feat(mcp): enhance multi-platform notification resilience and reactive wakeups

- AgentApiNotifier: Sort candidate process sessions by creation time descending to prioritize the latest active IDE session over stale PIDs. Implement automatic retry across candidate address/token pairs and persist working credentials to shared environment files (~/.gemini/jetski/.jetski_env and ~/.artemis/.artemis_env).
- DesktopNotifier: Enable native OS desktop toast notifications by default on macOS, Linux, and Windows unless explicitly disabled or running in CI. Ensure MCP installer sets ARTEMIS_DESKTOP_NOTIFY=true in generated IDE configurations.
- ScriptNotifier: Add universal command hook adapter (ARTEMIS_NOTIFY_CMD / MCP_NOTIFY_COMMAND) for custom IDE and CLI integration.
- Fault Isolation: Wrap CompositeNotifier and global notify entrypoint in strict try-except blocks to guarantee zero-crash execution even if any individual notifier fails.
- Tests & Docs: Add unit tests for session recovery, fault tolerance, script hook execution, and document multi-platform notification architecture in README.

tests/unit/mcp/test_notifiers.py

@@ -94,12 +94,40 @@ def test_webhook_notifier_not_configured(monkeypatch):
     assert notifier.notify("conv-1", "hello") is False
 
 
-def test_desktop_notifier_not_enabled(monkeypatch):
-    monkeypatch.delenv("ARTEMIS_DESKTOP_NOTIFY", raising=False)
+def test_desktop_notifier_disabled(monkeypatch):
+    monkeypatch.setenv("ARTEMIS_DESKTOP_NOTIFY", "false")
     notifier = DesktopNotifier()
     assert notifier.is_available() is False
 
 
+def test_desktop_notifier_enabled_by_default(monkeypatch):
+    monkeypatch.delenv("ARTEMIS_DESKTOP_NOTIFY", raising=False)
+    monkeypatch.delenv("CI", raising=False)
+    import shutil
+    import sys
+
+    if sys.platform == "linux":
+        monkeypatch.setattr(shutil, "which", lambda cmd: "/usr/bin/notify-send" if cmd == "notify-send" else None)
+    elif sys.platform == "darwin":
+        monkeypatch.setattr(shutil, "which", lambda cmd: "/usr/bin/osascript" if cmd == "osascript" else None)
+    notifier = DesktopNotifier()
+    assert notifier.is_available() is True
+
+
+def test_script_notifier(monkeypatch):
+    from mcp_server.notifiers.script import ScriptNotifier
+
+    monkeypatch.delenv("ARTEMIS_NOTIFY_CMD", raising=False)
+    monkeypatch.delenv("MCP_NOTIFY_COMMAND", raising=False)
+    notifier = ScriptNotifier()
+    assert notifier.is_available() is False
+
+    monkeypatch.setenv("ARTEMIS_NOTIFY_CMD", "echo 'Notify: {title} - {message}'")
+    assert notifier.is_available() is True
+    res = notifier.notify("conv-123", "Task done", title="Success", payload={"trace_id": "t-1"})
+    assert res is True
+
+
 def test_composite_notifier_dispatch():
     d1 = DummyNotifier(available=True, return_val=True)
     d2 = DummyNotifier(available=False, return_val=False)
@@ -122,6 +150,29 @@ def test_composite_notifier_dispatch():
     assert d3.called_with is not None
 
 
+class BrokenNotifier(BaseNotifier):
+    @property
+    def name(self) -> str:
+        return "broken"
+
+    def is_available(self) -> bool:
+        raise RuntimeError("Catastrophic error in is_available")
+
+    def notify(self, conversation_id, message, title=None, event_type="completed", payload=None):
+        raise RuntimeError("Catastrophic error in notify")
+
+
+def test_composite_notifier_fault_tolerance():
+    broken = BrokenNotifier()
+    d1 = DummyNotifier(available=True, return_val=True)
+    composite = CompositeNotifier(notifiers=[broken, d1])
+
+    # Must never raise an exception even if a notifier crashes in is_available or notify
+    assert composite.is_available() is True
+    assert composite.notify("conv-test", "Message") is True
+    assert d1.called_with is not None
+
+
 def test_global_notify_function():
     res = notify(
         conversation_id="conv-xyz",
@@ -129,3 +180,52 @@ def test_global_notify_function():
         payload={"trace_id": "test-trace"},
     )
     assert isinstance(res, bool)
+
+
+def test_agentapi_notifier_candidate_recovery_and_retry(monkeypatch, tmp_path):
+    from mcp_server.notifiers.agentapi import AgentApiNotifier
+    import subprocess
+
+    monkeypatch.delenv("ANTIGRAVITY_LS_ADDRESS", raising=False)
+    monkeypatch.delenv("ANTIGRAVITY_CSRF_TOKEN", raising=False)
+
+    shared_file = tmp_path / ".test_jetski_env"
+    monkeypatch.setattr(
+        AgentApiNotifier,
+        "_get_candidate_envs",
+        lambda self, force_proc_scan=False: [
+            ("localhost:9999", "bad-token"),
+            ("localhost:1234", "good-token"),
+        ],
+    )
+
+    saved_sessions = []
+    monkeypatch.setattr(
+        AgentApiNotifier,
+        "_save_shared_env",
+        lambda self, addr, token: saved_sessions.append((addr, token)),
+    )
+    monkeypatch.setattr(
+        AgentApiNotifier,
+        "_find_agentapi_path",
+        lambda self: "/mock/bin/agentapi",
+    )
+
+    calls = []
+
+    def mock_run(cmd, capture_output, text, check, timeout, env):
+        calls.append(env.get("ANTIGRAVITY_LS_ADDRESS"))
+        if env.get("ANTIGRAVITY_LS_ADDRESS") == "localhost:9999":
+            raise subprocess.CalledProcessError(1, cmd)
+        return subprocess.CompletedProcess(cmd, 0, stdout="success")
+
+    monkeypatch.setattr(subprocess, "run", mock_run)
+
+    notifier = AgentApiNotifier()
+    success = notifier.notify("conv-test-123", "Task done!")
+    assert success is True
+    assert calls == ["localhost:9999", "localhost:1234"]
+    assert saved_sessions == [("localhost:1234", "good-token")]
+    assert os.environ["ANTIGRAVITY_LS_ADDRESS"] == "localhost:1234"
+    assert os.environ["ANTIGRAVITY_CSRF_TOKEN"] == "good-token"
+