hermes-agent/tools/delegate_tool_dispatch.py

"""Batch execution + background dispatch for delegate_task: ``delegate_task`` builds a ``_Batch``
(children + origin identity) and hands it to ``_run_batch``, which runs it synchronously or as
detached async units — one per task ``group`` (ungrouped tasks are a unit each), so a finished
review does not wait for the slowest sibling."""

from __future__ import annotations

import contextvars
import json
import logging
import time
from concurrent.futures import FIRST_COMPLETED, wait as _cf_wait
from dataclasses import dataclass, replace
from typing import Any, Dict, List, Optional

from tools.async_delegation import _new_delegation_id, record_unit_child
from tools.delegate_tool_child_run import _attach_child, _detach_child, _fabricated_entry, _signal_child_stop
from tools.delegate_tool_progress import (
    SUBAGENT_FAILURE_STATUSES, _print_completion_line, _quiet, describe_subagent_failure, format_batch_tag,
)
from tools.delegate_tool_registry import _capture_gateway_steer_authority
from tools.delegate_tool_results import _finalize_child_results

logger = logging.getLogger("tools.delegate_tool")  # log-record parity with the origin module


@dataclass
class _Batch:
    """One delegate_task call's built children plus everything needed to run them
    and assemble the combined result (shared by the sync path and the background runner)."""

    task_list: List[Dict[str, Any]]
    children: List[tuple]
    parent_agent: Any
    creds: Dict[str, Any]
    context: Optional[str]
    top_role: str
    max_children: int
    live_deleg_id: Optional[str]
    live_writers: list
    live_paths: list
    origin_wake_sid: str
    origin_ui_session_id: str
    origin_owner_transport: Any
    origin_owner_session_record: Any
    origin_session_history_delivery: bool
    overall_start: float
    # Set on per-group units carved out by ``_dispatch_background``; None for the whole batch / ungrouped units.
    group: Optional[str] = None
    unit_id: Optional[str] = None  # the async registry id this unit runs under (``<call_id>-k`` for split calls)

    def owner_kwargs(self) -> Dict[str, Any]:
        """Steer/stop authority of the originating session, passed to every child run."""
        return {
            "owner_session_id": self.origin_ui_session_id or None, "owner_transport": self.origin_owner_transport,
            "owner_session_record": self.origin_owner_session_record,
        }

    def run_child(self, i: int, task: Dict[str, Any], child: Any) -> Dict[str, Any]:
        from tools.delegate_tool import _run_single_child
        return _run_single_child(task_index=i, goal=task["goal"], child=child, parent_agent=self.parent_agent, **self.owner_kwargs())


def _announce_batch(parent_agent, n_tasks: int, live_deleg_id: Optional[str]) -> None:
    """Announce the batch tag once so interleaved ``[tag n/N]`` lines are attributable."""
    if n_tasks > 1 and live_deleg_id:
        _hdr = f"  🔀 [{format_batch_tag(live_deleg_id, parent_agent)}] delegating {n_tasks} tasks"
        _print_completion_line(parent_agent, getattr(parent_agent, "_delegate_spinner", None), _hdr, console_line=_hdr)

def _capture_origin() -> tuple[str, str, Any, Any, bool]:
    """``(wake_sid, ui_session_id, owner_transport, owner_session_record, session_history_delivery)`` of the
    ORIGINATING session, captured BEFORE building any child: AIAgent construction
    clobbers the HERMES_SESSION_ID ContextVar/os.environ with the subagent's id.  The wake-
    capability flag rides the same request-scoped binding and is captured here for the same
    reason — and fails closed: a binding that never declared it (or a read error) leaves the
    session treated as non-wake-capable (#98619)."""
    from tools.async_delegation import _current_origin_session_id
    _origin_wake_sid = _current_origin_session_id()
    _origin_ui_session_id = ""
    _origin_session_history_delivery = False
    with _quiet(None):
        from gateway.session_context import get_session_env, session_history_delivery_supported
        _origin_ui_session_id = get_session_env("HERMES_UI_SESSION_ID", "")
        _origin_session_history_delivery = session_history_delivery_supported()
    return (_origin_wake_sid, _origin_ui_session_id, *_capture_gateway_steer_authority(_origin_ui_session_id), _origin_session_history_delivery)

