refactor(fingerprint): 移除请求头构建路径中的 per-key 指纹定制化注入

headers.py 删除 build_browser_fingerprint_headers / build_anthropic_extra_headers
函数及相关辅助，改为直接使用固定常量；PassthroughRequestBuilder 移除
Claude 格式的指纹注入步骤；Antigravity constants 移除 per-key 指纹
覆盖逻辑，统一使用进程级固定值。

src/services/provider/adapters/antigravity/constants.py

@@ -14,8 +14,6 @@ import uuid
 # ============== API 端点 ==============
 # 唯一定义在 core 层，此处 re-export 保持向后兼容
 from src.core.provider_templates.fixed_providers import ANTIGRAVITY_PROD_URL as PROD_BASE_URL
-from src.services.provider.fingerprint import resolve_platform_token
-from src.services.provider.request_context import get_current_fingerprint
 
 DAILY_BASE_URL = "https://daily-cloudcode-pa.googleapis.com"
 SANDBOX_BASE_URL = "https://daily-cloudcode-pa.sandbox.googleapis.com"
@@ -114,43 +112,17 @@ URL_UNAVAILABLE_TTL_SECONDS = 300  # 5 分钟
 _SESSION_ID = uuid.uuid4().hex  # 每次进程启动生成一个固定 session ID
 
 
-def _normalize_node_version(raw: str | None) -> str:
-    text = str(raw or "").strip()
-    if text.startswith(("v", "V")):
-        text = text[1:]
-    return text or "18.18.2"
-
-
 def get_v1internal_extra_headers() -> dict[str, str]:
     """构建 v1internal 请求需要的额外 header（对齐 AM upstream/client.rs）。"""
-    fp = get_current_fingerprint()
     with _ua_lock:
         version = _ua_version
 
-    user_agent = get_http_user_agent()
-    session_id = _SESSION_ID
-    node_version = "18.18.2"
-
-    if fp:
-        user_agent = _build_antigravity_http_user_agent(
-            platform_token=resolve_platform_token(
-                platform_info=fp.platform_info,
-                stainless_os=fp.stainless_os,
-                stainless_arch=fp.stainless_arch,
-            ),
-            version=version,
-            chrome_version=fp.chrome_version or _FALLBACK_CHROME,
-            electron_version=fp.electron_version or _FALLBACK_ELECTRON,
-        )
-        session_id = fp.vscode_session_id or _SESSION_ID
-        node_version = _normalize_node_version(fp.node_version)
-
     return {
-        "User-Agent": user_agent,
+        "User-Agent": get_http_user_agent(),
         "x-client-name": "antigravity",
         "x-client-version": version,
-        "x-vscode-sessionid": session_id,
-        "x-goog-api-client": f"gl-node/{node_version} fire/0.8.6 grpc/1.10.x",
+        "x-vscode-sessionid": _SESSION_ID,
+        "x-goog-api-client": "gl-node/18.18.2 fire/0.8.6 grpc/1.10.x",
     }