.agents/skills/lib_py/delegation/engine.py

@@ -284,11 +284,16 @@ def _notification(job_id, kind, **fields) -> Dict[str, Any]:
 def transition(job_id, request="merge", *, registry_dir=None, expected_status=None,
                expected_attempt=None, fields=None, source="unknown",
                notify=None, expected_notification=_UNSET,
-               expected_dispatch_token=None) -> TransitionResult:
+               expected_dispatch_token=None, guard=None) -> TransitionResult:
     """Decide and commit one state transition. The only writer of job status.
 
     Returns a result whose `notifications` have ALREADY been flushed; the field
     is kept so callers and tests can see what the transition emitted.
+
+    `guard(record)`, when given, runs under the registry lock before the
+    decision and refuses the commit by returning false: a precondition that
+    spans other records (Issue #50 dispatch admission), which the per-record
+    expectations cannot express. A refusal by the guard is not a conflict.
     """
     registry_dir = registry_dir or mqtt_common.DEFAULT_REGISTRY_DIR
     fields = dict(fields or {})
@@ -297,10 +302,13 @@ def transition(job_id, request="merge", *, registry_dir=None, expected_status=No
     with mqtt_common.registry_lock(registry_dir):
         record = mqtt_common.load_job(job_id, registry_dir)
         from_status = record.get("status")
-        decision = _decide(record, request, expected_status, expected_attempt,
-                           source=source, fields=fields,
-                           expected_notification=expected_notification,
-                           expected_dispatch_token=expected_dispatch_token)
+        if guard is not None and not guard(record):
+            decision = _Decision(False, from_status, "guard refused")
+        else:
+            decision = _decide(record, request, expected_status, expected_attempt,
+                               source=source, fields=fields,
+                               expected_notification=expected_notification,
+                               expected_dispatch_token=expected_dispatch_token)
 
         notifications: List[Dict[str, Any]] = []
         if decision.commit:

.agents/skills/lib_py/delegation/wrapper.py

@@ -63,9 +63,24 @@ EXIT_CODES = {"completed": 0, "error": 1, "timeout": 2, "broker_unavailable": 3,
 # 44 = the agent ended it with error (or it was cancelled), 45 = it did not end
 # within MAM_ONBOARD_WAIT_S (or its record is gone). The session is kept either way.
 ONBOARD_EXIT_CODES = {"completed": 0, "error": 44, "cancelled": 44, "timeout": 45, "missing": 45}
-DEFAULT_ACK_TIMEOUT_SEC, DEFAULT_IDLE_TIMEOUT_SEC = 180, 120  # registry.py's defaults, as a last resort
+DEFAULT_IDLE_TIMEOUT_SEC = 120  # registry.py's default, as a last resort
+# Issue #50: a pending record's liveness is its dispatcher's signal - written
+# every DISPATCH_SIGNAL_EVERY s while it waits and, once admitted, while it
+# holds the session - and it stays live for EVERY x MISSES s after the last
+# one (Issue #18's heartbeat x misses, on the dispatcher's side). The window
+# is not ack_timeout_sec: that is the agent's budget to answer a prompt and
+# goes down to 1 s, below any cadence a second-resolution signal can keep
+# (review aa1bff92 F2).
 DISPATCH_SIGNAL_FIELD = "dispatch_wait_at"
 DISPATCH_SIGNAL_EVERY = 10
+DISPATCH_SIGNAL_MISSES = 3
+DISPATCH_SIGNAL_WINDOW = DISPATCH_SIGNAL_EVERY * DISPATCH_SIGNAL_MISSES
+# The admission (review aa1bff92 F1): `clear` is persisted on the admitted
+# record, scoped to its attempt by the dispatch token, so a later candidate -
+# a lower id in the same second, a redispatched older loop job - waits for it
+# until it ends or its signal goes stale.
+ADMITTED_AT_FIELD = "dispatch_admitted_at"
+ADMITTED_TOKEN_FIELD = "dispatch_admitted_token"
 
