feat(rpc): add startup health-check and propagate server errors

Rpc.start() now calls get_system_info() after launching the server
to verify it started successfully. If the server exits early (e.g.
due to an invalid accounts directory), the core error message from
stderr is captured and included in the raised JsonRpcError.

The reader_loop now unblocks pending RPC requests when the server
closes stdout, so callers never hang on a dead server.

Export JsonRpcError from the deltachat_rpc_client package.

Add test_early_failure verifying that Rpc.start() raises with
the actual core error message for invalid accounts directories.

deltachat-rpc-client/tests/test_something.py

@@ -13,7 +13,7 @@ import pytest
 from deltachat_rpc_client import EventType, events
 from deltachat_rpc_client.const import DownloadState, MessageState
 from deltachat_rpc_client.pytestplugin import E2EE_INFO_MSGS
-from deltachat_rpc_client.rpc import JsonRpcError
+from deltachat_rpc_client.rpc import JsonRpcError, Rpc
 
 
 def test_system_info(rpc) -> None:
@@ -665,6 +665,24 @@ def test_openrpc_command_line() -> None:
     assert "methods" in openrpc
 
 
+def test_early_failure(tmp_path) -> None:
+    """Test that Rpc.start() raises on invalid accounts directories."""
+    # A file instead of a directory.
+    file_path = tmp_path / "not_a_dir"
+    file_path.write_text("I am a file, not a directory")
+    rpc = Rpc(accounts_dir=str(file_path))
+    with pytest.raises(JsonRpcError, match="(?i)directory"):
+        rpc.start()
+
+    # A non-empty directory that is not a deltachat accounts directory.
+    non_dc_dir = tmp_path / "invalid_dir"
+    non_dc_dir.mkdir()
+    (non_dc_dir / "some_file").write_text("content")
+    rpc = Rpc(accounts_dir=str(non_dc_dir))
+    with pytest.raises(JsonRpcError, match="invalid_dir"):
+        rpc.start()
+
+
 def test_provider_info(rpc) -> None:
     account_id = rpc.add_account()