"""Base class for all Hermes execution environment backends.

Unified spawn-per-call model: every command spawns a fresh ``bash -c`` process.
A session snapshot (env vars, functions, aliases) is captured once at init and
re-sourced before each command. CWD persists via in-band stdout markers (remote)
or a temp file (local).
"""

import codecs
import json
import logging
import os
import select
import shlex
import subprocess
import threading
import time
import uuid
from abc import ABC, abstractmethod
from pathlib import Path
from typing import IO, Callable, Protocol

from hermes_constants import get_hermes_home
from hermes_cli._subprocess_compat import windows_hide_flags
from tools.interrupt import is_interrupted

logger = logging.getLogger(__name__)

# Opt-in debug tracing for the interrupt/activity/poll machinery.  Set
# HERMES_DEBUG_INTERRUPT=1 to log loop entry/exit, periodic heartbeats, and
# every is_interrupted() state change from _wait_for_process.  Off by default
# to avoid flooding production gateway logs.
_DEBUG_INTERRUPT = bool(os.getenv("HERMES_DEBUG_INTERRUPT"))

if _DEBUG_INTERRUPT:
    # AIAgent's quiet_mode path (run_agent.py) forces the `tools` logger to
    # ERROR on CLI startup, which would silently swallow every trace we emit.
    # Force this module's own logger back to INFO so the trace is visible in
    # agent.log regardless of quiet-mode.  Scoped to the opt-in case only.
    logger.setLevel(logging.INFO)

# Thread-local activity callback.  The agent sets this before a tool call so
# long-running _wait_for_process loops can report liveness to the gateway.
_activity_callback_local = threading.local()


def set_activity_callback(cb: Callable[[str], None] | None) -> None:
    """Register a callback that _wait_for_process fires periodically."""
    _activity_callback_local.callback = cb


def _get_activity_callback() -> Callable[[str], None] | None:
    return getattr(_activity_callback_local, "callback", None)


def touch_activity_if_due(
    state: dict,
    label: str,
) -> None:
    """Fire the activity callback at most once every ``state['interval']`` seconds.

    *state* must contain ``last_touch`` (monotonic timestamp) and ``start``
    (monotonic timestamp of the operation start).  An optional ``interval``
    key overrides the default 10 s cadence.

    Swallows all exceptions so callers don't need their own try/except.
    """
    now = time.monotonic()
    interval = state.get("interval", 10.0)
    if now - state["last_touch"] < interval:
        return
    state["last_touch"] = now
    try:
        cb = _get_activity_callback()
        if cb:
            elapsed = int(now - state["start"])
            cb(f"{label} ({elapsed}s elapsed)")
    except Exception:
        pass


def get_sandbox_dir() -> Path:
    """Return the host-side root for all sandbox storage (Docker workspaces,
    Singularity overlays/SIF cache, etc.).

    Configurable via TERMINAL_SANDBOX_DIR. Defaults to {HERMES_HOME}/sandboxes/.
    """
    custom = os.getenv("TERMINAL_SANDBOX_DIR")
    if custom:
        p = Path(custom)
    else:
        p = get_hermes_home() / "sandboxes"
    p.mkdir(parents=True, exist_ok=True)
    return p


# ---------------------------------------------------------------------------
# Shared constants and utilities
# ---------------------------------------------------------------------------


def _pipe_stdin(proc: subprocess.Popen, data: str) -> None:
    """Write *data* to proc.stdin on a daemon thread to avoid pipe-buffer deadlocks.

    On Windows, text-mode stdin (``text=True`` / ``encoding="utf-8"``)
    translates ``\\n`` → ``\\r\\n`` as the data flows through the pipe —
    which corrupts every write_file / patch call because the bytes that
    land on disk include injected carriage returns.  The file IS created,
    but every subsequent byte-count / content compare against the
    caller's ``\\n``-only string fails.

    Workaround: write through ``proc.stdin.buffer`` (the underlying byte
    buffer), encoding to UTF-8 ourselves.  That bypasses Python's
    newline translation entirely on every platform.  No behaviour change
    on POSIX — the byte sequence is identical to what text-mode would
    produce there.
    """

    def _write():
        try:
            # proc.stdin is a TextIOWrapper when text=True was set on the
            # Popen.  Its ``.buffer`` attribute is the raw BufferedWriter
            # that bypasses newline translation.  When Popen was created
            # in byte mode, proc.stdin is already a BufferedWriter with
            # no ``.buffer`` attribute — fall back to .write() directly.
            raw = data.encode("utf-8") if isinstance(data, str) else data
            target = getattr(proc.stdin, "buffer", proc.stdin)
            target.write(raw)
            target.close()
        except (BrokenPipeError, OSError):
            pass

    threading.Thread(target=_write, daemon=True).start()


def _popen_bash(
    cmd: list[str], stdin_data: str | None = None, **kwargs
) -> subprocess.Popen:
    """Spawn a subprocess with standard stdout/stderr/stdin setup.

