claude-interactive.js

// claude-interactive.js — tmux-driven interactive Claude engine ("subscription" / Max).
//
// Instead of headless `claude -p` (which bills separate Agent SDK credits), this module
// keeps a PERSISTENT interactive Claude Code TUI session alive inside a detached tmux
// session (one per studio session) and exchanges messages with it via tmux buffers,
// reading replies from the session transcript at ~/.claude/projects/<encoded-cwd>/<cid>.jsonl.
// Interactive sessions run on the Claude Max subscription.
//
// Engine capabilities / behavior:
// - mcpServers: passed via --mcp-config at spawn time (works in interactive mode)
// - systemPrompt: applied at spawn time via --append-system-prompt
// - config changes (system prompt / MCP set / model) are detected via a hash stored
//   in the tmux session environment — the session is respawned with --resume, which
//   keeps writing to the SAME transcript file (verified empirically)
// - image attachments: saved to temp files, paths appended to the prompt (the agent
//   reads them with its Read tool); other structured blocks are flattened to text
// - maxTurns is IGNORED (not applicable to interactive sessions)
//
// - the tmux session lives on the PRIVATE `ccstudio` socket (see tmuxArgs below), the
//   same one terminal-bridge.js uses, so the browser can attach a read/write view of
//   this exact pane via /ws/terminal?view=engine — one claude process, one writer
//
// This module NEVER touches SQLite and NEVER sends the 'done' WS event — the caller
// (server.js WS chat handler) persists collected output and sends 'done' after return.

const { spawn, spawnSync } = require('node:child_process');
const fs = require('node:fs');
const path = require('node:path');
const os = require('node:os');
const crypto = require('node:crypto');

const { findClaudeBin } = require('./claude-cli');
const { agentsMdPreamble } = require('./agents-md');
const { seedClaudeFirstRun, SKIP_BYPASS_WARNING_SETTINGS } = require('./claude-firstrun');
// ONE definition of the socket name, imported — never a second copy of the string.
const { TMUX_SOCKET } = require('./terminal-bridge');

// tmux negotiates UTF-8 support for the server from LANG/LC_ALL at the FIRST
// `new-session` call's env — neither the Docker image (node:20-bookworm, no ENV
// LANG) nor a macOS GUI launch sets a UTF-8 locale, so without this the tmux
// server falls back to non-UTF-8 mode and mangles every multi-byte character
// sent through load-buffer/paste-buffer (e.g. each Cyrillic letter becomes
// "–" plus a stray glyph). Same bug and same fix as terminal-bridge.js.
const UTF8_LOCALE = process.platform === 'darwin' ? 'en_US.UTF-8' : 'C.UTF-8';
function utf8Env() {
  return { ...process.env, LANG: UTF8_LOCALE, LC_ALL: UTF8_LOCALE };
}

// Idle (inactivity) watchdog — the turn is abandoned after this long with no new
// transcript bytes. A turn that keeps writing output (the normal long-content case)
// resets the clock and is never cut off; a turn that shows the spinner but writes
// nothing for this long is treated as stuck. Default 10 min.
// Config: CLAUDE_IDLE_TIMEOUT_MS (legacy alias CLAUDE_TIMEOUT_MS).
const IDLE_TIMEOUT_MS = parseInt(process.env.CLAUDE_IDLE_TIMEOUT_MS || process.env.CLAUDE_TIMEOUT_MS || '600000', 10) || 600000;
// Optional absolute ceiling — backstop against a turn that stays "busy" forever. 0 = off.
const HARD_CAP_MS = parseInt(process.env.CLAUDE_HARD_CAP_MS || '0', 10) || 0;

// ─── Interactive-prompt watchdog (GitHub #20) ────────────────────────────────
// How often the turn loop looks at the transcript and the pane.
const POLL_MS = 1500;
// Consecutive polls a prompt must stay on screen before the browser is told. One
// frame can catch a half-drawn widget, or one the agent dismisses by itself.
const AWAIT_CONFIRM_POLLS = 2;
// Extra time a turn is held open while a prompt is pending, on top of the ordinary
// quiet-completion budget — the window in which a human can answer in the live pane.
// 0 disables the hold and the turn completes exactly as it did before. The idle
// watchdog above is untouched and stays the backstop for a prompt nobody answers.
const AWAIT_GRACE_MS = parseInt(process.env.CLAUDE_PROMPT_GRACE_MS || '300000', 10) || 0;
// How long a pane on a blocking dialog is given to be answered by a human before the
// turn gives up WITHOUT pasting (see the block before the paste). 0 skips the check
// and pastes immediately — the pre-#20 behaviour, kept as an explicit opt-out.
const SPAWN_PROMPT_WAIT_MS = parseInt(process.env.CLAUDE_STARTUP_PROMPT_WAIT_MS || '90000', 10) || 0;
// How many consecutive failed clarification pastes are attempted before the engine
// gives up for the rest of the turn. A dead or unreachable pane fails on every
// poll, and retrying at POLL_MS forever spawns three tmux processes per tick for
// nothing. The messages stay queued either way — the caller's finally block runs
// them as the next turn.
const INJECT_MAX_FAILS = 3;

// ─── tmux socket ─────────────────────────────────────────────────────────────
// The interactive engine's sessions (`ccs-<id>`) live on the SAME private tmux
// server as terminal sessions (socket `ccstudio`, owned by terminal-bridge.js),
// never on the default one. Two reasons, in order of weight:
//
//   1. A chat running on this engine can now be watched live from the browser
//      (`/ws/terminal?view=engine`), and terminal-bridge.js can only attach to a
//      session on its own socket. Split sockets made the attach impossible.
//   2. `tmux kill-server` typed in any shell is server-wide, so on the default
//      socket a single stray command destroys every live subscription session
//      mid-turn — the exact failure that moved terminal sessions off it.
//
// EVERY tmux invocation in this file goes through tmuxArgs(). A missed one would
// silently split state across two servers: has-session says "no" while the real
// TUI is still running on the other socket.
function tmuxArgs(args) { return ['-L', TMUX_SOCKET, ...args]; }

// ─── tmux availability (checked once, cached) ───────────────────────────────
let _tmuxAvailable = null;
function tmuxAvailable() {
  if (_tmuxAvailable === null) {
    try {
      const r = spawnSync('tmux', tmuxArgs(['-V']), { stdio: 'ignore' });
      _tmuxAvailable = !r.error && r.status === 0;
    } catch {
      _tmuxAvailable = false;
    }
  }
  return _tmuxAvailable;
}

