dsh-facet/lib/scope.js

/**
 * The facet scope: which part of a project one session is allowed to see.
 *
 * ## Why the scope is the session's own folder
 *
 * A multi-faceted system is built from modules that look alike. In the project
 * this was written against there are fourteen controllers — the same idioms, the
 * same naming, the same shape — and a conversation about one of them that can
 * see all fourteen is a conversation that keeps having to work out which one it
 * is looking at. Narrowing it to the one being worked on removes the
 * confusability rather than trying to steer through it.
 *
 * The scope is therefore not configured. It is **where the session already is**:
 * the session's working directory, which the harness records immutably at
 * creation. Starting a conversation in `src/controllers/room/occupancy` makes
 * that controller the world the agent sees; nothing has to be declared, and a
 * session started at the project root is simply not scoped, which is the honest
 * answer for a conversation that is genuinely about the whole project.
 *
 * ## Why scope is additive rather than exclusive
 *
 * A facet is a window, not a relevance filter. In the same project 41.6% of the
 * code — shared types, services, infrastructure — sits outside every controller,
 * so a wall that cannot be opened would not confine the agent, it would only
 * make it wrong. Scope is therefore a *default*, and the way past it is an
 * explicit grant: `facet action=add` records a path for the rest of the session,
 * with the user's approval. Nothing here tries to infer that a needed file is
 * needed.
 *
 * This module is the pure half — argument extraction, text, reasons. It performs
 * no I/O and knows nothing about Cordis, so every rule below is testable without
 * a harness.
 */

/**
 * Model-supplied arguments that name a location, per tool.
 *
 * Deliberately conservative: only tools whose path argument is a plain top-level
 * string are listed. A tool that takes a path in a shape this table cannot read
 * is not guessed at — it is left unguarded, which is a decision, not an
 * oversight. `bash` is the deliberate one: a shell command cannot be judged
 * reliably from argv, so the facet is enforced on the file tools and `bash`
 * remains a legitimate way out. The prompt says so rather than pretending
 * otherwise.
 */
export const PATH_ARGUMENTS = Object.freeze({
  read: ['file_path'],
  write: ['file_path'],
  edit: ['file_path'],
  read_image: ['file_path'],
  grep: ['path'],
  glob: ['path'],
  str_replace_editor: ['path'],
  recall: ['path', 'focus'],
})

/** The tool this plugin registers, and the action on it that widens the scope. */
export const FACET_TOOL = 'facet'
export const WIDENING_ACTION = 'add'

/**
 * Every path a tool call names, as the model wrote them.
 *
 * Tolerant by design: arguments arrive as unvalidated JSON, and a policy plugin
 * that throws on a malformed call would break tools it has no business breaking.
 * Anything that is not a non-empty string is skipped.
 *
 * An empty result means "no opinion" — either the tool names no path (so it
 * cannot leave the facet) or it names one in a shape we refuse to guess at.
 *
 * @param {string} toolName - the tool being called.
 * @param {unknown} args - the raw model arguments.
 * @returns {string[]} raw paths, in argument order.
 */
export function pathArgumentsFor(toolName, args) {
  if (args === null || typeof args !== 'object') return []
  const record = /** @type {Record<string, unknown>} */ (args)

  const names = PATH_ARGUMENTS[toolName]
  if (names === undefined) return []

  const out = []
  for (const name of names) {
    const value = record[name]
    if (typeof value !== 'string') continue
    const trimmed = value.trim()
    if (trimmed !== '') out.push(trimmed)
  }
  return out
}

/**
 * True when this call would widen the facet and therefore needs the user.
 *
 * Only `add` widens. `status` reads, `remove` narrows, `reset` returns to the
 * session's own folder — none of them can show the agent anything it could not
 * already see, so none of them is worth interrupting anyone for. Keeping the
 * interruption to the single case that matters is what stops the approval from
 * becoming something to click through.
 *
 * @param {string} toolName - the tool being called.
 * @param {unknown} args - the raw model arguments.
 * @returns {boolean} whether the call needs an explicit grant.
 */
export function isWideningCall(toolName, args) {
  if (toolName !== FACET_TOOL) return false
  if (args === null || typeof args !== 'object') return false
  return /** @type {Record<string, unknown>} */ (args).action === WIDENING_ACTION
}

