fix(vscode-ide-companion): optimize stream termination handling and fix style layering issues

Unify stream termination using the `sendStreamEnd` method to avoid duplicate code.
Add stream termination reason identification and handling for timeout and session expiration scenarios.
Centralize cleanup logic for various stream termination states in the WebView message hooks.
Adjust Tailwind CSS styles to resolve component layering display issues.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

packages/vscode-ide-companion/src/webview/handlers/SessionMessageHandler.ts

@@ -152,6 +152,24 @@ export class SessionMessageHandler extends BaseMessageHandler {
     this.currentStreamContent = '';
   }
 
+  /**
+   * Notify the webview that streaming has finished.
+   */
+  private sendStreamEnd(reason?: string): void {
+    const data: { timestamp: number; reason?: string } = {
+      timestamp: Date.now(),
+    };
+
+    if (reason) {
+      data.reason = reason;
+    }
+
+    this.sendToWebView({
+      type: 'streamEnd',
+      data,
+    });
+  }
+
   /**
    * Prompt user to login and invoke the registered login handler/command.
    * Returns true if a login was initiated.
@@ -373,10 +391,7 @@ export class SessionMessageHandler extends BaseMessageHandler {
         );
       }
 
-      this.sendToWebView({
-        type: 'streamEnd',
-        data: { timestamp: Date.now() },
-      });
+      this.sendStreamEnd();
     } catch (error) {
       console.error('[SessionMessageHandler] Error sending message:', error);
 
@@ -398,10 +413,7 @@ export class SessionMessageHandler extends BaseMessageHandler {
       if (isAbortLike) {
         // Do not show VS Code error popup for intentional cancellations.
         // Ensure the webview knows the stream ended due to user action.
-        this.sendToWebView({
-          type: 'streamEnd',
-          data: { timestamp: Date.now(), reason: 'user_cancelled' },
-        });
+        this.sendStreamEnd('user_cancelled');
         return;
       }
       // Check for session not found error and handle it appropriately
@@ -423,12 +435,23 @@ export class SessionMessageHandler extends BaseMessageHandler {
           type: 'sessionExpired',
           data: { message: 'Session expired. Please login again.' },
         });
+        this.sendStreamEnd('session_expired');
       } else {
-        vscode.window.showErrorMessage(`Error sending message: ${error}`);
+        const isTimeoutError =
+          lower.includes('timeout') || lower.includes('timed out');
+        if (!isTimeoutError) {
+          vscode.window.showErrorMessage(`Error sending message: ${error}`);
+        } else {
+          // 超时对用户没有可执行的操作，因此只在面板内重置信息，不弹出 VS Code 错误提醒
+          console.warn(
+            '[SessionMessageHandler] Prompt timed out; suppressing popup',
+          );
+        }
         this.sendToWebView({
           type: 'error',
           data: { message: errorMsg },
         });
+        this.sendStreamEnd(isTimeoutError ? 'timeout' : 'error');
       }
     }
   }