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 and operational
   rules verbatim from agents/fable-orchestrator.md.
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).

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).