// ─── helpers ─────────────────────────────────────────────────────────────────

// POSIX single-quote shell escaping: wrap in ', replace embedded ' with '\''
function shq(s) {
  return "'" + String(s).replace(/'/g, "'\\''") + "'";
}

function tmuxName(localSessionId) {
  return 'ccs-' + String(localSessionId).replace(/[^a-zA-Z0-9_-]/g, '_');
}

function tmuxHasSession(name) {
  try {
    const r = spawnSync('tmux', tmuxArgs(['has-session', '-t', name]), { stdio: 'ignore' });
    return !r.error && r.status === 0;
  } catch {
    return false;
  }
}

function capturePane(name) {
  try {
    const r = spawnSync('tmux', tmuxArgs(['capture-pane', '-p', '-t', name]), { encoding: 'utf8' });
    if (r.error || r.status !== 0) return null;
    return r.stdout || '';
  } catch {
    return null;
  }
}

// Is the Claude TUI actively working a turn? Used to hold completion until the
// spinner clears — a single assistant message is written to the transcript as
// SEPARATE records per block (thinking → text → tool_use), all stamped with the
// SAME final stop_reason, up to ~20s apart. So a terminal stop_reason can latch
// on the thinking record well before the final text record is flushed; breaking
// then would drop the trailing text. The spinner animates throughout that gap
// and only clears when the turn truly ends.
//
// Detection is defense-in-depth and version-independent — ANY of three signals
// means busy, biased so a false "busy" only DELAYS completion (caught by the
// safety-net) while never risking a premature break that loses text:
//   1. animation — the spinner's elapsed counter ticks every ~0.5–1s, so the
//      captured pane changes between polls during a turn (verified on live
//      2.1.x: idle sessions stay static, working ones change every poll);
//   2. elapsed-timer pattern — a seconds count followed by a "·" or ")", e.g.
//      "(8s ·" / "26m 44s ·" / "8s)", shown only during an active turn (the
//      persistent statusline uses "⏱ 5m" / "🕐 14:12", which don't match);
//   3. legacy "esc to interrupt" marker (older TUI builds).
function paneBusy(pane, prevPane) {
  if (pane === null) return false;
  if (prevPane !== null && pane !== prevPane) return true;     // 1. spinner animating
  if (/\d+s\s*[·)]/.test(pane)) return true;                  // 2. elapsed timer "(8s ·" / "43s ·" / "8s)"
  if (pane.includes('esc to interrupt')) return true;         // 3. legacy marker
  return false;
}

// Is the TUI blocked on a prompt only a human can answer? (GitHub #20)
//
// Structural, not wording-based. Every blocking prompt the Claude Code TUI renders —
// a tool-permission request, plan approval, the --dangerously-skip-permissions
// acceptance screen, the trust-this-folder dialog, the AskUserQuestion tool, /model —
// is the SAME widget: numbered options with a caret on the selected one.
//
//     ❯ 1. Yes
//       2. Yes, and don't ask again this session
//       3. No, and tell Claude what to do differently
//
// Two conditions must BOTH hold, and only in the tail of the pane (the widget is
// always at the bottom, just above the input box):
//   - at least two numbered option lines, and
//   - a selection caret directly in front of one of those numbers.
//
// The caret is what separates a widget from prose: an ordinary numbered list in
// Claude's answer text has no caret glyph in front of the digit. Wording is
// deliberately not matched — it is version- and locale-specific, and the widget
// shape has been stable across TUI releases.
//
// Known failure modes, both benign by construction:
//   - false positive: Claude prints a numbered list whose first item happens to be
//     prefixed with '>' or '❯'. Cost is a banner the user ignores plus a longer
//     quiet-completion budget for that turn — never a wrong answer sent anywhere.
//   - false negative: a prompt that is not this widget (a raw readline question from
//     a hook or an MCP server writing to the pane). Cost is the previous behaviour:
//     the turn ends on the idle watchdog. The live pane is still reachable by hand.
// Both are why the caller ALSO requires the spinner to be stopped before believing it.
const AWAIT_TAIL_LINES = 24;
const CARET_RE = /^([❯➤►▶›»>])?\s*(\d{1,2})[.)]\s+\S/;
function paneAwaitingInput(pane) {
  if (typeof pane !== 'string' || !pane) return false;
  const lines = _paneLines(pane);
  const from = Math.max(0, lines.length - AWAIT_TAIL_LINES);
  let numbered = 0, caretAt = -1;
  for (let i = from; i < lines.length; i++) {
    const m = CARET_RE.exec(lines[i].trim());
    if (!m) continue;
    numbered++;
    if (m[1]) caretAt = i;
  }
  // A numbered list the user TYPED into the input box ("1. fix the tests") is not a
  // widget, however much it looks like one.
  if (numbered >= 2 && caretAt >= 0 && !_inInputBox(lines, caretAt)) return true;
  return paneAwaitingSelection(pane);
}

// Non-blank lines, trailing space dropped, a leading box border turned into indent so
// "│ ❯ 1. Yes" reads like "  ❯ 1. Yes" and keeps its column.
function _paneLines(pane) {
  return pane.split('\n').map(l => l.replace(/\s+$/, '').replace(/^([│┃|╎╏┆┊╷╵]\s?)/, '  ')).filter(l => l.trim());
}

// Is line `i` inside the TUI's input box? The box is a region between two horizontal
// rules whose FIRST line is the prompt caret. Measured on CLI 2.1.288, the
// AskUserQuestion widget is ALSO framed by two rules — so "between two rules" alone
// would hide it — but its first framed line is a header ("☐ Color"), never the caret.
// Searched over the WHOLE capture, not the tail: a long draft pushes the box's top
// rule out of any fixed window.
const RULE_RE = /^[\s─━═╌╍┄┅-]{10,}$/;
function _inInputBox(lines, i) {
  let above = -1, below = -1;
  for (let k = i; k >= 0; k--) if (RULE_RE.test(lines[k])) { above = k; break; }
  for (let k = i + 1; k < lines.length; k++) if (RULE_RE.test(lines[k])) { below = k; break; }
  return above >= 0 && below >= 0 && /^\s?[❯➤►▶›»>](\s|$)/.test(lines[above + 1] || '');
}

// The OTHER widget: an unnumbered select. Measured on CLI 2.1.288, all three first-run
// screens are this shape — the theme picker, the trust-this-folder question and the
// Bypass Permissions warning — and the last two open with the caret on "No, exit":
//
//      Quick safety check: Is this a project you created or one you trust? …
//    ❯ No, exit
//      Yes, I trust this folder
//    Enter to confirm · Esc to cancel
//
// Still structural, still no wording: the LAST caret line in the tail, when it is not
// in the input box (_inInputBox), carries text and has at least one sibling option — an
// adjacent line indented deeper than the caret. History cannot trip it: past prompts
// render as "❯ text" too (measured), but the input box is below them while the pane is
// usable, so they are never the last caret line.
function paneAwaitingSelection(pane) {
  if (typeof pane !== 'string' || !pane) return false;
  const lines = _paneLines(pane);
  const from = Math.max(0, lines.length - AWAIT_TAIL_LINES);
  let at = -1, col = -1;
  for (let i = lines.length - 1; i >= from; i--) {
    const m = /^(\s*)[❯➤►▶›»]\s?/.exec(lines[i]);
    if (m) { at = i; col = m[1].length; break; }
  }
  if (at < 0 || _inInputBox(lines, at)) return false;
  if (!lines[at].slice(col + 1).trim()) return false;
  const indent = (l) => l.length - l.trimStart().length;
  const sibling = (l) => l !== undefined && !RULE_RE.test(l) && indent(l) > col;
  return sibling(lines[at - 1]) || sibling(lines[at + 1]);
}

