diff --git a/roboco/services/git.py b/roboco/services/git.py
index 543f563a..a9302988 100644
--- a/roboco/services/git.py
+++ b/roboco/services/git.py
@@ -3943,20 +3943,28 @@ class GitService(BaseService):
         pr_number: int,
         *,
         actor_agent_id: UUID | None = None,
+        project_id: UUID | None = None,
     ) -> str:
         """Return the current target (base) branch of an open PR.
 
         Workspace resolution mirrors pr_merge: actor → assigned_to →
         created_by. Lets the Main PM call pr_target after
         ``submit_qa`` has cleared ``assigned_to`` without ValidationError.
+
+        ``pr_number`` alone is ambiguous across projects (GitHub numbers PRs
+        per-repo), so when the caller knows which project the PR belongs to it
+        MUST pass ``project_id`` — the task lookup is then scoped to it so a
+        same-numbered PR in another project's repo is never resolved by
+        accident (mirrors ``close_pull_request``).
         """
         from sqlalchemy import select
 
         from roboco.db.tables import TaskTable as _TaskTable
 
-        result = await self.session.execute(
-            select(_TaskTable).where(_TaskTable.pr_number == pr_number).limit(1)
-        )
+        stmt = select(_TaskTable).where(_TaskTable.pr_number == pr_number)
+        if project_id is not None:
+            stmt = stmt.where(_TaskTable.project_id == project_id)
+        result = await self.session.execute(stmt.limit(1))
         task = result.scalar_one_or_none()
         if task is None:
             raise NotFoundError("PR", str(pr_number))
diff --git a/tests/unit/services/test_git_pr_target_scoping.py b/tests/unit/services/test_git_pr_target_scoping.py
new file mode 100644
index 00000000..23def34b
--- /dev/null
+++ b/tests/unit/services/test_git_pr_target_scoping.py
@@ -0,0 +1,141 @@
+"""F052: pr_target must scope its task lookup by project_id when the caller
+knows it, mirroring close_pull_request.
+
+GitHub numbers PRs per-repo, so ``pr_number`` is ambiguous across projects: a
+backend repo's PR #132 and a frontend repo's PR #132 are different PRs. The
+bare ``WHERE pr_number == N LIMIT 1`` query returns whichever task row comes
+first — the wrong repo's task, whose ``_project_for_task`` then resolves the
+wrong project and the GitHub fetch hits the wrong repo. When the caller knows
+the project (the Main PM coordinating a known root), it must pass
+``project_id`` so the lookup is scoped and a same-numbered PR in another
+project's repo is never resolved by accident — the pattern
+``close_pull_request`` already established.
+"""
+
+from __future__ import annotations
+
+from pathlib import Path
+from typing import TYPE_CHECKING
+from unittest.mock import AsyncMock, MagicMock, patch
+from uuid import uuid4
+
+import pytest
+from roboco.services.base import NotFoundError
+from roboco.services.git import GitService
+
+if TYPE_CHECKING:
+    from contextlib import AbstractContextManager
+
+_PR_NUMBER = 132
+
+
+def _make_session(recorder: list[object]) -> MagicMock:
+    session = MagicMock()
+
+    async def _execute(stmt: object) -> MagicMock:
+        recorder.append(stmt)
+        result = MagicMock()
+        result.scalar_one_or_none.return_value = None
+        return result
+
+    session.execute = AsyncMock(side_effect=_execute)
+    return session
+
+
+def _service(recorder: list[object]) -> GitService:
+    return GitService(_make_session(recorder))
+
+
+def _patch_project_service(project: object | None) -> AbstractContextManager[object]:
+    fake_service = MagicMock()
+    fake_service.get = AsyncMock(return_value=project)
+    fake_service.get_by_slug = AsyncMock(return_value=project)
+    return patch("roboco.services.git.get_project_service", return_value=fake_service)
+
+
+def _compiled_sql(stmt: object) -> str:
