fix(stream-text): ensure SSE handling conforms to the spec

packages/stream-text/src/index.ts

@@ -44,7 +44,7 @@ export interface StreamTextResult {
   usage?: Usage
 }
 
-const chunkHeaderPrefix = 'data:'
+const chunkHeaderPrefix = /^data(?:: ?)?/
 
 /**
  * @experimental WIP, does not support function calling (tools).
@@ -79,14 +79,10 @@ export const streamText = async (options: StreamTextOptions): Promise<StreamText
           // Check for comments
           if (line.startsWith(':'))
             continue
-          // Check if line starts with data: (allowing spaces)
-          if (line.startsWith(chunkHeaderPrefix)) {
+          // Check if line starts with chunk header
+          if (chunkHeaderPrefix.test(line)) {
             // Extract content after data: (remove leading single space if present)
-            const content = line.slice(chunkHeaderPrefix.length)
-            dataLines.push(content.length > 0 && content[0] === ' ' ? content.slice(1) : content)
-          }
-          else {
-            break // event ended, dispatch
+            dataLines.push(line.replace(chunkHeaderPrefix, ''))
           }
         }