// The pane tail the browser banner shows, so the user can recognise the question
// without opening the pane. Never the whole capture: it carries the entire visible
// conversation and is 50 lines of noise.
function promptExcerpt(pane, maxLines = 14) {
  return String(pane || '').split('\n').map(l => l.replace(/\s+$/, ''))
    .filter(l => l.trim()).slice(-maxLines).join('\n').slice(0, 2000);
}

// Locate <cid>.jsonl under ~/.claude/projects/* — do NOT hand-encode the cwd→dirname
// mapping (macOS realpath/encoding is non-trivial); scan subdirectories instead.
function findTranscript(cid) {
  try {
    const root = path.join(os.homedir(), '.claude', 'projects');
    if (!fs.existsSync(root)) return null;
    for (const dir of fs.readdirSync(root)) {
      const candidate = path.join(root, dir, cid + '.jsonl');
      if (fs.existsSync(candidate)) return candidate;
    }
  } catch {}
  return null;
}

function sleep(ms) {
  return new Promise(resolve => setTimeout(resolve, ms));
}

// Write the MCP servers map to a content-addressed temp file for --mcp-config.
// Files are tiny, idempotent by hash, and intentionally not deleted — the TUI
// reads the path at spawn time and a respawn with the same config reuses it.
function mcpConfigPath(mcpServers) {
  if (!mcpServers || typeof mcpServers !== 'object' || Object.keys(mcpServers).length === 0) return null;
  try {
    const json = JSON.stringify({ mcpServers });
    const hash = crypto.createHash('sha256').update(json).digest('hex').slice(0, 16);
    const p = path.join(os.tmpdir(), `ccs-mcp-${hash}.json`);
    // 0600: the config embeds internal MCP secrets (ASK_USER_SECRET etc.)
    if (!fs.existsSync(p)) fs.writeFileSync(p, json, { mode: 0o600 });
    return p;
  } catch {
    return null;
  }
}

// ─── Spawn command delivery (issue #96) ──────────────────────────────────────
// A tmux COMMAND travels to the tmux server over its imsg socket, which caps the
// whole message at ~16 KB. Measured on tmux 3.7c: a 16 300-byte command starts the
// session, 16 340 answers `failed to send command` and 20 000 `command too long`.
// The system prompt this engine spawns with (studio prompt + mode preamble + skills
// + AGENTS.md, which alone may be agents-md.MAX_BYTES = 64 KB) is routinely past
// that, so the spawn command must NEVER carry it inline. The ceiling that applies to
// the claude process itself is ARG_MAX (~1 MB macOS, ~2 MB Linux), which the prompt
// fits inside — the 16 KB wall belongs to tmux alone.
//
// So the whole invocation is written to a shell script and tmux is handed
// `sh <path>`: ~60 bytes whatever the prompt weighs.
//
// Why a script and not `--append-system-prompt "$(cat file)"`: tmux runs the command
// through `default-shell`, i.e. the user's LOGIN shell. `$( )` is a syntax error in
// csh/tcsh and strips trailing newlines everywhere else. `sh <path>` is plain words
// in every shell, and the script's own interpreter is one we choose.
//
// The scripts live in a private 0700 directory created once per process. A shared
// /tmp path would be pre-creatable by another local user, and this file is EXECUTED —
// the content-addressed reuse below would then run their script, not ours.
let _spawnDir = null;
function spawnScriptDir() {
  if (!_spawnDir) _spawnDir = fs.mkdtempSync(path.join(os.tmpdir(), 'ccs-spawn-'));
  return _spawnDir;
}

// Full `claude` invocation for the interactive engine. Pure — the prompt is inline
// here on purpose: this string becomes the script body, i.e. the child's argv.
//
// `configEnv` pins HOME and CLAUDE_CONFIG_DIR to the values claude-firstrun.js seeded:
// the pane inherits the TMUX SERVER's environment, which survives a studio restart, so
// a studio relaunched with a different CLAUDE_CONFIG_DIR would otherwise seed one config
// and start `claude` on another.
function buildInteractiveCommand({ claudeBin, idFlag, modelAlias, sp, mcpPath, configEnv = null }) {
  let pin = '';
  if (configEnv) {
    if (!configEnv.CLAUDE_CONFIG_DIR) pin += ' -u CLAUDE_CONFIG_DIR';
    if (configEnv.HOME) pin += ` HOME=${shq(configEnv.HOME)}`;
    if (configEnv.CLAUDE_CONFIG_DIR) pin += ` CLAUDE_CONFIG_DIR=${shq(configEnv.CLAUDE_CONFIG_DIR)}`;
  }
  // --settings answers the Bypass Permissions warning the TUI shows for the flag
  // before it — the same consent `claude -p` never asks for (claude-firstrun.js).
  let cmd = `env -u CLAUDECODE${pin} ${shq(claudeBin)} ${idFlag} --model ${shq(modelAlias)} --dangerously-skip-permissions --settings ${shq(SKIP_BYPASS_WARNING_SETTINGS)}`;
  if (sp) cmd += ` --append-system-prompt ${shq(sp)}`;
  if (mcpPath) cmd += ` --mcp-config ${shq(mcpPath)}`;
  return cmd;
}

// What tmux is actually given. Falls back to the pre-#96 inline command if the temp
// directory cannot be written (read-only /tmp): that still works below ~16 KB, and
// above it the tmux stderr is now surfaced instead of swallowed.
function tmuxLaunchCommand(innerCmd) {
  try {
    const hash = crypto.createHash('sha256').update(innerCmd).digest('hex').slice(0, 16);
    const p = path.join(spawnScriptDir(), `spawn-${hash}.sh`);
    // exec: the pane's process becomes `claude` itself, as before this indirection.
    if (!fs.existsSync(p)) fs.writeFileSync(p, `#!/bin/sh\n# claude-code-studio interactive engine (issue #96)\nexec ${innerCmd}\n`, { mode: 0o600 });
    return `sh ${shq(p)}`;
  } catch {
    return innerCmd;
  }
}

