ponytail/hooks/ponytail-activate.js

#!/usr/bin/env node
// ponytail — Claude Code SessionStart activation hook
//
// Runs on every session start:
//   1. Writes flag file at ~/.claude/.ponytail-active (statusline reads this)
//   2. Emits ponytail ruleset as hidden SessionStart context
//   3. Detects missing statusline config and emits setup nudge

const fs = require('fs');
const path = require('path');
const os = require('os');
const { getDefaultMode } = require('./ponytail-config');

const claudeDir = path.join(os.homedir(), '.claude');
const flagPath = path.join(claudeDir, '.ponytail-active');
const settingsPath = path.join(claudeDir, 'settings.json');

const mode = getDefaultMode();

// "off" mode — skip activation entirely, don't write flag or emit rules
if (mode === 'off') {
  try { fs.unlinkSync(flagPath); } catch (e) {}
  process.stdout.write('OK');
  process.exit(0);
}

// 1. Write flag file
try {
  fs.mkdirSync(path.dirname(flagPath), { recursive: true });
  fs.writeFileSync(flagPath, mode);
} catch (e) {
  // Silent fail -- flag is best-effort, don't block the hook
}

// 2. Emit the ponytail ruleset, filtered to the active intensity level.
//    A short summary is too weak — models drift back to over-building
//    mid-conversation, especially after context compression prunes it.
//    Full rules with examples anchor behavior much more reliably.
//
//    Reads SKILL.md at runtime so edits to the source of truth propagate
//    automatically — no hardcoded duplication to go stale.

// Modes that have their own independent skill files — not intensity levels.
// For these, emit a short activation line; the skill itself handles behavior.
const INDEPENDENT_MODES = new Set(['review']);

if (INDEPENDENT_MODES.has(mode)) {
  process.stdout.write('PONYTAIL MODE ACTIVE — level: ' + mode + '. Behavior defined by /ponytail-' + mode + ' skill.');
  process.exit(0);
}

// Read SKILL.md — the single source of truth for ponytail behavior.
// Plugin installs: __dirname = <plugin_root>/hooks/, SKILL.md at <plugin_root>/skills/ponytail/SKILL.md
let skillContent = '';
try {
  skillContent = fs.readFileSync(
    path.join(__dirname, '..', 'skills', 'ponytail', 'SKILL.md'), 'utf8'
  );
} catch (e) { /* standalone install — will use fallback below */ }

let output;

if (skillContent) {
  // Strip YAML frontmatter
  const body = skillContent.replace(/^---[\s\S]*?---\s*/, '');

  // Filter intensity table: keep header rows + only the active level's row
  const filtered = body.split('\n').reduce((acc, line) => {
    // Intensity table rows start with | **level** |
    const tableRowMatch = line.match(/^\|\s*\*\*(\S+?)\*\*\s*\|/);
    if (tableRowMatch) {
      if (tableRowMatch[1] === mode) {
        acc.push(line);
      }
      return acc;
    }

    // Example lines start with "- level:" — keep only lines matching active level
    const exampleMatch = line.match(/^- (\S+?):\s/);
    if (exampleMatch) {
      if (exampleMatch[1] === mode) {
        acc.push(line);
      }
      return acc;
    }

    acc.push(line);
    return acc;
  }, []);

  output = 'PONYTAIL MODE ACTIVE — level: ' + mode + '\n\n' + filtered.join('\n');
} else {
  // Fallback when SKILL.md is not found (hook installed without skills dir).
  // Minimum viable ruleset — better than nothing.
  output =
    'PONYTAIL MODE ACTIVE — level: ' + mode + '\n\n' +
    'You are a lazy senior developer. Lazy means efficient, not careless. The best code is the code never written.\n\n' +
    '## Persistence\n\n' +
    'ACTIVE EVERY RESPONSE. No drift back to over-building. Still active if unsure. Off only: "stop ponytail" / "normal mode".\n\n' +
    'Current level: **' + mode + '**. Switch: `/ponytail lite|full|ultra`.\n\n' +
    '## The ladder\n\n' +
    'Before any code, stop at the first rung that holds:\n' +
    '1. Does this need to be built at all? (YAGNI)\n' +
    '2. Does the standard library do this? Use it.\n' +
    '3. Does a native platform feature cover it? Use it.\n' +
    '4. Does an already-installed dependency solve it? Use it.\n' +
    '5. Can this be one line? Make it one line.\n' +
    '6. Only then: write the minimum code that works.\n\n' +
    '## Rules\n\n' +
    'No abstractions that were not requested. No avoidable dependencies. No boilerplate nobody asked for. ' +
    'Deletion over addition. Boring over clever. Fewest files possible. ' +
    'Ship the lazy version and question the complex request in the same response — never stall. ' +
    'Between two same-size stdlib options, pick the one correct on edge cases. ' +
    'Mark intentional simplifications with a `ponytail:` comment — a shortcut with a known ceiling names the ceiling and the upgrade path in the comment.\n\n' +
    '## Output\n\n' +
    'Code first. Then at most three short lines: what was skipped, when to add it. ' +
    'If the explanation is longer than the code, delete the explanation.\n\n' +
    '## When NOT to be lazy\n\n' +
    'Never simplify away: input validation at trust boundaries, error handling that prevents data loss, ' +
    'security measures, accessibility basics, anything the user explicitly asked to keep. ' +
    'Non-trivial logic leaves ONE runnable check behind (assert-based demo/self-check or one small test file; no frameworks). Trivial one-liners need no test.\n\n' +
    '## Boundaries\n\n' +
    'Ponytail governs what you build, not how you talk. "stop ponytail" or "normal mode": revert. Level persists until changed or session end.';
}

// 3. Detect missing statusline config — nudge Claude to help set it up
try {
  let hasStatusline = false;
  if (fs.existsSync(settingsPath)) {
    const settings = JSON.parse(fs.readFileSync(settingsPath, 'utf8'));
    if (settings.statusLine) {
      hasStatusline = true;
    }
  }

  if (!hasStatusline) {
    const isWindows = process.platform === 'win32';
    const scriptName = isWindows ? 'ponytail-statusline.ps1' : 'ponytail-statusline.sh';
    const scriptPath = path.join(__dirname, scriptName);
    const command = isWindows
      ? `powershell -ExecutionPolicy Bypass -File "${scriptPath}"`
      : `bash "${scriptPath}"`;
    const statusLineSnippet =
      '"statusLine": { "type": "command", "command": ' + JSON.stringify(command) + ' }';
    output += "\n\n" +
      "STATUSLINE SETUP NEEDED: The ponytail plugin includes a statusline badge showing active mode " +
      "(e.g. [PONYTAIL], [PONYTAIL:ULTRA]). It is not configured yet. " +
      "To enable, add this to ~/.claude/settings.json: " +
      statusLineSnippet + " " +
      "Proactively offer to set this up for the user on first interaction.";
  }
} catch (e) {
  // Silent fail — don't block session start over statusline detection
}

process.stdout.write(output);