fix(config): preserve unknown JSON fields during config updates

cmd/opencodereview/config_cmd.go

@@ -9,6 +9,7 @@ import (
 	"net/url"
 	"os"
 	"path/filepath"
+	"reflect"
 	"strconv"
 	"strings"
 
@@ -332,6 +333,11 @@ type ProviderEntry struct {
 	// first time any config command runs.
 	AWSProfile string `json:"aws_profile,omitempty"`
 	AWSRegion  string `json:"aws_region,omitempty"`
+
+	// unknownJSONFields keeps JSON keys with no matching struct field alive across
+	// a load/save cycle. Unexported: any struct-literal rebuild must copy it
+	// (see cloneProviderEntry) or the fields are dropped again
+	unknownJSONFields map[string]json.RawMessage
 }
 
 // MCPServerConfig holds configuration for a single MCP server.
@@ -345,6 +351,8 @@ type MCPServerConfig struct {
 	Headers map[string]string `json:"headers,omitempty"`
 	Tools   []string          `json:"tools,omitempty"`
 	Setup   string            `json:"setup,omitempty"`
+
+	unknownJSONFields map[string]json.RawMessage
 }
 
 // Config represents the user-level configuration file (~/.opencodereview/config.json).
@@ -359,6 +367,8 @@ type Config struct {
 	Language        string                     `json:"language,omitempty"`
 	Telemetry       *TelemetryConfig           `json:"telemetry,omitempty"`
 	MCPServers      map[string]MCPServerConfig `json:"mcp_servers,omitempty"`
+
+	unknownJSONFields map[string]json.RawMessage
 }
 
 type LlmConfig struct {
@@ -373,6 +383,8 @@ type LlmConfig struct {
 	ExtraBody    map[string]any    `json:"extra_body,omitempty"`
 	ExtraHeaders map[string]string `json:"extra_headers,omitempty"`
 	RetryCodes   []int             `json:"retry_codes,omitempty"`
+
+	unknownJSONFields map[string]json.RawMessage
 }
 
