feat(core): add stream object api (#12841)

Close [AI-193](https://linear.app/affine-design/issue/AI-193)

<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->
## Summary by CodeRabbit

- **New Features**
- Added support for streaming structured AI chat responses as objects,
enabling richer and more interactive chat experiences.
- Chat messages now include a new field displaying structured stream
objects, such as reasoning steps, text deltas, tool calls, and tool
results.
- GraphQL APIs and queries updated to expose these structured streaming
objects in chat histories.
  - Introduced a new streaming chat endpoint for object-based responses.

- **Bug Fixes**
- Improved error handling for streaming responses to ensure more robust
and informative error reporting.

- **Refactor**
- Centralized and streamlined session preparation and streaming logic
for AI chat providers.
  - Unified streaming setup across multiple AI model providers.

- **Tests**
- Extended test coverage for streaming object responses to ensure
reliability and correctness.

- **Documentation**
- Updated type definitions and schemas to reflect new streaming object
capabilities in both backend and frontend code.
<!-- end of auto-generated comment: release notes by coderabbit.ai -->

Co-authored-by: DarkSky <25152247+darkskygit@users.noreply.github.com>

packages/frontend/core/src/blocksuite/ai/components/ai-chat-messages/type.ts

@@ -1,10 +1,37 @@
 import { z } from 'zod';
 
+const StreamObjectSchema = z.discriminatedUnion('type', [
+  z.object({
+    type: z.literal('text-delta'),
+    textDelta: z.string(),
+  }),
+  z.object({
+    type: z.literal('reasoning'),
+    textDelta: z.string(),
+  }),
+  z.object({
+    type: z.literal('tool-call'),
+    toolCallId: z.string(),
+    toolName: z.string(),
+    args: z.record(z.any()),
+  }),
+  z.object({
+    type: z.literal('tool-result'),
+    toolCallId: z.string(),
+    toolName: z.string(),
+    args: z.record(z.any()),
+    result: z.any(),
+  }),
+]);
+
+export type StreamObject = z.infer<typeof StreamObjectSchema>;
+
 const ChatMessageSchema = z.object({
   id: z.string(),
   content: z.string(),
   role: z.union([z.literal('user'), z.literal('assistant')]),
   createdAt: z.string(),
+  streamObjects: z.array(StreamObjectSchema).optional(),
   attachments: z.array(z.string()).optional(),
   userId: z.string().optional(),
   userName: z.string().optional(),