The runner · pluggable

The orchestrator

The orchestrator is the build-loop runner — whatever drives a ratified spec to its acceptance checks, autonomously, between the two human gates. The key word is whatever: Specline defines the loop's contract and validates that a spec carries its inputs; it does not build the runner. The runner is pluggable.

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Specline owns the contract, not the runner. A capable model self-orchestrates a single spec (an agent + a thin loop harness like /loop); a fuller external orchestrator handles what one model can't do for itself — fresh-context re-entry, parallel builds across the decider budget, model-tier routing, and fresh-context verifier subagents.

What it runs

The build loop, defined in the canon. One iteration:

the loop

resume from status.md (last green checkpoint)
  → work toward the Goal
  → run the agent-loopable acceptance checks   # the mechanical exit
  → red→green? record a new green checkpoint
     else        burn a loop_budget cycle
  → repeat, until checks pass or a boundary fires

What it consumes vs. what doctor validates

Clean division of labor: doctor checks the spec carries the four loop inputs and they're well-shaped; the orchestrator reads them and acts.

Loop input	doctor (validates shape)	orchestrator (consumes)
Goal — the target	present & falsifiable-shaped	converges toward it
Agent-loopable checks — the exit	runnable command present	runs them each iteration
status.md — memory	required sections + entries	resumes from / appends to it
loop_budget / ttl_expires — autonomy	well-formed values	counts cycles / clock; escalates
blast_radius / target_model — routing	allowed values	selects model effort + reviewer depth

Boundaries

It hands control back to a human gate at the first of: loop_budget exhausted (no progress), ttl_expires reached (too much time), or a true gate — a destructive action, a real scope change, or input only the PO can give. It never silently extends a boundary, never edits a ratified spec, and communicates through artifacts and status.md, not a reasoning transcript.

See the handbook's How agents build and Escalation chapters for the narrative, and /spec.md § The build loop for the normative contract.