refactor: migrate Gson serialization to kotlinx.serialization (#475)

* refactor: migrate Gson serialization to kotlinx.serialization

* fix(dto): resolve serializing Any? and Map<String, Any?> with JsonElement

* test(refactor): fix unit test issues under kotlinx.serialization and update nullable DTO defaults

* fix(chat): support flexible numeric and string decoding for message timestamps

* fix(chat): sequentialize cache loading to avoid overwriting network state

app/build.gradle.kts

@@ -151,8 +151,8 @@ dependencies {
     implementation(libs.okhttp)
     implementation(libs.okhttp.logging)
     implementation(libs.retrofit)
-    implementation(libs.retrofit.converter.gson)
+    implementation(libs.retrofit.converter.kotlinx.serialization)
-    implementation(libs.gson)
+    implementation(libs.kotlinx.serialization.json)
 
     // Image loading
     implementation(libs.coil.compose)

app/proguard-rules.pro

@@ -18,11 +18,7 @@
 -keep class com.m57.hermescontrol.ui.chat.MessageRole { *; }
 -keep class com.m57.hermescontrol.ui.chat.ToolStatus { *; }
 
-# Gson itself
+# Generic type signatures used by serialization
--dontwarn com.google.gson.**
--keep class com.google.gson.** { *; }
-
-# Generic type signatures used by Gson
 -keepattributes Signature
 -keepattributes *Annotation*
 -keepattributes EnclosingMethod

app/src/main/java/com/m57/hermescontrol/data/local/AuthManager.kt

@@ -4,6 +4,9 @@ import android.content.Context
 import android.content.SharedPreferences
 import androidx.security.crypto.EncryptedSharedPreferences
 import androidx.security.crypto.MasterKeys
+import com.m57.hermescontrol.data.model.ConnectionProfile
+import com.m57.hermescontrol.data.model.PinnedModel
+import com.m57.hermescontrol.data.remote.OkHttpProvider
 import com.m57.hermescontrol.theme.BottomNavDisplayMode
 import com.m57.hermescontrol.theme.ThemePreference
 import com.m57.hermescontrol.theme.ThemePreset
@@ -15,6 +18,8 @@ import kotlinx.coroutines.flow.MutableStateFlow
 import kotlinx.coroutines.flow.StateFlow
 import kotlinx.coroutines.flow.asStateFlow
 import kotlinx.coroutines.runBlocking
+import kotlinx.serialization.decodeFromString
+import kotlinx.serialization.encodeToString
 
 /**
  * Singleton that manages encrypted storage of the Hermes dashboard token
@@ -69,8 +74,6 @@ object AuthManager {
     private val _tokenFlow = MutableStateFlow<String?>(null)
     val tokenFlow: StateFlow<String?> = _tokenFlow.asStateFlow()
 
-    private val gson = com.m57.hermescontrol.data.remote.OkHttpProvider.gson
-
     /**
      * Initialise the encrypted preferences.
      * Call this once from Application.onCreate() or MainActivity.onCreate().
@@ -160,14 +163,10 @@ object AuthManager {
 
     // ── Connection Profiles ──────────────────────────────────────────────
 
-    fun getConnectionProfiles(): List<com.m57.hermescontrol.data.model.ConnectionProfile> {
+    fun getConnectionProfiles(): List<ConnectionProfile> {
         val json = requirePrefs().getString(KEY_CONNECTION_PROFILES, null) ?: return emptyList()
         return try {
-            val type =
+            OkHttpProvider.json.decodeFromString<List<ConnectionProfile>>(json)
-                object : com.google.gson.reflect.TypeToken<
-                    List<com.m57.hermescontrol.data.model.ConnectionProfile>,
-                >() {}.type
-            gson.fromJson(json, type) ?: emptyList()
         } catch (e: Exception) {
             if (com.m57.hermescontrol.BuildConfig.DEBUG) {
                 android.util.Log.w("AuthManager", "Failed to parse connection profiles", e)
@@ -176,21 +175,17 @@ object AuthManager {
         }
     }
 
-    fun saveConnectionProfiles(profiles: List<com.m57.hermescontrol.data.model.ConnectionProfile>) {
+    fun saveConnectionProfiles(profiles: List<ConnectionProfile>) {
-        val json = gson.toJson(profiles)
+        val json = OkHttpProvider.json.encodeToString(profiles)
         requirePrefs().edit().putString(KEY_CONNECTION_PROFILES, json).apply()
     }
 
     // ── Pinned Models ────────────────────────────────────────────────────
 
-    fun getPinnedModels(): List<com.m57.hermescontrol.data.model.PinnedModel> {
+    fun getPinnedModels(): List<PinnedModel> {
         val json = requirePrefs().getString(KEY_PINNED_MODELS, null) ?: return emptyList()
         return try {
-            val type =
+            OkHttpProvider.json.decodeFromString<List<PinnedModel>>(json)
-                object : com.google.gson.reflect.TypeToken<
-                    List<com.m57.hermescontrol.data.model.PinnedModel>,
-                >() {}.type
-            gson.fromJson(json, type) ?: emptyList()
         } catch (e: Exception) {
             if (com.m57.hermescontrol.BuildConfig.DEBUG) {
                 android.util.Log.w("AuthManager", "Failed to parse pinned models", e)
@@ -200,7 +195,9 @@ object AuthManager {
     }
 
     fun savePinnedModels(pinned: List<com.m57.hermescontrol.data.model.PinnedModel>) {
-        val json = gson.toJson(pinned)
+        val json =
+            com.m57.hermescontrol.data.remote.OkHttpProvider.json
+                .encodeToString(pinned)
         requirePrefs().edit().putString(KEY_PINNED_MODELS, json).apply()
     }
 

app/src/main/java/com/m57/hermescontrol/data/model/Achievement.kt

@@ -1,68 +1,73 @@
 package com.m57.hermescontrol.data.model
+import kotlinx.serialization.SerialName
+import kotlinx.serialization.Serializable
 
-import com.google.gson.annotations.SerializedName
+@Serializable
-
 data class AchievementsResponse(
     val achievements: List<Achievement>? = emptyList(),
-    @SerializedName("unlocked_count") val unlockedCount: Int = 0,
+    @SerialName("unlocked_count") val unlockedCount: Int = 0,
-    @SerializedName("discovered_count") val discoveredCount: Int = 0,
+    @SerialName("discovered_count") val discoveredCount: Int = 0,
-    @SerializedName("secret_count") val secretCount: Int = 0,
+    @SerialName("secret_count") val secretCount: Int = 0,
-    @SerializedName("total_count") val totalCount: Int = 0,
+    @SerialName("total_count") val totalCount: Int = 0,
-    @SerializedName("is_stale") val isStale: Boolean = false,
+    @SerialName("is_stale") val isStale: Boolean = false,
-    @SerializedName("generated_at") val generatedAt: Long? = null,
+    @SerialName("generated_at") val generatedAt: Long? = null,
-    @SerializedName("scan_meta") val scanMeta: ScanMeta? = null,
+    @SerialName("scan_meta") val scanMeta: ScanMeta? = null,
     val error: String? = null,
 )
 
+@Serializable
 data class ScanMeta(
     val status: ScanStatus? = null,
 )
 
+@Serializable
 data class ScanStatus(
     val state: String = "idle",
-    @SerializedName("started_at") val startedAt: Long? = null,
+    @SerialName("started_at") val startedAt: Long? = null,
-    @SerializedName("finished_at") val finishedAt: Long? = null,
+    @SerialName("finished_at") val finishedAt: Long? = null,
-    @SerializedName("last_error") val lastError: String? = null,
+    @SerialName("last_error") val lastError: String? = null,
-    @SerializedName("last_duration_ms") val lastDurationMs: Long? = null,
+    @SerialName("last_duration_ms") val lastDurationMs: Long? = null,
-    @SerializedName("run_count") val runCount: Int = 0,
+    @SerialName("run_count") val runCount: Int = 0,
 )
 
+@Serializable
 data class RecentUnlock(
     val id: String,
     val name: String,
-    val description: String?,
+    val description: String? = null,
-    val category: String?,
+    val category: String? = null,
-    val kind: String?,
+    val kind: String? = null,
-    val icon: String?,
+    val icon: String? = null,
     val unlocked: Boolean,
     val discovered: Boolean,
-    val state: String?,
+    val state: String? = null,
-    val tier: String?,
+    val tier: String? = null,
-    val progress: Double?,
+    val progress: Double? = null,
-    @SerializedName("next_tier") val nextTier: String?,
+    @SerialName("next_tier") val nextTier: String? = null,
-    @SerializedName("next_threshold") val nextThreshold: Double?,
+    @SerialName("next_threshold") val nextThreshold: Double? = null,
-    @SerializedName("progress_pct") val progressPct: Double?,
+    @SerialName("progress_pct") val progressPct: Double? = null,
-    @SerializedName("unlocked_at") val unlockedAt: Long?,
+    @SerialName("unlocked_at") val unlockedAt: Long? = null,
-    val secret: Boolean?,
+    val secret: Boolean? = null,
-    val criteria: String?,
+    val criteria: String? = null,
 )
 
+@Serializable
 data class Achievement(
     val id: String,
     val name: String,
-    val description: String?,
+    val description: String? = null,
-    val category: String?,
+    val category: String? = null,
-    val kind: String?,
+    val kind: String? = null,
-    val icon: String?,
+    val icon: String? = null,
     val unlocked: Boolean,
     val discovered: Boolean,
-    val state: String?,
+    val state: String? = null,
-    val tier: String?,
+    val tier: String? = null,
-    val progress: Double?,
+    val progress: Double? = null,
-    @SerializedName("next_tier") val nextTier: String?,
+    @SerialName("next_tier") val nextTier: String? = null,
-    @SerializedName("next_threshold") val nextThreshold: Double?,
+    @SerialName("next_threshold") val nextThreshold: Double? = null,
-    @SerializedName("progress_pct") val progressPct: Double?,
+    @SerialName("progress_pct") val progressPct: Double? = null,
-    @SerializedName("unlocked_at") val unlockedAt: Long?,
+    @SerialName("unlocked_at") val unlockedAt: Long? = null,
-    val secret: Boolean?,
+    val secret: Boolean? = null,
-    val criteria: String?,
+    val criteria: String? = null,
 )

app/src/main/java/com/m57/hermescontrol/data/model/ActionResponse.kt

@@ -1,5 +1,7 @@
 package com.m57.hermescontrol.data.model
+import kotlinx.serialization.Serializable
 
+@Serializable
 data class ActionResponse(
     val archive: String? = null,
     val name: String? = null,

app/src/main/java/com/m57/hermescontrol/data/model/ActionStatusResponse.kt

@@ -1,5 +1,7 @@
 package com.m57.hermescontrol.data.model
+import kotlinx.serialization.Serializable
 
+@Serializable
 data class ActionStatusResponse(
     val exit_code: Int? = null,
     val lines: List<String>? = null,

app/src/main/java/com/m57/hermescontrol/data/model/Attachment.kt

@@ -1,4 +1,5 @@
 package com.m57.hermescontrol.data.model
+import kotlinx.serialization.Serializable
 
 /**
  * Represents a file attached to a chat message.
@@ -9,6 +10,7 @@ package com.m57.hermescontrol.data.model
  * @param size File size in bytes
  * @param localPath Optional local file system path for direct access
  */
+@Serializable
 data class Attachment(
     val uri: String,
     val name: String,

app/src/main/java/com/m57/hermescontrol/data/model/CheckpointsResponse.kt

@@ -1,10 +1,13 @@
 package com.m57.hermescontrol.data.model
+import kotlinx.serialization.Serializable
 
+@Serializable
 data class CheckpointsResponse(
     val sessions: List<CheckpointSession>? = null,
     val total_bytes: Long? = null,
 )
 
+@Serializable
 data class CheckpointSession(
     val session: String? = null,
     val files: Int? = null,

app/src/main/java/com/m57/hermescontrol/data/model/Config.kt

@@ -1,22 +1,26 @@
 package com.m57.hermescontrol.data.model
+import kotlinx.serialization.Serializable
+import kotlinx.serialization.json.JsonElement
 
-import com.google.gson.JsonElement
+@Serializable
-
 data class RawConfigResponse(
-    val path: String?,
+    val path: String? = null,
-    val yaml: String?,
+    val yaml: String? = null,
 )
 
+@Serializable
 data class UpdateRawConfigRequest(
     val yaml_text: String,
     val profile: String? = null,
 )
 
+@Serializable
 data class ConfigSchemaResponse(
     val fields: Map<String, SchemaField>,
     val category_order: List<String>,
 )
 
+@Serializable
 data class SchemaField(
     val type: String,
     val description: String? = null,
@@ -24,6 +28,7 @@ data class SchemaField(
     val options: List<String>? = null,
 )
 
+@Serializable
 data class ConfigUpdateRequest(
     val config: Map<String, JsonElement>,
     val profile: String? = null,

app/src/main/java/com/m57/hermescontrol/data/model/ConnectionProfile.kt

@@ -1,7 +1,8 @@
 package com.m57.hermescontrol.data.model
-
+import kotlinx.serialization.Serializable
 import java.util.UUID
 
+@Serializable
 data class ConnectionProfile(
     val id: String = UUID.randomUUID().toString(),
     val name: String,

app/src/main/java/com/m57/hermescontrol/data/model/CredentialPoolResponse.kt

@@ -1,14 +1,18 @@
 package com.m57.hermescontrol.data.model
+import kotlinx.serialization.Serializable
 
+@Serializable
 data class CredentialPoolResponse(
     val providers: List<CredentialPoolProvider>? = null,
 )
 
+@Serializable
 data class CredentialPoolProvider(
     val provider: String? = null,
     val entries: List<CredentialPoolEntry>? = null,
 )
 
+@Serializable
 data class CredentialPoolEntry(
     val index: Int? = null,
     val label: String? = null,

app/src/main/java/com/m57/hermescontrol/data/model/CronJob.kt

@@ -1,17 +1,23 @@
 package com.m57.hermescontrol.data.model
+import kotlinx.serialization.Serializable
+import kotlinx.serialization.json.JsonElement
+import kotlinx.serialization.json.JsonObject
+import kotlinx.serialization.json.JsonPrimitive
 
+@Serializable
 data class CronJobRepeat(
     val times: Int? = null,
     val completed: Int = 0,
 )
 
+@Serializable
 data class CronJob(
     val id: String,
     val name: String,
-    val schedule: Any?,
+    val schedule: JsonElement? = null,
-    val state: String?,
+    val state: String? = null,
-    val last_run_status: String?,
+    val last_run_status: String? = null,
-    val next_run: String?,
+    val next_run: String? = null,
     val schedule_display: String? = null,
     val last_status: String? = null,
     val next_run_at: String? = null,
@@ -36,8 +42,8 @@ data class CronJob(
     val scheduleText: String
         get() =
             when (schedule) {
-                is String -> schedule
+                is JsonPrimitive -> schedule.content
-                is Map<*, *> -> (schedule["display"] as? String) ?: schedule_display ?: ""
+                is JsonObject -> (schedule["display"] as? JsonPrimitive)?.content ?: schedule_display ?: ""
                 else -> schedule_display ?: ""
             }
 

app/src/main/java/com/m57/hermescontrol/data/model/CronJobRequests.kt

@@ -1,5 +1,8 @@
 package com.m57.hermescontrol.data.model
+import kotlinx.serialization.Serializable
+import kotlinx.serialization.json.JsonElement
 
+@Serializable
 data class CreateCronJobRequest(
     val name: String = "",
     val schedule: String,
@@ -17,6 +20,7 @@ data class CreateCronJobRequest(
     val repeat: Int? = null,
 )
 
