feat: T6.1 创作工具箱通用生成器框架地基 — 脑洞生成器 + run_generator

- schemas: Idea/IdeaListResult（脑洞生成器结构化产出，纯预览不入库）
- specs: brainstorm_spec（light 档，reads=[projects] writes=[]）
- orchestrator: build_brief_context（brief_only 策略）+ 通用 run_generator
  （据 spec.output_schema 校验 parsed，不绑定具体类型，任一声明式生成器共用）
- 新增 13 测；两包 ruff/format/mypy 干净、252 passed 无回归

P1 第一波（@llm）：证实「加生成器=加一份声明」。@backend T6.2/T6.3 待续。

packages/core/tests/test_generator_node.py

@@ -0,0 +1,91 @@
+"""T6 通用生成器执行器单测：`run_generator` + `build_brief_context`。
+
+注入 mock 网关（产 IdeaListResult parsed），无真 LLM、无真 Postgres。通用执行器据
+`spec.output_schema` 校验 parsed（不绑定具体类型）；只产结构化产物，**不写库**（纯预览，
+不变量 #3）。asyncio_mode=auto。
+"""
+
+from __future__ import annotations
+
+import uuid
+
+import pytest
+from fakes_orchestrator import FailingRunGateway, FakeRunGateway
+from ww_agents import Idea, IdeaListResult, brainstorm_spec
+from ww_core.orchestrator import build_brief_context, run_generator
+
+PROJECT = uuid.UUID("00000000-0000-0000-0000-000000000001")
+USER = uuid.UUID("00000000-0000-0000-0000-0000000000aa")
+
+_IDEAS = IdeaListResult(
+    ideas=[
+        Idea(premise="废柴觉醒吞噬瞳", hook="升级要付记忆", genre_fit="玄幻"),
+        Idea(premise="末世种粮农场主", hook="粮食成硬通货"),
+    ]
+)
+
+
+# ---- run_generator：返回结构化产物，据 output_schema 校验，只读不写库 ----
+
+
+async def test_run_generator_returns_structured_result() -> None:
+    gateway = FakeRunGateway(_IDEAS)
+
+    result = await run_generator(
+        brainstorm_spec,
+        context=build_brief_context(brief="来点逆袭流", project_context="题材：玄幻"),
+        gateway=gateway,
+        user_id=USER,
+        project_id=PROJECT,
+    )
+
+    assert isinstance(result, IdeaListResult)
+    assert len(result.ideas) == 2
+    assert result.ideas[0].premise == "废柴觉醒吞噬瞳"
+
+
+async def test_run_generator_passes_tier_and_schema_to_gateway() -> None:
+    # 不变量 #2：只透传档位（light），不传 model；output_schema 据 spec 绑定
+    gateway = FakeRunGateway(_IDEAS)
+
+    await run_generator(
+        brainstorm_spec,
+        context="x",
+        gateway=gateway,
+        user_id=USER,
+        project_id=PROJECT,
+    )
+
+    assert gateway.last_request is not None
+    assert gateway.last_request.tier == "light"
+    assert gateway.last_request.output_schema is IdeaListResult
+
+
+async def test_run_generator_raises_on_gateway_failure() -> None:
+    # 独立生成：网关失败直接上抛（端点处理），不静默吞
+    gateway = FailingRunGateway(RuntimeError("boom"))
+
+    with pytest.raises(RuntimeError, match="boom"):
+        await run_generator(
+            brainstorm_spec,
+            context="x",
+            gateway=gateway,
+            user_id=USER,
+            project_id=PROJECT,
+        )
+
+
+# ---- build_brief_context：确定性、空需求降级占位 ----
+
+
+def test_build_brief_context_is_deterministic() -> None:
+    a = build_brief_context(brief="逆袭", project_context="题材：玄幻")
+    b = build_brief_context(brief="逆袭", project_context="题材：玄幻")
+    assert a == b
+    assert "题材：玄幻" in a
+    assert "逆袭" in a
+
+
+def test_build_brief_context_empty_brief_falls_back() -> None:
+    ctx = build_brief_context(brief="   ", project_context="题材：都市")
+    assert "按题材自由发散" in ctx