AgentHub/server/lib/git-diff.js

/**
 * @file Reads a lane's code changes as structured hunks, for the Workspace's
 * Changes panel (overview / review / single-file / history / file). Three
 * ranges, because the questions a lane raises are different: `work` is "what
 * has the agent touched and not committed yet" (HEAD vs the working tree,
 * untracked files included), `branch` is "what does this lane add on top of
 * its base" (`<base>...HEAD`), and `commit` is one recorded commit.
 *
 * Everything here is READ-ONLY and every git call goes through worktree.js's
 * `git()` argv wrapper — no shell strings, same rule as the rest of the lane
 * git surface. Untracked files are rendered as an all-added patch from the file
 * itself rather than via `git diff --no-index`, which exits non-zero on a
 * difference and would read as a failure.
 *
 * Output is capped in three places (files listed, bytes per file, bytes in
 * total) because this rides an HTTP response a browser has to render: a lane
 * mid-`npm install` or holding a committed lockfile would otherwise ship
 * megabytes of patch to a React list. A cap that bites sets `truncated`.
 *
 * The lane's cwd is the boundary, even when it is a SUBDIRECTORY of its repo:
 * every path in and out is cwd-relative, status entries outside the cwd are
 * dropped, and every git call treats a path as a literal file name, never a
 * pathspec glob (`GIT_LITERAL_PATHSPECS`).
 *
 * The file explorer also serves a workspace folder that is NOT a git repo
 * (issue #78): `listTree`, `listTreeAll` and `listPaths` then read the disk
 * (`walkFolder` — confined to the folder's real path, never following a
 * symlink, capped) instead of `git ls-files`, and the file reads above never
 * needed git for the working copy.
 * @author Nguyễn Ngọc Trí Vĩ <vinnt@smartgift.vn>
 */

const crypto = require("node:crypto");
const fs = require("node:fs");
const path = require("node:path");

const worktree = require("./worktree");

/** Every git call here: argv only, and a path argument is a literal name. */
const git = (dir, args, opts) => worktree.git(dir, args, { literal: true, ...opts });

/**
 * A git READ whose output this module caps itself: the buffer is sized past
 * the cap (x4, a UTF-8 char is at most 4 bytes, plus headroom) so git's own
 * buffer can never be what fails first, and an overflow comes back as the
 * partial output — longer than `capChars`, so the caller's cap marks it
 * truncated — instead of an error read as "missing".
 */
async function readCapped(dir, args, capChars) {
  try {
    return (await git(dir, args, { maxBuffer: capChars * 4 + 64 * 1024 })).stdout;
  } catch (err) {
    if (err.code === "ERR_CHILD_PROCESS_STDIO_MAXBUFFER" && err.git?.stdout) {
      return String(err.git.stdout);
    }
    throw err;
  }
}

/** Most files one response names. Beyond this the list is `truncated`. */
const MAX_FILES = 300;
/** Most patch bytes read for ONE file before its hunks are cut short. */
const MAX_FILE_BYTES = 200_000;
/** Most patch bytes across all files in a `full` (review-mode) response. */
const MAX_TOTAL_BYTES = 1_000_000;
/** An untracked file larger than this is reported without content. */
const MAX_UNTRACKED_BYTES = 1_000_000;
/** Most bytes `readFileAt` returns before cutting the tail off. */
const MAX_FILE_VIEW_BYTES = 1_000_000;
/** Most paths `listPaths`/`listTree` answer with. */
const MAX_PATHS = 500;
/** Characters of `ls-files -z` read before the listing counts as truncated. */
const MAX_LS_CHARS = 16 * 1024 * 1024;
/** Lines of unchanged context around a hunk, and the ceiling "expand all"
 *  is clamped to — a whole large file rendered as context is the one way this
 *  panel can be made to ship more bytes than the caps above allow. */
const DEFAULT_CONTEXT = 3;
const MAX_CONTEXT = 5000;

const VALID_RANGES = new Set(["work", "branch", "commit"]);
/** A commit-ish this module will pass to git. Deliberately strict: a sha, or a
 *  ref name without the characters that would let it read as an option or a
 *  pathspec. `git` is called with an argv array, so this is belt-and-braces. */
const SAFE_REV = /^[A-Za-z0-9][A-Za-z0-9._\/-]{0,200}$/;
/** The file whose CONTENT this module never returns, at any rev and at ANY
 *  depth: `settings.local.json` is where AgentHub once wrote a lane's AI
 *  Proxy API key, and key material never leaves the server. Any depth,
 *  because a lane at the repo root sees a subdirectory lane's key as
 *  `sub/.claude/settings.local.json`. Lower-cased: a case-insensitive
 *  filesystem (macOS) opens it under any casing. */
const SECRET_FILE = ".claude/settings.local.json";
const SECRET_BASENAME = path.posix.basename(SECRET_FILE);

/** Whether a lane-relative path names a secret file, however it is spelled. */
function isSecret(rel) {
  const norm = path.posix
    .normalize(String(rel).replace(/\\/g, "/"))
    .replace(/^\.\//, "")
    .toLowerCase();
  // By BASENAME, in any directory: a `.claude` symlinked to `conf/` stores the
  // key as `conf/settings.local.json`, and a lane above that one (or a commit
  // of that target) never spells it through `.claude/`. A file with this name
  // is Claude Code's local settings in practice, so nothing legitimate is lost.
  return norm === SECRET_FILE || path.posix.basename(norm) === SECRET_BASENAME;
}

/**
 * S3: whether `abs` is a dot entry at the TOP of a member's home — `.claude`,
 * `.codex`, `.config/gh`, `.ssh`, `.git-credentials`, `.agenthub/handoff`…:
 * where that member's logins and pane tokens live. A workspace is a folder
 * under the home, so this never hides project files; it closes a workspace
 * rooted AT the home (made before that was refused, or a symlink) to anyone
 * reading it, analysts included. Not by basename: `auth`/`token` patterns
 * would hide `AuthGate.tsx` in every member workspace.
 */
function inMemberDotDir(abs) {
  const runAs = require("./run-as");
  const acct = require("./linux-accounts").s3Enabled() ? runAs.ownerForRead(abs) : null;
  if (!acct) return false;
  const rel = path.relative(acct.home, abs);
  return Boolean(rel) && !path.isAbsolute(rel) && rel.split(path.sep)[0].startsWith(".");
}

/**
 * The real path of a workspace folder for a filesystem read or write (S3:
 * refused, EFOREIGN, when it resolves into another account's files). The
 * account a read or write runs as comes from the PATH (run-as.js), so a
 * member who swaps their workspace folder for a link to another member's
 * folder, the host's home or /etc must not have the dashboard follow it.
 */
async function laneRoot(dir) {
  const root = await fs.promises.realpath(dir);
  if (!require("./run-as").sameOwner(path.resolve(dir), root)) {
    throw badRequest("EFOREIGN", "the workspace folder resolves outside its owner's files");
  }
  return root;
}