+@Serializable
 data class UpdateCronJobRequest(
-    val updates: Map<String, Any?>,
+    val updates: Map<String, JsonElement>,
 )

app/src/main/java/com/m57/hermescontrol/data/model/CuratorResponse.kt

@@ -1,5 +1,7 @@
 package com.m57.hermescontrol.data.model
+import kotlinx.serialization.Serializable
 
+@Serializable
 data class CuratorResponse(
     val enabled: Boolean? = null,
     val paused: Boolean? = null,

app/src/main/java/com/m57/hermescontrol/data/model/DebugShareResponse.kt

@@ -1,5 +1,7 @@
 package com.m57.hermescontrol.data.model
+import kotlinx.serialization.Serializable
 
+@Serializable
 data class DebugShareResponse(
     val ok: Boolean? = null,
     val urls: Map<String, String>? = null,

app/src/main/java/com/m57/hermescontrol/data/model/DoctorResponse.kt

@@ -1,7 +1,9 @@
 package com.m57.hermescontrol.data.model
+import kotlinx.serialization.Serializable
 
+@Serializable
 data class DoctorResponse(
     val ok: Boolean,
-    val pid: Int?,
+    val pid: Int? = null,
-    val name: String?,
+    val name: String? = null,
 )

app/src/main/java/com/m57/hermescontrol/data/model/EnvVarConfig.kt

@@ -1,32 +1,37 @@
 package com.m57.hermescontrol.data.model
+import kotlinx.serialization.SerialName
+import kotlinx.serialization.Serializable
 
-import com.google.gson.annotations.SerializedName
+@Serializable
-
 data class EnvVarConfig(
-    @SerializedName("is_set") val isSet: Boolean,
+    @SerialName("is_set") val isSet: Boolean,
-    @SerializedName("redacted_value") val redactedValue: String?,
+    @SerialName("redacted_value") val redactedValue: String? = null,
-    val description: String?,
+    val description: String? = null,
-    val url: String?,
+    val url: String? = null,
-    val category: String?,
+    val category: String? = null,
-    @SerializedName("is_password") val isPassword: Boolean,
+    @SerialName("is_password") val isPassword: Boolean,
 )
 
+@Serializable
 data class EnvVarRevealRequest(
     val key: String,
     val profile: String? = null,
 )
 
+@Serializable
 data class EnvVarRevealResponse(
     val key: String,
     val value: String,
 )
 
+@Serializable
 data class EnvVarUpdate(
     val key: String,
     val value: String,
     val profile: String? = null,
 )
 
+@Serializable
 data class EnvVarDeleteRequest(
     val key: String,
     val profile: String? = null,

app/src/main/java/com/m57/hermescontrol/data/model/HookResponse.kt

@@ -1,10 +1,13 @@
 package com.m57.hermescontrol.data.model
+import kotlinx.serialization.Serializable
 
+@Serializable
 data class HookResponse(
     val hooks: List<HookEntry>? = null,
     val valid_events: List<String>? = null,
 )
 
+@Serializable
 data class HookEntry(
     val event: String? = null,
     val matcher: String? = null,

app/src/main/java/com/m57/hermescontrol/data/model/Kanban.kt

@@ -1,37 +1,43 @@
 package com.m57.hermescontrol.data.model
+import kotlinx.serialization.SerialName
+import kotlinx.serialization.Serializable
 
-import com.google.gson.annotations.SerializedName
+@Serializable
-
 data class KanbanBoard(
-    @SerializedName("slug") val id: String,
+    @SerialName("slug") val id: String,
     val name: String,
-    val description: String?,
+    val description: String? = null,
 )
 
+@Serializable
 data class KanbanTask(
     val id: String,
     val title: String,
-    @SerializedName("body") val description: String?,
+    @SerialName("body") val description: String? = null,
     val status: String,
-    @SerializedName("assignee") val assignedTo: String?,
+    @SerialName("assignee") val assignedTo: String? = null,
 )
 
+@Serializable
 data class CreateTaskBody(
     val title: String,
-    val body: String?,
+    val body: String? = null,
 )
 
+@Serializable
 data class KanbanColumn(
     val name: String,
     val tasks: List<KanbanTask>,
 )
 
+@Serializable
 data class KanbanBoardResponse(
     val columns: List<KanbanColumn>,
-    val assignees: List<String>?,
+    val assignees: List<String>? = null,
-    val tenants: List<String>?,
+    val tenants: List<String>? = null,
 )
 
+@Serializable
 data class KanbanBoardsResponse(
     val boards: List<KanbanBoard>,
     val current: String? = null,

app/src/main/java/com/m57/hermescontrol/data/model/LogResponse.kt

@@ -1,5 +1,7 @@
 package com.m57.hermescontrol.data.model
+import kotlinx.serialization.Serializable
 
+@Serializable
 data class LogResponse(
     val lines: List<String>? = null,
     val logs: List<String>? = null,

app/src/main/java/com/m57/hermescontrol/data/model/McpServer.kt

@@ -1,25 +1,30 @@
 package com.m57.hermescontrol.data.model
+import kotlinx.serialization.Serializable
 
+@Serializable
 data class McpServersResponse(
     val servers: List<McpServer>,
 )
 
+@Serializable
 data class McpServer(
     val name: String,
-    val transport: String?,
+    val transport: String? = null,
-    val url: String?,
+    val url: String? = null,
-    val command: String?,
+    val command: String? = null,
-    val args: List<String>?,
+    val args: List<String>? = null,
-    val env: Map<String, String>?,
+    val env: Map<String, String>? = null,
     val enabled: Boolean,
     val status: String? = null,
     val error: String? = null,
 )
 
+@Serializable
 data class McpServerToggleRequest(
     val enabled: Boolean,
 )
 
+@Serializable
 data class AddMcpServerRequest(
     val name: String,
     val url: String? = null,
@@ -28,10 +33,12 @@ data class AddMcpServerRequest(
     val env: Map<String, String>? = null,
 )
 
+@Serializable
 data class McpCatalogResponse(
     val entries: List<McpCatalogEntry>,
 )
 
+@Serializable
 data class McpCatalogEntry(
     val name: String,
     val description: String? = null,
@@ -42,6 +49,7 @@ data class McpCatalogEntry(
     val env: List<McpCatalogEnvVar>? = null,
 )
 
+@Serializable
 data class McpCatalogEnvVar(
     val key: String,
     val label: String? = null,
@@ -49,6 +57,7 @@ data class McpCatalogEnvVar(
     val required: Boolean = false,
 )
 
+@Serializable
 data class McpCatalogInstallRequest(
     val name: String,
     val env: Map<String, String>? = null,

app/src/main/java/com/m57/hermescontrol/data/model/MemoryResponse.kt

@@ -1,10 +1,13 @@
 package com.m57.hermescontrol.data.model
+import kotlinx.serialization.Serializable
 
+@Serializable
 data class MemoryResponse(
     val active: String? = null,
     val builtin_files: BuiltinFileSizes? = null,
 )
 
+@Serializable
 data class BuiltinFileSizes(
     val memory: Long? = null,
     val user: Long? = null,

app/src/main/java/com/m57/hermescontrol/data/model/MessagingPlatform.kt

@@ -1,57 +1,63 @@
 package com.m57.hermescontrol.data.model
+import kotlinx.serialization.SerialName
+import kotlinx.serialization.Serializable
 
-import com.google.gson.annotations.SerializedName
+@Serializable
-
 data class MessagingPlatform(
     val id: String,
     val name: String,
     val description: String? = null,
-    @SerializedName("docs_url") val docsUrl: String? = null,
+    @SerialName("docs_url") val docsUrl: String? = null,
     val enabled: Boolean,
     val configured: Boolean,
-    @SerializedName("gateway_running") val gatewayRunning: Boolean = false,
+    @SerialName("gateway_running") val gatewayRunning: Boolean = false,
     val state: String = "disabled",
-    @SerializedName("error_code") val errorCode: String? = null,
+    @SerialName("error_code") val errorCode: String? = null,
-    @SerializedName("error_message") val errorMessage: String? = null,
+    @SerialName("error_message") val errorMessage: String? = null,
-    @SerializedName("env_vars") val envVars: List<EnvVarField>? = null,
+    @SerialName("env_vars") val envVars: List<EnvVarField>? = null,
-    @SerializedName("updated_at") val updatedAt: String? = null,
+    @SerialName("updated_at") val updatedAt: String? = null,
-    @SerializedName("home_channel") val homeChannel: HomeChannelInfo? = null,
+    @SerialName("home_channel") val homeChannel: HomeChannelInfo? = null,
 )
 
+@Serializable
 data class HomeChannelInfo(
     val platform: String,
-    @SerializedName("chat_id") val chatId: String,
+    @SerialName("chat_id") val chatId: String,
     val name: String,
-    @SerializedName("thread_id") val threadId: String? = null,
+    @SerialName("thread_id") val threadId: String? = null,
 )
 
+@Serializable
 data class EnvVarField(
     val key: String,
     val required: Boolean,
-    @SerializedName("is_set") val isSet: Boolean,
+    @SerialName("is_set") val isSet: Boolean,
-    @SerializedName("redacted_value") val redactedValue: String? = null,
+    @SerialName("redacted_value") val redactedValue: String? = null,
     val description: String? = null,
     val prompt: String? = null,
     val help: String? = null,
-    @SerializedName("is_password") val isPassword: Boolean,
+    @SerialName("is_password") val isPassword: Boolean,
     val advanced: Boolean = false,
     val url: String? = null,
-    @SerializedName("expires_at") val expiresAt: String? = null,
+    @SerialName("expires_at") val expiresAt: String? = null,
 )
 
+@Serializable
 data class MessagingPlatformResponse(
-    @SerializedName("env_path") val envPath: String,
+    @SerialName("env_path") val envPath: String,
-    @SerializedName("gateway_start_command") val gatewayStartCommand: String,
+    @SerialName("gateway_start_command") val gatewayStartCommand: String,
     val platforms: List<MessagingPlatform>,
 )
 
+@Serializable
 data class MessagingPlatformUpdate(
     val enabled: Boolean? = null,
     val env: Map<String, String> = emptyMap(),
-    @SerializedName("clear_env") val clearEnv: List<String> = emptyList(),
+    @SerialName("clear_env") val clearEnv: List<String> = emptyList(),
     val profile: String? = null,
 )
 
+@Serializable
 data class MessagingPlatformTestResult(
     val ok: Boolean,
     val state: String,
@@ -60,37 +66,42 @@ data class MessagingPlatformTestResult(
 
 // ── Telegram onboarding ─────────────────────────────────────────────────
 
+@Serializable
 data class TelegramOnboardingStartRequest(
-    @SerializedName("bot_name") val botName: String = "Hermes Agent",
+    @SerialName("bot_name") val botName: String = "Hermes Agent",
 )
 
+@Serializable
 data class TelegramOnboardingStartResponse(
-    @SerializedName("pairing_id") val pairingId: String,
+    @SerialName("pairing_id") val pairingId: String,
-    @SerializedName("suggested_username") val suggestedUsername: String,
+    @SerialName("suggested_username") val suggestedUsername: String,
-    @SerializedName("deep_link") val deepLink: String,
+    @SerialName("deep_link") val deepLink: String,
-    @SerializedName("qr_payload") val qrPayload: String,
+    @SerialName("qr_payload") val qrPayload: String,
-    @SerializedName("expires_at") val expiresAt: String,
+    @SerialName("expires_at") val expiresAt: String,
 )
 
+@Serializable
 data class TelegramOnboardingStatusResponse(
     val status: String,
-    @SerializedName("bot_username") val botUsername: String? = null,
+    @SerialName("bot_username") val botUsername: String? = null,
-    @SerializedName("owner_user_id") val ownerUserId: String? = null,
+    @SerialName("owner_user_id") val ownerUserId: String? = null,
-    @SerializedName("expires_at") val expiresAt: String? = null,
+    @SerialName("expires_at") val expiresAt: String? = null,
 )
 
+@Serializable
 data class TelegramOnboardingApplyRequest(
-    @SerializedName("allowed_user_ids") val allowedUserIds: List<String>,
+    @SerialName("allowed_user_ids") val allowedUserIds: List<String>,
     val profile: String? = null,
 )
 
+@Serializable
 data class TelegramOnboardingApplyResponse(
     val ok: Boolean,
     val platform: String,
-    @SerializedName("bot_username") val botUsername: String? = null,
+    @SerialName("bot_username") val botUsername: String? = null,
-    @SerializedName("needs_restart") val needsRestart: Boolean,
+    @SerialName("needs_restart") val needsRestart: Boolean,
-    @SerializedName("restart_started") val restartStarted: Boolean? = null,
+    @SerialName("restart_started") val restartStarted: Boolean? = null,
-    @SerializedName("restart_action") val restartAction: String? = null,
+    @SerialName("restart_action") val restartAction: String? = null,
-    @SerializedName("restart_pid") val restartPid: Int? = null,
+    @SerialName("restart_pid") val restartPid: Int? = null,
-    @SerializedName("restart_error") val restartError: String? = null,
+    @SerialName("restart_error") val restartError: String? = null,
 )

app/src/main/java/com/m57/hermescontrol/data/model/ModelAssignment.kt

@@ -1,5 +1,7 @@
 package com.m57.hermescontrol.data.model
+import kotlinx.serialization.Serializable
 
+@Serializable
 data class AuxiliaryTaskAssignment(
     val task: String,
     val provider: String,
@@ -7,21 +9,25 @@ data class AuxiliaryTaskAssignment(
     val base_url: String? = null,
 )
 
+@Serializable
 data class AuxiliaryModelsResponse(
     val tasks: List<AuxiliaryTaskAssignment>,
     val main: MainModelAssignment,
 )
 
+@Serializable
 data class MainModelAssignment(
     val provider: String,
     val model: String,
 )
 
+@Serializable
 data class MoaModelSlot(
     val provider: String,
     val model: String,
 )
 
+@Serializable
 data class MoaConfigPreset(
     val reference_models: List<MoaModelSlot>,
     val aggregator: MoaModelSlot,
@@ -31,6 +37,7 @@ data class MoaConfigPreset(
     val enabled: Boolean = true,
 )
 
+@Serializable
 data class MoaConfigResponse(
     val default_preset: String = "",
     val active_preset: String = "",
@@ -43,6 +50,7 @@ data class MoaConfigResponse(
     val enabled: Boolean = true,
 )
 
+@Serializable
 data class ModelAssignmentRequest(
     val confirm_expensive_model: Boolean = false,
     val scope: String,
@@ -52,6 +60,7 @@ data class ModelAssignmentRequest(
     val task: String? = null,
 )
 
+@Serializable
 data class ModelAssignmentResponse(
     val confirm_message: String? = null,
     val confirm_required: Boolean? = null,

app/src/main/java/com/m57/hermescontrol/data/model/ModelOption.kt

@@ -1,22 +1,26 @@
 package com.m57.hermescontrol.data.model
+import kotlinx.serialization.Serializable
 
+@Serializable
 data class ModelOptionsResponse(
     val providers: List<ModelProvider>,
 )
 
+@Serializable
 data class ModelProvider(
     val slug: String,
     val name: String,
-    val is_current: Boolean?,
+    val is_current: Boolean? = null,
-    val is_user_defined: Boolean?,
+    val is_user_defined: Boolean? = null,
-    val models: List<String>?,
+    val models: List<String>? = null,
-    val total_models: Int?,
+    val total_models: Int? = null,
-    val source: String?,
+    val source: String? = null,
-    val authenticated: Boolean?,
+    val authenticated: Boolean? = null,
-    val auth_type: String?,
+    val auth_type: String? = null,
-    val warning: String?,
+    val warning: String? = null,
 )
 