 
 def _now() -> int:
@@ -244,7 +259,10 @@ def open_jobs(registry_dir: str, session: str, job_id: str, now: Optional[int] =
     live:  [(created_at, job_id, status)] - open jobs the Issue #18 contract
            still calls alive: `running` with an event in events.log within
            idle_timeout_sec; `pending` with a dispatch signal (the waiter's
-           `dispatch_wait_at`, else created_at) within ack_timeout_sec.
+           `dispatch_wait_at`, else created_at) within DISPATCH_SIGNAL_WINDOW.
+           A live pending record whose admission names its current dispatch
+           token is reported as `admitted`: it holds the session as a running
+           job does, whatever its place in the FIFO.
     stale: [(job_id, reason)] - non-terminal records nothing has touched for
            longer than that: a wrapper killed before or while dispatching, a
            zombie's unclosed record. They are reported, never waited for, so
@@ -273,15 +291,98 @@ def open_jobs(registry_dir: str, session: str, job_id: str, now: Optional[int] =
             else:
                 stale.append((other, f"running, no event for {idle}s"))
         elif status == "pending":
-            ack = _int_field(rec, "ack_timeout_sec", DEFAULT_ACK_TIMEOUT_SEC)
             seen = _parse_ts(rec.get(DISPATCH_SIGNAL_FIELD) or rec.get("created_at"))
-            if seen is not None and now - seen <= ack:
-                live.append((str(rec.get("created_at") or ""), other, status))
+            if seen is not None and now - seen <= DISPATCH_SIGNAL_WINDOW:
+                admitted = bool(rec.get(ADMITTED_TOKEN_FIELD)) and \
+                    rec.get(ADMITTED_TOKEN_FIELD) == rec.get("dispatch_token")
+                live.append((str(rec.get("created_at") or ""), other, "admitted" if admitted else status))
             else:
-                stale.append((other, f"pending, no dispatch signal for {ack}s"))
+                stale.append((other, f"pending, no dispatch signal for {DISPATCH_SIGNAL_WINDOW}s"))
     return live, stale
 
 
+def _first_in_line(live, mine) -> bool:
+    """No live running or admitted job, and `mine` earliest among the live
+    pending ones (FIFO by (created_at, job_id))."""
+    if any(st != "pending" for _c, _j, st in live):
+        return False
+    return min([(c, j) for c, j, _st in live] + [mine]) == mine
+
+
+def _admit(registry_dir: str, session: str, job_id: str) -> bool:
+    """`clear`, persisted: one merge through the engine whose guard re-reads
+    the session's open jobs under the registry lock, so two waiters cannot
+    both be admitted. Scoped to this attempt (its dispatch token: a
+    redispatch voids it); the signal is renewed with it. False when the
+    record is not pending any more, its attempt changed, or another waiter
+    was admitted first - the caller keeps waiting and sees that one."""
+    from lib_py.delegation import engine, mqtt_common
+    me = _load_record(registry_dir, job_id) or {}
+    token = me.get("dispatch_token")
+    if not token:
+        print(f"dispatch wait: job {job_id} carries no dispatch token; cannot be admitted", file=sys.stderr)
+        return False
+    mine = (str(me.get("created_at") or ""), job_id)
+
+    def guard(record):
+        if record.get("status") != "pending" or record.get("dispatch_token") != token:
+            return False
+        live, _stale = open_jobs(registry_dir, session, job_id)
+        return _first_in_line(live, mine)
+
+    now = mqtt_common._utcnow()
+    try:
+        return engine.transition(job_id, "merge", registry_dir=registry_dir, source="dispatch_admit", guard=guard,
+                                 fields={DISPATCH_SIGNAL_FIELD: now, ADMITTED_AT_FIELD: now,
+                                         ADMITTED_TOKEN_FIELD: token}).committed
+    except Exception as exc:  # the record is gone or unwritable: not admitted, keep waiting
+        print(f"dispatch wait: could not admit {job_id}: {exc}", file=sys.stderr)
+        return False
+
+
+def _start_hold(a: argparse.Namespace) -> None:
+    """The waiter answers `clear` and ends; a detached hold keeps the admitted
+    record's signal fresh until the record leaves pending (the agent's
+    `started`, a close), its attempt changes, the wrapper is gone, or the
+    wall clock ends (review aa1bff92 F2). Its output is not the answer."""
+    cmd = [sys.executable, "-m", "lib_py.delegation.wrapper", "hold-admission", "--job", a.job,
+           "--registry-dir", a.registry_dir, "--timeout", str(a.timeout)]
+    if a.start_time is not None:
+        cmd += ["--start-time", str(a.start_time)]
+    if a.watch_pid:
+        cmd += ["--watch-pid", str(a.watch_pid)]
+    subprocess.Popen(cmd, stdin=subprocess.DEVNULL, stdout=subprocess.DEVNULL, stderr=subprocess.DEVNULL,
+                     start_new_session=True, env=dict(os.environ, PYTHONPATH=_pythonpath()))
+
+
+def _pythonpath() -> str:
+    skills = os.path.dirname(os.path.dirname(os.path.dirname(os.path.abspath(__file__))))
+    extra = os.environ.get("PYTHONPATH", "")
+    return skills + (os.pathsep + extra if extra else "")
+
+
+def hold_admission(a: argparse.Namespace) -> str:
+    """`released` once the record is not this attempt's admitted pending one
+    any more, `timeout` at the wall clock; the signal is renewed every
+    DISPATCH_SIGNAL_EVERY s in between. OwnerGone (the wrapper) ends it."""
+    me = _load_record(a.registry_dir, a.job) or {}
+    token = me.get(ADMITTED_TOKEN_FIELD)
+    deadline = (a.start_time if a.start_time is not None else _now()) + a.timeout
+    last_signal = _now()
+    while True:
+        _sleep(a, 1)
+        rec = _load_record(a.registry_dir, a.job)
+        if token is None or rec is None or rec.get("status") != "pending" \
+                or rec.get("dispatch_token") != token or rec.get(ADMITTED_TOKEN_FIELD) != token:
+            return "released"
+        now = _now()
+        if now >= deadline:
+            return "timeout"
+        if now - last_signal >= DISPATCH_SIGNAL_EVERY:
+            _signal_dispatch_wait(a.registry_dir, a.job)
+            last_signal = now
+
+
 def _signal_dispatch_wait(registry_dir: str, job_id: str) -> None:
     """The waiter's liveness: a merge of dispatch_wait_at into its own pending
     record through the registry's one transition boundary (status untouched,
@@ -295,12 +396,14 @@ def _signal_dispatch_wait(registry_dir: str, job_id: str) -> None:
 
