NW-SPIKE: Probe → Walking Skeleton

Wave: SPIKE (between DISCUSS and DESIGN) | Agent: Attila (nw-software-crafter) | Command: /nw-spike

Overview

Execute a two-phase wave that turns a risky assumption into visible, iterable value as fast as possible:

1. PROBE — quick throwaway validation of one core assumption (30-60 min, code in /tmp/)
2. PROMOTION GATE (interactive) — ask the user whether to promote the probe
3. WALKING SKELETON — refactor the probe into an end-to-end thin slice committed to the repository (1-3 h, code in src/ + 1 acceptance test)

The PROBE answers "does the mechanism work?". The WALKING SKELETON answers "can a user see it working end-to-end?". You never throw away working validated code — you promote it and iterate.

When to use

The spike is needed when the feature introduces:

• A new mechanism never tried in this codebase
• A performance requirement that cannot be validated by reasoning alone
• An external integration with unknown behaviour

If none of the above apply, skip SPIKE and go to DESIGN.

Prior Wave Consultation

1. DISCUSS artifacts: Read docs/feature/{feature-id}/discuss/ (required)
   • user-stories.md — scope and acceptance criteria
   • wave-decisions.md — constraints and assumptions to test
2. DIVERGE artifacts: Read docs/feature/{feature-id}/diverge/recommendation.md (if present)

Interactive decision points (Phase 1 entry)

Decision 1: Probe scope

Question: What is the ONE assumption you need to validate? Examples:

• "Can we parse pytest output reliably in <5 seconds?"
• "Can the CEL library evaluate 100 expressions in <1 second?"
• "Can we write to .git/hooks/ from a subprocess without corruption?"

Decision 2: Performance budget

Question: What is the timing constraint? (Enter "none" if mechanism validation only) Examples:

• "<5 seconds end-to-end"
• "<100ms per operation"
• "Handle 10K items without OOM"

Decision 3: End-to-end path preview

Question: If this probe works, what would the thinnest end-to-end slice look like? Capture the rough path: user-facing entry → business logic → persistence/services → user-visible output. This is not a commitment — it's context for the promotion gate later.

Phase 1 — PROBE

Throwaway validation of the assumption.

Agent invocation

@nw-software-crafter

Execute PROBE for "{feature-description}".

Probe question: {Decision 1 answer} Performance budget: {Decision 2 answer} Target e2e path (for later): {Decision 3 answer}

Rules:

• Code goes in /tmp/spike_{feature_id}/. Never in src/.
• Max 1 hour. No tests, no types, no error handling, no abstractions.
• One file preferred. Two files maximum.
• Use time.perf_counter() for timing.
• Print results to stdout.

After probe completes:

1. Write findings to docs/feature/{feature-id}/spike/findings.md — binary verdict (WORKS / DOESN'T WORK), timing, edge cases, design implications.
2. Do not delete the probe code yet — wait for the promotion gate.
3. Report verdict and ask the orchestrator to run the promotion gate.

Phase 2 — PROMOTION GATE (interactive)

Run this gate only after the probe completes and findings.md is written.

Present the user with three choices:

Default: if the probe verdict is WORKS and no reason to stop, recommend PROMOTE but let the user override.

Record the promotion decision in docs/feature/{feature-id}/spike/wave-decisions.md as an explicit wave decision with rationale.

Phase 3 — WALKING SKELETON (only if PROMOTE)

Refactor the probe into the thinnest end-to-end slice that is committed, tested, and demo-able.

Definition of Done (walking skeleton)

1. End-to-end path: the slice enters from a real user-facing entry point (CLI command, HTTP endpoint, UI action, hook) and exits at a real user-visible output (stdout, HTTP response, rendered screen, persisted file). Every layer in between is exercised — no layer is mocked unless that layer is an external paid service classified as costly in DISTILL's Walking Skeleton Strategy (then use the fake/contract test pattern).
2. One acceptance test: a @walking_skeleton @driving_port tagged scenario in tests/{test-type-path}/{feature-id}/acceptance/walking-skeleton.feature. The scenario MUST be green before hand-off.
3. Production location: code lives under src/{production-path}/, not in /tmp/. Minimal module skeleton is fine — no premature abstractions, no features beyond the walking skeleton.
4. Committed: the walking skeleton commit message is feat({feature-id}): walking skeleton — {one-line description}.
5. Demo-able: running the single acceptance test (or the real entry-point command) produces visible output that matches the user story from DISCUSS.
6. Back-propagation: if building the skeleton reveals a contradiction with DISCUSS or DESIGN, write the contradiction to docs/feature/{feature-id}/spike/upstream-issues.md and stop — do not hand off to DISTILL until resolved.

Agent invocation (Phase 3)

@nw-software-crafter

Promote probe for "{feature-description}" into a walking skeleton.

