[Feature] Generate reviewed routing proposals and orchestrate gated flywheel campaigns

[Xunzhuo]

Goal

Generate reviewed routing proposals from qualified flywheel evidence and orchestrate their shadow, gray, promotion, and rollback gates.

Proposed Workgroup

MoM & Routing

Scope

• Consume versioned datasets, model artifacts, evaluation results, and current recipe identity.
• Produce a reviewable routing proposal with explicit objective, candidate diff, expected gain, risks, and rollback target.
• Orchestrate offline evaluation, shadow, gray/canary, approval, activation, and rollback as explicit durable states.
• Require evidence thresholds and a human approval boundary before active routing changes.
• Record campaign provenance, decisions, operational outcomes, and terminal failure reasons.

Non-goals

• Training models inside the campaign controller.
• Mutating production routing directly from an unreviewed experiment.
• Replacing deployment-specific rollout mechanisms.

Completion signal

• One campaign can move a proposal through reproducible evaluation and shadow/gray gates to an explicit approve-or-reject decision.
• Every transition is auditable, retry-safe, and tied to an immutable rollback target.
• Failed gates cannot silently promote a candidate.

Parent Epic: #2238