feat(composer): move role picker into the input and keep it per conversation

Show the selected role as a compact chip in the input's top-left corner, persist the choice per conversation, and snapshot it on replies so the timeline shows the role as a caption under GoodBuddy.

src/main/assistant/assistant-database.test.ts

@@ -134,6 +134,27 @@ it('persists the story graph switch per conversation without schema migration or
   } finally { database.close() }
 })
 
+it('persists the composer role per conversation and the role snapshot on replies', async () => {
+  const database = await createDatabase()
+  const expertId = randomUUID()
+  const header = { id: randomUUID(), title: 'Role preference', updatedAt: 1000, selectedExpertId: expertId }
+  const team = { id: randomUUID(), title: 'Team preference', updatedAt: 1000, selectedExpertId: 'team' as const }
+  const plain = { id: randomUUID(), title: 'No preference', updatedAt: 1000 }
+  const reply = { id: randomUUID(), role: 'assistant' as const, content: 'Reviewed', state: 'complete' as const,
+    createdAt: 900, expert: { kind: 'expert' as const, id: expertId, name: '代码审查专家' } }
+  try {
+    database.saveLocalConversations([{ header, messages: [reply] }, { header: team, messages: [] }, { header: plain, messages: [] }])
+    database.close()
+    database.initialize('C:\\Workspace')
+    expect(database.getConversation(header.id)).toMatchObject({ selectedExpertId: expertId, messages: [{ expert: reply.expert }] })
+    expect(database.getConversation(team.id).selectedExpertId).toBe('team')
+    expect(database.getConversation(plain.id).selectedExpertId).toBeUndefined()
+    database.saveLocalConversations([{ header: { ...header, selectedExpertId: undefined, updatedAt: 1001 }, messages: [] }])
+    expect(database.getConversation(header.id).selectedExpertId).toBeUndefined()
+    expect(localConversationHeaderSchema.safeParse({ ...plain, selectedExpertId: 'not-an-id' }).success).toBe(false)
+  } finally { database.close() }
+})
+
 it('persists conversation pins without changing timestamps or allowing autosaves to overwrite them', async () => {
   const database = await createDatabase()
   const header = { id: randomUUID(), title: 'Pinned conversation', updatedAt: 1000 }

src/main/assistant/assistant-database.ts

@@ -364,6 +364,7 @@ type MessageMetadata = {
   contextCompressions?: ConversationSnapshot['messages'][number]['contextCompressions']
   tools?: ConversationSnapshot['messages'][number]['tools']
   subagents?: ConversationSnapshot['messages'][number]['subagents']
+  expert?: ConversationMessage['expert']
   sources?: string[]
   sourceReferences?: ConversationSnapshot['messages'][number]['sourceReferences']
   knowledgeRetrieval?: ConversationSnapshot['messages'][number]['knowledgeRetrieval']
@@ -1238,6 +1239,7 @@ const conversationContextStateSchema = conversationSnapshotSchema.pick({
   knowledgeLibraryIds: true,
   knowledgeRetrievalMode: true,
   storyGraphEnabled: true,
+  selectedExpertId: true,
   contextMetrics: true,
   contextCompressionState: true
 })
@@ -1246,7 +1248,7 @@ function parseConversationContextState(
   value: string | null
 ): Pick<
   ConversationSnapshot,
-  'knowledgeLibraryIds' | 'knowledgeRetrievalMode' | 'storyGraphEnabled' | 'contextMetrics' | 'contextCompressionState'
+  'knowledgeLibraryIds' | 'knowledgeRetrievalMode' | 'storyGraphEnabled' | 'selectedExpertId' | 'contextMetrics' | 'contextCompressionState'
 > {
   if (!value) {
     return {}
@@ -1264,18 +1266,20 @@ function parseConversationContextState(
 function serializeConversationContextState(
   conversation: Pick<
     ConversationSnapshot,
-    'knowledgeLibraryIds' | 'knowledgeRetrievalMode' | 'storyGraphEnabled' | 'contextMetrics' | 'contextCompressionState'
+    'knowledgeLibraryIds' | 'knowledgeRetrievalMode' | 'storyGraphEnabled' | 'selectedExpertId' | 'contextMetrics' | 'contextCompressionState'
   >
 ): string | null {
   return conversation.knowledgeLibraryIds !== undefined ||
     conversation.knowledgeRetrievalMode !== undefined ||
     conversation.storyGraphEnabled !== undefined ||
+    conversation.selectedExpertId !== undefined ||
     conversation.contextMetrics ||
     conversation.contextCompressionState
     ? JSON.stringify({
         knowledgeLibraryIds: conversation.knowledgeLibraryIds,
         knowledgeRetrievalMode: conversation.knowledgeRetrievalMode,
         storyGraphEnabled: conversation.storyGraphEnabled,
+        selectedExpertId: conversation.selectedExpertId,
         contextMetrics: conversation.contextMetrics,
         contextCompressionState: conversation.contextCompressionState
       })
@@ -1346,6 +1350,7 @@ function toConversationSnapshot(
         contextCompressions: metadata.contextCompressions,
         tools: metadata.tools,
         subagents: metadata.subagents,
+        expert: metadata.expert,
         sources: metadata.sources,
         sourceReferences: metadata.sourceReferences,
         knowledgeRetrieval: metadata.knowledgeRetrieval,
@@ -1377,6 +1382,7 @@ function serializeConversationMessageMetadata(
     contextCompressions: message.contextCompressions,
     tools: message.tools,
     subagents: message.subagents,
+    expert: message.expert,
     sources: message.sources,
     sourceReferences: message.sourceReferences,
     knowledgeRetrieval: message.knowledgeRetrieval,
@@ -1784,6 +1790,7 @@ function storedRemoteAssistantMessage(
     contextCompressions: metadata.contextCompressions,
     tools: metadata.tools,
     subagents: metadata.subagents,
+    expert: metadata.expert,
     sources: metadata.sources,
     sourceReferences: metadata.sourceReferences,
     knowledgeRetrieval: metadata.knowledgeRetrieval,
@@ -5638,6 +5645,7 @@ export class AssistantDatabase {
         contextCompressions: metadata.contextCompressions,
         tools: metadata.tools,
         subagents: metadata.subagents,
+        expert: metadata.expert,
         sources: metadata.sources,
         sourceReferences: metadata.sourceReferences,
         knowledgeRetrieval: metadata.knowledgeRetrieval,