feat(chat): integrate fast mode toggle into generation controls dropdown (#1093)

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

@@ -24,6 +24,10 @@ private data class ActiveModelSwitch(
     val previousModel: String?,
 )
 
+private data class ActiveFastSwitch(
+    val targetFast: Boolean,
+)
+
 /**
  * Owns model picker loading/caching, in-session model switches, model capabilities,
  * pinned model toggling, and expensive model switch confirmation dialogs.
@@ -48,6 +52,8 @@ class ChatModelSwitchDelegate(
     private val savePinnedModels: (List<PinnedModel>) -> Unit = { AuthManager.savePinnedModels(it) },
 ) {
     private val pendingModelSwitchRequests = ConcurrentHashMap<String, ActiveModelSwitch>()
+    private val pendingFastSwitchRequests = ConcurrentHashMap<String, ActiveFastSwitch>()
+    private val fastRejectedModels = ConcurrentHashMap.newKeySet<String>()
     private var activeModelSwitchConfirmation: ActiveModelSwitch? = null
     private var optimisticPreviousModel: String? = null
     private var cachedModelOptions: List<ModelProvider> = emptyList()
@@ -195,6 +201,7 @@ class ChatModelSwitchDelegate(
         result: Any?,
     ) {
         val pending = pendingModelSwitchRequests.remove(id)
+        val pendingFast = pendingFastSwitchRequests.remove(id)
         val map = result as? Map<*, *> ?: return
         val key = map["key"] as? String
         if (key == "model") {
@@ -209,6 +216,20 @@ class ChatModelSwitchDelegate(
                     it.copy(modelSwitchConfirmMessage = confirmMessage)
                 }
             }
+        } else if (key == "fast") {
+            val rawVal = map["value"] as? String
+            val confirmedFast =
+                if (rawVal != null) {
+                    rawVal == "fast" || rawVal == "priority"
+                } else {
+                    pendingFast?.targetFast ?: uiState.value.fastMode
+                }
+            uiState.update {
+                it.copy(
+                    fastMode = confirmedFast,
+                    isFastModeChanging = false,
+                )
+            }
         }
     }
 
@@ -234,6 +255,51 @@ class ChatModelSwitchDelegate(
         }
     }
 
+    fun toggleFastMode() {
+        val state = uiState.value
+        val sessionId = runtimeSessionId() ?: return
+        if (state.currentModelCapabilities?.fast != true) return
+        if (state.isFastModeChanging) return
+
+        val target = !state.fastMode
+        uiState.update { it.copy(isFastModeChanging = true) }
+        scope.launch(ioDispatcher) {
+            wsSend(
+                WsMethods.CONFIG_SET,
+                mapOf(
+                    "key" to "fast",
+                    "value" to if (target) "fast" else "normal",
+                    "session_id" to sessionId,
+                ),
+            ) { id ->
+                trackRequest(id, WsMethods.CONFIG_SET)
+                pendingFastSwitchRequests[id] = ActiveFastSwitch(target)
+            }
+        }
+    }
+
+    fun handleConfigSetError(
+        id: String,
+        error: Any?,
+    ) {
+        val pendingFast = pendingFastSwitchRequests.remove(id)
+        if (pendingFast != null) {
+            val errorMsg =
+                when (error) {
+                    is Map<*, *> -> error["message"] as? String ?: error.toString()
+                    else -> error.toString()
+                }.lowercase()
+            val currentModel = uiState.value.currentSessionModel
+            if (currentModel != null &&
+                (errorMsg.contains("fast mode is not available") || errorMsg.contains("unknown fast mode"))
+            ) {
+                fastRejectedModels.add(currentModel)
+                syncCurrentModelCapabilities()
+            }
+            uiState.update { it.copy(isFastModeChanging = false) }
+        }
+    }
+
     fun setReasoningLevel(level: String?) {
         uiState.update { it.copy(reasoningLevel = level) }
         val sessionId = runtimeSessionId() ?: return
@@ -276,7 +342,12 @@ class ChatModelSwitchDelegate(
                 } else {
                     val provider = label.substring(0, idx)
                     val model = label.substring(idx + 1)
-                    cachedModelOptions.find { it.slug == provider }?.capabilities?.get(model)
+                    val baseCaps = cachedModelOptions.find { it.slug == provider }?.capabilities?.get(model)
+                    if (fastRejectedModels.contains(label) && baseCaps?.fast == true) {
+                        baseCaps.copy(fast = false)
+                    } else {
+                        baseCaps
+                    }
                 }
             }
         uiState.update { state ->

