Arness Batch Implement

Orchestrate parallel worktree-isolated background agents to implement multiple features simultaneously. Each worker is a full independent session with all tools, operating in its own git worktree. The orchestrator (this skill) handles pre-flight validation, worker spawning, progress tracking, and handoff to batch-merge.

Key architectural constraint: This skill is a sequencer — it MUST NOT duplicate sub-skill logic. Workers handle all implementation details autonomously.

Pipeline position:

arn-code-batch-planning -> **arn-code-batch-implement** (pre-flight -> spawn workers -> track -> handoff) -> arn-code-batch-merge

Workflow

Step 0: Ensure Configuration

Read ${CLAUDE_PLUGIN_ROOT}/skills/arn-code-ensure-config/references/ensure-config.md and follow its instructions. Extract from ## Arness:

• Plans directory -- base path where project plans are saved
• Code patterns -- path to the directory containing stored pattern documentation
• Template path -- path to the report template set (JSON templates)

Step 1: Pre-flight Validation

Read ${CLAUDE_PLUGIN_ROOT}/skills/arn-code-batch-implement/references/preflight-validation.md and follow its procedure. The preflight reference handles scanning and returns a structured result. Based on that result:

If zero pending plans found: inform the user: "No pending plans found. Run /arn-code-batch-planning to plan features first." Exit.

If Git is no in ## Arness: "Batch implementation requires git for worktree-based parallel execution. Run /arn-implementing to implement features one at a time instead." STOP.

If gh/bkt auth not available (based on Platform): warn that PRs cannot be created — workers will commit but skip PR creation.

If uncommitted changes detected: warn and suggest committing first. Ask (using AskUserQuestion):

Uncommitted changes detected. Commit or stash before launching batch?

1. Proceed anyway
2. Cancel — I'll commit first

If Cancel, exit.

If not on main/master: plans should be on main (merged via the plans PR from batch-planning). Ask (using AskUserQuestion):

You're on branch [name], but plans should be on main. Checkout main?

1. Checkout main — run git checkout main && git pull
2. Proceed on this branch — I know what I'm doing

If Checkout main: git checkout main && git pull. Continue. If Proceed: continue on current branch.

Run git pull to ensure main is up to date with the latest plans.

Step 2: Pre-flight Summary

Present the validation results as a table:

Batch Implementation Pre-flight:

| # | Feature | Tier | Sketch | Est. Files | Overlap Warning |
|---|---------|------|--------|------------|-----------------|
| 1 | ...     | ...  | ...    | ...        | ...             |

Column values:

• Sketch: "ready" (manifest found with kept status), "recommended" (UI references but no sketch), "n/a" (no UI components)
• Overlap Warning: blank if none, or list of overlapping feature names

If file overlap detected between any features, show which features share files and note: "File overlap detected -- batch-merge will handle conflicts after implementation."

Show estimated context: "[N] features will be implemented in parallel, each as an independent session."

Step 3: Launch Confirmation

Ask (using AskUserQuestion):

Launch [N] parallel implementations?

1. Launch all
2. Select subset
3. Cancel

• Launch all -- proceed with all pending features.
• Select subset -- present a multi-select (using AskUserQuestion with multiSelect: true) listing all pending features by name. Proceed with selected features only.
• Cancel -- exit.

Step 4: Spawn Workers

Read the worker instructions template from ${CLAUDE_PLUGIN_ROOT}/skills/arn-code-batch-implement/references/worker-instructions.md.

For each feature to implement, spawn one Agent with:

• isolation: "worktree"
• run_in_background: true
• A self-contained prompt built from the worker-instructions template, filled with:
  • The feature's plan path (absolute)
  • The detected tier (thorough, standard, or swift)
  • The platform (github, bitbucket, or none — from ## Arness config)
  • Code patterns directory path (absolute)
  • Template path (absolute)
  • Sketch manifest path (absolute, if sketch exists; otherwise "none")

If a worker fails to spawn (Agent tool returns an error), report the failure, continue spawning remaining workers, and include the failed feature in the Step 5 summary with status "failed -- spawn error".

ALL agents MUST be spawned in a SINGLE message (multiple Agent tool calls in one response) so they run in parallel. Cap at 5 concurrent workers.

If more than 5 features are queued, batch into groups of 5. Launch the first group, wait for all workers in that group to complete, then launch the next group.

Step 5: Track Progress

As workers complete, collect their final messages. Each worker should end with PR: <url> or PR: none -- <reason>.

Present a status table as workers finish:

| Feature | Status | PR | Duration |
|---------|--------|----|----------|
| ...     | ...    | ...| ...      |

Status values: "done", "failed -- <reason>"

If a worker fails: report the failure, continue tracking other workers, include the failed feature in the summary.

When all workers in the current batch complete, present the summary: "[N/M] features implemented successfully."

If there are additional batches (>5 features), launch the next batch and repeat.

Step 6: Handoff

Ask (using AskUserQuestion):

Batch implementation complete. What next?

1. Merge PRs
2. Not yet

• Merge PRs -- invoke Skill: arn-code:arn-code-batch-merge.
• Not yet -- inform: "Run /arn-code-batch-merge when ready." Exit.