShell expects (00000005 63 00000001).

A follow-up PR with this fix is available against @zzmark's branch (which already includes this PR #91): zzmark#2