refactor: split backend into harness (deerflow.*) and app (app.*) (#1131)

* refactor: extract shared utils to break harness→app cross-layer imports

Move _validate_skill_frontmatter to src/skills/validation.py and
CONVERTIBLE_EXTENSIONS + convert_file_to_markdown to src/utils/file_conversion.py.
This eliminates the two reverse dependencies from client.py (harness layer)
into gateway/routers/ (app layer), preparing for the harness/app package split.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

* refactor: split backend/src into harness (deerflow.*) and app (app.*)

Physically split the monolithic backend/src/ package into two layers:

- **Harness** (`packages/harness/deerflow/`): publishable agent framework
  package with import prefix `deerflow.*`. Contains agents, sandbox, tools,
  models, MCP, skills, config, and all core infrastructure.

- **App** (`app/`): unpublished application code with import prefix `app.*`.
  Contains gateway (FastAPI REST API) and channels (IM integrations).

Key changes:
- Move 13 harness modules to packages/harness/deerflow/ via git mv
- Move gateway + channels to app/ via git mv
- Rename all imports: src.* → deerflow.* (harness) / app.* (app layer)
- Set up uv workspace with deerflow-harness as workspace member
- Update langgraph.json, config.example.yaml, all scripts, Docker files
- Add build-system (hatchling) to harness pyproject.toml
- Add PYTHONPATH=. to gateway startup commands for app.* resolution
- Update ruff.toml with known-first-party for import sorting
- Update all documentation to reflect new directory structure

Boundary rule enforced: harness code never imports from app.
All 429 tests pass. Lint clean.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

* chore: add harness→app boundary check test and update docs

Add test_harness_boundary.py that scans all Python files in
packages/harness/deerflow/ and fails if any `from app.*` or
`import app.*` statement is found. This enforces the architectural
rule that the harness layer never depends on the app layer.

Update CLAUDE.md to document the harness/app split architecture,
import conventions, and the boundary enforcement test.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

* feat: add config versioning with auto-upgrade on startup

When config.example.yaml schema changes, developers' local config.yaml
files can silently become outdated. This adds a config_version field and
auto-upgrade mechanism so breaking changes (like src.* → deerflow.*
renames) are applied automatically before services start.

- Add config_version: 1 to config.example.yaml
- Add startup version check warning in AppConfig.from_file()
- Add scripts/config-upgrade.sh with migration registry for value replacements
- Add `make config-upgrade` target
- Auto-run config-upgrade in serve.sh and start-daemon.sh before starting services
- Add config error hints in service failure messages

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

* fix comments

* fix: update src.* import in test_sandbox_tools_security to deerflow.*

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

* fix: handle empty config and search parent dirs for config.example.yaml

Address Copilot review comments on PR #1131:
- Guard against yaml.safe_load() returning None for empty config files
- Search parent directories for config.example.yaml instead of only
  looking next to config.yaml, fixing detection in common setups

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

* fix: correct skills root path depth and config_version type coercion

- loader.py: fix get_skills_root_path() to use 5 parent levels (was 3)
  after harness split, file lives at packages/harness/deerflow/skills/
  so parent×3 resolved to backend/packages/harness/ instead of backend/
- app_config.py: coerce config_version to int() before comparison in
  _check_config_version() to prevent TypeError when YAML stores value
  as string (e.g. config_version: "1")
- tests: add regression tests for both fixes

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

* fix: update test imports from src.* to deerflow.*/app.* after harness refactor

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

---------

Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>

backend/docs/TITLE_GENERATION_IMPLEMENTATION.md

@@ -4,27 +4,27 @@
 
 ### 1. 核心实现文件
 
-#### [`src/agents/thread_state.py`](../src/agents/thread_state.py)
+#### [`packages/harness/deerflow/agents/thread_state.py`](../packages/harness/deerflow/agents/thread_state.py)
 - ✅ 添加 `title: str | None = None` 字段到 `ThreadState`
 
-#### [`src/config/title_config.py`](../src/config/title_config.py) (新建)
+#### [`packages/harness/deerflow/config/title_config.py`](../packages/harness/deerflow/config/title_config.py) (新建)
 - ✅ 创建 `TitleConfig` 配置类
 - ✅ 支持配置：enabled, max_words, max_chars, model_name, prompt_template
 - ✅ 提供 `get_title_config()` 和 `set_title_config()` 函数
 - ✅ 提供 `load_title_config_from_dict()` 从配置文件加载
 
-#### [`src/agents/title_middleware.py`](../src/agents/title_middleware.py) (新建)
+#### [`packages/harness/deerflow/agents/title_middleware.py`](../packages/harness/deerflow/agents/title_middleware.py) (新建)
 - ✅ 创建 `TitleMiddleware` 类
 - ✅ 实现 `_should_generate_title()` 检查是否需要生成
 - ✅ 实现 `_generate_title()` 调用 LLM 生成标题
 - ✅ 实现 `after_agent()` 钩子，在首次对话后自动触发
 - ✅ 包含 fallback 策略（LLM 失败时使用用户消息前几个词）
 
-#### [`src/config/app_config.py`](../src/config/app_config.py)
+#### [`packages/harness/deerflow/config/app_config.py`](../packages/harness/deerflow/config/app_config.py)
 - ✅ 导入 `load_title_config_from_dict`
 - ✅ 在 `from_file()` 中加载 title 配置
 
-#### [`src/agents/lead_agent/agent.py`](../src/agents/lead_agent/agent.py)
+#### [`packages/harness/deerflow/agents/lead_agent/agent.py`](../packages/harness/deerflow/agents/lead_agent/agent.py)
 - ✅ 导入 `TitleMiddleware`
 - ✅ 注册到 `middleware` 列表：`[SandboxMiddleware(), TitleMiddleware()]`
 
@@ -131,7 +131,7 @@ checkpointer = SqliteSaver.from_conn_string("checkpoints.db")
 // langgraph.json
 {
   "graphs": {
-    "lead_agent": "src.agents:lead_agent"
+    "lead_agent": "deerflow.agents:lead_agent"
   },
   "checkpointer": "checkpointer:checkpointer"
 }