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

@@ -634,6 +634,10 @@ fun ChatScreen(
                 onReasoningTap = { level -> viewModel.setReasoningLevel(level) },
                 canDisableReasoning = state.currentModelCapabilities?.can_disable_reasoning,
                 supportsReasoning = state.currentModelCapabilities?.reasoning,
+                fastMode = state.fastMode,
+                fastSupported = state.currentModelCapabilities?.fast == true,
+                isFastModeChanging = state.isFastModeChanging,
+                onToggleFastMode = { viewModel.toggleFastMode() },
             )
         }
 

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

@@ -130,6 +130,9 @@ data class ChatUiState(
     val currentModelCapabilities: ModelCapabilities? = null,
     // Reasoning effort level for the current session
     val reasoningLevel: String? = null,
+    // Fast mode / Priority processing state for the current session
+    val fastMode: Boolean = false,
+    val isFastModeChanging: Boolean = false,
     val terminalBackend: String? = null,
     // Context-window meter (issue #756): tokens currently used by the session
     // prompt (numerator) and the active model's full context window (denominator).
@@ -733,6 +736,10 @@ class ChatViewModel(
                     val provider = info["provider"] as? String
                     val reasoningEffort = info["reasoning_effort"] as? String
                     val terminalBackend = info["terminal_backend"] as? String
+                    val serviceTier = (info["service_tier"] as? String)?.trim()?.lowercase()
+                    val fastFlag =
+                        (info["fast"] as? Boolean)
+                            ?: (if (serviceTier != null) serviceTier == "priority" else null)
                     val newModelLabel =
                         if (model != null && provider != null) {
                             "$provider/$model"
@@ -758,6 +765,8 @@ class ChatViewModel(
                                 } else {
                                     reasoningEffort
                                 },
+                            fastMode = fastFlag ?: state.fastMode,
+                            isFastModeChanging = if (fastFlag != null) false else state.isFastModeChanging,
                             terminalBackend = terminalBackend ?: state.terminalBackend,
                             fullContextTokens = if (modelSwapped) null else state.fullContextTokens,
                         )
@@ -1036,6 +1045,10 @@ class ChatViewModel(
                 val provider = infoMap?.get("provider") as? String
                 val reasoningEffort = infoMap?.get("reasoning_effort") as? String
                 val terminalBackend = infoMap?.get("terminal_backend") as? String
+                val serviceTier = (infoMap?.get("service_tier") as? String)?.trim()?.lowercase()
+                val fastFlag =
+                    (infoMap?.get("fast") as? Boolean)
+                        ?: (if (serviceTier != null) serviceTier == "priority" else null)
 
                 // B8 (Jun 20 2026, kanban t_session_resume): do NOT reload
                 // cached messages here — switchSession() already did so before
@@ -1059,6 +1072,8 @@ class ChatViewModel(
                             } else {
                                 reasoningEffort
                             },
+                        fastMode = fastFlag ?: false,
+                        isFastModeChanging = false,
                         terminalBackend = terminalBackend ?: it.terminalBackend,
                     )
                 }
@@ -1198,6 +1213,10 @@ class ChatViewModel(
             return
         }
 