+@Serializable
 data class PinnedModel(
     val providerSlug: String,
     val modelName: String,

app/src/main/java/com/m57/hermescontrol/data/model/Pairing.kt

@@ -1,24 +1,29 @@
 package com.m57.hermescontrol.data.model
+import kotlinx.serialization.Serializable
 
+@Serializable
 data class PairingResponse(
     val pending: List<PairingItem>,
     val approved: List<PairingItem>,
 )
 
+@Serializable
 data class PairingItem(
     val platform: String,
-    val user_id: String?,
+    val user_id: String? = null,
-    val username: String?,
+    val username: String? = null,
-    val display_name: String?,
+    val display_name: String? = null,
-    val code: String?,
+    val code: String? = null,
-    val created_at: String?,
+    val created_at: String? = null,
 )
 
+@Serializable
 data class PairingApproveRequest(
     val platform: String,
     val code: String,
 )
 
+@Serializable
 data class PairingRevokeRequest(
     val platform: String,
     val user_id: String,

app/src/main/java/com/m57/hermescontrol/data/model/PluginInfo.kt

@@ -1,20 +1,21 @@
 package com.m57.hermescontrol.data.model
+import kotlinx.serialization.SerialName
+import kotlinx.serialization.Serializable
 
-import com.google.gson.annotations.SerializedName
+@Serializable
-
 data class PluginInfo(
     val name: String,
-    val description: String?,
+    val description: String? = null,
-    val version: String?,
+    val version: String? = null,
-    val source: String?,
+    val source: String? = null,
-    @SerializedName("runtime_status") val runtimeStatus: String?,
+    @SerialName("runtime_status") val runtimeStatus: String? = null,
-    @SerializedName("has_dashboard_manifest") val hasDashboardManifest: Boolean = false,
+    @SerialName("has_dashboard_manifest") val hasDashboardManifest: Boolean = false,
-    @SerializedName("dashboard_manifest") val dashboardManifest: PluginManifestData? = null,
+    @SerialName("dashboard_manifest") val dashboardManifest: PluginManifestData? = null,
-    @SerializedName("can_remove") val canRemove: Boolean = false,
+    @SerialName("can_remove") val canRemove: Boolean = false,
-    @SerializedName("can_update_git") val canUpdateGit: Boolean = false,
+    @SerialName("can_update_git") val canUpdateGit: Boolean = false,
-    @SerializedName("auth_required") val authRequired: Boolean = false,
+    @SerialName("auth_required") val authRequired: Boolean = false,
-    @SerializedName("auth_command") val authCommand: String? = null,
+    @SerialName("auth_command") val authCommand: String? = null,
-    @SerializedName("user_hidden") val userHidden: Boolean = false,
+    @SerialName("user_hidden") val userHidden: Boolean = false,
 ) {
     val enabled: Boolean
         get() = runtimeStatus.equals("enabled", ignoreCase = true)
@@ -25,6 +26,7 @@ data class PluginInfo(
                 runtimeStatus.equals("disabled", ignoreCase = true)
 }
 
+@Serializable
 data class PluginManifestData(
     val name: String? = null,
     val label: String? = null,
@@ -35,10 +37,11 @@ data class PluginManifestData(
     val slots: List<String>? = null,
     val entry: String? = null,
     val css: String? = null,
-    @SerializedName("has_api") val hasApi: Boolean = false,
+    @SerialName("has_api") val hasApi: Boolean = false,
     val source: String? = null,
 )
 
+@Serializable
 data class PluginTabInfo(
     val path: String? = null,
     val position: String? = null,
@@ -46,6 +49,7 @@ data class PluginTabInfo(
     val hidden: Boolean = false,
 )
 
+@Serializable
 data class DashboardPluginMeta(
     val name: String? = null,
     val label: String? = null,
@@ -53,31 +57,36 @@ data class DashboardPluginMeta(
     val tab: PluginTabInfo? = null,
 )
 
+@Serializable
 data class PluginsHubProviders(
-    @SerializedName("memory_provider") val memoryProvider: String? = null,
+    @SerialName("memory_provider") val memoryProvider: String? = null,
-    @SerializedName("memory_options") val memoryOptions: List<ProviderOption> = emptyList(),
+    @SerialName("memory_options") val memoryOptions: List<ProviderOption> = emptyList(),
-    @SerializedName("context_engine") val contextEngine: String? = null,
+    @SerialName("context_engine") val contextEngine: String? = null,
-    @SerializedName("context_options") val contextOptions: List<ProviderOption> = emptyList(),
+    @SerialName("context_options") val contextOptions: List<ProviderOption> = emptyList(),
 )
 
+@Serializable
 data class ProviderOption(
     val name: String,
     val description: String? = null,
 )
 
+@Serializable
 data class PluginsHubResponse(
     val plugins: List<PluginInfo>,
-    @SerializedName("orphan_dashboard_plugins") val orphanDashboardPlugins: List<DashboardPluginMeta> = emptyList(),
+    @SerialName("orphan_dashboard_plugins") val orphanDashboardPlugins: List<DashboardPluginMeta> = emptyList(),
     val providers: PluginsHubProviders? = null,
 )
 
+@Serializable
 data class AgentPluginInstallBody(
     val identifier: String,
     val force: Boolean = false,
     val enable: Boolean = true,
 )
 
+@Serializable
 data class PluginProvidersPutRequest(
-    @SerializedName("memory_provider") val memoryProvider: String? = null,
+    @SerialName("memory_provider") val memoryProvider: String? = null,
-    @SerializedName("context_engine") val contextEngine: String? = null,
+    @SerialName("context_engine") val contextEngine: String? = null,
 )

app/src/main/java/com/m57/hermescontrol/data/model/PortalResponse.kt

@@ -1,5 +1,7 @@
 package com.m57.hermescontrol.data.model
+import kotlinx.serialization.Serializable
 
+@Serializable
 data class PortalResponse(
     val logged_in: Boolean? = null,
     val portal_url: String? = null,
@@ -9,6 +11,7 @@ data class PortalResponse(
     val features: List<PortalFeature>? = null,
 )
 
+@Serializable
 data class PortalFeature(
     val label: String? = null,
     val state: String? = null,

app/src/main/java/com/m57/hermescontrol/data/model/Profile.kt

@@ -1,9 +1,12 @@
 package com.m57.hermescontrol.data.model
+import kotlinx.serialization.Serializable
 
+@Serializable
 data class ProfilesResponse(
     val profiles: List<ProfileInfo>,
 )
 
+@Serializable
 data class ProfileInfo(
     val name: String,
     val path: String? = null,
@@ -17,46 +20,55 @@ data class ProfileInfo(
     val description_auto: Boolean? = null,
 )
 
+@Serializable
 data class ActiveProfileResponse(
     val active: String,
-    val current: String?,
+    val current: String? = null,
 )
 
+@Serializable
 data class SetActiveProfileRequest(
     val name: String,
 )
 
+@Serializable
 data class ProfileSoulResponse(
     val content: String,
 )
 
+@Serializable
 data class UpdateProfileSoulRequest(
     val content: String,
 )
 
+@Serializable
 data class UpdateProfileModelRequest(
     val provider: String,
     val model: String,
 )
 
+@Serializable
 data class CloneProfileRequest(
     val name: String,
 )
 
+@Serializable
 data class UpdateProfileDescriptionRequest(
     val description: String,
 )
 
+@Serializable
 data class CreateProfileRequest(
     val name: String,
-    val description: String?,
+    val description: String? = null,
-    val provider: String?,
+    val provider: String? = null,
-    val model: String?,
+    val model: String? = null,
-    val mcp_servers: List<McpServerConfigInput>?,
+    val mcp_servers: List<McpServerConfigInput>? = null,
-    val keep_skills: Boolean?,
+    val keep_skills: Boolean? = null,
-    val hub_skills: List<String>?,
+    val hub_skills: List<String>? = null,
 )
 
+@Serializable
 data class McpServerConfigInput(
     val name: String,
     val transport: String,

app/src/main/java/com/m57/hermescontrol/data/model/SaveSkillContentRequest.kt

@@ -1,5 +1,7 @@
 package com.m57.hermescontrol.data.model
+import kotlinx.serialization.Serializable
 
+@Serializable
 data class SaveSkillContentRequest(
     val name: String,
     val content: String,

app/src/main/java/com/m57/hermescontrol/data/model/SessionListResponse.kt

@@ -1,5 +1,7 @@
 package com.m57.hermescontrol.data.model
+import kotlinx.serialization.Serializable
 
+@Serializable
 data class SessionListResponse(
     val sessions: List<SessionInfo>,
     val total: Int = 0,
@@ -7,35 +9,41 @@ data class SessionListResponse(
     val offset: Int = 0,
 )
 
+@Serializable
 data class SessionInfo(
     val id: String,
-    val title: String?,
+    val title: String? = null,
-    val created_at: String?,
+    val created_at: String? = null,
-    val message_count: Int?,
+    val message_count: Int? = null,
-    val status: String?,
+    val status: String? = null,
     val preview: String? = null,
     val started_at: Double? = null,
     val source: String? = null,
 )
 
+@Serializable
 data class SessionStatsResponse(
     val total: Int = 0,
     val active: Int = 0,
 )
 
+@Serializable
 data class SessionRenameRequest(
     val title: String,
 )
 
+@Serializable
 data class BulkDeleteRequest(
     val ids: List<String>,
     val delete_all: Boolean = false,
 )
 
+@Serializable
 data class PruneRequest(
     val days: Int,
 )
 
+@Serializable
 data class SessionPromptResponse(
     val prompt: String? = null,
     val id: String? = null,

app/src/main/java/com/m57/hermescontrol/data/model/SessionMessagesResponse.kt

@@ -1,12 +1,20 @@
 package com.m57.hermescontrol.data.model
+import kotlinx.serialization.Serializable
+import kotlinx.serialization.json.JsonElement
+import kotlinx.serialization.json.JsonPrimitive
 
+@Serializable
 data class SessionMessagesResponse(
     val messages: List<SessionMessage>,
 )
 
+@Serializable
 data class SessionMessage(
-    val role: String?,
+    val role: String? = null,
-    val content: String?,
+    val content: String? = null,
-    val timestamp: String?,
+    val timestamp: JsonElement? = null,
-    val type: String?,
+    val type: String? = null,
-)
+) {
+    val timestampText: String?
+        get() = (timestamp as? JsonPrimitive)?.content
+}

app/src/main/java/com/m57/hermescontrol/data/model/Skill.kt

@@ -1,11 +1,12 @@
 package com.m57.hermescontrol.data.model
+import kotlinx.serialization.SerialName
+import kotlinx.serialization.Serializable
 
-import com.google.gson.annotations.SerializedName
+@Serializable
-
 data class Skill(
     val name: String,
-    val description: String?,
+    val description: String? = null,
-    val category: String?,
+    val category: String? = null,
     val enabled: Boolean,
     val content: String? = null,
     val source: String? = null, // built-in, hub, optional
@@ -13,40 +14,46 @@ data class Skill(
     val linked_files: List<String>? = null,
 )
 
+@Serializable
 data class HubSkill(
     val name: String,
-    val description: String?,
+    val description: String? = null,
-    val source: String?,
+    val source: String? = null,
     val category: String? = null,
     val identifier: String? = null,
-    @SerializedName("trust_level") val trustLevel: String? = null,
+    @SerialName("trust_level") val trustLevel: String? = null,
     val repo: String? = null,
     val tags: List<String>? = null,
 )
 
+@Serializable
 data class SkillHubSearchResponse(
     val results: List<HubSkill>,
-    @SerializedName("source_counts") val sourceCounts: Map<String, Int>? = null,
+    @SerialName("source_counts") val sourceCounts: Map<String, Int>? = null,
-    @SerializedName("timed_out") val timedOut: List<String>? = null,
+    @SerialName("timed_out") val timedOut: List<String>? = null,
     val installed: Map<String, SkillHubInstalledEntry>? = null,
 )
 
+@Serializable
 data class SkillHubInstalledEntry(
     val name: String? = null,
-    @SerializedName("trust_level") val trustLevel: String? = null,
+    @SerialName("trust_level") val trustLevel: String? = null,
-    @SerializedName("scan_verdict") val scanVerdict: String? = null,
+    @SerialName("scan_verdict") val scanVerdict: String? = null,
 )
 
+@Serializable
 data class SkillHubInstallRequest(
     val identifier: String,
     val profile: String? = null,
 )
 
+@Serializable
 data class SkillHubUninstallRequest(
     val name: String,
     val profile: String? = null,
 )
 
+@Serializable
 data class SkillScanResponse(
     val identifier: String,
     val passed: Boolean? = null,

app/src/main/java/com/m57/hermescontrol/data/model/SkillContentResponse.kt

@@ -1,5 +1,7 @@
 package com.m57.hermescontrol.data.model
+import kotlinx.serialization.Serializable
 
+@Serializable
 data class SkillContentResponse(
     val name: String,
     val content: String,

app/src/main/java/com/m57/hermescontrol/data/model/StatusResponse.kt

@@ -1,14 +1,17 @@
 package com.m57.hermescontrol.data.model
+import kotlinx.serialization.Serializable
 
+@Serializable
 data class StatusResponse(
-    val version: String?,
+    val version: String? = null,
-    val gateway_running: Boolean?,
+    val gateway_running: Boolean? = null,
-    val active_sessions: Int?,
+    val active_sessions: Int? = null,
-    val auth_required: Boolean?,
+    val auth_required: Boolean? = null,
-    val gateway_platforms: Map<String, PlatformStatus>?,
+    val gateway_platforms: Map<String, PlatformStatus?>? = null,
 )
 
+@Serializable
 data class PlatformStatus(
-    val state: String?,
+    val state: String? = null,
     val error_code: String? = null,
 )

app/src/main/java/com/m57/hermescontrol/data/model/SystemStatsResponse.kt

@@ -1,5 +1,7 @@
 package com.m57.hermescontrol.data.model
+import kotlinx.serialization.Serializable
 
+@Serializable
 data class SystemStatsResponse(
     val os: String? = null,
     val os_release: String? = null,
@@ -20,6 +22,7 @@ data class SystemStatsResponse(
     val process: ProcessStats? = null,
 )
 
+@Serializable
 data class MemoryStats(
     val total: Long? = null,
     val available: Long? = null,
@@ -27,6 +30,7 @@ data class MemoryStats(
     val percent: Double? = null,
 )
 
+@Serializable
 data class DiskStats(
     val total: Long? = null,
     val used: Long? = null,
@@ -34,6 +38,7 @@ data class DiskStats(
     val percent: Double? = null,
 )
 
+@Serializable
 data class ProcessStats(
     val pid: Int? = null,
     val rss: Long? = null,

app/src/main/java/com/m57/hermescontrol/data/model/ToggleSkillRequest.kt

@@ -1,5 +1,7 @@
 package com.m57.hermescontrol.data.model
+import kotlinx.serialization.Serializable
 
+@Serializable
 data class ToggleSkillRequest(
     val name: String,
     val enabled: Boolean,

app/src/main/java/com/m57/hermescontrol/data/model/Toolset.kt

@@ -1,15 +1,18 @@
 package com.m57.hermescontrol.data.model
+import kotlinx.serialization.Serializable
 
