[jiuwenswarm] LLM stream ReadError masked as "node agent returned empty output"

## Observed symptom [Bug] Design: LLM stream ReadError is masked as "node agent returned empty output" Paired: [GitHub #7657](https://github.com/openJiuwen-ai/jiuwenswarm/issues/7657) ↔ [GitCode #5001](https://gitcode.com/openJiuwen/jiuwenswarm/issues/5001) Summary In Designer mode, an LLM streaming failure is displayed as **`node agent returned empty output`**, hiding the actionable backend error: `[181001] model call failed, reason: ` The observed character-image node failed before invoking the image-generation tool. Reproduction environment Only software versions relevant to reproducing this error are included. Project/run identifiers, internal addresses, model connection settings and remote deployment details have been removed. Version metadata is inconsistent in this checkout: `pyproject.toml` reports `0.2.5.beta1`, while installed JiuwenSwarm distribution metadata reports `0.2.3`. The source commit above is the authoritative identifier. A GPU/image backend should not be required t ## Environment GitHub issue openJiuwen-ai/jiuwenswarm #7657 ## Trigger / context Public GitHub report in openJiuwen-ai/jiuwenswarm (FRESH_7D). ## Source evidence - https://github.com/openJiuwen-ai/jiuwenswarm/issues/7657 (2026-10-01T17:53:28Z) — evidence_class: PRIMARY_ISSUE_REPORT — #7657 ## Freshness - classification: FRESH_7D - retrieved_at: 2026-10-02T09:46:06.809152Z - scout_id: Ccaa9f180c7 ## Scout notes This Problem was published by the KFA Fresh Friction Scout from public sources. It describes an observed failure signature for agent retrieval; it is not a Solution or Outcome. Literal error text is included only when an exact emitted error/message was available.