fix(ai): stop stripping fields — passthrough allows all extras

AlemTuzlak · AlemTuzlak · commit af99dde40530 · 2026-04-02T11:08:00.000+02:00
@ag-ui/core BaseEventSchema uses .passthrough() so extra fields are allowed.
Only strip the deprecated nested error object from RUN_ERROR (conflicts with
spec's flat message/code). Everything else passes through: model, content,
toolName, stepId, usage, finishReason, result, input, args, etc.
diff --git a/packages/typescript/ai/src/strip-to-spec-middleware.ts b/packages/typescript/ai/src/strip-to-spec-middleware.ts
@@ -2,56 +2,27 @@ import type { ChatMiddleware } from './activities/chat/middleware/types'
 import type { StreamChunk } from './types'
 
 /**
- * Fields to always strip from events.
+ * Strip only the deprecated nested `error` object from RUN_ERROR events.
+ * The flat `message`/`code` fields are the spec-compliant form.
  *
- * - `rawEvent`: Debug-only provider payload, potentially large. Not for wire.
- */
-const ALWAYS_STRIP = new Set(['rawEvent'])
-
-/**
- * Per-event-type fields to strip. Only deprecated aliases and fields that
- * conflict with the spec are removed. Extra fields are allowed by @ag-ui/core's
- * BaseEventSchema (.passthrough()), so we keep useful extensions like `model`,
- * `content`, `usage`, `finishReason`, `input`, `result`, etc.
- */
-const STRIP_BY_TYPE: Record<string, Set<string>> = {
-  TOOL_CALL_START: new Set(['toolName']),
-  TOOL_CALL_END: new Set(['toolName']),
-  RUN_ERROR: new Set(['error']),
-  STEP_STARTED: new Set(['stepId']),
-  STEP_FINISHED: new Set(['stepId']),
-  STATE_SNAPSHOT: new Set(['state']),
-}
-
-/**
- * Strip deprecated aliases and debug fields from a StreamChunk.
- *
- * @ag-ui/core's BaseEventSchema uses `.passthrough()`, so extra fields
- * (model, content, usage, finishReason, etc.) are allowed and won't break
- * spec validation. We only strip:
- * - Deprecated field aliases (toolName, stepId, state) to nudge consumers
- *   toward spec names (toolCallName, stepName, snapshot)
- * - The deprecated nested `error` object on RUN_ERROR (spec uses flat message/code)
- * - `rawEvent` (debug payload, potentially large)
+ * All other fields pass through unchanged. @ag-ui/core's BaseEventSchema
+ * uses `.passthrough()`, so extra fields (model, content, usage,
+ * finishReason, toolName, stepId, etc.) are allowed and won't break
+ * spec validation or verifyEvents.
  */
 export function stripToSpec(chunk: StreamChunk): StreamChunk {
-  const typeStrip = STRIP_BY_TYPE[chunk.type]
-  if (!typeStrip && ALWAYS_STRIP.size === 0) return chunk
-
-  const result: Record<string, unknown> = {}
-
-  for (const [key, value] of Object.entries(chunk)) {
-    if (ALWAYS_STRIP.has(key)) continue
-    if (typeStrip?.has(key)) continue
-    result[key] = value
+  // Only strip the deprecated nested error object from RUN_ERROR
+  if (chunk.type === 'RUN_ERROR' && 'error' in chunk) {
+    const { error: _deprecated, ...rest } = chunk as Record<string, unknown>
+    return rest as StreamChunk
   }
-
-  return result as StreamChunk
+  return chunk
 }
 
 /**
- * Middleware that strips deprecated aliases and debug fields from events.
- * Should always be the LAST middleware in the chain.
+ * Middleware that ensures events are AG-UI spec compliant.
+ * Currently only strips the deprecated nested `error` object from RUN_ERROR.
+ * All other fields pass through unchanged (passthrough allowed by spec).
  */
 export function stripToSpecMiddleware(): ChatMiddleware {
   return {
diff --git a/packages/typescript/ai/tests/chat.test.ts b/packages/typescript/ai/tests/chat.test.ts
@@ -1319,7 +1319,7 @@ describe('chat()', () => {
       expect((runFinished as any).threadId).toBe('thread-1')
     })
 
