Fable Mode — Sonnet (v3, agent-routed)

v3 change: the worker is a real agent definition (agents/fable-worker-sonnet.md)
invoked by name, not a prose briefing the model can soft-ignore. Its system
prompt carries the loop and the operational rules; this skill only routes.

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 fable-worker-sonnet appears in the available agent types. If not,
   fall back to inline: spawn a general-purpose Sonnet agent and pass it the
   rules verbatim from agents/fable-worker-sonnet.md.
2. Spawn @fable-worker-sonnet via the Task tool (subagent_type: "fable-worker-sonnet"). Brief it with: the task, the exact output path(s),
   relevant context, and the pass condition its deliverable must satisfy —
   name the check, don't leave it to taste.
3. For independent sub-parts, spawn multiple workers concurrently and merge.
   Cap concurrency at a handful. Workers do not spawn workers.
4. For high-stakes deliverables, follow with @fable-verifier, briefed with
   only the spec and the artifact path — not the worker's report.
5. Relay results and anything marked unverified.