    If *stdin_data* is provided, writes it asynchronously via :func:`_pipe_stdin`.
    Backends with special Popen needs (e.g. local's ``preexec_fn``) can bypass
    this and call :func:`_pipe_stdin` directly.
    """
    kwargs.setdefault("creationflags", windows_hide_flags())
    proc = subprocess.Popen(
        cmd,
        stdout=subprocess.PIPE,
        stderr=subprocess.STDOUT,
        stdin=subprocess.PIPE if stdin_data is not None else subprocess.DEVNULL,
        text=True,
        **kwargs,
    )
    if stdin_data is not None:
        _pipe_stdin(proc, stdin_data)
    return proc


def _load_json_store(path: Path) -> dict:
    """Load a JSON file as a dict, returning ``{}`` on any error."""
    if path.exists():
        try:
            return json.loads(path.read_text(encoding="utf-8"))
        except Exception:
            pass
    return {}


def _save_json_store(path: Path, data: dict) -> None:
    """Write *data* as pretty-printed JSON to *path*."""
    path.parent.mkdir(parents=True, exist_ok=True)
    path.write_text(json.dumps(data, indent=2), encoding="utf-8")


def _file_mtime_key(host_path: str) -> tuple[float, int] | None:
    """Return ``(mtime, size)`` for cache comparison, or ``None`` if unreadable."""
    try:
        st = Path(host_path).stat()
        return (st.st_mtime, st.st_size)
    except OSError:
        return None


# ---------------------------------------------------------------------------
# ProcessHandle protocol
# ---------------------------------------------------------------------------


class ProcessHandle(Protocol):
    """Duck type that every backend's _run_bash() must return.

    subprocess.Popen satisfies this natively.  SDK backends (Modal, Daytona)
    return _ThreadedProcessHandle which adapts their blocking calls.
    """

    def poll(self) -> int | None: ...
    def kill(self) -> None: ...
    def wait(self, timeout: float | None = None) -> int: ...

    @property
    def stdout(self) -> IO[str] | None: ...

    @property
    def returncode(self) -> int | None: ...


class _ThreadedProcessHandle:
    """Adapter for SDK backends (Modal, Daytona) that have no real subprocess.

    Wraps a blocking ``exec_fn() -> (output_str, exit_code)`` in a background
    thread and exposes a ProcessHandle-compatible interface.  An optional
    ``cancel_fn`` is invoked on ``kill()`` for backend-specific cancellation
    (e.g. Modal sandbox.terminate, Daytona sandbox.stop).
    """

    def __init__(
        self,
        exec_fn: Callable[[], tuple[str, int]],
        cancel_fn: Callable[[], None] | None = None,
    ):
        self._cancel_fn = cancel_fn
        self._done = threading.Event()
        self._returncode: int | None = None
        self._error: Exception | None = None

        # Pipe for stdout — drain thread in _wait_for_process reads the read end.
        read_fd, write_fd = os.pipe()
        self._stdout = os.fdopen(read_fd, "r", encoding="utf-8", errors="replace")
        self._write_fd = write_fd

        def _worker():
            try:
                output, exit_code = exec_fn()
                self._returncode = exit_code
                # Write output into the pipe so drain thread picks it up.
                try:
                    os.write(self._write_fd, output.encode("utf-8", errors="replace"))
                except OSError:
                    pass
            except Exception as exc:
                self._error = exc
                self._returncode = 1
            finally:
                try:
                    os.close(self._write_fd)
                except OSError:
                    pass
                self._done.set()

        t = threading.Thread(target=_worker, daemon=True)
        t.start()

    @property
    def stdout(self):
        return self._stdout

    @property
    def returncode(self) -> int | None:
        return self._returncode

    def poll(self) -> int | None:
        return self._returncode if self._done.is_set() else None

    def kill(self):
        if self._cancel_fn:
            try:
                self._cancel_fn()
            except Exception:
                pass

    def wait(self, timeout: float | None = None) -> int:
        self._done.wait(timeout=timeout)
        return self._returncode


# ---------------------------------------------------------------------------
# CWD marker for remote backends
# ---------------------------------------------------------------------------


def _cwd_marker(session_id: str) -> str:
    return f"__HERMES_CWD_{session_id}__"


# ---------------------------------------------------------------------------
# BaseEnvironment
# ---------------------------------------------------------------------------


class BaseEnvironment(ABC):
    """Common interface and unified execution flow for all Hermes backends.

