Implementation Approach

Implementation Strategy Selection Framework (Meta-cognitive Approach)

Meta-cognitive Strategy Selection Process

Phase 1: Comprehensive 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, test coverage, 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?

Completion evidence: inspected paths, observed architecture/data-flow facts, known constraints, inferred historical rationale labeled as inferred, and unknowns that could change strategy selection.

Transition: proceed when every strategy-relevant claim is observed, explicitly inferred with evidence, or recorded as unknown.

Phase 2: Design Convergence

Core Question: "What is the smallest design that delivers the current required outcome, and what evidence forces each addition beyond it?"

Complete these steps in order before exploring implementation strategies:

• Direct MVP: Describe the simplest end-to-end design that delivers the current required outcome using existing system capabilities. Explicit user requirements and confirmed decisions are binding; technical mechanisms framed as suggestions or options remain candidates unless confirmed as mandatory.
• Failure Check: Test the Direct MVP against current requirements, verified constraints, observed problems within confirmed scope or dependencies required for the outcome, and evidence-backed material risks. Record only unmet items as Failed Items with their evidence; record None when all pass. Report problems outside that boundary separately for a scope decision.
• Targeted Expansion: For each Failed Item, first test reuse, derivation from existing data, on-demand computation, or responsibility at the current caller or boundary within the existing design surface. When these fail, select the smallest sufficient addition. Record Adopted Additions as addition -> Failed Item -> evidence that lower-surface resolutions fail; an addition requires a Failed Item.
• Subtraction Check: Temporarily remove each Adopted Addition and re-test its Failed Item. Keep the addition when the item becomes unmet again. Record options considered in step 3 but not adopted as Rejected Additions with a brief reason; record None when step 3 had no rejected candidate.

Design Doc output: Direct MVP, Failed Items, Adopted Additions, and Rejected Additions.

Completion evidence: all four outputs recorded; every Failed Item carries its evidence; every Adopted Addition names its Failed Item, the lower-surface resolutions that fail, and its subtraction result.

Transition: proceed when every supporting claim is observed, explicitly inferred with evidence, or recorded as unknown; when an unknown blocks a step, stop at that step and name the evidence or user decision required.

Phase 3: Strategy Exploration and Creation

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

Strategy Discovery Process

Research and Exploration: repository patterns first; then official documentation for the resolved dependency version; then maintained OSS implementations; use literature/blogs only for supplementary alternatives and label them as non-authoritative
Creative Thinking: Strategy combinations, constraint-based design, phase division, extension point design

Reference Strategy Patterns (Creative Combinations Encouraged)

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

Completion evidence: at least two feasible candidate approaches when the decision is non-trivial, with each candidate mapped to the observed constraints it satisfies and the constraints it leaves unresolved.

Transition: proceed when candidates are comparable against the same constraint set.

Phase 4: Risk Assessment and Control

Core Question: "What risks arise when applying this to the existing implementation, and which control measurably reduces likelihood or impact while preserving verification and rollback?"

Risk Analysis Matrix

Technical Risks: System impact, data consistency, performance degradation, integration complexity
Operational Risks: Service availability, deployment downtime, process changes, rollback procedures
Project Risks: Schedule delays, learning costs, quality achievement, team coordination

Risk Control Strategies

Preventive Measures: Phased migration, parallel operation verification, integration/regression tests, monitoring setup
Incident Response: Rollback procedures, log/metrics preparation, communication system, service continuation procedures

Completion evidence: each material risk has likelihood/impact evidence, one preventive or containment control, and a verification point.

Transition: proceed when no high-impact risk lacks a control or blocking escalation.

Phase 5: Constraint Compatibility Verification

Core Question: "What are this project's constraints?"

Constraint Checklist

Technical Constraints: Library compatibility, resource capacity, mandatory requirements, numerical targets
Temporal Constraints: Deadlines/priorities, dependencies, milestones, learning periods
Resource Constraints: Team/skills, work hours/systems, budget, external contracts
Business Constraints: Market launch timing, customer impact, regulatory compliance

Completion evidence: each constraint is observed, inferred, or unknown; every unknown that can invalidate a candidate names the required evidence or user decision.

