fix: reject non-finite timeout env overrides; test env paths

Address CodeRabbit review on #1320:

- _env_float now requires math.isfinite(value): "inf"/"Infinity"/"1e309"/
  "nan" are positive-or-parseable but would produce unusable socket/timeout
  behaviour, so they now fall back to the default like other invalid input.
- test_config_default_values clears the two env vars first so ambient env
  can't mask the defaults.
- Added coverage for valid overrides and for invalid/zero/negative/
  non-finite values falling back to defaults.

Author: amykhajlyshyn

Server/src/core/config.py

@@ -3,21 +3,23 @@
 This file contains all configurable parameters for the server.
 """
 
+import math
 import os
 from dataclasses import dataclass, field
 
 
 def _env_float(name: str, default: float) -> float:
-    """Read a positive float from an environment variable, falling back to default.
+    """Read a positive, finite float from an environment variable.
 
-    Invalid or non-positive values are ignored so a bad override can't disable
-    the timeout entirely.
+    Invalid, non-positive, or non-finite values (e.g. "inf", "1e309", "nan")
+    are ignored so a bad override can't disable the timeout or produce unusable
+    socket/timeout behaviour.
     """
     raw = os.environ.get(name)
     if raw:
         try:
             value = float(raw.strip())
-            if value > 0:
+            if math.isfinite(value) and value > 0:
                 return value
         except (TypeError, ValueError):
             pass

Server/tests/test_core_infrastructure_characterization.py

@@ -654,8 +654,11 @@ def error_tool():
 class TestServerConfigDefaults:
     """Tests for ServerConfig default values."""
 
-    def test_config_default_values(self):
+    def test_config_default_values(self, monkeypatch):
         """Verify ServerConfig has expected default values."""
+        # Clear env overrides so the defaults aren't masked by the ambient env.
+        monkeypatch.delenv("UNITY_MCP_CONNECTION_TIMEOUT", raising=False)
+        monkeypatch.delenv("UNITY_MCP_COMMAND_TOTAL_TIMEOUT", raising=False)
         config = ServerConfig()
 
         assert config.unity_host == "127.0.0.1"
@@ -670,6 +673,25 @@ def test_config_default_values(self):
         assert config.max_heartbeat_frames == 16
         assert config.heartbeat_timeout == 2.0
 
+    def test_timeout_env_overrides_are_honored(self, monkeypatch):
+        """Valid env overrides for the stdio timeouts are applied."""
+        monkeypatch.setenv("UNITY_MCP_CONNECTION_TIMEOUT", "120.5")
+        monkeypatch.setenv("UNITY_MCP_COMMAND_TOTAL_TIMEOUT", "240")
+        config = ServerConfig()
+
+        assert config.connection_timeout == 120.5
+        assert config.command_total_timeout == 240.0
+
+    @pytest.mark.parametrize("bad_value", ["0", "-5", "abc", "", "inf", "Infinity", "1e309", "nan"])
+    def test_timeout_env_invalid_values_fall_back(self, monkeypatch, bad_value):
+        """Invalid, non-positive, or non-finite overrides preserve the defaults."""
+        monkeypatch.setenv("UNITY_MCP_CONNECTION_TIMEOUT", bad_value)
+        monkeypatch.setenv("UNITY_MCP_COMMAND_TOTAL_TIMEOUT", bad_value)
+        config = ServerConfig()
+
+        assert config.connection_timeout == 300.0
+        assert config.command_total_timeout == 600.0
+
     def test_config_logging_defaults(self):
         """Verify logging configuration defaults."""
         config = ServerConfig()