feat(compression): configurable protect_first_n/protect_last_n turns

Add protect_first_n and protect_last_n to the compression config section
in config.yaml, allowing users to control how many initial and recent
turns are preserved during context compression.

- Default values: protect_first_n=3, protect_last_n=4 (no behavior change)
- Values clamped to 0-12 range (inspired by openclaw recentTurnsPreserve)
- Config version bumped to 6 for migration
- Also improved run_agent.py to read compression config from config.yaml
  (previously only read from env vars)

Related: #525 (microcompact)

tests/test_compression_config.py

@@ -0,0 +1,68 @@
+"""Tests for configurable compaction protection turns."""
+
+import unittest
+from unittest.mock import patch, MagicMock
+
+
+class TestCompressionConfigDefaults(unittest.TestCase):
+    """Verify DEFAULT_CONFIG includes protect_first_n / protect_last_n."""
+
+    def test_default_config_has_protection_fields(self):
+        from hermes_cli.config import DEFAULT_CONFIG
+        compression = DEFAULT_CONFIG["compression"]
+        self.assertIn("protect_first_n", compression)
+        self.assertIn("protect_last_n", compression)
+
+    def test_default_values(self):
+        from hermes_cli.config import DEFAULT_CONFIG
+        compression = DEFAULT_CONFIG["compression"]
+        self.assertEqual(compression["protect_first_n"], 3)
+        self.assertEqual(compression["protect_last_n"], 4)
+
+    def test_config_version_bumped(self):
+        from hermes_cli.config import DEFAULT_CONFIG
+        self.assertGreaterEqual(DEFAULT_CONFIG["_config_version"], 6)
+
+
+class TestContextCompressorAcceptsConfig(unittest.TestCase):
+    """Verify ContextCompressor properly receives custom protection values."""
+
+    @patch("agent.context_compressor.get_text_auxiliary_client")
+    def test_custom_protection_values(self, mock_aux):
+        mock_aux.return_value = (None, "test-model")
+        from agent.context_compressor import ContextCompressor
+        compressor = ContextCompressor(
+            model="test/model",
+            protect_first_n=5,
+            protect_last_n=8,
+        )
+        self.assertEqual(compressor.protect_first_n, 5)
+        self.assertEqual(compressor.protect_last_n, 8)
+
+    @patch("agent.context_compressor.get_text_auxiliary_client")
+    def test_default_protection_values(self, mock_aux):
+        mock_aux.return_value = (None, "test-model")
+        from agent.context_compressor import ContextCompressor
+        compressor = ContextCompressor(model="test/model")
+        self.assertEqual(compressor.protect_first_n, 3)
+        self.assertEqual(compressor.protect_last_n, 4)
+
+
+class TestProtectionClamping(unittest.TestCase):
+    """Verify protection values are clamped to 0-12 range."""
+
+    def test_clamp_negative_to_zero(self):
+        val = max(0, min(12, -5))
+        self.assertEqual(val, 0)
+
+    def test_clamp_over_max_to_twelve(self):
+        val = max(0, min(12, 50))
+        self.assertEqual(val, 12)
+
+    def test_valid_value_unchanged(self):
+        val = max(0, min(12, 7))
+        self.assertEqual(val, 7)
+
+
+if __name__ == "__main__":
+    unittest.main()