fix(server): abort behavior in sse stream (#12211)

fix AI-121
fix AI-118

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

- **Bug Fixes**
- Improved handling of connection closures and request abortion for
streaming and non-streaming chat endpoints, ensuring session data is
saved appropriately even if the connection is interrupted.
- **Refactor**
- Streamlined internal logic for managing request signals and connection
events, resulting in more robust and explicit session management during
streaming interactions.
<!-- end of auto-generated comment: release notes by coderabbit.ai -->

tests/affine-cloud-copilot/e2e/ai-action/generate-an-image-with-image.spec.ts

@@ -36,6 +36,9 @@ test.describe('AIAction/GenerateAnImageWithImage', () => {
     await expect(answer.getByTestId('ai-answer-image')).toBeVisible();
     const insert = answer.getByTestId('answer-insert-below');
     await insert.click();
+    await page.waitForSelector('.affine-image-container');
+    await page.reload();
+
     await utils.chatPanel.waitForHistory(page, [
       {
         role: 'action',

tests/affine-cloud-copilot/e2e/ai-action/generate-an-image-with-text.spec.ts

@@ -71,11 +71,15 @@ test.describe('AIAction/GenerateAnImageWithText', () => {
     const { answer } = await generateImage();
     const insert = answer.getByTestId('answer-insert-below');
     await insert.click();
+    await page.waitForSelector('.affine-image-container');
+    await page.reload();
+
     await utils.chatPanel.waitForHistory(page, [
       {
         role: 'action',
       },
     ]);
+
     const { answer: panelAnswer, actionName } =
       await utils.chatPanel.getLatestAIActionMessage(page);
     await expect(