From d53a1b040b3a590c42c63381780b4c117a540bf2 Mon Sep 17 00:00:00 2001
From: Evan Senter <evansenter@gmail.com>
Date: Tue, 31 Mar 2026 23:26:56 +0100
Subject: [PATCH] fix: Surface server errors in CLI events and unregister
 commands

CLI --json mode now outputs the full error dict and exits non-zero when
the server returns {"error": ...}. Text mode prints to stderr. Covers
both cmd_events (e.g., resume with nonexistent session) and
cmd_unregister (e.g., session not found).

Fixes #116

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
---
 src/agent_event_bus/cli.py | 13 ++++++++++
 tests/test_cli.py          | 53 ++++++++++++++++++++++++++++++++++++++
 2 files changed, 66 insertions(+)

diff --git a/src/agent_event_bus/cli.py b/src/agent_event_bus/cli.py
index 334dcb4..412b1fb 100644
--- a/src/agent_event_bus/cli.py
+++ b/src/agent_event_bus/cli.py
@@ -159,6 +159,11 @@ def cmd_unregister(args):
         sys.exit(1)
 
     result = call_tool("unregister_session", arguments, url=args.url, debug=args.debug)
+
+    if "error" in result:
+        print(f"Error: {result['error']}", file=sys.stderr)
+        sys.exit(1)
+
     print(json.dumps(result, indent=2))
 
 
@@ -253,6 +258,14 @@ def cmd_events(args):
         "get_events", arguments, url=args.url, timeout_ms=args.timeout, debug=args.debug
     )
 
+    # Check for server-side errors (e.g., session not found)
+    if "error" in result:
+        if args.json:
+            print(json.dumps(result))
+        else:
+            print(f"Error: {result['error']}", file=sys.stderr)
+        sys.exit(1)
+
     # Result is now a dict with "events" and "next_cursor"
     events = result.get("events", [])
     next_cursor = result.get("next_cursor")
diff --git a/tests/test_cli.py b/tests/test_cli.py
index 70eac20..5bb9845 100644
--- a/tests/test_cli.py
+++ b/tests/test_cli.py
@@ -1,5 +1,6 @@
 """Tests for CLI wrapper."""
 
+import json
 from argparse import Namespace
 from unittest.mock import MagicMock, patch
 
@@ -517,6 +518,58 @@ def test_events_resume_with_session_id_works(self, mock_call, capsys):
         assert call_args["session_id"] == "test-session"
 
 
+class TestCmdEventsErrorSurfacing:
+    """Tests for CLI surfacing server-side errors in events command."""
+
+    @patch("agent_event_bus.cli.call_tool")
+    def test_events_error_json_mode(self, mock_call, capsys):
+        """Test that --json mode outputs server error as JSON and exits non-zero."""
+        mock_call.return_value = {"error": "Session not found", "session_id": "bad-id"}
+
+        args = make_events_args(json=True, session_id="bad-id", resume=True)
+
+        with pytest.raises(SystemExit) as exc_info:
+            cli.cmd_events(args)
+
+        assert exc_info.value.code == 1
+        captured = capsys.readouterr()
+        output = json.loads(captured.out)
+        assert output["error"] == "Session not found"
+        assert output["session_id"] == "bad-id"
+
+    @patch("agent_event_bus.cli.call_tool")
+    def test_events_error_text_mode(self, mock_call, capsys):
+        """Test that text mode prints error to stderr and exits non-zero."""
+        mock_call.return_value = {"error": "Session not found", "session_id": "bad-id"}
+
+        args = make_events_args(session_id="bad-id", resume=True)
+
+        with pytest.raises(SystemExit) as exc_info:
+            cli.cmd_events(args)
+
+        assert exc_info.value.code == 1
+        captured = capsys.readouterr()
+        assert "Session not found" in captured.err
+
+
+class TestCmdUnregisterErrorSurfacing:
+    """Tests for CLI surfacing server-side errors in unregister command."""
+
+    @patch("agent_event_bus.cli.call_tool")
+    def test_unregister_error_surfaces(self, mock_call, capsys):
+        """Test that unregister surfaces server errors to stderr."""
+        mock_call.return_value = {"error": "Session not found", "session_id": "bad-id"}
+
+        args = Namespace(session_id="bad-id", client_id=None, url=None, debug=False)
+
+        with pytest.raises(SystemExit) as exc_info:
+            cli.cmd_unregister(args)
+
+        assert exc_info.value.code == 1
+        captured = capsys.readouterr()
+        assert "Session not found" in captured.err
+
+
 class TestCmdNotify:
     """Tests for notify command."""