Arbor agent executor

Arbor Executor

Use this when a pending Idea Tree leaf is selected for implementation.

Dispatch Contract

The executor receives:

• Isolated worktree path and experiment branch.
• Node id and exact hypothesis.
• Evaluation info from tree metadata with {cwd} and {node_id} substituted.
• Ancestor insights.
• Additional context from the coordinator.

The executor must implement the assigned idea faithfully. It may choose how to implement the idea, but it must not silently switch to a different direction.

Worktree Lifecycle

Native RunExecutor does this automatically:

1. Validate node exists and is pending or running.
2. Enforce leaf-only dispatch when max_tree_depth is set.
3. Mark node running.
4. Create a git worktree from current trunk.
5. Run the executor agent in that worktree.
6. Finalize useful code changes with a commit.
7. Snapshot plugin outputs such as submission.csv if configured.
8. Remove the worktree but preserve the experiment branch.
9. Parse the executor report.
10. Update the node as done with score, insight, result, and code_ref.
11. Save experiment artifacts under experiments/<node_id>/.
12. Propagate insights upward.

When emulating manually, do the same sequence. Use arbor-agent-tools for prompt generation and tree updates.

Executor Workflow

The executor follows this loop:

1. Understand: read relevant files before editing.
2. Implement: make the idea active in code.
3. Validate implementation: run 2-3 small representative checks.
4. Iterate until solid: fix bugs and integration misses before judging the idea.
5. Evaluate: run the full B_dev eval once implementation is credible.
6. Report: include changes, baseline vs result, absolute score, and insight.

A bad score is useful only if the implementation was correct. Do not conclude an idea failed from broken code.

Evaluation Rules

• Use B_dev only. Never run B_test during routine executor work.
• Use the eval command injected from metadata. It should already target the executor worktree after {cwd} substitution.
• Save results to results/<node_id>-<brief-description>/.
• Report absolute score, not delta.
• If full eval is expensive, run smoke/subset checks first, then full eval when code is correct.

In smoke-only forward tests, the executor is not a real implementer. Do not edit source, create a real worktree, commit, run training, or run the real eval command. Generate a smoke prompt, save it as an artifact, and record a mocked or cached-score report that is clearly labelled as plumbing evidence only.

Long Commands

Use RunTraining semantics for long training/eval commands:

• Under 5 minutes: normal shell/Bash is acceptable.
• 5 minutes or more: use RunTraining or the host equivalent with a generous timeout.
• Do not use sleep && tail polling loops.
• If timeout occurs, inspect partial metrics, logs, checkpoints, and decide whether to resume, reduce scope, debug, or report timeout as evidence.

For MLE/Kaggle, estimate:

estimated_time = epochs * sec_per_epoch * num_folds * 1.3

If it exceeds 70 percent of executor budget, scale down before continuing.

Report Schema

The coordinator extracts:

{
  "score": 45.2,
  "insight": "1-3 sentence key learning",
  "result": "1-2 sentence factual outcome",
  "code_ref": "experiment branch or null"
}

Make the final report easy to parse:

• Idea
• Changes
• Implementation Choices
• Baseline vs Result
• Score
• Analysis
• Insights

Parallel Dispatch

Use parallel dispatch for 2-4 independent pending leaves. Do not parallelize GPU-heavy or mutually competing experiments unless budget permits. Validate all nodes before launching. Respect human review gates and cycle caps.

Manual Emulation

If native RunExecutor is unavailable:

1. Create a worktree/branch or copy the repo if worktrees are unsafe.
2. Generate the prompt from the main session while substituting the executor worktree as {cwd}:

   python <tools>/arbor_state.py prompt-executor --cwd <project> --run-name <run> \
     --node-id <id> --workdir <worktree> \
     --output <project>/.arbor/sessions/<run>/experiments/<id>/executor_prompt.md
   

   For smoke/forward tests, add --smoke and include smoke-only additional context.
3. Launch a fresh agent in that worktree with the generated prompt.
4. Run B_dev from the worktree. With the fallback helper, keep session state in <project> and run the command in <worktree>:

   python <tools>/arbor_state.py eval --cwd <project> --run-name <run> \
     --split dev --exec-cwd <worktree> --cmd "<eval_cmd>" --node-id <id>
   

5. Capture the executor report. Before calling record --report-file, create the referenced report file. If no file exists yet, pass the report body with --raw-report instead.
6. Record outcome:

   python <tools>/arbor_state.py record --cwd <project> --run-name <run> \
     --node-id <id> --score <score> --insight "<insight>" \
     --result "<result>" --code-ref <branch>
   

7. Run propagate or manually update parent/root insights.

For smoke/forward tests, skip worktree creation, source edits, fresh agent launch, and B_dev execution. Save the generated prompt under experiments/<node_id>/, then use record with a cached or mocked report.