feat(persistence): PR6 T5.11 — ORM workspace_id nullable=False

Flip the 4 business ORM models (ThreadMetaRow, RunRow, FeedbackRow,
RunEventRow) to ``workspace_id: Mapped[str]`` with ``nullable=False``.
PR5's alembic 0003 already enforces NOT NULL at the DB layer; this
aligns the ORM-driven ``create_all()`` path (dev / tests) with the same
invariant so a new install ends up at the post-0003 schema without
running alembic.

Test fallout absorbed:

- `tests/conftest.py` autouse seed now produces a fully consistent
  pair: user row (default_workspace_id = test-workspace-autouse) plus
  the workspace itself. The PR5 backfill script's "users without
  default_workspace_id" query no longer picks the fixture up. Insert
  order is user → workspace → UPDATE user, walking around the chicken-
  and-egg FK between `workspaces.owner_id` and `users.default_workspace_id`.
- `tests/test_backfill_workspace_id.py` adds a file-scoped autouse
  fixture that temporarily flips `column.nullable = True` for the four
  business tables (production correctness comes from alembic 0003;
  the script's own job is exactly to fill rows between 0002 and 0003
  so its tests need that transient state to be representable). Its
  `_init_engine` also deletes the autouse seed rows to match the
  "fresh DB" model the tests assume.
- `test_thread_meta_workspace_filter::test_create_workspace_none_bypasses`
  renamed to `test_create_workspace_none_rejected_by_orm` and asserts
  the new IntegrityError on explicit None — write paths can no longer
  bypass workspace scope.
- 5 `test_workspace_context` tests + the auth-middleware reset test
  get `@pytest.mark.no_auto_workspace` so they keep testing the
  unset-contextvar path.
- `test_workspace_repo::test_list_by_user_bypass_returns_all` switches
  to membership assertions instead of strict equality since the
  autouse fixture surfaces under `user_id=None`.

3214 passed, 30 skipped; the remaining 17 are the documented
pre-existing caplog ordering flakes (all pass in isolation).

backend/packages/harness/deerflow/persistence/feedback/model.py

@@ -22,11 +22,11 @@ class FeedbackRow(Base):
     run_id: Mapped[str] = mapped_column(String(64), nullable=False, index=True, comment="关联的运行 ID（runs.run_id）")
     thread_id: Mapped[str] = mapped_column(String(64), nullable=False, index=True, comment="关联的会话 ID（threads_meta.thread_id）")
     user_id: Mapped[str | None] = mapped_column(String(64), index=True, comment="反馈作者；为 NULL 表示历史无主数据")
-    workspace_id: Mapped[str | None] = mapped_column(
+    workspace_id: Mapped[str] = mapped_column(
         String(36),
         ForeignKey("workspaces.id", ondelete="CASCADE"),
-        nullable=True,
-        comment="所属 workspace；PR5 期间 nullable（回填中），PR5 0003 迁移后改 NOT NULL",
+        nullable=False,
+        comment="所属 workspace。PR5 引入时 nullable 用于回填；alembic 0003 + PR6 仓储接入完成后 NOT NULL",
     )
     message_id: Mapped[str | None] = mapped_column(String(64), comment="可选的 RunEventStore 事件 ID；为 NULL 表示针对整次运行而非单条消息")
     rating: Mapped[int] = mapped_column(nullable=False, comment="评分：+1 点赞，-1 点踩")

backend/packages/harness/deerflow/persistence/models/run_event.py

@@ -22,11 +22,11 @@ class RunEventRow(Base):
         index=True,
         comment="会话所有者；为 NULL 表示鉴权引入之前的历史数据，新写入由 auth 中间件填充，启动期 orphan 迁移会回填存量",
     )
-    workspace_id: Mapped[str | None] = mapped_column(
+    workspace_id: Mapped[str] = mapped_column(
         String(36),
         ForeignKey("workspaces.id", ondelete="CASCADE"),
-        nullable=True,
-        comment="所属 workspace；PR5 期间 nullable（回填中），PR5 0003 迁移后改 NOT NULL",
+        nullable=False,
+        comment="所属 workspace。PR5 引入时 nullable 用于回填；alembic 0003 + PR6 仓储接入完成后 NOT NULL",
     )
     event_type: Mapped[str] = mapped_column(String(32), nullable=False, comment="事件子类型（具体含义由 category 决定，如 ai_message_chunk、tool_call、run_started）")
     category: Mapped[str] = mapped_column(String(16), nullable=False, comment='事件大类："message" 消息 / "trace" 追踪 / "lifecycle" 生命周期')

backend/packages/harness/deerflow/persistence/run/model.py

@@ -17,11 +17,11 @@ class RunRow(Base):
     thread_id: Mapped[str] = mapped_column(String(64), nullable=False, index=True, comment="所属会话 ID（threads_meta.thread_id）")
     assistant_id: Mapped[str | None] = mapped_column(String(128), comment="使用的 Assistant ID（自定义智能体名）；为 NULL 表示默认 lead agent")
     user_id: Mapped[str | None] = mapped_column(String(64), index=True, comment="发起本次运行的用户 ID")
-    workspace_id: Mapped[str | None] = mapped_column(
+    workspace_id: Mapped[str] = mapped_column(
         String(36),
         ForeignKey("workspaces.id", ondelete="CASCADE"),
-        nullable=True,
-        comment="所属 workspace；PR5 期间 nullable（回填中），PR5 0003 迁移后改 NOT NULL",
+        nullable=False,
+        comment="所属 workspace。PR5 引入时 nullable 用于回填；alembic 0003 + PR6 仓储接入完成后 NOT NULL",
     )
     status: Mapped[str] = mapped_column(
         String(20),

backend/packages/harness/deerflow/persistence/thread_meta/model.py

@@ -16,11 +16,11 @@ class ThreadMetaRow(Base):
     thread_id: Mapped[str] = mapped_column(String(64), primary_key=True, comment="会话主键（LangGraph thread_id）")
     assistant_id: Mapped[str | None] = mapped_column(String(128), index=True, comment="关联的 Assistant ID（自定义智能体名）；为 NULL 表示默认 lead agent")
     user_id: Mapped[str | None] = mapped_column(String(64), index=True, comment="会话所有者；为 NULL 表示历史无主数据")
-    workspace_id: Mapped[str | None] = mapped_column(
+    workspace_id: Mapped[str] = mapped_column(
         String(36),
         ForeignKey("workspaces.id", ondelete="CASCADE"),
-        nullable=True,
-        comment="所属 workspace；PR5 期间 nullable（回填中），PR5 0003 迁移后改 NOT NULL",
+        nullable=False,
+        comment="所属 workspace。PR5 引入时 nullable 用于回填；alembic 0003 + PR6 仓储接入完成后 NOT NULL",
     )
     display_name: Mapped[str | None] = mapped_column(String(256), comment="会话显示名（自动生成的标题或用户手改）")
     status: Mapped[str] = mapped_column(String(20), default="idle", comment='会话状态："idle" 空闲 / "busy" 正在产出')