feat(chat): add system prompt editor & personas (M9.2)

Named personas with system prompt, model preference, and accent colour.
Persona pill selector above chat input, editor modal for create/edit/delete.
Default persona auto-applied to new conversations. Persona system prompt
prepended to AI context.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

packages/app/src/components/chat/ChatWindow.vue

@@ -20,6 +20,8 @@
 
     <ContextBar :messages="messages" />
 
+    <PersonaSelector />
+
     <!-- Collapsed: prompt index -->
     <PromptIndex
       v-if="chatCollapsed"
@@ -116,6 +118,7 @@ import BranchSwitcher from './BranchSwitcher.vue'
 import ChatSearch from './ChatSearch.vue'
 import ContextBar from './ContextBar.vue'
 import ComparisonView from './ComparisonView.vue'
+import PersonaSelector from './PersonaSelector.vue'
 import ErrorBoundary from '@/components/ui/ErrorBoundary.vue'
 import type { Message, ImageAttachment } from '@aiui/core/types/message'
 
@@ -142,6 +145,8 @@ const { sendMessage, stopGeneration, editAndResend, regenerateLastResponse } = u
 const { updatePanelFromText, panelOpen, activeTab, availableTabs, setActiveTab } = useContentPanel()
 import { useCodeContext } from '@/composables/useCodeContext'
 const codeContext = useCodeContext()
+import { usePersonaStore } from '@/stores/personas'
+const personaStore = usePersonaStore()
 const comparison = useComparisonMode()
 const messageListRef = ref<HTMLElement | null>(null)
 const chatSearchRef = ref<InstanceType<typeof ChatSearch> | null>(null)
@@ -220,7 +225,7 @@ function getTriggeringQuery(msgs: typeof messages.value, idx: number): string {
 }
 
 function handleNewChat() {
-  chatStore.createConversation()
+  chatStore.createConversation('New Chat', personaStore.defaultPersona?.id)
 }
 
