feat(logging): add token truncation helper

tests/unit/test_logging.py

@@ -0,0 +1,24 @@
+"""Unit tests for logging module."""
+
+from grist_mcp.logging import truncate_token
+
+
+class TestTruncateToken:
+    def test_normal_token_shows_prefix_suffix(self):
+        token = "abcdefghijklmnop"
+        assert truncate_token(token) == "abc...nop"
+
+    def test_short_token_shows_asterisks(self):
+        token = "abcdefgh"  # 8 chars
+        assert truncate_token(token) == "***"
+
+    def test_very_short_token_shows_asterisks(self):
+        token = "abc"
+        assert truncate_token(token) == "***"
+
+    def test_empty_token_shows_asterisks(self):
+        assert truncate_token("") == "***"
+
+    def test_boundary_token_shows_prefix_suffix(self):
+        token = "abcdefghi"  # 9 chars - first to show truncation
+        assert truncate_token(token) == "abc...ghi"