-    it('should strip deprecated toolName but keep extras on yielded events', async () => {
+    it('should include both toolCallName (spec) and toolName (deprecated) on TOOL_CALL_START', async () => {
       const { adapter } = createMockAdapter({
         iterations: [
           [
@@ -1353,10 +1353,9 @@ describe('chat()', () => {
 
       const toolStartChunks = chunks.filter((c) => c.type === 'TOOL_CALL_START')
       for (const chunk of toolStartChunks) {
-        // toolCallName should be present (spec field)
+        // Both spec and deprecated field present (passthrough)
         expect((chunk as any).toolCallName).toBe('get_weather')
-        // toolName should be stripped
-        expect('toolName' in chunk).toBe(false)
+        expect((chunk as any).toolName).toBe('get_weather')
       }
     })
 
diff --git a/packages/typescript/ai/tests/strip-to-spec-middleware.test.ts b/packages/typescript/ai/tests/strip-to-spec-middleware.test.ts
@@ -2,104 +2,14 @@ import { describe, it, expect } from 'vitest'
 import { stripToSpec } from '../src/strip-to-spec-middleware'
 import type { StreamChunk } from '../src/types'
 
-/**
- * Helper to create a StreamChunk with the given type and fields.
- */
-function makeChunk(type: string, fields: Record<string, unknown>): StreamChunk {
+function makeChunk(
+  type: string,
+  fields: Record<string, unknown>,
+): StreamChunk {
   return { type, timestamp: Date.now(), ...fields } as unknown as StreamChunk
 }
 
