feat(chat): wire sidebar to real conversations + persist history

Sidebar now lists the user's conversations from GET /api/v1/conversations
(date-grouped, pinned first, active highlighted) instead of mock data. Sending
creates a server conversation on the first message, persists each exchange via
POST .../messages, and auto-titles new conversations. Tapping a chat loads its
stored messages; new-chat/logout reset the active conversation. Linear model
(no branching); locked chats are skipped (no in-app unlock yet).

app/src/main/java/dev/kaizen/app/chat/Background.kt

@@ -36,6 +36,7 @@ import androidx.compose.ui.Alignment
 import androidx.compose.ui.Modifier
 import androidx.compose.ui.draw.BlurredEdgeTreatment
 import androidx.compose.ui.draw.blur
+import androidx.compose.ui.draw.drawWithContent
 import androidx.compose.ui.draw.scale
 import androidx.compose.ui.geometry.Offset
 import androidx.compose.ui.graphics.BlendMode
@@ -51,6 +52,8 @@ import dev.kaizen.app.ui.theme.AmberDeep
 import dev.kaizen.app.ui.theme.BlobAmber
 import dev.kaizen.app.ui.theme.BlobBlue
 import dev.kaizen.app.ui.theme.BlobTeal
+import dev.kaizen.app.ui.theme.DITHER_ALPHA
+import dev.kaizen.app.ui.theme.rememberDitherBrush
 
 /** Mesh/blob background: large, heavily blurred color circles that drift slowly. */
 @Composable
@@ -66,7 +69,17 @@ fun MeshBackground(content: @Composable BoxScope.() -> Unit) {
         animationSpec = infiniteRepeatable(tween(22000, easing = LinearEasing), RepeatMode.Reverse),
         label = "drift",
     )
-    Box(Modifier.fillMaxSize().background(base)) {
+    // Dither overlay (drawn last, over everything) — kills 8-bit gradient banding.
+    val ditherBrush = rememberDitherBrush()
+    Box(
+        Modifier
+            .fillMaxSize()
+            .background(base)
+            .drawWithContent {
+                drawContent()
+                drawRect(brush = ditherBrush, alpha = DITHER_ALPHA)
+            },
+    ) {
         Blob(BlobAmber, 360.dp, (-60f + drift * 30f).dp, (-40f + drift * 24f).dp, 0.30f * factor)
         Blob(BlobBlue, 380.dp, (170f - drift * 44f).dp, (150f + drift * 40f).dp, 0.24f * factor)
         Blob(BlobTeal, 300.dp, (30f + drift * 50f).dp, (560f - drift * 36f).dp, 0.22f * factor)

app/src/main/java/dev/kaizen/app/chat/ChatModels.kt

@@ -18,6 +18,9 @@ data class Message(
     val content: String,
     val streaming: Boolean = false,
     val thinking: Boolean = false,
+    // Stable server-side id (UUID) used for persistence + parentId chaining. Generated
+    // on creation; overwritten with the DB id when loading an existing conversation.
+    val wireId: String = java.util.UUID.randomUUID().toString(),
 )
 
 // Empty-state suggestion pills (mirrors the web hero)

app/src/main/java/dev/kaizen/app/chat/ChatScreen.kt

@@ -8,6 +8,7 @@ import androidx.compose.foundation.layout.Arrangement
 import androidx.compose.foundation.layout.Box
 import androidx.compose.foundation.layout.Column
 import androidx.compose.foundation.layout.PaddingValues
+import androidx.compose.foundation.layout.Row
 import androidx.compose.foundation.layout.Spacer
 import androidx.compose.foundation.layout.fillMaxSize
 import androidx.compose.foundation.layout.fillMaxWidth
@@ -49,7 +50,11 @@ import androidx.compose.ui.platform.LocalConfiguration
 import androidx.compose.ui.unit.dp
 import dev.kaizen.app.haptics.rememberHaptics
 import dev.kaizen.app.net.ChatHttpException
+import dev.kaizen.app.net.ChatSpeed
+import dev.kaizen.app.net.ConversationSummary
 import dev.kaizen.app.net.KaizenApi
+import dev.kaizen.app.net.KaizenModel
+import dev.kaizen.app.net.SaveMessage
 import dev.kaizen.app.net.SessionViewModel
 import dev.kaizen.app.net.WireMessage
 import dev.kaizen.app.settings.SettingsScreen
@@ -87,16 +92,67 @@ fun ChatScreen(
     // Native sidebar drawer state
     val drawerState = rememberDrawerState(initialValue = DrawerValue.Closed)
 
