lib/client: reopen an agent connection for each request

[zmb3]

Our SSH agent client would open a connection to the local SSH agent and then never close it. This is okay for short-lived tsh processes, but leaks connections for long-lived processes like the tsh daemon in Teleport Connect.

This commit introduces a client implementation that establishes a client per-request and closes the connection when the request completes.

Closes #69549
Closes gravitational/customer-sensitive-requests#701

Changelog: fixed an issue that caused Teleport Connect to leak connections to the local SSH agent.

Manual Test Plan

Test Environment

Local Connect (pnpm start-term) connected to platform.teleport.sh.

while true; do echo "[$(date +'%H:%M:%S')] Open sockets: $(lsof "$SSH_AUTH_SOCK" 2>/dev/null | wc -l)"; sleep 5; done

Test Cases

• Run the lsof loop above in a terminal tab. Navigate around in Connect. Verify connections stay contstant.
• tsh successfully connects to a Cygwin agent and caches the UID between dials (custom build to force re-dial and log)

[Joerger]

LGTM, we just need to use the new single request client here as well.

Edit: nevermind we handle closure correctly there

[zmb3]

Test plan results

Before:

➜ while true; do echo "[$(date +'%H:%M:%S')] Open sockets: $(lsof "$SSH_AUTH_SOCK" 2>/dev/null | wc -l)"; sleep 5; done

[15:49:57] Open sockets:       23
[15:50:02] Open sockets:       23
[15:50:07] Open sockets:       24
[15:50:12] Open sockets:       25
[15:50:17] Open sockets:       26
[15:50:23] Open sockets:       26
[15:50:28] Open sockets:       27

After:

➜ while true; do echo "[$(date +'%H:%M:%S')] Open sockets: $(lsof "$SSH_AUTH_SOCK" 2>/dev/null | wc -l)"; sleep 5; done

[15:50:33] Open sockets:        2
[15:50:38] Open sockets:        2
[15:50:43] Open sockets:        2
[15:50:48] Open sockets:        2
[15:50:53] Open sockets:        2
[15:50:59] Open sockets:        2
[15:51:04] Open sockets:        2
[15:51:09] Open sockets:        2
[15:51:14] Open sockets:        2
[15:51:19] Open sockets:        2
[15:51:24] Open sockets:        2
[15:51:29] Open sockets:        2
[15:51:34] Open sockets:        2
[15:51:40] Open sockets:        2
[15:51:45] Open sockets:        2
[15:51:50] Open sockets:        2
[15:51:55] Open sockets:        2
[15:52:00] Open sockets:        2
[15:52:05] Open sockets:        2
[15:52:10] Open sockets:        2
[15:52:15] Open sockets:        2

[zmb3]

@codex review

[chatgpt-codex-connector]

Codex Review: Didn't find any major issues. Breezy!

Reviewed commit: f734efd8b3

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