RPI — Research-Plan-Implement Sub-Cycle

Every feature phase in CKS follows a disciplined R-P-I sub-cycle: Research → Plan → Implement, with quality gates between each transition.

The Sub-Cycle

Research ──[R→P gate]──→ Plan ──[P→I gate]──→ Implement
    ↑                                              │
    └──────── iteration refresh ◄──────────────────┘

RPI operates within the 5-phase lifecycle. It is not a replacement for Discover/Design/Sprint/Review/Release — it is the micro-discipline inside each phase that ensures research informs planning and planning informs implementation.

Sub-Stage Definitions

Research (R)

Purpose: Gather knowledge before making decisions. Who: prd-researcher, deep-researcher, context-research skill Artifacts produced:

• .context/{slug}.md — technology briefs (API patterns, gotchas, code examples)
• .research/{slug}/report.md — deep research reports (strategic findings, competitive analysis)
• .prd/phases/{NN}-{name}/{NN}-RESEARCH.md — feature-specific technical investigation

When complete: At least one of the above exists for the technologies/domains relevant to the feature.

Plan (P)

Purpose: Define what to build and how, informed by research. Who: prd-discoverer (requirements), prd-planner (execution plan) Artifacts produced:

• .prd/phases/{NN}-{name}/{NN}-CONTEXT.md — discovery output (11 Elements)
• .prd/phases/{NN}-{name}/{NN}-PLAN.md — execution plan with tasks and acceptance criteria
• docs/prds/PRD-{NNN}-{name}.md — PRD document

When complete: PLAN.md exists with tasks, acceptance criteria, and file scopes.

Implement (I)

Purpose: Build what the plan specifies, using research findings. Who: prd-executor, prd-executor-worker, prd-verifier Artifacts produced:

• .prd/phases/{NN}-{name}/{NN}-SUMMARY.md — implementation summary
• .prd/phases/{NN}-{name}/{NN}-VERIFICATION.md — test results and acceptance checks
• Source code changes per PLAN.md task list

When complete: VERIFICATION.md exists with PASS verdict.

Quality Gates

R→P Gate (Research → Plan)

Blocks planning if research is insufficient.

Check: Does at least ONE research artifact exist for the feature?

• {NN}-RESEARCH.md in the phase directory, OR
• .context/*.md briefs for technologies referenced in the feature, OR
• .research/*/report.md for the feature's domain

Pass: At least one research artifact exists. Proceed to Plan. Fail: No research artifacts found. Message:

R→P gate blocked: No research artifacts found for phase {NN}.
Run /cks:context "{technology}" or /cks:research "{topic}" first.

Skip condition: If the feature brief explicitly states no external technologies or integrations are involved, the gate may be marked SKIP:trivial with justification.

P→I Gate (Plan → Implement)

Blocks implementation if plan is incomplete.

Check: Does the plan exist and contain acceptance criteria?

• {NN}-PLAN.md exists in the phase directory
• PLAN.md contains at least one ### Task section
• PLAN.md contains an ## Acceptance Criteria section with at least one item

Pass: Plan exists with tasks and acceptance criteria. Proceed to Implement. Fail: Plan incomplete. Message:

P→I gate blocked: {specific missing item}.
Run /cks:sprint to generate the execution plan.

Iteration Refresh Protocol

When iteration_count > 0 in PRD-STATE.md (feature returning from Phase 4 Review):

1. Research re-runs: All .context/ briefs for the feature are refreshed (not skipped)
2. Deep research checked: If .research/ reports exist and the iteration feedback references technology issues, flag them for manual refresh
3. Plan re-evaluates: The planner reads refreshed research before producing an iteration plan
4. Gate re-checks: Both gates re-evaluate with fresh artifacts

Status Derivation

RPI status is derived from filesystem artifacts — no new state fields needed:

Phase directory: .prd/phases/{NN}-{name}/

Research:  EXISTS({NN}-RESEARCH.md) OR EXISTS(.context/*.md relevant) → done
Plan:      EXISTS({NN}-PLAN.md) with tasks                           → done
Implement: EXISTS({NN}-VERIFICATION.md) with PASS                    → done

Artifacts Present	Current Sub-Stage
None	Research (start here)
Research only	Plan (R→P gate: passed)
Research + Plan	Implement (P→I gate: passed)
Research + Plan + Verification(PASS)	Complete

Workflow

For step-by-step gate check procedures, iteration refresh logic, and status display format:

Read: ${SKILL_ROOT}/workflows/rpi-subcycle.md