/**
 * Whether `file` in the lane is a secret by what it RESOLVES to, not by how
 * it is spelled: a symlinked `.claude` (→ `conf/`) makes the key file
 * `conf/settings.local.json`, which no name check catches. Secret when the
 * real path, relative to the lane's real root, is one by `isSecret`, or when
 * it is the very file `<lane>/.claude/settings.local.json` resolves to. A
 * path that does not exist on disk is judged by its name alone.
 */
async function isSecretOnDisk(dir, file) {
  if (isSecret(file) || inMemberDotDir(path.resolve(dir, file))) return true;
  let root;
  let real;
  try {
    root = await fs.promises.realpath(dir);
    real = await fs.promises.realpath(path.resolve(root, file));
  } catch {
    return false;
  }
  if (isSecret(path.relative(root, real)) || inMemberDotDir(real)) return true;
  try {
    return real === (await fs.promises.realpath(path.join(root, SECRET_FILE)));
  } catch {
    return false;
  }
}

/**
 * The ONE lexical guard for a caller-supplied path, at every rev: a relative
 * path with no `..` segment, normalised (`./a//b` → `a/b`) so the secret
 * check and git both see the lane-relative spelling. Throws EBADPATH.
 */
function lanePath(file) {
  if (typeof file !== "string" || !file || file.includes("\0")) {
    throw badRequest("EBADPATH", "path must be a relative path inside the workspace");
  }
  // A backslash is an ordinary file-name byte to git on POSIX, not a separator.
  if (file.startsWith("/") || file.split("/").includes("..")) {
    throw badRequest("EBADPATH", "path must be a relative path inside the workspace");
  }
  const norm = path.posix
    .normalize(file)
    .replace(/^(\.\/)+/, "")
    .replace(/\/+$/, "");
  if (!norm || norm === ".") throw badRequest("EBADPATH", "path must name a file");
  return norm;
}

/**
 * Resolve `file` inside the lane for a CONTENT read: realpath-confined to the
 * lane's own realpath, so neither `..` nor a symlink can walk out of it, and
 * refused when either the requested or the resolved path is a secret file.
 * Throws EBADPATH / ESECRET / ENOFILE.
 */
async function resolveInLane(dir, file) {
  if (isSecret(file))
    throw badRequest("ESECRET", "that file holds secrets and is not readable here");
  const escapes = (base, target) => {
    const r = path.relative(base, target);
    return !r || r === ".." || r.startsWith(`..${path.sep}`) || path.isAbsolute(r);
  };
  // Lexically first, so `../x` is EBADPATH whether or not x exists.
  if (escapes(path.resolve(dir), path.resolve(dir, file))) {
    throw badRequest("EBADPATH", "path escapes the workspace directory");
  }
  const root = await laneRoot(dir);
  let real;
  try {
    real = await fs.promises.realpath(path.resolve(root, file));
  } catch {
    throw badRequest("ENOFILE", "no such file in the working tree");
  }
  if (escapes(root, real)) throw badRequest("EBADPATH", "path escapes the workspace directory");
  if (await isSecretOnDisk(root, file))
    throw badRequest("ESECRET", "that file holds secrets and is not readable here");
  return real;
}

/** Throw a coded error the routes map onto a 400. */
function badRequest(code, message) {
  const err = new Error(message);
  err.code = code;
  return err;
}

/** Clamp a caller's context request into [0, MAX_CONTEXT]. */
function normalizeContext(value) {
  const n = Number(value);
  if (!Number.isFinite(n) || n < 0) return DEFAULT_CONTEXT;
  return Math.min(Math.floor(n), MAX_CONTEXT);
}

/**
 * Parse one file's unified diff into hunks with both gutters resolved, so the
 * client renders rows instead of re-parsing `@@` headers.
 *
 * Returns `[]` for an empty patch (an unchanged file, or a mode-only change).
 */
function parseUnifiedDiff(patch) {
  const hunks = [];
  let current = null;
  let oldLine = 0;
  let newLine = 0;

  for (const raw of patch.split("\n")) {
    const header = raw.match(/^@@ -(\d+)(?:,\d+)? \+(\d+)(?:,\d+)? @@(.*)$/);
    if (header) {
      oldLine = Number(header[1]);
      newLine = Number(header[2]);
      current = {
        header: raw,
        context: header[3].trim(),
        oldStart: oldLine,
        newStart: newLine,
        lines: [],
      };
      hunks.push(current);
      continue;
    }
    if (!current) continue; // preamble: ---/+++/index/diff lines
    // "\ No newline at end of file" annotates the previous line; it is not a
    // row of its own and carries no line number.
    if (raw.startsWith("\\")) continue;
    const marker = raw[0];
    const text = raw.slice(1);
    if (marker === "+") {
      current.lines.push({ type: "add", oldLine: null, newLine: newLine++, text });
    } else if (marker === "-") {
      current.lines.push({ type: "del", oldLine: oldLine++, newLine: null, text });
    } else if (marker === " ") {
      // An unchanged EMPTY line is " " — one space, no text. A truly empty
      // string is the tail of the final "\n", not a row.
      current.lines.push({ type: "ctx", oldLine: oldLine++, newLine: newLine++, text });
    }
  }
  return hunks;
}

/** Whether a buffer looks binary — the same NUL-byte heuristic git uses. */
function looksBinary(buf) {
  return buf.includes(0);
}

/**
 * Resolve the ref a `branch`-range diff measures against: `origin/<base>` when
 * the remote-tracking ref exists, else the local branch, else null (a lane with
 * no base, or a base that has since been deleted — reported, not guessed).
 */
async function resolveBaseRef(dir, base) {
  if (!base) return null;
  for (const ref of [`origin/${base}`, base]) {
    try {
      await git(dir, ["rev-parse", "--verify", "--quiet", ref]);
      return ref;
    } catch {
      /* try the next candidate */
    }
  }
  return null;
}

/**
 * The repo's default branch, for a lane that recorded no base of its own (an
 * adopted folder, a session's `claude --worktree` tree): what `origin/HEAD`
 * points at, else `main` or `master` when one exists, else null.
 */
async function defaultBranch(dir) {
  const head = await git(dir, ["symbolic-ref", "-q", "--short", "refs/remotes/origin/HEAD"]).then(
    (r) => r.stdout.trim(),
    () => ""
  );
  if (head.startsWith("origin/")) return head.slice("origin/".length);
  for (const name of ["main", "master"]) {
    if (await resolveBaseRef(dir, name)) return name;
  }
  return null;
}

/**
 * `git diff --numstat -z` output → Map<path, {added, deleted, binary}>. `-z`
 * because without it git C-quotes any path with a space, a quote or a
 * non-ASCII byte (`"t\303\240i.txt"`), which then keys nothing. A rename is
 * `a\td\t\0old\0new\0`; the path that exists now is the key. Shared with
 * worktree.js's `laneFiles` (the lane card), so the card and the Changes panel
 * count a file the same way.
 */
function parseNumstat(stdout) {
  const stats = new Map();
  const tokens = stdout.split("\0");
  for (let i = 0; i < tokens.length; i++) {
    const m = tokens[i].replace(/^\n/, "").match(/^(\d+|-)\t(\d+|-)\t(.*)$/s);
    if (!m) continue;
    let file = m[3];
    if (!file) {
      file = tokens[i + 2];
      i += 2;
    }
    if (!file) continue;
    stats.set(file, {
      added: m[1] === "-" ? null : Number(m[1]),
      deleted: m[2] === "-" ? null : Number(m[2]),
      binary: m[1] === "-",
    });
  }
  return stats;
}

