fix: include full conversation history in AI chat requests

- Add trimHistory() to keep most recent messages within 100k token budget
- Add formatMessageWithHistory() to prepend conversation context to each message
- Wire up in useAIChat.ts: sendMessage now includes full history
- Keep --resume as belt-and-suspenders for same-session continuity
- 14 new tests in ai-chat.test.ts and useAIChat.test.ts

src/utils/ai-chat.test.ts

@@ -8,6 +8,8 @@ vi.mock('../mock-tauri', () => ({
 import {
   estimateTokens, buildSystemPrompt,
   nextMessageId, checkClaudeCli, streamClaudeChat,
+  trimHistory, formatMessageWithHistory,
+  type ChatMessage, MAX_HISTORY_TOKENS,
 } from './ai-chat'
 import type { VaultEntry } from '../types'
 
@@ -73,6 +75,107 @@ describe('checkClaudeCli', () => {
   })
 })
 
+// --- trimHistory ---
+
+describe('trimHistory', () => {
+  const msg = (role: 'user' | 'assistant', content: string): ChatMessage => ({
+    role, content, id: `msg-${content}`,
+  })
+
+  it('returns empty array for empty history', () => {
+    expect(trimHistory([], 1000)).toEqual([])
+  })
+
+  it('returns all messages when under token limit', () => {
+    const history = [msg('user', 'hi'), msg('assistant', 'hello')]
+    expect(trimHistory(history, 1000)).toEqual(history)
+  })
+
+  it('drops oldest messages when over token limit', () => {
+    const history = [
+      msg('user', 'a'.repeat(400)),      // 100 tokens
+      msg('assistant', 'b'.repeat(400)),  // 100 tokens
+      msg('user', 'c'.repeat(400)),       // 100 tokens
+    ]
+    const result = trimHistory(history, 200)
+    // Should keep the two most recent messages (200 tokens)
+    expect(result).toHaveLength(2)
+    expect(result[0].content).toBe('b'.repeat(400))
+    expect(result[1].content).toBe('c'.repeat(400))
+  })
+
+  it('keeps at least one message if it fits', () => {
+    const history = [
+      msg('user', 'a'.repeat(2000)),  // 500 tokens
+      msg('assistant', 'b'.repeat(80)), // 20 tokens
+    ]
+    const result = trimHistory(history, 30)
+    expect(result).toHaveLength(1)
+    expect(result[0].content).toBe('b'.repeat(80))
+  })
+
+  it('returns empty when single message exceeds limit', () => {
+    const history = [msg('user', 'a'.repeat(4000))] // 1000 tokens
+    expect(trimHistory(history, 10)).toEqual([])
+  })
+})
+
+// --- formatMessageWithHistory ---
+
+describe('formatMessageWithHistory', () => {
+  const msg = (role: 'user' | 'assistant', content: string): ChatMessage => ({
+    role, content, id: `msg-${content}`,
+  })
+
+  it('returns bare message when no history', () => {
+    expect(formatMessageWithHistory([], 'hello')).toBe('hello')
+  })
+
+  it('includes conversation history before the new message', () => {
+    const history = [msg('user', 'What is Rust?'), msg('assistant', 'A systems language.')]
+    const result = formatMessageWithHistory(history, 'How does it compare to Go?')
+    expect(result).toContain('What is Rust?')
+    expect(result).toContain('A systems language.')
+    expect(result).toContain('How does it compare to Go?')
+  })
+
+  it('labels user and assistant messages correctly', () => {
+    const history = [msg('user', 'Q1'), msg('assistant', 'A1')]
+    const result = formatMessageWithHistory(history, 'Q2')
+    expect(result).toContain('[user]: Q1')
+    expect(result).toContain('[assistant]: A1')
+    expect(result).toContain('[user]: Q2')
+  })
+
+  it('preserves message order', () => {
+    const history = [
+      msg('user', 'first'),
+      msg('assistant', 'second'),
+      msg('user', 'third'),
+      msg('assistant', 'fourth'),
+    ]
+    const result = formatMessageWithHistory(history, 'fifth')
+    const firstIdx = result.indexOf('first')
+    const secondIdx = result.indexOf('second')
+    const thirdIdx = result.indexOf('third')
+    const fourthIdx = result.indexOf('fourth')
+    const fifthIdx = result.indexOf('fifth')
+    expect(firstIdx).toBeLessThan(secondIdx)
+    expect(secondIdx).toBeLessThan(thirdIdx)
+    expect(thirdIdx).toBeLessThan(fourthIdx)
+    expect(fourthIdx).toBeLessThan(fifthIdx)
+  })
+})
+
+// --- MAX_HISTORY_TOKENS ---
+
+describe('MAX_HISTORY_TOKENS', () => {
+  it('is a reasonable token limit', () => {
+    expect(MAX_HISTORY_TOKENS).toBeGreaterThan(10_000)
+    expect(MAX_HISTORY_TOKENS).toBeLessThan(200_000)
+  })
+})
+
 // --- streamClaudeChat ---
 
 describe('streamClaudeChat', () => {

src/utils/ai-chat.ts

@@ -76,6 +76,34 @@ export function nextMessageId(): string {
   return `msg-${++msgIdCounter}-${Date.now()}`
 }
 
+// --- Conversation history ---
+
+/** Max tokens of history to include in each request. */
+export const MAX_HISTORY_TOKENS = 100_000
+
+/** Keep the most recent messages that fit within `maxTokens`. Drops oldest first. */
+export function trimHistory(history: ChatMessage[], maxTokens: number): ChatMessage[] {
+  let tokenCount = 0
+  const result: ChatMessage[] = []
+  for (let i = history.length - 1; i >= 0; i--) {
+    const tokens = estimateTokens(history[i].content)
+    if (tokenCount + tokens > maxTokens) break
+    result.unshift(history[i])
+    tokenCount += tokens
+  }
+  return result
+}
+
+/** Format conversation history + new message into a single prompt for the CLI. */
+export function formatMessageWithHistory(history: ChatMessage[], newMessage: string): string {
+  if (history.length === 0) return newMessage
+
+  const lines = history.map(m => `[${m.role}]: ${m.content}`)
+  lines.push(`[user]: ${newMessage}`)
+
+  return `<conversation_history>\n${lines.join('\n\n')}\n</conversation_history>\n\nContinue the conversation. Respond only to the latest [user] message.`
+}
+
 // --- Claude CLI status ---
 
 export interface ClaudeCliStatus {