feat(US1): text triple extraction — POST /api/v1/text/extract

- app/models/text_models.py: TripleItem, SourceOffset, TextExtract{Request,Response}
- app/services/text_service.py: TXT/PDF/DOCX parsing + LLM call + JSON parse
- app/routers/text.py: POST /text/extract handler with Depends injection
- tests/test_text_service.py: 6 unit tests (formats, errors)
- tests/test_text_router.py: 4 router tests (200, 400, 502×2)
- 10/10 tests passing

app/services/text_service.py

@@ -0,0 +1,95 @@
+import io
+
+import pdfplumber
+import docx
+
+from app.clients.llm.base import LLMClient
+from app.clients.storage.base import StorageClient
+from app.core.config import get_config
+from app.core.exceptions import UnsupportedFileTypeError
+from app.core.json_utils import extract_json
+from app.core.logging import get_logger
+from app.models.text_models import (
+    SourceOffset,
+    TextExtractRequest,
+    TextExtractResponse,
+    TripleItem,
+)
+
+logger = get_logger(__name__)
+
+_SUPPORTED_EXTENSIONS = {".txt", ".pdf", ".docx"}
+
+_DEFAULT_PROMPT = (
+    "请从以下文本中提取知识三元组，以 JSON 数组格式返回，每条包含字段："
+    "subject（主语）、predicate（谓语）、object（宾语）、"
+    "source_snippet（原文证据片段）、source_offset（{{start, end}} 字符偏移）。\n\n"
+    "文本内容：\n{text}"
+)
+
+
+def _file_extension(file_name: str) -> str:
+    idx = file_name.rfind(".")
+    return file_name[idx:].lower() if idx != -1 else ""
+
+
+def _parse_txt(data: bytes) -> str:
+    return data.decode("utf-8", errors="replace")
+
+
+def _parse_pdf(data: bytes) -> str:
+    with pdfplumber.open(io.BytesIO(data)) as pdf:
+        pages = [page.extract_text() or "" for page in pdf.pages]
+    return "\n".join(pages)
+
+
+def _parse_docx(data: bytes) -> str:
+    doc = docx.Document(io.BytesIO(data))
+    return "\n".join(p.text for p in doc.paragraphs)
+
+
+async def extract_triples(
+    req: TextExtractRequest,
+    llm: LLMClient,
+    storage: StorageClient,
+) -> TextExtractResponse:
+    ext = _file_extension(req.file_name)
+    if ext not in _SUPPORTED_EXTENSIONS:
+        raise UnsupportedFileTypeError(f"不支持的文件格式: {ext}")
+
+    cfg = get_config()
+    bucket = cfg["storage"]["buckets"]["source_data"]
+    model = req.model or cfg["models"]["default_text"]
+
+    data = await storage.download_bytes(bucket, req.file_path)
+
+    if ext == ".txt":
+        text = _parse_txt(data)
+    elif ext == ".pdf":
+        text = _parse_pdf(data)
+    else:
+        text = _parse_docx(data)
+
+    prompt_template = req.prompt_template or _DEFAULT_PROMPT
+    prompt = prompt_template.format(text=text) if "{text}" in prompt_template else prompt_template + "\n\n" + text
+
+    messages = [{"role": "user", "content": prompt}]
+    raw = await llm.chat(model, messages)
+
+    logger.info("text_extract", extra={"file": req.file_name, "model": model})
+
+    items_raw = extract_json(raw)
+    items = [
+        TripleItem(
+            subject=item["subject"],
+            predicate=item["predicate"],
+            object=item["object"],
+            source_snippet=item["source_snippet"],
+            source_offset=SourceOffset(
+                start=item["source_offset"]["start"],
+                end=item["source_offset"]["end"],
+            ),
+        )
+        for item in items_raw
+    ]
+    return TextExtractResponse(items=items)