/**
 * `git status --porcelain=v1 -z` → [{code, path, from}]. Each record is
 * `XY path\0`; a rename/copy carries its ORIGINAL path as the next record.
 * Shared with git-ops.js so the paths a write may name are the paths shown.
 */
function parsePorcelainZ(stdout) {
  const entries = [];
  const tokens = stdout.split("\0");
  for (let i = 0; i < tokens.length; i++) {
    const rec = tokens[i];
    if (rec.length < 4) continue;
    const code = rec.slice(0, 2);
    const entry = { code, path: rec.slice(3), from: null };
    if (code[0] === "R" || code[0] === "C" || code[1] === "R" || code[1] === "C") {
      entry.from = tokens[++i] || null;
    }
    entries.push(entry);
  }
  return entries;
}

/**
 * `git status` for the LANE: porcelain paths are always repo-ROOT-relative,
 * while every pathspec and every fs read here resolves from the lane's cwd.
 * So entries are cut down to the ones inside the cwd and re-spelled relative
 * to it — a subdirectory lane neither shows nor can name a change outside
 * itself. A rename whose original path is outside keeps `from: null`.
 * Shared with git-ops.js so the paths a write may name are the paths shown.
 * `--untracked-files=all` (#64): `normal` folds a wholly untracked folder
 * into one "dir/" entry, which the panel can neither open nor diff — every
 * new file is listed instead, as JetBrains and VS Code do.
 */
async function laneStatus(dir) {
  const [status, prefix] = await Promise.all([
    git(dir, ["status", "--porcelain=v1", "-z", "--untracked-files=all"]),
    git(dir, ["rev-parse", "--show-prefix"]),
  ]);
  const pre = prefix.stdout.trim();
  const inside = (p) => (p && p.startsWith(pre) ? p.slice(pre.length) || null : null);
  const entries = [];
  for (const e of parsePorcelainZ(status.stdout)) {
    const rel = inside(e.path);
    if (rel) entries.push({ code: e.code, path: rel, from: inside(e.from) });
  }
  return entries;
}

/**
 * Porcelain codes that mean "unmerged" — a merge or a rebase left this file
 * with conflict markers. git's own list; `UU` is the common one, but a
 * delete/modify conflict reports `DU`/`UD` and an add/add reports `AA`.
 */
const CONFLICT_CODES = new Set(["DD", "AU", "UD", "UA", "DU", "AA", "UU"]);

/** Working-tree summary: porcelain status, plus numstat deltas for tracked files. */
async function summarizeWork(dir) {
  const [entries, numstat] = await Promise.all([
    laneStatus(dir),
    // --relative: cwd-scoped, cwd-relative paths, so they key the status ones.
    git(dir, ["diff", "--numstat", "-z", "--relative", "HEAD"]).catch(() => null),
  ]);
  const stats = parseNumstat(numstat?.stdout ?? "");
  const files = [];
  for (const { code, path: file } of entries) {
    const untracked = code === "??";
    const stat = stats.get(file);
    // `MM` with no line against HEAD: a staged change the working tree has
    // reverted — nothing to commit from the file on disk. JetBrains' Changes
    // view drops it the same way (#72). Only when the numstat answered.
    if (code === "MM" && numstat && !stat) continue;
    // One read per untracked file, not two: its line count and its
    // binary-ness are the same buffer answered twice.
    // Sequential on purpose: `normal` folds untracked dirs, so this is short.
    const fresh = untracked ? await untrackedFacts(dir, file) : null;
    files.push({
      path: file,
      status: code,
      untracked,
      // The two porcelain columns are the index and the working tree, which
      // is the whole of what per-file staging needs to render: a file can be
      // BOTH (edited, staged, edited again) and the row has to say so rather
      // than pick one.
      staged: !untracked && code[0] !== " " && code[0] !== "?",
      unstaged: untracked || (code[1] !== " " && code[1] !== "?"),
      conflicted: CONFLICT_CODES.has(code),
      added: untracked ? fresh.lines : (stat?.added ?? 0),
      deleted: untracked ? 0 : (stat?.deleted ?? 0),
      binary: untracked ? fresh.binary : !!stat?.binary,
    });
  }
  return files;
}

/**
 * An untracked file's line count and binary-ness, from ONE read.
 *
 * `lines` is null when the file is too big, binary, or unreadable — git has no
 * delta for an untracked file either, and a null there already means "unknown"
 * everywhere else in this response. A file over the cap counts as binary so
 * nothing downstream tries to render it.
 */
async function untrackedFacts(dir, file) {
  try {
    const abs = await resolveInLane(dir, file);
    if ((await fs.promises.stat(abs)).size > MAX_UNTRACKED_BYTES)
      return { lines: null, binary: true };
    const buf = await require("./run-as").readFileSafeAsync(abs);
    if (looksBinary(buf)) return { lines: null, binary: true };
    const text = buf.toString("utf8");
    if (!text) return { lines: 0, binary: false };
    const lines = text.endsWith("\n") ? text.split("\n").length - 1 : text.split("\n").length;
    return { lines, binary: false };
  } catch {
    // A directory entry (git reports untracked DIRS with a trailing slash), a
    // dangling symlink, a file deleted between the status call and this read,
    // or one resolveInLane refuses (a secret, a symlink out of the lane).
    return { lines: null, binary: false };
  }
}

/** Branch summary: `<baseRef>...HEAD`, name-status for the letter, numstat for counts. */
async function summarizeBranch(dir, baseRef) {
  const spec = `${baseRef}...HEAD`;
  const [nameStatus, numstat] = await Promise.all([
    git(dir, ["diff", "--name-status", "-z", "--relative", spec]),
    git(dir, ["diff", "--numstat", "-z", "--relative", spec]),
  ]);
  return parseNameStatus(nameStatus.stdout, parseNumstat(numstat.stdout));
}

/**
 * One commit's summary. `git show` against a MERGE commit prints nothing by
 * default (it diffs against no single parent), so `-m --first-parent` picks
 * the mainline side — which is what "what did this commit bring in" means to
 * a reader scrolling a branch's history.
 */
async function summarizeCommit(dir, sha) {
  const base = ["show", "--format=", "-m", "--first-parent", "--relative", sha];
  const [nameStatus, numstat] = await Promise.all([
    git(dir, [...base, "--name-status", "-z"]),
    git(dir, [...base, "--numstat", "-z"]),
  ]);
  return parseNameStatus(nameStatus.stdout, parseNumstat(numstat.stdout));
}