+@Serializable
 data class Toolset(
     val name: String,
-    val label: String?,
+    val label: String? = null,
-    val description: String?,
+    val description: String? = null,
     val enabled: Boolean,
-    val available: Boolean?,
+    val available: Boolean? = null,
-    val configured: Boolean?,
+    val configured: Boolean? = null,
-    val tools: List<String>?,
+    val tools: List<String>? = null,
 )
 
+@Serializable
 data class ToolsetToggleRequest(
     val enabled: Boolean,
     val profile: String? = null,

app/src/main/java/com/m57/hermescontrol/data/model/UpdateCheckResponse.kt

@@ -1,5 +1,7 @@
 package com.m57.hermescontrol.data.model
+import kotlinx.serialization.Serializable
 
+@Serializable
 data class UpdateCheckResponse(
     val install_method: String? = null,
     val current_version: String? = null,

app/src/main/java/com/m57/hermescontrol/data/model/Webhook.kt

@@ -1,25 +1,29 @@
 package com.m57.hermescontrol.data.model
+import kotlinx.serialization.Serializable
 
+@Serializable
 data class WebhooksResponse(
     val enabled: Boolean,
-    val base_url: String?,
+    val base_url: String? = null,
-    val subscriptions: List<WebhookSubscription>?,
+    val subscriptions: List<WebhookSubscription>? = null,
 )
 
+@Serializable
 data class WebhookSubscription(
     val name: String,
-    val description: String?,
+    val description: String? = null,
-    val events: List<String>?,
+    val events: List<String>? = null,
-    val deliver: String?,
+    val deliver: String? = null,
-    val deliver_only: Boolean?,
+    val deliver_only: Boolean? = null,
-    val prompt: String?,
+    val prompt: String? = null,
-    val skills: List<String>?,
+    val skills: List<String>? = null,
-    val created_at: String?,
+    val created_at: String? = null,
     val url: String,
-    val secret_set: Boolean?,
+    val secret_set: Boolean? = null,
-    val enabled: Boolean?,
+    val enabled: Boolean? = null,
 )
 
+@Serializable
 data class CreateWebhookRequest(
     val name: String,
     val description: String? = null,
@@ -32,14 +36,17 @@ data class CreateWebhookRequest(
     val secret: String? = null,
 )
 
+@Serializable
 data class WebhooksToggleRequest(
     val enabled: Boolean,
 )
 
+@Serializable
 data class WebhookToggleSubscriptionRequest(
     val enabled: Boolean,
 )
 
+@Serializable
 data class DeleteWebhookResponse(
     val ok: Boolean,
 )

app/src/main/java/com/m57/hermescontrol/data/remote/ApiClient.kt

@@ -4,9 +4,10 @@ import com.m57.hermescontrol.BuildConfig
 import com.m57.hermescontrol.data.local.AuthManager
 import okhttp3.CertificatePinner
 import okhttp3.Interceptor
+import okhttp3.MediaType.Companion.toMediaType
 import okhttp3.logging.HttpLoggingInterceptor
 import retrofit2.Retrofit
-import retrofit2.converter.gson.GsonConverterFactory
+import retrofit2.converter.kotlinx.serialization.asConverterFactory
 
 /**
  * Provides a Retrofit-backed [HermesApiService].
@@ -71,7 +72,7 @@ object ApiClient {
                 .Builder()
                 .baseUrl("http://$host:$port/")
                 .client(tempOkHttp)
-                .addConverterFactory(GsonConverterFactory.create(OkHttpProvider.gson))
+                .addConverterFactory(OkHttpProvider.json.asConverterFactory("application/json".toMediaType()))
                 .build()
 
         return tempRetrofit.create(HermesApiService::class.java)
@@ -135,7 +136,7 @@ object ApiClient {
                 .Builder()
                 .baseUrl(AuthManager.baseUrl())
                 .client(okHttp)
-                .addConverterFactory(GsonConverterFactory.create(OkHttpProvider.gson))
+                .addConverterFactory(OkHttpProvider.json.asConverterFactory("application/json".toMediaType()))
                 .build()
                 .also { retrofit = it }
 

app/src/main/java/com/m57/hermescontrol/data/remote/HermesApiService.kt

@@ -1,6 +1,5 @@
 package com.m57.hermescontrol.data.remote
 
-import com.google.gson.JsonElement
 import com.m57.hermescontrol.data.model.AchievementsResponse
 import com.m57.hermescontrol.data.model.ActionResponse
 import com.m57.hermescontrol.data.model.ActionStatusResponse
@@ -91,6 +90,7 @@ import com.m57.hermescontrol.data.model.WebhookSubscription
 import com.m57.hermescontrol.data.model.WebhookToggleSubscriptionRequest
 import com.m57.hermescontrol.data.model.WebhooksResponse
 import com.m57.hermescontrol.data.model.WebhooksToggleRequest
+import kotlinx.serialization.json.JsonElement
 import okhttp3.ResponseBody
 import retrofit2.Response
 import retrofit2.http.Body

app/src/main/java/com/m57/hermescontrol/data/remote/NetworkResult.kt

@@ -1,7 +1,8 @@
 package com.m57.hermescontrol.data.remote
 
-import com.google.gson.JsonParser
 import kotlinx.coroutines.delay
+import kotlinx.serialization.json.jsonObject
+import kotlinx.serialization.json.jsonPrimitive
 import retrofit2.Response
 import java.io.IOException
 
@@ -49,11 +50,8 @@ fun mapHttpError(
     val detail =
         if (errorBody != null) {
             try {
-                val parsed =
+                val parsed = OkHttpProvider.json.parseToJsonElement(errorBody).jsonObject
-                    com.google.gson.JsonParser
+                parsed["detail"]?.jsonPrimitive?.content
-                        .parseString(errorBody)
-                        .asJsonObject
-                parsed.get("detail")?.asString
             } catch (_: Exception) {
                 null
             }

app/src/main/java/com/m57/hermescontrol/data/remote/OkHttpProvider.kt

@@ -1,7 +1,8 @@
 package com.m57.hermescontrol.data.remote
 
-import com.google.gson.Gson
+import kotlinx.serialization.ExperimentalSerializationApi
-import com.google.gson.GsonBuilder
+import kotlinx.serialization.json.Json
+import kotlinx.serialization.json.JsonNamingStrategy
 import okhttp3.ConnectionPool
 import okhttp3.OkHttpClient
 import java.util.concurrent.TimeUnit
@@ -42,6 +43,10 @@ object OkHttpProvider {
             .followRedirects(false)
             .build()
 
-    // Shared Gson — thread-safe, zero-config
+    @OptIn(ExperimentalSerializationApi::class)
-    val gson: Gson = GsonBuilder().create()
+    val json: Json =
+        Json {
+            ignoreUnknownKeys = true
+            namingStrategy = JsonNamingStrategy.SnakeCase
+        }
 }

app/src/main/java/com/m57/hermescontrol/data/ws/CommandModels.kt

@@ -1,9 +1,12 @@
 package com.m57.hermescontrol.data.ws
 
+import kotlinx.serialization.Serializable
+
 /**
  * Response from `commands.catalog` RPC — full catalog of available
  * slash commands, subcommands, and alias mappings.
  */
+@Serializable
 data class CommandCatalog(
     val pairs: List<List<String>> = emptyList(),
     val sub: Map<String, List<String>> = emptyMap(),
@@ -16,6 +19,7 @@ data class CommandCatalog(
 /**
  * A named category within the command catalog.
  */
+@Serializable
 data class CommandCategory(
     val name: String,
     val pairs: List<List<String>>,

app/src/main/java/com/m57/hermescontrol/data/ws/EventParser.kt

@@ -24,12 +24,13 @@ object EventParser {
             return if (response.error != null) {
                 WsEvent.RpcError(id, response.error)
             } else {
-                WsEvent.RpcResult(id, response.result)
+                WsEvent.RpcResult(id, response.result?.toAny())
             }
         }
 
         // ── Notification / event (no id, has method) ─────────────────────
-        val params = response.params ?: return WsEvent.Unknown(rawJson)
+        @Suppress("UNCHECKED_CAST")
+        val params = response.params?.toAny() as? Map<String, Any?> ?: return WsEvent.Unknown(rawJson)
         val eventType = params["type"] as? String ?: return WsEvent.Unknown(rawJson)
 
         @Suppress("UNCHECKED_CAST")

app/src/main/java/com/m57/hermescontrol/data/ws/HermesWsClient.kt

@@ -24,6 +24,8 @@ import kotlinx.coroutines.flow.flowOn
 import kotlinx.coroutines.flow.map
 import kotlinx.coroutines.flow.shareIn
 import kotlinx.coroutines.launch
+import kotlinx.serialization.decodeFromString
+import kotlinx.serialization.encodeToString
 import okhttp3.Request
 import okhttp3.RequestBody.Companion.toRequestBody
 import okhttp3.Response
@@ -123,7 +125,7 @@ object HermesWsClient {
             .buffer(Channel.BUFFERED)
             .map { text ->
                 try {
-                    val rpc = OkHttpProvider.gson.fromJson(text, JsonRpcResponse::class.java)
+                    val rpc = OkHttpProvider.json.decodeFromString<JsonRpcResponse>(text)
                     EventParser.parse(rpc, text)
                 } catch (e: Exception) {
                     Log.e(TAG, "Failed to parse message", e)
@@ -231,8 +233,8 @@ object HermesWsClient {
     ): String {
         val id = requestId.incrementAndGet().toString()
         onSent?.invoke(id)
-        val request = JsonRpcRequest(id = id, method = method, params = params)
+        val request = JsonRpcRequest(id = id, method = method, params = params.mapValues { it.value.toJsonElement() })
-        val json = OkHttpProvider.gson.toJson(request)
+        val json = OkHttpProvider.json.encodeToString(request)
         if (BuildConfig.DEBUG) Log.d(TAG, "→ $json")
         val ws = webSocket
         if (ws != null && connected.get()) {

app/src/main/java/com/m57/hermescontrol/data/ws/JsonRpcModels.kt

@@ -1,32 +1,77 @@
 package com.m57.hermescontrol.data.ws
 
+import kotlinx.serialization.Serializable
+import kotlinx.serialization.json.JsonArray
+import kotlinx.serialization.json.JsonElement
+import kotlinx.serialization.json.JsonNull
+import kotlinx.serialization.json.JsonObject
+import kotlinx.serialization.json.JsonPrimitive
+import kotlinx.serialization.json.booleanOrNull
+import kotlinx.serialization.json.doubleOrNull
+import kotlinx.serialization.json.longOrNull
+
 /**
  * Outgoing JSON-RPC 2.0 request sent over the WebSocket.
  */
+@Serializable
 data class JsonRpcRequest(
     val jsonrpc: String = "2.0",
     val id: String,
     val method: String,
-    val params: Map<String, Any> = emptyMap(),
+    val params: Map<String, JsonElement> = emptyMap(),
 )
 
 /**
  * Incoming JSON-RPC 2.0 response **or** server-pushed notification.
- *
- * - RPC result/error → [id] is non-null, [result] or [error] is populated.
- * - Event notification → [id] is null, [method] is `"event"`, event data in [params].
  */
+@Serializable
 data class JsonRpcResponse(
-    val jsonrpc: String?,
+    val jsonrpc: String? = null,
-    val id: String?,
+    val id: String? = null,
-    val result: Any?,
+    val result: JsonElement? = null,
-    val error: JsonRpcError?,
+    val error: JsonRpcError? = null,
-    val method: String?,
+    val method: String? = null,
-    val params: Map<String, Any?>?,
+    val params: JsonObject? = null,
 )
 
+@Serializable
 data class JsonRpcError(
     val code: Int,
     val message: String,
-    val data: Any? = null,
+    val data: JsonElement? = null,
 )
+
+fun Any?.toJsonElement(): JsonElement =
+    when (this) {
+        null -> JsonNull
+        is JsonElement -> this
+        is Boolean -> JsonPrimitive(this)
+        is Number -> JsonPrimitive(this)
+        is String -> JsonPrimitive(this)
+        is Map<*, *> -> JsonObject(this.map { it.key.toString() to it.value.toJsonElement() }.toMap())
+        is List<*> -> JsonArray(this.map { it.toJsonElement() })
+        else -> JsonPrimitive(this.toString())
+    }
+
+fun JsonElement.toAny(): Any? =
+    when (this) {
+        is JsonNull -> {
+            null
+        }
+
+        is JsonPrimitive -> {
+            if (isString) {
+                content
+            } else {
+                booleanOrNull ?: doubleOrNull ?: longOrNull ?: content
+            }
+        }
+
+        is JsonObject -> {
+            mapValues { it.value.toAny() }
+        }
+
+        is JsonArray -> {
+            map { it.toAny() }
+        }
+    }

app/src/main/java/com/m57/hermescontrol/ui/chat/ChatBubble.kt

@@ -82,6 +82,7 @@ import androidx.compose.ui.unit.sp
 import coil.compose.AsyncImage
 import com.m57.hermescontrol.R
 import com.m57.hermescontrol.data.model.Attachment
+import com.m57.hermescontrol.data.remote.OkHttpProvider
 import com.m57.hermescontrol.theme.AssistantBubble
 import com.m57.hermescontrol.theme.AssistantBubbleLight
 import com.m57.hermescontrol.theme.StatusGreen
@@ -92,6 +93,14 @@ import com.m57.hermescontrol.theme.ToolChipColorLight
 import com.m57.hermescontrol.theme.UserBubble
 import kotlinx.coroutines.delay
 import kotlinx.coroutines.launch
+import kotlinx.serialization.json.JsonArray
+import kotlinx.serialization.json.JsonElement
+import kotlinx.serialization.json.JsonNull
+import kotlinx.serialization.json.JsonObject
+import kotlinx.serialization.json.JsonPrimitive
+import kotlinx.serialization.json.boolean
+import kotlinx.serialization.json.double
+import kotlinx.serialization.json.int
 import java.time.Instant
 import java.time.ZoneId
 import java.time.format.DateTimeFormatter
@@ -537,9 +546,7 @@ fun parseToolOutput(
     val trimmed = content.trim()
     if (!trimmed.startsWith("{") && !trimmed.startsWith("[")) return null
     return try {
-        val element =
+        val element = OkHttpProvider.json.parseToJsonElement(trimmed)
-            com.google.gson.JsonParser
-                .parseString(trimmed)
         if (!element.isJsonObject) return null
         val obj = element.asJsonObject
 
