Ln 23 System Design Proposal Builder

System Design Proposal Builder

Goal: Create a proportionate, evidence-backed target system design that turns requirements into explicit boundaries, contracts, data flow, failure behavior, operations, and tradeoffs. Change only the approved design document; do not implement, audit, or approve the delivery.

Execution contract: The checklist defines completion. Track each item internally as PENDING, PROVEN with evidence, CLEARED with evidence its condition is absent, or UNPROVEN with a gap; reading, delegation, tool failure, a zero exit status, or a self-reported success is not proof; only the observed outcome is. Reconcile after each section. Before returning, resolve all PENDING, count only PROVEN and CLEARED, and apply verdict and approval rules to every gap. Preserve intent, scope, and existing authorization. Continue authorized work; ask only for consequential unresolved choices or required external approval. When no one can answer during the run, state the exact question and apply the skill's verdict for the remaining gap instead of waiting or guessing. Scale depth to material risk without skipping checks. Preserve dependency and safety order; otherwise choose an appropriate verification method. Accept equivalent user or repository evidence; no other skill, named artifact, or complete lifecycle is required. Preserve source requirement and decision IDs. Bind reused evidence to relevant source versions, dirty changes, configuration, and environment; invalidate only affected claims. On continuation, reconcile task, authorization, current state, and unresolved evidence. For long work, return a compact continuation record or update an already authorized artifact; read-only skills do not persist it. Distinguish artifact readiness, verified behavior, and external-action authority. Prepare authorized work before required approval. If blocked by an instruction, cite its exact source and unresolved boundary; do not invent approval gates from caution.

Tool Routing

Use patterns as candidate solutions, not goals. Introduce infrastructure only when a requirement, failure mode, ownership boundary, or measured horizon pays for its lifecycle cost.

Artifact Rules

• Reuse a clear target-design document; otherwise use docs/architecture/target-design.md.
• Read available baseline, current-state, decision, interface, diagram, and migration artifacts by path; none is mandatory.
• Label facts, assumptions, estimates, proposed decisions, and unresolved choices separately.
• Compare credible alternatives for consequential decisions, including the simplest feasible option; when constraints permit only one, document why rather than inventing another.
• Prefer reversible choices and the simplest topology fitting the system. For a new application, consider a modular monolith before independent services; do not force that shape onto libraries, plugins, or an established topology.
• Do not silently change an accepted decision; record the conflict and required governance action.

Checklist

1. Frame the Design

• Resolve business outcome, actors, journeys, scope, non-goals, horizon, readers, language, and the approved canonical destination before editing.
• Read repository instructions and inspect relevant architecture artifacts and current implementation.
• Extract functional requirements and measurable quality drivers, preserving their source and status.
• Identify architecture-critical unknowns and ask only questions whose answers change the target shape.
• Return BLOCKED when a required business boundary or safety constraint cannot be responsibly assumed.

2. Estimate Before Choosing Components

• Estimate average and peak request or event rates, concurrency, payload and bandwidth, storage growth, retention, and recovery volume where relevant.
• Show formulas, ranges, growth horizon, and assumptions; identify the variables that can reverse a choice.
• Identify likely first bottlenecks and explicit thresholds for deferred scaling mechanisms.
• Separate availability, latency, durability, consistency, security, cost, and operability requirements from implementation preferences.
• Reject speculative scale and list complex mechanisms intentionally deferred.

3. Define Domains, Data, and Contracts

• Map business capabilities, domains or modules, ownership, invariants, and allowed dependency direction.
• Define systems of record, data models at architecture depth, lifecycle, retention, consistency, and transaction boundaries.
• Define public APIs, events, commands, schemas, errors, idempotency, ordering, versioning, and compatibility expectations.
• Define trust boundaries, identities, authorization, sensitive data, secrets, abuse controls, and audit needs proportionate to risk.
• Keep framework and vendor details outside the core model unless they are genuine constraints.