test: add coverage for plugin context engine init (#9071)

Verify that plugin context engines receive update_model() with correct
context_length during AIAgent init — regression test for the ctx -- bug.

tests/run_agent/test_plugin_context_engine_init.py

@@ -0,0 +1,89 @@
+"""Tests that plugin context engines get update_model() called during init.
+
+Regression test for #9071 — plugin engines were never initialized with
+context_length, causing the CLI status bar to show 'ctx --'.
+"""
+
+from unittest.mock import MagicMock, patch
+
+from agent.context_engine import ContextEngine
+
+
+class _StubEngine(ContextEngine):
+    """Minimal concrete context engine for testing."""
+
+    @property
+    def name(self) -> str:
+        return "stub"
+
+    def update_from_response(self, usage):
+        pass
+
+    def should_compress(self, prompt_tokens=None):
+        return False
+
+    def compress(self, messages, current_tokens=None):
+        return messages
+
+
+def test_plugin_engine_gets_context_length_on_init():
+    """Plugin context engine should have context_length set during AIAgent init."""
+    engine = _StubEngine()
+    assert engine.context_length == 0  # ABC default before fix
+
+    cfg = {"context": {"engine": "stub"}, "agent": {}}
+
+    with (
+        patch("hermes_cli.config.load_config", return_value=cfg),
+        patch("plugins.context_engine.load_context_engine", return_value=engine),
+        patch("agent.model_metadata.get_model_context_length", return_value=204_800),
+        patch("run_agent.get_tool_definitions", return_value=[]),
+        patch("run_agent.check_toolset_requirements", return_value={}),
+        patch("run_agent.OpenAI"),
+    ):
+        from run_agent import AIAgent
+
+        agent = AIAgent(
+            api_key="test-key-1234567890",
+            quiet_mode=True,
+            skip_context_files=True,
+            skip_memory=True,
+        )
+
+    assert agent.context_compressor is engine
+    assert engine.context_length == 204_800
+    assert engine.threshold_tokens == int(204_800 * engine.threshold_percent)
+
+
+def test_plugin_engine_update_model_args():
+    """Verify update_model() receives model, context_length, base_url, api_key, provider."""
+    engine = _StubEngine()
+    engine.update_model = MagicMock()
+
+    cfg = {"context": {"engine": "stub"}, "agent": {}}
+
+    with (
+        patch("hermes_cli.config.load_config", return_value=cfg),
+        patch("plugins.context_engine.load_context_engine", return_value=engine),
+        patch("agent.model_metadata.get_model_context_length", return_value=131_072),
+        patch("run_agent.get_tool_definitions", return_value=[]),
+        patch("run_agent.check_toolset_requirements", return_value={}),
+        patch("run_agent.OpenAI"),
+    ):
+        from run_agent import AIAgent
+
+        agent = AIAgent(
+            model="openrouter/auto",
+            api_key="test-key-1234567890",
+            quiet_mode=True,
+            skip_context_files=True,
+            skip_memory=True,
+        )
+
+    engine.update_model.assert_called_once()
+    kw = engine.update_model.call_args.kwargs
+    assert kw["context_length"] == 131_072
+    assert "model" in kw
+    assert "provider" in kw
+    # Should NOT pass api_mode — the ABC doesn't accept it
+    assert "api_mode" not in kw