 
 def wait_open_jobs(a: argparse.Namespace) -> str:
-    """`clear` when no live open job of the session remains and this job is
-    the earliest live pending one (FIFO by (created_at, job_id)); `busy <ids>`
-    when the bound runs out first. The bound is min(--wait-s, this job's
-    remaining wall clock). Every DISPATCH_SIGNAL_EVERY s the waiter signals on
-    its own record so later waiters see it alive; a waiter whose wrapper is
-    gone stops (OwnerGone) and its signal goes stale."""
+    """`clear` when no live running or admitted job of the session remains,
+    this job is the earliest live pending one (FIFO by (created_at, job_id))
+    and its admission is committed (_admit); `busy <ids>` when the bound runs
+    out first. The bound is min(--wait-s, this job's remaining wall clock).
+    Every DISPATCH_SIGNAL_EVERY s the waiter signals on its own record so
+    later waiters see it alive; a waiter whose wrapper is gone stops
+    (OwnerGone) and its signal goes stale. With --hold the admission is kept
+    alive after the answer (_start_hold)."""
     me = _load_record(a.registry_dir, a.job) or {}
     mine = (str(me.get("created_at") or ""), a.job)
     remaining = (a.start_time if a.start_time is not None else _now()) + a.timeout - _now()
@@ -314,10 +417,10 @@ def wait_open_jobs(a: argparse.Namespace) -> str:
             if other not in reported:
                 reported.add(other)
                 print(f"stale open job {other} ignored ({reason})", file=sys.stderr)
-        if not any(st == "running" for _c, _j, st in live):
-            queue = [(c, j) for c, j, st in live if st == "pending"] + [mine]
-            if min(queue) == mine:
-                return "clear"
+        if _first_in_line(live, mine) and _admit(a.registry_dir, a.agent_session, a.job):
+            if getattr(a, "hold", False):
+                _start_hold(a)
+            return "clear"
         if now >= deadline:
             return "busy " + " ".join(j for _c, j, _st in live)
         if last_signal is None or now - last_signal >= DISPATCH_SIGNAL_EVERY:
@@ -480,6 +583,13 @@ def _parser() -> argparse.ArgumentParser:
             s.add_argument("--start-time", type=int, default=None)
             s.add_argument("--timeout", type=int, required=True, help="the job's wall-clock budget")
             s.add_argument("--watch-pid", type=int, default=None, help="the wrapper's pid; gone -> stop waiting")
+            s.add_argument("--hold", action="store_true", help="keep the admission's signal fresh after `clear`")
+    s = sub.add_parser("hold-admission")
+    s.add_argument("--job", required=True)
+    s.add_argument("--registry-dir", required=True)
+    s.add_argument("--start-time", type=int, default=None)
+    s.add_argument("--timeout", type=int, required=True)
+    s.add_argument("--watch-pid", type=int, default=None, help="the wrapper's pid; gone -> stop holding")
     for name in ("finalize-begin", "finalize-end"):
         s = sub.add_parser(name)
         s.add_argument("--job", required=True)
@@ -544,6 +654,11 @@ def main(argv: Optional[List[str]] = None) -> int:
             print(wait_open_jobs(a))
         except OwnerGone:
             print(f"wait-open-jobs: wrapper pid {a.watch_pid} is gone; stopped waiting on job {a.job}", file=sys.stderr)
+    elif a.cmd == "hold-admission":
+        try:
+            print(hold_admission(a))
+        except OwnerGone:
+            print(f"hold-admission: wrapper pid {a.watch_pid} is gone; stopped holding job {a.job}", file=sys.stderr)
     else:
         try:
             _answer(finalize_end(a))

