Additive Bias Defense

---
name: additive-bias-defense
description: "Inverts burden of proof for code additions. Use when reviewing PRs, planning refactors, or running unbloat to challenge every addition's necessity."
allowed-tools: "[]"
category: general-purpose
source_repo: athola/claude-night-market
source_path: "plugins/leyline/skills/additive-bias-defense/SKILL.md"
source_url: https://github.com/athola/claude-night-market/blob/HEAD/plugins/leyline/skills/additive-bias-defense/SKILL.md
---


> The default answer to "should we add this?" is no.
> The burden of proof is on the addition.

# Additive Bias Defense

> **Note (#444):** Frontmatter declares ``provides.guidance``, not
> ``provides.contract``. The scrutiny questions are consumed by
> partner skills (``pensive:code-refinement``, ``conserve:unbloat``,
> ``imbue:scope-guard``) that voluntarily embed them; no validator or
> hook in leyline enforces them directly. If a future contributor
> adds enforcement, restore the ``contract`` label and link the
> validator path here.

## When NOT To Use

- Removing bloat that already landed (use `conserve:bloat-detector`)
- Scoring whether a feature is worth building (use `imbue:scope-guard`)

## The Problem

LLMs are additive by nature. They reinvent wheels, add
unnecessary complexity, hallucinate issues and modify
tests to justify them, and deviate from priorities. This
contract provides a systemic defense.

## The Scrutiny Questions

Applied to every proposed addition (code, files,
abstractions, error handling, configuration):

1. **Priority alignment**: Is this a deviation from the
   current priority?
2. **Criticality**: Is it critical to implement at this
   juncture?
3. **Simplicity**: Does a simpler or more elegant
   solution exist?
4. **Evidence**: What evidence proves this is needed
   (not assumed)?
5. **Consequence**: What breaks if we do not add this?

If the proposer cannot answer questions 4 and 5 with
concrete evidence, the addition is unjustified.

## Anti-Pattern Detection

| Pattern | Signal | Challenge |
|---------|--------|-----------|
| Wheel reinvention | New utility/helper overlapping existing code | "Does X already do this?" |
| Hallucinated issues | Fix for a bug with no reproduction evidence | "Show the failing test before the fix" |
| Test manipulation | Test changed to match behavior rather than spec | "Did the spec change, or did you change the test?" |
| Complexity creep | Abstraction introduced for single use case | "Is this the 3rd use, or the 1st?" |
| Priority deviation | Work not traceable to current task/spec | "Which requirement does this serve?" |
| Gold plating | Error handling or flexibility beyond need | "What breaks without this?" |

## Burden of Proof Verdict

After applying scrutiny questions and anti-pattern
detection, produce a verdict:

| Verdict | Meaning | Action |
|---------|---------|--------|
| `justified` | Evidence supports the addition | Proceed |
| `needs_evidence` | Plausible but unproven | Provide evidence or remove |
| `unjustified` | No evidence, likely bias | Remove or justify |

## Integration Contract

Review-oriented skills MUST consult this contract by:

1. Applying the 5 scrutiny questions to each addition
2. Scanning for the 6 anti-patterns
3. Producing a burden-of-proof verdict
4. Including the verdict in their output

### Consuming Skills

| Skill | Integration Point |
|-------|-------------------|
| `attune:war-room` | Prosecution Counsel role uses scrutiny questions |
| `sanctum:pr-review` | Every added file/function challenged |
| `pensive:code-refinement` | Refactors pass "3rd use" test |
| `conserve:unbloat` | Findings feed removal candidates |
| `attune:mission-orchestrator` | Plan sections scanned before user review |
| `imbue:justify` | Scrutiny questions extend audit protocol |

## Related Skills

- `imbue:karpathy-principles` - "Simplicity First" and "Surgical Changes" principles invoke this contract from a higher-level four-principle synthesis
- See `docs/quality-gates.md#skill-level-quality-gate-composition` for the full gate-skill federation graph

## The Subtraction Principle

> Rely less on AI and initial lines of thinking.
> Challenge yourself to think of a more elegant
> implementation or a simpler solution.

Before accepting any addition, ask: "Could I achieve
this by removing code instead of adding it?" If yes,
prefer the subtractive approach.

## Exit Criteria

- [ ] All 5 scrutiny questions applied to every proposed addition;
  questions 4 (evidence) and 5 (consequence) answered with
  concrete evidence, not assumptions
- [ ] All 6 anti-patterns scanned (wheel reinvention, hallucinated
  issues, test manipulation, complexity creep, priority deviation,
  gold plating); any match named with the pattern label
- [ ] A burden-of-proof verdict produced for each addition:
  `justified`, `needs_evidence`, or `unjustified`; the verdict
  appears in the consuming skill's output
- [ ] Subtraction principle applied: at least one check for
  "could this be achieved by removing code instead?" before
  accepting any net-positive line-count change

---

**Source:** [`athola/claude-night-market`](https://github.com/athola/claude-night-market) → `plugins/leyline/skills/additive-bias-defense/SKILL.md`