 // TelemetryConfig holds telemetry-specific settings.
@@ -381,6 +393,188 @@ type TelemetryConfig struct {
 	Exporter     string `json:"exporter,omitempty"`        // "console" or "otlp"
 	OTLPEndpoint string `json:"otlp_endpoint,omitempty"`   // OTLP collector address
 	ContentLog   bool   `json:"content_logging,omitempty"` // Include prompt/response content
+
+	unknownJSONFields map[string]json.RawMessage
+}
+
+func jsonFieldNames(value any) []string {
+	typeOf := reflect.TypeOf(value)
+	for typeOf.Kind() == reflect.Pointer {
+		typeOf = typeOf.Elem()
+	}
+
+	fields := make([]string, 0, typeOf.NumField())
+	for i := 0; i < typeOf.NumField(); i++ {
+		field := typeOf.Field(i)
+		if field.PkgPath != "" {
+			continue
+		}
+		tag := field.Tag.Get("json")
+		name, _, _ := strings.Cut(tag, ",")
+		if name != "" && name != "-" {
+			fields = append(fields, name)
+		}
+	}
+	return fields
+}
+
+func collectUnknownJSONFields(data []byte, knownFields []string) (map[string]json.RawMessage, error) {
+	var fields map[string]json.RawMessage
+	if err := json.Unmarshal(data, &fields); err != nil {
+		return nil, err
+	}
+
+	known := make(map[string]struct{}, len(knownFields))
+	for _, field := range knownFields {
+		known[field] = struct{}{}
+	}
+	for field := range fields {
+		if _, ok := known[strings.ToLower(field)]; ok {
+			delete(fields, field)
+		}
+	}
+	return fields, nil
+}
+
+func mergeUnknownJSONFields(data []byte, unknown map[string]json.RawMessage) ([]byte, error) {
+	if len(unknown) == 0 {
+		return data, nil
+	}
+
+	var fields map[string]json.RawMessage
+	if err := json.Unmarshal(data, &fields); err != nil {
+		return nil, err
+	}
+	known := make(map[string]struct{}, len(fields))
+	for field := range fields {
+		known[strings.ToLower(field)] = struct{}{}
+	}
+	for field, value := range unknown {
+		if _, exists := known[strings.ToLower(field)]; !exists {
+			fields[field] = value
+		}
+	}
+	return json.Marshal(fields)
+}
+
+func (c *Config) UnmarshalJSON(data []byte) error {
+	type configAlias Config
+	var decoded configAlias
+	if err := json.Unmarshal(data, &decoded); err != nil {
+		return err
+	}
+	unknown, err := collectUnknownJSONFields(data, jsonFieldNames(Config{}))
+	if err != nil {
+		return err
+	}
+	*c = Config(decoded)
+	c.unknownJSONFields = unknown
+	return nil
+}
+
+func (c Config) MarshalJSON() ([]byte, error) {
+	type configAlias Config
+	data, err := json.Marshal(configAlias(c))
+	if err != nil {
+		return nil, err
+	}
+	return mergeUnknownJSONFields(data, c.unknownJSONFields)
+}
+
+func (e *ProviderEntry) UnmarshalJSON(data []byte) error {
+	type providerEntryAlias ProviderEntry
+	var decoded providerEntryAlias
+	if err := json.Unmarshal(data, &decoded); err != nil {
+		return err
+	}
+	unknown, err := collectUnknownJSONFields(data, jsonFieldNames(ProviderEntry{}))
+	if err != nil {
+		return err
+	}
+	*e = ProviderEntry(decoded)
+	e.unknownJSONFields = unknown
+	return nil
+}
+
+func (e ProviderEntry) MarshalJSON() ([]byte, error) {
+	type providerEntryAlias ProviderEntry
+	data, err := json.Marshal(providerEntryAlias(e))
+	if err != nil {
+		return nil, err
+	}
+	return mergeUnknownJSONFields(data, e.unknownJSONFields)
+}
+
+func (c *MCPServerConfig) UnmarshalJSON(data []byte) error {
+	type mcpServerConfigAlias MCPServerConfig
+	var decoded mcpServerConfigAlias
+	if err := json.Unmarshal(data, &decoded); err != nil {
+		return err
+	}
+	unknown, err := collectUnknownJSONFields(data, jsonFieldNames(MCPServerConfig{}))
+	if err != nil {
+		return err
+	}
+	*c = MCPServerConfig(decoded)
+	c.unknownJSONFields = unknown
+	return nil
+}
+
+func (c MCPServerConfig) MarshalJSON() ([]byte, error) {
+	type mcpServerConfigAlias MCPServerConfig
+	data, err := json.Marshal(mcpServerConfigAlias(c))
+	if err != nil {
+		return nil, err
+	}
+	return mergeUnknownJSONFields(data, c.unknownJSONFields)
+}
+
+func (c *LlmConfig) UnmarshalJSON(data []byte) error {
+	type llmConfigAlias LlmConfig
+	var decoded llmConfigAlias
+	if err := json.Unmarshal(data, &decoded); err != nil {
+		return err
+	}
+	unknown, err := collectUnknownJSONFields(data, jsonFieldNames(LlmConfig{}))
+	if err != nil {
+		return err
+	}
+	*c = LlmConfig(decoded)
+	c.unknownJSONFields = unknown
+	return nil
+}
+
+func (c LlmConfig) MarshalJSON() ([]byte, error) {
+	type llmConfigAlias LlmConfig
+	data, err := json.Marshal(llmConfigAlias(c))
+	if err != nil {
+		return nil, err
+	}
+	return mergeUnknownJSONFields(data, c.unknownJSONFields)
+}
+
+func (c *TelemetryConfig) UnmarshalJSON(data []byte) error {
+	type telemetryConfigAlias TelemetryConfig
+	var decoded telemetryConfigAlias
+	if err := json.Unmarshal(data, &decoded); err != nil {
+		return err
+	}
+	unknown, err := collectUnknownJSONFields(data, jsonFieldNames(TelemetryConfig{}))
+	if err != nil {
+		return err
+	}
+	*c = TelemetryConfig(decoded)
+	c.unknownJSONFields = unknown
+	return nil
+}
+
+func (c TelemetryConfig) MarshalJSON() ([]byte, error) {
+	type telemetryConfigAlias TelemetryConfig
+	data, err := json.Marshal(telemetryConfigAlias(c))
+	if err != nil {
+		return nil, err
+	}
+	return mergeUnknownJSONFields(data, c.unknownJSONFields)
 }
 
 func loadOrCreateConfig(path string) (*Config, error) {

cmd/opencodereview/config_cmd_test.go

@@ -4,9 +4,11 @@
 package main
 
 import (
+	"encoding/json"
 	"io"
 	"os"
 	"path/filepath"
+	"reflect"
 	"strconv"
 	"strings"
 	"testing"
@@ -1534,6 +1536,80 @@ func TestConfigRoundTripPreservesTimeoutSec(t *testing.T) {
 	}
 }
 