/** Shared `--name-status -z` reader for the ranges that have no working tree. */
function parseNameStatus(stdout, stats) {
  const files = [];
  const seen = new Set();
  const tokens = stdout.split("\0");
  for (let i = 0; i < tokens.length; i++) {
    const status = tokens[i].replace(/^\n/, "");
    if (!/^[A-Z]/.test(status)) continue;
    const letter = status[0];
    // A rename/copy is "R100\0old\0new" — the new path is the live one.
    const file = letter === "R" || letter === "C" ? tokens[(i += 2)] : tokens[++i];
    if (!file) continue;
    // `-m` prints one diff per parent for a merge; --first-parent keeps it to
    // one, but a defensive de-dup costs nothing and a doubled row is a lie.
    if (seen.has(file)) continue;
    seen.add(file);
    const stat = stats.get(file);
    files.push({
      path: file,
      status: `${letter} `,
      untracked: false,
      staged: false,
      unstaged: false,
      conflicted: false,
      added: stat?.added ?? 0,
      deleted: stat?.deleted ?? 0,
      binary: !!stat?.binary,
    });
  }
  return files;
}

/** One file's patch text, for any range. Empty string when there is none. */
async function patchFor(dir, { range, baseRef, sha, file, untracked, context }) {
  // A secret file may be tracked by mistake; its hunks would carry the key —
  // under its own name, or under a symlinked `.claude`'s target name.
  if (await isSecretOnDisk(dir, file)) return "";
  if (untracked) return synthesizeAddedPatch(dir, file);
  const u = `-U${context}`;
  const args =
    range === "commit"
      ? ["show", "--format=", "-m", "--first-parent", u, sha, "--", file]
      : range === "branch"
        ? ["diff", u, `${baseRef}...HEAD`, "--", file]
        : ["diff", u, "HEAD", "--", file];
  return readCapped(dir, [...args, "--no-color", "--no-ext-diff"], MAX_FILE_BYTES).catch(() => "");
}

/**
 * An untracked file has no git-side "before", so its patch is synthesized: one
 * hunk starting at line 1 with every line added. This is what `git diff
 * --no-index /dev/null <file>` would print, without the non-zero exit that
 * wrapper treats as a failure.
 */
async function synthesizeAddedPatch(dir, file) {
  let buf;
  try {
    buf = await require("./run-as").readFileSafeAsync(await resolveInLane(dir, file));
  } catch {
    return "";
  }
  if (looksBinary(buf)) return "";
  const text = buf.toString("utf8");
  if (!text) return "";
  const lines = text.split("\n");
  if (lines[lines.length - 1] === "") lines.pop();
  const body = lines.map((l) => `+${l}`).join("\n");
  return `@@ -0,0 +1,${lines.length} @@\n${body}\n`;
}

/**
 * The lane's changes for one range.
 *
 * @param {string} dir Lane working directory.
 * @param {object} opts
 * @param {"work"|"branch"|"commit"} [opts.range="work"]
 * @param {string|null} [opts.base] The lane's base branch, for `range="branch"`;
 *   none falls back to the repo's default branch (`defaultBranch`).
 * @param {string|null} [opts.sha] The commit to read, for `range="commit"`.
 * @param {string|null} [opts.file] Only this path, with its hunks (single-file mode).
 * @param {boolean} [opts.full] Hunks for EVERY file (review mode). Ignored when
 *   `file` is set, which is already a full read of one file.
 * @param {number} [opts.context] Unchanged lines around each hunk. The panel
 *   raises this to expand a diff towards the whole file.
 * @returns {Promise<{range, base, baseRef, mergeBase, sha, context, files, truncated}>}
 */
async function collectChanges(
  dir,
  { range = "work", base = null, sha = null, file = null, full = false, context } = {}
) {
  if (!VALID_RANGES.has(range)) {
    throw badRequest("EBADRANGE", `unknown range ${range}`);
  }
  const ctx = normalizeContext(context);

  let baseRef = null;
  // The commit a branch diff is taken from (`<baseRef>...HEAD`): the editor
  // reads a file's original text there.
  let mergeBase = null;
  if (range === "branch") {
    base = base || (await defaultBranch(dir));
    baseRef = await resolveBaseRef(dir, base);
    if (!baseRef) {
      throw badRequest("ENOBASE", "no base branch to compare against");
    }
    mergeBase = await git(dir, ["merge-base", baseRef, "HEAD"])
      .then((r) => r.stdout.trim() || null)
      .catch(() => null);
  }
  if (range === "commit") {
    if (!sha || !SAFE_REV.test(sha)) throw badRequest("EBADREV", "sha is not a valid revision");
    try {
      // Resolve it once, so a bad ref is a 400 here rather than an empty diff
      // three calls later, and so the response reports the full sha.
      sha = (await git(dir, ["rev-parse", "--verify", "--quiet", `${sha}^{commit}`])).stdout.trim();
    } catch {
      throw badRequest("EBADREV", "no such commit in this repository");
    }
  }

  let files =
    range === "branch"
      ? await summarizeBranch(dir, baseRef)
      : range === "commit"
        ? await summarizeCommit(dir, sha)
        : await summarizeWork(dir);
  files.sort((a, b) => a.path.localeCompare(b.path));

  let truncated = false;
  if (file) {
    const one = files.find((f) => f.path === file);
    if (!one) {
      throw badRequest("ENOFILECHANGE", "file has no changes in this range");
    }
    files = [one];
  } else if (files.length > MAX_FILES) {
    files = files.slice(0, MAX_FILES);
    truncated = true;
  }

  if (file || full) {
    let budget = file ? MAX_FILE_BYTES : MAX_TOTAL_BYTES;
    for (const entry of files) {
      if (entry.binary) {
        entry.hunks = [];
        continue;
      }
      if (budget <= 0) {
        entry.hunks = [];
        entry.truncated = true;
        truncated = true;
        continue;
      }
      let patch = await patchFor(dir, {
        range,
        baseRef,
        sha,
        file: entry.path,
        untracked: entry.untracked,
        context: ctx,
      });
      const cap = Math.min(MAX_FILE_BYTES, budget);
      if (patch.length > cap) {
        // Cut on a line boundary so the last row is a whole line — but only
        // when that boundary is near the cap. A minified file is one enormous
        // line, so its last newline inside the cap is the HUNK HEADER's, and
        // honouring it would return a hunk with no lines at all (and with no
        // newline anywhere, `lastIndexOf` is -1 and the patch came back empty)
        // — a file changed by a megabyte rendering as "no textual change".
        // Past the halfway mark the boundary is worth keeping; before it, the
        // content is, so the last row is cut mid-line instead.
        const nl = patch.lastIndexOf("\n", cap);
        patch = patch.slice(0, nl > cap / 2 ? nl + 1 : cap);
        entry.truncated = true;
        truncated = true;
      }
      budget -= patch.length;
      entry.hunks = parseUnifiedDiff(patch);
    }
  }

  return { range, base, baseRef, mergeBase, sha, context: ctx, files, truncated };
}

