Summary

When [flux_sandbox] use_tls = true, the first asynchronous lifecycle operation fails before issuing its RPC: _ensure_channel() calls grpc.aio.ssl_channel_credentials(), which does not exist. With the locked grpcio 1.82.1 dependency this raises AttributeError. The synchronous provider already uses the correct shared credentials factory.

Use grpc.ssl_channel_credentials() with grpc.aio.secure_channel(). Preserve lazy initialization, channel reuse, timeout/auth settings and the plaintext path. Add regression coverage for real synchronous/asynchronous channel initialization with TLS enabled and disabled, and document the existing Flux TLS option.

This issue was found in the current GitCode branch, with no linked Issue. All 11 historical GitCode PRs were checked by title, with discussion pages and current file history reviewed. Publication-time API checks found no open PRs or prior contributions by this account. Some historical web discussions are collapsed, so this is not an exhaustive check of all inline comments or off-platform work.

Testing

• Unit tests: baseline provider tests 1 failed / 9 passed; after the fix, provider + Flux snapshot runtime + runtime resolver tests 34 passed.
• Changed Python files pass ruff check; pip check and git diff --check pass.
• Documentation: pnpm install --frozen-lockfile, pnpm docs:build pass.
• Integration tests
• e2e / manual verification

From server/, with project dependencies prepared:

PYTHONPATH=. python -m pytest tests/test_flux_sandbox_provider.py tests/test_flux_snapshot_runtime.py tests/test_runtime_resolver.py -q
python -m ruff check opensandbox_server/services/flux/flux_sandbox_provider.py tests/test_flux_sandbox_provider.py

Environment: Python 3.11.9; runtime/test dependencies constrained to server/uv.lock versions through pip in an isolated environment because uv was unavailable. No lockfile or dependency declaration changes. Tests construct real gRPC channels and stubs but do not establish a TLS handshake or invoke a live controller. Existing pause/resume tests mock RPC methods. The full server suite, deployment and GitCode CI have not been run. Existing dependency deprecation warnings remain.

Breaking Changes

• None
• Yes (describe impact and migration path)

Checklist

• Linked Issue or clearly described motivation
• Added/updated docs (if needed)
• Added/updated tests (if needed)
• Security impact considered: retains the secure channel and default trust roots; does not disable verification or fall back to plaintext.
• Backward compatibility considered: no API/config shape or default changes.