+    // Model picker: catalog (best-effort fetch) + sheet visibility
+    var models by remember { mutableStateOf<List<KaizenModel>>(emptyList()) }
+    var showModelSheet by remember { mutableStateOf(false) }
+
+    // Conversation persistence: the active server conversation + the sidebar list
+    var conversationId by remember { mutableStateOf<String?>(null) }
+    var conversations by remember { mutableStateOf<List<ConversationSummary>>(emptyList()) }
+
+    LaunchedEffect(session.config?.baseUrl, session.config?.token) {
+        val cfg = session.config ?: return@LaunchedEffect
+        models = KaizenApi.fetchModels(cfg.baseUrl, cfg.token)
+        conversations = KaizenApi.fetchConversations(cfg.baseUrl, cfg.token)
+    }
+
+    fun refreshConversations() {
+        val cfg = session.config ?: return
+        scope.launch { conversations = KaizenApi.fetchConversations(cfg.baseUrl, cfg.token) }
+    }
+
+    /** Start a fresh chat — drops the active conversation, the next send creates a new one. */
+    fun newChat() {
+        messages.clear()
+        conversationId = null
+    }
+
+    /** Load a stored conversation into the linear message list. Locked ones are skipped (no in-app unlock yet). */
+    fun openConversation(summary: ConversationSummary) {
+        if (summary.locked) return
+        val cfg = session.config ?: return
+        scope.launch {
+            val stored = KaizenApi.fetchMessages(cfg.baseUrl, cfg.token, summary.id)
+            messages.clear()
+            stored.forEach { m ->
+                messages.add(
+                    Message(
+                        id = nextId++,
+                        role = if (m.role == "assistant") Role.Assistant else Role.User,
+                        content = m.content,
+                        wireId = m.id,
+                    ),
+                )
+            }
+            conversationId = summary.id
+        }
+    }
+
     fun send(text: String) {
         val trimmed = text.trim()
         if (trimmed.isEmpty() || isStreaming) return
         val cfg = session.config ?: return
         haptics.click()
-        messages.add(Message(nextId++, Role.User, trimmed))
+        // parentId chains the linear history: the user msg hangs off the last message.
+        val userParentId = messages.lastOrNull()?.wireId
+        val userMsg = Message(nextId++, Role.User, trimmed)
+        messages.add(userMsg)
         input = ""
         val assistantId = nextId++
-        messages.add(Message(assistantId, Role.Assistant, "", streaming = true, thinking = true))
+        val assistantWireId = java.util.UUID.randomUUID().toString()
+        messages.add(Message(assistantId, Role.Assistant, "", streaming = true, thinking = true, wireId = assistantWireId))
         isStreaming = true
+        val wasNewConversation = conversationId == null
 
         // Wire history = the visible conversation minus the streaming placeholder.
         val history = messages
@@ -107,7 +163,12 @@ fun ChatScreen(
             haptics.thinkingStart()
             var sawContent = false
             try {
-                KaizenApi.chat(cfg.baseUrl, cfg.token, cfg.model, history).collect { visible ->
+                // Ensure a server conversation exists before the exchange is persisted.
+                val convId = conversationId ?: KaizenApi.createConversation(cfg.baseUrl, cfg.token)?.also {
+                    conversationId = it
+                }
+
+                KaizenApi.chat(cfg.baseUrl, cfg.token, cfg.model, history, cfg.speed).collect { visible ->
                     val idx = messages.indexOfLast { it.id == assistantId }
                     if (idx < 0) return@collect
                     if (!sawContent && visible.isNotEmpty()) {
@@ -120,7 +181,21 @@ fun ChatScreen(
                     )
                 }
                 val idx = messages.indexOfLast { it.id == assistantId }
+                val finalContent = if (idx >= 0) messages[idx].content else ""
                 if (idx >= 0) messages[idx] = messages[idx].copy(streaming = false, thinking = false)
+
+                // Persist the exchange (best-effort); auto-title + sidebar refresh on a new conversation.
+                if (convId != null && finalContent.isNotEmpty()) {
+                    val saved = KaizenApi.saveMessages(
+                        cfg.baseUrl, cfg.token, convId,
+                        listOf(
+                            SaveMessage(id = userMsg.wireId, parentId = userParentId, role = "user", content = trimmed),
+                            SaveMessage(id = assistantWireId, parentId = userMsg.wireId, role = "assistant", content = finalContent, model = cfg.model),
+                        ),
+                    )
+                    if (saved && wasNewConversation) KaizenApi.generateTitle(cfg.baseUrl, cfg.token, convId)
+                    if (saved) refreshConversations()
+                }
             } catch (e: Exception) {
                 val idx = messages.indexOfLast { it.id == assistantId }
                 if (idx >= 0) messages[idx] = messages[idx].copy(
@@ -157,10 +232,17 @@ fun ChatScreen(
                 drawerContent = {
                     KaizenSidebar(
                         userName = userName,
+                        conversations = conversations,
+                        currentId = conversationId,
                         onClose = { scope.launch { drawerState.close() } },
                         onNewChat = {
                             haptics.tick()
-                            messages.clear()
+                            newChat()
+                            scope.launch { drawerState.close() }
+                        },
+                        onSelectConversation = { summary ->
+                            haptics.tick()
+                            openConversation(summary)
                             scope.launch { drawerState.close() }
                         },
                         onOpenSettings = {
@@ -170,7 +252,7 @@ fun ChatScreen(
                         },
                         onLogout = {
                             haptics.tick()
-                            messages.clear()
+                            newChat()
                             scope.launch { drawerState.close() }
                             session.logout()
                         }
@@ -222,11 +304,15 @@ fun ChatScreen(
                             Brush.verticalGradient(listOf(Color.White.copy(alpha = 0.16f), Color.White.copy(alpha = 0.03f)))
                         }
 
-                        Box(
+                        Row(
                             modifier = Modifier
                                 .align(Alignment.TopStart)
                                 .statusBarsPadding()
-                                .padding(start = 16.dp, top = 10.dp)
+                                .padding(start = 16.dp, top = 10.dp, end = 16.dp),
+                            verticalAlignment = Alignment.CenterVertically,
+                        ) {
+                            Box(
+                                modifier = Modifier
                                     .shadow(elevation = 6.dp, shape = CircleShape, clip = false) // Floats above backgrounds
                                     .clip(CircleShape)
                                     .background(menuGlassBg)
@@ -242,6 +328,13 @@ fun ChatScreen(
                                     modifier = Modifier.size(20.dp)
                                 )
                             }
+                            Spacer(Modifier.width(8.dp))
+                            ModelPill(
+                                label = modelDisplayName(session.config?.model ?: "", models),
+                                onClick = { haptics.tick(); showModelSheet = true },
+                                modifier = Modifier.weight(1f, fill = false),
+                            )
+                        }
 
