[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: ```text [181001] model call failed, reason: openAI API async stream error: ReadError ``` 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 ## Literal error text ``` ReadError masked as empty output ``` ## Environment GitHub issue openJiuwen-ai/jiuwenswarm #7657 ## Trigger / context 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: ```text [181001] model call failed, reason: openAI API async stream error: ReadError ``` 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. | Component | Version | | --- | --- | | OS | Windows 11, build 26200 | | JiuwenSwarm source | `0.2.8.beta1` checkout; commit `d164ad4ae3b0784d4b6689d1b557b7f21e1cb893` | | Python | 3.12.12 | | uv | 0.9.5 | | OpenJiuwen | Distribution 0.1.19; Git ref `release/v0.1.19.post1`; commit `8f9f112698d5580b749158b21b1a89a54e16a8f9` | | openai / httpx | 2.32.0 / 0.28.1 | | Conversation model interface | OpenAI-compatible streaming client | | Designer agent settings | `enable_task ## Source evidence - https://github.com/openJiuwen-ai/jiuwenswarm/issues/7657 (2026-10-01T17:53:28Z) — #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.