Source probe: /tmp/spike_{feature_id}/ Target driving adapter: {from Decision 3, refined with user} Target acceptance test path: tests/{test-type-path}/{feature-id}/acceptance/walking-skeleton.feature

Rules:

• Max 3 hours. Stop and escalate if over budget.
• One acceptance test only. No unit tests unless they are strictly required to make the acceptance test pass.
• No premature abstractions. The skeleton should be obviously incomplete — only the single path from the user story works. Error paths, edge cases, and other scenarios are DISTILL's job.
• Use the real driving adapter, the real domain code, the real driven adapter. In-memory doubles only for costly external services.
• Delete /tmp/spike_{feature_id}/ after promotion.

Walking skeleton commit checklist

• 1 acceptance test @walking_skeleton green
• Real user-facing entry point exercised (not a service function call)
• Real driven adapters for local resources (filesystem, git, subprocess, SQLite)
• Code in src/, not /tmp/
• Committed with conventional commit message
• Probe directory deleted
• Findings.md includes the "promoted on {date}" note

Progress tracking

The invoked agent MUST create a task list from its workflow phases at the start of execution using TaskCreate. Each phase becomes a task with the gate condition as completion criterion. Phase 1, Phase 2, and Phase 3 are separate task groups — Phase 3 tasks are only created if the promotion gate says PROMOTE.

Success criteria

Phase 1 (always)

• Exactly one assumption tested (not two, not zero)
• Probe code lives in /tmp/, never in src/
• Completed within 1 hour (or escalated with "BIGGER THAN EXPECTED")
• findings.md written with binary verdict, timing, and edge cases

Phase 2 (always)

• Promotion gate decision captured in wave-decisions.md
• One of: PROMOTE / DISCARD / PIVOT selected by user

Phase 3 (only if PROMOTE)

• Walking skeleton acceptance test green
• E2E path exercised through all non-costly layers
• Skeleton code in src/, committed
• Probe directory deleted
• No upstream contradictions left unresolved

Next wave

Handoff to: nw-solution-architect (DESIGN) — DESIGN reads findings.md and the walking skeleton (if promoted) before starting. The skeleton is a fait accompli — DESIGN designs the rest of the feature around it, not in place of it.

DISTILL (next wave after DESIGN) reads the walking skeleton as a prior artifact and adds additional scenarios and integration tests on top of it — it does not write the walking skeleton from scratch.

Wave decisions summary

Before completing SPIKE, produce docs/feature/{feature-id}/spike/wave-decisions.md:

# SPIKE Decisions -- {feature-id}

## Assumption Tested
- {the one question}

## Probe Verdict
- {WORKS / DOESN'T WORK}: {one-line summary}

## Promotion Decision
- {PROMOTE / DISCARD / PIVOT}: {rationale}

## Walking Skeleton (only if PROMOTE)
- Driving adapter: {entry point}
- Acceptance test: {path to .feature file}
- Commit: {commit sha of walking skeleton}
- Demo command: {how to run the skeleton}

## Design Implications
- {what DESIGN must account for based on probe results and skeleton learnings}

## Constraints Discovered
- {any new constraints from edge cases}

Examples

Example 1: Performance probe → promoted skeleton

/nw-spike "wave-matrix -- derive feature status from pytest + filesystem"

Probe question: "Can we collect pytest markers + parse filesystem state in <5 seconds?" Agent writes 50-line script in /tmp/spike_wave_matrix/. Result: 44 seconds (budget blown), but discovers pytest --collect-only --cache-only completes in 200 ms. Gate: user picks PROMOTE with the cache-only approach. Phase 3: agent refactors the probe into src/des/cli/wave_matrix.py with a wave-matrix CLI command; one acceptance test exercises subprocess.run(["wave-matrix", "--feature", "alpha"]) end-to-end and asserts the markdown output contains a row for alpha. DESIGN now designs the rest (multi-feature aggregation, cell navigation, refresh strategy) around the already-working skeleton.

Example 2: Integration probe → discard

/nw-spike "cel-policy-engine -- evaluate access control expressions"

Probe question: "Can cel-python evaluate 100 policy expressions in <1 second?" Agent installs cel-python, writes evaluation loop, measures 23 ms for 100 expressions. Verdict: WORKS. Edge case: nested map access syntax differs from Go CEL. Gate: user picks DISCARD — the findings are enough, the real access-control feature is large enough to deserve its own design wave. Phase 3 skipped. Findings committed. DESIGN reads findings.md.

Example 3: Mechanism probe → pivot

/nw-spike "git-hook-wiring -- install hooks via subprocess"

Probe question: "Can we write to .git/hooks/ from a Python subprocess without file corruption?" Agent tries concurrent access, discovers that the real risk is not corruption but the existing user hook being silently overwritten. Gate: user picks PIVOT — the real question is "how do we install alongside existing user hooks?". Findings annotated with the pivot, new probe scheduled.

Expected outputs

docs/feature/{feature-id}/spike/
  findings.md           # always
  wave-decisions.md     # always (with promotion decision)
  upstream-issues.md    # only if skeleton revealed prior-wave contradictions

src/{production-path}/  # only if PROMOTE
  {module}.py           # minimal walking skeleton

tests/{test-type-path}/{feature-id}/acceptance/
  walking-skeleton.feature  # only if PROMOTE — 1 scenario, @walking_skeleton @driving_port
  steps/                    # only if PROMOTE