# Duck Patch

> Surgical implementation for small, bounded code edits after direction is clear. Use when: "apply this fix", "make a targeted edit", "patch this", "implement the agreed change".

- Skill: `sprngr/duck-patch` (Agent Skill, multi-file: 2 files)
- Install (CLI): `npx skillmds@latest add sprngr/duck-patch`
- Raw SKILL.md: https://api.skillmd.com/api/skills/sprngr/duck-patch/raw
- Safety review: pending
- Works with: Claude Code, Claude.ai, OpenAI Codex
- Category: Coding & Dev Tools
- License: MIT
- Author: sprngr (https://skillmd.com/u/sprngr)
- Updated: 2026-09-17
- Page: https://skillmd.com/skills/sprngr/duck-patch

---


Patch execution 🦆. Smallest safe diff first.

## Purpose

Execute a narrowly scoped code change once the fix direction is known.

## Philosophy Guardrails (skill-local)

Inherit shared guardrails from `references/GUARDRAILS.md`.

Skill-specific delta:

- Executes bounded implementation only; product and architecture decisions remain with user.

## Activation

Use when user asks for a targeted code edit and scope is clear (or can be clarified quickly).

## Method

### Subagent execution mode

When running as a subagent without a user channel (e.g., via duckling): do not apply edits or run commands. Execute scope clarification, Duck Ladder, and patch derivation as analysis; replace "apply minimal safe diff" and "run smallest agreed check" with approval-package content: the derived per-file diff blocks and verification plan. Emit per the host wrapper's contract (preflight + diffs + approval ask + status footer).

### 1. Clarify scope (if incomplete)

- ask 1-3 targeted clarifying questions when context is incomplete
- state assumptions explicitly when evidence is missing

**Mutating action gate:**
**Workspace-changing actions** (require approval based on change type):

**Semantic changes** (require full execution approval):

- Code/logic changes
- Documentation/planning changes (README, markdown docs, ADRs, CONTEXT.md, runbooks, design notes), except typo-only fixes in non-code text files
- Config/schema changes (settings, env vars, build config)
- Dependency changes (package.json, requirements.txt, etc.)
- File operations (create, delete, move)
- Mutating commands (git commit, install, build, deploy)
- Task delegation for implementation/patching

**Cosmetic changes** (require lightweight confirmation):

- Formatting/whitespace-only changes
- Typo fixes in non-code text files
- Confirmation phrase: "Confirm to proceed with [formatting change/typo fix]?"

**Edge cases:**

- JSDoc/docstring changes in code files are semantic (affects generated docs, code contracts)
- Comments explaining logic in code are semantic (affects maintainability understanding)
- Config comments are semantic (affects interpretation)
- Document updates (ADRs, CONTEXT.md) are semantic
- Examples in README that are code snippets are semantic (users copy-paste)

**Approval workflow:**
Before any semantic change, require execution approval:

  1. **Preflight** (required for every approval ask; if a field is missing, ask one clarifying question):
     - target phase:
       - Phase 1: stubs/skeleton/interfaces
       - Phase 2: wiring/integration
       - Phase 3: concrete implementation
     - phase-fit statement (why this diff matches phase constraints)
     - target files (bounded for selected phase)
     - expected behavior change
     - smallest verification check
  2. **Present list of changes broken down by file as formatted diff**
     - File exists: unified diff (`---`/`+++`/`@@` hunks, `-`/`+` prefixes)
     - File does not exist: full content in fenced code block, file path as header
     - One file per diff block
     - Inline an annotation above the diff hunks explaining each change
     - If any file violates phase constraints, split and re-propose before approval ask
  3. **Approval ask**: `Approve this scope? (examples: approve/ok/confirm)`
  4. **Wait for approval**: do not proceed with edits/commands/task delegation until user replies with explicit approval intent

**Rules:**

- No workspace-changing action without user approval/confirmation
**Approval intent tokens:**

- Accept as approval intent: "approve", "approved", "ok", "go ahead", "confirm", "yes"
- Also accept option-referencing approval sentences: "Proceed with option B in files X and Y.", "Approved. Run verification plan as proposed."
- Examples are non-exhaustive. Any clear approval intent is accepted.
- Do not treat non-approval continuation signals as approval: bare "continue", bare option letters ("B"), "next". No approval verb, no scope reference — not approval.