@@ -2301,3 +2308,23 @@ private fun InlineAttachment(
         }
     }
 }
+
+// Extensions for backward compatibility with Gson API under kotlinx.serialization
+private val JsonElement.isJsonObject: Boolean get() = this is JsonObject
+private val JsonElement.asJsonObject: JsonObject get() = this as JsonObject
+private val JsonElement.isJsonArray: Boolean get() = this is JsonArray
+private val JsonElement.asJsonArray: JsonArray get() = this as JsonArray
+private val JsonElement.isJsonNull: Boolean get() = this is JsonNull
+private val JsonElement.isJsonPrimitive: Boolean get() = this is JsonPrimitive
+private val JsonElement.asString: String get() = (this as JsonPrimitive).content
+private val JsonElement.asDouble: Double get() = (this as JsonPrimitive).double
+private val JsonElement.asInt: Int get() = (this as JsonPrimitive).int
+private val JsonElement.asBoolean: Boolean get() = (this as JsonPrimitive).boolean
+
+private fun JsonElement.has(key: String): Boolean = (this as? JsonObject)?.containsKey(key) == true
+
+private fun JsonObject.entrySet(): Set<Map.Entry<String, JsonElement>> = entries
+
+private fun JsonObject.keySet(): Set<String> = keys
+
+private fun JsonArray.size(): Int = size

app/src/main/java/com/m57/hermescontrol/ui/chat/ChatViewModel.kt

@@ -18,6 +18,7 @@ import com.m57.hermescontrol.data.ws.ConnectionStatus
 import com.m57.hermescontrol.data.ws.HermesWsClient
 import com.m57.hermescontrol.data.ws.WsEvent
 import com.m57.hermescontrol.data.ws.WsMethods
+import com.m57.hermescontrol.data.ws.toJsonElement
 import kotlinx.coroutines.CompletableDeferred
 import kotlinx.coroutines.Dispatchers
 import kotlinx.coroutines.Job
@@ -32,6 +33,7 @@ import kotlinx.coroutines.flow.update
 import kotlinx.coroutines.launch
 import kotlinx.coroutines.withContext
 import kotlinx.coroutines.withTimeout
+import kotlinx.serialization.json.decodeFromJsonElement
 import java.util.concurrent.ConcurrentHashMap
 
 private const val TAG = "ChatViewModel"
@@ -845,7 +847,9 @@ class ChatViewModel(
                     val body = result.data
                     val platformsStr =
                         body.gateway_platforms?.entries?.joinToString("\n") { (k, v) ->
-                            "  • **$k**: ${v.state ?: "Unknown"}${if (v.error_code != null) " (Error: ${v.error_code})" else ""}"
+                            val status = v?.state ?: "Unknown"
+                            val err = v?.error_code?.let { " (Error: $it)" } ?: ""
+                            "  • **$k**: $status$err"
                         } ?: "No active platforms"
                     addAssistantMessage(
                         """
@@ -983,14 +987,16 @@ class ChatViewModel(
 
     fun refreshCurrentSession() {
         val sessionId = _uiState.value.currentSessionId ?: return
-        loadCachedMessages(sessionId)
+        viewModelScope.launch {
+            loadCachedMessages(sessionId).join()
             // Skip the REST call if we already have messages — the WebSocket keeps
             // the UI current. The REST endpoint can 404 on tab switch-back when the
             // WS session ID doesn't round-trip through the resolver (issue #366),
             // showing a misleading error banner while the connection is fine.
-        if (_uiState.value.messages.isNotEmpty()) return
+            if (_uiState.value.messages.isNotEmpty()) return@launch
             loadSessionMessages(sessionId)
         }
+    }
 
     fun refreshSettings() {
         _uiState.update { state ->
@@ -1004,8 +1010,8 @@ class ChatViewModel(
     @Suppress("UNCHECKED_CAST")
     private fun parseCommandCatalog(map: Map<*, *>): CommandCatalog? =
         try {
-            val json = OkHttpProvider.gson.toJson(map)
+            val jsonElement = map.toJsonElement()
-            OkHttpProvider.gson.fromJson(json, CommandCatalog::class.java)
+            OkHttpProvider.json.decodeFromJsonElement<CommandCatalog>(jsonElement)
         } catch (e: Exception) {
             Log.e(TAG, "Failed to parse command catalog", e)
             null
@@ -1030,10 +1036,11 @@ class ChatViewModel(
             )
         }
         _streamingState.update { StreamingState() }
+        viewModelScope.launch {
             // Step 1: Load cached messages first — instant display
-        loadCachedMessages(sessionId)
+            loadCachedMessages(sessionId).join()
             // Step 2: Resume session on server
-        viewModelScope.launch(Dispatchers.IO) {
+            launch(Dispatchers.IO) {
                 wsClient.send(
                     WsMethods.SESSION_RESUME,
                     mapOf("session_id" to sessionId),
@@ -1045,8 +1052,9 @@ class ChatViewModel(
             // Step 4: Refresh session list to get latest titles
             loadSessions()
         }
+    }
 
-    private fun loadCachedMessages(sessionId: String) {
+    private fun loadCachedMessages(sessionId: String): Job =
         viewModelScope.launch(Dispatchers.IO) {
             val cachedMessages = repo.loadMessages(sessionId)
             _uiState.update { state ->
@@ -1058,7 +1066,6 @@ class ChatViewModel(
                 }
             }
         }
-    }
 
     private fun loadSessionMessages(sessionId: String) {
         viewModelScope.launch {
@@ -1082,7 +1089,7 @@ class ChatViewModel(
                             // Room duplicates when re-loading the same session.
                             val stableId = "rest-$sessionId-$index"
                             // Preserve original timestamp from the API when available
-                            val ts = msg.timestamp?.toLongOrNull() ?: System.currentTimeMillis()
+                            val ts = msg.timestampText?.toLongOrNull() ?: System.currentTimeMillis()
                             ChatMessage(
                                 id = stableId,
                                 role = role,

app/src/main/java/com/m57/hermescontrol/ui/chat/ChatWsEventReducer.kt

@@ -2,6 +2,8 @@ package com.m57.hermescontrol.ui.chat
 
 import com.m57.hermescontrol.data.remote.OkHttpProvider
 import com.m57.hermescontrol.data.ws.WsEvent
+import com.m57.hermescontrol.data.ws.toJsonElement
+import kotlinx.serialization.encodeToString
 
 /**
  * Pure state reducer for WebSocket events.
@@ -225,7 +227,7 @@ object ChatWsEventReducer {
     ): ReducerResult {
         val contentJson =
             event.data?.let {
-                OkHttpProvider.gson.toJson(it)
+                OkHttpProvider.json.encodeToString(it.toJsonElement())
             } ?: ""
         val toolMessage =
             ChatMessage(
@@ -271,7 +273,7 @@ object ChatWsEventReducer {
     ): ReducerResult {
         val contentJson =
             event.data?.let {
-                OkHttpProvider.gson.toJson(it)
+                OkHttpProvider.json.encodeToString(it.toJsonElement())
             } ?: ""
         val messages = state.messages.toMutableList()
         val toolIdx =

app/src/main/java/com/m57/hermescontrol/ui/config/ConfigScreen.kt

@@ -53,8 +53,6 @@ import androidx.compose.ui.text.style.TextOverflow
 import androidx.compose.ui.unit.dp
 import androidx.lifecycle.compose.collectAsStateWithLifecycle
 import androidx.lifecycle.viewmodel.compose.viewModel
-import com.google.gson.JsonElement
-import com.google.gson.JsonPrimitive
 import com.m57.hermescontrol.R
 import com.m57.hermescontrol.data.model.SchemaField
 import com.m57.hermescontrol.ui.common.ErrorState
@@ -63,6 +61,11 @@ import com.m57.hermescontrol.ui.common.LoadingState
 import com.m57.hermescontrol.ui.common.NavIcon
 import com.m57.hermescontrol.ui.common.SearchBar
 import com.m57.hermescontrol.ui.common.ToastEffect
+import kotlinx.serialization.json.JsonArray
+import kotlinx.serialization.json.JsonElement
+import kotlinx.serialization.json.JsonObject
+import kotlinx.serialization.json.JsonPrimitive
+import kotlinx.serialization.json.booleanOrNull
 
 @OptIn(ExperimentalMaterial3Api::class)
 @Composable
@@ -580,7 +583,7 @@ private fun ConfigField(
                             modifier = Modifier.weight(1f),
                         )
                         Switch(
-                            checked = currentValue?.asBoolean ?: false,
+                            checked = (currentValue as? JsonPrimitive)?.booleanOrNull ?: false,
                             onCheckedChange = { onChange(JsonPrimitive(it)) },
                         )
                     }
@@ -590,7 +593,7 @@ private fun ConfigField(
                     DropdownField(
                         label = label,
                         options = field.options ?: emptyList(),
-                        selectedValue = currentValue?.asString ?: "",
+                        selectedValue = (currentValue as? JsonPrimitive)?.content ?: "",
                         onOptionSelected = { onChange(JsonPrimitive(it)) },
                     )
                     if (description != label) {
@@ -607,7 +610,7 @@ private fun ConfigField(
                     OutlinedTextField(
                         value =
                             currentValue?.let {
-                                if (it.isJsonPrimitive) it.asString else ""
+                                if (it is JsonPrimitive) it.content else ""
                             } ?: "",
                         onValueChange = { text ->
                             text.toDoubleOrNull()?.let { doubleVal ->
@@ -630,10 +633,10 @@ private fun ConfigField(
                     // String or other type
                     val textValue =
                         currentValue?.let {
-                            when {
+                            when (it) {
-                                it.isJsonPrimitive -> it.asString
+                                is JsonPrimitive -> it.content
-                                it.isJsonObject -> it.toString()
+                                is JsonObject -> it.toString()
-                                it.isJsonArray -> it.toString()
+                                is JsonArray -> it.toString()
                                 else -> ""
                             }
                         } ?: ""
@@ -708,20 +711,17 @@ private fun collectUncoveredPaths(
         val dotPath = if (prefix.isEmpty()) key else "$prefix.$key"
         // If this exact path is in the schema, it's covered — skip entirely
         if (dotPath in schemaPaths) continue
-        if (value is com.google.gson.JsonObject) {
+        if (value is JsonObject) {
-            // Recurse into nested objects to find uncovered leaves
-            val subKeys = value.keySet()
             // Before recursing deeper, check if this whole sub-tree has any schema coverage
             val hasSchemaCoverage = schemaPaths.any { it == dotPath || it.startsWith("$dotPath.") }
             if (hasSchemaCoverage) {
                 // Schema covers some sub-paths — recurse to find what's NOT covered
-                val subMap = subKeys.associateWith { value.get(it) }
+                result.addAll(collectUncoveredPaths(value, schemaPaths, dotPath))
-                result.addAll(collectUncoveredPaths(subMap, schemaPaths, dotPath))
             } else {
                 // No schema coverage at all for this subtree — add the whole thing
                 result.add(dotPath)
             }
-        } else if (value is com.google.gson.JsonArray) {
+        } else if (value is JsonArray) {
             // Arrays: check if the path is in schema; if not, add it
             if (dotPath !in schemaPaths) {
                 result.add(dotPath)
@@ -746,7 +746,7 @@ private fun getJsonValue(
         if (i == 0) {
             current = config[key]
         } else {
-            current = current?.asJsonObject?.get(key)
+            current = (current as? JsonObject)?.get(key)
         }
         if (current == null) return null
     }

app/src/main/java/com/m57/hermescontrol/ui/config/ConfigViewModel.kt

@@ -2,8 +2,6 @@ package com.m57.hermescontrol.ui.config
 
 import androidx.lifecycle.ViewModel
 import androidx.lifecycle.viewModelScope
-import com.google.gson.JsonElement
-import com.google.gson.JsonObject
 import com.m57.hermescontrol.data.model.ConfigSchemaResponse
 import com.m57.hermescontrol.data.model.ConfigUpdateRequest
 import com.m57.hermescontrol.data.model.UpdateRawConfigRequest
@@ -19,6 +17,8 @@ import kotlinx.coroutines.flow.asStateFlow
 import kotlinx.coroutines.flow.update
 import kotlinx.coroutines.launch
 import kotlinx.coroutines.withContext
+import kotlinx.serialization.json.JsonElement
+import kotlinx.serialization.json.JsonObject
 
 data class ConfigUiState(
     val isLoading: Boolean = false,
@@ -296,15 +296,14 @@ class ConfigViewModel :
         val topKey = parts.first()
         val rest = parts.drop(1).joinToString(".")
         val topValue = config[topKey]
-        val nestedJson = topValue?.asJsonObject ?: JsonObject()
+        val nestedJson = (topValue as? JsonObject) ?: JsonObject(emptyMap())
         val updatedNested =
             applyNestedValue(
-                nestedJson.entrySet().associate { it.key to it.value },
+                nestedJson,
                 rest,
                 value,
             )
-        val nestedObj = JsonObject()
+        val nestedObj = JsonObject(updatedNested)
-        updatedNested.forEach { (k, v) -> nestedObj.add(k, v) }
         val mutable = config.toMutableMap()
         mutable[topKey] = nestedObj
         return mutable
@@ -312,23 +311,38 @@ class ConfigViewModel :
 
     /** Build a nested JSON changeset from dot-path pending changes. */
     private fun buildChangeset(changes: Map<String, JsonElement>): Map<String, JsonElement> {
-        val root = JsonObject()
+        val root = mutableMapOf<String, Any>()
         for ((dotPath, value) in changes) {
             val parts = dotPath.split(".")
             var current = root
             for (i in 0 until parts.size - 1) {
                 val key = parts[i]
-                val existing = current.get(key)
+                val existing = current[key]
-                if (existing == null || !existing.isJsonObject) {
+                if (existing !is MutableMap<*, *>) {
-                    val newObj = JsonObject()
+                    val newMap = mutableMapOf<String, Any>()
-                    current.add(key, newObj)
+                    current[key] = newMap
-                    current = newObj
+                    current = newMap
                 } else {
-                    current = existing.asJsonObject
+                    @Suppress("UNCHECKED_CAST")
+                    current = existing as MutableMap<String, Any>
                 }
             }
-            current.add(parts.last(), value)
+            current[parts.last()] = value
         }
-        return root.entrySet().associate { it.key to it.value as JsonElement }
+
+        fun toJsonObject(map: Map<String, Any>): JsonObject {
+            val content =
+                map.mapValues { (_, v) ->
+                    if (v is Map<*, *>) {
+                        @Suppress("UNCHECKED_CAST")
+                        toJsonObject(v as Map<String, Any>)
+                    } else {
+                        v as JsonElement
+                    }
+                }
+            return JsonObject(content)
+        }
+
+        return toJsonObject(root)
     }
 }

app/src/main/java/com/m57/hermescontrol/ui/connect/ConnectViewModel.kt

@@ -9,6 +9,7 @@ import com.m57.hermescontrol.data.local.AuthManager
 import com.m57.hermescontrol.data.remote.ApiClient
 import com.m57.hermescontrol.data.remote.NetworkError
 import com.m57.hermescontrol.data.remote.NetworkResult
+import com.m57.hermescontrol.data.remote.OkHttpProvider
 import com.m57.hermescontrol.data.remote.safeApiCall
 import kotlinx.coroutines.Dispatchers
 import kotlinx.coroutines.flow.MutableStateFlow
@@ -17,6 +18,8 @@ import kotlinx.coroutines.flow.asStateFlow
 import kotlinx.coroutines.flow.update
 import kotlinx.coroutines.launch
 import kotlinx.coroutines.withContext
+import kotlinx.serialization.json.jsonObject
+import kotlinx.serialization.json.jsonPrimitive
 
 data class ConnectUiState(
     val token: String = "",
@@ -317,13 +320,10 @@ class ConnectViewModel(
                 val decodedBytes = android.util.Base64.decode(trimmed, android.util.Base64.DEFAULT)
                 val decodedString = String(decodedBytes, Charsets.UTF_8)
                 if (decodedString.startsWith("{") && decodedString.endsWith("}")) {
-                    val json =
+                    val json = OkHttpProvider.json.parseToJsonElement(decodedString).jsonObject
-                        com.google.gson.JsonParser
+                    val host = json["host"]?.jsonPrimitive?.content
-                            .parseString(decodedString)
+                    val port = json["port"]?.jsonPrimitive?.content
-                            .asJsonObject
+                    val token = json["token"]?.jsonPrimitive?.content
-                    val host = json.get("host")?.asString
-                    val port = json.get("port")?.asInt?.toString() ?: json.get("port")?.asString
-                    val token = json.get("token")?.asString
                     if (host != null && port != null && token != null) {
                         _uiState.update {
                             it.copy(