                         // 3. Floating Bottom Control Dock (responsive centering and clear bottom margins)
                         Column(
@@ -260,6 +353,20 @@ fun ChatScreen(
                             )
                             Spacer(Modifier.height(16.dp)) // Completely clears keyboard edges on all screens
                         }
+
+                        // Model + speed picker (bottom sheet), opened by the top pill
+                        if (showModelSheet) {
+                            ModelSheet(
+                                models = models,
+                                selectedModelId = session.config?.model ?: "",
+                                favorites = session.favorites,
+                                speed = session.config?.speed ?: ChatSpeed.Normal,
+                                onSelectModel = { session.setModel(it); haptics.tick() },
+                                onToggleFavorite = { session.toggleFavorite(it) },
+                                onSelectSpeed = { session.setSpeed(it); haptics.tick() },
+                                onDismiss = { showModelSheet = false },
+                            )
+                        }
                     }
                 }
             }

app/src/main/java/dev/kaizen/app/chat/ModelSheet.kt

@@ -0,0 +1,269 @@
+package dev.kaizen.app.chat
+
+import androidx.compose.foundation.background
+import androidx.compose.foundation.border
+import androidx.compose.foundation.clickable
+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.Spacer
+import androidx.compose.foundation.layout.fillMaxWidth
+import androidx.compose.foundation.layout.heightIn
+import androidx.compose.foundation.layout.padding
+import androidx.compose.foundation.layout.size
+import androidx.compose.foundation.lazy.LazyColumn
+import androidx.compose.foundation.lazy.items
+import androidx.compose.foundation.shape.RoundedCornerShape
+import androidx.compose.material.icons.Icons
+import androidx.compose.material.icons.rounded.Check
+import androidx.compose.material.icons.rounded.ExpandMore
+import androidx.compose.material.icons.rounded.Search
+import androidx.compose.material.icons.rounded.Star
+import androidx.compose.material3.ExperimentalMaterial3Api
+import androidx.compose.material3.Icon
+import androidx.compose.material3.MaterialTheme
+import androidx.compose.material3.ModalBottomSheet
+import androidx.compose.material3.SegmentedButton
+import androidx.compose.material3.SegmentedButtonDefaults
+import androidx.compose.material3.SingleChoiceSegmentedButtonRow
+import androidx.compose.material3.Text
+import androidx.compose.material3.TextField
+import androidx.compose.material3.TextFieldDefaults
+import androidx.compose.material3.rememberModalBottomSheetState
+import androidx.compose.runtime.Composable
+import androidx.compose.runtime.getValue
+import androidx.compose.runtime.mutableStateOf
+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.clip
+import androidx.compose.ui.graphics.Color
+import androidx.compose.ui.text.font.FontWeight
+import androidx.compose.ui.unit.dp
+import androidx.compose.ui.unit.sp
+import dev.kaizen.app.net.ChatSpeed
+import dev.kaizen.app.net.KaizenModel
+import dev.kaizen.app.ui.theme.Amber
+
+/** Human label + composite-id resolver for the top pill — falls back to a de-prefixed id. */
+fun modelDisplayName(modelId: String, models: List<KaizenModel>): String =
+    models.firstOrNull { it.id == modelId }?.name ?: modelId.substringAfter(":")
+
+/** The glass top pill showing the active model — tap opens [ModelSheet]. */
+@Composable
+fun ModelPill(label: String, onClick: () -> Unit, modifier: Modifier = Modifier) {
+    val cs = MaterialTheme.colorScheme
+    Row(
+        modifier = modifier
+            .clip(RoundedCornerShape(22.dp))
+            .background(cs.surface.copy(alpha = 0.7f))
+            .border(1.dp, cs.onSurface.copy(alpha = 0.08f), RoundedCornerShape(22.dp))
+            .clickable { onClick() }
+            .padding(start = 14.dp, end = 8.dp, top = 9.dp, bottom = 9.dp),
+        verticalAlignment = Alignment.CenterVertically,
+    ) {
+        Text(
+            label,
+            color = cs.onBackground,
+            fontSize = 14.sp,
+            fontWeight = FontWeight.SemiBold,
+            maxLines = 1,
+        )
+        Icon(
+            Icons.Rounded.ExpandMore,
+            contentDescription = null,
+            tint = cs.onSurfaceVariant,
+            modifier = Modifier.size(18.dp),
+        )
+    }
+}
+
+/** A logical group of models in the picker (Favorites, Vertex AI, then by publisher). */
+private data class ModelGroup(val label: String, val models: List<KaizenModel>)
+
+private fun groupFor(m: KaizenModel): String = when {
+    m.provider == "vertex" -> "Vertex AI"
+    else -> m.id.substringBefore("/", "").ifEmpty { "Andere" }
+        .replaceFirstChar { it.uppercase() }
+}
+
+private fun buildGroups(models: List<KaizenModel>, favorites: Set<String>, query: String): List<ModelGroup> {
+    val q = query.trim().lowercase()
+    val filtered = if (q.isEmpty()) models
+    else models.filter { it.name.lowercase().contains(q) || it.id.lowercase().contains(q) }
+
+    val groups = mutableListOf<ModelGroup>()
+    val favs = filtered.filter { it.id in favorites }
+    if (favs.isNotEmpty()) groups += ModelGroup("★ Favoriten", favs)
+
+    // Vertex first, then publishers alphabetically — favorites still appear in their home group too.
+    filtered.groupBy { groupFor(it) }
+        .toSortedMap(compareBy({ if (it == "Vertex AI") "" else it.lowercase() }))
+        .forEach { (label, list) -> groups += ModelGroup(label, list.sortedBy { it.name }) }
+    return groups
+}
+
+@OptIn(ExperimentalMaterial3Api::class)
+@Composable
+fun ModelSheet(
+    models: List<KaizenModel>,
+    selectedModelId: String,
+    favorites: Set<String>,
+    speed: ChatSpeed,
+    onSelectModel: (String) -> Unit,
