fix(bootstrap): add no-progress timeout to image build

[laitingsheng]

Summary

Wrap bollard's build_image() stream poll in tokio::time::timeout so a deadlocked Docker builder no longer hangs openshell sandbox create --from <Dockerfile> indefinitely. On macOS Colima with the default 2 vCPU / 2 GiB allocation, BuildKit reliably deadlocks partway through a multi-step build and the stream stops emitting events; without a timeout the caller waits forever for output that never arrives. The default threshold is 30 minutes, overridable via OPENSHELL_BUILD_NO_PROGRESS_TIMEOUT_SECS.

Related Issue

Refs NVIDIA/NemoClaw#2514 (sub-issue C: BuildKit deadlock has no timeout, openshell sandbox create waits forever).

Changes

• crates/openshell-bootstrap/src/build.rs:
  • New DEFAULT_BUILD_NO_PROGRESS_TIMEOUT_SECS = 1800 constant with a docstring covering the rationale (deadlock detection vs. headroom for legitimately quiet RUN steps, override env var for both directions).
  • Replaced the while let Some(result) = stream.next().await loop with a loop { match timeout(...).await { ... } } form. On Err(Elapsed) the function returns a miette error that names the threshold, points at docker info NCPU/MemTotal as the likely root cause, and tells the user how to relax the threshold if a legitimate build step is just quiet.
  • Inlined the env read directly (matches the existing connect_local_for_large_transfers() pattern in docker.rs:36-42 for OPENSHELL_DOCKER_TIMEOUT_SECS).
  • Reject zero-valued overrides (OPENSHELL_BUILD_NO_PROGRESS_TIMEOUT_SECS=0) so they fall back to the default instead of failing every build at 0s.
• architecture/sandbox-custom-containers.md: documents the new env var alongside the existing Dockerfile build-flow description.

Testing

• mise run pre-commit passes
• Unit tests added/updated
• E2E tests added/updated (if applicable)

Checklist

• Follows Conventional Commits
• Commits are signed off (DCO)
• Architecture docs updated (if applicable)