    Subclasses implement ``_run_bash()`` and ``cleanup()``.  The base class
    provides ``execute()`` with session snapshot sourcing, CWD tracking,
    interrupt handling, and timeout enforcement.
    """

    # Subclasses that embed stdin as a heredoc (Modal, Daytona) set this.
    _stdin_mode: str = "pipe"  # "pipe" or "heredoc"

    # Snapshot creation timeout (override for slow cold-starts).
    _snapshot_timeout: int = 30

    def get_temp_dir(self) -> str:
        """Return the backend temp directory used for session artifacts.

        Most sandboxed backends use ``/tmp`` inside the target environment.
        LocalEnvironment overrides this on platforms like Termux where ``/tmp``
        may be missing and ``TMPDIR`` is the portable writable location.
        """
        return "/tmp"

    def __init__(self, cwd: str, timeout: int, env: dict = None):
        self.cwd = cwd
        self.timeout = timeout
        self.env = env or {}

        self._session_id = uuid.uuid4().hex[:12]
        temp_dir = self.get_temp_dir().rstrip("/") or "/"
        self._snapshot_path = f"{temp_dir}/hermes-snap-{self._session_id}.sh"
        self._cwd_file = f"{temp_dir}/hermes-cwd-{self._session_id}.txt"
        self._cwd_marker = _cwd_marker(self._session_id)
        self._snapshot_ready = False

    # ------------------------------------------------------------------
    # Abstract methods
    # ------------------------------------------------------------------

    def _run_bash(
        self,
        cmd_string: str,
        *,
        login: bool = False,
        timeout: int = 120,
        stdin_data: str | None = None,
    ) -> ProcessHandle:
        """Spawn a bash process to run *cmd_string*.

        Returns a ProcessHandle (subprocess.Popen or _ThreadedProcessHandle).
        Must be overridden by every backend.
        """
        raise NotImplementedError(f"{type(self).__name__} must implement _run_bash()")

    @abstractmethod
    def cleanup(self):
        """Release backend resources (container, instance, connection)."""
        ...

    # ------------------------------------------------------------------
    # Session snapshot (init_session)
    # ------------------------------------------------------------------

    def init_session(self):
        """Capture login shell environment into a snapshot file.