+    onToggleFavorite: (String) -> Unit,
+    onSelectSpeed: (ChatSpeed) -> Unit,
+    onDismiss: () -> Unit,
+) {
+    val cs = MaterialTheme.colorScheme
+    val sheetState = rememberModalBottomSheetState(skipPartiallyExpanded = true)
+    var query by remember { mutableStateOf("") }
+    val groups = remember(models, favorites, query) { buildGroups(models, favorites, query) }
+
+    ModalBottomSheet(onDismissRequest = onDismiss, sheetState = sheetState) {
+        Column(Modifier.fillMaxWidth().padding(horizontal = 20.dp)) {
+            // --- Response speed segment ---
+            Text(
+                "Geschwindigkeit",
+                color = cs.onSurfaceVariant,
+                fontSize = 12.sp,
+                fontWeight = FontWeight.SemiBold,
+                modifier = Modifier.padding(bottom = 8.dp),
+            )
+            SingleChoiceSegmentedButtonRow(Modifier.fillMaxWidth()) {
+                val options = ChatSpeed.entries
+                options.forEachIndexed { i, opt ->
+                    SegmentedButton(
+                        selected = speed == opt,
+                        onClick = { onSelectSpeed(opt) },
+                        shape = SegmentedButtonDefaults.itemShape(i, options.size),
+                    ) { Text(speedLabel(opt)) }
+                }
+            }
+
+            Spacer(Modifier.size(16.dp))
+
+            // --- Search ---
+            TextField(
+                value = query,
+                onValueChange = { query = it },
+                placeholder = { Text("Modell suchen…") },
+                leadingIcon = { Icon(Icons.Rounded.Search, contentDescription = null) },
+                singleLine = true,
+                modifier = Modifier.fillMaxWidth(),
+                shape = RoundedCornerShape(14.dp),
+                colors = TextFieldDefaults.colors(
+                    focusedIndicatorColor = Color.Transparent,
+                    unfocusedIndicatorColor = Color.Transparent,
+                    disabledIndicatorColor = Color.Transparent,
+                ),
+            )
+
+            Spacer(Modifier.size(12.dp))
+
+            LazyColumn(Modifier.fillMaxWidth().heightIn(max = 460.dp)) {
+                if (groups.isEmpty()) {
+                    item {
+                        Text(
+                            if (models.isEmpty()) "Modelle werden geladen…" else "Keine Treffer",
+                            color = cs.onSurfaceVariant,
+                            fontSize = 14.sp,
+                            modifier = Modifier.padding(vertical = 24.dp),
+                        )
+                    }
+                }
+                groups.forEach { group ->
+                    item(key = "h_${group.label}") {
+                        Text(
+                            group.label,
+                            color = cs.onSurfaceVariant.copy(alpha = 0.6f),
+                            fontSize = 11.sp,
+                            fontWeight = FontWeight.Bold,
+                            modifier = Modifier.padding(top = 14.dp, bottom = 6.dp, start = 4.dp),
+                        )
+                    }
+                    items(group.models, key = { "${group.label}_${it.id}" }) { model ->
+                        ModelRow(
+                            model = model,
+                            selected = model.id == selectedModelId,
+                            favorite = model.id in favorites,
+                            onClick = { onSelectModel(model.id); onDismiss() },
+                            onToggleFavorite = { onToggleFavorite(model.id) },
+                        )
+                    }
+                }
+                item { Spacer(Modifier.size(24.dp)) }
+            }
+        }
+    }
+}
+
+@Composable
+private fun ModelRow(
+    model: KaizenModel,
+    selected: Boolean,
+    favorite: Boolean,
+    onClick: () -> Unit,
+    onToggleFavorite: () -> Unit,
+) {
+    val cs = MaterialTheme.colorScheme
+    Row(
+        modifier = Modifier
+            .fillMaxWidth()
+            .clip(RoundedCornerShape(12.dp))
+            .background(if (selected) Amber.copy(alpha = 0.12f) else Color.Transparent)
+            .clickable { onClick() }
+            .padding(horizontal = 8.dp, vertical = 12.dp),
+        verticalAlignment = Alignment.CenterVertically,
+    ) {
+        Box(
+            Modifier
+                .size(36.dp)
+                .clip(RoundedCornerShape(10.dp))
+                .clickable { onToggleFavorite() },
+            contentAlignment = Alignment.Center,
+        ) {
+            Icon(
+                Icons.Rounded.Star,
+                contentDescription = "Favorit",
+                tint = if (favorite) Amber else cs.onSurfaceVariant.copy(alpha = 0.35f),
+                modifier = Modifier.size(18.dp),
+            )
+        }
+        Spacer(Modifier.size(4.dp))
+        Text(
+            model.name,
+            color = cs.onBackground,
+            fontSize = 15.sp,
+            fontWeight = if (selected) FontWeight.SemiBold else FontWeight.Normal,
+            modifier = Modifier.weight(1f),
+        )
+        if (model.provider == "vertex") {
+            VertexBadge()
+            Spacer(Modifier.size(8.dp))
+        }
+        if (selected) {
+            Icon(Icons.Rounded.Check, contentDescription = "Ausgewählt", tint = Amber, modifier = Modifier.size(20.dp))
+        }
+    }
+}
+
+@Composable
+private fun VertexBadge() {
+    Box(
+        Modifier
+            .clip(RoundedCornerShape(6.dp))
+            .background(Amber.copy(alpha = 0.16f))
+            .padding(horizontal = 7.dp, vertical = 2.dp),
+    ) {
+        Text("Vertex", color = Amber, fontSize = 10.sp, fontWeight = FontWeight.Bold)
+    }
+}
+
+private fun speedLabel(s: ChatSpeed): String = when (s) {
+    ChatSpeed.Instant -> "Instant"
+    ChatSpeed.Normal -> "Normal"
+    ChatSpeed.Max -> "Max"
+}

