fix(cloudflare,deno): Remove overly aggressive text/plain streaming classification

The `classifyResponseStreaming` function classified `text/plain` responses
without a `Content-Length` header as streaming. This heuristic was too
aggressive because `new Response('some text')` creates a `text/plain`
response without Content-Length, causing simple non-streaming responses
to take the streaming code path.

In the streaming path, the span end and transaction flush are delayed
until a stream monitor completes, which can cause timing issues when
the response is passed between Durable Objects and Workers in the
Cloudflare runtime, leading to flaky test timeouts.

Removing this rule ensures simple text/plain responses are processed
through the non-streaming (immediate span end + flush) code path.
Known streaming content types (SSE, NDJSON, JSON streaming) are still
correctly detected.

Fixes #20209

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

Agent-Logs-Url: https://github.com/getsentry/sentry-javascript/sessions/b58267a8-c6d6-4fc0-b4fb-82b5843bbf70

Co-authored-by: Lms24 <8420481+Lms24@users.noreply.github.com>

Author: Copilot

packages/cloudflare/src/utils/streaming.ts

@@ -8,7 +8,6 @@ export type StreamingGuess = {
  * Heuristics:
  * - No body → not streaming
  * - Known streaming Content-Types → streaming (SSE, NDJSON, JSON streaming)
- * - text/plain without Content-Length → streaming (some AI APIs)
  * - Otherwise → not streaming (conservative default, including HTML/SSR)
  *
  * We avoid probing the stream to prevent blocking on transform streams (like injectTraceMetaTags)
@@ -20,18 +19,15 @@ export function classifyResponseStreaming(res: Response): StreamingGuess {
   }
 
   const contentType = res.headers.get('content-type') ?? '';
-  const contentLength = res.headers.get('content-length');
 
   // Streaming: Known streaming content types
   // - text/event-stream: Server-Sent Events (Vercel AI SDK, real-time APIs)
   // - application/x-ndjson, application/ndjson: Newline-delimited JSON
   // - application/stream+json: JSON streaming
-  // - text/plain (without Content-Length): Some AI APIs use this for streaming text
   if (
     /^text\/event-stream\b/i.test(contentType) ||
     /^application\/(x-)?ndjson\b/i.test(contentType) ||
-    /^application\/stream\+json\b/i.test(contentType) ||
-    (/^text\/plain\b/i.test(contentType) && !contentLength)
+    /^application\/stream\+json\b/i.test(contentType)
   ) {
     return { isStreaming: true };
   }

packages/deno/src/utils/streaming.ts

@@ -10,7 +10,6 @@ export type StreamingGuess = {
  * Heuristics:
  * - No body → not streaming
  * - Known streaming Content-Types → streaming (SSE, NDJSON, JSON streaming)
- * - text/plain without Content-Length → streaming (some AI APIs)
  * - Otherwise → not streaming (conservative default, including HTML/SSR)
  *
  * We avoid probing the stream to prevent blocking on transform streams (like injectTraceMetaTags)
@@ -22,18 +21,15 @@ export function classifyResponseStreaming(res: Response): StreamingGuess {
   }
 
   const contentType = res.headers.get('content-type') ?? '';
-  const contentLength = res.headers.get('content-length');
 
   // Streaming: Known streaming content types
   // - text/event-stream: Server-Sent Events (Vercel AI SDK, real-time APIs)
   // - application/x-ndjson, application/ndjson: Newline-delimited JSON
   // - application/stream+json: JSON streaming
-  // - text/plain (without Content-Length): Some AI APIs use this for streaming text
   if (
     /^text\/event-stream\b/i.test(contentType) ||
     /^application\/(x-)?ndjson\b/i.test(contentType) ||
-    /^application\/stream\+json\b/i.test(contentType) ||
-    (/^text\/plain\b/i.test(contentType) && !contentLength)
+    /^application\/stream\+json\b/i.test(contentType)
   ) {
     return { isStreaming: true };
   }