        Called once after backend construction.  On success, sets
        ``_snapshot_ready = True`` so subsequent commands source the snapshot
        instead of running with ``bash -l``.
        """
        # Full capture: env vars, functions, aliases, shell options.
        # Restore configured cwd after login shell profile scripts, which may
        # change the working directory (e.g. bashrc `cd ~`).  Without this,
        # pwd -P captures the profile's directory, not terminal.cwd.
        # Route through ``_quote_cwd_for_cd`` (not a bare ``shlex.quote``) so
        # the Windows subclass override converts a native ``C:\Users\x`` cwd to
        # the Git-Bash ``/c/Users/x`` form the bootstrap ``cd`` can resolve.
        # Without this the snapshot bootstrap ``cd`` below fails on Windows and
        # ``pwd -P`` captures the login shell's directory, not ``terminal.cwd``.
        _quoted_cwd = self._quote_cwd_for_cd(self.cwd)
        # Quote the snapshot / cwd-file paths so Git Bash on Windows handles
        # ``C:/Users/...``-shaped paths without glob-splitting the colon or
        # tripping on drive letters.  On POSIX this is a no-op (no colons /
        # special chars in a /tmp path).  Previously unquoted interpolation
        # caused ``C:/Users/.../hermes-snap-*.sh: No such file or directory``
        # errors on Windows, leaking via stderr (merged into stdout on Linux
        # backends) into every terminal-tool response.
        _quoted_snap = shlex.quote(self._snapshot_path)
        _quoted_cwd_file = shlex.quote(self._cwd_file)
        # Use atomic file replacement: assemble the snapshot in a temp file,
        # then mv it over the final path.  This prevents concurrent source()
        # calls from reading a half-written snapshot when another terminal
        # command finishes and rewrites the env vars (issue #38249).  `mv` is
        # atomic on POSIX when src and dest are on the same filesystem, so
        # source() either sees the old complete snapshot or the new complete
        # one — never a partial/truncated file.
        #
        # The temp name MUST be unique per concurrent writer.  ``$$`` is the
        # bash PID, but in ``&``-launched subshells (how concurrent terminal
        # calls run) ``$$`` stays the *parent* shell's PID — so two concurrent
        # writers would pick the SAME temp name, clobber each other's temp
        # mid-write, and mv would then publish a torn file (the corruption is
        # only narrowed, not closed).  ``$BASHPID`` is the actual subshell PID
        # and is genuinely unique per writer, which closes the race.  The
        # static path is shlex-quoted (Windows/Git-Bash drive letters, spaces)
        # with ``$BASHPID`` left outside the quotes so it still expands.
        _snap_tmp = shlex.quote(self._snapshot_path + ".tmp.") + "$BASHPID"
        bootstrap = (
            f"umask 077\n"
            f"export -p > {_snap_tmp}\n"
            # Dump function definitions, filtering out private (``_``-prefixed)
            # helpers — mainly bash-completion internals (``_git``, ``_make``…)
            # — by NAME, not by line.  A naive ``declare -f | grep -vE '^_[^_]'``
            # is line-based: it strips the function *header* line but leaves the
            # orphaned ``{ … }`` body behind, which corrupts the snapshot and
            # makes every sourced command fail (e.g. exit 127).  Selecting the
            # wanted names with ``declare -F`` first, then dumping only those
            # whole definitions, preserves the filter's intent without ever
            # tearing a function body.  The non-empty guard matters: bare
            # ``declare -f`` with no name args dumps ALL functions, so an empty
            # name list (only private funcs present) would otherwise leak the
            # very functions we meant to drop.
            f"__hermes_fns=$(declare -F | awk '{{print $3}}' | grep -vE '^_[^_]') || true\n"
            f"[ -n \"$__hermes_fns\" ] && declare -f $__hermes_fns "
            f">> {_snap_tmp} 2>/dev/null || true\n"
            f"alias -p >> {_snap_tmp}\n"
            f"echo 'shopt -s expand_aliases' >> {_snap_tmp}\n"
            f"echo 'set +e' >> {_snap_tmp}\n"
            f"echo 'set +u' >> {_snap_tmp}\n"
            # Publish atomically only if assembly succeeded; otherwise drop the
            # partial temp rather than leave it to be sourced or orphaned.
            f"mv -f {_snap_tmp} {_quoted_snap} || rm -f {_snap_tmp}\n"
            f"builtin cd -- {_quoted_cwd} 2>/dev/null || true\n"
            f"pwd -P > {_quoted_cwd_file} 2>/dev/null || true\n"
            f"printf '\\n{self._cwd_marker}%s{self._cwd_marker}\\n' \"$(pwd -P)\"\n"
        )
        try:
            proc = self._run_bash(bootstrap, login=True, timeout=self._snapshot_timeout)
            result = self._wait_for_process(proc, timeout=self._snapshot_timeout)
            if int(result.get("returncode") or 0) != 0:
                raise RuntimeError(
                    f"snapshot bootstrap failed with exit code {result.get('returncode')}"
                )
            self._snapshot_ready = True
            self._update_cwd(result)
            logger.info(
                "Session snapshot created (session=%s, cwd=%s)",
                self._session_id,
                self.cwd,
            )
        except Exception as exc:
            logger.warning(
                "init_session failed (session=%s): %s — "
                "falling back to bash -l per command",
                self._session_id,
                exc,
            )
            self._snapshot_ready = False

    # ------------------------------------------------------------------
    # Command wrapping
    # ------------------------------------------------------------------

    @staticmethod
    def _quote_cwd_for_cd(cwd: str) -> str:
        """Quote a ``cd`` target while preserving ``~`` expansion."""
        if cwd == "~":
            return cwd
        if cwd == "~/":
            return "$HOME"
        if cwd.startswith("~/"):
            return f"$HOME/{shlex.quote(cwd[2:])}"
        return shlex.quote(cwd)

    def _wrap_command(self, command: str, cwd: str) -> str:
        """Build the full bash script that sources snapshot, cd's, runs command,
        re-dumps env vars, and emits CWD markers."""
        escaped = command.replace("'", "'\\''")

        # Quote the snapshot / cwd-file paths so Git Bash on Windows handles
        # ``C:/Users/...``-shaped paths without glob-splitting the colon or
        # tripping on drive letters.  POSIX paths are unaffected.  See
        # :meth:`init_session` for the same fix on the bootstrap block.
        _quoted_snap = shlex.quote(self._snapshot_path)
        _quoted_cwd_file = shlex.quote(self._cwd_file)
        # Use atomic file replacement for env snapshot updates (issue #38249).
        # Assemble into a per-writer-unique temp file, then mv to atomically
        # replace the snapshot so concurrent source() calls never read a
        # truncated/half-written file.  ``$BASHPID`` (not ``$$``) is the actual
        # subshell PID — unique per concurrent ``&``-launched writer — so two
        # writers never share a temp name and clobber each other before the mv.
        # Static path shlex-quoted (Windows/spaces); ``$BASHPID`` left to expand.
        _snap_tmp = shlex.quote(self._snapshot_path + ".tmp.") + "$BASHPID"

        parts = []