app/src/main/java/dev/kaizen/app/chat/Sidebar.kt

@@ -46,35 +46,35 @@ import androidx.compose.ui.text.font.FontStyle
 import androidx.compose.ui.text.font.FontWeight
 import androidx.compose.ui.unit.dp
 import androidx.compose.ui.unit.sp
+import dev.kaizen.app.net.ConversationSummary
 import dev.kaizen.app.ui.theme.Amber
+import java.time.Instant
+import java.time.LocalDate
+import java.time.ZoneId
+import java.time.format.DateTimeFormatter
+import java.util.Locale
 
-// Mock sidebar history item representing a past conversation
-data class ConvoHistoryItem(
-    val id: String,
-    val title: String,
-    val dateGroup: String,
-    val locked: Boolean = false,
-    val pinned: Boolean = false
-)
+/** Date-bucket header for a conversation, from its ISO `updatedAt` (Heute/Gestern/dd. MMM yyyy). */
+private fun dateLabel(updatedAt: String?): String {
+    val instant = runCatching { Instant.parse(updatedAt) }.getOrNull() ?: return "FRÜHER"
+    val date = instant.atZone(ZoneId.systemDefault()).toLocalDate()
+    val today = LocalDate.now()
+    return when (date) {
+        today -> "HEUTE"
+        today.minusDays(1) -> "GESTERN"
+        else -> date.format(DateTimeFormatter.ofPattern("dd. MMM yyyy", Locale.GERMAN)).uppercase()
+    }
+}
 
-// Authentically mirrored mock history from sidebar.png
-val mockConvoHistory = listOf(
-    ConvoHistoryItem("1", "Planetenübersicht P...", "16. JUNI 2026"),
-    ConvoHistoryItem("2", "Orbitaltheorie in der ...", "16. JUNI 2026", locked = true),
-    ConvoHistoryItem("3", "Wetter in Magdeburg", "16. JUNI 2026"),
-    ConvoHistoryItem("4", "Aktuelle Uhrzeit in To...", "16. JUNI 2026"),
-    
-    ConvoHistoryItem("5", "📷 Aussehen und Styl...", "15. JUNI 2026"),
-    ConvoHistoryItem("6", "👤 Objektive Bewertu...", "15. JUNI 2026"),
-    
-    ConvoHistoryItem("7", "Beziehungen und ihre...", "14. JUNI 2026"),
-    
-    ConvoHistoryItem("8", "Online-Test erfolgreic...", "12. JUNI 2026"),
-    
-    ConvoHistoryItem("9", "Hallo Gemini", "11. JUNI 2026"),
-    
-    ConvoHistoryItem("10", "Gesperrter Chat", "10. JUNI 2026", locked = true)
-)
+/** Pinned first, then chronological date buckets — preserves the API's desc-updatedAt order. */
+private fun groupConversations(conversations: List<ConversationSummary>): Map<String, List<ConversationSummary>> {
+    val groups = LinkedHashMap<String, MutableList<ConversationSummary>>()
+    conversations.filter { it.pinned }.takeIf { it.isNotEmpty() }?.let { groups["★ ANGEHEFTET"] = it.toMutableList() }
+    conversations.filterNot { it.pinned }.forEach {
+        groups.getOrPut(dateLabel(it.updatedAt)) { mutableListOf() }.add(it)
+    }
+    return groups
+}
 
 /**
  * Floating glassmorphic sidebar drawer content.
@@ -85,8 +85,11 @@ val mockConvoHistory = listOf(
 @Composable
 fun KaizenSidebar(
     userName: String,
+    conversations: List<ConversationSummary>,
+    currentId: String?,
     onClose: () -> Unit,
     onNewChat: () -> Unit,
+    onSelectConversation: (ConversationSummary) -> Unit,
     onOpenSettings: () -> Unit,
     onLogout: () -> Unit,
     modifier: Modifier = Modifier
@@ -212,14 +215,22 @@ fun KaizenSidebar(
 
             // --- BODY Sektion: Scrollable Chats list grouped by Date ---
             Box(Modifier.weight(1f).fillMaxWidth()) {
-                val groupedHistory = remember { mockConvoHistory.groupBy { it.dateGroup } }
+                if (conversations.isEmpty()) {
+                    Text(
+                        text = "Noch keine Chats",
+                        color = cs.onSurfaceVariant.copy(alpha = 0.5f),
+                        fontSize = 14.sp,
+                        modifier = Modifier.padding(start = 12.dp, top = 12.dp)
+                    )
+                } else {
+                    val grouped = remember(conversations) { groupConversations(conversations) }
 
                     LazyColumn(
                         modifier = Modifier.fillMaxSize(),
                         verticalArrangement = Arrangement.spacedBy(8.dp)
                     ) {
-                    groupedHistory.forEach { (dateGroup, items) ->
-                        // Date header (e.g., 16. JUNI 2026)
+                        grouped.forEach { (dateGroup, items) ->
+                            // Date header (e.g., HEUTE, 16. JUN 2026)
                             item(key = "header_$dateGroup") {
                                 Text(
                                     text = dateGroup,
@@ -230,9 +241,13 @@ fun KaizenSidebar(
                                 )
                             }
 