// tmux session environment — survives studio server restarts, dies with the session
function getTmuxEnv(name, key) {
  try {
    const r = spawnSync('tmux', tmuxArgs(['show-environment', '-t', name, key]), { encoding: 'utf8' });
    if (r.error || r.status !== 0) return null;
    const line = (r.stdout || '').trim();
    const eq = line.indexOf('=');
    return eq >= 0 ? line.slice(eq + 1) : null;
  } catch {
    return null;
  }
}

function setTmuxEnv(name, key, val) {
  try { spawnSync('tmux', tmuxArgs(['set-environment', '-t', name, key, val]), { stdio: 'ignore' }); } catch {}
}

// ─── public API ──────────────────────────────────────────────────────────────

// One-time upgrade aid. Before the socket move, sessions were created on the
// DEFAULT tmux socket; after it, tmuxHasSession() looks only at `ccstudio` and
// therefore reports "gone" for every session that is in fact still running there.
// The engine handles that on its own — an absent session is respawned with
// `--resume <cid>`, so the conversation continues in the right place — but the
// old TUI keeps running, holding the same transcript open. It is never sent
// anything again (nothing in this process talks to the default socket any more),
// yet a turn that was mid-flight when the server restarted will finish and write
// to that transcript, which the resumed session has also opened.
//
// This is READ-ONLY on purpose: `kill-session` on the default socket would reach
// into a tmux server this project does not own. We report and let the user close
// them. Returns [] when no default tmux server is running at all.
function listOrphanedDefaultSocketSessions() {
  try {
    const r = spawnSync('tmux', ['list-sessions', '-F', '#{session_name}'], { encoding: 'utf8' });
    if (r.error || r.status !== 0) return [];
    return String(r.stdout || '').split('\n').map(x => x.trim()).filter(x => /^ccs-/.test(x));
  } catch { return []; }
}

// Best-effort tmux session kill (called on studio session delete)
function killInteractiveTmux(localSessionId) {
  try {
    spawnSync('tmux', tmuxArgs(['kill-session', '-t', tmuxName(localSessionId)]), { stdio: 'ignore' });
  } catch {}
}

// Run one message through the persistent interactive tmux session.
// Params: same object as server.js runCliSingle — uses prompt, systemPrompt, model,
// mode, ws, sessionId, abortController, claudeSessionId, workdir, tabId; ignores the rest.
// Returns { cid, completed, resultMeta, fullText, fullThinking, toolEvents }.
async function runInteractiveSingle(params) {
  const { prompt, systemPrompt, model, mode, ws, sessionId, abortController, claudeSessionId, workdir, tabId, mcpServers, userContent, drainInterrupts, markInterruptsDelivered, requeueInterrupts, fanout } = params;
  const start = Date.now();
  const wsSend = (obj) => {
    try { ws.send(JSON.stringify({ ...obj, ...(tabId ? { tabId } : {}) })); } catch {}
  };
  // input_needed / input_resolved are the only frames a SECOND window watching the
  // same chat must also receive: they are the difference between "the turn is running"
  // and "the turn is blocked waiting for a human", and a window that never sees them
  // shows a spinner until the timeout. The rest of the stream reaches other windows
  // through history replay, so it stays on wsSend alone. `fanout` is optional — the
  // task-runner path already sends through a broadcasting proxy.
  const wsSendAll = (obj) => {
    wsSend(obj);
    if (typeof fanout === 'function') { try { fanout({ ...obj, ...(tabId ? { tabId } : {}) }); } catch {} }
  };

  let fullText = '', fullThinking = '';
  const toolEvents = [];

  if (!tmuxAvailable()) {
    wsSend({ type: 'error', error: 'tmux not found — interactive engine unavailable' });
    return { cid: claudeSessionId || null, completed: false, resultMeta: null, fullText: '', fullThinking: '', toolEvents: [] };
  }

  const name = tmuxName(sessionId);
  let cid = claudeSessionId || null;
  // Declared OUTSIDE the try so the finally below can clear the banner. Every early
  // return inside — abort, idle timeout, hard cap, grace expiry, dead-end, throw —
  // used to leave the browser showing "waiting for your answer" over a dead turn,
  // because the client clears it only on input_resolved or on the next send.
  let awaitAnnounced = false;       // 'input_needed' already sent for the prompt now on screen
  let firstRunSeed = null;          // what claude-firstrun.js did before this spawn, for the error text

  try {
    // ── Resolve per-session config (system prompt, MCP, model) ─────────────
    const mp = mode === 'planning' ? 'MODE: PLANNING ONLY. Analyze, plan, DO NOT modify files.\n\n'
      : mode === 'task' ? 'MODE: EXECUTION.\n\n' : '';
    // AGENTS.md (issue #54) rides along in the same --append-system-prompt this
    // engine already spawns with. It lands in cfgHash below on purpose: editing
    // AGENTS.md then respawns the tmux session with --resume, exactly as changing
    // skills or the model does. Empty string when there is nothing to add, so a
    // project without AGENTS.md keeps its previous hash and does NOT respawn.
    const agentsMd = agentsMdPreamble(workdir || process.cwd());
    const sp = [(mp + (systemPrompt || '')).trim(), agentsMd].filter(Boolean).join('\n\n');
    const modelAlias = /^[a-zA-Z0-9._-]+$/.test(String(model || '')) ? model : 'sonnet';
    const mcpPath = mcpConfigPath(mcpServers);
    let mcpJson = '';
    if (mcpPath) { try { mcpJson = fs.readFileSync(mcpPath, 'utf8'); } catch {} }
    const cfgHash = crypto.createHash('sha256').update(JSON.stringify([sp, mcpJson, modelAlias])).digest('hex').slice(0, 16);

    // ── Spawn (or reuse) the tmux session ──────────────────────────────────
    // tmux alive but no recorded claude session id: without a cid we cannot
    // locate the transcript — kill and respawn fresh.
    if (!cid && tmuxHasSession(name)) killInteractiveTmux(sessionId);

    // Config changed since spawn (skills/mode/MCP/model)? Respawn with --resume —
    // verified to keep writing to the SAME <cid>.jsonl transcript.
    if (cid && tmuxHasSession(name) && getTmuxEnv(name, 'CCS_CFG') !== cfgHash) {
      killInteractiveTmux(sessionId);
    }

    let spawned = false;
    if (!tmuxHasSession(name)) {
      spawned = true;
      const resuming = !!cid;
      if (!cid) cid = crypto.randomUUID();
      const idFlag = resuming ? `--resume ${shq(cid)}` : `--session-id ${shq(cid)}`;