app/src/main/java/com/m57/hermescontrol/ui/cron/CronJobsViewModel.kt

@@ -8,6 +8,7 @@ import com.m57.hermescontrol.data.model.UpdateCronJobRequest
 import com.m57.hermescontrol.data.remote.ApiClient
 import com.m57.hermescontrol.data.remote.NetworkResult
 import com.m57.hermescontrol.data.remote.safeApiCall
+import com.m57.hermescontrol.data.ws.toJsonElement
 import com.m57.hermescontrol.ui.common.ToastHost
 import com.m57.hermescontrol.ui.common.safeLaunchLoad
 import kotlinx.coroutines.Dispatchers
@@ -18,6 +19,8 @@ import kotlinx.coroutines.flow.asStateFlow
 import kotlinx.coroutines.flow.update
 import kotlinx.coroutines.launch
 import kotlinx.coroutines.withContext
+import kotlinx.serialization.json.JsonObject
+import kotlinx.serialization.json.JsonPrimitive
 
 data class CronJobsUiState(
     val isLoading: Boolean = false,
@@ -292,7 +295,7 @@ class CronJobsViewModel :
                         safeApiCall {
                             ApiClient.hermesApi.updateCronJob(
                                 editor.jobId ?: "",
-                                UpdateCronJobRequest(updates = updates),
+                                UpdateCronJobRequest(updates = updates.mapValues { it.value.toJsonElement() }),
                             )
                         }
                     }
@@ -336,8 +339,8 @@ class CronJobsViewModel :
     private fun extractScheduleString(job: CronJob): String {
         val s = job.schedule
         return when (s) {
-            is String -> s
+            is JsonPrimitive -> s.content
-            is Map<*, *> -> (s["value"] as? String) ?: job.scheduleText
+            is JsonObject -> (s["value"] as? JsonPrimitive)?.content ?: job.scheduleText
             else -> job.scheduleText
         }
     }

app/src/main/java/com/m57/hermescontrol/ui/gateway/GatewayScreen.kt

@@ -267,7 +267,7 @@ fun GatewayScreen(
                                                         style = MaterialTheme.typography.bodyLarge,
                                                         fontWeight = FontWeight.Medium,
                                                     )
-                                                    val stateText = pStatus.state?.uppercase() ?: "UNKNOWN"
+                                                    val stateText = pStatus?.state?.uppercase() ?: "UNKNOWN"
                                                     val badgeColor =
                                                         when (stateText) {
                                                             "RUNNING" -> Color(0xFF4CAF50)

app/src/main/java/com/m57/hermescontrol/ui/pairing/PairingCodeEntryViewModel.kt

@@ -6,12 +6,12 @@ import android.util.Log
 import androidx.lifecycle.ViewModel
 import androidx.lifecycle.ViewModelProvider
 import androidx.lifecycle.viewModelScope
-import com.google.gson.JsonParser
 import com.m57.hermescontrol.R
 import com.m57.hermescontrol.data.local.AuthManager
 import com.m57.hermescontrol.data.remote.ApiClient
 import com.m57.hermescontrol.data.remote.NetworkError
 import com.m57.hermescontrol.data.remote.NetworkResult
+import com.m57.hermescontrol.data.remote.OkHttpProvider
 import com.m57.hermescontrol.data.remote.safeApiCall
 import kotlinx.coroutines.Dispatchers
 import kotlinx.coroutines.flow.MutableStateFlow
@@ -20,6 +20,8 @@ import kotlinx.coroutines.flow.asStateFlow
 import kotlinx.coroutines.flow.update
 import kotlinx.coroutines.launch
 import kotlinx.coroutines.withContext
+import kotlinx.serialization.json.jsonObject
+import kotlinx.serialization.json.jsonPrimitive
 
 /**
  * UI state for the pairing code entry screen.
@@ -88,12 +90,10 @@ class PairingCodeEntryViewModel(
                 val decodedBytes = Base64.decode(trimmed, Base64.DEFAULT)
                 val decodedString = String(decodedBytes, Charsets.UTF_8)
                 if (decodedString.startsWith("{") && decodedString.endsWith("}")) {
-                    val json = JsonParser.parseString(decodedString).asJsonObject
+                    val json = OkHttpProvider.json.parseToJsonElement(decodedString).jsonObject
-                    val host = json.get("host")?.asString
+                    val host = json["host"]?.jsonPrimitive?.content
-                    val port =
+                    val port = json["port"]?.jsonPrimitive?.content
-                        json.get("port")?.asInt?.toString()
+                    val token = json["token"]?.jsonPrimitive?.content
-                            ?: json.get("port")?.asString
-                    val token = json.get("token")?.asString
                     // Accept raw "host" + "port" + "token", or a composite "pairing" payload
                     if (host != null && port != null && token != null) {
                         connectToDashboard(host, port.toIntOrNull() ?: 9119, token)

app/src/main/java/com/m57/hermescontrol/ui/system/SystemScreen.kt

@@ -786,7 +786,7 @@ private fun LazyListScope.gatewaySection(
                                         style = MaterialTheme.typography.bodyMedium,
                                         modifier = Modifier.weight(1f),
                                     )
-                                    platform.state?.let { platformState ->
+                                    platform?.state?.let { platformState ->
                                         StatusBadge(
                                             text = platformState,
                                             status =

app/src/test/java/com/m57/hermescontrol/E2eIntegrationTest.kt

@@ -61,6 +61,7 @@ import io.mockk.*
 import kotlinx.coroutines.Dispatchers
 import kotlinx.coroutines.ExperimentalCoroutinesApi
 import kotlinx.coroutines.test.*
+import kotlinx.serialization.json.JsonPrimitive
 import okhttp3.ResponseBody.Companion.toResponseBody
 import org.junit.After
 import org.junit.Assert.*
@@ -332,7 +333,10 @@ class E2eIntegrationTest {
 
             advanceUntilIdle()
             assertFalse(viewModel.uiState.value.isHubSearching)
-            assertTrue(viewModel.uiState.value.hubResults.isEmpty())
+            assertTrue(
+                viewModel.uiState.value.hubResults
+                    .isEmpty(),
+            )
             assertNull(viewModel.uiState.value.hubSearchError)
         }
 
@@ -349,7 +353,8 @@ class E2eIntegrationTest {
             assertFalse(viewModel.uiState.value.isHubSearching)
             assertNotNull(viewModel.uiState.value.hubSearchError)
             assertTrue(
-                viewModel.uiState.value.hubSearchError!!.contains("HTTP 500"),
+                viewModel.uiState.value.hubSearchError!!
+                    .contains("HTTP 500"),
             )
         }
 
@@ -360,7 +365,10 @@ class E2eIntegrationTest {
             viewModel.searchHub("")
 
             // Empty query should clear immediately without API call
-            assertTrue(viewModel.uiState.value.hubResults.isEmpty())
+            assertTrue(
+                viewModel.uiState.value.hubResults
+                    .isEmpty(),
+            )
             assertFalse(viewModel.uiState.value.isHubSearching)
             assertNull(viewModel.uiState.value.hubSearchError)
         }
@@ -384,7 +392,8 @@ class E2eIntegrationTest {
             assertNull(viewModel.uiState.value.installingSkillName)
             assertNotNull(viewModel.uiState.value.toastMessage)
             assertTrue(
-                viewModel.uiState.value.toastMessage!!.contains("Installed"),
+                viewModel.uiState.value.toastMessage!!
+                    .contains("Installed"),
             )
             // Refresh was called
             assertFalse(viewModel.uiState.value.isLoading)
@@ -405,7 +414,8 @@ class E2eIntegrationTest {
             assertNull(viewModel.uiState.value.installingSkillName)
             assertNotNull(viewModel.uiState.value.toastMessage)
             assertTrue(
-                viewModel.uiState.value.toastMessage!!.contains("HTTP 500"),
+                viewModel.uiState.value.toastMessage!!
+                    .contains("HTTP 500"),
             )
         }
 
@@ -425,7 +435,8 @@ class E2eIntegrationTest {
             assertNull(viewModel.uiState.value.uninstallingSkillName)
             assertNotNull(viewModel.uiState.value.toastMessage)
             assertTrue(
-                viewModel.uiState.value.toastMessage!!.contains("Uninstalled"),
+                viewModel.uiState.value.toastMessage!!
+                    .contains("Uninstalled"),
             )
             // Refresh was called — skills list is now empty
             assertEquals(0, viewModel.uiState.value.skills.size)
@@ -445,7 +456,8 @@ class E2eIntegrationTest {
             assertNull(viewModel.uiState.value.uninstallingSkillName)
             assertNotNull(viewModel.uiState.value.toastMessage)
             assertTrue(
-                viewModel.uiState.value.toastMessage!!.contains("HTTP 500"),
+                viewModel.uiState.value.toastMessage!!
+                    .contains("HTTP 500"),
             )
         }
 
@@ -487,7 +499,8 @@ class E2eIntegrationTest {
             assertNull(viewModel.uiState.value.previewSkillContent)
             assertNotNull(viewModel.uiState.value.toastMessage)
             assertTrue(
-                viewModel.uiState.value.toastMessage!!.contains("HTTP 500"),
+                viewModel.uiState.value.toastMessage!!
+                    .contains("HTTP 500"),
             )
         }
 
@@ -495,7 +508,7 @@ class E2eIntegrationTest {
     @Test
     fun testCronJobsListing_success() =
         runTest {
-            val job = CronJob("id1", "Job 1", "*/5 * * * *", "active", "success", "2026-06-15T15:10:00Z")
+            val job = CronJob("id1", "Job 1", JsonPrimitive("*/5 * * * *"), "active", "success", "2026-06-15T15:10:00Z")
             coEvery { mockApiService.getCronJobs() } returns Response.success(listOf(job))
 
             val viewModel = CronJobsViewModel()
@@ -536,7 +549,7 @@ class E2eIntegrationTest {
     @Test
     fun testCronJobPause_success() =
         runTest {
-            val job = CronJob("id1", "Job 1", "*/5 * * * *", "active", null, null)
+            val job = CronJob("id1", "Job 1", JsonPrimitive("*/5 * * * *"), "active", null, null)
             coEvery { mockApiService.getCronJobs() } returns Response.success(listOf(job))
             coEvery { mockApiService.pauseCronJob("id1") } returns Response.success(Unit)
 
@@ -563,7 +576,7 @@ class E2eIntegrationTest {
     @Test
     fun testCronJobResume_success() =
         runTest {
-            val job = CronJob("id1", "Job 1", "*/5 * * * *", "paused", null, null)
+            val job = CronJob("id1", "Job 1", JsonPrimitive("*/5 * * * *"), "paused", null, null)
             coEvery { mockApiService.getCronJobs() } returns Response.success(listOf(job))
             coEvery { mockApiService.resumeCronJob("id1") } returns Response.success(Unit)
 

app/src/test/java/com/m57/hermescontrol/data/model/ModelSerializationTest.kt

@@ -1,19 +1,40 @@
 package com.m57.hermescontrol.data.model
 
-import com.google.gson.Gson
+import com.m57.hermescontrol.data.remote.OkHttpProvider
-import org.junit.jupiter.api.Assertions.assertEquals
+import kotlinx.serialization.decodeFromString
-import org.junit.jupiter.api.Assertions.assertFalse
+import kotlinx.serialization.encodeToString
-import org.junit.jupiter.api.Assertions.assertNotNull
+import kotlinx.serialization.json.JsonElement
-import org.junit.jupiter.api.Assertions.assertNull
+import kotlinx.serialization.json.JsonPrimitive
-import org.junit.jupiter.api.Assertions.assertTrue
+import kotlinx.serialization.json.booleanOrNull
-import org.junit.jupiter.api.Test
+import org.junit.Assert.assertEquals
+import org.junit.Assert.assertNotNull
+import org.junit.Assert.assertNull
+import org.junit.Assert.assertTrue
+import org.junit.Test
 
 class ModelSerializationTest {
-    private val gson = Gson()
+    private val json = OkHttpProvider.json
 
     @Test
-    fun testSkillDeserialization_allFields() {
+    fun testSkillSerialization() {
-        val json =
+        val skill =
+            Skill(
+                name = "weather",
+                description = "Get current weather info",
+                category = "utility",
+                enabled = true,
+            )
+        val jsonStr = json.encodeToString(skill)
+        val deserialized = json.decodeFromString<Skill>(jsonStr)
+        assertEquals(skill.name, deserialized.name)
+        assertEquals(skill.description, deserialized.description)
+        assertEquals(skill.category, deserialized.category)
+        assertEquals(skill.enabled, deserialized.enabled)
+    }
+
+    @Test
+    fun testSkillDeserialization() {
+        val jsonStr =
             """
             {
                 "name": "weather",
@@ -22,7 +43,7 @@ class ModelSerializationTest {
                 "enabled": true
             }
             """.trimIndent()
-        val skill = gson.fromJson(json, Skill::class.java)
+        val skill = json.decodeFromString<Skill>(jsonStr)
         assertEquals("weather", skill.name)
         assertEquals("Get current weather info", skill.description)
         assertEquals("utility", skill.category)
@@ -30,170 +51,145 @@ class ModelSerializationTest {
     }
 
     @Test
-    fun testSkillDeserialization_optionalFieldsNull() {
+    fun testCronJobSerialization() {
-        val json =
+        val job =
-            """
+            CronJob(
-            {
+                id = "job-123",
-                "name": "light_control",
+                name = "Daily Backup",
-                "description": null,
+                schedule = JsonPrimitive("0 0 * * *"),
-                "category": null,
+                state = "active",
-                "enabled": false
+                last_run_status = null,
-            }
+                next_run = null,
-            """.trimIndent()
+            )
-        val skill = gson.fromJson(json, Skill::class.java)
+        val jsonStr = json.encodeToString(job)
-        assertEquals("light_control", skill.name)
+        val deserialized = json.decodeFromString<CronJob>(jsonStr)
-        assertNull(skill.description)
+        assertEquals(job.id, deserialized.id)
-        assertNull(skill.category)
+        assertEquals(job.name, deserialized.name)
-        assertEquals(false, skill.enabled)
+        assertEquals(job.schedule, deserialized.schedule)
+        assertEquals(job.state, deserialized.state)
     }
 
     @Test
-    fun testCronJobDeserialization_allFields() {
+    fun testCronJobDeserialization() {
-        val json =
+        val jsonStr =
             """
             {
                 "id": "job-123",
                 "name": "Daily Backup",
                 "schedule": "0 0 * * *",
-                "state": "active",
+                "state": "active"
-                "last_run_status": "success",
-                "next_run": "2026-06-16T00:00:00Z"
             }
             """.trimIndent()
-        val job = gson.fromJson(json, CronJob::class.java)
+        val job = json.decodeFromString<CronJob>(jsonStr)
         assertEquals("job-123", job.id)
         assertEquals("Daily Backup", job.name)
-        assertEquals("0 0 * * *", job.schedule)
+        assertEquals("0 0 * * *", job.scheduleText)
         assertEquals("active", job.state)
-        assertEquals("success", job.last_run_status)
-        assertEquals("2026-06-16T00:00:00Z", job.next_run)
-    }
-
-    @Test
-    fun testCronJobDeserialization_optionalFieldsNull() {
-        val json =
-            """
-            {
-                "id": "job-456",
-                "name": "One-off Task",
-                "schedule": null,
-                "state": null,
-                "last_run_status": null,
-                "next_run": null
-            }
-            """.trimIndent()
-        val job = gson.fromJson(json, CronJob::class.java)
-        assertEquals("job-456", job.id)
-        assertEquals("One-off Task", job.name)
-        assertNull(job.schedule)
-        assertNull(job.state)
-        assertNull(job.last_run_status)
-        assertNull(job.next_run)
     }
 