/**
 * Recent commits on the lane's current branch, for the history list.
 *
 * `%x1f`/`%x1e` (unit/record separators) delimit the format instead of a
 * printable character: a commit SUBJECT can legally contain a tab, a pipe or
 * any punctuation a hand-picked delimiter would have used.
 *
 * @param {string} dir Lane working directory.
 * @param {object} [opts]
 * @param {number} [opts.limit=30] Commits to read, clamped to 200.
 * @param {string|null} [opts.file] Only commits touching this path.
 * @param {string|null} [opts.ref] Another branch's history instead of HEAD's
 *   (where cherry-pick finds its commits): a short branch name, looked up
 *   with `branchRef` and ENOBRANCH when it is not one.
 */
async function listCommits(dir, { limit = 30, file = null, ref = null } = {}) {
  const n = Math.min(Math.max(Number(limit) || 30, 1), 200);
  const format = ["%H", "%h", "%s", "%an", "%aI", "%D", "%P"].join("%x1f");
  // --date-order: no parent before all its children, which the history's
  // commit graph needs to draw a lane down to each parent.
  const args = ["log", `-${n}`, "--date-order", `--format=${format}%x1e`];
  if (ref) {
    const full = await worktree.branchRef(dir, ref);
    if (!full) throw badRequest("ENOBRANCH", `no branch ${ref}`);
    args.push(full);
  }
  // Through the same lexical guard as every other path: in a subdirectory
  // lane `../x` would list commit metadata for a path outside the lane.
  // `--parents` makes git REWRITE each parent to the file's own previous
  // commit, so a file's history draws one joined-up line, not loose ends.
  if (file) args.push("--parents", "--", lanePath(file));
  const result = await git(dir, args);
  const commits = [];
  for (const record of result.stdout.split("\x1e")) {
    const line = record.replace(/^\n/, "");
    if (!line.trim()) continue;
    const [sha, short, subject, author, date, refs, parents] = line.split("\x1f");
    commits.push({
      sha,
      short,
      subject,
      author,
      date,
      // `%D` is "HEAD -> main, origin/main, tag: v1" — the decorations, split
      // into the chips a history row shows.
      refs: (refs || "")
        .split(", ")
        .map((r) => r.trim())
        .filter(Boolean),
      parents: (parents || "").split(" ").filter(Boolean),
    });
  }
  return commits;
}

/**
 * Annotate (JetBrains' blame gutter): who last changed each line of the
 * working-tree file. `git blame --porcelain` on the file on disk, so a line
 * nobody committed yet is `null`. Same guards as a whole-file read: the
 * lexical lane guard, a secret refused (ESECRET), and the file's size capped.
 * Answers `{commits: {sha: {short, author, date, summary}}, lines: [sha|null]}`.
 */
async function blameFile(dir, requested) {
  const file = lanePath(requested);
  if (await isSecretOnDisk(dir, file)) {
    throw badRequest("ESECRET", "that file holds secrets and is not readable here");
  }
  const st = await fs.promises.stat(path.join(dir, file)).catch(() => null);
  if (!st?.isFile()) throw badRequest("ENOFILE", "no such file");
  if (st.size > MAX_FILE_VIEW_BYTES) throw badRequest("ETOOBIG", "file too large to annotate");
  const out = (
    await git(dir, ["blame", "--porcelain", "--", file], { maxBuffer: 64 * 1024 * 1024 })
  ).stdout;
  const commits = {};
  const lines = [];
  let sha = null;
  for (const line of out.split("\n")) {
    const head = /^([0-9a-f]{40,64}) \d+ \d+/.exec(line);
    if (head) {
      sha = head[1];
      if (!/^0+$/.test(sha)) commits[sha] ??= { short: sha.slice(0, 7) };
      continue;
    }
    if (line.startsWith("\t")) {
      lines.push(/^0+$/.test(sha) ? null : sha);
      continue;
    }
    const c = commits[sha];
    if (!c) continue;
    const sp = line.indexOf(" ");
    const key = line.slice(0, sp);
    const val = line.slice(sp + 1);
    if (key === "author") c.author = val;
    else if (key === "author-time") c.date = new Date(Number(val) * 1000).toISOString();
    else if (key === "summary") c.summary = val;
  }
  return { path: file, commits, lines };
}

/**
 * One file's full content at a revision, for the "read the whole file" view
 * that a diff's three lines of context cannot answer.
 *
 * `rev` is `work` (the file on disk, including an untracked one), `HEAD`, or a
 * commit-ish. The path is resolved against git's own index/tree rather than
 * trusted: for `work` it is realpath-confined to the lane directory, because
 * that is the one branch that reads the filesystem directly. A SECRET_PATHS
 * file is refused (ESECRET) at every rev.
 */
async function readFileAt(dir, requested, rev = "work") {
  // Lexical guard FIRST and for every rev: `git show <rev>:<path>` reads the
  // whole repo, so a `../` here is a committed file outside the lane.
  const file = lanePath(requested);
  if (rev !== "work" && !SAFE_REV.test(rev)) {
    throw badRequest("EBADREV", "rev is not a valid revision");
  }
  // By resolved path too, at every rev: the key committed under a symlinked
  // `.claude`'s target name is still the key.
  if (await isSecretOnDisk(dir, file)) {
    throw badRequest("ESECRET", "that file holds secrets and is not readable here");
  }

  let text;
  let binary = false;
  let sha;
  if (rev === "work") {
    // Neither `..` nor a symlink may walk out of the lane: resolveInLane
    // compares REAL paths, not the string the caller sent.
    const abs = await resolveInLane(dir, file);
    let buf;
    try {
      // Only cap+1 bytes: a multi-gigabyte log in the lane must not be read
      // whole to answer with its first megabyte. The extra byte is what
      // tells the cap below the file was longer.
      const fh = await require("./run-as").openSafeAsync(abs);
      try {
        const size = Math.min((await fh.stat()).size, MAX_FILE_VIEW_BYTES + 1);
        buf = Buffer.alloc(size);
        let off = 0;
        while (off < size) {
          const { bytesRead } = await fh.read(buf, off, size - off, off);
          if (!bytesRead) break;
          off += bytesRead;
        }
        buf = buf.subarray(0, off);
      } finally {
        await fh.close();
      }
    } catch {
      throw badRequest("ENOFILE", "no such file in the working tree");
    }
    binary = looksBinary(buf);
    text = binary ? "" : buf.toString("utf8");
    // What an editor must send back to save over THIS content and nothing
    // newer (lane-file-write.js). Only for a whole, textual file.
    if (!binary && buf.length <= MAX_FILE_VIEW_BYTES) sha = contentSha(buf);
  } else {
    try {
      // `./`: resolve from the lane's cwd, not the repo root (a bare
      // `<rev>:<path>` is root-relative) — `file` has no `..`, so it stays in.
      text = await readCapped(dir, ["show", `${rev}:./${file}`], MAX_FILE_VIEW_BYTES);
    } catch {
      throw badRequest("ENOFILE", "no such file at that revision");
    }
    binary = text.includes("\0");
    if (binary) text = "";
  }

  let truncated = false;
  if (text.length > MAX_FILE_VIEW_BYTES) {
    const nl = text.lastIndexOf("\n", MAX_FILE_VIEW_BYTES);
    text = text.slice(0, nl > MAX_FILE_VIEW_BYTES / 2 ? nl + 1 : MAX_FILE_VIEW_BYTES);
    truncated = true;
  }
  const lines = text ? text.split("\n") : [];
  if (lines[lines.length - 1] === "") lines.pop();
  return { path: file, rev, binary, truncated, lines, ...(sha ? { sha } : {}) };
}