-                        // History items
                             items(items, key = { it.id }) { item ->
-                            HistoryItemRow(item, onClick = { onClose() })
+                                HistoryItemRow(
+                                    item = item,
+                                    selected = item.id == currentId,
+                                    onClick = { onSelectConversation(item) },
+                                )
+                            }
                         }
                     }
                 }
@@ -321,12 +336,20 @@ fun KaizenSidebar(
 }
 
 @Composable
-private fun HistoryItemRow(item: ConvoHistoryItem, onClick: () -> Unit) {
+private fun HistoryItemRow(item: ConversationSummary, selected: Boolean, onClick: () -> Unit) {
     val cs = MaterialTheme.colorScheme
     val isDark = isSystemInDarkTheme()
 
-    val itemBg = if (isDark) Color(0x0AFFFFFF) else Color(0x05000000)
-    val itemBorder = if (isDark) Color.White.copy(alpha = 0.04f) else Color.Black.copy(alpha = 0.03f)
+    val itemBg = when {
+        selected -> Amber.copy(alpha = 0.14f)
+        isDark -> Color(0x0AFFFFFF)
+        else -> Color(0x05000000)
+    }
+    val itemBorder = when {
+        selected -> Amber.copy(alpha = 0.35f)
+        isDark -> Color.White.copy(alpha = 0.04f)
+        else -> Color.Black.copy(alpha = 0.03f)
+    }
 
     Row(
         modifier = Modifier

app/src/main/java/dev/kaizen/app/net/KaizenApi.kt

@@ -23,7 +23,59 @@ import java.util.concurrent.TimeUnit
 @Serializable private data class TokenResponse(val token: String)
 @Serializable private data class MeResponse(val defaultModel: String? = null)
 @Serializable data class WireMessage(val role: String, val content: String)
-@Serializable private data class ChatRequest(val model: String, val messages: List<WireMessage>)
+@Serializable private data class ChatRequest(
+    val model: String,
+    val messages: List<WireMessage>,
+    val reasoningEffort: String? = null,
+    val preferThroughput: Boolean? = null,
+)
+
+/** One entry from GET /api/v1/models — the picker's row. `provider == "vertex"` drives the hoster badge. */
+@Serializable
+data class KaizenModel(
+    val id: String,
+    val name: String,
+    val provider: String? = null,
+)
+
+@Serializable private data class ModelsResponse(val models: List<KaizenModel> = emptyList())
+
+/** A conversation as shown in the sidebar list. Extra fields from the API are ignored. */
+@Serializable
+data class ConversationSummary(
+    val id: String,
+    val title: String = "",
+    val locked: Boolean = false,
+    val pinned: Boolean = false,
+    val updatedAt: String? = null,
+)
+
+@Serializable private data class ConversationsResponse(val conversations: List<ConversationSummary> = emptyList())
+@Serializable private data class CreateConvoRequest(val title: String? = null)
+@Serializable private data class CreatedConversation(val id: String)
+
+/** One persisted message from GET /api/v1/conversations/[id]. */
+@Serializable
+data class StoredMessage(
+    val id: String,
+    val role: String,
+    val content: String = "",
+)
+
+@Serializable private data class ConversationDetail(val messages: List<StoredMessage> = emptyList())
+
+/** A message to persist. `parentId` chains the linear history; `kind` is always "chat" for the app. */
+@Serializable
+data class SaveMessage(
+    val id: String,
+    val parentId: String?,
+    val role: String,
+    val content: String,
+    val kind: String = "chat",
+    val model: String? = null,
+)
+
+@Serializable private data class SaveMessagesRequest(val messages: List<SaveMessage>)
 
 /** Outcome of an in-app login attempt — surfaced as distinct UI states on the login screen. */
 sealed interface LoginResult {
@@ -90,14 +142,130 @@ object KaizenApi {
             }
         }
 
