arc-looping

arc-looping

Run arcforge workflows overnight without human intervention. Each iteration spawns a fresh Claude session. DAG + git persist state across sessions.

Core principle: Fresh session per task + file-based state = reliable cross-session execution with full auditability.

When to Use

digraph when_to_use {
    "Have a DAG with tasks?" [shape=diamond];
    "Tasks can run unattended?" [shape=diamond];
    "Need human judgment per task?" [shape=diamond];
    "arc-looping" [shape=box];
    "arc-agent-driven" [shape=box];
    "arc-executing-tasks" [shape=box];
    "Create DAG first (arc-planning)" [shape=box];

    "Have a DAG with tasks?" -> "Tasks can run unattended?" [label="yes"];
    "Have a DAG with tasks?" -> "Create DAG first (arc-planning)" [label="no"];
    "Tasks can run unattended?" -> "Need human judgment per task?" [label="yes"];
    "Tasks can run unattended?" -> "arc-executing-tasks" [label="no - need human"];
    "Need human judgment per task?" -> "arc-agent-driven" [label="yes - within session"];
    "Need human judgment per task?" -> "arc-looping" [label="no - fully autonomous"];
}

vs. arc-agent-driven:

• arc-agent-driven: subagents within ONE session (shared context, human available)
• arc-looping: fresh session per task (cross-session, unattended)

Loop Patterns

Sequential (Default — Safest)

node scripts/loop.js --pattern sequential --max-runs 20

• One task at a time
• Stop on failure
• Best for: linear task lists, dependent tasks, first-time use

DAG (Parallel-aware)

node scripts/loop.js --pattern dag --max-runs 20

• Uses parallelTasks() to find independent epics
• Processes parallel tasks before sequential ones
• Continues past failures (tries other tasks)
• Best for: independent epics, large DAGs, overnight runs

The Process

Before Starting

1. DAG must exist — run arc-planning first to create specs/<spec-id>/dag.yaml. In multi-spec repos, pass --spec-id <id> to the loop; cross-spec loops are not supported.
2. Verify baseline — run npm test to confirm clean state
3. Choose pattern — sequential for safety, DAG for throughput
4. Set limits — --max-runs and --max-cost to bound execution

Worktree Awareness

Run loops from the project root, not from inside a worktree.

If you are in a worktree (.arcforge-epic exists), the loop auto-detects both the epic and the spec from the marker (spec_id field) and scopes to that spec's dag.yaml. But running from project root with --pattern dag is the correct approach for multi-epic execution — it handles parallelism internally via parallelTasks().

Never run separate loops in separate worktrees. Each worktree's marker points back to its base spec's dag.yaml, so multiple loops against the same spec will pick up the same tasks and do duplicate work.

For scoped single-epic execution, use --epic:

node scripts/cli.js loop --epic epic-001 --pattern sequential --max-runs 20

During Execution

Each iteration:

1. Read specs/<spec-id>/dag.yaml → find next task (via coordinator)
2. Build prompt with task context
3. Spawn: claude -p < prompt
4. On success: coordinator.completeTask(taskId)
5. On failure: log error, retry once, then block task
6. Repeat until: all done, max-runs hit, or stop condition

Stop Conditions

Condition	What Happens
All tasks complete	Loop ends with status "complete"
Max runs reached	Loop ends with status "max_runs"
Cost limit hit	Loop ends with status "cost_limit"
Stall detected	No progress in 2+ iterations → stops
Retry storm	Same error 3+ times → stops
Sequential failure	Task fails after retry → stops (sequential only)

Monitoring

Spawn the loop-operator agent to check a running loop:

Use the loop-operator agent to check loop health

It reads .arcforge-loop.json and reports:

• Progress (completed/remaining/failed)
• Problems (stalls, retry storms, cost)
• Recommendations (continue/pause/intervene)

State File

.arcforge-loop.json tracks loop state across iterations:

{
  "iteration": 12,
  "pattern": "sequential",
  "started_at": "2026-03-17T22:00:00Z",
  "completed_tasks": ["feat-001-01", "feat-001-02"],
  "failed_tasks": ["feat-002-03"],
  "errors": [{"task_id": "...", "error": "...", "timestamp": "..."}],
  "total_cost": 0,
  "last_progress_at": "2026-03-17T23:15:00Z",
  "status": "running"
}

CLI Usage

# Sequential — safest
node scripts/cli.js loop --pattern sequential --max-runs 20

# DAG — parallel-aware
node scripts/cli.js loop --pattern dag --max-runs 50

# With cost limit
node scripts/cli.js loop --max-cost 10 --max-runs 100

# Scoped to one epic (safe for parallel execution)
node scripts/cli.js loop --epic epic-001 --pattern sequential --max-runs 20

Red Flags

Never:

• Run loops without a verified DAG
• Run loops without --max-runs on unfamiliar projects
• Ignore stall detection — it means something is fundamentally wrong
• Skip monitoring for loops > 10 iterations
• Run separate loops in separate worktrees — causes duplicate work

If loop is failing:

1. Check .arcforge-loop.json errors — are they the same error repeating?
2. Check specs/<spec-id>/dag.yaml — are blocked tasks preventing progress?
3. Run npm test — is the project in a broken state?
4. Check git log — are commits being made correctly?

Integration

Required before:

• arc-planning — creates the dag.yaml that the loop executes

Works with:

• loop-operator agent — monitors running loops
• arc-evaluating — can run evals between loop iterations
• arc-compacting — not needed (each iteration is a fresh session)

After loop completes (in order):

1. arc-verifying — verify all requirements met and tests pass
2. arc-finishing or arc-finishing-epic — wrap up and decide merge/PR