+    """Render a SQLAlchemy stmt to literal-bound SQL for assertion."""
+    return str(stmt.compile(compile_kwargs={"literal_binds": True}))  # type: ignore[arg-type]
+
+
+@pytest.mark.asyncio
+async def test_pr_target_scopes_task_lookup_by_project_id_when_provided() -> None:
+    """With ``project_id`` the task lookup WHERE clause filters on BOTH
+    pr_number and project_id — a same-numbered PR in another project's repo
+    can't be resolved by accident."""
+    recorder: list[object] = []
+    svc = _service(recorder)
+    project_id = uuid4()
+
+    # Task lookup returns None → NotFoundError, but we only care about the SQL
+    # the lookup was issued with.
+    with _patch_project_service(MagicMock(slug="roboco")), pytest.raises(NotFoundError):
+        await svc.pr_target(_PR_NUMBER, project_id=project_id)
+
+    assert len(recorder) == 1
+    sql = _compiled_sql(recorder[0])
+    assert "tasks.pr_number =" in sql
+    # The WHERE clause filters on project_id (the select list renders the
+    # column as ``tasks.project_id,`` with a trailing comma; the WHERE
+    # comparison renders as ``tasks.project_id =``).
+    assert "tasks.project_id =" in sql
+
+
+@pytest.mark.asyncio
+async def test_pr_target_without_project_id_does_not_scope() -> None:
+    """Without ``project_id`` the lookup stays unscoped (backward-compatible
+    with callers that don't know the project) — only pr_number is filtered."""
+    recorder: list[object] = []
+    svc = _service(recorder)
+
+    with _patch_project_service(MagicMock(slug="roboco")), pytest.raises(NotFoundError):
+        await svc.pr_target(_PR_NUMBER)
+
+    assert len(recorder) == 1
+    sql = _compiled_sql(recorder[0])
+    assert "tasks.pr_number =" in sql
+    # No project_id WHERE filter (the column still appears in the select list
+    # with a trailing comma, but the ``=`` comparison is absent).
+    assert "tasks.project_id =" not in sql
+
+
+@pytest.mark.asyncio
+async def test_pr_target_with_project_id_skips_wrong_repo_task() -> None:
+    """Two tasks share pr_number #132 but live in different projects. With the
+    correct ``project_id`` the scoped query returns ONLY the matching task (the
+    other repo's task is filtered out), so the GitHub fetch hits the right
+    repo. (Here the scoped lookup finds nothing in the requested project →
+    NotFoundError, NOT a silent wrong-repo resolution.)"""
+    project_id = uuid4()
+    other_project_id = uuid4()
+    # The wrong-repo task (other project) shares the pr_number.
+    wrong_repo_task = MagicMock(
+        id=uuid4(), project_id=other_project_id, assigned_to=uuid4()
+    )
+    recorder: list[object] = []
+
+    session = MagicMock()
+
+    async def _execute(stmt: object) -> MagicMock:
+        recorder.append(stmt)
+        result = MagicMock()
+        # Simulate the DB applying the project_id filter: the scoped query
+        # finds no row in the requested project (the only matching pr_number
+        # belongs to the OTHER project).
+        result.scalar_one_or_none.return_value = None
+        return result
+
+    session.execute = AsyncMock(side_effect=_execute)
+    svc = GitService(session)
+    _bind = object.__setattr__
+    _bind(svc, "get_workspace", AsyncMock(return_value=Path("/tmp/ws")))
+    _bind(svc, "_parse_github_remote", MagicMock(return_value=("acme", "repo")))
+    _bind(svc, "_get_project_token_or_raise", AsyncMock(return_value="token"))
+
+    with _patch_project_service(MagicMock(slug="roboco")), pytest.raises(NotFoundError):
+        await svc.pr_target(_PR_NUMBER, project_id=project_id)
+
+    # The query WAS scoped by project_id (the wrong-repo task did not leak in).
+    sql = _compiled_sql(recorder[0])
+    assert "tasks.project_id =" in sql
+    _ = wrong_repo_task  # exists to document the cross-repo collision scenario