# 471 2026 01 26 Boundary Contracts Not Enforced 3ce89fbf

> Summary

- Skill: `tools-only/471-2026-01-26-boundary-contracts-not-enforced-3ce89fbf` (Agent Skill, multi-file: 3 files)
- Install (CLI): `npx skillmds@latest add tools-only/471-2026-01-26-boundary-contracts-not-enforced-3ce89fbf`
- Raw SKILL.md: https://api.skillmd.com/api/skills/tools-only/471-2026-01-26-boundary-contracts-not-enforced-3ce89fbf/raw
- Safety review: pending (external: skill-scanner PASS, skillspector PASS)
- Works with: Claude Code, Claude.ai, OpenAI Codex
- Category: Coding & Dev Tools
- Author: tools-only (https://skillmd.com/u/tools-only)
- Updated: 2026-09-22
- Page: https://skillmd.com/skills/tools-only/471-2026-01-26-boundary-contracts-not-enforced-3ce89fbf

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## Summary

Boundary contracts between UI, core, and tools are partially implicit: several callbacks and tool entry points are typed as `Any` or use broad protocols, so the contract is not enforced by typing or tests. This makes boundary drift harder to detect and allows accidental coupling across layers.

## Context

Recent refactors established clean import direction and layer ordering, but contract surfaces (callbacks, tool factories, and state accessors) remain loosely typed in a few places.

## Root Cause

Contracts were defined informally via usage instead of explicit callback type aliases and minimal protocols. We missed it because there is no boundary-contract audit or type gate for these callback signatures; prevention is to encode contracts in `types/` and add a focused type/check step.

## Changes

- Pending: define explicit callback type aliases for tool results, plan approval, and streaming.
- Pending: narrow `StateManagerProtocol` into per-tool protocols (todo, plan approval, authorization).
- Pending: update tool factories and UI hooks to accept only the minimal protocols and callbacks.

## Behavioral Impact

**What users notice:**
- No immediate behavior change, but boundary leaks can manifest as subtle UI/core coupling and harder-to-debug callback misuse.

**What didn't change:**
- Runtime behavior and tool execution flow remain unchanged.

## Related Cards

- [[tool-registry-todo-alignment]]