arc-implementing

name	arc-implementing
description	Orchestrate implementation of a large multi-feature project inside a worktree. Use when driving one epic's build end-to-end; for cross-epic worktree and DAG-state management use arc-coordinating instead.
category	sdd
status	promoted

arc-implementing

Overview

Orchestrator for large projects. Automatically expands epic → features → tasks → execution. It calls other skills and does not write code itself.

Use when in a worktree session with specs/<spec-id>/dag.yaml, an .arcforge-epic marker (supplies both epic and spec_id), and specs/<spec-id>/epics/<epic-id>/epic.md or .../features/*.md present.

Do not use for small projects (use writing-tasks + agent-driven directly) or tasks without a structured spec.

The Process

For each epic in the worktree, run these phases in order:

1. Phase 0 — Sync and check dependencies. Run arc-coordinating to sync from base and check blocked_by. If blocked_by is not empty: STOP and use the blocked format. If ready: continue.
2. Phase 1 — Confirm features exist. specs/<spec-id>/epics/<epic-id>/features/*.md was produced by arc-planning Phase 3 and already exists. Read the feature files directly; no skill call here.
3. Phase 2 — Per feature:
   • 2a: Feature → Tasks. Call arc-writing-tasks. Input: specs/<spec-id>/epics/<epic-id>/features/<feature>.md. Output: docs/tasks/<feature>-tasks.md. Quality gate: if tasks are vague or missing tests/commands, STOP and re-run to refine — max 2 refinement cycles, then escalate to human.
   • 2b: Execute Tasks. Call arc-agent-driven. Input: tasks file. Output: completed code + commits. Model tiers: arc-agent-driven's Model Selection ladder governs per-dispatch model choice (never inherit).
4. Phase 3 — Feature complete. Move to next feature, or finish the epic.

Skills Called

Phase	Skill	Input	Output
0	arc-coordinating	worktree	sync + blocked status
2a	arc-writing-tasks	specs/<spec-id>/epics/<epic-id>/features/<feature>.md	tasks file
2b	arc-agent-driven	tasks file	completed code
2b	arc-dispatching-parallel	(via arc-agent-driven, if review finds multiple issues)	parallel fixes
End	arc-finishing	completed epic	merge decision

What Implementer Does NOT Do

• ❌ Write code directly (delegate to agent-driven)
• ❌ Split tasks manually (delegate to writing-tasks)
• ❌ Perform reviews or run the TDD cycle (handled inside agent-driven)

Durable Progress

Phase 2b runs through arc-agent-driven, which records each completed task to the .arcforge/sdd/progress.md ledger (a self-ignoring runtime recovery artifact) as Task N: complete (commits <base7>..<head7>, review clean). If a compaction or fresh session drops your place mid-epic, read that ledger plus git log and resume AFTER the last task marked complete — never re-dispatch a feature or task the ledger already records as done.

Completion Format

─────────────────────────────────────────────────
✅ Epic complete: <epic-name>

Features implemented:
- feature-1: 4 tasks, all passing
- feature-2: 6 tasks, all passing

Total: N tasks, 0 failures
Commits: N

Next: Use arc-finishing to decide merge/PR/keep/discard
─────────────────────────────────────────────────

Blocked Format

─────────────────────────────────────────────────
⚠️ Implementer blocked

Epic: <epic-name>
[Dependencies] Blocked by: <dep-1>, <dep-2>
  → Complete blocking epics, run `arc-coordinating` sync from base, verify `blocked_by` empty
[Task failure] Feature: <feature-name>  Task: <task-id>  Issue: [description]
  → [action]

Then resume implementer
─────────────────────────────────────────────────

Integration

• Before: arc-coordinating (creates worktrees), arc-planning (creates DAG)
• Uses: arc-writing-tasks, arc-agent-driven, arc-dispatching-parallel
• After: arc-finishing (Step 0 selects the epic path)