/implementation-approach

name: implementation-approach
description: Implementation strategy selection framework. Use when planning implementation strategy, selecting development approach, or defining verification criteria.

Implementation Strategy Selection Framework (Meta-cognitive Approach)

Meta-cognitive Strategy Selection Process

Phase 1: Decision-Sufficient Current State Analysis

**Core Question**: "What does the existing implementation look like?"

Analysis Framework

Architecture Analysis: Responsibility separation, data flow, dependencies, technical debt
Implementation Quality Assessment: Code quality, behavior-relevant test evidence, performance, security
Historical Context Understanding: Current form rationale, past decision validity, constraint changes, requirement evolution

Meta-cognitive Question List

• What is the true responsibility of this implementation?
• Which parts are business essence and which derive from technical constraints?
• What dependencies or implicit preconditions are unclear from the code?
• What benefits and constraints does the current design bring?

Stop when the current-state facts that could change responsibility, reuse, option validity, total complexity, a contract, or verification have been checked; find existing code as coding-principles Reference Representativeness describes.

Phase 2: Design Convergence

Complete these steps in order before selecting an implementation strategy:

1. **Existing-Surface Baseline**: Form the simplest end-to-end path that delivers the current outcome through existing responsibilities. Explicit requirements and accepted decisions are binding; suggested mechanisms remain candidates. 2. **Evidence Check**: Test that path against current requirements, verified constraints, observed in-scope problems, and evidence-backed material risks. Keep only the unmet conditions that can change the selected design. Where the requirements leave a quality level unset, such as performance, freshness, consistency, availability, or protection beyond the required trust boundary, test against the lowest level that still delivers the outcome and record it as the selected level. 3. **Targeted Comparison**: For each unmet condition, test reuse, derivation from existing data, on-demand computation, or responsibility at the current caller or boundary before adding design surface. Compare viable choices by total complexity across the dimensions that materially differ: user decisions, settings, modes, concepts, outputs, persistent state, implementation paths, UX, runtime, implementation, testing, documentation, and maintenance. A second implementation of a responsibility that already has an owner with the same contract and change reason, including one added earlier in the same change, adds design surface; reusing or relocating that owner removes it. Select the lowest-total-complexity choice that satisfies the condition. 4. **Subtraction Check**: Remove each proposed addition and re-test its governing condition. Retain it only when the outcome, a required boundary, or necessary proof becomes unmet at its origin (a requirement, an accepted decision, or a repository rule or contract); a criterion, invariant, or constraint that a workflow artifact derived from that origin is narrowed to what the origin requires instead.

Classify supporting claims as observed, inferred, or unknown. Route an unknown that blocks the next step as an exact evidence prerequisite; the caller's value-boundary and irreversible-action gates determine whether user interaction is required.

Candidate paths and rejected additions remain active analysis. The durable output is the **Selected Design**: the complete chosen path plus evidence for each added design surface and the condition that fails when it is removed. An accepted ADR may retain alternatives as decision history. An implementer uses the same convergence check without producing a separate artifact.

Phase 3: Strategy Exploration and Creation

**Core Question**: "When determining before → after, what implementation patterns or strategies should be referenced?"

Strategy Discovery Process

Direct Strategy: Smallest repository-supported change that satisfies the accepted requirements and constraints
Repository Alternatives: Existing patterns that materially differ in migration, dependency order, or verification boundary
External Research: Official/current sources only when repository evidence cannot resolve a time-sensitive capability, compatibility, or dependency decision

Reference Strategy Patterns

**Legacy Handling Strategies**:

• Strangler Pattern: Gradual migration through phased replacement
• Facade Pattern: Complexity hiding through unified interface
• Adapter Pattern: Bridge with existing systems

**New Development Strategies**:

• Feature-driven Development: Vertical implementation prioritizing user value
• Foundation-driven Development: Foundation-first construction prioritizing stability
• Risk-driven Development: Prioritize addressing maximum risk elements

**Integration/Migration Strategies**:

• Proxy Pattern: Transparent feature extension
• Decorator Pattern: Phased enhancement of existing features
• Bridge Pattern: Flexibility through abstraction

Use these patterns only when their named migration or dependency problem exists. Start with the direct strategy. Compare an alternative when it would materially change risk, rollout, compatibility, or the early verification point. Keep the option set limited to patterns that produce one of those material differences.

Phase 4: Material Risk Assessment and Control

**Core Question**: "What risks arise when applying this to existing implementation, and what's the best way to control them?"

Evaluate only risk categories for which current evidence can change the strategy, public contract, rollout, rollback, or verification boundary.

Conditional Risk Categories

Technical Risks: System impact, data consist