        # Source snapshot (env vars from previous commands).
        # Redirect stdout to /dev/null: on macOS (bash 3.2 and certain
        # Homebrew bash builds) sourcing a file containing ``declare -x``
        # can emit the declarations to stdout, leaking ~60 lines of env
        # vars into every tool response (issue #15459).  Linux bash is
        # silent here, but the redirect is harmless.
        if self._snapshot_ready:
            parts.append(
                f"source {_quoted_snap} >/dev/null 2>&1 || true"
            )

        # Preserve bare ``~`` expansion, but rewrite ``~/...`` through
        # ``$HOME`` so suffixes with spaces remain a single shell word.
        quoted_cwd = self._quote_cwd_for_cd(cwd)
        # ``--`` keeps hyphen-prefixed directory names from being parsed as options.
        parts.append(f"builtin cd -- {quoted_cwd} || exit 126")

        # Run the actual command
        parts.append(f"eval '{escaped}'")
        parts.append("__hermes_ec=$?")
        # Restrict Hermes metadata files without changing the user's command
        # umask. Snapshot files may contain env-carried secrets.
        parts.append("umask 077")

        # Re-dump env vars to snapshot (atomic replacement to avoid races).
        # Chain mv on the export succeeding so a failed/partial dump never
        # replaces a good snapshot; drop the temp on failure so it isn't
        # orphaned (cleaned up wholesale in LocalEnvironment.cleanup too).
        if self._snapshot_ready:
            parts.append(
                f"{{ export -p > {_snap_tmp} && mv -f {_snap_tmp} {_quoted_snap}; }} "
                f"2>/dev/null || rm -f {_snap_tmp} 2>/dev/null || true"
            )

        # Write CWD to file (local reads this) and stdout marker (remote parses this)
        parts.append(f"pwd -P > {_quoted_cwd_file} 2>/dev/null || true")
        # Use a distinct line for the marker. The leading \n ensures
        # the marker starts on its own line even if the command doesn't
        # end with a newline (e.g. printf 'exact'). We'll strip this
        # injected newline in _extract_cwd_from_output.
        parts.append(
            f"printf '\\n{self._cwd_marker}%s{self._cwd_marker}\\n' \"$(pwd -P)\""
        )
        parts.append("exit $__hermes_ec")

        return "\n".join(parts)

    # ------------------------------------------------------------------
    # Stdin heredoc embedding (for SDK backends)
    # ------------------------------------------------------------------

    @staticmethod
    def _embed_stdin_heredoc(command: str, stdin_data: str) -> str:
        """Append stdin_data as a shell heredoc to the command string."""
        delimiter = f"HERMES_STDIN_{uuid.uuid4().hex[:12]}"
        return f"{command} << '{delimiter}'\n{stdin_data}\n{delimiter}"

    # ------------------------------------------------------------------
    # Process lifecycle
    # ------------------------------------------------------------------

    def _wait_for_process(self, proc: ProcessHandle, timeout: int = 120) -> dict:
        """Poll-based wait with interrupt checking and stdout draining.

        Shared across all backends — not overridden.

        Fires the ``activity_callback`` (if set on this instance) every 10s
        while the process is running so the gateway's inactivity timeout
        doesn't kill long-running commands.

        Also wraps the poll loop in a ``try/finally`` that guarantees we
        call ``self._kill_process(proc)`` if we exit via ``KeyboardInterrupt``
        or ``SystemExit``.  Without this, the local backend (which spawns
        subprocesses with ``os.setsid`` into their own process group) leaves
        an orphan with ``PPID=1`` when python is shut down mid-tool — the
        ``sleep 300``-survives-30-min bug Physikal and I both hit.
        """
        output_chunks: list[str] = []

        # Non-blocking drain via select().
        #
        # The old pattern — ``for line in proc.stdout`` — blocks on
        # ``readline()`` until the pipe reaches EOF.  When the user's command
        # backgrounds a process (``cmd &``, ``setsid cmd & disown``, etc.),
        # that backgrounded grandchild inherits the write-end of our stdout
        # pipe via ``fork()``.  Even after ``bash`` itself exits, the pipe
        # stays open because the grandchild still holds it — so the drain
        # thread never returns and the tool hangs for the full lifetime of
        # the grandchild (issue #8340: users reported indefinite hangs when
        # restarting uvicorn with ``setsid ... & disown``).
        #
        # The fix: select() with a short poll interval, and stop draining
        # shortly after ``bash`` exits even if the pipe hasn't EOF'd yet.
        # Any output the grandchild writes after that point goes to an
        # orphaned pipe (harmless — the kernel reaps it when our end closes).
        #
        # Decoding: we ``os.read()`` raw bytes in fixed-size chunks (4096)
        # so a single multibyte UTF-8 character can split across reads.  An
        # incremental decoder buffers partial sequences across chunks, and
        # ``errors="replace"`` mirrors the baseline ``TextIOWrapper`` (which
        # was constructed with ``encoding="utf-8", errors="replace"`` on
        # ``Popen``) so binary or mis-encoded output is preserved with
        # U+FFFD substitution rather than clobbering the whole buffer.
        decoder = codecs.getincrementaldecoder("utf-8")(errors="replace")

