warpgate-ssh: remote Linux/macOS terminals through the relay; oregon launched remotely

The dispatcher moves to an LXC without agent CLIs (design 9), so every terminal is
reached through Warpgate. The relay call (agent-access.py run --target <t>) lives in
one helper; the target comes from the terminal config.

os linux/darwin (PosixWarpgateTransport): each primitive is one bash -c call. Files
go up as base64 (chunked above 60k), start_run stages prompt.md + run.sh and launches
in a single round trip; the runner is detached with setsid nohup (pid == pgid == sid,
$! kept in launch.pid); kill signals the process group and session (TERM, then KILL),
skipped once exit.txt exists. macOS detaches with perl POSIX::setsid.

os windows keeps the win10-ps.sh / win10-put.sh helper scripts (target win10) and
schtasks, now through the shared call() helper.

oregon is now warpgate-ssh (target oregon, run_root ~/.gwent-board/agentd-runs);
the local transport stays for co-located setups and tests.

tests/test_transports.py

@@ -12,11 +12,11 @@ from agentd.config import Config
 from agentd.executors import Run, make_executor
 from agentd.store import Store
 from agentd.transports.local import LocalTransport
-from agentd.transports.warpgate_ssh import WarpgateSshTransport
+from agentd.transports.warpgate_ssh import PosixWarpgateTransport, WarpgateSshTransport, WindowsWarpgateTransport
 from tests.fakes import config_data
 
 
-class RecordingWin(WarpgateSshTransport):
+class RecordingWin(WindowsWarpgateTransport):
     """Windows transport with the relay replaced by an in-memory recorder."""
     def __init__(self, cfg, terminal):
         super().__init__(cfg, terminal)
@@ -95,7 +95,7 @@ class WindowsScriptTest(unittest.TestCase):
 
         def fake_run(args, **kw):
             seen.update(kw["env"])
-            return mock.Mock(returncode=0, stdout="X=ok", stderr="")
+            return mock.Mock(returncode=0, stdout=b"X=ok", stderr=b"")
         with mock.patch.dict(os.environ, {"PLANE_WINDOW10_API_TOKEN": "s"}), \
                 mock.patch("agentd.transports.warpgate_ssh.subprocess.run", fake_run):
             WarpgateSshTransport(self.cfg, "win10").ps("'X=ok'")