+func TestConfigRoundTripPreservesUnknownFields(t *testing.T) {
+	configPath := filepath.Join(t.TempDir(), "config.json")
+	original := `{
+    "provider": "anthropic",
+    "future_top_level": {"enabled": true},
+    "providers": {
+        "anthropic": {
+            "model": "claude-opus-4-6",
+            "future_provider": {"value": "preserve-me"}
+        }
+    },
+    "llm": {
+        "model": "claude-opus-4-6",
+        "future_llm": 7
+    },
+    "telemetry": {
+        "enabled": true,
+        "future_telemetry": "keep-me"
+    },
+    "mcp_servers": {
+        "docs": {
+            "command": "docs-server",
+            "future_mcp": {"version": 2}
+        }
+    }
+}`
+	if err := os.WriteFile(configPath, []byte(original), 0o600); err != nil {
+		t.Fatalf("write config: %v", err)
+	}
+
+	cfg, err := loadOrCreateConfig(configPath)
+	if err != nil {
+		t.Fatalf("loadOrCreateConfig: %v", err)
+	}
+	if err := setConfigValue(cfg, "language", "English"); err != nil {
+		t.Fatalf("setConfigValue: %v", err)
+	}
+	if err := saveConfig(configPath, cfg); err != nil {
+		t.Fatalf("saveConfig: %v", err)
+	}
+
+	data, err := os.ReadFile(configPath)
+	if err != nil {
+		t.Fatalf("read config: %v", err)
+	}
+	var got map[string]any
+	if err := json.Unmarshal(data, &got); err != nil {
+		t.Fatalf("parse saved config: %v", err)
+	}
+	assertJSONValue(t, got, []string{"future_top_level", "enabled"}, true)
+	assertJSONValue(t, got, []string{"providers", "anthropic", "future_provider", "value"}, "preserve-me")
+	assertJSONValue(t, got, []string{"llm", "future_llm"}, float64(7))
+	assertJSONValue(t, got, []string{"telemetry", "future_telemetry"}, "keep-me")
+	assertJSONValue(t, got, []string{"mcp_servers", "docs", "future_mcp", "version"}, float64(2))
+}
+
+func assertJSONValue(t *testing.T, root map[string]any, path []string, want any) {
+	t.Helper()
+	var current any = root
+	for _, part := range path {
+		object, ok := current.(map[string]any)
+		if !ok {
+			t.Fatalf("JSON path %q entered %T at %q", strings.Join(path, "."), current, part)
+		}
+		current, ok = object[part]
+		if !ok {
+			t.Fatalf("JSON path %q is missing", strings.Join(path, "."))
+		}
+	}
+	if !reflect.DeepEqual(current, want) {
+		t.Errorf("JSON path %q = %#v, want %#v", strings.Join(path, "."), current, want)
+	}
+}
+
 func TestSetMCPServerValue_Type(t *testing.T) {
 	cfg := &Config{}
 	if err := setMCPServerValue(cfg, "mcp_servers.gh.type", "remote"); err != nil {

cmd/opencodereview/provider_tui.go

@@ -4,6 +4,7 @@
 package main
 
 import (
+	"encoding/json"
 	"fmt"
 	"os"
 	"sort"
@@ -1300,6 +1301,7 @@ func cloneProviderEntry(v ProviderEntry) ProviderEntry {
 		AWSProfile: v.AWSProfile,
 		AWSRegion:  v.AWSRegion,
 	}
+	out.unknownJSONFields = cloneUnknownJSONFields(v.unknownJSONFields)
 	if v.ExtraBody != nil {
 		out.ExtraBody = make(map[string]any, len(v.ExtraBody))
 		for k, val := range v.ExtraBody {
@@ -1315,6 +1317,17 @@ func cloneProviderEntry(v ProviderEntry) ProviderEntry {
 	return out
 }
 
+func cloneUnknownJSONFields(src map[string]json.RawMessage) map[string]json.RawMessage {
+	if src == nil {
+		return nil
+	}
+	out := make(map[string]json.RawMessage, len(src))
+	for key, value := range src {
+		out[key] = append(json.RawMessage(nil), value...)
+	}
+	return out
+}
+
 func cloneCustomProvidersMap(src map[string]ProviderEntry) map[string]ProviderEntry {
 	if src == nil {
 		return nil

cmd/opencodereview/provider_tui_funcs_test.go

@@ -4,6 +4,7 @@
 package main
 
 import (
+	"encoding/json"
 	"os"
 	"path/filepath"
 	"reflect"
@@ -294,6 +295,9 @@ func TestCloneProviderEntry_CopiesEveryField(t *testing.T) {
 		ExtraHeaders: map[string]string{"X-Trace": "on"},
 		AWSRegion:    "us-west-2",
 		AWSProfile:   "example-profile",
+		unknownJSONFields: map[string]json.RawMessage{
+			"future_provider": json.RawMessage(`{"value":"preserve-me"}`),
+		},
 	}
 
 	rv := reflect.ValueOf(orig)