chore: establish YCode replication baseline and TODO

scripts/message-order-regression.ts

@@ -0,0 +1,121 @@
+import assert from 'node:assert/strict'
+import { applyAssistantEvent, getMessageParts } from '../src/shared/message-parts'
+import type { ChatEvent, ChatMessage, ToolCallRecord } from '../src/shared/types'
+
+function tool(overrides: Partial<ToolCallRecord> = {}): ToolCallRecord {
+  return {
+    id: 'tool-1',
+    name: 'read_file',
+    args: { path: 'notes.txt' },
+    argsRaw: '{"path":"notes.txt"}',
+    status: 'running',
+    ...overrides
+  }
+}
+
+function reduce(message: ChatMessage, event: ChatEvent): ChatMessage {
+  return applyAssistantEvent(message, event)
+}
+
+function testOrderedPartsAndImmutableUpdates(): void {
+  const initial: ChatMessage = {
+    id: 'assistant-1',
+    role: 'assistant',
+    content: '',
+    tools: [],
+    parts: [],
+    createdAt: 1,
+    status: 'streaming'
+  }
+
+  const afterFirstText = reduce(initial, { runId: 'run-1', type: 'text', delta: 'before' })
+  const afterToolCall = reduce(afterFirstText, { runId: 'run-1', type: 'tool_call', call: tool() })
+  const afterSecondText = reduce(afterToolCall, { runId: 'run-1', type: 'text', delta: 'after' })
+  const afterToolResult = reduce(afterSecondText, {
+    runId: 'run-1',
+    type: 'tool_result',
+    call: tool({ status: 'ok', output: 'file contents', summary: 'file contents', durationMs: 12 })
+  })
+  const final = reduce(afterToolResult, {
+    runId: 'run-1',
+    type: 'done',
+    turnDurationMs: 22000,
+    content: 'beforeafter',
+    tools: [tool({ status: 'ok', output: 'file contents', summary: 'file contents', durationMs: 12 })]
+  })
+
+  assert.deepEqual(final.parts, [
+    { type: 'text', text: 'before' },
+    { type: 'tool', toolId: 'tool-1' },
+    { type: 'text', text: 'after' }
+  ])
+  assert.equal(final.content, 'beforeafter')
+  assert.equal(final.status, 'done')
+  assert.equal(final.turnDurationMs, 22000, 'terminal duration survives the shared live/persistence projection')
+  assert.equal(final.tools?.length, 1, 'tool updates must not create duplicate tool records')
+  assert.equal(final.parts?.filter((part) => part.type === 'tool' && part.toolId === 'tool-1').length, 1,
+    'tool updates must not create duplicate ordered references')
+  assert.equal(final.tools?.[0].status, 'ok')
+  assert.equal(final.tools?.[0].output, 'file contents')
+
+  assert.equal(initial.content, '', 'reducing events must not mutate the original message')
+  assert.deepEqual(initial.parts, [], 'reducing events must not mutate the original parts array')
+  assert.deepEqual(afterFirstText.parts, [{ type: 'text', text: 'before' }],
+    'later text and tool updates must not mutate prior message snapshots')
+  assert.equal(afterFirstText.content, 'before')
+  assert.deepEqual(afterToolResult.parts, [
+    { type: 'text', text: 'before' },
+    { type: 'tool', toolId: 'tool-1' },
+    { type: 'text', text: 'after' }
+  ])
+}
+
+function testLegacyFallback(): void {
+  const legacy: ChatMessage = {
+    id: 'legacy-1',
+    role: 'assistant',
+    content: 'legacy response',
+    tools: [tool({ id: 'legacy-tool', status: 'ok' })],
+    createdAt: 2
+  }
+
+  assert.deepEqual(getMessageParts(legacy), [
+    { type: 'text', text: 'legacy response' },
+    { type: 'tool', toolId: 'legacy-tool' }
+  ])
+}
+
+function testTerminalToolFinalization(): void {
+  const initial: ChatMessage = {
+    id: 'assistant-terminal',
+    role: 'assistant',
+    content: 'partial answer',
+    tools: [tool({ output: 'retained output' })],
+    parts: [
+      { type: 'text', text: 'partial answer' },
+      { type: 'tool', toolId: 'tool-1' }
+    ],
+    createdAt: 3,
+    status: 'streaming'
+  }
+
+  const cancelled = reduce(initial, { runId: 'run-cancel', type: 'cancelled' })
+  assert.equal(cancelled.status, 'cancelled')
+  assert.equal(cancelled.tools?.[0].status, 'cancelled')
+  assert.equal(cancelled.tools?.[0].output, 'retained output')
+
+  const errored = reduce(initial, { runId: 'run-error', type: 'error', message: 'connection lost' })
+  assert.equal(errored.status, 'error')
+  assert.equal(errored.error, 'connection lost')
+  assert.equal(errored.tools?.[0].status, 'error')
+  assert.equal(errored.tools?.[0].output, 'retained output')
+
+  assert.equal(initial.status, 'streaming', 'terminal updates must leave the prior message unchanged')
+  assert.equal(initial.tools?.[0].status, 'running', 'terminal updates must leave prior tool state unchanged')
+  assert.equal(initial.tools?.[0].output, 'retained output')
+}
+
+testOrderedPartsAndImmutableUpdates()
+testLegacyFallback()
+testTerminalToolFinalization()
+console.log('message-order-regression: all checks passed')