.agents/skills/multi-agent-mux-delegate-job/multi-agent-mux-delegate-job

@@ -855,7 +855,7 @@ _registry_wait() {
   local job_id="$1" sess="$2" res
   _decided res wait-open-jobs --job "$job_id" --agent-session "$sess" --registry-dir "$REGISTRY_DIR" \
       --wait-s "$(mam_int_knob MAM_DISPATCH_WAIT_S 600 0)" ${START_TIME:+--start-time "$START_TIME"} \
-      --timeout "$TIMEOUT" --watch-pid "$$"
+      --timeout "$TIMEOUT" --watch-pid "$$" --hold
   case "$res" in
     clear) return 0 ;;
     busy*)

tests/test_issue50_dispatch.py

@@ -2,8 +2,10 @@
 
 - U: the decisions in lib_py.delegation.wrapper - the open-job table (status x
   signal age x session spelling), FIFO release among live pending waiters,
-  the waiter's own signal written through the registry, the bound, a dead
-  wrapper, and finalize-end's `registry_wait` phase closing as session_busy.
+  the admission persisted on the released record (review aa1bff92 F1) and
+  held alive after the answer (F2), the waiter's own signal written through
+  the registry, the bound, a dead wrapper, and finalize-end's `registry_wait`
+  phase closing as session_busy.
 - H: against a real herdr 0.9.3 server (one-off session, fake claude in the
   pane, the real publish path through publish_event.py and the suite's local
   broker): see test_issue50_dispatch_herdr.py.
@@ -16,6 +18,7 @@ import json
 import os
 import subprocess
 import sys
+import threading
 import time
 from pathlib import Path
 
@@ -24,6 +27,8 @@ import pytest
 REPO_ROOT = Path(__file__).resolve().parent.parent
 SKILLS = REPO_ROOT / ".agents" / "skills"
 WRAPPER = SKILLS / "multi-agent-mux-delegate-job" / "multi-agent-mux-delegate-job"
+REGISTRY_PY = SKILLS / "multi-agent-mux-delegate-job" / "scripts" / "registry.py"
+WINDOW = 30   # DISPATCH_SIGNAL_EVERY (10) x DISPATCH_SIGNAL_MISSES (3), pinned here
 if str(SKILLS) not in sys.path:
     sys.path.insert(0, str(SKILLS))
 
@@ -49,6 +54,21 @@ def _edit(reg, jid, **fields):
     path.write_text(json.dumps(rec))
 
 
+def _rec(reg, jid):
+    return json.loads((reg / f"{jid}.json").read_text())
+
+
+def _at(text):
+    return calendar.timegm(time.strptime(text, "%Y-%m-%dT%H:%M:%SZ"))
+
+
+def _register_as(reg, jid, **over):
+    """A record under a chosen id (the file name is what open_jobs keys on)."""
+    real = _register(reg, job_id=jid, **over)
+    os.rename(reg / f"{real}.json", reg / f"{jid}.json")
+    return jid
+
+
 def _event(reg, jid, epoch, event="progress"):
     with open(reg / f"{jid}.events.log", "a") as fh:
         fh.write(json.dumps({"job_id": jid, "event": event, "timestamp": _iso(epoch)}) + "\n")
@@ -67,18 +87,20 @@ def _ns(reg, job, session="herdr:s", wait_s=0, start_time=None, timeout=3600, wa
     ("running", 10, None, "live"),          # an event idle_timeout_sec (120) ago at most
     ("running", 121, None, "stale"),
     ("running", None, None, "stale"),       # running with no events.log at all
-    ("pending", 10, None, "live"),          # created within ack_timeout_sec (180)
-    ("pending", 181, None, "stale"),
+    ("pending", 10, None, "live"),          # created within the signal window (30)
+    ("pending", 30, None, "live"),
+    ("pending", 31, None, "stale"),
     ("pending", 181, 5, "live"),            # old record, fresh dispatch_wait_at
-    ("pending", 181, 181, "stale"),
-    ("pending", 10, 181, "stale"),          # the signal, once present, is what counts
+    ("pending", 181, 31, "stale"),
+    ("pending", 10, 31, "stale"),           # the signal, once present, is what counts
+    ("pending", 1, 2, "live"),              # ack_timeout_sec (1 here) is not the window
     ("completed", 10, None, None),
     ("error", 10, None, None),
     ("cancelled", 10, None, None),
 ])
 def test_u1_open_jobs_table(tmp_path, status, age, signal, want):
     NOW = int(time.time())   # the running check reads the real clock (recent_disk_heartbeat)
-    other = _register(tmp_path, status=status)
+    other = _register(tmp_path, status=status, ack=1)
     if status == "running" and age is not None:
         _event(tmp_path, other, NOW - age)
     if status == "pending":
@@ -97,6 +119,22 @@ def test_u1_open_jobs_table(tmp_path, status, age, signal, want):
         assert got == (set(), set())
 