/**
 * The stable half of the facet, for the system prompt.
 *
 * This states the rule and never the binding: the binding moves (a grant is
 * added), and a changing system prompt invalidates the prompt cache for the
 * whole conversation. The mutable half goes in {@link facetContextText}, which
 * the harness materialises as a durable runtime-context snapshot — the same
 * treatment the sandbox policy and approval policy already get, for the same
 * reason.
 *
 * It takes no configuration, and that is deliberate rather than an oversight.
 * A system-prompt section is a plain string registered once; there is no
 * callback to re-render it, and a settings write to a `volatile()` field
 * updates the config reference *without* re-applying the plugin. So anything
 * this function interpolated would freeze at whatever the value was at load —
 * the prompt would go on describing the old `mode` while the guard enforced the
 * new one. Everything that depends on `mode` therefore lives in the binding,
 * which is a callback and therefore live.
 *
 * @returns {string} prompt section text.
 */
export function facetRuleText() {
  return [
    '# Facet scope',
    '',
    'This session is scoped to one facet of the project — one module rather than the whole system. Your runtime context states which, and says how a call outside it is treated.',
    '',
    'Work inside the facet.',
    '',
    'Never widen the scope on your own initiative: a grant is the user\u2019s decision, and an unrequested one is a bug, not initiative. Do not add paths you merely expect to need — ask when you actually need them.',
    '',
    '`bash` is not scope-checked, so it is not a way to look outside the facet without asking. Use the file tools when the answer is a file.',
  ].join('\n')
}

/**
 * Split a path into the form worth showing a reader.
 *
 * Relative reads better when the path is under the session, and absolute is the
 * only honest form when it is not. This is presentation only — containment is
 * decided on canonical targets, never on strings.
 *
 * @param {string} cwd - the session working directory.
 * @param {string} path - an absolute path.
 * @returns {string} the shortest unambiguous form.
 */
export function displayPath(cwd, path) {
  if (typeof cwd !== 'string' || cwd === '') return path
  const prefix = cwd.endsWith('/') ? cwd : `${cwd}/`
  return path === cwd ? '.' : path.startsWith(prefix) ? path.slice(prefix.length) : path
}

/**
 * The mutable half of the facet, for the runtime-context snapshot.
 *
 * Kept short because it is re-sent as part of the conversation whenever it
 * changes, and a scope statement that costs more than the scope is worth is a
 * scope that does not pay for itself. It carries one sentence more than the bare
 * binding used to, because `mode` now belongs here: this is the only half that
 * is re-rendered per request, so it is the only half that can follow a settings
 * change. See {@link facetRuleText}.
 *
 * @param {object} input
 * @param {string} input.cwd - the session working directory.
 * @param {string|undefined} input.root - the facet root, or undefined when unscoped.
 * @param {readonly string[]} input.extras - absolute granted paths, outside the root.
 * @param {'ask'|'deny'|'off'} input.mode - how an out-of-scope call is handled.
 * @returns {string} context text, or `''` to contribute nothing.
 */
export function facetContextText(input) {
  const { cwd, root, extras = [], mode } = input
  if (mode === 'off' || typeof root !== 'string' || root === '') return ''

  // Stated in terms of what the model should *do*, because the same sentence is
  // what the user reads in an approval prompt. A denial that does not say how to
  // proceed is a denial the agent works around with `bash`.
  const reach =
    mode === 'deny'
      ? 'refused — `facet action=add` asks the user to grant a path, and is the only way to widen the scope'
      : 'put to the user as a question — say in one line what you need and why, then record it with `facet action=add` so the rest of the session does not have to ask again'

  // The root is stated absolutely even though it is the session's own directory
  // and a relative form would be shorter. `facet: .` is true and useless: the
  // model needs a path it can reason about, and the user reading an approval
  // prompt needs to see which folder they are being asked about.
  const lines = [`facet: ${root}`]
  if (extras.length > 0) lines.push(`granted outside it: ${extras.map((path) => displayPath(cwd, path)).join(', ')}`)
  lines.push(`outside the facet: ${reach}`)
  return lines.join('\n')
}

/**
 * Why one call is being questioned, in a sentence that reads for both audiences.
 *
 * The same string is the user's approval prompt and the model's error text, so
 * it names the path, the boundary, and the way forward — a denial that does not
 * say how to proceed is a denial the agent works around with `bash`.
 *
 * @param {object} input
 * @param {string} input.cwd - the session working directory.
 * @param {string} input.path - the raw path the model named.
 * @param {string} input.root - the facet root.
 * @param {'ask'|'deny'} input.mode - the decision this reason explains.
 * @returns {string} the reason.
 */
export function outsideReason(input) {
  const { cwd, path, root, mode } = input
  const what = displayPath(cwd, path)
  const verb = mode === 'deny' ? 'refused' : 'outside'
  // The boundary is named absolutely: the person reading this is deciding
  // whether to open it, and "the facet is ." tells them nothing.
  return `${what} is ${verb} — this session's facet is ${root}. Ask the user to grant it (\`facet action=add\`), or work within the facet.`
}

/**
 * Why widening the scope is being put to the user.
 *
 * @param {readonly string[]} paths - the raw paths the model asked to add.
 * @returns {string} the reason.
 */
export function widenReason(paths) {
  const list = paths.length === 0 ? 'nothing' : paths.join(', ')
  return `Grant ${list} to this session — outside its facet — for the rest of the conversation?`
}