diff --git a/roboco/services/prompter.py b/roboco/services/prompter.py
index e3c91db3..d7fa43e4 100644
--- a/roboco/services/prompter.py
+++ b/roboco/services/prompter.py
@@ -827,12 +827,7 @@ class PrompterService:
         #    sequence = its wave index and the umbrella as parent.
         task_of: dict[int, UUID] = {}
         for idx, draft in enumerate(drafts):
-            # Root-subtasks are coordination roots: assignment is the
-            # PM-activation flow's call, not a draft-carried field. Strip a
-            # hallucinated/injected assigned_to so a board-role uuid can't
-            # deadlock the umbrella (board roles have no dev delivery verbs).
-            sub_draft = dict(draft)
-            sub_draft.pop("assigned_to", None)
+            sub_draft = _batch_subtask_draft(draft)
             sub = await self.create_task_from_draft(
                 sub_draft,
                 agent_id,
@@ -1087,6 +1082,30 @@ def _cell_teams(the_work: list[Any]) -> list[str]:
     return seen
 
 
+def _batch_subtask_draft(draft: dict[str, Any]) -> dict[str, Any]:
+    """A batch root-subtask's draft: a copy with the non-targeting fields dropped.
+
+    ``assigned_to`` is stripped — assignment is the PM-activation flow's call, not
+    a draft-carried field, and a hallucinated/injected board-role uuid would
+    deadlock the umbrella (board roles have no dev delivery verbs). The top-level
+    ``project_id``/``product_id`` is stripped when the ``the_work`` per-cell map
+    carries the real target: the intake agent authors the top-level as the repo
+    SLUG it read (e.g. ``"roboco-api"``), which the panel only clears on a manual
+    picker toggle, so an untouched draft would reach ``create_task_from_draft``'s
+    UUID parse and 400 the whole batch. A legacy no-``the_work`` draft keeps its
+    panel-filled top-level target.
+    """
+    out = dict(draft)
+    out.pop("assigned_to", None)
+    if any(
+        isinstance(cell, dict) and cell.get("project_id")
+        for cell in (out.get("the_work") or [])
+    ):
+        out.pop("project_id", None)
+        out.pop("product_id", None)
+    return out
+
+
 def _draft_cell_map(draft: dict[str, Any]) -> list[tuple[Team, UUID]]:
     """The draft's ad-hoc per-cell project map.
 
diff --git a/tests/unit/services/test_prompter_batch_panel_shape.py b/tests/unit/services/test_prompter_batch_panel_shape.py
index 1d27d241..0a287862 100644
--- a/tests/unit/services/test_prompter_batch_panel_shape.py
+++ b/tests/unit/services/test_prompter_batch_panel_shape.py
@@ -73,6 +73,59 @@ async def test_confirm_live_batch_panel_the_work_shape(db_session: Any) -> None:
     assert len(ids) == len(drafts)
 
 
+@pytest.mark.asyncio
+async def test_confirm_live_batch_ignores_vestigial_top_level_slug(
+    db_session: Any,
+) -> None:
+    """A batch draft whose the_work cell-map carries the real project UUID but
+    that also still has the intake agent's top-level project_id SLUG (the panel
+    only nulls it on a manual picker toggle) must NOT 400 the whole batch on the
+    UUID parse — the cell map is authoritative. Repro for the live 400
+    "Invalid project_id UUID: roboco-api"."""
+    project1, ceo_id = await _seed_project_and_ceo(db_session)
+    project2 = await _seed_second_project(db_session, ceo_id)
+    service = get_prompter_service(db=db_session)
+
+    drafts: list[dict[str, Any]] = [
+        {
+            "title": "A: backend work",
+            "acceptance_criteria": ["a"],
+            "project_id": "roboco-api",  # agent's slug, panel left it in place
+            "the_work": [
+                {
+                    "team": "backend",
+                    "summary": "s",
+                    "items": ["u"],
+                    "project_id": str(project1),
+                },
+            ],
+        },
+        {
+            "title": "B: frontend work",
+            "acceptance_criteria": ["b"],
+            "project_id": "roboco-panel",  # slug on the other draft too
+            "the_work": [
+                {
+                    "team": "frontend",
+                    "summary": "s",
+                    "items": ["u"],
+                    "project_id": str(project2),
+                },
+            ],
+        },
+    ]
+    with patch("roboco.services.prompter.redis.from_url", return_value=_FakeRedis()):
+        result = await service.confirm_live_batch(
+            "Slug batch",
+            drafts,
+            ceo_id,
+            project_ids=[project1, project2],
+            route="main_pm",
+            session_id=f"sess-slug-{uuid4().hex[:8]}",
+        )
+    assert len(result["root_subtask_ids"]) == len(drafts)
+
+
 @pytest.mark.asyncio
 async def test_confirm_live_batch_panel_multicell_root_subtask(db_session: Any) -> None:
     """A batch draft that targets TWO cells (backend+frontend, one repo each) →