/** The image types the viewer shows, by extension. Raster and SVG only. */
const IMAGE_TYPES = {
  png: "image/png",
  jpg: "image/jpeg",
  jpeg: "image/jpeg",
  gif: "image/gif",
  webp: "image/webp",
  avif: "image/avif",
  bmp: "image/bmp",
  ico: "image/x-icon",
  svg: "image/svg+xml",
};
const MAX_IMAGE_BYTES = 20 * 1024 * 1024;

/**
 * One image's bytes at a revision, for the viewer's `<img>`: `readFileAt`'s
 * guards (lexical path, safe rev, secret, realpath-in-lane for `work`), plus
 * an extension allowlist that also picks the Content-Type and a size cap.
 */
async function readImageAt(dir, requested, rev = "work") {
  const file = lanePath(requested);
  const type = IMAGE_TYPES[path.extname(file).slice(1).toLowerCase()];
  if (!type) throw badRequest("ENOTIMAGE", "not an image file");
  if (rev !== "work" && !SAFE_REV.test(rev)) {
    throw badRequest("EBADREV", "rev is not a valid revision");
  }
  if (await isSecretOnDisk(dir, file)) {
    throw badRequest("ESECRET", "that file holds secrets and is not readable here");
  }
  const tooBig = () => badRequest("ETOOBIG", "image is larger than 20 MB");
  if (rev === "work") {
    const abs = await resolveInLane(dir, file);
    let stat;
    try {
      stat = await fs.promises.stat(abs);
    } catch {
      throw badRequest("ENOFILE", "no such file in the working tree");
    }
    if (!stat.isFile()) throw badRequest("ENOFILE", "no such file in the working tree");
    if (stat.size > MAX_IMAGE_BYTES) throw tooBig();
    return { type, buf: await require("./run-as").readFileSafeAsync(abs) };
  }
  try {
    const { stdout } = await git(dir, ["show", `${rev}:./${file}`], {
      encoding: "buffer",
      maxBuffer: MAX_IMAGE_BYTES,
    });
    return { type, buf: stdout };
  } catch (err) {
    if (err.code === "ERR_CHILD_PROCESS_STDIO_MAXBUFFER") throw tooBig();
    throw badRequest("ENOFILE", "no such file at that revision");
  }
}

/** The version stamp of a file's bytes, for a stale-save check. */
function contentSha(buf) {
  return crypto.createHash("sha1").update(buf).digest("hex");
}

/**
 * Tracked paths matching a substring query — the quick-open list.
 *
 * `git ls-files` rather than a filesystem walk: it already honours
 * `.gitignore`, so `node_modules` and build output never enter the list and no
 * skip-list has to be maintained here.
 */
async function listPaths(dir, { q = "", limit = MAX_PATHS } = {}) {
  const { all, cut } = await lsFiles(dir, []).catch(async (err) => {
    if (await inRepo(dir)) throw err;
    const walk = await walkFolder(dir);
    return { all: walk.files, cut: walk.cut };
  });
  const needle = String(q || "")
    .toLowerCase()
    .trim();
  const cap = Math.min(Math.max(Number(limit) || MAX_PATHS, 1), MAX_PATHS);
  const hits = needle ? all.filter((p) => p.toLowerCase().includes(needle)) : all;
  // A basename hit beats a directory hit: typing "api" wants `api.ts`, not
  // every file under `src/api/`.
  if (needle) {
    hits.sort((a, b) => {
      const ab = path.basename(a).toLowerCase().includes(needle) ? 0 : 1;
      const bb = path.basename(b).toLowerCase().includes(needle) ? 0 : 1;
      return ab - bb || a.length - b.length || a.localeCompare(b);
    });
  }
  return { paths: hits.slice(0, cap), truncated: cut || hits.length > cap, total: hits.length };
}

/** `git ls-files -z [args]` → paths, and whether a huge listing was cut short. */
async function lsFiles(dir, args) {
  const out = await readCapped(dir, ["ls-files", "-z", ...args], MAX_LS_CHARS);
  const all = out.split("\0");
  // A complete listing ends in NUL (last token ""); a cut one ends mid-path.
  const cut = all.pop() !== "";
  // Mid-merge, `ls-files --cached` prints a conflicted path once per stage
  // (base, ours, theirs): one path is one file.
  return { all: [...new Set(all.filter(Boolean))], cut };
}

/** Whether `dir` is inside a git work tree (false for a plain folder). */
async function inRepo(dir) {
  try {
    return (await git(dir, ["rev-parse", "--is-inside-work-tree"])).stdout.trim() === "true";
  } catch {
    return false;
  }
}

/** Most entries one `walkFolder` visits before it stops and reports `cut`. */
const MAX_WALK = 20_000;
/** Folders a walk lists but never enters (a repo's tree shows them as ignored). */
const WALK_SHUT = new Set(["node_modules"]);

/**
 * A plain folder's files and folders under `sub`, read off the disk, for a
 * workspace that is not a git repo: `depth` levels down (1 = `sub`'s own
 * entries), `.git` never listed, a `WALK_SHUT` folder listed but not entered,
 * a symlink listed as a file and never followed, the start confined to the
 * workspace's real path like `addIgnored`. Paths are workspace-relative.
 */
async function walkFolder(dir, sub = "", depth = Infinity) {
  const root = await laneRoot(dir);
  const start = await fs.promises.realpath(path.join(root, sub));
  const r = path.relative(root, start);
  if (r === ".." || r.startsWith(`..${path.sep}`) || path.isAbsolute(r)) {
    throw badRequest("EBADPATH", "path escapes the workspace");
  }
  const files = [];
  const dirs = [];
  const shut = new Set();
  let seen = 0;
  let cut = false;
  const queue = [[sub, 1]];
  while (queue.length && !cut) {
    const [rel, level] = queue.shift();
    let dirents;
    try {
      dirents = await fs.promises.readdir(path.join(root, rel), { withFileTypes: true });
    } catch {
      continue;
    }
    for (const d of dirents) {
      if (d.name === ".git") continue;
      if (++seen > MAX_WALK) {
        cut = true;
        break;
      }
      const p = rel ? `${rel}/${d.name}` : d.name;
      if (!d.isDirectory()) files.push(p);
      else {
        dirs.push(p);
        if (WALK_SHUT.has(d.name)) shut.add(p);
        else if (level < depth) queue.push([p, level + 1]);
      }
    }
  }
  return { files, dirs, shut, cut };
}

