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.
Comment and Documentation Integrity
- Document durable constraints, invariants, contracts, and behavior.
- Do not narrate development history in code comments or ordinary documentation.
- Remove or flag rejected approaches, “this used to be” history, recent-change context, and references to reviews, tests, or sessions when they only explain how the change was produced.
- Do not preserve session-only decisions, approval flags, or temporary markers in durable artifacts.
- Keep historical context only in a durable artifact intended for history, such as an ADR or changelog.
- Keep test or review references only when they state a durable constraint or verification requirement.
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:
- 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
- target phase:
- 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
- File exists: unified diff (
- Approval ask:
Approve this scope? (examples: approve/ok/confirm) - 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
- Phase 1 (stubs/skeleton/interfaces) must contain only:
-
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.
- Phase 1 (stubs/skeleton/interfaces):
-
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:
- No change needed (YAGNI)
- Reuse existing local helper/pattern
- Replace with stdlib/native
- Use already-installed dependency
- Shrink to smallest safe diff
- Only then add new code/abstraction
When adding or modifying comments, write only the durable constraint or behavior a later reader needs.
3. Execute patch
- Restate bounded scope and expected behavior.
- Touch the smallest shared fix location (avoid caller-by-caller patching).
- Reuse existing local helpers/patterns before adding new abstraction.
- Apply minimal safe diff.
- Run smallest agreed check.
- 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.