      // The theme picker and the trust question have no flag; seed the two keys that
      // skip them before the TUI reads its config (claude-firstrun.js).
      firstRunSeed = seedClaudeFirstRun({ workdir: workdir || process.cwd() });

      const claudeBin = findClaudeBin();
      const innerCmd = buildInteractiveCommand({ claudeBin, idFlag, modelAlias, sp, mcpPath,
        configEnv: { HOME: process.env.HOME || os.homedir(), CLAUDE_CONFIG_DIR: process.env.CLAUDE_CONFIG_DIR ? path.resolve(process.env.CLAUDE_CONFIG_DIR) : '' } });

      const env = utf8Env();
      delete env.CLAUDECODE; // parent Claude Code session sets this and it confuses the child
      // stderr is PIPED, not ignored: `command too long` was the whole content of
      // issue #96 and it used to be discarded, leaving only the generic line below.
      let tmuxErr = '';
      const child = spawn('tmux', tmuxArgs(['new-session', '-d', '-s', name, '-x', '220', '-y', '50', '-c', workdir || process.cwd(), tmuxLaunchCommand(innerCmd)]), { env, stdio: ['ignore', 'ignore', 'pipe'] });
      if (child.stderr) child.stderr.on('data', (d) => { if (tmuxErr.length < 2000) tmuxErr += String(d); });
      await new Promise((resolve) => {
        child.on('exit', resolve);
        child.on('error', (e) => { tmuxErr += String(e && e.message || e); resolve(); });
      });

      if (!tmuxHasSession(name)) {
        const detail = tmuxErr.trim().split('\n')[0].trim();
        wsSend({ type: 'error', error: 'failed to start tmux session for interactive engine' + (detail ? `: ${detail}` : '') });
        return { cid, completed: false, resultMeta: null, fullText: '', fullThinking: '', toolEvents: [] };
      }

      setTmuxEnv(name, 'CCS_CFG', cfgHash);

      // Wait for the TUI to settle: two consecutive identical, non-empty captures
      let prev = null;
      const settleDeadline = Date.now() + 20000;
      while (Date.now() < settleDeadline) {
        await sleep(500);
        const cap = capturePane(name);
        if (cap && cap.trim() && cap === prev) break;
        prev = cap;
      }

      // A brand-new TUI can settle ON A DIALOG rather than on its input box — the
      // --dangerously-skip-permissions acceptance screen and the trust-this-folder
      // question both look "settled" because they are static. Pasting the user's
      // message into one answers it with whichever option the text lands on. Tell
      // the browser and give a human a bounded window to clear it in the live pane
      // (GitHub #20). Most of them never appear now — claude-firstrun.js answers the
      // three first-run screens before the spawn — and the check below catches the rest.
    }

    // A pane can be sitting on a blocking widget for either reason: a fresh TUI that
    // settled on the trust-this-folder / skip-permissions screen, or a REUSED pane
    // whose previous turn ended (idle timeout, grace expiry, a closed browser tab)
    // while its dialog was still up. Both fail the same way — the paste-buffer below
    // answers the widget with whatever option the caret sits on, which can be a
    // permission grant. So the check runs before EVERY paste, not only after a spawn.
    // On timeout the turn ends with the screen in the error instead of pasting: a
    // false positive costs a delay and a resend, a true one no longer costs the
    // message AND the session.
    if (SPAWN_PROMPT_WAIT_MS > 0 && paneAwaitingInput(capturePane(name))) {
      awaitAnnounced = true;
      wsSendAll({ type: 'input_needed', sessionId, engine: 'subscription', phase: spawned ? 'startup' : 'resume', prompt: promptExcerpt(capturePane(name)) });
      const until = Date.now() + SPAWN_PROMPT_WAIT_MS;
      while (Date.now() < until) {
        await sleep(POLL_MS);
        if (abortController?.signal?.aborted) break;
        if (!paneAwaitingInput(capturePane(name))) break;
      }
      awaitAnnounced = false;
      wsSendAll({ type: 'input_resolved', sessionId });
      // Stop pressed while we waited: end here, before the paste. Falling through sent
      // the message and Enter into the very dialog the wait was holding off.
      if (abortController?.signal?.aborted) {
        return { cid, completed: false, resultMeta: { durationMs: Date.now() - start }, fullText: '', fullThinking: '', toolEvents: [] };
      }
      // Still up after the whole window: do NOT paste. The old fall-through answered the
      // widget with whatever the caret sat on — and two of the three startup screens
      // open on "No, exit", so the paste quit `claude` and the message was lost anyway.
      // Saying so, with the screen, is the only outcome that leaves anything to act on.
      const still = capturePane(name);
      if (paneAwaitingInput(still)) {
        const why = firstRunSeed && firstRunSeed.reason && firstRunSeed.reason !== 'disabled'
          ? ` (could not pre-answer the first-run screens in ${firstRunSeed.path}: ${firstRunSeed.reason})` : '';
        wsSend({ type: 'error', error: `Claude is waiting on a screen in its terminal pane, so your message was not sent${why}. Answer it in the engine pane, then send again:\n\n${promptExcerpt(still, 10)}` });
        return { cid, completed: false, resultMeta: null, fullText: '', fullThinking: '', toolEvents: [] };
      }
    }

    // ── Record transcript offset BEFORE sending ────────────────────────────
    let transcriptPath = findTranscript(cid);
    let offset = 0;
    if (transcriptPath) {
      try { offset = fs.statSync(transcriptPath).size; } catch { offset = 0; }
    }

    // ── Flatten structured userContent: extra text blocks are prepended, image
    // blocks are saved to temp files the agent can open with its Read tool ─────
    let sendText = String(prompt || '');
    if (Array.isArray(userContent)) {
      const extra = [];
      for (const block of userContent) {
        if (!block || typeof block !== 'object') continue;
        if (block.type === 'text') {
          // the main prompt text is already in sendText — keep only extra blocks (e.g. SSH host info)
          if (block.text && block.text !== prompt) extra.push(block.text);
        } else if (block.type === 'image' && block.source?.data) {
          try {
            const ext = String(block.source.media_type || 'image/png').split('/')[1] || 'png';
            const imgFile = path.join(os.tmpdir(), `ccs-att-${crypto.randomBytes(6).toString('hex')}.${ext}`);
            fs.writeFileSync(imgFile, Buffer.from(block.source.data, 'base64'));
            extra.push(`[Attached image saved at: ${imgFile} — use the Read tool to view it]`);
          } catch {}
        } else if (block.type === 'file' && block.source?.data) {
          // Without this branch every non-image attachment is silently dropped on the
          // way into the pane. buildAttachmentContentBlocks emits `file` for text files
          // AND binaries, and the deferred clarification follow-up (server.js finally
          // block) rehydrates base64 specifically so it can travel this path — the
          // original temp file is already unlinked by then, so ignoring the block loses
          // the attachment outright.
          try {
            const safe = path.basename(String(block.source.name || 'attachment.bin')).replace(/[^\w.\-]+/g, '_').slice(0, 60) || 'attachment.bin';
            const outFile = path.join(os.tmpdir(), `ccs-att-${crypto.randomBytes(6).toString('hex')}-${safe}`);
            fs.writeFileSync(outFile, Buffer.from(block.source.data, 'base64'));
            extra.push(`[Attached file saved at: ${outFile} — use the Read tool to open it]`);
          } catch {}
        }
      }
      if (extra.length) sendText = extra.join('\n') + '\n\n' + sendText;
    }

