BE-PR-007: refactor Proposal Accept to generate story tasks from all Essentials

- Removed old logic that created a single story/feature task on accept
- Accept now iterates all Essentials under the Proposal
- Each Essential.type maps to a story/* task (feature/improvement/refactor)
- All tasks created in a single transaction
- Added ProposalAcceptResponse and GeneratedTaskSummary schemas
- Proposal must have at least one Essential to be accepted
- No longer writes to deprecated feat_task_id field

app/api/routers/proposals.py

@@ -236,7 +236,7 @@ class AcceptRequest(schemas.BaseModel):
     milestone_id: int
 
 
-@router.post("/{proposal_id}/accept", response_model=schemas.ProposalResponse)
+@router.post("/{proposal_id}/accept", response_model=schemas.ProposalAcceptResponse)
 def accept_proposal(
     project_id: str,
     proposal_id: str,
@@ -244,7 +244,16 @@ def accept_proposal(
     db: Session = Depends(get_db),
     current_user: models.User = Depends(get_current_user_or_apikey),
 ):
-    """Accept a proposal: create a feature story task in the chosen milestone."""
+    """Accept a proposal: generate story tasks from all Essentials into the chosen milestone.
+
+    Each Essential under the Proposal produces a corresponding ``story/*`` task:
+      - feature     → story/feature
+      - improvement → story/improvement
+      - refactor    → story/refactor
+
+    All tasks are created in a single transaction.  The Proposal must have at
+    least one Essential to be accepted.
+    """
     project = _find_project(db, project_id)
     if not project:
         raise HTTPException(status_code=404, detail="Project not found")
@@ -270,43 +279,86 @@ def accept_proposal(
     if ms_status != "open":
         raise HTTPException(status_code=400, detail="Target milestone must be in 'open' status")
 
-    # Generate task code
-    milestone_code = milestone.milestone_code or f"m{milestone.id}"
-    max_task = db.query(Task).filter(Task.milestone_id == milestone.id).order_by(Task.id.desc()).first()
-    next_num = (max_task.id + 1) if max_task else 1
-    task_code = f"{milestone_code}:T{next_num:05x}"
-
-    # Create feature story task
-    task = Task(
-        title=proposal.title,
-        description=proposal.description,
-        task_type="story",
-        task_subtype="feature",
-        status=TaskStatus.PENDING,
-        priority=TaskPriority.MEDIUM,
-        project_id=project.id,
-        milestone_id=milestone.id,
-        reporter_id=proposal.created_by_id or current_user.id,
-        created_by_id=proposal.created_by_id or current_user.id,
-        task_code=task_code,
+    # Fetch all Essentials for this Proposal
+    essentials = (
+        db.query(Essential)
+        .filter(Essential.proposal_id == proposal.id)
+        .order_by(Essential.id.asc())
+        .all()
     )
-    db.add(task)
-    db.flush()  # get task.id
+    if not essentials:
+        raise HTTPException(
+            status_code=400,
+            detail="Proposal has no Essentials. Add at least one Essential before accepting.",
+        )
 
-    # Update proposal
+    # Map Essential type → task subtype
+    ESSENTIAL_TYPE_TO_SUBTYPE = {
+        "feature": "feature",
+        "improvement": "improvement",
+        "refactor": "refactor",
+    }
+
+    # Determine next task number in this milestone
+    milestone_code = milestone.milestone_code or f"m{milestone.id}"
+    max_task = (
+        db.query(sa_func.max(Task.id))
+        .filter(Task.milestone_id == milestone.id)
+        .scalar()
+    )
+    next_num = (max_task + 1) if max_task else 1
+
+    # Create one story task per Essential — all within the current transaction
+    generated_tasks = []
+    for essential in essentials:
+        etype = essential.type.value if hasattr(essential.type, "value") else essential.type
+        task_subtype = ESSENTIAL_TYPE_TO_SUBTYPE.get(etype, "feature")
+        task_code = f"{milestone_code}:T{next_num:05x}"
+
+        task = Task(
+            title=essential.title,
+            description=essential.description,
+            task_type="story",
+            task_subtype=task_subtype,
+            status=TaskStatus.PENDING,
+            priority=TaskPriority.MEDIUM,
+            project_id=project.id,
+            milestone_id=milestone.id,
+            reporter_id=proposal.created_by_id or current_user.id,
+            created_by_id=proposal.created_by_id or current_user.id,
+            task_code=task_code,
+        )
+        db.add(task)
+        db.flush()  # materialise task.id
+
+        generated_tasks.append({
+            "task_id": task.id,
+            "task_code": task_code,
+            "task_type": "story",
+            "task_subtype": task_subtype,
+            "title": essential.title,
+            "essential_id": essential.id,
+            "essential_code": essential.essential_code,
+        })
+        next_num = task.id + 1  # use real id for next code to stay consistent
+
+    # Update proposal status (do NOT write feat_task_id — deprecated)
     proposal.status = ProposalStatus.ACCEPTED
-    proposal.feat_task_id = str(task.id)
 
     db.commit()
     db.refresh(proposal)
 
     log_activity(db, "accept", "proposal", proposal.id, user_id=current_user.id, details={
         "milestone_id": milestone.id,
-        "generated_task_id": task.id,
-        "task_code": task_code,
+        "generated_tasks": [
+            {"task_id": t["task_id"], "task_code": t["task_code"], "essential_id": t["essential_id"]}
+            for t in generated_tasks
+        ],
     })
 
-    return _serialize_proposal(db, proposal)
+    result = _serialize_proposal(db, proposal, include_essentials=True)
+    result["generated_tasks"] = generated_tasks
+    return result
 
 
 class RejectRequest(schemas.BaseModel):