Ultra-scale issue coordination

Use one Codex thread as the coordinator. Give each active GitHub issue its own Codex worker thread, worktree, branch, and pull request. Keep implementation context in workers and dependency state in GitHub.

Explicitly naming /issue-coordinator, or explicitly telling the coordinator that agents may merge, authorizes in-scope workers to merge their own pull requests after every merge gate below passes. An implicit skill match does not grant merge authority: run in no-merge mode unless the user's words grant it. Neither mode authorizes deployment, release publication, destructive operations, branch-protection bypasses, or changes outside the supplied batch.

Preconditions