def _report_child_done(parent_agent, spinner_ref, entry, tag, task_labels, n_tasks, remaining) -> None:
    """Print one completion line for a finished child and refresh the spinner text. Failed/errored/timed-out children
    say WHY on the same line — a bare ✗ reads as "silently dropped"."""
    idx = entry["task_index"]
    label = task_labels[idx] if idx < len(task_labels) else f"Task {idx}"
    status = entry.get("status", "?")
    _slot = f"{tag} · {idx+1}/{n_tasks}" if tag else f"{idx+1}/{n_tasks}"
    schema_invalid = entry.get("schema_valid") is False and status == "completed"
    icon = "⚠" if schema_invalid else ("✓" if status == "completed" else "✗")
    completion_line = f"{icon} [{_slot}] {label}  ({entry.get('duration_seconds', 0)}s)"
    _err_line = (
        describe_subagent_failure(entry.get("failure_reason"), entry.get("error"), max_chars=120)
        if status in SUBAGENT_FAILURE_STATUSES else "")
    if schema_invalid:
        _err_line = "output_schema not satisfied — raw text returned (schema_valid=false)"
    if _err_line:
        completion_line += f" — {_err_line}"
    _print_completion_line(parent_agent, spinner_ref, completion_line)
    if spinner_ref and remaining > 0:
        with _quiet("Spinner update_text failed: %s"):
            spinner_ref.update_text(f"🔀 {'[' + tag + '] ' if tag else ''}{remaining} task{'s' if remaining != 1 else ''} remaining")

def _record_finished_child(batch: _Batch, entry: Any, honor_parent_interrupt: bool) -> None:
    """Detached (background) unit: durably record a child on the unit's own row the moment it finishes, so an owner
    death before the unit's join — or anywhere before its durable completion write, the whole remaining window for a
    one-child unit — loses only children still running, never finished work (#116000). Best-effort by construction:
    ``record_unit_child`` never raises into the join."""
    if not honor_parent_interrupt and batch.unit_id and isinstance(entry, dict):
        record_unit_child(batch.unit_id, entry)

def _run_children_parallel(batch: _Batch, results: list, *, honor_parent_interrupt: bool) -> None:
    """Run the batch's children in parallel, appending entries to ``results`` (sorted by task_index on return, one
    completion line printed per child). Polls futures with a short ``wait()`` timeout instead of ``as_completed()``
    so a wedged child cannot block the parent forever after an interrupt; on parent interrupt the still-pending
    children are reported ``interrupted`` and abandoned (they already got the interrupt signal)."""
    # Daemon workers (tools.daemon_pool): the `with` block still joins normally, but if the parent is interrupted
    # while a child is wedged, the abandoned worker must not block interpreter exit.
    from tools.daemon_pool import DaemonThreadPoolExecutor
    parent_agent, n_tasks = batch.parent_agent, len(batch.task_list)
    task_labels = [t["goal"][:40] for t in batch.task_list]
    spinner_ref = getattr(parent_agent, "_delegate_spinner", None)
    _tag = format_batch_tag(batch.live_deleg_id, parent_agent)
    # Fabricated entries for still-pending / raised futures carry the correct _delegate_role.
    _child_by_index = {i: child for (i, _, child) in batch.children}
    n_here = len(batch.children)  # a per-group unit runs a subset; ``n_tasks`` keeps the call-wide ``i/N`` slot

    def _entry_of(future, idx):
        if not future.done():
            return _fabricated_entry(
                idx, "interrupted", "Parent agent interrupted — child did not finish in time", _child_by_index.get(idx),
            )
        try:
            return future.result()
        except Exception as exc:
            return _fabricated_entry(idx, "error", str(exc), _child_by_index.get(idx))

