config-audit/scanners/lib/write-scope.mjs

/**
 * Write-target scope classification (M-BUG-41).
 *
 * The workflow observes configuration across repos, but every write it then
 * proposes was presented as though it landed where the session stands. Five
 * arms were measured carrying that hole: `implement` (approval prompt names no
 * path at all — only a count), `rollback` (renders repo-relative-looking paths
 * while writing to absolute originals), `fix` (`--global` mixes user-scope and
 * repo rows into one unmarked table), `plan`, and `campaign export`.
 *
 * The gate's STRENGTH comes from the target's scope class, never from which
 * command is asking. Command-owned policy would be five policies to drift apart
 * — the shape that put the lever table in five copies (#61). Both required
 * outcomes then fall out of one table without an exception rule: a plan
 * exported into another repo is *disclosed* (cross-repo is by design there),
 * while a rewrite of `~/.claude/CLAUDE.md` *requires explicit approval*,
 * because it costs in every repo on every turn.
 *
 * `silent` means "no gate of its own", not "no approval": the existing
 * confirmation surfaces stand untouched, and this module only adds location to
 * them.
 *
 * Two orderings below are load-bearing, and both were measured rather than
 * reasoned about:
 *
 *   `plugin-managed` before `user-scope` — the canonical
 *   `~/.claude/config-audit/` and the legacy `~/.config-audit/` both exist on a
 *   real machine, and every command writes session state into them. Matched the
 *   other way round, the gate fires on every write ever made and gets switched
 *   off, which is worse than having no gate.
 *
 *   `user-scope` before `cross-repo` — `~/.claude/.git` exists (the operator's
 *   `~/.claude` is a git repo whose `.gitignore` is `*`). A plain
 *   `.git`-upward-walk therefore answers "another repo" for
 *   `~/.claude/CLAUDE.md`, silently downgrading the strongest gate on the
 *   subtraction axis's primary target to disclosure-only.
 *
 * This module classifies. It never writes, never prompts, and never decides
 * whether an approved write is a good idea.
 */

import { existsSync } from 'node:fs';
import { homedir } from 'node:os';
import { isAbsolute, join, relative, resolve } from 'node:path';

/**
 * True when `child` is `parent` itself or lives underneath it.
 *
 * Uses `relative()` rather than `startsWith()`: a sibling directory whose name
 * merely prefixes the parent's (`my-plugin-2` against `my-plugin`) satisfies
 * `startsWith` and would skip the gate entirely.
 *
 * @param {string} parent - Absolute directory path.
 * @param {string} child - Absolute path to test.
 * @returns {boolean}
 */
function isWithin(parent, child) {
  const rel = relative(parent, child);
  return rel === '' || (!rel.startsWith('..') && !isAbsolute(rel));
}

/**
 * Default repo-root test. Kept injectable so classification is testable
 * without a fixture tree.
 *
 * @param {string} dir - Absolute directory path.
 * @returns {boolean}
 */
function defaultIsRepoRoot(dir) {
  return existsSync(join(dir, '.git'));
}

/**
 * Walk upwards from `absPath` looking for the nearest enclosing repo root.
 *
 * @param {string} absPath - Absolute path to start from.
 * @param {(dir: string) => boolean} isRepoRoot - Repo-root predicate.
 * @returns {string|null} The nearest repo root, or null if there is none.
 */
function nearestRepoRoot(absPath, isRepoRoot) {
  let dir = absPath;
  for (;;) {
    if (isRepoRoot(dir)) return dir;
    const parent = resolve(dir, '..');
    if (parent === dir) return null;
    dir = parent;
  }
}

/**
 * The scope classes, in match order.
 *
 * Declaration order IS match order — this object is the single source for the
 * class name, its gate, its disclosure wording and its predicate, so no caller
 * and no test can hold a second copy that drifts.
 *
 * @type {Record<string, {gate: 'silent'|'disclose'|'require-ok', disclosure: string|null, matches: Function}>}
 */
export const SCOPE_CLASSES = {
  // The plugin's own bookkeeping: session state, backups, ledgers. Not the
  // user's configuration, and written on essentially every run.
  'plugin-managed': {
    gate: 'silent',
    disclosure: null,
    matches: (target, ctx) => ctx.pluginRoots.some((root) => isWithin(root, target)),
  },

  // Where the session stands. The ordinary case.
  'in-repo': {
    gate: 'silent',
    disclosure: null,
    matches: (target, ctx) => ctx.repoRoot !== null && isWithin(ctx.repoRoot, target),
  },

  // Machine-wide configuration: loaded in every repo, on every turn, so the
  // cost of a change here is not confined to the project in front of the user.
  'user-scope': {
    gate: 'require-ok',
    disclosure: 'This writes to your machine-wide Claude configuration, outside this project. '
      + 'It affects every project you open, so it needs your explicit go-ahead.',
    matches: (target, ctx) => isWithin(ctx.userConfigRoot, target),
  },

  // A different project. Some commands do this by design; the gate is to say
  // so, not to refuse.
  'cross-repo': {
    gate: 'disclose',
    disclosure: 'This writes into a different project than the one you are working in. '
      + 'Any directories it needs there will be created.',
    matches: (target, ctx) => {
      const root = nearestRepoRoot(target, ctx.isRepoRoot);
      return root !== null && root !== ctx.repoRoot;
    },
  },

  // Neither this project, nor another project, nor machine-wide config.
  'outside': {
    gate: 'require-ok',
    disclosure: 'This writes to a location outside any project and outside your Claude '
      + 'configuration, so it needs your explicit go-ahead.',
    matches: () => true,
  },
};

/**
 * Classify a write target relative to the repo the session stands in.
 *
 * @param {string} targetPath - The path that is about to be written.
 * @param {string|null} sessionRepoRoot - Repo root of the current session.
 * @param {object} [options]
 * @param {(dir: string) => boolean} [options.isRepoRoot] - Repo-root predicate.
 * @param {string} [options.home] - Override for the home directory.
 * @returns {{scopeClass: string, gate: string, disclosure: string|null, target: string}}
 */
export function classifyWriteTarget(targetPath, sessionRepoRoot, options = {}) {
  const home = options.home ?? homedir();
  const isRepoRoot = options.isRepoRoot ?? defaultIsRepoRoot;

  const target = resolve(targetPath);
  const ctx = {
    repoRoot: sessionRepoRoot === null || sessionRepoRoot === undefined
      ? null
      : resolve(sessionRepoRoot),
    userConfigRoot: join(home, '.claude'),
    // Both roots are live: `backup.mjs` prefers `~/.claude/config-audit/` and
    // falls back to the legacy `~/.config-audit/`.
    pluginRoots: [
      join(home, '.claude', 'config-audit'),
      join(home, '.config-audit'),
    ],
    isRepoRoot,
  };

  for (const [scopeClass, spec] of Object.entries(SCOPE_CLASSES)) {
    if (spec.matches(target, ctx)) {
      return { scopeClass, gate: spec.gate, disclosure: spec.disclosure, target };
    }
  }

  // Unreachable: `outside` matches unconditionally. Kept so a future edit that
  // narrows the last predicate fails loudly instead of returning undefined.
  throw new Error(`write-scope: no class matched ${target}`);
}