 
+@pytest.mark.parametrize("token_match,signal,want", [(True, 5, "admitted"), (False, 5, "pending"), (True, 31, "stale")])
+def test_u1d_an_admission_is_scoped_to_the_attempt_and_lives_by_the_signal(tmp_path, token_match, signal, want):
+    NOW = int(time.time())
+    other = _register(tmp_path)
+    token = _rec(tmp_path, other)["dispatch_token"] if token_match else "a-previous-attempt"
+    _edit(tmp_path, other, dispatch_wait_at=_iso(NOW - signal), dispatch_admitted_at=_iso(NOW - signal),
+          dispatch_admitted_token=token)
+    me = _register(tmp_path)
+    live, stale = decide.open_jobs(str(tmp_path), "herdr:s", me, now=NOW)
+    if want == "stale":
+        assert (live, [j for j, _r in stale]) == ([], [other])
+    else:
+        assert [(j, st) for _c, j, st in live] == [(other, want)]
+    assert decide.DISPATCH_SIGNAL_WINDOW == WINDOW
+
+
 @pytest.mark.parametrize("record_session,asked", [("herdr:s", "s"), ("s", "herdr:s"), ("herdr:s", "herdr:s")])
 def test_u1b_the_session_spelling_is_normalised(tmp_path, record_session, asked):
     other = _register(tmp_path, session=record_session)
@@ -135,20 +173,61 @@ def test_u2_clear_only_when_no_live_running_and_this_job_is_the_earliest_pending
 
 def test_u2b_a_tie_on_created_at_is_broken_by_job_id(tmp_path):
     same = _iso(time.time())
-    first = _register(tmp_path, created_at=same, job_id="aaaa0001")
-    second = _register(tmp_path, created_at=same, job_id="aaaa0002")
-    # records carry their job_id inside; the file name is what open_jobs keys on
-    for jid, real in ((first, "aaaa0001"), (second, "aaaa0002")):
-        os.rename(tmp_path / f"{jid}.json", tmp_path / f"{real}.json")
+    _register_as(tmp_path, "aaaa0001", created_at=same)
+    _register_as(tmp_path, "aaaa0002", created_at=same)
     assert decide.wait_open_jobs(_ns(tmp_path, "aaaa0001")) == "clear"
     assert decide.wait_open_jobs(_ns(tmp_path, "aaaa0002")) == "busy aaaa0001"
 