    executor = DaemonThreadPoolExecutor(max_workers=batch.max_children)
    # ``with`` would join every worker on exit, so a child wedged in an
    # uninterruptible call defeats the interrupt fast-path: the poll loop marks
    # it interrupted and returns, then the join hangs forever. Shutdown without
    # waiting on the interrupt path instead (same shape as moa_loop).
    interrupted = False
    try:
        futures = {executor.submit(contextvars.copy_context().run, batch.run_child, i, t, child): i for i, t, child in batch.children}
        pending = set(futures)
        while pending:
            if honor_parent_interrupt and getattr(parent_agent, "_interrupt_requested", False) is True:
                results.extend(_entry_of(f, futures[f]) for f in pending)
                interrupted = True
                break
            done, pending = _cf_wait(pending, timeout=0.5, return_when=FIRST_COMPLETED)
            for future in done:
                entry = _entry_of(future, futures[future])
                results.append(entry)
                # Detached unit: a crash before the join must not lose children that already finished.
                _record_finished_child(batch, entry, honor_parent_interrupt)
                _report_child_done(parent_agent, spinner_ref, entry, _tag, task_labels, n_tasks, n_here - len(results))
                if (not honor_parent_interrupt and batch.unit_id and entry.get("status") in SUBAGENT_FAILURE_STATUSES
                        and len(results) < n_here):
                    # Detached unit, a sibling is still running: tell the parent NOW, not when the last one finishes.
                    # Non-durable and separate from the unit's final result (which is still delivered once).
                    with _quiet("task failure notice failed", exc_info=True):
                        from tools.async_delegation import push_task_failure_notice
                        _i = entry.get("task_index", -1)
                        _live = batch.live_paths[_i] if isinstance(_i, int) and 0 <= _i < len(batch.live_paths) else None
                        push_task_failure_notice(
                            batch.unit_id, {**entry, **({"live_transcript": _live} if _live else {})}, n_tasks=n_tasks)
    finally:
        # Abandoned workers unwind on their own (daemon threads, and the
        # child-run layer already applies the deferred-close transport drain).
        executor.shutdown(wait=not interrupted, cancel_futures=interrupted)
    results.sort(key=lambda r: r["task_index"])  # match input order

def _execute_and_aggregate(batch: _Batch, *, honor_parent_interrupt: bool = True) -> dict:
    """Run the batch's built children, join, finalize (hooks + cost rollup), return the combined dict. Shared by the
    sync path and the background runner; a background runner receives a per-group unit (a subset of the call's
    children) so each group JOINS only on itself. Live transcripts are finalized but retained as the full-fidelity
    record (retention pruning happens on future dispatches)."""
    from tools.delegation_live_log import update_manifest_statuses
    results: list = []
    if len(batch.children) == 1:
        results.append(batch.run_child(*batch.children[0]))
        # A one-child unit has no join to wait on, but everything after the child returns — host-owned finalize,
        # transcript, manifest, then the durable write — is still owner-lifetime: record before any of it (#116000).
        _record_finished_child(batch, results[-1], honor_parent_interrupt)
    else:
        _run_children_parallel(batch, results, honor_parent_interrupt=honor_parent_interrupt)

    _finalize_child_results(results, batch.task_list, batch.children, batch.parent_agent)
    total_duration = round(time.monotonic() - batch.overall_start, 2)
    for entry in results:
        _idx = entry.get("task_index", -1)
        if isinstance(_idx, int) and 0 <= _idx < len(batch.live_writers) and batch.live_writers[_idx] is not None:
            with _quiet("Live transcript finalize failed", exc_info=True):
                batch.live_writers[_idx].finalize(entry)
            if _idx < len(batch.live_paths):
                entry["live_transcript"] = batch.live_paths[_idx]
    update_manifest_statuses(batch.live_deleg_id, results)

    combined: Dict[str, Any] = {"results": results, "total_duration_seconds": total_duration}
    # Runtime truth about children's background processes, as prose the parent can't miss inside the JSON.
    from tools.process_registry_notifications import _process_accounting_lines
    process_notes = [line for entry in results for line in _process_accounting_lines(entry)]
    if process_notes:
        combined["process_notes"] = process_notes
    unit_paths = [batch.live_paths[i] for (i, _, _) in batch.children if i < len(batch.live_paths)]
    if unit_paths:
        combined["live_transcripts"] = unit_paths
    if batch.group is not None:
        combined["group"] = batch.group
    return combined

