Fable Mode — Opus (v3, agent-routed)

v3 change: delegation is enforced structurally, not requested in prose. The orchestrator is a real agent definition (agents/fable-orchestrator.md) with no Write/Edit tool — it cannot do the work inline, so "spawn a worker" stops being a suggestion the model can skip. (Change prompted by field report: prose-level "you may spawn workers" almost always ran inline on the main thread.)

If a task has one obvious correct approach and fits in a single pass, skip this loop and do it directly.

How to run it

1. Confirm the fable agents are installed (fable-orchestrator, fable-worker-sonnet, fable-worker-haiku, fable-verifier appear in the available agent types). If they are not, fall back to the inline method: spawn a general-purpose Opus agent and pass it the Core Loop, domain patterns, and operational rules verbatim from the fable-mode skill, which is installed alongside this one. Do NOT try to read agents/fable-orchestrator.md — agent files exist only on surfaces that load an agents/ directory (Claude Code), never on skill-only surfaces (Cowork), which is exactly where this fallback fires.
2. Spawn @fable-orchestrator via the Task tool (subagent_type: "fable-orchestrator"). Brief it with: the user's task, the output directory, relevant session context, and any user-set limits (warning threshold, worker cap, deadline).
3. Do not restate the Core Loop or operational rules in the briefing — the orchestrator's agent definition carries them. Brief the task, not the method.
4. When it returns, relay the result, every stage it marked unverified, and its recommendations (surfaced scope it did not build). If it reports the task beyond Opus's capability, offer a fable-fable rerun (Fable 5.1) rather than retrying Opus.
5. Mandatory delivery gate: before presenting the result to the user, invoke the double-check skill on the finished deliverable. Pass it the orchestrator's closing FINAL-COLD-CHECK: line verbatim — yes means fable-verifier already checked the finished deliverable and double-check runs the seam check only; intermediates-only, no, or a missing line means the full panel runs. Do not skip the gate; the user relies on it instead of re-checking the work themselves.

Known limitation

Write-removal closes the front door, not the side door: the orchestrator keeps Bash for running verification commands, and Bash can technically create files. Its definition forbids that use; if audits show it writing through Bash, the next tightening is removing Bash and routing even check-execution through workers (cost: one extra hop per check).