fix(issue-45): the shim bootstrap starts MAM servers with restore-on-restart off

The headless bootstrap regenerates the server config on every start and hands
it to the server as HERDR_CONFIG_PATH. Without a file the server still starts,
with a warning. mam_sandbox unsets HERDR_CONFIG_PATH/XDG_CONFIG_HOME so the
file lands in the sandbox HOME.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

tests/conftest.py

@@ -236,6 +236,11 @@ def mam_sandbox(tmp_path, monkeypatch, request):
     monkeypatch.delenv("HERDR_SESSION_NAME", raising=False)
     monkeypatch.delenv("HERDR_SERVER_NAME", raising=False)
     monkeypatch.delenv("HERDR_WORKSPACE_ID", raising=False)
+    # Issue #45: the shim bootstrap writes a herdr server config next to the
+    # user's; with these unset that is $HOME/.config/herdr, inside the sandbox.
+    # Every pane of a MAM server inherits HERDR_CONFIG_PATH.
+    monkeypatch.delenv("HERDR_CONFIG_PATH", raising=False)
+    monkeypatch.delenv("XDG_CONFIG_HOME", raising=False)
     import sys
     monkeypatch.setenv("AGENT_PYTHON_BIN", sys.executable)