feat: build lightweight benchmark images by default

[simonrosenberg]

Summary

• Add --agent-type CLI flag to SWE-bench and SWT-bench image build scripts
• Thread extra_build_args through the full call chain: build_all_images → _build_with_logging → build_image → SDK BuildOptions
• Both workflows default agent-type to "default", which skips ACP and boto3 installation
• Can be toggled via workflow dispatch input (agent-type: acp-claude or acp-codex) when ACP images are needed

Changes

• benchmarks/utils/build_utils.py: LIGHTWEIGHT_BUILD_ARGS / ACP_BUILD_ARGS constants, --agent-type CLI flag, build_args_for_agent_type() helper, extra_build_args parameter threaded through all build functions
• benchmarks/swebench/build_images.py: Pass lightweight build args to build_all_images
• benchmarks/swtbench/build_images.py: Same
• .github/workflows/build-swebench-images.yml: agent-type input (default default), passed as --agent-type flag
• .github/workflows/build-swtbench-images.yml: Same
• vendor/software-agent-sdk: Updated to SDK main (62c2e7cf) which includes extra_build_args support (#2541), optional ACP (#2535), and optional boto3 (#2536)

Expected impact (from analysis of 433-image build logs, #537)

Dependency skipped	Per-image saving	Cumulative (433 imgs)
npm ACP + nodejs	~32s install + ~4s export/push	4.5h
boto3/botocore	~3s export/push	0.4h
Total	~36s/image	~4.9h cumulative

Wall-clock improvement: ~1.4–2.5h (at 3.5× effective parallelism), plus non-linear savings from reduced disk pressure.

SDK dependencies (all merged to main)

• feat(docker): make ACP npm package installation optional via build arg software-agent-sdk#2535 — INSTALL_ACP Dockerfile ARG
• feat(docker): make boto3 installation optional via build arg software-agent-sdk#2536 — INSTALL_BOTO3 Dockerfile ARG
• feat(docker): add extra_build_args to BuildOptions software-agent-sdk#2541 — extra_build_args on BuildOptions

Relation to #548

This is a slimmed-down version of #548 that works with SDK main today. It excludes INSTALL_BROWSER (browser-use optional support hasn't been merged to the SDK yet). Once browser-use lands, a follow-up can add INSTALL_BROWSER: "false" to LIGHTWEIGHT_BUILD_ARGS.

Test plan

• Run SWT-bench build with --agent-type default on 4–10 images to verify builds succeed
• Verify image can run a basic SWT-bench evaluation
• Run with --agent-type acp-claude to verify ACP images still build correctly
• Full 433-image build to measure actual wall-clock improvement

Closes #537

🤖 Generated with Claude Code

[all-hands-bot]

🟡 Taste Rating: Acceptable - Pragmatic solution to a real problem (4.9h build savings), but parameter defaulting needs cleanup.

Verdict: ✅ Core logic is sound. The config threading is straightforward. Fix the inconsistent defaults and this is good to merge.

[all-hands-bot]

🟢 Good taste - Pragmatic solution to a real problem (4.9h build savings) with clean execution.

Previous review issues resolved:

• Consistent defaulting throughout: All functions now default extra_build_args to LIGHTWEIGHT_BUILD_ARGS instead of None
• Eliminated unnecessary conditionals

Implementation is solid:

• Simple, straightforward parameter threading
• Clean constants with clear documentation
• build_args_for_agent_type() uses startswith() pattern that allows future extensions
• No special cases, no unnecessary complexity

Minor observation (not blocking):
Mutable dict as default argument is technically a Python code smell, but it's pragmatic here since:

• Functions don't mutate, just pass through to SDK
• Constants use SCREAMING_SNAKE_CASE signaling immutability
• Making them immutable would add complexity without solving a real problem

✅ Verdict: Ship it