feat: route SBOM writes to Nexus behind flag

Assistant: codex
Assistant-Model: gpt-5.6-sol
Assistant-Session: 01a028f0-a42f-7582-89a8-ebaad7343834

api/services/sbom_nexus.py

@@ -21,12 +21,18 @@ def reads_from_nexus() -> bool:
     return settings.sbom_nexus_read_mode == "nexus"
 
 
-async def get_json(
+def writes_to_nexus() -> bool:
+    return settings.sbom_nexus_write_mode == "nexus"
+
+
+async def request_json(
+    method: str,
     path: str,
     *,
     params: dict[str, Any] | None = None,
+    body: dict[str, Any] | None = None,
 ) -> Any:
-    """Fetch one Nexus resource; never fall back silently to legacy storage."""
+    """Call Nexus; never fall back silently to legacy storage."""
     if not settings.sbom_nexus_url:
         raise SBOMNexusError(503, "SBOM Nexus read mode is enabled without SBOM_NEXUS_URL")
 
@@ -35,7 +41,7 @@ async def get_json(
             base_url=settings.sbom_nexus_url.rstrip("/"),
             timeout=settings.sbom_nexus_timeout_seconds,
         ) as client:
-            response = await client.get(path, params=params)
+            response = await client.request(method, path, params=params, json=body)
     except httpx.RequestError as exc:
         raise SBOMNexusError(502, f"SBOM Nexus is unavailable: {exc.__class__.__name__}") from exc
 
@@ -54,3 +60,11 @@ async def get_json(
         return response.json()
     except ValueError as exc:
         raise SBOMNexusError(502, "SBOM Nexus returned invalid JSON") from exc
+
+
+async def get_json(path: str, *, params: dict[str, Any] | None = None) -> Any:
+    return await request_json("GET", path, params=params)
+
+
+async def post_json(path: str, *, body: dict[str, Any]) -> Any:
+    return await request_json("POST", path, body=body)