_SYNC_FALLBACK_NOTES = {
    "no_async": (
        "background=true is not available in this session — it cannot "
        "receive a detached subagent result after the turn ends (a "
        "finite chat using -Q, --oneshot, or non-TTY stdio, `hermes -z`, a cron job, a Kanban "
        "worker, or a stateless HTTP endpoint). The subagent(s) ran SYNCHRONOUSLY and the result is included above."
    ),
    "at_capacity": (
        "The background delegation pool was at capacity (delegation.max_concurrent_children), so the subagent(s) ran "
        "SYNCHRONOUSLY and the result is included above. Raise "
        "delegation.max_concurrent_children in config.yaml to allow more concurrent background delegations."
    ),
}

def _run_sync_with_note(batch: _Batch, reason: str) -> str:
    """Inline fallback: run the batch now and explain why it was not detached."""
    result = _execute_and_aggregate(batch)
    if isinstance(result, dict):
        result["note"] = _SYNC_FALLBACK_NOTES[reason]
    return json.dumps(result, ensure_ascii=False)

def _resolve_async_wake_sid(origin_wake_sid: str, origin_session_history_delivery: bool = False) -> Optional[str]:
    """Detached result target: empty for push, a resumable API id, or None for inline.

    API completion only persists a row; this does not authorize a model wake. The
    continuation must read that row, not an authoritative caller-owned snapshot."""
    from gateway.session_context import get_session_env

    # Finite chat owns no later turn to consume a detached result. Reuse its
    # approval/lifecycle marker without disabling terminal notify completions:
    # those have their own bounded exit linger and durable result receipts.
    if get_session_env("HERMES_SINGLE_QUERY_SESSION") == "1":
        return None

    try:
        # Finite sessions cannot route a detached subagent result back to the agent after their turn/process
        # ends. This includes stateless HTTP requests (#10760) and one-shot Kanban workers (#63169). Fall
        # back to SYNCHRONOUS execution so the result returns in this same turn instead of handing out a
        # handle with no durable consumer. Mirrors the pool-at-capacity inline fallback below.
        from gateway.session_context import async_delivery_supported
        if async_delivery_supported():
            return ""
    except Exception:
        return ""
    if origin_wake_sid and origin_session_history_delivery:
        logger.info(
            "delegate_task: session %s resumes server history — detached result will be persisted "
            "for the next client turn (no model wake).", origin_wake_sid,
        )
        return origin_wake_sid
    if origin_wake_sid:
        logger.info(
            "delegate_task: session %s has no declared server-history consumer — running the batch "
            "synchronously so the result returns in this turn.", origin_wake_sid,
        )
    return None

def _resolve_async_session_key(parent_agent: Any, origin_ui_session_id: str) -> tuple[str, str]:
    """``(session_key, origin_ui_session_id)`` the async registry routes completions by.

    Desktop/TUI: the routable key is the durable AIAgent.session_id — compression can rotate it mid-turn before the
    TUI-side dict is re-anchored, and a stale approval-context key would orphan the completion. Gateway chats keep the
    platform conversation key (agent:main:...). The CLI has no bound approval contextvar and no HERMES_SESSION_KEY, so
    the key resolves empty; its drain is a positive-ownership filter on the durable session_id (empty would fail
    closed), so stamp the parent's durable id.
    """
    from tools.approval_context import get_current_session_key
    session_key = get_current_session_key(default="")
    agent_session_id = str(getattr(parent_agent, "session_id", "") or "")
    with _quiet(None):
        from gateway.session_context import get_session_env
        source = get_session_env("HERMES_SESSION_SOURCE", "")
        # Refresh from the task-local source when available, else retain the
        # immutable value captured before child construction.
        origin_ui_session_id = get_session_env("HERMES_UI_SESSION_ID", "") or origin_ui_session_id
        if source == "tui" and agent_session_id:
            session_key = agent_session_id
    return session_key or agent_session_id, origin_ui_session_id

def _batch_progress_token(child_agents: List[Any]) -> tuple:
    """Progress token for the async registry's stale monitor: every child's (api_call_count, current_tool,
    last_activity_ts). last_activity_ts ticks on streamed chunks, tool transitions and API-call start/completion,
    so a child streaming a long response counts as alive; a fully frozen token past the threshold means the batch
    is wedged. ``in_tool`` is True while ANY child is inside a tool so slow tools get the higher ceiling (mirrors
    the sync heartbeat)."""
    # Progress token for the async registry's stale monitor: the combined (api_call_count, current_tool,
    # last_activity_ts) of every child. last_activity_ts is ticked by _touch_activity on every streamed
    # chunk ("receiving stream response"), every tool transition, and every API-call start/completion — so a
    # child streaming a long response is alive even though api_call_count only advances when the call
    # completes (same liveness signal as the compaction inactivity budget, PR #71508).
    parts = []
    in_tool = False
    for c in child_agents:
        try:
            summary = c.get_activity_summary()
            tool = summary.get("current_tool")
            parts.append((summary.get("api_call_count", 0), tool, summary.get("last_activity_ts")))
            in_tool = in_tool or bool(tool)
        except Exception:
            parts.append(None)
    return tuple(parts), in_tool

