fix(ci): target managed Python wheel ABI

Assistant: codex
Assistant-Model: gpt-5.6-sol
Assistant-Session: 01a06ba0-10aa-7ea0-b20a-4f3fac39efe9

.forgejo/workflows/runtime-contract.yaml

@@ -67,5 +67,11 @@ jobs:
           git -C "${work_dir}/sand-boxer" checkout --detach "${sandbox_sha}"
 
           cd "${work_dir}/rein-aharness"
-          "${uv_bin}" sync --python "${python_bin}" --frozen --no-editable --extra glas --extra llm --extra dev
+          # uv itself is a static musl bootstrap binary so it can execute on
+          # the NixOS runner. The managed CPython ABI is GNU/Linux, which must
+          # be explicit or native wheels are selected for the bootstrap ABI.
+          "${uv_bin}" sync \
+            --python "${python_bin}" \
+            --python-platform x86_64-unknown-linux-gnu \
+            --frozen --no-editable --extra glas --extra llm --extra dev
           ./scripts/verify-runtime-contracts.sh