fix(swtbench): prevent build workflow from hanging indefinitely

[juanmichelini]

Summary

This PR addresses issue #400 where SWT-Bench image build workflows were hanging indefinitely (2+ hours) at the "Build and push SWT-Bench images" step, blocking evaluation runs.

Problem

SWT-Bench builds after 14:12 UTC on 2026-02-06 were freezing with no progress updates, while earlier builds completed successfully in ~10 minutes. The builds were consuming runner resources indefinitely and blocking evaluation pods.

Root Cause Analysis

Comparing the SWT-Bench workflow with the working SWE-Bench workflow revealed several missing safeguards:

1. No preflight step - SWE-Bench has a preflight step that prunes BuildKit cache and verifies disk space before building
2. No BUILDKIT_RESET_ON_FAILURE - SWE-Bench sets this env var to help recover from BuildKit failures
3. No timeout - Neither workflow had timeouts, but SWT-Bench was more susceptible to hangs
4. Per-ref concurrency - Concurrent builds on different refs could interfere with each other

Changes

1. Add preflight step to prune BuildKit cache and verify disk space

   • Matches the existing safeguard in build-swebench-images.yml
   • Prunes cache to 60GB max and checks for 75GB free space
   • Fails early if disk space is insufficient

2. Add timeout-minutes to build steps

   • 30 minutes for main image build (expected ~10 min)
   • 60 minutes for prebaked eval env images
   • Prevents indefinite hangs from blocking runners

3. Add BUILDKIT_RESET_ON_FAILURE=1 environment variable

   • Helps recover from BuildKit failures/corruption

4. Change concurrency group to global (not per-ref)

   • Prevents concurrent builds from interfering with each other
   • Uses cancel-in-progress: true to cancel old runs when new ones start

Testing

This is a workflow configuration change. The fix will be validated when the workflow runs in GitHub Actions. The changes align with the working SWE-Bench workflow configuration.

Fixes #400

@juanmichelini can click here to continue refining the PR