**Scope rules:**

- Phase caps (default):
  - Phase 1 (stubs/skeleton/interfaces): up to 6 files
  - Phase 2 (wiring/integration): up to 4 files
  - Phase 3 (concrete implementation): up to 2 files

- **Phase content constraints (hard gate):**
  - **Phase 1 (stubs/skeleton/interfaces) must contain only:**
    - file/module skeleton shape (folders, exports, section layout)
    - type/interface declarations
    - function/class signatures
    - placeholder returns/errors/TODO markers
    - minimal no-op wiring with no business logic
  - **Phase 1 must not contain:**
    - full feature/business logic
    - side-effectful flows (DB/network/auth/file writes)
    - complete UI behavior beyond placeholders
  - **Phase 2 (wiring/integration) can contain:**
    - route registration, DI/container wiring, module composition, event hookups
    - adaptation glue between existing components
  - **Phase 2 must not contain:**
    - substantial new business logic blocks
  - **Phase 3 (concrete implementation) contains:**
    - business logic, algorithms, side effects, full behavior completion

- **New-file bootstrap rule:**
  - If scope introduces new feature files, first approval pass must be Phase 1 stubs/skeleton/interfaces only.
  - Implement bodies in later Phase 2/3 approvals.
  - If a new file exceeds stub/skeleton intent, split that file into stub-first then implementation follow-up.
- If a phase exceeds its cap, split into smaller bounded approvals before executing.
- Review-fatigue triggers (objective):
  - Phase 1 (stubs/skeleton/interfaces):
    - If proposed diff in one approval exceeds 180 changed lines (additions + deletions) total, reduce current phase cap by at least 1 file (minimum cap is 1 file).
    - If any single file exceeds 90 changed lines (additions + deletions), split that file into a separate approval or smaller sequential edits.
  - Phase 2 (wiring/integration):
    - If proposed diff in one approval exceeds 120 changed lines (additions + deletions) total, reduce current phase cap by at least 1 file (minimum cap is 1 file).
    - If any single file exceeds 60 changed lines (additions + deletions), split that file into a separate approval or smaller sequential edits.
  - Phase 3 (concrete implementation):
    - If proposed diff in one approval exceeds 80 changed lines (additions + deletions) total, reduce current phase cap by at least 1 file (minimum cap is 1 file).
    - If any single file exceeds 40 changed lines (additions + deletions), split that file into a separate approval or smaller sequential edits.
  - If reviewer requests clarification on more than 2 files in same batch, reduce next batch by at least 1 file.
- If complexity or review fatigue increases, reduce cap further and continue in smaller batches.
- Reopen execution approval between phases, even when objective stays same.
- If scope changes after approval, reopen scope confirmation before continuing.

- Phase examples (application):
  - Phase 1 example: 5 files, 170 changed lines (additions + deletions) total, max single file 80 changed lines (additions + deletions). This is within cap and thresholds, so one approval can proceed.
  - Phase 2 example: 4 files, 130 changed lines (additions + deletions) total. This exceeds phase total threshold, so split into 2 approvals before execution.
  - Phase 3 example: 2 files, one file at 45 changed lines (additions + deletions). This exceeds single-file threshold, so split into smaller sequential edits.

### 2. Apply Duck Ladder

Before introducing new constructs, stop at first rung that holds:
1. No change needed (YAGNI)
2. Reuse existing local helper/pattern
3. Replace with stdlib/native
4. Use already-installed dependency
5. Shrink to smallest safe diff
6. Only then add new code/abstraction

### 3. Execute patch

1. Restate bounded scope and expected behavior.
2. Touch the smallest shared fix location (avoid caller-by-caller patching).
3. Reuse existing local helpers/patterns before adding new abstraction.
4. Apply minimal safe diff.
5. Run smallest agreed check.
6. Report exactly: changed files, behavior delta, verification result.

Output:

- one-line execution plan (file(s) + expected behavior)
- minimal patch summary (what changed, not a full essay)
- one smallest verification check and result
- if blocked: one-line blocker + next required input

## Boundaries

- Do not weaken security, trust boundaries, data-loss prevention, accessibility, or explicit user requirements.
- If root cause is unclear, hand back to `duck-debug` (trace mode if needed) instead of speculative edits.
- If verification cannot run locally, provide exact command user should run and expected signal.