ContextSessionStart· compact

Re-inject context after compaction

Re-injects the project conventions and critical context into the session after Claude Code compacts the context window, preventing the loss of important information.

Use cases

Recall the project conventions (package manager, code style) after compaction
Re-inject the current sprint or critical tasks
Recall important test or build commands

Providers & tags

Claude Code

#context#compaction#session#conventions

settings.json fragment

{
  "hooks": {
    "SessionStart": [
      {
        "hooks": [
          {
            "command": "node $CLAUDE_PROJECT_DIR/.claude/hooks/reinject-after-compact.mjs",
            "type": "command"
          }
        ],
        "matcher": "compact"
      }
    ]
  }
}

Script · .claude/hooks/reinject-after-compact.mjs

#!/usr/bin/env node
// Réinjecte le contexte sauvegardé avant la dernière compaction (SessionStart)
import { readFileSync, existsSync, readdirSync } from 'fs';
import { join } from 'path';
import { fileURLToPath } from 'url';

export function run(
  input,
  {
    exists = existsSync,
    readFile = readFileSync,
    readdir = readdirSync,
    backupDir = '/tmp/claude-compact-backups',
  } = {},
) {
  const sessionId = input.session_id ?? '';
  if (!exists(backupDir)) return null;

  // Cherche le backup de la session courante en priorité, sinon le plus récent
  let backupFile = sessionId ? join(backupDir, `${sessionId}.json`) : null;

  if (!backupFile || !exists(backupFile)) {
    const files = readdir(backupDir)
      .filter((f) => f.endsWith('.json'))
      .map((f) => ({
        f,
        mtime: new Date(readFile(join(backupDir, f), 'utf8').split('"saved_at":"')[1]?.split('"')[0] ?? 0),
      }))
      .sort((a, b) => b.mtime - a.mtime);
    backupFile = files[0] ? join(backupDir, files[0].f) : null;
  }

  if (!backupFile || !exists(backupFile)) return null;

  try {
    const { summary, saved_at } = JSON.parse(readFile(backupFile, 'utf8'));
    if (summary) {
      return `## Contexte de la session précédente (avant compaction du ${saved_at})\n\n${summary}\n`;
    }
  } catch {
    // Fichier corrompu — ignorer silencieusement
  }
  return null;
}

/* v8 ignore next 5 */
if (process.argv[1] === fileURLToPath(import.meta.url)) {
  const input = JSON.parse(readFileSync(0, 'utf8'));
  const result = run(input);
  if (result) process.stdout.write(result);
}