    // ── Send the prompt (tmp file → tmux buffer → bracketed paste → Enter) ─
    const tmpFile = path.join(os.tmpdir(), `ccs-msg-${crypto.randomBytes(8).toString('hex')}.txt`);
    const bufName = `ccsbuf-${crypto.randomBytes(4).toString('hex')}`;
    try {
      fs.writeFileSync(tmpFile, sendText);
      spawnSync('tmux', tmuxArgs(['load-buffer', '-b', bufName, tmpFile]), { stdio: 'ignore' });
      spawnSync('tmux', tmuxArgs(['paste-buffer', '-dpr', '-t', name, '-b', bufName]), { stdio: 'ignore' });
      await sleep(300);
      spawnSync('tmux', tmuxArgs(['send-keys', '-t', name, 'Enter']), { stdio: 'ignore' });
    } finally {
      try { fs.unlinkSync(tmpFile); } catch {}
    }

    // ── Poll loop: completion = transcript turn-end (stop_reason) gated by the
    //    TUI spinner having cleared; pane is the gate, never the primary signal ──
    let remainder = '';
    let endTurnSeen = false;          // latched when an assistant record ends the turn (stop_reason ≠ tool_use)
    let sawOutput = false;
    let quietPolls = 0;               // consecutive polls with spinner gone (!busy) AND no new transcript bytes
    let prevPaneCap = null;           // previous pane capture — for spinner-animation detection in paneBusy()
    let lastActivityAt = start;       // idle watchdog cursor — bumped on transcript progress (new bytes)
    let injectFails = 0;              // consecutive failed clarification pastes — see INJECT_MAX_FAILS
    let awaitPolls = 0;               // consecutive polls showing a blocking prompt

    while (true) {
      await sleep(POLL_MS);

      if (abortController?.signal?.aborted) {
        // Interrupt the turn, keep the tmux session alive
        try { spawnSync('tmux', tmuxArgs(['send-keys', '-t', name, 'Escape']), { stdio: 'ignore' }); } catch {}
        return { cid, completed: false, resultMeta: { durationMs: Date.now() - start }, fullText, fullThinking, toolEvents };
      }

      if (Date.now() - lastActivityAt > IDLE_TIMEOUT_MS) {
        const mins = Math.round(IDLE_TIMEOUT_MS / 60000);
        wsSend({ type: 'error', error: `interactive engine timed out — no activity for ${mins} min (idle). Raise CLAUDE_IDLE_TIMEOUT_MS to allow longer silences.` });
        return { cid, completed: false, resultMeta: { durationMs: Date.now() - start }, fullText, fullThinking, toolEvents };
      }
      if (HARD_CAP_MS > 0 && Date.now() - start > HARD_CAP_MS) {
        const mins = Math.round(HARD_CAP_MS / 60000);
        wsSend({ type: 'error', error: `interactive engine timed out — exceeded hard cap of ${mins} min (CLAUDE_HARD_CAP_MS).` });
        return { cid, completed: false, resultMeta: { durationMs: Date.now() - start }, fullText, fullThinking, toolEvents };
      }

      // Locate transcript lazily — file may not exist until the first reply starts
      if (!transcriptPath) {
        transcriptPath = findTranscript(cid);
        if (transcriptPath) offset = 0;
      }

      // Tail new transcript bytes from the recorded offset
      let gotNewBytes = false;
      if (transcriptPath) {
        let size = 0;
        try { size = fs.statSync(transcriptPath).size; } catch { size = 0; }
        if (size > offset) {
          gotNewBytes = true;
          let chunk = '';
          try {
            const fd = fs.openSync(transcriptPath, 'r');
            try {
              const buf = Buffer.alloc(size - offset);
              const bytesRead = fs.readSync(fd, buf, 0, buf.length, offset);
              chunk = buf.subarray(0, bytesRead).toString('utf8');
              offset += bytesRead;
            } finally {
              fs.closeSync(fd);
            }
          } catch {}

          const data = remainder + chunk;
          const lines = data.split('\n');
          remainder = lines.pop() || ''; // keep trailing partial line
          for (const line of lines) {
            if (!line.trim()) continue;
            let rec;
            try { rec = JSON.parse(line); } catch { continue; }
            if (rec.type !== 'assistant') continue; // ignore user/system/attachment records
            const blocks = rec.message?.content;
            if (Array.isArray(blocks)) {
              for (const block of blocks) {
                if (block.type === 'text' && block.text) {
                  fullText += block.text;
                  sawOutput = true;
                  wsSend({ type: 'text', text: block.text });
                } else if (block.type === 'thinking' && block.thinking) {
                  fullThinking += block.thinking;
                  sawOutput = true;
                  wsSend({ type: 'thinking', text: block.thinking });
                } else if (block.type === 'tool_use') {
                  const input = JSON.stringify(block.input || {}).substring(0, 600);
                  toolEvents.push({ name: block.name, input });
                  sawOutput = true;
                  wsSend({ type: 'tool', tool: block.name, input });
                }
              }
            }
            // Turn-completion signal (authoritative, version-independent):
            // `tool_use` is the ONLY stop_reason meaning "the agent will continue
            // after the tool result". Every other terminal value — end_turn |
            // stop_sequence | refusal (the full set observed across the local
            // transcript corpus) — ends the turn. The old code matched only
            // `end_turn` AND was gated behind `!busy`, a pane marker
            // ('esc to interrupt') that no longer exists in the TUI, so `busy`
            // was always false and completion fell through to a 3s-quiet
            // heuristic that fired mid-task — reporting "done" while the agent
            // was still working.
            const _sr = rec.message?.stop_reason;
            if (_sr === 'tool_use') endTurnSeen = false;
            else if (_sr) endTurnSeen = true;
          }
        }
      }

      const pane = capturePane(name);
      const busy = paneBusy(pane, prevPaneCap);
      prevPaneCap = pane;