+        if (method == WsMethods.CONFIG_SET) {
+            modelSwitchDelegate.handleConfigSetError(id, error)
+        }
+
         if (method == WsMethods.SESSION_CREATE) {
             val pending = pendingInitialPrompt
             pendingInitialPrompt = null
@@ -2221,6 +2240,8 @@ class ChatViewModel(
 
     fun setReasoningLevel(level: String?) = modelSwitchDelegate.setReasoningLevel(level)
 
+    fun toggleFastMode() = modelSwitchDelegate.toggleFastMode()
+
     fun getModelCapabilities(
         providerSlug: String,
         modelName: String,
@@ -2471,6 +2492,8 @@ class ChatViewModel(
                 currentSessionModel = null,
                 currentModelCapabilities = null,
                 reasoningLevel = null,
+                fastMode = false,
+                isFastModeChanging = false,
                 terminalBackend = null,
                 usedContextTokens = null,
                 fullContextTokens = null,

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

@@ -103,6 +103,10 @@ fun ChatInputBar(
     onReasoningTap: (String?) -> Unit = {},
     canDisableReasoning: Boolean? = null,
     supportsReasoning: Boolean? = null,
+    fastMode: Boolean = false,
+    fastSupported: Boolean = false,
+    isFastModeChanging: Boolean = false,
+    onToggleFastMode: () -> Unit = {},
 ) {
     // Allow sending while the agent is mid-turn or awaiting approval: the
     // gateway's prompt.submit busy-input policy queues it as the next turn
@@ -377,6 +381,10 @@ fun ChatInputBar(
                     modifier = Modifier.testTag("chat_composer_toolbar"),
                     canDisableReasoning = canDisableReasoning,
                     supportsReasoning = supportsReasoning,
+                    fastMode = fastMode,
+                    fastSupported = fastSupported,
+                    isFastModeChanging = isFastModeChanging,
+                    onToggleFastMode = onToggleFastMode,
                 )
 
                 // Attachment dropdown (anchored to the attach button in ComposerToolbar)

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

@@ -3,16 +3,20 @@ package com.m57.hermescontrol.ui.chat.components
 import androidx.compose.foundation.horizontalScroll
 import androidx.compose.foundation.layout.Arrangement
 import androidx.compose.foundation.layout.Box
+import androidx.compose.foundation.layout.Column
 import androidx.compose.foundation.layout.Row
 import androidx.compose.foundation.layout.fillMaxWidth
 import androidx.compose.foundation.layout.height
 import androidx.compose.foundation.layout.padding
 import androidx.compose.foundation.layout.size
+import androidx.compose.foundation.layout.widthIn
 import androidx.compose.foundation.rememberScrollState
 import androidx.compose.material.icons.Icons
 import androidx.compose.material.icons.filled.AttachFile
+import androidx.compose.material.icons.filled.Bolt
 import androidx.compose.material.icons.filled.Mic
 import androidx.compose.material.icons.filled.Stop
+import androidx.compose.material3.CircularProgressIndicator
 import androidx.compose.material3.DropdownMenu
 import androidx.compose.material3.DropdownMenuItem
 import androidx.compose.material3.FilterChip
@@ -21,6 +25,8 @@ import androidx.compose.material3.Icon
 import androidx.compose.material3.IconButton
 import androidx.compose.material3.IconButtonDefaults
 import androidx.compose.material3.MaterialTheme
+import androidx.compose.material3.Switch
+import androidx.compose.material3.SwitchDefaults
 import androidx.compose.material3.Text
 import androidx.compose.runtime.Composable
 import androidx.compose.runtime.getValue
@@ -29,8 +35,12 @@ import androidx.compose.runtime.remember
 import androidx.compose.runtime.setValue
 import androidx.compose.ui.Alignment
 import androidx.compose.ui.Modifier
+import androidx.compose.ui.draw.scale
 import androidx.compose.ui.platform.testTag
 import androidx.compose.ui.res.stringResource
+import androidx.compose.ui.semantics.contentDescription
+import androidx.compose.ui.semantics.semantics
+import androidx.compose.ui.text.font.FontWeight
 import androidx.compose.ui.text.style.TextOverflow
 import androidx.compose.ui.unit.dp
 import com.m57.hermescontrol.R
@@ -60,6 +70,10 @@ fun ComposerToolbar(
     modifier: Modifier = Modifier,
     canDisableReasoning: Boolean? = null,
     supportsReasoning: Boolean? = null,
+    fastMode: Boolean = false,
+    fastSupported: Boolean = false,
+    isFastModeChanging: Boolean = false,
+    onToggleFastMode: () -> Unit = {},
 ) {
     var showReasoningMenu by remember { mutableStateOf(false) }
     val reasoningDisabledForModel = supportsReasoning == false
@@ -109,24 +123,44 @@ fun ComposerToolbar(
                     .testTag("model_chip"),
         )
 
