Initial commit

hooks/context_restorer.js

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+#!/usr/bin/env node
+/**
+ * Context Restorer (SessionStart Hook)
+ *
+ * Automatically injects preserved context from scratch_pad.md into new session.
+ * Complements PreCompact hook (context_preserver.py) for DRY workflow:
+ *
+ * Session 1: Work → /compact → PreCompact writes scratch_pad.md
+ * Session 2: SessionStart injects scratch_pad.md → Claude has context (no Read needed!)
+ *
+ * DRY Benefit: No redundant file reading - context injected once at session start.
+ *
+ * Context Cost: Variable (size of scratch_pad.md content, typically 2-5K tokens)
+ */
+
+const fs = require('fs');
+const path = require('path');
+
+/**
+ * Find project root by walking up from current directory
+ * @returns {string|null} Project root path or null if not found
+ */
+function findProjectRoot() {
+  let currentDir = process.cwd();
+  const root = path.parse(currentDir).root;
+
+  while (currentDir !== root) {
+    // Check for common project indicators
+    if (
+      fs.existsSync(path.join(currentDir, '.git')) ||
+      fs.existsSync(path.join(currentDir, 'pyproject.toml')) ||
+      fs.existsSync(path.join(currentDir, 'package.json')) ||
+      fs.existsSync(path.join(currentDir, 'Cargo.toml'))
+    ) {
+      return currentDir;
+    }
+    currentDir = path.dirname(currentDir);
+  }
+
+  return null;
+}
+
+/**
+ * Read and format scratch_pad.md for injection
+ * @param {string} scratchPadPath Path to scratch_pad.md
+ * @returns {string|null} Formatted context or null if not found
+ */
+function readScratchPad(scratchPadPath) {
+  if (!fs.existsSync(scratchPadPath)) {
+    return null;
+  }
+
+  try {
+    const content = fs.readFileSync(scratchPadPath, 'utf8');
+
+    // Don't inject if file is empty or very small
+    if (content.trim().length < 100) {
+      return null;
+    }
+
+    // Format for injection
+    const formatted = [
+      '━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━',
+      '📋 WORKING CONTEXT RESTORED FROM PREVIOUS SESSION',
+      '━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━',
+      '',
+      content,
+      '',
+      '━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━',
+      '✅ You can continue from where you left off.',
+      '   Context preserved automatically by PreCompact hook.',
+      '━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━',
+      ''
+    ].join('\n');
+
+    return formatted;
+
+  } catch (err) {
+    console.error(`DEBUG: Failed to read scratch_pad.md: ${err.message}`);
+    return null;
+  }
+}
+
+/**
+ * Delete scratch_pad.md after successful injection
+ * @param {string} scratchPadPath Path to scratch_pad.md
+ */
+function cleanupScratchPad(scratchPadPath) {
+  try {
+    if (fs.existsSync(scratchPadPath)) {
+      fs.unlinkSync(scratchPadPath);
+      console.error('DEBUG: ✅ Cleaned up scratch_pad.md (context injected)');
+    }
+  } catch (err) {
+    console.error(`DEBUG: Failed to cleanup scratch_pad.md: ${err.message}`);
+    // Non-fatal
+  }
+}
+
+/**
+ * Main hook execution
+ */
+function main() {
+  try {
+    // Read SessionStart event (contains source: startup|resume|clear|compact)
+    const event = JSON.parse(fs.readFileSync(0, 'utf-8'));
+    const source = event.source || 'unknown';
+
+    console.error(`DEBUG: SessionStart triggered (source: ${source})`);
+
+    // Find project root
+    const projectRoot = findProjectRoot();
+    if (!projectRoot) {
+      console.error('DEBUG: Project root not found, skipping context restoration');
+      process.exit(0);
+    }
+
+    console.error(`DEBUG: Project root: ${projectRoot}`);
+
+    // Check for scratch_pad.md
+    const scratchPadPath = path.join(projectRoot, 'scratch_pad.md');
+    const scratchPadContent = readScratchPad(scratchPadPath);
+
+    if (!scratchPadContent) {
+      console.error('DEBUG: No scratch_pad.md found or content too small');
+      // No context to restore, continue normally
+      const output = { continue: true };
+      console.log(JSON.stringify(output));
+      process.exit(0);
+    }
+
+    // Calculate token estimate (rough: 4 chars per token)
+    const estimatedTokens = Math.ceil(scratchPadContent.length / 4);
+    console.error(`DEBUG: Restoring context (~${estimatedTokens.toLocaleString()} tokens)`);
+
+    // Inject context via additionalContext
+    const output = {
+      continue: true,
+      hookSpecificOutput: {
+        hookEventName: 'SessionStart',
+        additionalContext: scratchPadContent
+      },
+      feedback: `📋 Working context restored from previous session (~${estimatedTokens.toLocaleString()} tokens)`,
+      suppressOutput: false  // Show in transcript for transparency
+    };
+
+    console.log(JSON.stringify(output));
+
+    // Cleanup scratch_pad.md after successful injection
+    // (prevents re-injection in future sessions)
+    cleanupScratchPad(scratchPadPath);
+
+    process.exit(0);
+
+  } catch (err) {
+    console.error('Context restoration error:', err.message);
+    // Fail gracefully - don't block session
+    const output = { continue: true };
+    console.log(JSON.stringify(output));
+    process.exit(0);
+  }
+}
+
+main();