      // ── Blocked on an interactive prompt? (GitHub #20) ─────────────────────
      // The widget is on screen AND the spinner is stopped AND nothing was written
      // this poll: the agent is not working, it is waiting for a human. Announce it
      // so the browser can offer the live pane instead of letting the turn die on a
      // timeout with no explanation. Both edges are reported — the banner has to be
      // able to clear itself when the prompt is answered.
      const awaiting = !busy && !gotNewBytes && paneAwaitingInput(pane);
      awaitPolls = awaiting ? awaitPolls + 1 : 0;
      if (awaiting && !awaitAnnounced && awaitPolls >= AWAIT_CONFIRM_POLLS) {
        awaitAnnounced = true;
        wsSendAll({ type: 'input_needed', sessionId, engine: 'subscription', prompt: promptExcerpt(pane) });
      } else if (awaitAnnounced && !awaiting) {
        awaitAnnounced = false;
        wsSendAll({ type: 'input_resolved', sessionId });
      }

      // Mid-run clarifications. The hook mechanism the headless engine uses cannot
      // apply here — there is no per-run --settings to inject, the CLI is already
      // running interactively. The equivalent for a live TUI is to type the message
      // into it, which is exactly what a person sitting at the terminal would do —
      // and a person cannot type into a busy TUI (spinner running) or into a
      // permission/plan prompt without hijacking whatever option is selected. Only
      // drain (and thus mark delivered) once the pane genuinely has an open input
      // line: not busy, not showing a blocking widget, AND actually captured — a
      // failed capture must NOT read as idle (paneBusy/paneAwaitingInput both
      // return false for a null pane, the one case we can least confirm it's safe).
      //
      // This runs BEFORE the completion check below, not after. `busy` normally
      // stays true (spinner/timer animation) right up until endTurnSeen latches, so
      // the "idle and the loop hasn't exited yet" window IS the tick the turn ends —
      // draining after the break left this code effectively dead on a normal,
      // healthy completion, silently losing the clarification instead of typing it.
      let injected = false;
      // Independent re-check of the pane's prompt state, not the `awaiting` variable
      // computed above: `awaiting` is forced false whenever `gotNewBytes` is true this
      // tick (see its definition), so a permission/plan widget that appears in the
      // same poll as trailing transcript bytes would otherwise pass this gate and get
      // hijacked by a pasted clarification.
      if (pane && !busy && !paneAwaitingInput(pane) && injectFails < INJECT_MAX_FAILS && typeof drainInterrupts === 'function') {
        let pending = [];
        try { pending = drainInterrupts() || []; } catch {}
        // One paste + one Enter for the whole batch: busy/awaiting were sampled
        // once for this tick, so pasting item 2 after item 1's Enter already
        // restarted the spinner would land in a pane no longer listening.
        const parts = [];
        for (const m of pending) {
          if (m.content) parts.push(m.content);
          for (const att of (Array.isArray(m.attachments) ? m.attachments : [])) {
            if (att.type === 'ssh') {
              // An SSH entry has no `path` — without this it contributed nothing and the
              // pane got a bare "[See attached files]". Mirrors buildAttachmentContentBlocks:
              // host and key path only, never the credential (this text lands in the CLI
              // transcript on disk).
              let t = `[SSH Host: ${att.label || att.host || 'SSH'}]\nHost: ${att.host}:${att.port || 22}`;
              if (att.sshKeyPath) t += `\nSSH Key: ${att.sshKeyPath}`;
              else if (att.authMethod === 'password') t += `\nAuth: password (held server-side, not exposed)`;
              parts.push(t);
            } else if (att.path) {
              parts.push(`[Attached ${att.mimeType && att.mimeType.startsWith('image/') ? 'image' : 'file'}: ${att.name || 'file'}]\nSaved at: ${att.path}\nRead it before continuing.`);
            }
          }
        }
        const body = parts.join('\n\n').trim();
        if (body) {
          const note = `USER CLARIFICATION${pending.length > 1 ? 'S' : ''} (sent while you were working):\n\n${body}`;
          const tmpFile = path.join(os.tmpdir(), `ccs-int-${crypto.randomBytes(6).toString('hex')}.txt`);
          const bufName = `ccsint-${crypto.randomBytes(4).toString('hex')}`;
          let delivered = false;
          try {
            fs.writeFileSync(tmpFile, note);
            const load = spawnSync('tmux', tmuxArgs(['load-buffer', '-b', bufName, tmpFile]), { stdio: 'ignore' });
            const paste = spawnSync('tmux', tmuxArgs(['paste-buffer', '-dpr', '-t', name, '-b', bufName]), { stdio: 'ignore' });
            if (load.status === 0 && paste.status === 0) {
              await sleep(250);
              const enter = spawnSync('tmux', tmuxArgs(['send-keys', '-t', name, 'Enter']), { stdio: 'ignore' });
              delivered = enter.status === 0;
            }
          } catch {} finally { try { fs.unlinkSync(tmpFile); } catch {} }
          if (delivered) {
            injected = true;
            injectFails = 0;
            if (typeof markInterruptsDelivered === 'function') { try { markInterruptsDelivered(pending); } catch {} }
          } else if (typeof requeueInterrupts === 'function') {
            // Genuinely undo the drain: put it back for the next idle tick to retry,
            // or — if the turn ends first — for the caller's finally-block follow-up
            // to run it as the next turn instead of it vanishing after being popped.
            try { requeueInterrupts(pending); } catch {}
            injectFails++;
            // Only the last attempt talks to the user. A dead pane fails every poll,
            // and one error frame per ~1.5s tick for the rest of a long turn is a
            // toast storm, not a diagnostic.
            if (injectFails >= INJECT_MAX_FAILS) {
              // nonTerminal: the poll loop is still running this turn. Without the flag the
              // client's `error` case tears the turn down — clears isGen, the Stop button
              // and tab.generating — and the user is invited to send into a live turn.
              wsSend({ type: 'error', nonTerminal: true, error: 'clarification could not be typed into the interactive session — it will be sent as the next message instead' });
            }
          } else {
            // No requeue channel (a caller that predates it): the batch is already
            // drained and cannot be put back, so report the loss rather than imply
            // a retry that will not happen.
            injectFails++;
            wsSend({ type: 'error', nonTerminal: true, error: 'clarification could not be typed into the interactive session' });
          }
        } else if (pending.length && typeof markInterruptsDelivered === 'function') {
          // Nothing left to type (e.g. an SSH-only attachment, which has no file path
          // to reference) — there's no pane action to retry, so don't leave it queued.
          try { markInterruptsDelivered(pending); } catch {}
        }
      }

      if (injected) {
        // A new turn was just kicked off in the pane — the endTurnSeen/busy/
        // gotNewBytes gathered above describe the turn that just ended, not what
        // comes next. Skip the completion checks below and let the next poll
        // observe the new turn fresh instead of breaking on stale state.
        endTurnSeen = false;
        quietPolls = 0;
        lastActivityAt = Date.now();
        continue;
      }

