fix(tests): realign two more stream-utils passthrough cases with the #10017 control-line rules (#10796)

Merged via merge-train (release/v3.8.50, batch1 2026-08-20) — static gates (typecheck/file-size/complexity/cognitive/changelog) green on the combined tree; test:unit reds observed in the boarded run were verified pre-existing on the pure release tip (unrelated flake), not caused by this PR. Thanks for the contribution!

changelog.d/maintenance/release-v3850-basereds-stream-utils-20260820.md

@@ -0,0 +1 @@
+- **fix(tests):** realign the two `stream-utils` passthrough cases that still asserted the pre-#10017 SSE framing — the event-boundary case declares the OpenAI Responses client format it actually exercises, and the metadata case now pins that surviving lines stay inside one event instead of expecting the `:`/`id:` control lines that #10473 stopped forwarding to every client format.

tests/unit/stream-utils.test.ts

@@ -706,6 +706,7 @@ test("createSSEStream passthrough forwards data only after the complete SSE even
     {
       mode: "passthrough",
       sourceFormat: FORMATS.OPENAI,
+      clientResponseFormat: FORMATS.OPENAI_RESPONSES,
       provider: "openai",
       model: "responses-model",
       body: {
@@ -747,8 +748,13 @@ test("createSSEStream passthrough preserves event metadata in a single SSE event
     }
   );
 
-  assert.match(text, /^: upstream-note\nid: 42\ntrace: upstream-abc\ndata: /);
-  assert.doesNotMatch(text, /^: upstream-note\n\nid: 42/s);
+  // #10017 drops `:` comments, `id:` and `retry:` for every client format — none of
+  // the OpenAI Chat-Completions, OpenAI Responses or Claude Messages protocols define
+  // them. What this case still pins is the framing: the surviving lines stay inside ONE
+  // event instead of being split apart by blank lines.
+  assert.match(text, /^trace: upstream-abc\ndata: /);
+  assert.doesNotMatch(text, /: upstream-note/);
+  assert.doesNotMatch(text, /\bid: 42\b/);
   assert.doesNotMatch(text, /\ntrace: upstream-abc\n\n/s);
   assert.match(text, /metadata content/);
 });