[Soham Das (SohamDas2021)]

📖 Description

Prevents Bubblewrap workloads from running when network-rule installation fails. Startup failures now terminate the blocked sandbox and clean up its helpers before returning the original error.

Adds regression coverage for proxy-only and firewall-enforced networking through SDK run, spawn, and spawn_with_pty. The existing CLI failure-path assertion remains unchanged.

No design spec is required: this restores documented failure behavior without changing public APIs, request formats, or supported policy.

🔗 References

Fixes #1636.

🔍 Validation

Validated on WSL2 with Bubblewrap 0.9.0 and strict prerequisite checks enabled.

The existing CLI regression reproduced WORKLOAD_STARTED before the fix and passes unchanged afterward. The SDK regression checks the original error, absence of workload file writes, and descendant cleanup across all six network-mode/API combinations.

Commands run from src/:

Command	Result
cargo test --locked --quiet -p mxc-sdk --lib backend_modules::bubblewrap::common::proxy_network::	Passed: 170 tests
cargo test --locked --quiet -p mxc-sdk --lib backend_modules::bubblewrap::common::bwrap_runner::	Passed: 37 tests
cargo test --locked --quiet -p mxc-sdk --test streaming_bubblewrap	Passed: 17 tests
cargo test --locked --release --quiet -p mxc-sdk --test streaming_bubblewrap	Passed: 17 tests
cargo clippy --locked --quiet -p mxc-sdk --lib --test streaming_bubblewrap -- -D warnings	Passed
cargo fmt --all -- --check	Passed

From the repository root, with LXC_EXEC pointing to the release executable:

• timeout 90 bash tests/scripts/run_bwrap_namespace_startup_test.sh — passed three consecutive runs.

Remote CI and other Linux distributions were not run.

✅ Checklist

• Signed the Contributor License Agreement
• Linked to an issue
• For features or changes requiring a spec: linked the issue with maintainer-applied feature-accepted
• For implementation: linked the required approved and merged design/API spec, or explained why no spec is required
• Feature issue remains open unless this PR completes all agreed implementation, validation, and documentation
• Updated documentation (if applicable)
• Updated Copilot instructions (if build, architecture, or conventions changed)
• If this PR changes Cargo.lock, the dependency-feed-check check passes (see pull request builds)

📋 Issue Type

• Bug fix
• Feature
• Task

Microsoft Reviewers: Open in CodeFlow

[azure-pipelines]

Azure Pipelines:
There may be pipelines that require an authorized user to comment /azp run to run.

[Copilot]

🔵 Needs a closer look

Containment-sensitive startup and process-group cleanup changes need maintainer confirmation and broader Linux validation because runtime evidence is WSL2-only and Linux CI remains pending.

No open issues 🎉

What changed in this PR

Fixes #1636 by keeping Bubblewrap workloads blocked when network-rule installation fails, restoring fail-closed startup behavior without changing public APIs or request formats.

Changes:

• Terminates the sandbox process group before releasing the startup barrier and preserves the launcher for cleanup.
• Adds regression coverage for proxy-only and firewall-enforced failures through SDK run, spawn, and spawn_with_pty.
• Documents startup cleanup guarantees and validation coverage.

File	Description
src/​mxc-sdk/​tests/​streaming_bubblewrap.rs	Tests setup errors, absence of workload writes, and descendant cleanup across six combinations.
src/​mxc-sdk/​src/​backends/​bubblewrap/​common/​proxy_network.rs	Preserves startup-barrier ownership and avoids prematurely reaping the launcher.
src/​mxc-sdk/​src/​backends/​bubblewrap/​common/​bwrap_runner.rs	Kills the startup process group before dropping the barrier and reports cleanup errors.
docs/​development/​build-and-test/​ci-validation-infrastructure.md	Describes CLI and SDK startup-failure coverage.
docs/​backends/​bwrap/​bubblewrap-backend.md	Documents fail-closed startup and helper cleanup behavior.

_{Review effort: Balanced}

[Copilot]

🔵 Needs a closer look

Startup-barrier and process-group changes affect sandbox containment, requiring confirmation of strict Linux CI and namespace-startup validation on supported distributions because runtime validation was unavailable during review.

No open issues 🎉

_{Review effort: Balanced}