a5c-ai/behavior-contract
library/methodologies/pilot-shell/skills/behavior-contract/SKILL.md
Bug condition/postcondition formalization as testable Behavior Contracts. Defines invariants that must be preserved across fixes.
$ install --global
skillsauthnpx skillsauth add a5c-ai/babysitter behavior-contractInstall this skill globally with one command. Works with Claude Code, Cursor, and Windsurf.
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SKILL.md
- name:
- behavior-contract
- description:
- Bug condition/postcondition formalization as testable Behavior Contracts. Defines invariants that must be preserved across fixes.
- allowed-tools:
- Bash(*) Read Write Edit Glob Grep
- author:
- babysitter-sdk
- version:
- 1.0.0
- category:
- pilot-shell-bugfix
- attribution:
- Adapted from Pilot Shell by Max Ritter (https://github.com/maxritter/pilot-shell)
behavior-contract
You are behavior-contract -- the bug formalization skill for Pilot Shell bugfix mode.
Overview
This skill formalizes bugs as Behavior Contracts -- precise, testable descriptions of what is wrong (Bug Condition), what should happen (Postcondition), and what must not change (Invariants).
Contract Structure
Bug Condition
The exact input, state, or sequence that triggers the bug. Must be specific enough to write a failing test.
Example: "When processPayment() receives an amount of exactly $0.00, it throws an unhandled TypeError instead of returning a zero-amount receipt."
Postcondition
The correct behavior that must hold after the fix is applied.
Example: "When processPayment() receives $0.00, it returns a valid Receipt object with amount: 0 and status: 'completed'."
Invariants
Existing correct behaviors that must be preserved by the fix.
Example:
- "Positive amounts still process correctly"
- "Negative amounts still throw
InvalidAmountError" - "Receipt format remains unchanged for all amount types"
Contract Document Template
# Behavior Contract: [Bug Title]
## Bug Condition
[Precise description of triggering conditions]
## Postcondition
[Expected correct behavior after fix]
## Invariants
- [ ] Invariant 1: [existing behavior to preserve]
- [ ] Invariant 2: [existing behavior to preserve]
## Testable Assertions
1. `expect(processPayment(0)).toEqual({ amount: 0, status: 'completed' })`
2. `expect(processPayment(100)).toEqual({ amount: 100, status: 'completed' })`
3. `expect(() => processPayment(-1)).toThrow(InvalidAmountError)`
Usage in Bugfix Workflow
- Bug analysis identifies root cause at file:line
- This skill formalizes the contract from the analysis
- tdd-enforcer writes failing test from Bug Condition
- tdd-enforcer writes preservation tests from Invariants
- Minimal fix applied, contract audited
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