+    /** GET /api/v1/models — the full model catalog for the picker (best-effort, empty on any failure). */
+    suspend fun fetchModels(baseUrl: String, token: String): List<KaizenModel> =
+        withContext(Dispatchers.IO) {
+            val req = Request.Builder()
+                .url("$baseUrl/api/v1/models")
+                .header("Authorization", "Bearer $token")
+                .build()
+            try {
+                client.newCall(req).execute().use { resp ->
+                    if (!resp.isSuccessful) return@use emptyList()
+                    json.decodeFromString<ModelsResponse>(resp.body!!.string()).models
+                }
+            } catch (e: IOException) {
+                emptyList()
+            }
+        }
+
+    /** GET /api/v1/conversations — the sidebar list (best-effort, empty on any failure). */
+    suspend fun fetchConversations(baseUrl: String, token: String): List<ConversationSummary> =
+        withContext(Dispatchers.IO) {
+            val req = Request.Builder()
+                .url("$baseUrl/api/v1/conversations")
+                .header("Authorization", "Bearer $token")
+                .build()
+            try {
+                client.newCall(req).execute().use { resp ->
+                    if (!resp.isSuccessful) return@use emptyList()
+                    json.decodeFromString<ConversationsResponse>(resp.body!!.string()).conversations
+                }
+            } catch (e: IOException) {
+                emptyList()
+            }
+        }
+
+    /** POST /api/v1/conversations — create one, returns its id (null on failure). */
+    suspend fun createConversation(baseUrl: String, token: String, title: String? = null): String? =
+        withContext(Dispatchers.IO) {
+            val body = json.encodeToString(CreateConvoRequest(title)).toRequestBody(jsonMedia)
+            val req = Request.Builder()
+                .url("$baseUrl/api/v1/conversations")
+                .post(body)
+                .header("Authorization", "Bearer $token")
+                .build()
+            try {
+                client.newCall(req).execute().use { resp ->
+                    if (!resp.isSuccessful) return@use null
+                    json.decodeFromString<CreatedConversation>(resp.body!!.string()).id
+                }
+            } catch (e: IOException) {
+                null
+            }
+        }
+
+    /** GET /api/v1/conversations/[id] — the stored messages, in order (empty on failure/locked). */
+    suspend fun fetchMessages(baseUrl: String, token: String, id: String): List<StoredMessage> =
+        withContext(Dispatchers.IO) {
+            val req = Request.Builder()
+                .url("$baseUrl/api/v1/conversations/$id")
+                .header("Authorization", "Bearer $token")
+                .build()
+            try {
+                client.newCall(req).execute().use { resp ->
+                    if (!resp.isSuccessful) return@use emptyList()
+                    json.decodeFromString<ConversationDetail>(resp.body!!.string()).messages
+                }
+            } catch (e: IOException) {
+                emptyList()
+            }
+        }
+
+    /** POST /api/v1/conversations/[id]/messages — persist an exchange. Returns success. */
+    suspend fun saveMessages(baseUrl: String, token: String, id: String, messages: List<SaveMessage>): Boolean =
+        withContext(Dispatchers.IO) {
+            val body = json.encodeToString(SaveMessagesRequest(messages)).toRequestBody(jsonMedia)
+            val req = Request.Builder()
+                .url("$baseUrl/api/v1/conversations/$id/messages")
+                .post(body)
+                .header("Authorization", "Bearer $token")
+                .build()
+            try {
+                client.newCall(req).execute().use { resp -> resp.isSuccessful }
+            } catch (e: IOException) {
+                false
+            }
+        }
+
+    /** POST /api/v1/conversations/[id]/title — fire-and-forget auto-title after the first exchange. */
+    suspend fun generateTitle(baseUrl: String, token: String, id: String) =
+        withContext(Dispatchers.IO) {
+            val req = Request.Builder()
+                .url("$baseUrl/api/v1/conversations/$id/title")
+                .post("{}".toRequestBody(jsonMedia))
+                .header("Authorization", "Bearer $token")
+                .build()
+            try {
+                client.newCall(req).execute().use { }
+            } catch (e: IOException) {
+                // best-effort: a missing title is cosmetic
+            }
+        }
+
     /**
      * POST /api/v1/chat — streams the assistant reply. Emits the cumulative *visible*
      * text after each network chunk (sentinels stripped), so the caller just assigns
      * it to the message content. The full byte buffer is re-decoded each chunk to keep
      * UTF-8 multi-byte sequences that span chunk boundaries intact.
+     *
+     * [speed] maps to the additive `reasoningEffort`/`preferThroughput` v1 fields.
      */
-    fun chat(baseUrl: String, token: String, model: String, messages: List<WireMessage>): Flow<String> = flow {
-        val payload = json.encodeToString(ChatRequest(model, messages)).toRequestBody(jsonMedia)
+    fun chat(
+        baseUrl: String,
+        token: String,
+        model: String,
+        messages: List<WireMessage>,
+        speed: ChatSpeed = ChatSpeed.Normal,
+    ): Flow<String> = flow {
+        val payload = json.encodeToString(
+            ChatRequest(
+                model = model,
+                messages = messages,
+                reasoningEffort = speed.reasoningEffort,
+                preferThroughput = if (speed.preferThroughput) true else null,
+            ),
+        ).toRequestBody(jsonMedia)
         val req = Request.Builder()
             .url("$baseUrl/api/v1/chat")
             .post(payload)

app/src/main/java/dev/kaizen/app/net/SecureStore.kt

@@ -33,7 +33,9 @@ class SecureStore(context: Context) {
         val token = prefs.getString(KEY_TOKEN, null) ?: return null
         val model = prefs.getString(KEY_MODEL, null) ?: DEFAULT_MODEL
         val email = prefs.getString(KEY_EMAIL, null) ?: ""
-        return ServerConfig(baseUrl, token, model, email)
+        val speed = prefs.getString(KEY_SPEED, null)
+            ?.let { runCatching { ChatSpeed.valueOf(it) }.getOrNull() } ?: ChatSpeed.Normal
+        return ServerConfig(baseUrl, token, model, email, speed)
     }
 
     fun save(config: ServerConfig) {
@@ -42,9 +44,17 @@ class SecureStore(context: Context) {
             .putString(KEY_TOKEN, config.token)
             .putString(KEY_MODEL, config.model)
             .putString(KEY_EMAIL, config.email)
+            .putString(KEY_SPEED, config.speed.name)
             .apply()
     }
 
+    /** Favorite model ids — pinned to the top of the picker. Not sensitive, but lives here to share one store. */
+    fun loadFavorites(): Set<String> = prefs.getStringSet(KEY_FAVORITES, emptySet())!!.toSet()
+
+    fun saveFavorites(ids: Set<String>) {
+        prefs.edit().putStringSet(KEY_FAVORITES, ids).apply()
+    }
+
     fun clear() {
         prefs.edit().clear().apply()
     }
@@ -54,5 +64,7 @@ class SecureStore(context: Context) {
         const val KEY_TOKEN = "token"
         const val KEY_MODEL = "model"
         const val KEY_EMAIL = "email"
+        const val KEY_SPEED = "speed"
+        const val KEY_FAVORITES = "favorite_models"
     }
 }