-        // Reasoning chip with dropdown menu (right side, next to mic)
+        // Reasoning & Generation controls with dropdown menu (Option 3)
         Box {
             FilterChip(
-                selected = reasoningLevel != null,
+                selected = reasoningLevel != null || fastMode,
                 onClick = { showReasoningMenu = true },
-                enabled = !reasoningDisabledForModel,
+                enabled = isConnected,
                 label = {
-                    Text(
+                    Row(
-                        text =
+                        verticalAlignment = Alignment.CenterVertically,
-                            if (reasoningDisabledForModel) {
+                        horizontalArrangement = Arrangement.spacedBy(4.dp),
-                                "No reasoning"
+                    ) {
-                            } else {
+                        if (fastMode) {
-                                buildReasoningLabel(reasoningLevel)
+                            Icon(
-                            },
+                                imageVector = Icons.Filled.Bolt,
-                        style = MaterialTheme.typography.bodySmall,
+                                contentDescription = stringResource(R.string.chat_fast_mode_label),
-                        maxLines = 1,
+                                tint = MaterialTheme.colorScheme.primary,
-                        overflow = TextOverflow.Ellipsis,
+                                modifier = Modifier.size(14.dp),
-                    )
+                            )
+                        }
+                        Text(
+                            text =
+                                if (reasoningDisabledForModel) {
+                                    if (fastMode) stringResource(R.string.chat_fast_mode_label) else "No reasoning"
+                                } else {
+                                    val rLabel = buildReasoningLabel(reasoningLevel)
+                                    if (fastMode) {
+                                        "${stringResource(
+                                            R.string.chat_fast_mode_label,
+                                        )} · $rLabel"
+                                    } else {
+                                        rLabel
+                                    }
+                                },
+                            style = MaterialTheme.typography.bodySmall,
+                            maxLines = 1,
+                            overflow = TextOverflow.Ellipsis,
+                        )
+                    }
                 },
                 modifier =
                     Modifier
@@ -137,11 +171,74 @@ fun ComposerToolbar(
             DropdownMenu(
                 expanded = showReasoningMenu,
                 onDismissRequest = { showReasoningMenu = false },
+                modifier = Modifier.widthIn(min = 220.dp),
             ) {
+                // ── Fast Mode Toggle Item ──
+                val fastAvailable = isConnected && fastSupported
+                DropdownMenuItem(
+                    leadingIcon = {
+                        Icon(
+                            imageVector = Icons.Filled.Bolt,
+                            contentDescription = null,
+                            tint =
+                                if (fastMode) {
+                                    MaterialTheme.colorScheme.primary
+                                } else {
+                                    MaterialTheme.colorScheme.onSurfaceVariant
+                                },
+                            modifier = Modifier.size(20.dp),
+                        )
+                    },
+                    text = {
+                        Column {
+                            Text(
+                                text = stringResource(R.string.chat_fast_mode_label),
+                                style = MaterialTheme.typography.bodyMedium,
+                                fontWeight = if (fastMode) FontWeight.SemiBold else FontWeight.Normal,
+                            )
+                            if (!fastSupported) {
+                                Text(
+                                    text = stringResource(R.string.chat_fast_mode_unavailable),
+                                    style = MaterialTheme.typography.labelSmall,
+                                    color = MaterialTheme.colorScheme.onSurfaceVariant.copy(alpha = 0.6f),
+                                )
+                            }
+                        }
+                    },
+                    trailingIcon = {
+                        if (isFastModeChanging) {
+                            CircularProgressIndicator(
+                                modifier = Modifier.size(16.dp),
+                                strokeWidth = 2.dp,
+                                color = MaterialTheme.colorScheme.primary,
+                            )
+                        } else {
+                            Switch(
+                                checked = fastMode,
+                                onCheckedChange = null, // MenuItem click owns the trigger
+                                enabled = fastAvailable && !isFastModeChanging,
+                                modifier =
+                                    Modifier
+                                        .scale(0.85f)
+                                        .testTag("fast_mode_switch"),
+                            )
+                        }
+                    },
+                    onClick = {
+                        if (fastAvailable && !isFastModeChanging) {
+                            onToggleFastMode()
+                        }
+                    },
+                    enabled = fastAvailable && !isFastModeChanging,
+                )
+
+                HorizontalDivider()
+
                 Text(
-                    text = "Reasoning",
+                    text = "REASONING",
                     style = MaterialTheme.typography.labelSmall,
-                    color = MaterialTheme.colorScheme.onSurfaceVariant,
+                    color = MaterialTheme.colorScheme.onSurfaceVariant.copy(alpha = 0.8f),
+                    fontWeight = FontWeight.Bold,
                     modifier = Modifier.padding(horizontal = 12.dp, vertical = 6.dp),
                 )
                 if (canDisable == false) {
@@ -160,7 +257,6 @@ fun ComposerToolbar(
                         modifier = Modifier.padding(horizontal = 12.dp, vertical = 2.dp),
                     )
                 }
-                HorizontalDivider()
                 val allLevels =
                     listOf(
                         "none" to "None",

