fix(db): 修复 alembic 多 head 导致后端启动失败

迁移图存在两处问题导致 `alembic upgrade head`(网关启动时执行)报
"Multiple head revisions are present":
1. 20260612_01 分叉出 20260615_01 与 20260616_03 两个 head 未合并;
2. 20260611_01、20260616_02 各被两个文件重复占用,污染 DAG 产生幽灵 head。

处理:
- roundtable_draft_task_id 20260611_01 -> 20260611_02(接在 square_id 之后),
  20260612_01 父节点改指 20260611_02;
- skill_favorites 20260616_02 -> 20260616_04(接在 knowledge_folders 之后),
  20260616_03 父节点改指 20260616_04;
- 新增 no-op 合并迁移 20260617_01 合并 (20260615_01, 20260616_03)。

保留 20260611_01 / 20260616_02 原 id 不变,仅重命名重复副本,已 stamp 的库不受影响;
所有迁移均有 _has_table/_has_column 守卫,全链路在已建表的库上重跑为安全 no-op。
`alembic heads` 现仅余单一 head 20260617_01,无重复告警。

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

offline-backend-20260512/backend/CLAUDE.md

@@ -368,7 +368,7 @@ shown to users ARE the **recommended questions** (`recommended_questions` table)
 types into the existing "我的" tables, idempotently:
 - agents → `agent_favorites` rows with `origin='position'`
 - **skills → `skill_favorites` rows with `origin='position'`** (table
-  `SkillFavoriteRow`, migration `20260616_02`, auto-created by `create_all`)
+  `SkillFavoriteRow`, migration `20260616_04`, auto-created by `create_all`)
 - scheduled tasks → `scheduled_task_subscriptions` rows with `origin='position'`
 
 Skills behave **exactly like agents**: a position only *adds* its tagged skills

offline-backend-20260512/backend/packages/harness/deerflow/persistence/migrations/versions/20260611_02_roundtable_draft_task_id.py

@@ -7,8 +7,14 @@ draft is keyed/shared by ``task_id`` and is no longer partitioned by ``user_id``
 ``create_all`` adds the column for brand-new DBs; this revision patches DBs that
 already have the table.
 
-Revision ID: 20260611_01
-Revises: 20260609_02
+Note: this migration originally shared the revision id ``20260611_01`` with
+``20260611_01_agents_skills_square_id`` (both branched off ``20260609_02``),
+which corrupted the alembic DAG ("present more than once" + phantom heads). It
+was renumbered to ``20260611_02`` and re-chained after that revision so the
+history is linear and single-headed.
+
+Revision ID: 20260611_02
+Revises: 20260611_01
 Create Date: 2026-06-11
 """
 
@@ -19,8 +25,8 @@ from alembic import op
 from sqlalchemy import inspect
 
 
-revision = "20260611_01"
-down_revision = "20260609_02"
+revision = "20260611_02"
+down_revision = "20260611_01"
 branch_labels = None
 depends_on = None
 

offline-backend-20260512/backend/packages/harness/deerflow/persistence/migrations/versions/20260612_01_roundtable_jobs_orchestration_plan.py

@@ -6,7 +6,7 @@
 LONGTEXT（计划 JSON 可超 64 KB）。
 
 Revision ID: 20260612_01
-Revises: 20260611_01
+Revises: 20260611_02
 Create Date: 2026-06-12
 """
 
@@ -19,7 +19,7 @@ from sqlalchemy.dialects.mysql import LONGTEXT
 
 
 revision = "20260612_01"
-down_revision = "20260611_01"
+down_revision = "20260611_02"
 branch_labels = None
 depends_on = None
 

offline-backend-20260512/backend/packages/harness/deerflow/persistence/migrations/versions/20260616_03_skill_always_on.py

@@ -1,7 +1,7 @@
 """Add always_on (常驻/免压缩) column to skills table.
 
 Revision ID: 20260616_03
-Revises: 20260616_02
+Revises: 20260616_04
 Create Date: 2026-06-16
 """
 
@@ -13,7 +13,7 @@ from sqlalchemy import inspect
 
 
 revision = "20260616_03"
-down_revision = "20260616_02"
+down_revision = "20260616_04"
 branch_labels = None
 depends_on = None
 

offline-backend-20260512/backend/packages/harness/deerflow/persistence/migrations/versions/20260616_04_skill_favorites.py

@@ -10,8 +10,14 @@ startup (new tables are always created, even on existing DBs); this migration
 keeps the alembic history consistent per the repo convention (see
 backend/CLAUDE.md → Schema Migrations).
 
-Revision ID: 20260616_02
-Revises: 20260616_01
+Note: this migration originally shared the revision id ``20260616_02`` with
+``20260616_02_knowledge_folders_templates`` (both branched off ``20260616_01``),
+which corrupted the alembic DAG ("present more than once" + phantom heads). It
+was renumbered to ``20260616_04`` and re-chained after that revision so the
+history is linear and single-headed.
+
+Revision ID: 20260616_04
+Revises: 20260616_02
 Create Date: 2026-06-16
 """
 
@@ -22,8 +28,8 @@ from alembic import op
 from sqlalchemy import inspect
 
 
-revision = "20260616_02"
-down_revision = "20260616_01"
+revision = "20260616_04"
+down_revision = "20260616_02"
 branch_labels = None
 depends_on = None
 

offline-backend-20260512/backend/packages/harness/deerflow/persistence/migrations/versions/20260617_01_merge_chain_seat_and_skill_always_on_heads.py

@@ -0,0 +1,30 @@
+"""Merge the chain-seat-mode and skill-always-on migration heads.
+
+Two lineages both descend from ``20260612_01`` (roundtable_jobs orchestration
+plan): ``20260615_01`` (chain seat mode) branched directly off it, while the
+``20260616_*`` line (positions → knowledge folders/templates → skill_favorites →
+skill always_on) is the other branch. That left the graph with two heads
+(``20260615_01`` and ``20260616_03``) so ``alembic upgrade head`` failed with
+"Multiple head revisions are present". This no-op merge revision joins both
+lineages so ``upgrade head`` resolves to a single head again.
+
+Revision ID: 20260617_01
+Revises: 20260615_01, 20260616_03
+Create Date: 2026-06-17
+"""
+
+from __future__ import annotations
+
+
+revision = "20260617_01"
+down_revision = ("20260615_01", "20260616_03")
+branch_labels = None
+depends_on = None
+
+
+def upgrade() -> None:
+    pass
+
+
+def downgrade() -> None:
+    pass