feat(M7): 第11环裂变引擎端到端打通

- fission_service: 1源任务扇出N套子任务(回填source_fission_id,复用主管道),MAX_FANOUT=5红线
- fission_prompt: 三档参考度(high/mid/low)占位规则,真实措辞待北哥定义
- tasks.py: worker识别裂变子任务→注入对应档位规则进文案上下文(关键缺口修复)
- api/v1/fission: POST触发 + GET进度聚合, main.py注册路由
- 实测: fission_id=2扇出task70/71,worker注入日志level=high,进度端点聚合正确

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

backend/app/api/v1/fission.py

@@ -0,0 +1,78 @@
+"""
+app/api/v1/fission.py — 第11环裂变路由
+
+POST /fission           触发裂变(1源任务→N套子任务)
+GET  /fission/{id}      查裂变进度(聚合N个子任务状态)
+工作台内呈现,子任务走标准 SSE 流回进度。
+"""
+import logging
+from typing import Annotated
+
+from fastapi import APIRouter, Depends
+from pydantic import BaseModel, Field
+from sqlalchemy.orm import Session
+
+from app.core.database import get_db
+from app.core.response import ok, raise_not_found
+from app.middleware.workspace_guard import CurrentUser, require_write_permission
+from app.models.fission import FissionTask
+from app.models.task import GenerationTask
+
+logger = logging.getLogger(__name__)
+router = APIRouter(tags=["fission"])
+
+
+class FissionCreate(BaseModel):
+    source_task_id: int
+    reference_level: str = Field(default="mid")   # low/mid/high
+    fanout_count: int = Field(default=3, ge=1, le=5)
+
+
+@router.post("/fission")
+def create_fission_endpoint(
+    body: FissionCreate,
+    current_user: Annotated[CurrentUser, Depends(require_write_permission)] = None,
+    db: Session = Depends(get_db),
+):
+    """触发裂变：从源任务扇出 N 套完整笔记包。返回 fission_id + 子 task_ids。"""
+    from app.services.fission_service import create_fission
+    fission_id, task_ids = create_fission(
+        db, current_user, body.source_task_id, body.reference_level, body.fanout_count,
+    )
+    return ok({"fission_id": fission_id, "task_ids": task_ids,
+               "reference_level": body.reference_level, "fanout_count": len(task_ids)})
+
+
+@router.get("/fission/{fission_id}")
+def get_fission_progress(
+    fission_id: int,
+    current_user: Annotated[CurrentUser, Depends(require_write_permission)] = None,
+    db: Session = Depends(get_db),
+):
+    """查裂变进度：聚合 N 个子任务状态（x/N 完成）。"""
+    ft = db.query(FissionTask).filter(
+        FissionTask.id == fission_id,
+        FissionTask.workspace_id == current_user.workspace_id,
+    ).first()
+    if not ft:
+        raise_not_found("裂变任务不存在")
+
+    subs = db.query(GenerationTask).filter(
+        GenerationTask.source_fission_id == fission_id,
+        GenerationTask.workspace_id == current_user.workspace_id,
+    ).all()
+    done_states = {"pending_selection", "pending_review", "approved", "archived"}
+    done = sum(1 for s in subs if s.status in done_states)
+    failed = sum(1 for s in subs if s.status == "failed")
+    total = len(subs)
+    # 聚合状态：全失败=failed,全完成=done,否则generating
+    agg = "done" if done == total and total > 0 else ("failed" if failed == total and total > 0 else "generating")
+    if ft.status != agg:
+        ft.status = agg; db.commit()
+
+    return ok({
+        "fission_id": ft.id, "reference_level": ft.reference_level,
+        "fanout_count": ft.fanout_count, "status": agg,
+        "progress": {"done": done, "failed": failed, "total": total},
+        "task_ids": [s.id for s in subs],
+    })