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/backend/server/src/__tests__/mocks/copilot.mock.ts

@@ -9,6 +9,7 @@ import {
   ModelInputType,
   ModelOutputType,
   PromptMessage,
+  StreamObject,
 } from '../../plugins/copilot/providers';
 import {
   DEFAULT_DIMENSIONS,
@@ -23,7 +24,7 @@ export class MockCopilotProvider extends OpenAIProvider {
       capabilities: [
         {
           input: [ModelInputType.Text],
-          output: [ModelOutputType.Text],
+          output: [ModelOutputType.Text, ModelOutputType.Object],
           defaultForOutputType: true,
         },
       ],
@@ -43,7 +44,7 @@ export class MockCopilotProvider extends OpenAIProvider {
       capabilities: [
         {
           input: [ModelInputType.Text, ModelInputType.Image],
-          output: [ModelOutputType.Text],
+          output: [ModelOutputType.Text, ModelOutputType.Object],
         },
       ],
     },
@@ -52,7 +53,7 @@ export class MockCopilotProvider extends OpenAIProvider {
       capabilities: [
         {
           input: [ModelInputType.Text, ModelInputType.Image],
-          output: [ModelOutputType.Text],
+          output: [ModelOutputType.Text, ModelOutputType.Object],
         },
       ],
     },
@@ -61,7 +62,7 @@ export class MockCopilotProvider extends OpenAIProvider {
       capabilities: [
         {
           input: [ModelInputType.Text, ModelInputType.Image],
-          output: [ModelOutputType.Text],
+          output: [ModelOutputType.Text, ModelOutputType.Object],
         },
       ],
     },
@@ -70,7 +71,7 @@ export class MockCopilotProvider extends OpenAIProvider {
       capabilities: [
         {
           input: [ModelInputType.Text, ModelInputType.Image],
-          output: [ModelOutputType.Text],
+          output: [ModelOutputType.Text, ModelOutputType.Object],
         },
       ],
     },
@@ -79,7 +80,11 @@ export class MockCopilotProvider extends OpenAIProvider {
       capabilities: [
         {
           input: [ModelInputType.Text, ModelInputType.Image],
-          output: [ModelOutputType.Text, ModelOutputType.Structured],
+          output: [
+            ModelOutputType.Text,
+            ModelOutputType.Object,
+            ModelOutputType.Structured,
+          ],
         },
       ],
     },
@@ -98,7 +103,11 @@ export class MockCopilotProvider extends OpenAIProvider {
       capabilities: [
         {
           input: [ModelInputType.Text, ModelInputType.Image],
-          output: [ModelOutputType.Text, ModelOutputType.Structured],
+          output: [
+            ModelOutputType.Text,
+            ModelOutputType.Object,
+            ModelOutputType.Structured,
+          ],
         },
       ],
     },
@@ -195,4 +204,24 @@ export class MockCopilotProvider extends OpenAIProvider {
     await sleep(100);
     return [Array.from(randomBytes(options.dimensions)).map(v => v % 128)];
   }
+
+  override async *streamObject(
+    cond: ModelConditions,
+    messages: PromptMessage[],
+    options: CopilotChatOptions = {}
+  ): AsyncIterable<StreamObject> {
+    const fullCond = { ...cond, outputType: ModelOutputType.Object };
+    await this.checkParams({ messages, cond: fullCond, options });
+
+    // make some time gap for history test case
+    await sleep(100);
+
+    const result = 'generate text to object stream';
+    for (const data of result) {
+      yield { type: 'text-delta', textDelta: data } as const;
+      if (options.signal?.aborted) {
+        break;
+      }
+    }
+  }
 }