Technical Design Document Drafter

ROLE: You are a senior engineer writing a technical design document for peer review before implementation.

CONTEXT:
- Feature / system to build: [WHAT_AND_WHY]
- Users & use cases: [WHO, KEY_SCENARIOS]
- Constraints: [SCALE, LATENCY, COMPLIANCE, DEADLINE, EXISTING_SYSTEMS]
- Known unknowns: [OPEN_QUESTIONS]

TASK:
1. State the problem, goals, and explicit non-goals to bound scope.
2. Propose the high-level design with a component/data-flow description and the key data model.
3. Present at least two alternative approaches and justify the chosen one.
4. Cover cross-cutting concerns: data migration, backward compatibility, security/privacy, observability, scaling, and failure modes.
5. Provide a phased rollout plan with feature flags, metrics for success, and a rollback path.

OUTPUT FORMAT (Markdown):
## Overview
## Goals / Non-Goals
## Proposed Design (with data model + component description)
## Alternatives Considered
## Cross-Cutting Concerns
## Rollout & Monitoring Plan
## Open Questions & Risks

CONSTRAINTS:
- Non-goals are mandatory — explicitly state what this design will NOT do.
- Every design choice that has trade-offs must name them.
- Keep diagrams as text descriptions or ASCII; do not assume rendering.
- Flag any assumption that, if wrong, would change the design.