app/src/main/res/values-ar/strings.xml

@@ -1031,6 +1031,9 @@
 <string name="channels_expiry_format">ينتهي في: %1$s</string>
 <string name="channels_search_placeholder">البحث في القنوات…</string>
 <string name="chat_attach_file">إرفاق ملف</string>
+<string name="chat_fast_mode_label">سريع</string>
+<string name="chat_fast_mode_desc">الوضع السريع</string>
+<string name="chat_fast_mode_unavailable">الوضع السريع غير مدعوم لهذا النموذج</string>
 <string name="chat_save_attachment">حفظ %1$s</string>
 <string name="chat_switch_model_title">تبديل النموذج (لهذه المحادثة)</string>
 <string name="config_clear_value">مسح القيمة</string>

app/src/main/res/values-ko/strings.xml

@@ -883,4 +883,7 @@
     <string name="subagent_status_cancelled">취소됨</string>
     <string name="subagent_status_failed">실패</string>
     <string name="subagent_duration">%1$.1f초</string>
+    <string name="chat_fast_mode_label">빠름</string>
+    <string name="chat_fast_mode_desc">빠른 모드</string>
+    <string name="chat_fast_mode_unavailable">이 모델에서는 빠른 모드를 사용할 수 없습니다</string>
 </resources>

app/src/main/res/values-zh/strings.xml

@@ -1022,6 +1022,9 @@
     <string name="channels_expiry_format">过期时间：%1$s</string>
     <string name="channels_search_placeholder">搜索渠道…</string>
     <string name="chat_attach_file">附加文件</string>
+    <string name="chat_fast_mode_label">快速</string>
+    <string name="chat_fast_mode_desc">快速模式</string>
+    <string name="chat_fast_mode_unavailable">此模型不支持快速模式</string>
     <string name="chat_save_attachment">保存 %1$s</string>
     <string name="chat_switch_model_title">切换模型（当前对话）</string>
     <string name="config_clear_value">清除值</string>