/** One explorer level of a plain folder (`listTree` off the disk). */
async function folderLevel(dir, sub) {
  const { files, dirs, shut, cut } = await walkFolder(dir, sub, 1);
  const prefix = sub ? `${sub}/` : "";
  const name = (p) => p.slice(prefix.length);
  const entries = [
    ...dirs
      .map((p) => ({
        name: name(p),
        path: p,
        dir: true,
        ...(shut.has(p) ? { ignored: true } : {}),
      }))
      .sort((a, b) => a.name.localeCompare(b.name)),
    ...files
      .map((p) => ({ name: name(p), path: p, dir: false }))
      .sort((a, b) => a.name.localeCompare(b.name)),
  ];
  return { entries: entries.slice(0, MAX_PATHS), truncated: cut || entries.length > MAX_PATHS };
}

/** What the explorer lists: tracked files plus untracked ones git does not
 *  ignore — the new file an agent just wrote is the one you want to open. */
const TREE_LS = ["--cached", "--others", "--exclude-standard"];

/**
 * A lane's working-copy status for decorating the explorer, from ONE
 * `laneStatus`: `fileStatus(path)` is the porcelain code of a changed file,
 * `dirChanged(path)` is whether anything under a folder is.
 */
async function treeStatus(dir) {
  const codes = new Map();
  const dirs = new Set();
  for (const { code, path: p } of await laneStatus(dir).catch(() => [])) {
    codes.set(p, code);
    const parts = p.split("/");
    for (let i = 1; i < parts.length; i++) dirs.add(parts.slice(0, i).join("/"));
  }
  return {
    fileStatus: (p) => codes.get(p),
    dirChanged: (p) => dirs.has(p),
  };
}

/**
 * Adds to one level what git does not list there — ignored files and folders
 * (and an empty folder, which git never lists either) — marked `ignored`,
 * read off the disk because `ls-files --ignored` cannot list INSIDE an
 * ignored folder. Returns the folder names it added.
 */
async function addIgnored(dir, sub, dirNames, files) {
  const added = new Set();
  let dirents;
  try {
    const root = await laneRoot(dir);
    const real = await fs.promises.realpath(path.join(root, sub));
    const r = path.relative(root, real);
    // A symlinked folder pointing out of the workspace lists nothing.
    if (r === ".." || r.startsWith(`..${path.sep}`) || path.isAbsolute(r)) return added;
    dirents = await fs.promises.readdir(real, { withFileTypes: true });
  } catch {
    return added;
  }
  const prefix = sub ? `${sub}/` : "";
  const listed = new Set(files.map((f) => f.name));
  for (const d of dirents) {
    if (d.name === ".git" || dirNames.has(d.name) || listed.has(d.name)) continue;
    if (d.isDirectory()) {
      dirNames.add(d.name);
      added.add(d.name);
    } else {
      files.push({ name: d.name, path: `${prefix}${d.name}`, dir: false, ignored: true });
    }
  }
  return added;
}

/** A folded level's entries, each carrying its status (see `treeStatus`). */
function treeEntries(prefix, dirNames, files, st, ignoredDirs = new Set()) {
  return [
    ...[...dirNames].sort().map((name) => {
      const p = `${prefix}${name}`;
      if (ignoredDirs.has(name)) return { name, path: p, dir: true, ignored: true };
      return { name, path: p, dir: true, ...(st.dirChanged(p) ? { changed: true } : {}) };
    }),
    ...files
      .sort((a, b) => a.name.localeCompare(b.name))
      .map((f) => {
        const status = st.fileStatus(f.path);
        return status ? { ...f, status } : f;
      }),
  ];
}

/**
 * One directory level of the working tree, for the file explorer: tracked
 * files plus untracked-but-not-ignored ones (`TREE_LS`) and, marked
 * `ignored`, what git ignores there (`addIgnored`), folded into
 * directories at this level — a tree that lists a repo's every file at once is
 * both slow to render and not what "expand a folder" means. A changed file
 * carries its porcelain `status`, a folder holding one `changed: true`.
 */
async function listTree(dir, { subdir = "" } = {}) {
  const clean = String(subdir || "")
    .replace(/^\/+|\/+$/g, "")
    .trim();
  if (clean.split("/").includes("..")) throw badRequest("EBADPATH", "path escapes the workspace");
  let listed;
  try {
    listed = await lsFiles(dir, clean ? [...TREE_LS, "--", `${clean}/`] : TREE_LS);
  } catch (err) {
    if (await inRepo(dir)) throw err;
    return { path: clean, ...(await folderLevel(dir, clean)) };
  }
  const { all, cut } = listed;
  const st = await treeStatus(dir);
  const prefix = clean ? `${clean}/` : "";
  const dirs = new Set();
  const files = [];
  for (const p of all) {
    const rest = p.slice(prefix.length);
    const slash = rest.indexOf("/");
    if (slash === -1) files.push({ name: rest, path: p, dir: false });
    else dirs.add(rest.slice(0, slash));
  }
  const ignored = await addIgnored(dir, clean, dirs, files);
  const entries = treeEntries(prefix, dirs, files, st, ignored);
  return {
    path: clean,
    entries: entries.slice(0, MAX_PATHS),
    truncated: cut || entries.length > MAX_PATHS,
  };
}

/**
 * ONE hunk of a tracked file's working-copy diff (`git diff HEAD`, the same
 * read the Changes panel shows), as a standalone patch `git apply` accepts:
 * the file's own header lines plus that hunk. The hunk is named by its `@@`
 * line and matched against a FRESH diff at the caller's context, so what gets
 * applied is always git's own text of the current tree — never a patch a
 * request carried. Null when no hunk matches (the tree moved on, or the file
 * is a secret, binary or too large to read whole).
 *
 * `block` narrows it to one CHANGE BLOCK of that hunk — a run of consecutive
 * +/- lines. git merges changes up to 2×context lines apart into one hunk, so
 * without this a single Undo/Keep acted on every nearby edit at once (#50).
 * `reverse` says which side the patch will be applied to (see `onlyBlock`).
 */
async function hunkPatch(dir, file, header, context, { block, reverse = false } = {}) {
  if (!header) return null;
  const diff = await diffHunks(dir, file, context);
  const hunk = diff?.hunks.find((h) => h.slice(0, h.indexOf("\n")) === header);
  if (!hunk) return null;
  const body = block === undefined ? hunk : onlyBlock(hunk, block, reverse);
  return body ? diff.head + (body.endsWith("\n") ? body : `${body}\n`) : null;
}

/** A tracked file's fresh `git diff HEAD` at `context`: its header lines and
 *  its hunks' texts, in order. Null for a secret, binary or too-large file. */
async function diffHunks(dir, file, context) {
  if (await isSecretOnDisk(dir, file)) return null;
  const u = `-U${normalizeContext(context)}`;
  const raw = await readCapped(
    dir,
    ["diff", u, "HEAD", "--no-color", "--no-ext-diff", "--", file],
    MAX_FILE_BYTES
  ).catch(() => "");
  // A capped read may end mid-hunk; applying half a hunk is worse than none.
  if (!raw || raw.length >= MAX_FILE_BYTES) return null;
  const at = raw.indexOf("\n@@ ");
  if (at < 0) return null;
  // A content line starts with " ", "+", "-" or "\\" — never "@@" — so every
  // line that does is a hunk boundary.
  return { head: raw.slice(0, at + 1), hunks: raw.slice(at + 1).split(/^(?=@@ )/m) };
}