 function handleStop() {

packages/app/src/components/chat/PersonaSelector.vue

@@ -0,0 +1,248 @@
+<template>
+  <div v-if="personaStore.personas.length > 0" class="px-3 md:px-4">
+    <div class="flex items-center gap-1.5 flex-wrap">
+      <button
+        v-for="p in personaStore.sortedPersonas"
+        :key="p.id"
+        class="px-2.5 py-1 rounded-full text-[11px] font-medium transition-all duration-200 border"
+        :class="isActive(p.id)
+          ? 'bg-accent/20 text-accent border-accent/30'
+          : 'bg-white/5 text-white/50 border-white/10 hover:text-white/70 hover:bg-white/10'"
+        @click="selectPersona(p.id)"
+      >
+        <span
+          v-if="p.accentColor"
+          class="inline-block w-2 h-2 rounded-full mr-1"
+          :style="{ backgroundColor: p.accentColor }"
+        />
+        {{ p.name }}
+      </button>
+      <button
+        class="px-2 py-1 rounded-full text-[11px] text-white/30 hover:text-white/60 border border-transparent hover:border-white/10 transition-all duration-200"
+        @click="showEditor = true"
+      >
+        + New
+      </button>
+      <button
+        v-if="activePersonaId"
+        class="px-2 py-1 rounded-full text-[11px] text-white/30 hover:text-white/60 transition-all"
+        title="Clear persona"
+        @click="clearPersona"
+      >
+        ✕
+      </button>
+    </div>
+
+    <!-- Persona editor modal -->
+    <Teleport to="body">
+      <div
+        v-if="showEditor"
+        class="fixed inset-0 z-50 flex items-center justify-center p-4"
+        @click.self="closeEditor"
+      >
+        <div class="absolute inset-0 bg-black/60 backdrop-blur-sm" />
+        <div class="relative glass-card w-full max-w-md p-5 space-y-4 animate-scale-in">
+          <div class="flex items-center justify-between">
+            <h3 class="text-sm font-semibold text-white/90">
+              {{ editingPersona ? 'Edit Persona' : 'New Persona' }}
+            </h3>
+            <button
+              class="w-7 h-7 flex items-center justify-center rounded-lg text-white/40 hover:text-white/70 hover:bg-white/10 transition-all"
+              @click="closeEditor"
+            >
+              <svg class="w-4 h-4" fill="none" stroke="currentColor" viewBox="0 0 24 24">
+                <path stroke-linecap="round" stroke-linejoin="round" stroke-width="2" d="M6 18L18 6M6 6l12 12" />
+              </svg>
+            </button>
+          </div>
+
+          <div class="space-y-3">
+            <div>
+              <label class="block text-[11px] text-white/40 mb-1">Name</label>
+              <input
+                v-model="formName"
+                type="text"
+                class="w-full bg-white/5 border border-white/10 rounded-lg px-3 py-2 text-sm text-white/90 focus:outline-none focus:border-accent/50"
+                placeholder="e.g. Film Critic"
+              />
+            </div>
+
+            <div>
+              <label class="block text-[11px] text-white/40 mb-1">System Prompt</label>
+              <textarea
+                v-model="formPrompt"
+                class="w-full bg-white/5 border border-white/10 rounded-lg px-3 py-2 text-sm text-white/90 resize-none focus:outline-none focus:border-accent/50"
+                rows="5"
+                placeholder="You are a film critic who..."
+              />
+            </div>
+
+            <div class="flex gap-3">
+              <div class="flex-1">
+                <label class="block text-[11px] text-white/40 mb-1">Model Preference</label>
+                <select
+                  v-model="formModel"
+                  class="w-full bg-white/5 border border-white/10 rounded-lg px-3 py-2 text-sm text-white/90 focus:outline-none focus:border-accent/50"
+                >
+                  <option value="">Default</option>
+                  <option value="claude-haiku-4.5">Claude 4.5 Haiku</option>
+                  <option value="claude-sonnet-4">Claude Sonnet 4</option>
+                  <option value="claude-opus-4">Claude Opus 4</option>
+                </select>
+              </div>
+              <div class="w-20">
+                <label class="block text-[11px] text-white/40 mb-1">Colour</label>
+                <input
+                  v-model="formColor"
+                  type="color"
+                  class="w-full h-9 rounded-lg bg-white/5 border border-white/10 cursor-pointer"
+                />
+              </div>
+            </div>
+
+            <label class="flex items-center gap-2 text-xs text-white/60">
+              <input
+                v-model="formDefault"
+                type="checkbox"
+                class="accent-[#F7931A]"
+              />
+              Set as default for new conversations
+            </label>
+          </div>
+
+          <div class="flex items-center gap-2 pt-1">
+            <button
+              v-if="editingPersona"
+              class="px-3 py-1.5 rounded-lg text-xs text-red-400/80 hover:text-red-400 hover:bg-red-400/10 transition-all"
+              @click="handleDelete"
+            >
+              Delete
+            </button>
+            <div class="flex-1" />
+            <button
+              class="px-3 py-1.5 rounded-lg text-xs text-white/50 hover:text-white/70 hover:bg-white/10 transition-all"
+              @click="closeEditor"
+            >
+              Cancel
+            </button>
+            <button
+              class="px-4 py-1.5 rounded-lg text-xs bg-accent/20 text-accent hover:bg-accent/30 transition-all"
+              :disabled="!formName.trim()"
+              @click="handleSave"
+            >
+              {{ editingPersona ? 'Save' : 'Create' }}
+            </button>
+          </div>
+        </div>
+      </div>
+    </Teleport>
+  </div>
+</template>
+
+<script setup lang="ts">
+import { ref, computed } from 'vue'
+import { usePersonaStore, type Persona } from '@/stores/personas'
+import { useChatStore } from '@/stores/chat'
+
+const personaStore = usePersonaStore()
+const chatStore = useChatStore()
+
+const showEditor = ref(false)
+const editingPersona = ref<Persona | null>(null)
+
+// Form state
+const formName = ref('')
+const formPrompt = ref('')
+const formModel = ref('')
+const formColor = ref('#F7931A')
+const formDefault = ref(false)
+
+const activePersonaId = computed(() => chatStore.activeConversation?.personaId ?? null)
+
+function isActive(id: string): boolean {
+  return activePersonaId.value === id
+}
+
+function selectPersona(id: string) {
+  const conv = chatStore.activeConversation
+  if (!conv) return
+
+  if (conv.personaId === id) {
+    // Double-click to edit
+    openEditorFor(personaStore.getPersona(id))
+    return
+  }
+
+  conv.personaId = id
+  conv.updatedAt = Date.now()
+}
+
+function clearPersona() {
+  const conv = chatStore.activeConversation
+  if (!conv) return
+  conv.personaId = undefined
+  conv.updatedAt = Date.now()
+}
+
+function openEditorFor(persona?: Persona) {
+  if (persona) {
+    editingPersona.value = persona
+    formName.value = persona.name
+    formPrompt.value = persona.systemPrompt
+    formModel.value = persona.modelPreference ?? ''
+    formColor.value = persona.accentColor ?? '#F7931A'
+    formDefault.value = persona.isDefault ?? false
+  } else {
+    editingPersona.value = null
+    formName.value = ''
+    formPrompt.value = ''
+    formModel.value = ''
+    formColor.value = '#F7931A'
+    formDefault.value = false
+  }
+  showEditor.value = true
+}
+
+function closeEditor() {
+  showEditor.value = false
+  editingPersona.value = null
+}
+
+function handleSave() {
+  if (!formName.value.trim()) return
+
+  const data = {
+    name: formName.value.trim(),
+    systemPrompt: formPrompt.value.trim(),
+    modelPreference: formModel.value || undefined,
+    accentColor: formColor.value,
+    isDefault: formDefault.value,
+  }
+
+  if (editingPersona.value) {
+    personaStore.updatePersona(editingPersona.value.id, data)
+  } else {
+    const created = personaStore.addPersona(data)
+    // Auto-select the new persona
+    const conv = chatStore.activeConversation
+    if (conv) {
+      conv.personaId = created.id
+      conv.updatedAt = Date.now()
+    }
+  }
+
+  closeEditor()
+}
+
+function handleDelete() {
+  if (!editingPersona.value) return
+  const id = editingPersona.value.id
+  // Clear from any active conversation
+  const conv = chatStore.activeConversation
+  if (conv?.personaId === id) {
+    conv.personaId = undefined
+  }
+  personaStore.deletePersona(id)
+  closeEditor()
+}
+</script>