app/src/main/res/values/strings.xml

@@ -1158,6 +1158,9 @@
     <string name="channels_expiry_format">Expires: %1$s</string>
     <string name="channels_search_placeholder">Search channels…</string>
     <string name="chat_attach_file">Attach file</string>
+    <string name="chat_fast_mode_label">Fast</string>
+    <string name="chat_fast_mode_desc">Fast mode</string>
+    <string name="chat_fast_mode_unavailable">Fast mode unavailable for this model</string>
     <string name="chat_save_attachment">Save %1$s</string>
     <string name="chat_switch_model_title">Switch model (this chat)</string>
     <string name="config_clear_value">Clear value</string>

app/src/test/java/com/m57/hermescontrol/ui/chat/ChatModelSwitchDelegateTest.kt

@@ -40,7 +40,7 @@ class ChatModelSwitchDelegateTest {
                         slug = "openai",
                         name = "OpenAI",
                         models = listOf("gpt-4o"),
-                        capabilities = mapOf("gpt-4o" to ModelCapabilities(reasoning = true)),
+                        capabilities = mapOf("gpt-4o" to ModelCapabilities(fast = true, reasoning = true)),
                     ),
                 ),
         )
@@ -138,4 +138,73 @@ class ChatModelSwitchDelegateTest {
             assertNull(uiState.value.modelSwitchConfirmMessage)
             assertEquals("anthropic/claude-3", uiState.value.currentSessionModel)
         }
+
+    @Test
+    fun toggleFastMode_sendsConfigSetFast_andUpdatesOnAck() =
+        testScope.runTest {
+            delegate.preloadModelOptions()
+            advanceUntilIdle()
+
+            // Switch to model with fast capability
+            delegate.sendSlashModel("openai", "gpt-4o")
+            advanceUntilIdle()
+            sentMethods.clear()
+            sentParams.clear()
+
+            assertTrue(uiState.value.currentModelCapabilities?.fast == true)
+            assertFalse(uiState.value.fastMode)
+            assertFalse(uiState.value.isFastModeChanging)
+
+            delegate.toggleFastMode()
+            advanceUntilIdle()
+            assertTrue(uiState.value.isFastModeChanging)
+            assertFalse(uiState.value.fastMode) // Still unconfirmed!
+            assertEquals(listOf(WsMethods.CONFIG_SET), sentMethods)
+            assertEquals("fast", sentParams.first()["key"])
+            assertEquals("fast", sentParams.first()["value"])
+            assertEquals("runtime-1", sentParams.first()["session_id"])
+
+            // Backend acknowledges
+            delegate.handleConfigSetResult("req-1", mapOf("key" to "fast", "value" to "fast"))
+            assertTrue(uiState.value.fastMode)
+            assertFalse(uiState.value.isFastModeChanging)
+
+            // Toggle off
+            delegate.toggleFastMode()
+            advanceUntilIdle()
+            assertTrue(uiState.value.isFastModeChanging)
+            assertEquals("normal", sentParams.last()["value"])
+
+            delegate.handleConfigSetResult("req-2", mapOf("key" to "fast", "value" to "normal"))
+            assertFalse(uiState.value.fastMode)
+            assertFalse(uiState.value.isFastModeChanging)
+        }
+
+    @Test
+    fun toggleFastMode_whenRejectedByBackend_clearsChangingAndLatchesUnavailable() =
+        testScope.runTest {
+            delegate.preloadModelOptions()
+            advanceUntilIdle()
+            delegate.sendSlashModel("openai", "gpt-4o")
+            advanceUntilIdle()
+            sentMethods.clear()
+            sentParams.clear()
+            assertTrue(uiState.value.currentModelCapabilities?.fast == true)
+
+            delegate.toggleFastMode()
+            advanceUntilIdle()
+            assertTrue(uiState.value.isFastModeChanging)
+
+            // Backend returns error indicating fast mode not available
+            delegate.handleConfigSetError("req-1", mapOf("message" to "fast mode is not available for this model"))
+            assertFalse(uiState.value.isFastModeChanging)
+            assertFalse(uiState.value.fastMode)
+            assertEquals(false, uiState.value.currentModelCapabilities?.fast)
+
+            // Further toggle attempts are no-ops
+            val sentCount = sentMethods.size
+            delegate.toggleFastMode()
+            advanceUntilIdle()
+            assertEquals(sentCount, sentMethods.size)
+        }
 }