/**
 * The hunk-level commit's patch for one file (JetBrains' partial commit):
 * the file's header plus each picked hunk cut down to its picked `blocks`,
 * in file order, to be applied FORWARD onto an index holding HEAD. Every
 * header is matched against a fresh diff like `hunkPatch`'s; null when one is
 * gone or names a block the hunk lacks. Each hunk's new-side start is left as
 * git wrote it — `git apply` locates a hunk by its old side.
 */
async function selectionPatch(dir, file, context, picks) {
  const diff = await diffHunks(dir, file, context);
  if (!diff || !picks.length) return null;
  const at = (header) => diff.hunks.findIndex((h) => h.slice(0, h.indexOf("\n")) === header);
  if (picks.some((p) => at(p.hunk) < 0)) return null;
  const bodies = [];
  for (const p of [...picks].sort((x, y) => at(x.hunk) - at(y.hunk))) {
    const body = onlyBlock(diff.hunks[at(p.hunk)], p.blocks, false);
    if (!body) return null;
    bodies.push(body);
  }
  return diff.head + bodies.join("");
}

/**
 * One hunk's text cut down to its `block`-th change block, the way an edited
 * `git add -p` hunk is: every OTHER block is folded into the side the patch
 * will be checked against, so that side stays byte-for-byte the hunk's own and
 * `git apply` finds it exactly where git put it.
 *
 *  - forward (stage, applied to the index = the OLD side): another block's
 *    "-" lines become context and its "+" lines are dropped;
 *  - reverse (undo, `apply -R` on the working tree = the NEW side): its "+"
 *    lines become context and its "-" lines are dropped.
 *
 * A "\ No newline" marker follows the line it annotates, kept or dropped with
 * it. The header's counts are recomputed; its starts do not move, because the
 * checked side is unchanged. Null when the hunk has no such block.
 */
function onlyBlock(hunk, block, reverse) {
  // One block, or several (the hunk-level commit keeps every ticked one).
  const keep = Array.isArray(block) ? block : [block];
  if (!keep.length || keep.some((b) => !Number.isInteger(b) || b < 0)) return null;
  const [header, ...lines] = hunk.replace(/\n$/, "").split("\n");
  const m = header.match(/^@@ -(\d+)(?:,\d+)? \+(\d+)(?:,\d+)? @@(.*)$/);
  if (!m) return null;
  const out = [];
  let index = -1;
  let inBlock = false;
  let keptPrev = false;
  let oldCount = 0;
  let newCount = 0;
  for (const line of lines) {
    const mark = line[0];
    if (mark === "\\") {
      if (keptPrev) out.push(line);
      continue;
    }
    const change = mark === "+" || mark === "-";
    if (change && !inBlock) index += 1;
    inBlock = change;
    let kept = line;
    if (change && !keep.includes(index)) {
      const fold = reverse ? "+" : "-";
      kept = mark === fold ? ` ${line.slice(1)}` : null;
    }
    keptPrev = kept !== null;
    if (kept === null) continue;
    out.push(kept);
    if (kept[0] !== "+") oldCount += 1;
    if (kept[0] !== "-") newCount += 1;
  }
  if (Math.max(...keep) > index) return null;
  return [`@@ -${m[1]},${oldCount} +${m[2]},${newCount} @@${m[3]}`, ...out].join("\n") + "\n";
}

/**
 * Every level of the explorer tree (tracked + untracked-not-ignored, plus each level's ignored entries) from ONE `git ls-files`, keyed by directory
 * path ("" is the root), each level shaped and capped exactly like
 * `listTree`'s. "Expand all folders" used to be one request — one ls-files —
 * per folder, which on a large repo is thousands of git processes.
 */
async function listTreeAll(dir) {
  let listed;
  try {
    listed = await lsFiles(dir, TREE_LS);
  } catch (err) {
    if (await inRepo(dir)) throw err;
    return plainTreeAll(dir);
  }
  const { all, cut } = listed;
  const st = await treeStatus(dir);
  const byDir = new Map();
  const level = (d) => {
    let l = byDir.get(d);
    if (!l) byDir.set(d, (l = { dirs: new Set(), files: [] }));
    return l;
  };
  level("");
  for (const p of all) {
    const parts = p.split("/");
    for (let i = 0; i < parts.length - 1; i++) {
      level(parts.slice(0, i).join("/")).dirs.add(parts[i]);
    }
    const parent = parts.slice(0, -1).join("/");
    level(parent).files.push({ name: parts[parts.length - 1], path: p, dir: false });
  }
  const levels = {};
  let truncated = cut;
  // An ignored folder gets no level of its own: it stays shut (node_modules).
  const ignored = new Map(
    await Promise.all(
      [...byDir].map(async ([d, l]) => [d, await addIgnored(dir, d, l.dirs, l.files)])
    )
  );
  for (const [d, { dirs, files }] of byDir) {
    const entries = treeEntries(d ? `${d}/` : "", dirs, files, st, ignored.get(d));
    if (entries.length > MAX_PATHS) truncated = true;
    levels[d] = entries.slice(0, MAX_PATHS);
  }
  return { levels, truncated };
}

/** `listTreeAll` for a plain folder: one capped walk, every level from it. */
async function plainTreeAll(dir) {
  const { files, dirs, shut, cut } = await walkFolder(dir);
  const levels = { "": [] };
  const parentOf = (p) => (p.includes("/") ? p.slice(0, p.lastIndexOf("/")) : "");
  const nameOf = (p) => p.slice(p.lastIndexOf("/") + 1);
  // A shut folder (node_modules) gets no level of its own: it stays closed.
  for (const p of dirs) if (!shut.has(p)) levels[p] = [];
  for (const p of dirs) {
    levels[parentOf(p)]?.push({
      name: nameOf(p),
      path: p,
      dir: true,
      ...(shut.has(p) ? { ignored: true } : {}),
    });
  }
  for (const p of files) levels[parentOf(p)]?.push({ name: nameOf(p), path: p, dir: false });
  let truncated = cut;
  for (const [d, entries] of Object.entries(levels)) {
    entries.sort((a, b) => Number(b.dir) - Number(a.dir) || a.name.localeCompare(b.name));
    if (entries.length > MAX_PATHS) truncated = true;
    levels[d] = entries.slice(0, MAX_PATHS);
  }
  return { levels, truncated };
}

module.exports = {
  collectChanges,
  CONFLICT_CODES,
  contentSha,
  inRepo,
  isSecretOnDisk,
  lanePath,
  laneRoot,
  looksBinary,
  resolveInLane,
  MAX_FILE_VIEW_BYTES,
  hunkPatch,
  selectionPatch,
  blameFile,
  laneStatus,
  listCommits,
  listPaths,
  listTree,
  listTreeAll,
  parseNumstat,
  parsePorcelainZ,
  parseUnifiedDiff,
  readFileAt,
  readImageAt,
  resolveBaseRef,
  defaultBranch,
  DEFAULT_CONTEXT,
  MAX_CONTEXT,
  MAX_FILES,
  MAX_FILE_BYTES,
  MAX_TOTAL_BYTES,
};