_BACKGROUND_NOTES = {
    "one": (
        "Subagent is running in the background; its full result re-enters the conversation as a new message when it "
        "finishes. Results are delivered only after you END YOUR TURN: do anything that does not depend on it, then "
        "stop with a one-line status. Do not poll its transcript or artifacts to wait for it."
    ),
    "many": (
        "{n} subagents are running in parallel in the background as {k} completion unit(s); each unit's results "
        "re-enter the conversation as their own new message when THAT unit finishes. Results are delivered only "
        "after you END YOUR TURN: do anything that does not depend on them, then stop with a one-line status. Do not "
        "poll transcripts or artifacts to wait for them."
    ),
    "control_hint": (
        "While a child runs you can orchestrate it live with this same tool: delegate_task(action='list') to see live "
        "children, action='steer' with subagent_id + message to redirect one, action='stop' with subagent_id to end "
        "one early."
    ),
    "live_transcripts_hint": (
        "Each subagent streams a human-readable transcript of its operations to the file listed above (append-only, "
        "one per task). Read or `tail -f` these paths at any time to watch a child work while it runs."
    ),
}

def _dispatched_payload(batch: _Batch, units: List[tuple[_Batch, str]]) -> dict:
    """Model-facing handle for an accepted background call: one entry per async unit."""
    goals = [t["goal"] for t in batch.task_list]
    n = len(goals)
    payload = {
        "status": "dispatched", "mode": "background", "count": n,
        "delegation_id": batch.live_deleg_id or units[0][1], "goals": goals,
        "note": _BACKGROUND_NOTES["one"] if n == 1 else _BACKGROUND_NOTES["many"].format(n=n, k=len(units)),
    }
    if len(units) > 1:
        payload["units"] = [
            {"delegation_id": uid, "group": unit.group, "task_indexes": [i for (i, _, _) in unit.children]}
            for unit, uid in units
        ]
    sids = [getattr(c, "_subagent_id", None) for (_, _, c) in batch.children]
    if any(isinstance(s, str) and s for s in sids):
        payload["subagent_ids"] = sids
        payload["control_hint"] = _BACKGROUND_NOTES["control_hint"]
    if batch.live_paths:
        payload["live_transcripts"] = list(batch.live_paths)
        payload["live_transcripts_hint"] = _BACKGROUND_NOTES["live_transcripts_hint"]
    return payload

def _units_of(batch: _Batch) -> List[_Batch]:
    """Partition the call's children into async units: one per distinct task ``group`` (first-appearance order) and
    one per ungrouped task. Each unit is a ``_Batch`` sharing the call's task_list/transcripts but owning a subset of
    ``children``, so a unit joins only on itself and its completion re-enters the conversation on its own.

    Off by default (``delegation.independent_completions``): the whole call is ONE unit and returns as one message.
    A per-task flurry of completions (one new turn each) fragmented orchestrators that had no plan for it."""
    from tools.delegate_tool_config import _get_independent_completions
    if not _get_independent_completions():
        return [batch]
    members: Dict[Any, List[tuple]] = {}
    for i, t, c in batch.children:
        g = t.get("group")
        key = ("g", str(g)) if g not in (None, "") else ("i", i)
        members.setdefault(key, []).append((i, t, c))
    return [replace(batch, children=ch, group=(key[1] if key[0] == "g" else None)) for key, ch in members.items()]

def _dispatch_unit(unit: _Batch, unit_id: Optional[str], slot_key: Optional[str], routing: dict) -> dict:
    """Hand ONE unit to the async registry; the runner joins on that unit's children only."""
    from tools.async_delegation import dispatch_async_delegation_batch
    child_agents = [c for (_, _, c) in unit.children]

    def _interrupt():
        for c in child_agents:
            _signal_child_stop(c, "Async delegation cancelled")

