refactor(docker): tighten binary perms via --chown + 0550

Replace `COPY --chmod=755` with `COPY --chown=<user> --chmod=0550` in
the gateway and supervisor Dockerfiles. The binary is no longer
world-readable or world-executable; ownership is pinned to the runtime
user.

- Gateway uses `--chown=nvs:nvs` + `USER nvs:nvs`, matching the only
  non-root user defined in `nvcr.io/nvidia/distroless/cc` (UID 1000) and
  the Helm chart's `securityContext.runAsUser: 1000`, which overrides
  the Dockerfile USER at runtime.
- Supervisor uses numeric `--chown=65534:65534` because the scratch base
  has no `/etc/passwd` for name resolution. The supervisor image is
  only consumed by the init-container copy-self path; the destination
  pod's runAsUser governs execute access.

Validated by deploying to a local k3d cluster via `helm:skaffold:run`
and confirming the gateway StatefulSet reaches 1/1 Running.

Author: TaylorMutch

deploy/docker/Dockerfile.gateway

@@ -26,11 +26,15 @@ ARG TARGETARCH
 
 WORKDIR /app
 
-# --chmod=755 preserves the executable bit through actions/upload-artifact +
-# download-artifact, which strip exec perms during the roundtrip.
-COPY --chmod=755 deploy/docker/.build/prebuilt-binaries/${TARGETARCH}/openshell-gateway /usr/local/bin/openshell-gateway
-
-USER 65532:65532
+# --chmod=0550 preserves the executable bit through actions/upload-artifact +
+# download-artifact (which strip exec perms during the roundtrip) without
+# granting world-execute. --chown=nvs:nvs matches the image's only defined
+# non-root user (`nvs:1000`, the NVIDIA distroless convention) and aligns
+# with the Helm chart's `securityContext.runAsUser: 1000`, which overrides
+# the Dockerfile's USER at runtime.
+COPY --chown=nvs:nvs --chmod=0550 deploy/docker/.build/prebuilt-binaries/${TARGETARCH}/openshell-gateway /usr/local/bin/openshell-gateway
+
+USER nvs:nvs
 EXPOSE 8080
 
 ENTRYPOINT ["/usr/local/bin/openshell-gateway"]

deploy/docker/Dockerfile.supervisor

@@ -23,8 +23,12 @@ FROM scratch AS supervisor
 
 ARG TARGETARCH
 
-# --chmod=755 preserves the executable bit through actions/upload-artifact +
-# download-artifact, which strip exec perms during the roundtrip.
-COPY --chmod=755 deploy/docker/.build/prebuilt-binaries/${TARGETARCH}/openshell-sandbox /openshell-sandbox
+# --chmod=0550 preserves the executable bit through actions/upload-artifact +
+# download-artifact (which strip exec perms during the roundtrip) without
+# granting world-execute. --chown uses numeric 65534:65534 (nobody:nobody)
+# because scratch has no /etc/passwd to resolve a named user against. This
+# scratch image is only consumed by the init-container copy-self path, so
+# the destination pod's USER governs what can execute the binary.
+COPY --chown=65534:65534 --chmod=0550 deploy/docker/.build/prebuilt-binaries/${TARGETARCH}/openshell-sandbox /openshell-sandbox
 
 ENTRYPOINT ["/openshell-sandbox"]