feat: add ai writing imitation mode

offline-backend-20260512/backend/CLAUDE.md

@@ -273,6 +273,8 @@ The AI-writing graph (`packages/harness/deerflow/agents/ai_writing/`) has four s
 
 Seeding mirrors the roundtable pattern: verified `config.yaml` + `SOUL.md` ship in `app/gateway/routers/_ai_writing_seed_assets/<id>/`; `_ai_writing_seed.py::ensure_ai_writing_functional_agents()` copies them to `.deer-flow/agents/` when missing (never overwrites local edits), called from the startup lifespan (before `_sync_legacy_agents`, so the agents appear in `/api/agents` on first boot) and self-heals from `GET /api/ai-writing/sessions` + `GET /api/ai-writing/article-types`. Tests: `tests/test_ai_writing_seed.py`, `tests/test_ai_writing_agent_runner.py`.
 
+**Sample imitation mode (样文仿写).** The initial writing form supports `writing_mode_type=imitate`: the user can paste sample text or upload Word/PDF/Markdown/TXT. `POST /api/ai-writing/sample/extract` converts supported document files to Markdown via `deerflow.utils.file_conversion` and returns capped plain text to the frontend. The LangGraph entry point now starts at `sample_analyzer` before `intent_parser`; non-imitation sessions return immediately, while imitation sessions analyze up to 12k chars into `sample_style_profile` (`SampleStyleProfile` in `state.py`) and emit `sample_profile_ready`. `writer_outline` and `writer_draft` call `render_sample_style_section(state)` so both outline planning and section drafting receive the same style profile, imitation strength (`light|medium|strong`), optional structure-preservation preference, and guardrails: learn structure/tone/paragraph rhythm/sentence style, but do not copy sample sentences, proprietary facts, people, organizations, cases, or data. Frontend state mirrors this with `analyzing_sample`, uploaded/pasted sample controls, history/timeline restoration of `sampleStyleProfile`, and the setup-chat direct-start path preserves the same fields. Tests live with the knowledge-base AI-writing tests (`tests/test_ai_writing_knowledge_base.py`).
+
 **Skill-driven retrieval (检索类型).** `material_source` has three values: `general` (通用检索, default), `knowledge_base` (知识库检索), and `notebook` (我的空间); legacy `skill` is normalized to `general` by the researcher node. **`knowledge_base` 直连内网 ES 接口（= 旧版「内网直连检索」）** — it bypasses skill orchestration entirely and calls `IntranetSearchProvider` over `ai_writing.intranet_search_url` (concurrent over the generated keywords; `intranet_knowledge_base`/`intranet_search_timeout` apply). **An empty/unconfigured `intranet_search_url` does NOT disable it** — the empty string is passed straight to `IntranetSearchProvider`, which falls back to its built-in default endpoint (`intranet_stub._DEFAULT_ENDPOINT`), exactly like the legacy `get_search_provider(search_provider=intranet)` path. So 内网直连检索 works out of the box without configuring an address (configure `intranet_search_url` only to point at a different endpoint). This is the "弱模型识别不了技能" escape hatch — the old no-skill retrieval path restored as an explicit option (weak models like deepseek-chat often fail to invoke configured skills). Tests: `tests/test_ai_writing_knowledge_base.py`. General retrieval is orchestrated from the **skills configured on the `ai-writing-researcher` agent** (`config.yaml → skills`, editable from the agent management page): the built-in `knowledge-base-search` skill (知识库检索) runs the native keyword fan-out web/intranet search (the old default path), while any other configured skill searches with a `description`-targeted query; skills run in configured order with early-stop at `max_materials`, and an empty/unresolvable skills config falls back to the built-in knowledge search so retrieval always works. The skill itself is seeded from `_ai_writing_seed_assets/skills/knowledge-base-search/SKILL.md` into `skills/public/` (never overwrites), and a pre-existing researcher `config.yaml` lacking the `skills` key is patched in place with the default (explicit `skills: []` is respected). **PAUSE-1 input append flow**: when the user types natural language into the material-confirm input (`re_search`/legacy `enable_skill_search` + `user_query`), the node matches the most relevant configured skill via `SkillPicker(candidates=…)` (skipped when only one skill is configured), searches with the user's words, and **appends** the new materials to the existing package (URL-dedup, original order preserved, no LLM re-rank/truncation, 100-item hard cap). **Skill-failure fault tolerance**: a configured skill that times out / raises / has all its keyword searches fail (vs. legitimately returning 0 results) no longer just silently moves on — the researcher node emits a `skill_search_step` of type `skill_error` (carrying the error `reason`), and if the configured skills collected **no** new materials at all it runs a `fallback` pass over other available skills (`_fallback_candidate_skills`: the built-in `knowledge-base-search` native path first, then other enabled catalog skills not yet tried) instead of erroring out. The frontend `SkillStepsCard` renders `skill_error` (rose) and `fallback` (amber) so the timeline shows "技能报错 → 改用其他技能搜集". Tests: `tests/test_ai_writing_material_source.py`.
 
 **Skill-call timeout** is hardcoded **300s (5 min)** — `researcher.py` `_SKILL_SEARCH_TIMEOUT_SECONDS` (per-skill wrapper) and `_skill_agent.py` `_REAL_AGENT_TIMEOUT_SECONDS` (whole real-agent skill run). The intranet ES fallback (`IntranetSearchProvider`) gets a longer **600s (10 min)** default (`intranet_stub.py`; overridable via `ai_writing.intranet_search_timeout`) — that interface is the slow one, so our own fallback timeout is generous to avoid being blamed for "检不出".