AgentSkillsCN

slice

Implement one tracer-bullet slice following the inside-out methodology. Use when you have a tracer-bullet card ready to build. Implements functional core first, then imperative shell, then end-to-end wiring, then alignment refactor.

SKILL.md
--- frontmatter
name: slice
description: Implement one tracer-bullet slice following the inside-out methodology. Use when you have a tracer-bullet card ready to build. Implements functional core first, then imperative shell, then end-to-end wiring, then alignment refactor.
argument-hint: "[paste tracer-bullet card (or provide path to it)]"

Tracer-Bullet Slice

Implement one thin end-to-end slice of functionality, following the inside-out procedure.

Input

The slice is defined by a tracer-bullet card: $ARGUMENTS

Preconditions:

  • •A concept capsule must exist. If none → /pragma:capsule first.
  • •A card must exist. If none → /pragma:card first.

Extract from the card: (1) target behavior, (2) boundary crossings, (3) risks/assumptions, (4) definition of done. If the card is incomplete, stop and recommend rerunning /pragma:card.

Procedure

Follow these steps in order. Do not skip or reorder.

0. Preflight gates

Before writing implementation code:

  • •Confirm card includes explicit BUY-OR-BUILD decision. If missing, stop and refine /pragma:card.
  • •If requirement behavior is still unclear in practice, stop and run /pragma:spike first to prototype/observe.

1. Spec tests first (red)

Before implementing behavior, translate card Definition of Done into tests:

  • •Add or update tests named in the card DoD
  • •Run tests and confirm at least one fails for the expected reason
  • •If tests pass unexpectedly, tighten test assertions or refine the card scope before writing implementation code

This is the "create the needle" step: define a narrow path to success first.

2. Functional core (pure domain logic)

Implement using the functional core / imperative shell pattern (Bernhardt):

  • •Define types/structures using capsule glossary terms
  • •Write core function(s) as pure transformations — no I/O, no side effects
  • •Write tests covering the target behavior
  • •Enforce invariants at construction boundaries

No frameworks, no infrastructure, no I/O in this step. No speculative abstractions.

3. Imperative shell (thin I/O adapter)

Add the minimal I/O boundary connecting the core to the real world. The shell calls the core, never the reverse. No business logic in the shell.

4. Wire end-to-end

Connect the full path: entry point → shell → core → shell → output. Make it actually run. Write or update an integration test proving the target behavior.

4.5. Commit the behavior (recommended)

Commit the smallest set of changes that makes the E2E path pass. Message style: Behavior: <target behavior>

5. Alignment refactor — NOT optional

Refactor immediately while context is fresh:

  • •Naming: all names match the capsule glossary? Rename if not.
  • •Module boundaries: can you complete "This module hides the decision about ___" (Parnas) for each module?
  • •Dead code: delete anything speculative, unused, or "for later."
  • •Slice cohesion: does this slice form a coherent vertical unit?

6. Verify

Run the project's existing verification harness. All checks must pass. If any fails, fix and re-run from step 1 of verification.

7. Commit the refactor

Separate from the behavior commit. Message style: Refactor: align slice to capsule

8. Classify authority deltas (mandatory)

Before closing the slice, classify what changed and route updates to the correct authority artifact:

  • •Semantics changed (glossary/invariant/happy-path/non-goal meaning) → /pragma:capsule update
  • •Strategy changed (cross-cutting decision/rationale/reversal trigger) → /pragma:roadmap update
  • •Phase control changed (scope/status/ordering/deferment/exit criteria) → /pragma:milestone update
  • •Confidence changed (assumption validated/invalidated/confidence shift) → /pragma:assumptions update
  • •Enforcement readiness changed (invariant now enforceable in code/tests) → /pragma:contract

Use explicit none for lanes with no change.

9. Update the assumptions ledger (mandatory)

Run /pragma:assumptions update with the slice summary, assumptions made, and validation evidence.

Constraints

  • •One slice only. No adjacent behaviors, future features, or "while we're here" improvements.
  • •Needle before thread. Do not write behavior code until spec tests go red for the right reason.
  • •No speculative abstractions. No generic frameworks, no "future extensibility."
  • •No new abstractions unless forced. Only abstract when two concrete cases demand it.
  • •Refactor is part of done. A slice is not done until step 5 is complete.
  • •Explicit assumptions. State them. If risky, flag for a spike.
  • •No silent authority drift. Any non-none authority delta must be surfaced and routed before additional delivery work.

Output

  1. •Behavior delivered: what is now true that wasn't before
  2. •Files changed: list
  3. •Authority Delta:
    • •Semantics: none | /pragma:capsule update — [reason]
    • •Strategy: none | /pragma:roadmap update — [reason]
    • •Phase control: none | /pragma:milestone update — [reason]
    • •Assumptions: none | /pragma:assumptions update — [reason]
    • •Enforcement: none | /pragma:contract — [reason]
  4. •Assumptions made: anything that should be validated
  5. •Suggested next step: what slice or action follows
  6. •Ledger: run /pragma:assumptions update (mandatory after every slice)
  7. •Lifecycle: State: delivery, Next: first non-'none' authority delta command (otherwise /pragma:assumptions update), Loop: /pragma:consult (default unless user explicitly continues directly)