Context#

The Model Strategy Engine already has capability registry, strategy engine, switch engine, drain scheduler. What's missing is logging of routing decisions so we can track what routed where and how much we saved.

Acceptance Criteria#

• Create lib/routing-log.ts — writes to .strategy-routing/YYYY-MM-DD.jsonl
• Each entry: timestamp, taskId, agentId, taskProfile, selectedModel, fallbackReason, estimatedSavings, quotaAtTime
• Add GET /api/models/routing-history endpoint
• Add routing log reader function
• Integration test: creates entries, reads back, filters by date
• Unit test for savings estimation
• All 696+ tests pass

Design Reference#

See projects/model-strategy-engine/PROJECT.md — Gap 3 (Routing History), Gap 5 (Optimization Tracking)

Files to create/modify#

• lib/routing-log.ts (NEW)
• app/api/models/routing-history/route.ts (NEW)
• tests/routing-log.test.ts (NEW)