fanout — safe parallel execution

Use ONLY for subtasks that are parallel-safe (no shared files, no ordering dependency).

Procedure

1. Per task, create an isolated worktree: sys_os_shell("git worktree add .worktrees/<task_id> -b polly/<task_id>"). Record the worktree path + branch in the registry (.polly/registry.json).
2. Dispatch one implementation sub-agent per task, scoped to its worktree: sys_session_send(agent="claude_code"|"codex"|"opencode"|"cursor"|"hermes"|"agy", title="<task_slug>", args={purpose: "implement", input: "<task + acceptance contract + worktree path>"}). Use a short task-based title such as auth-refactor or fix-sse-error, never the raw vendor name. State the scope and that it must work only inside .worktrees/<task_id>. The worker drives the task to green and opens its OWN PR for the branch. Every commit the worker authors must end with a blank line followed by the exact co-sign trailer as its final line — Co-authored-by: omnigent <noreply@omnigent.ai>. For a long-running claude_code or codex implementation with an explicit completion condition, the input may instead be one standalone /goal <condition> command containing that same task, worktree, acceptance contract, green gates, and PR requirement. Do not use child goal mode for other workers or non-implementation purposes. Record each handle's conversation_id in the registry. Emit the worktree + sys_session_send tool calls in THIS turn — never end a turn having only said you will dispatch; the dispatch calls and their announcement go in the same turn. Dispatch the whole parallel-safe set, THEN (and only then) END YOUR TURN. Do not poll.
3. Each sub-agent runs autonomously and notifies you through the inbox when it finishes. Collect its structured result with sys_read_inbox and record the PR URL in the registry. If the inbox result is empty/unclear, inspect that worker conversation with sys_session_get_history before deciding what to do next.
4. Send each finished task's PR through cross-review.
5. polly does NOT merge — the PR is the deliverable. When cross-review passes, the task is done: mark it ready in the registry with its PR URL and leave it for the human to review and merge. Never run git merge / gh pr merge.
6. Remove a finished worktree (git worktree remove) only once its PR is open and review is clean — the branch lives on the remote, so the worktree is disposable. Don't remove a worktree that still has open fix-tasks.

Notes

• Respect the per-turn dispatch cap (enforced by policy). More tasks than the cap → dispatch in waves (let the running batch finish before dispatching more).
• The human can open any sub-agent in the UI's Subagents panel and read its conversation while it runs.
• If a running worker is wrong, runaway, superseded, or no longer useful, call sys_cancel_task with task_id set to the recorded conversation_id before dispatching a replacement. claude_code is hard-stopped; codex cancellation is best-effort until its runner-side hard-stop exists.
• A sub-agent that returns a dark or failing result: don't re-prompt it in a loop — re-dispatch a fresh implementation sub-agent in a clean worktree, or escalate to the user.
• Because polly never merges, cross-PR conflicts surface when the human merges, not here. Keeping each parallel task's file scope disjoint is what keeps that rare — honor it.