Regression: #8162 (port of #8081) added an unconditional `.trim()` to
stripInternalReasoningPlaceholder(), applied to every streaming
delta.content chunk across 3 call-sites (openai-to-claude.ts,
openai-responses.ts, responsesTransformer.ts). Leading/trailing
whitespace at a chunk boundary is a real word boundary between
streaming fragments; trimming it glues adjacent chunks together on
the client ("Hello, " + "world." + " Bye." -> "Hello,world.Bye.").
Fix: early-return via .includes() before the replaceAll+trim, so the
function is a true no-op when the sentinel is absent from the chunk.
Behavior when the sentinel IS present is unchanged.
Validation:
- tests/unit/streaming-reasoning-dedup-5786.test.ts: the "(A-guard)"
test was RED on the base branch ('Hello,world.Bye.' vs
'Hello, world. Bye.'); GREEN after the fix (4/4 passing).
- tests/unit/translator-resp-openai-to-claude.test.ts: added a new
multi-chunk boundary-whitespace regression test, proven RED against
the pre-fix code (12/13), GREEN after (13/13).
- No regressions in responses-transformer.test.ts (17/17),
responses-transformer-dense-output.test.ts (3/3), or the other
suites exercising the shared placeholder utility (160/160 total
across all consumers).
Refs #8162
Refs #8081
d095555d68