        def _drain_iterable(stream):
            # Fallback path: ``stream`` is not backed by a real OS file
            # descriptor (no usable ``fileno()``).  This covers in-memory
            # ProcessHandle adapters that expose stdout as a plain iterator of
            # already-collected output (the legacy ``for line in proc.stdout``
            # contract) rather than a live pipe.  Iterate it to EOF.  Without
            # this, the drain thread would raise an unhandled exception and die
            # silently, losing all of the process's output.
            try:
                for piece in stream:
                    if piece is None:
                        continue
                    if isinstance(piece, bytes):
                        output_chunks.append(decoder.decode(piece))
                    else:
                        output_chunks.append(str(piece))
            except Exception:
                pass
            finally:
                try:
                    tail = decoder.decode(b"", final=True)
                    if tail:
                        output_chunks.append(tail)
                except Exception:
                    pass

        def _drain():
            # Resolve a real OS file descriptor up front.  Real subprocesses and
            # the SDK ``_ThreadedProcessHandle`` (os.pipe-backed) both return an
            # integer fd here.  Mocks / iterator-style stdout streams either lack
            # ``fileno()`` entirely or return a non-integer — in that case fall
            # back to draining the stream as an iterable instead of crashing the
            # thread (issue: 'list_iterator' object has no attribute 'fileno').
            stream = proc.stdout
            if stream is None:
                return
            fileno = getattr(stream, "fileno", None)
            try:
                fd = fileno() if callable(fileno) else None
            except Exception:
                fd = None
            if not isinstance(fd, int) or fd < 0:
                _drain_iterable(stream)
                return
            # select.select does NOT work on pipe fds on Windows (only sockets).
            # Use blocking os.read in a daemon thread instead — safe because
            # EOF arrives promptly when bash exits.
            if os.name == "nt":
                try:
                    while True:
                        chunk = os.read(fd, 4096)
                        if not chunk:
                            break
                        output_chunks.append(decoder.decode(chunk))
                except (ValueError, OSError):
                    pass
                finally:
                    try:
                        tail = decoder.decode(b"", final=True)
                        if tail:
                            output_chunks.append(tail)
                    except Exception:
                        pass
                return
            idle_after_exit = 0
            try:
                while True:
                    try:
                        ready, _, _ = select.select([fd], [], [], 0.1)
                    except (ValueError, OSError):
                        break  # fd already closed
                    if ready:
                        try:
                            chunk = os.read(fd, 4096)
                        except (ValueError, OSError):
                            break
                        if not chunk:
                            break  # true EOF — all writers closed
                        output_chunks.append(decoder.decode(chunk))
                        idle_after_exit = 0
                    elif proc.poll() is not None:
                        # bash is gone and the pipe was idle for ~100ms.  Give
                        # it two more cycles to catch any buffered tail, then
                        # stop — otherwise we wait forever on a grandchild pipe.
                        idle_after_exit += 1
                        if idle_after_exit >= 3:
                            break
            finally:
                # Flush any bytes buffered mid-sequence.  With ``errors="replace"``
                # this emits U+FFFD for any final incomplete sequence rather than
                # raising.
                try:
                    tail = decoder.decode(b"", final=True)
                    if tail:
                        output_chunks.append(tail)
                except Exception:
                    pass

        drain_thread = threading.Thread(target=_drain, daemon=True)
        drain_thread.start()
        deadline = time.monotonic() + timeout
        _now = time.monotonic()
        _activity_state = {
            "last_touch": _now,
            "start": _now,
        }