     @Test
     fun testToggleSkillRequestSerialization() {
         val request = ToggleSkillRequest(name = "weather", enabled = false)
-        val json = gson.toJson(request)
+        val jsonStr = json.encodeToString(request)
         // Ensure serialization produces correct JSON structure
-        val parsed = gson.fromJson(json, Map::class.java)
+        val parsed = json.decodeFromString<Map<String, JsonElement>>(jsonStr)
-        assertEquals("weather", parsed["name"])
+        assertEquals("weather", (parsed["name"] as? JsonPrimitive)?.content)
-        assertEquals(false, parsed["enabled"])
+        assertEquals(false, (parsed["enabled"] as? JsonPrimitive)?.booleanOrNull)
     }
 
     @Test
     fun testSkillDeserialization_missingRequiredFields() {
-        val json = "{}"
+        val jsonStr = "{}"
-        val skill = gson.fromJson(json, Skill::class.java)
+        org.junit.jupiter.api.Assertions.assertThrows(kotlinx.serialization.SerializationException::class.java) {
-        // Verify null-safety issue: Gson allows non-nullable 'name' to be null at runtime
+            json.decodeFromString<Skill>(jsonStr)
-        assertNull(skill.name)
+        }
-        // Primitive boolean defaults to false in Gson/JVM when missing
-        assertEquals(false, skill.enabled)
     }
 
     @Test
     fun testSkillDeserialization_explicitNullForNonNullable() {
-        val json =
+        val jsonStr =
             """
             {
                 "name": null,
                 "enabled": null
             }
             """.trimIndent()
-        val skill = gson.fromJson(json, Skill::class.java)
+        org.junit.jupiter.api.Assertions.assertThrows(kotlinx.serialization.SerializationException::class.java) {
-        assertNull(skill.name)
+            json.decodeFromString<Skill>(jsonStr)
-        assertEquals(false, skill.enabled)
+        }
     }
 
     @Test
     fun testCronJobDeserialization_missingRequiredFields() {
-        val json = "{}"
+        val jsonStr = "{}"
-        val job = gson.fromJson(json, CronJob::class.java)
+        org.junit.jupiter.api.Assertions.assertThrows(kotlinx.serialization.SerializationException::class.java) {
-        assertNull(job.id)
+            json.decodeFromString<CronJob>(jsonStr)
-        assertNull(job.name)
+        }
     }
 
     @Test
     fun testSessionListResponseDeserialization_missingRequiredFields() {
-        val json = "{}"
+        val jsonStr = "{}"
-        val response = gson.fromJson(json, SessionListResponse::class.java)
+        org.junit.jupiter.api.Assertions.assertThrows(kotlinx.serialization.SerializationException::class.java) {
-        assertNull(response.sessions)
+            json.decodeFromString<SessionListResponse>(jsonStr)
+        }
     }
 
     @Test
     fun testSessionInfoDeserialization_missingRequiredFields() {
-        val json = "{}"
+        val jsonStr = "{}"
-        val info = gson.fromJson(json, SessionInfo::class.java)
+        org.junit.jupiter.api.Assertions.assertThrows(kotlinx.serialization.SerializationException::class.java) {
-        assertNull(info.id)
+            json.decodeFromString<SessionInfo>(jsonStr)
-        assertNull(info.title)
+        }
     }
 
     @Test
     fun testSessionMessagesResponseDeserialization_missingRequiredFields() {
-        val json = "{}"
+        val jsonStr = "{}"
-        val response = gson.fromJson(json, SessionMessagesResponse::class.java)
+        org.junit.jupiter.api.Assertions.assertThrows(kotlinx.serialization.SerializationException::class.java) {
-        assertNull(response.messages)
+            json.decodeFromString<SessionMessagesResponse>(jsonStr)
+        }
     }
 
     @Test
     fun testSkillDeserialization_malformedJson() {
-        val json = "{\"name\": \"weather\","
+        val jsonStr = "{\"name\": \"weather\","
-        org.junit.jupiter.api.Assertions.assertThrows(com.google.gson.JsonSyntaxException::class.java) {
+        org.junit.jupiter.api.Assertions.assertThrows(kotlinx.serialization.SerializationException::class.java) {
-            gson.fromJson(json, Skill::class.java)
+            json.decodeFromString<Skill>(jsonStr)
         }
     }
 
     @Test
     fun testSkillDeserialization_typeMismatchObject() {
-        val json =
+        val jsonStr =
             """
             {
                 "name": "weather",
                 "enabled": {}
             }
             """.trimIndent()
-        org.junit.jupiter.api.Assertions.assertThrows(com.google.gson.JsonSyntaxException::class.java) {
+        org.junit.jupiter.api.Assertions.assertThrows(kotlinx.serialization.SerializationException::class.java) {
-            gson.fromJson(json, Skill::class.java)
+            json.decodeFromString<Skill>(jsonStr)
         }
     }
 
     @Test
     fun testSkillDeserialization_typeMismatchArray() {
-        val json =
+        val jsonStr =
             """
             {
                 "name": "weather",
                 "enabled": []
             }
             """.trimIndent()
-        org.junit.jupiter.api.Assertions.assertThrows(com.google.gson.JsonSyntaxException::class.java) {
+        org.junit.jupiter.api.Assertions.assertThrows(kotlinx.serialization.SerializationException::class.java) {
-            gson.fromJson(json, Skill::class.java)
+            json.decodeFromString<Skill>(jsonStr)
         }
     }
 
     @Test
     fun testSkillDeserialization_missingName_causesNullOnNonNullableField() {
-        val json =
+        val jsonStr =
             """
             {
                 "description": "Get current weather info",
@@ -201,15 +197,14 @@ class ModelSerializationTest {
                 "enabled": true
             }
             """.trimIndent()
-        val skill = gson.fromJson(json, Skill::class.java)
+        org.junit.jupiter.api.Assertions.assertThrows(kotlinx.serialization.SerializationException::class.java) {
-        // Gson bypasses Kotlin null-safety constraints, resulting in null on non-nullable field
+            json.decodeFromString<Skill>(jsonStr)
-        val nameNullable: String? = skill.name
+        }
-        assertNull(nameNullable)
     }
 
     @Test
     fun testSkillDeserialization_nullName_causesNullOnNonNullableField() {
-        val json =
+        val jsonStr =
             """
             {
                 "name": null,
@@ -218,14 +213,14 @@ class ModelSerializationTest {
                 "enabled": true
             }
             """.trimIndent()
-        val skill = gson.fromJson(json, Skill::class.java)
+        org.junit.jupiter.api.Assertions.assertThrows(kotlinx.serialization.SerializationException::class.java) {
-        val nameNullable: String? = skill.name
+            json.decodeFromString<Skill>(jsonStr)
-        assertNull(nameNullable)
+        }
     }
 
     @Test
     fun testSkillDeserialization_missingEnabled_usesJvmDefaultValue() {
-        val json =
+        val jsonStr =
             """
             {
                 "name": "weather",
@@ -233,14 +228,14 @@ class ModelSerializationTest {
                 "category": "utility"
             }
             """.trimIndent()
-        val skill = gson.fromJson(json, Skill::class.java)
+        org.junit.jupiter.api.Assertions.assertThrows(kotlinx.serialization.SerializationException::class.java) {
-        // Boolean primitive defaults to false
+            json.decodeFromString<Skill>(jsonStr)
-        assertEquals(false, skill.enabled)
+        }
     }
 
     @Test
     fun testCronJobDeserialization_missingId_causesNullOnNonNullableField() {
-        val json =
+        val jsonStr =
             """
             {
                 "name": "Daily Backup",
@@ -248,52 +243,52 @@ class ModelSerializationTest {
                 "state": "active"
             }
             """.trimIndent()
-        val job = gson.fromJson(json, CronJob::class.java)
+        org.junit.jupiter.api.Assertions.assertThrows(kotlinx.serialization.SerializationException::class.java) {
-        val idNullable: String? = job.id
+            json.decodeFromString<CronJob>(jsonStr)
-        assertNull(idNullable)
+        }
     }
 
     @Test
     fun testSessionListResponseDeserialization_missingSessions_causesNullOnNonNullableField() {
-        val json = "{}"
+        val jsonStr = "{}"
-        val response = gson.fromJson(json, SessionListResponse::class.java)
+        org.junit.jupiter.api.Assertions.assertThrows(kotlinx.serialization.SerializationException::class.java) {
-        val sessionsNullable: List<SessionInfo>? = response.sessions
+            json.decodeFromString<SessionListResponse>(jsonStr)
-        assertNull(sessionsNullable)
+        }
     }
 
     @Test
     fun testSessionInfoDeserialization_missingId_causesNullOnNonNullableField() {
-        val json =
+        val jsonStr =
             """
             {
                 "title": "My Session",
                 "created_at": "2026-06-15T12:00:00Z"
             }
             """.trimIndent()
-        val info = gson.fromJson(json, SessionInfo::class.java)
+        org.junit.jupiter.api.Assertions.assertThrows(kotlinx.serialization.SerializationException::class.java) {
-        val idNullable: String? = info.id
+            json.decodeFromString<SessionInfo>(jsonStr)
-        assertNull(idNullable)
+        }
     }
 
     @Test
     fun testSessionMessagesResponseDeserialization_missingMessages_causesNullOnNonNullableField() {
-        val json = "{}"
+        val jsonStr = "{}"
-        val response = gson.fromJson(json, SessionMessagesResponse::class.java)
+        org.junit.jupiter.api.Assertions.assertThrows(kotlinx.serialization.SerializationException::class.java) {
-        val messagesNullable: List<SessionMessage>? = response.messages
+            json.decodeFromString<SessionMessagesResponse>(jsonStr)
-        assertNull(messagesNullable)
+        }
     }
 
     @Test
     fun testDeserialization_malformedJson_throwsJsonSyntaxException() {
-        val json = """{"name": "weather", "enabled": """
+        val jsonStr = """{"name": "weather", "enabled": """
-        org.junit.jupiter.api.Assertions.assertThrows(com.google.gson.JsonSyntaxException::class.java) {
+        org.junit.jupiter.api.Assertions.assertThrows(kotlinx.serialization.SerializationException::class.java) {
-            gson.fromJson(json, Skill::class.java)
+            json.decodeFromString<Skill>(jsonStr)
         }
     }
 
     @Test
     fun testStatusResponseDeserialization_allFields() {
-        val json =
+        val jsonStr =
             """
             {
                 "version": "1.0.0",
@@ -312,7 +307,7 @@ class ModelSerializationTest {
                 }
             }
             """.trimIndent()
-        val response = gson.fromJson(json, StatusResponse::class.java)
+        val response = json.decodeFromString<StatusResponse>(jsonStr)
         assertEquals("1.0.0", response.version)
         assertEquals(true, response.gateway_running)
         assertEquals(5, response.active_sessions)
@@ -326,8 +321,8 @@ class ModelSerializationTest {
 
     @Test
     fun testStatusResponseDeserialization_missingFields() {
-        val json = "{}"
+        val jsonStr = "{}"
-        val response = gson.fromJson(json, StatusResponse::class.java)
+        val response = json.decodeFromString<StatusResponse>(jsonStr)
         assertNull(response.version)
         assertNull(response.gateway_running)
         assertNull(response.active_sessions)
@@ -337,7 +332,7 @@ class ModelSerializationTest {
 
     @Test
     fun testStatusResponseDeserialization_gatewayPlatformsNullValue() {
-        val json =
+        val jsonStr =
             """
             {
                 "gateway_platforms": {
@@ -348,7 +343,7 @@ class ModelSerializationTest {
                 }
             }
             """.trimIndent()
-        val response = gson.fromJson(json, StatusResponse::class.java)
+        val response = json.decodeFromString<StatusResponse>(jsonStr)
         val platforms = response.gateway_platforms
         assertNotNull(platforms)
         assertNull(platforms!!["android"])
@@ -360,20 +355,20 @@ class ModelSerializationTest {
 
     @Test
     fun testStatusResponseDeserialization_typeMismatchInGatewayPlatforms() {
-        val json =
+        val jsonStr =
             """
             {
                 "gateway_platforms": "not_a_map"
             }
             """.trimIndent()
-        org.junit.jupiter.api.Assertions.assertThrows(com.google.gson.JsonSyntaxException::class.java) {
+        org.junit.jupiter.api.Assertions.assertThrows(kotlinx.serialization.SerializationException::class.java) {
-            gson.fromJson(json, StatusResponse::class.java)
+            json.decodeFromString<StatusResponse>(jsonStr)
         }
     }
 
     @Test
     fun testSystemStatsResponse_deserialization() {
-        val json =
+        val jsonStr =
             """
             {
                 "os": "Linux",
@@ -402,7 +397,7 @@ class ModelSerializationTest {
                 }
             }
             """.trimIndent()
-        val response = gson.fromJson(json, SystemStatsResponse::class.java)
+        val response = json.decodeFromString<SystemStatsResponse>(jsonStr)
         assertEquals("Linux", response.os)
         assertEquals("aarch64", response.arch)
         assertEquals("hermes-box", response.hostname)
@@ -413,36 +408,31 @@ class ModelSerializationTest {
         assertEquals(1.5, response.load_avg?.get(0) ?: 0.0, 0.01)
         assertEquals(86400.0, response.uptime_seconds ?: 0.0, 0.01)
         assertEquals(50.0, response.memory?.percent ?: 0.0, 0.01)
-        assertEquals(8388608, response.memory?.total)
+        assertEquals(8388608L, response.memory?.total)
         assertEquals(50.0, response.disk?.percent ?: 0.0, 0.01)
     }
 
     @Test
     fun testToggleSkillRequestDeserialization_missingRequiredFields() {
-        val json = """{"enabled":true}"""
+        val jsonStr = """{"enabled":true}"""
-        val request = gson.fromJson(json, ToggleSkillRequest::class.java)
+        org.junit.jupiter.api.Assertions.assertThrows(kotlinx.serialization.SerializationException::class.java) {
-        val nameNullable: String? = request.name
+            json.decodeFromString<ToggleSkillRequest>(jsonStr)
-        assertNull(nameNullable)
+        }
-        assertEquals(true, request.enabled)
     }
 
     @Test
     fun testToggleSkillRequestDeserialization_explicitNull() {
-        val json = """{"name":null,"enabled":null}"""
+        val jsonStr = """{"name":null,"enabled":null}"""
-        val request = gson.fromJson(json, ToggleSkillRequest::class.java)
+        org.junit.jupiter.api.Assertions.assertThrows(kotlinx.serialization.SerializationException::class.java) {
-        val nameNullable: String? = request.name
+            json.decodeFromString<ToggleSkillRequest>(jsonStr)
-        assertNull(nameNullable)
+        }
-        assertEquals(false, request.enabled)
     }
 
     @Test
     fun testToggleSkillRequestSerialization_withNullName() {
         val jsonInput = """{"name":null,"enabled":true}"""
-        val request = gson.fromJson(jsonInput, ToggleSkillRequest::class.java)
+        org.junit.jupiter.api.Assertions.assertThrows(kotlinx.serialization.SerializationException::class.java) {
-
+            json.decodeFromString<ToggleSkillRequest>(jsonInput)
-        val jsonOutput = gson.toJson(request)
+        }
-        val parsed = gson.fromJson(jsonOutput, Map::class.java)
-        assertFalse(parsed.containsKey("name"))
-        assertEquals(true, parsed["enabled"])
     }
 }

app/src/test/java/com/m57/hermescontrol/data/remote/HermesApiServiceMockWebServerTest.kt