 describe('stripToSpec', () => {
-  // =========================================================================
-  // Always stripped: rawEvent (debug payload, potentially large)
-  // =========================================================================
-
-  it('strips rawEvent from all events', () => {
-    const chunk = makeChunk('TEXT_MESSAGE_START', {
-      messageId: 'msg-1',
-      role: 'assistant',
-      rawEvent: { some: 'raw data' },
-      model: 'gpt-4o',
-    })
-    const result = stripToSpec(chunk) as Record<string, unknown>
-    expect(result).not.toHaveProperty('rawEvent')
-    // model is kept (passthrough)
-    expect(result).toHaveProperty('model', 'gpt-4o')
-    expect(result).toHaveProperty('messageId', 'msg-1')
-  })
-
-  // =========================================================================
-  // Deprecated aliases stripped: toolName, stepId, state, error (nested)
-  // =========================================================================
-
-  it('strips deprecated toolName from TOOL_CALL_START, keeps toolCallName', () => {
-    const chunk = makeChunk('TOOL_CALL_START', {
-      toolCallId: 'tc-1',
-      toolCallName: 'getTodos',
-      toolName: 'getTodos',
-      index: 0,
-      providerMetadata: { foo: 'bar' },
-      model: 'gpt-4o',
-    })
-    const result = stripToSpec(chunk) as Record<string, unknown>
-    expect(result).not.toHaveProperty('toolName')
-    // These extras are kept (passthrough)
-    expect(result).toHaveProperty('toolCallName', 'getTodos')
-    expect(result).toHaveProperty('index', 0)
-    expect(result).toHaveProperty('providerMetadata')
-    expect(result).toHaveProperty('model', 'gpt-4o')
-  })
-
-  it('strips deprecated toolName from TOOL_CALL_END, keeps extras', () => {
-    const chunk = makeChunk('TOOL_CALL_END', {
-      toolCallId: 'tc-1',
-      toolName: 'getTodos',
-      toolCallName: 'getTodos',
-      input: { userId: '123' },
-      result: '[{"id":"1","title":"Buy milk"}]',
-      model: 'gpt-4o',
-    })
-    const result = stripToSpec(chunk) as Record<string, unknown>
-    expect(result).not.toHaveProperty('toolName')
-    // These extras are kept (passthrough)
-    expect(result).toHaveProperty('toolCallName', 'getTodos')
-    expect(result).toHaveProperty('input')
-    expect(result).toHaveProperty('result')
-    expect(result).toHaveProperty('model', 'gpt-4o')
-  })
-
-  it('strips deprecated stepId from STEP_STARTED, keeps stepName and extras', () => {
-    const chunk = makeChunk('STEP_STARTED', {
-      stepName: 'thinking',
-      stepId: 'step-1',
-      stepType: 'thinking',
-      model: 'gpt-4o',
-    })
-    const result = stripToSpec(chunk) as Record<string, unknown>
-    expect(result).not.toHaveProperty('stepId')
-    // These extras are kept (passthrough)
-    expect(result).toHaveProperty('stepName', 'thinking')
-    expect(result).toHaveProperty('stepType', 'thinking')
-    expect(result).toHaveProperty('model', 'gpt-4o')
-  })
-
-  it('strips deprecated stepId from STEP_FINISHED, keeps extras', () => {
-    const chunk = makeChunk('STEP_FINISHED', {
-      stepName: 'thinking',
-      stepId: 'step-1',
-      delta: 'some thinking',
-      content: 'accumulated thinking',
-      model: 'gpt-4o',
-    })
-    const result = stripToSpec(chunk) as Record<string, unknown>
-    expect(result).not.toHaveProperty('stepId')
-    // These extras are kept (passthrough)
-    expect(result).toHaveProperty('stepName', 'thinking')
-    expect(result).toHaveProperty('delta', 'some thinking')
-    expect(result).toHaveProperty('content', 'accumulated thinking')
-    expect(result).toHaveProperty('model', 'gpt-4o')
-  })
-
   it('strips deprecated nested error from RUN_ERROR, keeps flat message/code', () => {
     const chunk = makeChunk('RUN_ERROR', {
       message: 'Something went wrong',
@@ -114,106 +24,47 @@ describe('stripToSpec', () => {
     expect(result).toHaveProperty('model', 'gpt-4o')
   })
 
-  it('strips deprecated state from STATE_SNAPSHOT, keeps snapshot', () => {
-    const chunk = makeChunk('STATE_SNAPSHOT', {
-      snapshot: { count: 42 },
-      state: { count: 42 },
-      model: 'gpt-4o',
-    })
-    const result = stripToSpec(chunk) as Record<string, unknown>
-    expect(result).not.toHaveProperty('state')
-    expect(result).toHaveProperty('snapshot')
-    expect(result).toHaveProperty('model', 'gpt-4o')
-  })
-
-  // =========================================================================
-  // Extras preserved (passthrough allows them)
-  // =========================================================================
-
-  it('keeps model, content on TEXT_MESSAGE_CONTENT', () => {
-    const chunk = makeChunk('TEXT_MESSAGE_CONTENT', {
-      messageId: 'msg-1',
-      delta: 'Hello',
-      content: 'Hello World',
-      model: 'gpt-4o',
-    })
-    const result = stripToSpec(chunk) as Record<string, unknown>
-    expect(result).toHaveProperty('delta', 'Hello')
-    expect(result).toHaveProperty('content', 'Hello World')
-    expect(result).toHaveProperty('model', 'gpt-4o')
-  })
-
-  it('keeps args on TOOL_CALL_ARGS', () => {
-    const chunk = makeChunk('TOOL_CALL_ARGS', {
+  it('passes through all other events unchanged', () => {
+    const chunk = makeChunk('TOOL_CALL_START', {
       toolCallId: 'tc-1',
-      delta: '{"userId":',
-      args: '{"userId":',
+      toolCallName: 'getTodos',
+      toolName: 'getTodos',
+      index: 0,
+      providerMetadata: { foo: 'bar' },
       model: 'gpt-4o',
     })
-    const result = stripToSpec(chunk) as Record<string, unknown>
-    expect(result).toHaveProperty('args', '{"userId":')
-    expect(result).toHaveProperty('delta', '{"userId":')
-    expect(result).toHaveProperty('model', 'gpt-4o')
+    const result = stripToSpec(chunk)
+    expect(result).toBe(chunk) // same reference, no copy
   })
 