      // COMPLETE on the transcript turn-end signal, but ONLY once the spinner has
      // cleared and no bytes arrived this poll. `tool_use` is the sole "continue"
      // stop_reason; any other terminal value latches endTurnSeen. Because a
      // single message's blocks are written as separate records up to ~20s apart
      // (thinking → text), endTurnSeen can latch on the thinking record before the
      // final text is flushed — the !busy guard (spinner still animating during
      // that gap) holds the break until the whole message is out. Pane text is
      // never the PRIMARY signal (spinner wording is version-specific); it only
      // gates when to trust the already-latched transcript signal.
      if (endTurnSeen && !busy && !gotNewBytes) break;

      if (gotNewBytes) lastActivityAt = Date.now(); // transcript progress = real work; resets idle watchdog
      if (gotNewBytes || busy) quietPolls = 0; else quietPolls++;

      // Safety-net completion: output WAS produced, then the spinner cleared and
      // no new bytes arrived for ~18s. Covers a missed turn-end stop_reason (e.g.
      // a corrupt final transcript line that failed to JSON.parse). Safe because
      // a working agent keeps `busy` true (animation/timer), so quietPolls only
      // climbs once the turn has genuinely ended.
      // While a prompt is pending, "quiet" is the expected state, not a stalled turn:
      // widen both quiet-based exits by the grace budget so there is time to answer in
      // the live pane. Without this the safety-net below fires ~18s into the wait and
      // reports the turn DONE while the TUI is still blocked — after which the next web
      // message gets pasted into the open widget instead of into the prompt box.
      const graceP = awaitAnnounced ? Math.ceil(AWAIT_GRACE_MS / POLL_MS) : 0;
      if (sawOutput && quietPolls >= 12 + graceP) break;

      // Dead-end guard: zero output AND spinner gone for ~30s — the message never
      // registered with the TUI; fail fast instead of waiting out the idle timeout.
      // A long thinking phase or slow first tool keeps `busy` true (spinner
      // animating) or writes a record (sawOutput), so neither trips this.
      if (!sawOutput && quietPolls >= 20 + graceP) {
        wsSend({ type: 'error', error: 'interactive session went idle without producing a reply' });
        return { cid, completed: false, resultMeta: { durationMs: Date.now() - start }, fullText, fullThinking, toolEvents };
      }
    }

    return { cid, completed: true, resultMeta: { durationMs: Date.now() - start }, fullText, fullThinking, toolEvents };
  } catch (e) {
    wsSend({ type: 'error', error: 'interactive engine error: ' + (e?.message || String(e)) });
    return { cid, completed: false, resultMeta: { durationMs: Date.now() - start }, fullText, fullThinking, toolEvents };
  } finally {
    // The turn is over whichever way it ended; the banner must not outlive it.
    if (awaitAnnounced) { awaitAnnounced = false; wsSendAll({ type: 'input_resolved', sessionId }); }
  }
}

// ─── Catch-up: pull transcript activity done OUTSIDE the web UI ───────────────
// When the user opens a real terminal on a session (the "⚡ Claude Code" button →
// `claude --resume <cid>`), their typing + Claude's replies are appended to the
// SAME <cid>.jsonl this module reads. These helpers let the server pull that gap
// into the web chat on demand. Pure: no tmux, no WebSocket, no SQLite — the
// caller persists the events and re-renders.

// Current byte size of <cid>.jsonl, or null if no transcript exists yet. The
// server calls this to advance the catch-up cursor to EOF after every web turn,
// so a later catch-up only surfaces bytes a terminal session appended afterwards.
function transcriptSize(cid) {
  const p = cid ? findTranscript(cid) : null;
  if (!p) return null;
  try { return fs.statSync(p).size; } catch { return null; }
}

// Extract the human-typed text from a transcript `user` record. Records carrying
// only tool_result / image blocks (tool output fed back to the agent, not
// something a person typed) return '' and are skipped by the caller.
function userRecordText(rec) {
  const c = rec && rec.message ? rec.message.content : undefined;
  if (typeof c === 'string') return c.trim();
  if (Array.isArray(c)) {
    const parts = [];
    for (const b of c) {
      if (b && b.type === 'text' && typeof b.text === 'string') parts.push(b.text);
    }
    return parts.join('\n').trim();
  }
  return '';
}

// Read <cid>.jsonl records appended since `startOffset` and return them as an
// ordered event list plus the new byte offset. The offset advances ONLY past
// COMPLETE lines (to the last '\n'); a half-written trailing record is left for
// the next call. Returns { found, offset, events }.
function catchUpFromTranscript({ cid, startOffset = 0 } = {}) {
  const out = { found: false, offset: Number(startOffset) || 0, events: [] };
  const transcriptPath = cid ? findTranscript(cid) : null;
  if (!transcriptPath) return out;
  out.found = true;

  let size = 0;
  try { size = fs.statSync(transcriptPath).size; } catch { return out; }
  const from = Math.max(0, Math.min(Number(startOffset) || 0, size));
  out.offset = from;
  if (size <= from) return out;

  let buf;
  try {
    const fd = fs.openSync(transcriptPath, 'r');
    try {
      buf = Buffer.alloc(size - from);
      const n = fs.readSync(fd, buf, 0, buf.length, from);
      buf = buf.subarray(0, n);
    } finally { fs.closeSync(fd); }
  } catch { return out; }

  const lastNl = buf.lastIndexOf(0x0A);
  if (lastNl < 0) return out;                 // no complete line yet — keep offset
  out.offset = from + lastNl + 1;             // byte-accurate advance past last newline

  const text = buf.subarray(0, lastNl + 1).toString('utf8');
  for (const line of text.split('\n')) {
    if (!line.trim()) continue;
    let rec;
    try { rec = JSON.parse(line); } catch { continue; }
    const ts = rec.timestamp || null;   // real record time → caller uses it as created_at
    if (rec.type === 'user') {
      const txt = userRecordText(rec);
      if (txt) out.events.push({ role: 'user', type: 'text', content: txt, ts });
    } else if (rec.type === 'assistant') {
      const blocks = rec.message && rec.message.content;
      if (!Array.isArray(blocks)) continue;
      for (const block of blocks) {
        if (block.type === 'text' && block.text) {
          out.events.push({ role: 'assistant', type: 'text', content: block.text, ts });
        } else if (block.type === 'thinking' && block.thinking) {
          out.events.push({ role: 'assistant', type: 'thinking', content: block.thinking, ts });
        } else if (block.type === 'tool_use') {
          out.events.push({ role: 'assistant', type: 'tool', content: JSON.stringify(block.input || {}).substring(0, 600), tool_name: block.name, ts });
        }
      }
    }
  }
  return out;
}

module.exports = { runInteractiveSingle, killInteractiveTmux, tmuxAvailable, catchUpFromTranscript, transcriptSize, tmuxName, listOrphanedDefaultSocketSessions, paneAwaitingInput, paneAwaitingSelection, promptExcerpt, buildInteractiveCommand, tmuxLaunchCommand };