 
 def test_u2c_a_dead_waiter_is_ignored_and_reported(tmp_path, capsys):
-    b = _register(tmp_path, ack=5, created_at=_iso(time.time() - 60), dispatch_wait_at=_iso(time.time() - 6))
+    b = _register(tmp_path, ack=5, created_at=_iso(time.time() - 60), dispatch_wait_at=_iso(time.time() - WINDOW - 1))
     me = _register(tmp_path)
     assert decide.wait_open_jobs(_ns(tmp_path, me)) == "clear"
-    assert f"stale open job {b} ignored (pending, no dispatch signal for 5s)" in capsys.readouterr().err
+    assert f"stale open job {b} ignored (pending, no dispatch signal for {WINDOW}s)" in capsys.readouterr().err
+
+
+# review aa1bff92 F1: `clear` is an admission the record carries, so a candidate
+# that would sort first - a lower id in the same second, a redispatched older
+# loop job - waits for the admitted job until it ends
+
+def test_u2e_a_lower_id_arriving_after_clear_waits_for_the_admitted_job(tmp_path):
+    same = _iso(time.time())
+    _register_as(tmp_path, "ffff0001", created_at=same)
+    assert decide.wait_open_jobs(_ns(tmp_path, "ffff0001")) == "clear"
+    _register_as(tmp_path, "0000000a", created_at=same)
+    assert decide.wait_open_jobs(_ns(tmp_path, "0000000a")) == "busy ffff0001"
+    assert decide.wait_open_jobs(_ns(tmp_path, "0000000a", wait_s=2)) == "busy ffff0001", "still, at the bound"
+    # the admitted job's `started` keeps the hold (running, with an event)...
+    _edit(tmp_path, "ffff0001", status="running")
+    _event(tmp_path, "ffff0001", time.time(), "started")
+    assert decide.wait_open_jobs(_ns(tmp_path, "0000000a")) == "busy ffff0001"
+    # ... and its end releases the next one
+    _edit(tmp_path, "ffff0001", status="completed")
+    assert decide.wait_open_jobs(_ns(tmp_path, "0000000a")) == "clear"
+
+
+def test_u2f_an_older_loop_attempt_redispatched_after_another_admission_waits(tmp_path):
+    old = _register(tmp_path, status="completed")
+    time.sleep(1.1)
+    cur = _register(tmp_path)
+    assert decide.wait_open_jobs(_ns(tmp_path, cur)) == "clear"
+    res = subprocess.run([sys.executable, str(REGISTRY_PY), "--registry-dir", str(tmp_path), "update", "--job", old,
+                          "--status", "pending", "--attempt-id", "2"], capture_output=True, text=True, timeout=60)
+    assert res.returncode == 0 and _rec(tmp_path, old)["status"] == "pending", res.stdout + res.stderr
+    assert _rec(tmp_path, old)["created_at"] < _rec(tmp_path, cur)["created_at"], "it would sort first"
+    assert decide.wait_open_jobs(_ns(tmp_path, old)) == f"busy {cur}"
+    _edit(tmp_path, cur, status="completed")
+    assert decide.wait_open_jobs(_ns(tmp_path, old)) == "clear"
+
+
+def test_u2g_an_admission_whose_owner_stopped_signalling_expires(tmp_path, capsys):
+    a = _register(tmp_path)
+    assert decide.wait_open_jobs(_ns(tmp_path, a)) == "clear"
+    b = _register(tmp_path)
+    assert decide.wait_open_jobs(_ns(tmp_path, b)) == f"busy {a}"
+    _edit(tmp_path, a, dispatch_wait_at=_iso(time.time() - WINDOW - 1))     # its hold is gone
+    assert decide.wait_open_jobs(_ns(tmp_path, b)) == "clear"
+    assert f"stale open job {a} ignored (pending, no dispatch signal for {WINDOW}s)" in capsys.readouterr().err
 
 
 def test_u2d_the_bound_is_the_remaining_wall_clock(tmp_path):
@@ -185,6 +264,45 @@ def test_u3_the_waiter_signals_on_its_own_record(tmp_path):
     assert me in {j for _c, j, _s in live}
 