app/src/main/java/dev/kaizen/app/net/ServerConfig.kt

@@ -1,5 +1,17 @@
 package dev.kaizen.app.net
 
+/**
+ * Response speed — the user-facing framing of the backend's reasoning/throughput
+ * knobs (`ChatOptions.reasoningEffort` + `preferThroughput`). [Normal] sends no
+ * override (provider default); [Instant] is the web "instant" preset (no reasoning
+ * + `:nitro` throughput routing); [Max] asks for high reasoning effort.
+ */
+enum class ChatSpeed(val reasoningEffort: String?, val preferThroughput: Boolean) {
+    Instant(reasoningEffort = "none", preferThroughput = true),
+    Normal(reasoningEffort = null, preferThroughput = false),
+    Max(reasoningEffort = "high", preferThroughput = false),
+}
+
 /**
  * The app is deployment-agnostic: one binary that points at EITHER the official
  * server OR any self-hosted instance, via one uniform `Authorization: Bearer`
@@ -9,12 +21,14 @@ package dev.kaizen.app.net
  * @param token   the `kzn_...` personal access token (stored encrypted, never logged)
  * @param model   composite model id sent to /api/v1/chat, e.g. "vertex:gemini-2.5-flash"
  * @param email   the signed-in email (for display in the sidebar/settings)
+ * @param speed   response-speed preset sent with each chat request
  */
 data class ServerConfig(
     val baseUrl: String,
     val token: String,
     val model: String,
     val email: String,
+    val speed: ChatSpeed = ChatSpeed.Normal,
 )
 
 /** Default origin pre-filled on the login screen (editable — self-host points it elsewhere). */

app/src/main/java/dev/kaizen/app/net/SessionViewModel.kt

@@ -17,6 +17,10 @@ class SessionViewModel(private val store: SecureStore) {
     var config by mutableStateOf(store.load())
         private set
 
+    /** Favorite model ids (pinned to the top of the picker), as Compose snapshot state. */
+    var favorites by mutableStateOf(store.loadFavorites())
+        private set
+
     val isLoggedIn: Boolean get() = config != null
 
     /**
@@ -38,8 +42,34 @@ class SessionViewModel(private val store: SecureStore) {
         }
     }
 
+    /** Switch the chat model (persisted). No-op if not logged in. */
+    fun setModel(modelId: String) {
+        val cfg = config ?: return
+        if (cfg.model == modelId) return
+        val updated = cfg.copy(model = modelId)
+        store.save(updated)
+        config = updated
+    }
+
+    /** Switch the response-speed preset (persisted). */
+    fun setSpeed(speed: ChatSpeed) {
+        val cfg = config ?: return
+        if (cfg.speed == speed) return
+        val updated = cfg.copy(speed = speed)
+        store.save(updated)
+        config = updated
+    }
+
+    /** Toggle a model id in/out of favorites (persisted). */
+    fun toggleFavorite(modelId: String) {
+        val next = favorites.toMutableSet().apply { if (!add(modelId)) remove(modelId) }
+        store.saveFavorites(next)
+        favorites = next
+    }
+
     fun logout() {
         store.clear()
         config = null
+        favorites = emptySet()
     }
 }

app/src/main/java/dev/kaizen/app/ui/theme/Dither.kt

@@ -0,0 +1,52 @@
+package dev.kaizen.app.ui.theme
+
+import android.graphics.Bitmap
+import androidx.compose.runtime.Composable
+import androidx.compose.runtime.remember
+import androidx.compose.ui.graphics.ImageBitmap
+import androidx.compose.ui.graphics.ImageShader
+import androidx.compose.ui.graphics.ShaderBrush
+import androidx.compose.ui.graphics.TileMode
+import androidx.compose.ui.graphics.asImageBitmap
+import kotlin.random.Random
+
+/**
+ * Cross-version gradient dither.
+ *
+ * 8-bit sRGB radial gradients quantize into visible concentric rings (the
+ * "verpickelt"/banding look on the orb and mesh blobs). Overlaying a tiled,
+ * ~1-LSB black/white/transparent noise pattern trades those hard bands for
+ * imperceptible fine grain — the standard fix that works on every API level
+ * (no AGSL / API-33 gating needed, so it covers minSdk 26).
+ *
+ * The pattern is deterministic (fixed seed) so it never shimmers between
+ * recompositions; ~⅓ black, ⅓ white, ⅓ transparent makes the perturbation
+ * symmetric (darkens and brightens equally) at a low overall [DITHER_ALPHA].
+ *
+ * [DITHER_ALPHA] is the single tuning knob: higher = bands vanish faster but
+ * fine grain creeps in (worst on the near-black Obsidian background); lower =
+ * cleaner but bands may survive. ~0.012–0.018 is the sweet spot — dial on device.
+ */
+const val DITHER_ALPHA = 0.015f
+
+private fun buildNoiseBitmap(size: Int = 160): ImageBitmap {
+    val pixels = IntArray(size * size)
+    val rnd = Random(0x4A1B)
+    for (i in pixels.indices) {
+        pixels[i] = when (rnd.nextInt(3)) {
+            0 -> 0xFF000000.toInt() // darken
+            1 -> 0xFFFFFFFF.toInt() // brighten
+            else -> 0x00000000      // leave untouched
+        }
+    }
+    val bmp = Bitmap.createBitmap(size, size, Bitmap.Config.ARGB_8888)
+    bmp.setPixels(pixels, 0, size, 0, 0, size, size)
+    return bmp.asImageBitmap()
+}
+
+/** A tiled noise [ShaderBrush] for dithering. Build once, fill the whole surface at [DITHER_ALPHA]. */
+@Composable
+fun rememberDitherBrush(): ShaderBrush {
+    val image = remember { buildNoiseBitmap() }
+    return remember(image) { ShaderBrush(ImageShader(image, TileMode.Repeated, TileMode.Repeated)) }
+}