chore: migrate Rust server runtime images from debian:trixie-slim to ubi-minimal

[claudia-gray]

Pull Request

🔗 Related Issue

Closes #5403

---

📝 Summary

Migrates the runtime stage of all Rust server container build files from debian:trixie-slim to registry.access.redhat.com/ubi10/ubi-minimal:10.2-1777462752.

Affected files:

• a2a-agents/rust/a2a-echo-agent/Dockerfile
• mcp-servers/rust/benchmark-server/Dockerfile
• mcp-servers/rust/benchmark-server/Containerfile
• mcp-servers/rust/fast-time-server/Dockerfile
• mcp-servers/rust/fast-time-server/Containerfile
• mcp-servers/rust/slow-time-server/Containerfile

The builder stages are unaffected — they remain on rust:*-slim. Only the runtime stages change. apt-get is replaced with microdnf and shadow-utils is added to provide useradd. Aligns them with the rest of the project (the main Containerfile, nginx, Go servers all already use UBI).

---

📏 Reviewability

• This PR has one clear purpose
• The linked issue is not labeled triage
• Unrelated bugs or improvements are tracked in separate issues/PRs
• If AI-assisted, I understand and can explain the generated changes

---

🏷️ Type of Change

• Bug fix
• Feature / Enhancement
• Documentation
• Refactor
• Chore (deps, CI, tooling)
• Other (describe below)

---

🧪 Verification

Check	Command	Status
Build image	docker build --no-cache -f a2a-agents/rust/a2a-echo-agent/Dockerfile .	✅
Health endpoint	curl -sf http://localhost:9199/health	✅ {"name":"a2a-echo-agent","status":"healthy","version":"0.1.0"}
Non-root user	docker run --rm --entrypoint whoami <image>	✅ mcpuser
Lint suite	make lint
Unit tests	make test
Coverage ≥ 80%	make coverage

---

✅ Checklist

• Code formatted (make black isort pre-commit)
• No secrets or credentials committed

---

📓 Notes (optional)

Will negate:

• Internal issue
• Internal issue

[ja8zyjits]

LGMT
only rust mcp server examples and a2a-agents affected.

[lucarlig]

LGTM
some of the image do not build but this is from previous issues that i will fix in #5299
let's get this merged so i can rebase on top of it and fix the images