    return dispatch_async_delegation_batch(
        # Call-wide goals: completion formatting indexes them by task_index.
        goals=[t["goal"] for t in unit.task_list], context=unit.context,
        toolsets=None,  # metadata for the completion block only; subagents inherit the parent's toolsets
        role=unit.top_role, model=unit.creds["model"],
        runner=lambda: _execute_and_aggregate(unit, honor_parent_interrupt=False),
        interrupt_fn=_interrupt, delegation_id=unit_id, slot_key=slot_key,
        task_indexes=[i for (i, _, _) in unit.children] if len(unit.children) < len(unit.task_list) else None,
        # Persist locators before starting workers; live_paths omits failed writers and can be compressed.
        task_transcripts={str(i): str(unit.live_writers[i].path) for i, _, _ in unit.children
                          if i < len(unit.live_writers) and unit.live_writers[i] is not None
                          and unit.live_writers[i].path is not None},
        progress_fn=lambda: _batch_progress_token(child_agents), **routing,
    )

def _restore_parent_cancellation(unit: _Batch) -> None:
    """Rejected children stay owned by the parent: re-attach them (``_attach_child`` replays a stop that
    arrived while async admission had them detached)."""
    for _, _, child in unit.children:
        _attach_child(unit.parent_agent, child)

def _dispatch_background(batch: _Batch) -> str:
    """Dispatch the call as independent async units (see ``_units_of``) and return the tool result JSON. Every unit
    of one call shares ONE pool slot (``slot_key``), so grouping never changes capacity accounting. Falls back to
    running synchronously (with an explanatory ``note``) when the session cannot receive detached completions or the
    async pool is at capacity."""
    from tools.delegate_tool import _get_max_async_children
    wake_sid = _resolve_async_wake_sid(batch.origin_wake_sid, batch.origin_session_history_delivery)
    if wake_sid is None:
        logger.info("delegate_task: async delivery unsupported on this session runtime; running the batch synchronously instead.")
        return _run_sync_with_note(batch, "no_async")

    parent_agent = batch.parent_agent
    session_key, origin_ui_session_id = _resolve_async_session_key(parent_agent, batch.origin_ui_session_id)
    routing = dict(
        session_key=session_key, origin_ui_session_id=origin_ui_session_id, origin_session_id=wake_sid,
        parent_session_id=getattr(parent_agent, "session_id", None), max_async_children=_get_max_async_children(),
    )

    units = _units_of(batch)
    dispatched: List[tuple[_Batch, str]] = []
    inline_results: List[dict] = []
    slot_key: Optional[str] = None
    for k, unit in enumerate(units):
        # One unit keeps the live-transcript directory's id so the returned delegation_id matches
        # cache/delegation/live/<id>/; several units suffix it (-1, -2, ...) and the call keeps the bare id.
        unit_id = batch.live_deleg_id if len(units) == 1 else (f"{batch.live_deleg_id}-{k + 1}" if batch.live_deleg_id else None)
        unit.unit_id = unit_id = unit_id or _new_delegation_id()  # fixed before the runner can start
        # The worker can start before admission returns. Detach only this unit:
        # unsubmitted units must still receive parent stops while a fallback runs.
        for _, _, child in unit.children:
            _detach_child(parent_agent, child)
        dispatch = _dispatch_unit(unit, unit_id, slot_key, routing)
        if dispatch.get("status") == "dispatched":
            slot_key = slot_key or dispatch["delegation_id"]
            dispatched.append((unit, dispatch["delegation_id"]))
            continue
        _restore_parent_cancellation(unit)
        if not dispatched:
            logger.info(
                "delegate_task: async pool at capacity (%s); running the whole batch synchronously instead.",
                dispatch.get("error", "rejected"),
            )
            return _run_sync_with_note(batch, "at_capacity")
        # Later units of an admitted call share its slot and cannot be capacity-rejected; a scheduler failure runs
        # the unit inline so no task is silently dropped.
        logger.warning("delegate_task: unit %d/%d not accepted (%s); running it inline.", k + 1, len(units), dispatch.get("error"))
        inline_results.extend(_execute_and_aggregate(unit)["results"])
    payload = _dispatched_payload(batch, dispatched)
    if inline_results:
        payload["inline_results"] = inline_results
    return json.dumps(payload, ensure_ascii=False)

def _run_batch(batch: _Batch, background: bool) -> str:
    """Tool result JSON: a dispatch handle (background) or the joined combined results."""
    if background:
        return _dispatch_background(batch)
    return json.dumps(_execute_and_aggregate(batch), ensure_ascii=False)