Add tests for config.StdinServerConfig.UnmarshalJSON error paths

Cover previously untested branches in UnmarshalJSON:
- invalid JSON input returns error
- connect_timeout with non-integer value returns error
- tool_timeout with non-integer value returns error
- connect_timeout/tool_timeout as floats return error
- null for connect_timeout decodes to pointer to 0
- both camelCase and snake_case timeout fields present simultaneously
- only snake_case tool_timeout sets toolTimeoutFieldName correctly
- unknown fields are collected in AdditionalProperties

Coverage improvement: UnmarshalJSON 79.2% → 91.7%

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: github-actions[bot]

internal/config/config_stdin_unmarshal_coverage_test.go

@@ -0,0 +1,162 @@
+package config
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+// TestStdinServerConfig_UnmarshalJSON_ErrorPaths tests the error branches of
+// StdinServerConfig.UnmarshalJSON that are not covered by existing tests.
+func TestStdinServerConfig_UnmarshalJSON_ErrorPaths(t *testing.T) {
+	t.Run("invalid JSON returns error", func(t *testing.T) {
+		var server StdinServerConfig
+		err := server.UnmarshalJSON([]byte(`not valid json`))
+		require.Error(t, err)
+	})
+
+	t.Run("connect_timeout with non-integer value returns error", func(t *testing.T) {
+		// The legacy snake_case alias connect_timeout must be a valid integer.
+		// Passing a non-integer triggers the assignLegacyIntAlias error path.
+		data := []byte(`{
+			"type": "http",
+			"url": "https://example.com/mcp",
+			"connect_timeout": "not-a-number"
+		}`)
+
+		var server StdinServerConfig
+		err := server.UnmarshalJSON(data)
+		require.Error(t, err)
+		assert.Contains(t, err.Error(), "connect_timeout")
+	})
+
+	t.Run("tool_timeout with non-integer value returns error", func(t *testing.T) {
+		// The legacy snake_case alias tool_timeout must be a valid integer.
+		// Passing a non-integer triggers the assignLegacyIntAlias error path.
+		data := []byte(`{
+			"type": "http",
+			"url": "https://example.com/mcp",
+			"tool_timeout": "not-a-number"
+		}`)
+
+		var server StdinServerConfig
+		err := server.UnmarshalJSON(data)
+		require.Error(t, err)
+		assert.Contains(t, err.Error(), "tool_timeout")
+	})
+
+	t.Run("connect_timeout as float returns error", func(t *testing.T) {
+		// Floats are not valid integers for connect_timeout.
+		data := []byte(`{
+			"type": "http",
+			"url": "https://example.com/mcp",
+			"connect_timeout": 3.14
+		}`)
+
+		var server StdinServerConfig
+		err := server.UnmarshalJSON(data)
+		require.Error(t, err)
+		assert.Contains(t, err.Error(), "connect_timeout")
+	})
+
+	t.Run("tool_timeout as float returns error", func(t *testing.T) {
+		// Floats are not valid integers for tool_timeout.
+		data := []byte(`{
+			"type": "http",
+			"url": "https://example.com/mcp",
+			"tool_timeout": 1.5
+		}`)
+
+		var server StdinServerConfig
+		err := server.UnmarshalJSON(data)
+		require.Error(t, err)
+		assert.Contains(t, err.Error(), "tool_timeout")
+	})
+
+	t.Run("connect_timeout as null is treated as zero", func(t *testing.T) {
+		// json.Unmarshal decodes null into an int as 0, so the field gets a pointer to 0.
+		data := []byte(`{
+			"type": "http",
+			"url": "https://example.com/mcp",
+			"connect_timeout": null
+		}`)
+
+		var server StdinServerConfig
+		err := server.UnmarshalJSON(data)
+		require.NoError(t, err)
+		require.NotNil(t, server.ConnectTimeout, "null connect_timeout decodes to a pointer to 0")
+		assert.Equal(t, 0, *server.ConnectTimeout)
+	})
+
+	t.Run("both legacy timeout fields present simultaneously", func(t *testing.T) {
+		// When both snake_case and camelCase are present the camelCase value wins
+		// because it is decoded first by the embedded alias struct.
+		data := []byte(`{
+			"type": "http",
+			"url": "https://example.com/mcp",
+			"connectTimeout": 60,
+			"toolTimeout": 300,
+			"connect_timeout": 30,
+			"tool_timeout": 120
+		}`)
+
+		var server StdinServerConfig
+		err := server.UnmarshalJSON(data)
+		require.NoError(t, err)
+		require.NotNil(t, server.ConnectTimeout)
+		require.NotNil(t, server.ToolTimeout)
+		// camelCase fields are decoded by the embedded alias; snake_case aliases
+		// are only applied when the primary pointer is nil.
+		assert.Equal(t, 60, *server.ConnectTimeout)
+		assert.Equal(t, 300, *server.ToolTimeout)
+	})
+
+	t.Run("only tool_timeout snake_case sets toolTimeoutFieldName", func(t *testing.T) {
+		// When toolTimeout (camelCase) is absent and tool_timeout (snake_case) is
+		// present, toolTimeoutFieldName should be set to "tool_timeout".
+		data := []byte(`{
+			"type": "http",
+			"url": "https://example.com/mcp",
+			"tool_timeout": 90
+		}`)
+
+		var server StdinServerConfig
+		err := server.UnmarshalJSON(data)
+		require.NoError(t, err)
+		assert.Equal(t, "tool_timeout", server.toolTimeoutField())
+	})
+
+	t.Run("toolTimeout camelCase keeps default toolTimeoutFieldName", func(t *testing.T) {
+		// When toolTimeout (camelCase) is present, toolTimeoutFieldName stays as
+		// "toolTimeout" (the default set in UnmarshalJSON).
+		data := []byte(`{
+			"type": "http",
+			"url": "https://example.com/mcp",
+			"toolTimeout": 90
+		}`)
+
+		var server StdinServerConfig
+		err := server.UnmarshalJSON(data)
+		require.NoError(t, err)
+		assert.Equal(t, "toolTimeout", server.toolTimeoutField())
+	})
+
+	t.Run("unknown fields are collected in AdditionalProperties", func(t *testing.T) {
+		data := []byte(`{
+			"type": "stdio",
+			"container": "ghcr.io/example/server:latest",
+			"customField": "customValue",
+			"anotherExtra": 42
+		}`)
+
+		var server StdinServerConfig
+		err := server.UnmarshalJSON(data)
+		require.NoError(t, err)
+		assert.Equal(t, "customValue", server.AdditionalProperties["customField"])
+		assert.Equal(t, float64(42), server.AdditionalProperties["anotherExtra"])
+		// Known fields must not appear in AdditionalProperties.
+		_, typeExists := server.AdditionalProperties["type"]
+		assert.False(t, typeExists, "known field 'type' should not appear in AdditionalProperties")
+	})
+}