        # --- Debug tracing (opt-in via HERMES_DEBUG_INTERRUPT=1) -------------
        # Captures loop entry/exit, interrupt state changes, and periodic
        # heartbeats so we can diagnose "agent never sees the interrupt"
        # reports without reproducing locally.
        _tid = threading.current_thread().ident
        _pid = getattr(proc, "pid", None)
        _iter_count = 0
        _last_heartbeat = _now
        _last_interrupt_state = False
        _cb_was_none = _get_activity_callback() is None
        if _DEBUG_INTERRUPT:
            logger.info(
                "[interrupt-debug] _wait_for_process ENTER tid=%s pid=%s "
                "timeout=%ss activity_cb=%s initial_interrupt=%s",
                _tid, _pid, timeout,
                "set" if not _cb_was_none else "MISSING",
                is_interrupted(),
            )

        try:
            _poll_sleep = 0.005
            while proc.poll() is None:
                _iter_count += 1
                if is_interrupted():
                    if _DEBUG_INTERRUPT:
                        logger.info(
                            "[interrupt-debug] _wait_for_process INTERRUPT DETECTED "
                            "tid=%s pid=%s iter=%d elapsed=%.1fs — killing process group",
                            _tid, _pid, _iter_count, time.monotonic() - _activity_state["start"],
                        )
                    self._kill_process(proc)
                    drain_thread.join(timeout=2)
                    return {
                        "output": "".join(output_chunks) + "\n[Command interrupted]",
                        "returncode": 130,
                    }
                if time.monotonic() > deadline:
                    if _DEBUG_INTERRUPT:
                        logger.info(
                            "[interrupt-debug] _wait_for_process TIMEOUT "
                            "tid=%s pid=%s iter=%d timeout=%ss",
                            _tid, _pid, _iter_count, timeout,
                        )
                    self._kill_process(proc)
                    drain_thread.join(timeout=2)
                    partial = "".join(output_chunks)
                    timeout_msg = f"\n[Command timed out after {timeout}s]"
                    return {
                        "output": partial + timeout_msg
                        if partial
                        else timeout_msg.lstrip(),
                        "returncode": 124,
                    }
                # Periodic activity touch so the gateway knows we're alive
                touch_activity_if_due(_activity_state, "terminal command running")

                # Heartbeat every ~30s: proves the loop is alive and reports
                # the activity-callback state (thread-local, can get clobbered
                # by nested tool calls or executor thread reuse).
                if _DEBUG_INTERRUPT and time.monotonic() - _last_heartbeat >= 30.0:
                    _cb_now_none = _get_activity_callback() is None
                    logger.info(
                        "[interrupt-debug] _wait_for_process HEARTBEAT "
                        "tid=%s pid=%s iter=%d elapsed=%.0fs "
                        "interrupt=%s activity_cb=%s%s",
                        _tid, _pid, _iter_count,
                        time.monotonic() - _activity_state["start"],
                        is_interrupted(),
                        "set" if not _cb_now_none else "MISSING",
                        " (LOST during run)" if _cb_now_none and not _cb_was_none else "",
                    )
                    _last_heartbeat = time.monotonic()
                    _cb_was_none = _cb_now_none

                # Adaptive poll: start at 5ms so fast commands (echo, pwd,
                # date, cat short files) return in ~6ms instead of being
                # stuck waiting for the next 200ms tick. Back off
                # exponentially toward 200ms so long-running commands
                # (builds, tests, sleeps) don't pay measurable CPU in the
                # poll loop. For an `echo` this saves ~195ms per tool call;
                # for a 10s build the steady-state poll rate is identical
                # to the old behavior.
                time.sleep(_poll_sleep)
                if _poll_sleep < 0.2:
                    _poll_sleep = min(_poll_sleep * 1.5, 0.2)
        except (KeyboardInterrupt, SystemExit):
            # Signal arrived (SIGTERM/SIGHUP/SIGINT) or sys.exit() was called
            # while we were polling.  The local backend spawns subprocesses
            # with os.setsid, which puts them in their own process group — so
            # if we let the interrupt propagate without killing the child,
            # python exits and the child is reparented to init (PPID=1) and
            # keeps running as an orphan.  Killing the process group here
            # guarantees the tool's side effects stop when the agent stops.
            if _DEBUG_INTERRUPT:
                logger.info(
                    "[interrupt-debug] _wait_for_process EXCEPTION_EXIT "
                    "tid=%s pid=%s iter=%d elapsed=%.1fs — killing subprocess group before re-raise",
                    _tid, _pid, _iter_count,
                    time.monotonic() - _activity_state["start"],
                )
            try:
                self._kill_process(proc)
                drain_thread.join(timeout=2)
            except Exception:
                pass  # cleanup is best-effort
            raise

