gsd-read-guard.js

#!/usr/bin/env node
// gsd-hook-version: {{GSD_VERSION}}
// GSD Read Guard — PreToolUse hook
// Injects advisory guidance when Write/Edit targets an existing file,
// reminding the model to Read the file first.
//
// Background: Non-Claude models (e.g. MiniMax M2.5 on OpenCode) don't
// natively follow the read-before-edit pattern. When they attempt to
// Write/Edit an existing file without reading it, the runtime rejects
// with "You must read file before overwriting it." The model retries
// without reading, creating an infinite loop that burns through usage.
//
// This hook prevents that loop by injecting clear guidance BEFORE the
// tool call reaches the runtime. The model sees the advisory and can
// issue a Read call on the next turn.
//
// Triggers on: Write and Edit tool calls
// Action: Advisory (does not block) — injects read-first guidance
// Only fires when the target file already exists on disk.

const fs = require('fs');
const path = require('path');

let input = '';
const stdinTimeout = setTimeout(() => process.exit(0), 3000);
process.stdin.setEncoding('utf8');
process.stdin.on('data', chunk => input += chunk);
process.stdin.on('end', () => {
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