fix(mcp): pin cwd to project root so .tenets.yml is reliably loaded

An MCP stdio server's spawn cwd is not guaranteed to be the project root, so
.tenets.yml (discovered relative to cwd) could be silently skipped. Honor
CLAUDE_PROJECT_DIR (set by Claude Code) and a generic TENETS_PROJECT_ROOT
override by chdir-ing to it at startup, before the config is built.

Author: jddunn

tenets/mcp/server.py

@@ -1649,6 +1649,27 @@ def _configure_mcp_logging(transport: str) -> None:
             logging.getLogger(logger_name).setLevel(logging.WARNING)
 
 
+def _chdir_to_project_root() -> None:
+    """Pin the working directory to the project root for config discovery.
+
+    ``.tenets.yml`` is discovered relative to the process cwd, but an MCP stdio
+    server's spawn cwd is not guaranteed to be the project root. Claude Code sets
+    ``CLAUDE_PROJECT_DIR`` in the spawned server's environment to the project root;
+    honor that (and a generic ``TENETS_PROJECT_ROOT`` override) so the project's
+    ``.tenets.yml`` is reliably loaded regardless of where the server was launched.
+    """
+    import os
+
+    for var in ("TENETS_PROJECT_ROOT", "CLAUDE_PROJECT_DIR"):
+        root = os.environ.get(var)
+        if root and os.path.isdir(root):
+            try:
+                os.chdir(root)
+            except OSError:
+                pass
+            return
+
+
 def main() -> None:
     """CLI entry point for tenets-mcp server.
 
@@ -1698,6 +1719,9 @@ def main() -> None:
     # Configure logging BEFORE importing anything else
     _configure_mcp_logging(args.transport)
 
+    # Pin cwd to the project root so .tenets.yml is discovered reliably
+    _chdir_to_project_root()
+
     try:
         server = create_server()
         server.run(

tests/mcp/test_project_root.py

@@ -0,0 +1,52 @@
+"""tenets-mcp pins cwd to the project root so .tenets.yml is discovered."""
+import os
+
+from tenets.mcp.server import _chdir_to_project_root
+
+
+def _real(p):
+    return os.path.realpath(str(p))
+
+
+def test_chdir_honors_tenets_project_root(tmp_path, monkeypatch):
+    monkeypatch.delenv("CLAUDE_PROJECT_DIR", raising=False)
+    monkeypatch.setenv("TENETS_PROJECT_ROOT", str(tmp_path))
+    monkeypatch.chdir(tmp_path.parent)
+    _chdir_to_project_root()
+    assert _real(os.getcwd()) == _real(tmp_path)
+
+
+def test_chdir_honors_claude_project_dir(tmp_path, monkeypatch):
+    monkeypatch.delenv("TENETS_PROJECT_ROOT", raising=False)
+    monkeypatch.setenv("CLAUDE_PROJECT_DIR", str(tmp_path))
+    monkeypatch.chdir(tmp_path.parent)
+    _chdir_to_project_root()
+    assert _real(os.getcwd()) == _real(tmp_path)
+
+
+def test_tenets_project_root_takes_precedence(tmp_path, monkeypatch):
+    a = tmp_path / "a"
+    a.mkdir()
+    b = tmp_path / "b"
+    b.mkdir()
+    monkeypatch.setenv("TENETS_PROJECT_ROOT", str(a))
+    monkeypatch.setenv("CLAUDE_PROJECT_DIR", str(b))
+    monkeypatch.chdir(tmp_path)
+    _chdir_to_project_root()
+    assert _real(os.getcwd()) == _real(a)
+
+
+def test_chdir_noop_when_unset(tmp_path, monkeypatch):
+    monkeypatch.delenv("TENETS_PROJECT_ROOT", raising=False)
+    monkeypatch.delenv("CLAUDE_PROJECT_DIR", raising=False)
+    monkeypatch.chdir(tmp_path)
+    _chdir_to_project_root()
+    assert _real(os.getcwd()) == _real(tmp_path)
+
+
+def test_chdir_ignores_invalid_dir(tmp_path, monkeypatch):
+    monkeypatch.delenv("CLAUDE_PROJECT_DIR", raising=False)
+    monkeypatch.setenv("TENETS_PROJECT_ROOT", str(tmp_path / "does-not-exist"))
+    monkeypatch.chdir(tmp_path)
+    _chdir_to_project_root()
+    assert _real(os.getcwd()) == _real(tmp_path)