diff --git a/backend/app/services/quote_service.py b/backend/app/services/quote_service.py
index f428df3..e7fa272 100644
--- a/backend/app/services/quote_service.py
+++ b/backend/app/services/quote_service.py
@@ -416,6 +416,9 @@ async def accept_quote(db: AsyncSession, quote_id: UUID, payload: AcceptQuoteIn,
 
         # --- process item decisions (UPSERT) ---
         chosen_ts_ids: set[UUID] = set()
+        # پروژه‌های ارسالی در payload.item_projects — منبع اصلی برای
+        # decision.project_id (مدیر تدارکات برای هر قلم یک پروژه انتخاب می‌کند)
+        proj_by_line: dict[UUID, list[UUID]] = {e.line_item_id: list(e.project_ids) for e in payload.item_projects}
         for decision_in in payload.item_decisions:
             decision = await db.scalar(
                 select(ItemDecision).where(ItemDecision.line_item_id == decision_in.line_item_id).with_for_update()
@@ -460,22 +463,31 @@ async def accept_quote(db: AsyncSession, quote_id: UUID, payload: AcceptQuoteIn,
                 decision.adjusted_unit_price = decision_in.adjusted_unit_price
                 decision.adjusted_notes = decision_in.adjusted_notes
                 decision.decided_at = utcnow()
-                # v2.6: the SINGLE purchased project (proc manager picks it;
-                # auto-filled when the offer had exactly one project).
+                # v2.6: the SINGLE purchased project (proc manager picks it).
+                # Derivation order:
+                #   1) explicit decision_in.project_id
+                #   2) payload.item_projects for this line item (exactly one)
+                #   3) existing line_item_projects (exactly one)
+                # otherwise NULL — the item stays visible only to the office
+                # until a project is assigned (never wrongly visible to a PM).
                 if decision_in.project_id is not None:
                     decision.project_id = decision_in.project_id
                 else:
-                    line_projs = (
-                        (await db.execute(
-                            select(LineItemProjects.project_id).where(
-                                LineItemProjects.line_item_id == decision_in.line_item_id
-                            )
-                        ))
-                        .scalars()
-                        .all()
-                    )
-                    if len(line_projs) == 1:
-                        decision.project_id = line_projs[0]
+                    accept_projs = proj_by_line.get(decision_in.line_item_id) or []
+                    if len(accept_projs) == 1:
+                        decision.project_id = accept_projs[0]
+                    else:
+                        line_projs = (
+                            (await db.execute(
+                                select(LineItemProjects.project_id).where(
+                                    LineItemProjects.line_item_id == decision_in.line_item_id
+                                )
+                            ))
+                            .scalars()
+                            .all()
+                        )
+                        if len(line_projs) == 1:
+                            decision.project_id = line_projs[0]
                 if decision.project_id is not None:
                     if await db.get(Project, decision.project_id) is None:
                         raise NotFoundError("پروژه یافت نشد", field="item_decisions.project_id")