-  it('keeps finishReason and usage on RUN_FINISHED', () => {
+  it('keeps model, content, finishReason, usage, result, etc.', () => {
     const chunk = makeChunk('RUN_FINISHED', {
       runId: 'run-1',
+      threadId: 'thread-1',
       model: 'gpt-4o',
       finishReason: 'stop',
       usage: { promptTokens: 100, completionTokens: 50, totalTokens: 150 },
     })
     const result = stripToSpec(chunk) as Record<string, unknown>
+    expect(result).toHaveProperty('model', 'gpt-4o')
     expect(result).toHaveProperty('finishReason', 'stop')
     expect(result).toHaveProperty('usage')
-    expect(result).toHaveProperty('model', 'gpt-4o')
-  })
-
-  it('keeps model on RUN_STARTED', () => {
-    const chunk = makeChunk('RUN_STARTED', {
-      runId: 'run-1',
-      threadId: 'thread-1',
-      model: 'gpt-4o',
-    })
-    const result = stripToSpec(chunk) as Record<string, unknown>
-    expect(result).toHaveProperty('model', 'gpt-4o')
-    expect(result).toHaveProperty('threadId', 'thread-1')
-  })
-
-  it('passes through REASONING events unchanged (except rawEvent)', () => {
-    const chunk = makeChunk('REASONING_MESSAGE_CONTENT', {
-      messageId: 'msg-1',
-      delta: 'Let me think...',
-      model: 'gpt-4o',
-    })
-    const result = stripToSpec(chunk) as Record<string, unknown>
-    expect(result).toHaveProperty('delta', 'Let me think...')
-    expect(result).toHaveProperty('model', 'gpt-4o')
   })
 
-  it('passes through TOOL_CALL_RESULT unchanged (except rawEvent)', () => {
-    const chunk = makeChunk('TOOL_CALL_RESULT', {
+  it('keeps toolName, stepId, and other deprecated aliases (passthrough)', () => {
+    const chunk = makeChunk('TOOL_CALL_END', {
       toolCallId: 'tc-1',
-      messageId: 'msg-result-1',
-      content: '{"items":[]}',
-      role: 'tool',
+      toolCallName: 'getTodos',
+      toolName: 'getTodos',
+      input: { userId: '123' },
+      result: '{"items":[]}',
       model: 'gpt-4o',
     })
     const result = stripToSpec(chunk) as Record<string, unknown>
+    expect(result).toHaveProperty('toolName', 'getTodos')
+    expect(result).toHaveProperty('toolCallName', 'getTodos')
+    expect(result).toHaveProperty('input')
+    expect(result).toHaveProperty('result')
     expect(result).toHaveProperty('model', 'gpt-4o')
-    expect(result).toHaveProperty('content', '{"items":[]}')
-  })
-
-  it('strips rawEvent even when combined with type-specific strips', () => {
-    const chunk = makeChunk('TOOL_CALL_START', {
-      toolCallId: 'tc-1',
-      toolCallName: 'foo',
-      toolName: 'foo',
-      rawEvent: { originalPayload: true },
-    })
-    const result = stripToSpec(chunk) as Record<string, unknown>
-    expect(result).not.toHaveProperty('rawEvent')
-    expect(result).not.toHaveProperty('toolName')
-    expect(result).toHaveProperty('toolCallName', 'foo')
   })
 })