 
+def test_u3d_clear_is_persisted_on_the_record_scoped_to_its_attempt(tmp_path):
+    me = _register(tmp_path)
+    t0 = int(time.time())
+    assert decide.wait_open_jobs(_ns(tmp_path, me)) == "clear"
+    rec = _rec(tmp_path, me)
+    assert rec["status"] == "pending" and rec["dispatch_admitted_token"] == rec["dispatch_token"]
+    assert _at(rec["dispatch_admitted_at"]) >= t0 and _at(rec["dispatch_wait_at"]) >= t0, "the signal is renewed with it"
+    assert not (tmp_path / f"{me}.events.log").exists(), "an admission is not the agent's `started`"
+    later = _register(tmp_path)
+    assert decide.open_jobs(str(tmp_path), "herdr:s", later)[0] == [(rec["created_at"], me, "admitted")]
+    # a redispatch (new attempt, new token) voids it
+    res = subprocess.run([sys.executable, str(REGISTRY_PY), "--registry-dir", str(tmp_path), "update", "--job", me,
+                          "--status", "pending", "--attempt-id", "2"], capture_output=True, text=True, timeout=60)
+    assert res.returncode == 0, res.stdout + res.stderr
+    assert _rec(tmp_path, me)["dispatch_token"] != rec["dispatch_token"]
+    assert decide.open_jobs(str(tmp_path), "herdr:s", later)[0] == [(rec["created_at"], me, "pending")]
+
+
+def test_u3e_the_admission_is_rechecked_under_the_registry_lock(tmp_path, monkeypatch):
+    # the waiter's read said "first in line"; by the time its merge holds the
+    # lock another waiter was admitted: the guard refuses, the wait goes on
+    me = _register(tmp_path)
+    other = _register(tmp_path)
+    real_open_jobs = decide.open_jobs
+    calls = []
+
+    def open_jobs(registry_dir, session, job_id, now=None):
+        calls.append(job_id)
+        live, stale = real_open_jobs(registry_dir, session, job_id, now)
+        if len(calls) >= 2:   # the guard's read (and every poll after it)
+            live = [(c, j, "admitted") for c, j, _st in live]
+        return live, stale
+
+    monkeypatch.setattr(decide, "open_jobs", open_jobs)
+    assert decide.wait_open_jobs(_ns(tmp_path, me, wait_s=1)) == f"busy {other}"
+    assert "dispatch_admitted_token" not in _rec(tmp_path, me)
+    assert len(calls) >= 2
+
+
 def test_u3c_a_terminal_self_record_cannot_carry_the_signal(tmp_path):
     # why the loop path resets its record to pending before it waits (s1):
     # the engine refuses a merge into a terminal record, so the waiter would
@@ -227,7 +345,50 @@ def test_u4_open_jobs_prints_live_and_stale(tmp_path):
     me = _register(tmp_path)
     res = _cli(tmp_path, "open-jobs", "--job", me, "--agent-session", "herdr:s", "--registry-dir", str(tmp_path))
     assert res.returncode == 0, res.stderr
-    assert f"{a}  running" in res.stdout and f"{b}  stale     pending, no dispatch signal for 180s" in res.stdout
+    assert f"{a}  running" in res.stdout and f"{b}  stale     pending, no dispatch signal for {WINDOW}s" in res.stdout
+
+
+def _hold_pids(jid):
+    out = subprocess.run(["pgrep", "-f", f"hold-admission --job {jid}"], capture_output=True, text=True).stdout
+    return [int(p) for p in out.split()]
+
+
+def test_u4c_the_wait_holds_its_admission_until_the_record_leaves_pending(tmp_path):
+    # review aa1bff92 F2: after `clear` the waiter ends with its answer; the
+    # hold renews the admitted record's signal until the agent's `started`
+    me = _register(tmp_path)
+    try:
+        res = _cli(tmp_path, "wait-open-jobs", "--job", me, "--agent-session", "herdr:s", "--registry-dir",
+                   str(tmp_path), "--wait-s", "0", "--timeout", "3600", "--watch-pid", str(os.getpid()), "--hold")
+        assert res.stdout.strip() == "clear", res.stderr
+        first = _rec(tmp_path, me)["dispatch_wait_at"]
+        assert _hold_pids(me), "a detached hold is running"
+        deadline = time.time() + decide.DISPATCH_SIGNAL_EVERY + 5
+        while time.time() < deadline and _rec(tmp_path, me)["dispatch_wait_at"] == first:
+            time.sleep(0.5)
+        assert _at(_rec(tmp_path, me)["dispatch_wait_at"]) >= _at(first) + decide.DISPATCH_SIGNAL_EVERY - 1
+        assert _rec(tmp_path, me)["status"] == "pending" and not (tmp_path / f"{me}.events.log").exists()
+        _edit(tmp_path, me, status="running")   # the agent's `started`
+        deadline = time.time() + 5
+        while time.time() < deadline and _hold_pids(me):
+            time.sleep(0.2)
+        assert not _hold_pids(me), "released with the record"
+    finally:
+        for pid in _hold_pids(me):
+            os.kill(pid, 9)
+
+
+def test_u4d_the_hold_ends_with_its_wrapper_and_without_an_admission(tmp_path):
+    me = _register(tmp_path)
+    res = _cli(tmp_path, "hold-admission", "--job", me, "--registry-dir", str(tmp_path), "--timeout", "3600")
+    assert res.stdout.strip() == "released", res.stderr    # never admitted: nothing to hold
+    assert decide.wait_open_jobs(_ns(tmp_path, me)) == "clear"
+    gone = subprocess.Popen(["true"])
+    gone.wait()
+    t0 = time.time()
+    res = _cli(tmp_path, "hold-admission", "--job", me, "--registry-dir", str(tmp_path), "--timeout", "3600",
+               "--watch-pid", str(gone.pid))
+    assert res.stdout == "" and "is gone" in res.stderr and time.time() - t0 < 10, res.stdout + res.stderr
 
 
 def test_u4b_wait_open_jobs_stops_with_its_wrapper(tmp_path):
@@ -292,3 +453,4 @@ def test_s1_both_dispatch_paths_wait_by_the_registry_before_the_idle_wait():
     body = src.split("_registry_wait() {")[1].split("\n}\n")[0]
     assert "wait-open-jobs" in body and 'finalize_unfinished "$job_id" "error" "$SUB_RC_ERROR" "registry_wait"' in body
     assert "exit 5" in body and "mam_int_knob MAM_DISPATCH_WAIT_S 600 0" in body
+    assert "--hold" in body, "the admission is held alive after the answer (u4c)"

tests/test_issue50_dispatch_herdr.py

@@ -329,7 +329,8 @@ def test_c3_a_dead_running_record_does_not_block_the_session(box):
     assert rc == 0, out + err
     assert f"stale open job {a} ignored (running, no event for 2s)" in err, err
     assert box.record(b)["status"] == "completed"
-    assert "dispatch_wait_at" not in box.record(b), "nothing to wait for: no signal written"
+    rec = box.record(b)   # nothing to wait for: the only signal is the admission's own
+    assert rec["dispatch_admitted_token"] == rec["dispatch_token"] and rec["dispatch_wait_at"] == rec["dispatch_admitted_at"]
 