        # Drain thread now exits promptly after bash does (~300ms idle
        # check).  A short join is enough; a long one would be a bug since
        # it means the non-blocking loop itself stopped cooperating.
        drain_thread.join(timeout=2)

        try:
            proc.stdout.close()
        except Exception:
            pass

        if _DEBUG_INTERRUPT:
            logger.info(
                "[interrupt-debug] _wait_for_process EXIT (natural) "
                "tid=%s pid=%s iter=%d elapsed=%.1fs returncode=%s",
                _tid, _pid, _iter_count,
                time.monotonic() - _activity_state["start"],
                proc.returncode,
            )

        return {"output": "".join(output_chunks), "returncode": proc.returncode}

    def _kill_process(self, proc: ProcessHandle):
        """Terminate a process. Subclasses may override for process-group kill."""
        try:
            proc.kill()
        except (ProcessLookupError, PermissionError, OSError):
            pass

    # ------------------------------------------------------------------
    # CWD extraction
    # ------------------------------------------------------------------

    def _update_cwd(self, result: dict):
        """Extract CWD from command output. Override for local file-based read."""
        self._extract_cwd_from_output(result)

    def _extract_cwd_from_output(self, result: dict):
        """Parse the __HERMES_CWD_{session}__ marker from stdout output.

        Updates self.cwd and strips the marker from result["output"].
        Used by remote backends (Docker, SSH, Modal, Daytona, Singularity).
        """
        output = result.get("output", "")
        marker = self._cwd_marker
        last = output.rfind(marker)
        if last == -1:
            return

        # Find the opening marker before this closing one
        search_start = max(0, last - 4096)  # CWD path won't be >4KB
        first = output.rfind(marker, search_start, last)
        if first == -1 or first == last:
            return

        cwd_path = output[first + len(marker) : last].strip()
        if cwd_path:
            self.cwd = cwd_path

        # Strip the marker line AND the \n we injected before it.
        # The wrapper emits: printf '\n__MARKER__%s__MARKER__\n'
        # So the output looks like: <cmd output>\n__MARKER__path__MARKER__\n
        # We want to remove everything from the injected \n onwards.
        line_start = output.rfind("\n", 0, first)
        if line_start == -1:
            line_start = first
        line_end = output.find("\n", last + len(marker))
        line_end = line_end + 1 if line_end != -1 else len(output)

        result["output"] = output[:line_start] + output[line_end:]

    # ------------------------------------------------------------------
    # Hooks
    # ------------------------------------------------------------------

    def _before_execute(self) -> None:
        """Hook called before each command execution.

        Remote backends (SSH, Modal, Daytona) override this to trigger
        their FileSyncManager.  Bind-mount backends (Docker, Singularity)
        and Local don't need file sync — the host filesystem is directly
        visible inside the container/process.
        """
        pass

    # ------------------------------------------------------------------
    # Unified execute()
    # ------------------------------------------------------------------

    def execute(
        self,
        command: str,
        cwd: str = "",
        *,
        timeout: int | None = None,
        stdin_data: str | None = None,
        rewrite_compound_background: bool = True,
    ) -> dict:
        """Execute a command, return {"output": str, "returncode": int}."""
        self._before_execute()

        exec_command, sudo_stdin = self._prepare_command(command)
        # Guard against the `A && B &` subshell-wait trap by default.
        # Some callers (spawn_via_env) already produce shell-safe wrappers and
        # pass rewrite_compound_background=False.
        if rewrite_compound_background:
            from tools.terminal_tool import _rewrite_compound_background
            exec_command = _rewrite_compound_background(exec_command)
        effective_timeout = timeout or self.timeout
        effective_cwd = cwd or self.cwd

        # Merge sudo stdin with caller stdin
        if sudo_stdin is not None and stdin_data is not None:
            effective_stdin = sudo_stdin + stdin_data
        elif sudo_stdin is not None:
            effective_stdin = sudo_stdin
        else:
            effective_stdin = stdin_data

        # Embed stdin as heredoc for backends that need it
        if effective_stdin and self._stdin_mode == "heredoc":
            exec_command = self._embed_stdin_heredoc(exec_command, effective_stdin)
            effective_stdin = None

        wrapped = self._wrap_command(exec_command, effective_cwd)

        # Use login shell if snapshot failed (so user's profile still loads)
        login = not self._snapshot_ready

        proc = self._run_bash(
            wrapped, login=login, timeout=effective_timeout, stdin_data=effective_stdin
        )
        result = self._wait_for_process(proc, timeout=effective_timeout)
        self._update_cwd(result)

        return result

    # ------------------------------------------------------------------
    # Shared helpers
    # ------------------------------------------------------------------

    def stop(self):
        """Alias for cleanup (compat with older callers)."""
        self.cleanup()

    def __del__(self):
        try:
            self.cleanup()
        except Exception:
            pass

    def _prepare_command(self, command: str) -> tuple[str, str | None]:
        """Transform sudo commands if SUDO_PASSWORD is available."""
        from tools.terminal_tool import _transform_sudo_command

        return _transform_sudo_command(command)