app/src/test/java/com/m57/hermescontrol/ui/chat/ChatViewModelTest.kt

@@ -2951,6 +2951,92 @@ class ChatViewModelTest {
             assertEquals("nous/tencent/hy3:free", viewModel.uiState.value.currentSessionModel)
         }
 
+    @Test
+    fun testSessionInfo_hydratesFastModeState() =
+        runTest {
+            stubEmptySessionRests("session-a")
+            val (viewModel, _) = createViewModelWithSession()
+            advanceUntilIdle()
+
+            assertFalse(viewModel.uiState.value.fastMode)
+
+            // Fast = true in session.info
+            mockEventsFlow.emit(
+                WsEvent.SessionInfo(
+                    mapOf("fast" to true, "service_tier" to "priority"),
+                ),
+            )
+            advanceUntilIdle()
+            assertTrue(viewModel.uiState.value.fastMode)
+            assertFalse(viewModel.uiState.value.isFastModeChanging)
+
+            // Fast = false / normal in session.info
+            mockEventsFlow.emit(
+                WsEvent.SessionInfo(
+                    mapOf("fast" to false, "service_tier" to "normal"),
+                ),
+            )
+            advanceUntilIdle()
+            assertFalse(viewModel.uiState.value.fastMode)
+
+            // Partial session.info without fast/service_tier does NOT clear state
+            mockEventsFlow.emit(
+                WsEvent.SessionInfo(
+                    mapOf("fast" to true),
+                ),
+            )
+            advanceUntilIdle()
+            assertTrue(viewModel.uiState.value.fastMode)
+
+            mockEventsFlow.emit(
+                WsEvent.SessionInfo(
+                    mapOf("terminal_backend" to "tmux"),
+                ),
+            )
+            advanceUntilIdle()
+            assertTrue(viewModel.uiState.value.fastMode) // preserved!
+        }
+
+    @Test
+    fun testSessionResume_hydratesFastModeState() =
+        runTest {
+            stubEmptySessionRests("session-b")
+            val (viewModel, _) = createViewModelWithSession()
+            var resumeReqId = ""
+            every { HermesWsClient.send(WsMethods.SESSION_RESUME, any(), any()) } answers {
+                val reqId = "resume-req-1"
+                resumeReqId = reqId
+                arg<((String) -> Unit)?>(2)?.invoke(reqId)
+                reqId
+            }
+
+            viewModel.switchSession("session-b")
+            runCurrent()
+
+            // Simulate SESSION_RESUME response with fast=true in info
+            mockEventsFlow.emit(
+                WsEvent.RpcResult(
+                    id = resumeReqId,
+                    result =
+                        mapOf(
+                            "session_id" to "sess-runtime-1",
+                            "resumed" to "session-b",
+                            "info" to
+                                mapOf(
+                                    "model" to "gpt-4o",
+                                    "provider" to "openai",
+                                    "fast" to true,
+                                    "service_tier" to "priority",
+                                ),
+                        ),
+                ),
+            )
+            advanceUntilIdle()
+
+            assertTrue(viewModel.uiState.value.fastMode)
+            assertFalse(viewModel.uiState.value.isFastModeChanging)
+        }
+
     @Test
     fun testResumeNotFound_recoversWithNewSession() =
         runTest {