 
 # ---------------------------------------------------------------------------
@@ -434,6 +435,9 @@ def test_c7_two_waiters_run_one_after_the_other_and_neither_is_cancelled(box):
     assert "cancelled" not in out_b + out_c and "stale open job" not in err_b + err_c
     assert _ts(box.events(b)[0]) >= _ts(box.events(a)[-1])
     assert _ts(box.events(c)[0]) >= _ts(box.events(b)[-1]), "C started only after B ended"
+    # the admission (review aa1bff92 F1): B's before its own `started`, C's only once B ended
+    assert box.record(b)["dispatch_admitted_at"] <= _ts(box.events(b)[0])
+    assert box.record(c)["dispatch_admitted_at"] >= _ts(box.events(b)[-1])
     pane = box.pane_text()
     assert pane.index(f'Your job_id is "{b}"') < pane.index(f'Your job_id is "{c}"'), "injected in FIFO order"
 
@@ -456,16 +460,49 @@ def test_c8_a_dead_waiter_is_skipped_once_its_signal_is_stale(box):
     c = box.wait_new_job(known | {b})
     assert box.record(b)["created_at"] < box.record(c)["created_at"]
     _after(2, box.publish, a, "completed", "prior done")
-    _after(14, box.publish, c, "started")           # after B's 5 s ack window has long passed
-    _after(16, box.publish, c, "completed", "c done")
+    _after(40, box.publish, c, "started")           # after B's signal window (30 s) has passed
+    _after(42, box.publish, c, "completed", "c done")
     rc, out, err = box.finish(proc_c)
     assert rc == 0, out + err
-    assert f"stale open job {b} ignored (pending, no dispatch signal for 5s)" in err, err
+    assert f"stale open job {b} ignored (pending, no dispatch signal for 30s)" in err, err
     assert box.record(c)["status"] == "completed", (box.record(c), box.events(c), out, err)
     assert box.record(b)["status"] == "pending", "the dead waiter's record is left as it is"
     assert _ts(box.events(c)[0]) >= _ts(box.events(a)[-1])
 
 
+# ---------------------------------------------------------------------------
+# C9 - C8's live counterpart (review aa1bff92 F2): waiters with short ack
+# windows, held across many of them, are never stale and never co-admitted
+# ---------------------------------------------------------------------------
+
+def test_c9_live_waiters_with_short_ack_windows_are_never_stale_nor_co_admitted(box):
+    a = box.register()
+    box.publish(a, "started")
+    known = box.job_ids()
+    proc_b = box.submit(prompt="work B", ack="5", MAM_DISPATCH_WAIT_S="60")
+    b = box.wait_new_job(known)
+    time.sleep(1.2)
+    proc_c = box.submit(prompt="work C", ack="5", MAM_DISPATCH_WAIT_S="60")
+    c = box.wait_new_job(known | {b})
+    box.wait_field(c, "dispatch_wait_at")
+    box.wait_field(b, "dispatch_wait_at")
+    _after(12, box.publish, a, "completed", "prior done")   # both waited through two ack windows
+    _after(16, box.publish, b, "started")                   # B is injected at ~13 s
+    _after(19, box.publish, b, "completed", "b done")
+    _after(23, box.publish, c, "started")                   # C at ~20 s
+    _after(25, box.publish, c, "completed", "c done")
+    rc_b, out_b, err_b = box.finish(proc_b)
+    rc_c, out_c, err_c = box.finish(proc_c)
+    assert (rc_b, rc_c) == (0, 0), out_b + err_b + out_c + err_c
+    assert "stale open job" not in err_b + err_c, err_b + err_c
+    assert "cancelled" not in out_b + out_c
+    assert box.record(b)["status"] == box.record(c)["status"] == "completed"
+    assert box.record(c)["dispatch_admitted_at"] >= _ts(box.events(b)[-1]), "C admitted only once B ended"
+    assert _ts(box.events(c)[0]) >= _ts(box.events(b)[-1])
+    pane = box.pane_text()
+    assert pane.index(f'Your job_id is "{b}"') < pane.index(f'Your job_id is "{c}"'), "injected in FIFO order"
+
+
 # ---------------------------------------------------------------------------
 # A - three `create --onboard` at once in one server
 # ---------------------------------------------------------------------------