LLM 호출 규격 전환: 고객사 사내 LLM(FabriX/Gauss) 헤더 지원 (LLM_PROVIDER=fabrix)

- settings: LLM_PROVIDER/LLM_CHAT_PATH/LLM_BODY_MODEL/LLM_JSON_MODE/LLM_MAX_TOKENS, FABRIX_* 3종, llm_enabled()
- llm_client: headers()/body() 를 규격별로 구성. fabrix 는 x-openapi-token(Bearer)/x-generative-ai-client/
  x-llm-model-id/x-generative-ai-user-email, body model 은 LLM_BODY_MODEL
- summarize/ping: 접속 점검 명령 (--show 로 요청만 확인)
- docs/llm-provider-plan.md: 계획·.env 값·오류별 조치. 기본값은 openai 라 기존 동작 불변

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

tests/test_llm_backends.py

@@ -201,3 +201,65 @@ def test_ingest_backend_file_queues_without_key(api_client, monkeypatch):
     q = c.get("/summaries/jobs").json()
     assert q["pending"] >= 1, q
     assert any(n["task"] == "program_summary" for n in q["next"]), q
+
+
+# ------------------------------------------------------------------ 호출 규격 (LLM_PROVIDER)
+
+def _configure(monkeypatch, **kw):
+    from config.settings import settings
+    base = {"llm_base_url": "http://x", "llm_api_key": "", "llm_provider": "openai",
+            "llm_chat_path": "/chat/completions", "llm_body_model": "", "llm_json_mode": True,
+            "llm_max_tokens": 0, "llm_model": "m", "fabrix_client_key": "", "fabrix_openapi_token": "",
+            "fabrix_user_email": ""}
+    base.update(kw)
+    for k, v in base.items():
+        monkeypatch.setattr(settings, k, v)
+
+
+def test_openai_provider_headers_and_body(monkeypatch):
+    from summarize import llm_client
+    _configure(monkeypatch, llm_api_key="k", llm_max_tokens=800)
+    c = llm_client.OpenAICompatClient()
+    assert c.url == "http://x/chat/completions"
+    assert c.headers() == {"Content-Type": "application/json", "Authorization": "Bearer k"}
+    b = c.body("s", "u")
+    assert b["model"] == "m" and b["response_format"] == {"type": "json_object"} and b["max_tokens"] == 800
+
+
+def test_fabrix_provider_headers_and_body(monkeypatch):
+    from summarize import llm_client
+    _configure(monkeypatch, llm_provider="fabrix", llm_base_url="https://h/dxhq/prod/api-llm",
+               llm_chat_path="", llm_model="581", llm_body_model="/mnt/models", llm_json_mode=False,
+               fabrix_client_key="CK", fabrix_openapi_token="TOK", fabrix_user_email="me@x.com")
+    c = llm_client.OpenAICompatClient()
+    assert c.url == "https://h/dxhq/prod/api-llm"           # 완성 주소면 경로를 안 붙인다
+    h = c.headers()
+    assert h["x-openapi-token"] == "Bearer TOK"              # Bearer 접두를 코드가 붙인다
+    assert h["x-generative-ai-client"] == "CK"
+    assert h["x-llm-model-id"] == "581"
+    assert h["x-generative-ai-user-email"] == "me@x.com"
+    assert "Authorization" not in h
+    b = c.body("s", "u")
+    assert b["model"] == "/mnt/models" and "response_format" not in b and "max_tokens" not in b
+
+
+def test_fabrix_keeps_existing_bearer_prefix(monkeypatch):
+    from summarize import llm_client
+    _configure(monkeypatch, llm_provider="fabrix", fabrix_client_key="CK", fabrix_openapi_token="Bearer TOK")
+    assert llm_client.OpenAICompatClient().headers()["x-openapi-token"] == "Bearer TOK"
+
+
+def test_provider_requires_its_credentials(monkeypatch):
+    from config.settings import settings
+    from summarize import llm_client
+    _configure(monkeypatch, llm_provider="fabrix")            # 키 없음
+    with pytest.raises(RuntimeError):
+        llm_client.OpenAICompatClient()
+    assert settings.llm_enabled() is False
+    _configure(monkeypatch, llm_provider="fabrix", fabrix_client_key="a", fabrix_openapi_token="b")
+    assert settings.llm_enabled() is True
+    _configure(monkeypatch, llm_provider="openai")            # api key 없음
+    assert settings.llm_enabled() is False
+    _configure(monkeypatch, llm_provider="bogus", llm_api_key="k")
+    with pytest.raises(RuntimeError):
+        llm_client.OpenAICompatClient()