[chaliy]

Requested by Михайло · project thread

Large command output can now be written in full to a file on the virtual filesystem as the command runs, and the Deep Agents backend uses this to keep big execute results greppable.

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What changed

• Core: Execution::output_file(path, max_bytes). Combined stdout and stderr are written, in the order they're produced, into a VFS file that is created (or truncated) before the script runs.
  • The file is bounded by its own byte cap and FsLimits, not by max_stdout_bytes/max_stderr_bytes. The bytes stay in the sandbox, the same as a { script; } > file 2>&1 redirect. capture and the sinks keep the in-memory caps.
  • If the filesystem refuses a write (for example a size limit), the tee stops but the call still succeeds.
  • The script runs in the current shell, so cd, export and functions carry over to the next call.
• Python: Bash/BashTool execute and execute_sync accept output_file= and max_output_file_bytes= (absolute VFS path, 10 MiB default). These can't be combined with on_output.
• Deep Agents: BashkitBackend now subclasses BaseSandbox with enable_capture_offload = True, because the framework only offers capture to BaseSandbox types.
  • execute_with_offload/aexecute_with_offload use the native file output instead of the upstream bash wrapper. That wrapper's ( eval … ) subshell would drop shell state between commands.
  • Small output is returned whole and the file is removed. Large output stays at /large_tool_results/<id>, with the same head/tail preview and clip notices as upstream.
  • Every inherited shell or python3 helper, including als/awrite/aedit, is overridden with direct VFS code.

Why

Today, large execute output passes through Bashkit's 1 MB in-memory stdout limit before deepagents saves it to a file, so anything past 1 MB is lost. Upstream's capture wrapper avoids that, but it runs the command in a subshell, which would break Bashkit's persistent shell. Writing to the file natively keeps up to 10 MB and keeps the shell state.

Before / After

	Before (main)	After
3 MB of output through the agent's execute	Cut at 1 MB in memory; deepagents' fallback saves what's left	All 3 MB saved at /large_tool_results/<id>; model gets a head/tail preview
cd /tmp; export K=1 in a large-output command, then echo $K $PWD	1 /tmp	1 /tmp (no subshell)
execute_sync(cmd, output_file="/tmp/o.log")	n/a	/tmp/o.log holds 3,000,004 bytes while stdout is capped at 1 MiB with stdout_truncated=True

Tests:

• New Rust integration tests in output_file_tests: output beyond the stdout cap plus shell state, the file's own cap and truncation of old content, FsLimits bounding without failing the call, and rejection of relative or missing-parent paths.
• New Python tests: offload keeps the full output and stays greppable, the inline, capped and timeout cases, and the real create_deep_agent loop offloading 2 MB.
• pytest crates/bashkit-python/tests: 975 passed, 2 skipped. The three suites that need the bashkit_random_fs fixture crate were not run locally.
• clippy (including --no-default-features), cargo doc -D warnings --all-features, ruff, just check-okf and just check-doc-links are clean.

Risk

• Medium-low.
• This is a new host-requested write path that is not subject to the in-memory output caps. It is bounded by its cap and FsLimits, and is noted in TM-DOS-058.
• BashkitBackend's base class changes to BaseSandbox. All of that class's execute-based helpers are overridden.

Checklist

• Tests added or updated
• Backward compatibility considered (additive APIs; the backend's public methods are unchanged)

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