Transition: proceed when remaining unknowns cannot change the valid candidate set, or the user resolves them.

Phase 6: Implementation Approach Decision

Select the approach that satisfies all hard constraints and current requirements with the lowest transition risk and smallest verification delay. Use lifecycle cost and implementation effort only as tiebreakers after requirement coverage, compatibility, and risk control are equal.

Vertical Slice (Feature-driven)

Characteristics: Vertical implementation across all layers by feature unit

Application Conditions: Low inter-feature dependencies, output in user-usable form, changes needed across all architecture layers

Verification Method: End-user value delivery at each feature completion

Horizontal Slice (Foundation-driven)

Characteristics: Phased construction by architecture layer

Application Conditions: Foundation system stability important, multiple features depend on common foundation, layer-by-layer verification effective

Verification Method: Integrated operation verification when all foundation layers complete

Hybrid (Creative Combination)

Characteristics: Flexible combination according to project characteristics

Application Conditions: Unclear requirements, need to change approach per phase, transition from prototyping to full implementation

Verification Method: Assign L1 when the phase produces end-user-operable behavior, L2 when it produces a testable internal behavior or contract, and L3 only when the phase produces build-time structure with no runnable behavior yet

For Hybrid, assign one explicit L1/L2/L3 verification level and observable completion result to every phase.

Completion evidence: one selected approach, its phase boundaries, integration points, and a verification result for every phase.

Transition: proceed to documentation when the selected approach covers every hard constraint and its risks have controls. Otherwise return to candidate exploration (Phase 3), or to Design Convergence (Phase 2) when a Phase 4-5 result changes the Direct MVP, Failed Items, or Adopted Additions.

Phase 7: Decision Rationale Documentation

Return the following structure in the Design Doc or planning handoff:

implementationApproachDecision:
  observedConstraints: [<constraint + evidence>]
  inferredConstraints: [<constraint + evidence and inference>]
  unknowns: [<unknown + required evidence or decision>]
  candidates: [<approach + requirements covered + risks + verification delay>]
  selectedApproach: <vertical | horizontal | hybrid description>
  selectionRationale: <hard-constraint coverage, compatibility, risk control, then tiebreakers>
  rejectedApproaches: [<approach + unmet requirement or higher material risk>]
  phaseVerification: [<phase + L1/L2/L3 + observable completion evidence>]

Completion evidence: every selected/rejected decision traces to an observed constraint, accepted inference, or resolved user decision.

Verification Level Definitions

Priority for completion verification of each task:

• L1: Functional Operation Verification - Operates as end-user feature (e.g., search executable)
• L2: Test Operation Verification - New tests added and passing (e.g., type definition tests)
• L3: Build Success Verification - No compile errors (e.g., interface definitions)

Priority: L1 > L2 > L3 in order of verifiability importance

Integration Point Definitions

Define integration points according to selected strategy:

• Strangler-based: When switching between old and new systems for each feature
• Feature-driven: When users can actually use the feature
• Foundation-driven: When all architecture layers are ready and E2E tests pass
• Hybrid: When individual goals defined for each phase are achieved

Decision Gate Checklist

• [ ] Phase 1 evidence exists before strategy selection
• [ ] Phase 2 records all four Design Convergence outputs, with evidence for every Failed Item and Adopted Addition
• [ ] Candidate generation includes combinations when no listed strategy satisfies all hard constraints
• [ ] Every material risk has a control and verification point
• [ ] Every hard constraint maps to the selected approach
• [ ] Phase 7 output records the selection and rejection rationale

When evidence required by a checked item is unknown, stop at that phase and report the exact repository evidence or user decision needed to continue.

Guidelines for Meta-cognitive Execution

• Leverage Known Patterns: Use as starting point, explore creative combinations
• Evidence-Ordered Research: Use repository evidence, version-matched official documentation, maintained OSS examples, then supplementary secondary sources
• Apply 5 Whys: Pursue root causes to grasp essence
• Multi-perspective Evaluation: Complete the evidence and transition checks for Phases 1-5
• Strategy Composition: Combine strategies when one strategy cannot satisfy all hard constraints
• Decision Traceability: Map every selection reason to evidence in the Phase 7 output