Deduplicate partial streamed narration in process history

Why: A dropped delta batch can leave a short event prefix next to the complete saved message.

Evidence: 271 frontend unit tests, build, and 14 isolated browser scenarios.

Impact: Suppress overlapping partial replay text and thinking while retaining saved content.

Refs: Agent-System-Dev feature/work-companion-visibility UI1

e2e/work-companion.playwright.ts

@@ -226,18 +226,20 @@ test('replay enriches saved notes and keeps collaboration progress after complet
     ({ seq, type, payload, runId, conversationId: 'c1', ts: stamp, v: 1 })
   const events = [
     event(1, 'message.delta', { index: 0, text: '<think>已解析的思考</think>' }),
-    event(2, 'tool.call', { callId: 'call-1', name: 'run_shell', arguments: '{"command":"read"}' }),
-    event(3, 'tool.output', { callId: 'call-1', text: '完整输出留存' }),
-    event(4, 'tool.result', { callId: 'call-1', status: 'ok', summary: '读取成功' }),
-    event(5, 'agent.spawn', { agentRun: 'child', name: '资料核对', task: '读附录' }),
-    event(6, 'run.phase', { phase: 'finalizing' }),
-    event(7, 'message.delta', { index: 1, text: '最终回复已完成' }),
-    event(8, 'agent.progress', { agentRun: 'child', note: '正在核对附录' }, 'child'),
-    event(9, 'agent.result', { agentRun: 'child', status: 'completed', summary: '附录已核对' }, 'child'),
+    event(2, 'message.delta', { index: 1, text: '开始读取' }),
+    event(3, 'tool.call', { callId: 'call-1', name: 'run_shell', arguments: '{"command":"read"}' }),
+    event(4, 'tool.output', { callId: 'call-1', text: '完整输出留存' }),
+    event(5, 'tool.result', { callId: 'call-1', status: 'ok', summary: '读取成功' }),
+    event(6, 'agent.spawn', { agentRun: 'child', name: '资料核对', task: '读附录' }),
+    event(7, 'run.phase', { phase: 'finalizing' }),
+    event(8, 'message.delta', { index: 1, text: '最终回复已完成' }),
+    event(9, 'agent.progress', { agentRun: 'child', note: '正在核对附录' }, 'child'),
+    event(10, 'agent.result', { agentRun: 'child', status: 'completed', summary: '附录已核对' }, 'child'),
   ]
   const savedParts: Part[] = [
     { type: 'text', process: true, text: '模型在输出前失败，正在重试' },
     { type: 'thinking', process: true, text: '已解析的思考' },
+    { type: 'text', process: true, text: '开始读取材料' },
     { type: 'tool_call', process: true, toolCall: { id: 'call-1', name: 'run_shell' } },
     { type: 'tool_result', process: true, toolResult: { callId: 'call-1', status: 'ok' } },
     { type: 'text', text: '最终回复已完成' },
@@ -247,6 +249,8 @@ test('replay enriches saved notes and keeps collaboration progress after complet
   await message.getByRole('button', { name: /执行记录/ }).click()
   await expect(message.getByText('模型在输出前失败，正在重试')).toBeVisible()
   await expect(message.getByText('已解析的思考')).toBeVisible()
+  await expect(message.getByText('开始读取材料')).toBeVisible()
+  await expect(message.getByText('开始读取', { exact: true })).toHaveCount(0)
   await expect(message.getByText('协作进展：正在核对附录')).toBeVisible()
   await expect(message.getByText('协作结束：附录已核对')).toBeVisible()
   await expect(message.getByText('<think>已解析的思考</think>')).toHaveCount(0)

src/messageparts.ts

@@ -48,17 +48,29 @@ function sameProcessPart(saved: Part, replayed: Part): boolean {
  * contain retry notes or parsed inline thinking that the event stream cannot reconstruct. */
 export function mergeProcessTimeline(saved: Part[], replayed: Part[], final: Part[]): Part[] {
   if (replayed.length === 0) return saved
-  const finalTexts = new Set(final.filter(part => part.type === 'text').map(part => normalized(part.text)))
+  const finalTexts = final.filter(part => part.type === 'text').map(part => normalized(part.text)).filter(Boolean)
   const merged: Part[] = []
   let cursor = 0
   let pending: Part[] = []
   for (const part of replayed) {
-    if (part.type === 'text' && (finalTexts.has(normalized(part.text)) || /<\/?think\b/i.test(part.text ?? ''))) continue
+    const text = normalized(part.text)
+    if (part.type === 'text' && ((text && finalTexts.some(value => value.includes(text) || text.includes(value)))
+      || /<\/?think\b/i.test(part.text ?? ''))) continue
     let match = -1
     for (let i = cursor; i < saved.length; i++) {
       if (sameProcessPart(saved[i], part)) { match = i; break }
     }
-    if (match < 0) { pending.push(part); continue }
+    if (match < 0) {
+      // A missing delta batch can leave only a prefix in events. The complete
+      // terminal part is authoritative; never render that prefix beside it.
+      if ((part.type === 'text' || part.type === 'thinking') && text && saved.some(item => {
+        if (item.type !== part.type) return false
+        const value = normalized(item.text)
+        return value && (value.includes(text) || text.includes(value))
+      })) continue
+      pending.push(part)
+      continue
+    }
     merged.push(...saved.slice(cursor, match), ...pending)
     pending = []
     const output = (part as Part & { toolOutput?: string }).toolOutput

test/messageparts.test.ts

@@ -135,6 +135,14 @@ it('enriches saved process without losing retry notes or parsed inline thinking'
   expect(merged.filter(part => part.type === 'tool_call')).toHaveLength(1)
 })
 
+it('does not repeat a partial event delta beside the complete saved narration', () => {
+  const saved = [p({ type: 'text', process: true, text: '开始读取材料' }),
+    p({ type: 'tool_call', process: true, toolCall: { id: 'call-1', name: 'fs_read_file' } })]
+  const replayed = [p({ type: 'text', process: true, text: '开始读取' }),
+    p({ type: 'tool_call', process: true, toolCall: { id: 'call-1', name: 'fs_read_file' } })]
+  expect(mergeProcessTimeline(saved, replayed, []).map(part => part.text).filter(Boolean)).toEqual(['开始读取材料'])
+})
+
 describe('artifact ids in reply text', () => {
   it('extracts unique ids in order', () => {
     expect(artifactIdsIn('见 art_0123456789ab 和 `art_abcdefabcdef`，再提 art_0123456789ab'))