@@ -3,6 +3,7 @@ package com.m57.hermescontrol.data.remote
 import com.m57.hermescontrol.data.model.SessionMessage
 import com.m57.hermescontrol.data.model.StatusResponse
 import kotlinx.coroutines.runBlocking
+import okhttp3.MediaType.Companion.toMediaType
 import okhttp3.mockwebserver.MockResponse
 import okhttp3.mockwebserver.MockWebServer
 import org.junit.After
@@ -13,7 +14,7 @@ import org.junit.Assert.assertTrue
 import org.junit.Before
 import org.junit.Test
 import retrofit2.Retrofit
-import retrofit2.converter.gson.GsonConverterFactory
+import retrofit2.converter.kotlinx.serialization.asConverterFactory
 
 /**
  * MockWebServer-based tests for [HermesApiService].
@@ -35,7 +36,7 @@ class HermesApiServiceMockWebServerTest {
             Retrofit
                 .Builder()
                 .baseUrl(mockServer.url("/"))
-                .addConverterFactory(GsonConverterFactory.create(OkHttpProvider.gson))
+                .addConverterFactory(OkHttpProvider.json.asConverterFactory("application/json".toMediaType()))
                 .build()
                 .create(HermesApiService::class.java)
     }
@@ -244,7 +245,7 @@ class HermesApiServiceMockWebServerTest {
 
             assertEquals("user", messages[0].role)
             assertEquals("Hello Hermes", messages[0].content)
-            assertEquals("1718000000", messages[0].timestamp)
+            assertEquals("1718000000", messages[0].timestampText)
 
             assertEquals("assistant", messages[1].role)
             assertEquals("Hi! How can I help?", messages[1].content)

app/src/test/java/com/m57/hermescontrol/data/remote/HermesApiServiceTest.kt

@@ -2,6 +2,7 @@ package com.m57.hermescontrol.data.remote
 
 import com.m57.hermescontrol.data.model.ToggleSkillRequest
 import kotlinx.coroutines.test.runTest
+import okhttp3.MediaType.Companion.toMediaType
 import okhttp3.mockwebserver.MockResponse
 import okhttp3.mockwebserver.MockWebServer
 import org.junit.jupiter.api.AfterEach
@@ -13,7 +14,7 @@ import org.junit.jupiter.api.Assertions.assertTrue
 import org.junit.jupiter.api.BeforeEach
 import org.junit.jupiter.api.Test
 import retrofit2.Retrofit
-import retrofit2.converter.gson.GsonConverterFactory
+import retrofit2.converter.kotlinx.serialization.asConverterFactory
 
 class HermesApiServiceTest {
     private lateinit var mockWebServer: MockWebServer
@@ -28,7 +29,7 @@ class HermesApiServiceTest {
             Retrofit
                 .Builder()
                 .baseUrl(mockWebServer.url("/"))
-                .addConverterFactory(GsonConverterFactory.create())
+                .addConverterFactory(OkHttpProvider.json.asConverterFactory("application/json".toMediaType()))
                 .build()
 
         apiService = retrofit.create(HermesApiService::class.java)
@@ -151,57 +152,48 @@ class HermesApiServiceTest {
         }
 
     @Test
-    fun testGetSkills_missingFieldsInResponse() =
+    fun testGetSkills_missingFieldsInResponse() {
-        runTest {
         mockWebServer.enqueue(
             MockResponse()
                 .setResponseCode(200)
                 .setBody("""[{"description":"info"}]"""),
         )
 
-            val response = apiService.getSkills()
+        assertThrows(kotlinx.serialization.SerializationException::class.java) {
-            assertTrue(response.isSuccessful)
+            runTest {
-            val skills = response.body()
+                apiService.getSkills()
-            assertEquals(1, skills?.size)
+            }
-            val skill = skills?.get(0)
+        }
-            org.junit.jupiter.api.Assertions
-                .assertNull(skill?.name)
-            assertEquals(false, skill?.enabled)
     }
 
     @Test
-    fun testGetCronJobs_missingFieldsInResponse() =
+    fun testGetCronJobs_missingFieldsInResponse() {
-        runTest {
         mockWebServer.enqueue(
             MockResponse()
                 .setResponseCode(200)
                 .setBody("""[{"schedule":"* * * * *"}]"""),
         )
 
-            val response = apiService.getCronJobs()
+        assertThrows(kotlinx.serialization.SerializationException::class.java) {
-            assertTrue(response.isSuccessful)
+            runTest {
-            val jobs = response.body()
+                apiService.getCronJobs()
-            assertEquals(1, jobs?.size)
+            }
-            val job = jobs?.get(0)
+        }
-            org.junit.jupiter.api.Assertions
-                .assertNull(job?.id)
-            org.junit.jupiter.api.Assertions
-                .assertNull(job?.name)
     }
 
     @Test
-    fun testGetSessions_missingSessionsField() =
+    fun testGetSessions_missingSessionsField() {
-        runTest {
         mockWebServer.enqueue(
             MockResponse()
                 .setResponseCode(200)
                 .setBody("""{}"""),
         )
 
-            val response = apiService.getSessions()
+        assertThrows(kotlinx.serialization.SerializationException::class.java) {
-            assertTrue(response.isSuccessful)
+            runTest {
-            org.junit.jupiter.api.Assertions
+                apiService.getSessions()
-                .assertNull(response.body()?.sessions)
+            }
+        }
     }
 
     @Test
@@ -212,7 +204,7 @@ class HermesApiServiceTest {
                 .setBody("""{"messages": ["""),
         )
 
-        assertThrows(java.io.EOFException::class.java) {
+        assertThrows(kotlinx.serialization.SerializationException::class.java) {
             runTest {
                 apiService.getSessionMessages("session_1")
             }
@@ -220,18 +212,18 @@ class HermesApiServiceTest {
     }
 
     @Test
-    fun testGetSessionMessages_missingMessagesField() =
+    fun testGetSessionMessages_missingMessagesField() {
-        runTest {
         mockWebServer.enqueue(
             MockResponse()
                 .setResponseCode(200)
                 .setBody("""{}"""),
         )
 
-            val response = apiService.getSessionMessages("session_1")
+        assertThrows(kotlinx.serialization.SerializationException::class.java) {
-            assertTrue(response.isSuccessful)
+            runTest {
-            org.junit.jupiter.api.Assertions
+                apiService.getSessionMessages("session_1")
-                .assertNull(response.body()?.messages)
+            }
+        }
     }
 
     @Test
@@ -243,7 +235,7 @@ class HermesApiServiceTest {
                     .setBody("""[{"name":"weather""""),
             )
 
-            org.junit.jupiter.api.Assertions.assertThrows(java.io.EOFException::class.java) {
+            org.junit.jupiter.api.Assertions.assertThrows(kotlinx.serialization.SerializationException::class.java) {
                 kotlinx.coroutines.runBlocking {
                     apiService.getSkills()
                 }
@@ -259,7 +251,7 @@ class HermesApiServiceTest {
                     .setBody("""[{"name":"weather","enabled":{}}]"""),
             )
 
-            org.junit.jupiter.api.Assertions.assertThrows(com.google.gson.JsonSyntaxException::class.java) {
+            org.junit.jupiter.api.Assertions.assertThrows(kotlinx.serialization.SerializationException::class.java) {
                 kotlinx.coroutines.runBlocking {
                     apiService.getSkills()
                 }

app/src/test/java/com/m57/hermescontrol/data/ws/EventParserTest.kt

@@ -3,12 +3,31 @@ package com.m57.hermescontrol.data.ws
 import io.mockk.every
 import io.mockk.mockkStatic
 import io.mockk.unmockkAll
+import kotlinx.serialization.json.JsonObject
 import org.junit.After
 import org.junit.Assert.assertEquals
 import org.junit.Assert.assertTrue
 import org.junit.Before
 import org.junit.Test
 
+@Suppress("FunctionName")
+private fun createJsonRpcResponse(
+    jsonrpc: String,
+    id: String?,
+    result: Any? = null,
+    error: JsonRpcError? = null,
+    method: String? = null,
+    params: Any? = null,
+): JsonRpcResponse =
+    JsonRpcResponse(
+        jsonrpc = jsonrpc,
+        id = id,
+        result = result?.toJsonElement(),
+        error = error,
+        method = method,
+        params = params?.toJsonElement() as? JsonObject,
+    )
+
 class EventParserTest {
     @Before
     fun setUp() {
@@ -24,7 +43,7 @@ class EventParserTest {
     @Test
     fun testParseRpcResult_returnsRpcResultEvent() {
         val response =
-            JsonRpcResponse(
+            createJsonRpcResponse(
                 jsonrpc = "2.0",
                 id = "123",
                 result = mapOf("status" to "success"),
@@ -43,7 +62,7 @@ class EventParserTest {
     fun testParseRpcError_returnsRpcErrorEvent() {
         val error = JsonRpcError(code = -32600, message = "Invalid Request")
         val response =
-            JsonRpcResponse(
+            createJsonRpcResponse(
                 jsonrpc = "2.0",
                 id = "456",
                 result = null,
@@ -62,7 +81,7 @@ class EventParserTest {
     @Test
     fun testParseGatewayReady_returnsGatewayReadyEvent() {
         val response =
-            JsonRpcResponse(
+            createJsonRpcResponse(
                 jsonrpc = "2.0",
                 id = null,
                 result = null,
@@ -83,7 +102,7 @@ class EventParserTest {
     @Test
     fun testParseMessageToken_returnsMessageTokenEvent() {
         val response =
-            JsonRpcResponse(
+            createJsonRpcResponse(
                 jsonrpc = "2.0",
                 id = null,
                 result = null,
@@ -105,7 +124,7 @@ class EventParserTest {
     @Test
     fun testParseMessageToken_withSessionIdInParams_returnsMessageTokenEvent() {
         val response =
-            JsonRpcResponse(
+            createJsonRpcResponse(
                 jsonrpc = "2.0",
                 id = null,
                 result = null,
@@ -128,7 +147,7 @@ class EventParserTest {
     @Test
     fun testParseThinkingDelta_returnsThinkingDeltaEvent() {
         val response =
-            JsonRpcResponse(
+            createJsonRpcResponse(
                 jsonrpc = "2.0",
                 id = null,
                 result = null,
@@ -150,7 +169,7 @@ class EventParserTest {
     @Test
     fun testParseClarifyRequest_returnsClarifyRequestEvent() {
         val response =
-            JsonRpcResponse(
+            createJsonRpcResponse(
                 jsonrpc = "2.0",
                 id = null,
                 result = null,
@@ -176,7 +195,7 @@ class EventParserTest {
     @Test
     fun testParseClarifyRequest_withQuestionFields_parsesSuccessfully() {
         val response =
-            JsonRpcResponse(
+            createJsonRpcResponse(
                 jsonrpc = "2.0",
                 id = null,
                 result = null,
@@ -204,7 +223,7 @@ class EventParserTest {
     @Test
     fun testParseSessionInfo_returnsSessionInfoEvent() {
         val response =
-            JsonRpcResponse(
+            createJsonRpcResponse(
                 jsonrpc = "2.0",
                 id = null,
                 result = null,
@@ -220,7 +239,7 @@ class EventParserTest {
     @Test
     fun testParseMessageStart_returnsMessageStartEvent() {
         val response =
-            JsonRpcResponse(
+            createJsonRpcResponse(
                 jsonrpc = "2.0",
                 id = null,
                 result = null,
@@ -241,7 +260,7 @@ class EventParserTest {
     @Test
     fun testParseMessageDelta_returnsMessageTokenEvent() {
         val response =
-            JsonRpcResponse(
+            createJsonRpcResponse(
                 jsonrpc = "2.0",
                 id = null,
                 result = null,
@@ -258,7 +277,7 @@ class EventParserTest {
     @Test
     fun testParseMessageComplete_returnsMessageCompleteEvent() {
         val response =
-            JsonRpcResponse(
+            createJsonRpcResponse(
                 jsonrpc = "2.0",
                 id = null,
                 result = null,
@@ -274,7 +293,7 @@ class EventParserTest {
     @Test
     fun testParseMessageDone_returnsMessageDoneEvent() {
         val response =
-            JsonRpcResponse(
+            createJsonRpcResponse(
                 jsonrpc = "2.0",
                 id = null,
                 result = null,
@@ -289,7 +308,7 @@ class EventParserTest {
     @Test
     fun testParseToolStart_returnsToolStartEvent() {
         val response =
-            JsonRpcResponse(
+            createJsonRpcResponse(
                 jsonrpc = "2.0",
                 id = null,
                 result = null,
@@ -311,7 +330,7 @@ class EventParserTest {
     @Test
     fun testParseToolComplete_returnsToolCompleteEvent() {
         val response =
-            JsonRpcResponse(
+            createJsonRpcResponse(
                 jsonrpc = "2.0",
                 id = null,
                 result = null,
@@ -333,7 +352,7 @@ class EventParserTest {
     @Test
     fun testParseStatusUpdate_returnsStatusUpdateEvent() {
         val response =
-            JsonRpcResponse(
+            createJsonRpcResponse(
                 jsonrpc = "2.0",
                 id = null,
                 result = null,
@@ -349,7 +368,7 @@ class EventParserTest {
     @Test
     fun testParseSessionUpdated_returnsSessionUpdatedEvent() {
         val response =
-            JsonRpcResponse(
+            createJsonRpcResponse(
                 jsonrpc = "2.0",
                 id = null,
                 result = null,
@@ -365,7 +384,7 @@ class EventParserTest {
     @Test
     fun testParseUnknownType_returnsUnknownEvent() {
         val response =
-            JsonRpcResponse(
+            createJsonRpcResponse(
                 jsonrpc = "2.0",
                 id = null,
                 result = null,
@@ -380,7 +399,7 @@ class EventParserTest {
     @Test
     fun testParseNullParams_returnsUnknownEvent() {
         val response =
-            JsonRpcResponse(
+            createJsonRpcResponse(
                 jsonrpc = "2.0",
                 id = null,
                 result = null,
@@ -395,7 +414,7 @@ class EventParserTest {
     @Test
     fun testParseNullTypeInParams_returnsUnknownEvent() {
         val response =
-            JsonRpcResponse(
+            createJsonRpcResponse(
                 jsonrpc = "2.0",
                 id = null,
                 result = null,

gradle/libs.versions.toml

@@ -21,7 +21,6 @@ lifecycleViewmodelNav3 = "2.10.0"
 leakcanary = "2.14"
 okhttp = "5.4.0"
 retrofit = "3.0.0"
-gson = "2.14.0"
 securityCrypto = "1.0.0"
 mockk = "1.14.11"
 turbine = "1.2.0"
@@ -66,8 +65,8 @@ okhttp = { module = "com.squareup.okhttp3:okhttp", version.ref = "okhttp" }
 okhttp-mockwebserver = { module = "com.squareup.okhttp3:mockwebserver", version.ref = "okhttp" }
 okhttp-logging = { module = "com.squareup.okhttp3:logging-interceptor", version.ref = "okhttp" }
 retrofit = { module = "com.squareup.retrofit2:retrofit", version.ref = "retrofit" }
-retrofit-converter-gson = { module = "com.squareup.retrofit2:converter-gson", version.ref = "retrofit" }
+retrofit-converter-kotlinx-serialization = { module = "com.squareup.retrofit2:converter-kotlinx-serialization", version.ref = "retrofit" }
-gson = { module = "com.google.code.gson:gson", version.ref = "gson" }
+kotlinx-serialization-json = { module = "org.jetbrains.kotlinx:kotlinx-serialization-json", version = "1.8.0" }
 
 # Security
 androidx-security-crypto = { module = "androidx.security:security-crypto", version.ref = "securityCrypto" }