MASTER Validation

# 000_MASTER_validation - Phase 3: Validation and Rollout

> Phase entry-point. Read this before any task in Phase 3.

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## Phase Summary

Phase 3 validates the feature against its spec and rolls it to production. This is procedural work - the implementation is done; this phase is about gates, monitoring, and the deliberate ramp from 0 → 100% production traffic.

The phase opens with a load test (task 18) and closes with the rollback drill (task 22) executed in staging. Production rollout (task 20) runs over the 7-day soak window described in `release-readiness.md`.

## Goals

By the end of Phase 3:

1. Load test confirms NFR-1.x performance budgets met.
2. Feature flag `users.search.enabled` works on/off; develop deploy gated.
3. Production at 100% traffic with stable metrics for 7 days.
4. Documentation updated per PRD Section 12.
5. Rollback procedure drilled and confirmed.
6. PRD acceptance criteria (Section 23) all checked.

## Prerequisites

- [ ] Phase 2 acceptance met.
- [ ] Develop environment runs the full stack.
- [ ] Staging environment mirrors production.
- [ ] On-call team identified for production rollout window.

## Task Prompts

| # | Task | Primary Agent | Supporting Agents |
|---|---|---|---|
| 018 | [`018_load_test.md`](018_load_test.md) | `deployment-validator` | `backend-engineer` |
| 019 | [`019_feature_flag.md`](019_feature_flag.md) | `backend-engineer` | `frontend-engineer` |
| 020 | [`020_production_rollout.md`](020_production_rollout.md) | `deployment-validator` | `backend-engineer` |
| 021 | [`021_documentation.md`](021_documentation.md) | `prd-author` | `spec-author` |
| 022 | [`022_rollback_drill.md`](022_rollback_drill.md) | `deployment-validator` | `backend-engineer` |

### Execution order