turnstone/tests/test_compaction_checkpoint.py

"""Tests for persisted compaction checkpoints (rehydration-deadlock fix).

Compaction swaps a session's in-memory history for a summary but leaves the full
transcript in storage.  Without a durable marker, ``resume()`` reloaded the full
pre-compaction history, which on a long session — or one switched to a smaller-
context model — exceeds the window and deadlocks the first send.

The fix persists one ``_source="compaction"`` marker (summary + watermark) so
resume rehydrates ``[summary] + [rows after the watermark]`` while the full
history stays in storage for ``/history``/export.  Covered here:

- ``get_compaction_watermark`` — the boundary id (max-summarized), with and
  without a preserved tail, and on an empty workstream.
- ``load_message_turns`` (resume) — checkpoint-aware slice, latest-marker-wins,
  preserved-tail handling, and the full-history fallbacks (no marker, malformed
  marker) that keep every pre-checkpoint session loading exactly as before.
- ``load_messages`` (display) — markers stay invisible to ``/history``.
- End-to-end: ``_compact_messages`` writes the marker and a fresh ``resume()``
  rehydrates the bounded view, not the full transcript.
"""

from __future__ import annotations

import json

import pytest

from tests._session_helpers import make_session
from turnstone.core.session import _SummaryResult
from turnstone.core.storage._utils import _fork_turn_insert_row
from turnstone.core.trajectory import PROVENANCE_META_KEY, TurnProvenance, turns_from_dicts


def _marker_meta(watermark: int | None) -> str | None:
    """The marker's stored ``meta`` JSON (``None`` simulates a legacy/malformed marker)."""
    return json.dumps({"watermark": watermark}) if watermark is not None else None


def _register(st, ws: str = "ws1") -> str:
    st.register_workstream(ws, user_id="u1", title="t", kind="interactive")
    return ws


# ---------------------------------------------------------------------------
# get_compaction_watermark
# ---------------------------------------------------------------------------


class TestWatermark:
    def test_preserve_tail_zero_is_max_id(self, storage_backend):
        st = storage_backend
        ws = _register(st)
        ids = [st.save_message(ws, "user", f"m{i}") for i in range(5)]
        assert st.get_compaction_watermark(ws, 0) == max(ids)

    def test_preserve_tail_n_is_nth_newest(self, storage_backend):
        st = storage_backend
        ws = _register(st)
        ids = sorted(st.save_message(ws, "user", f"m{i}") for i in range(5))
        # Keep the newest 2 verbatim → boundary is the 3rd-newest id.
        assert st.get_compaction_watermark(ws, 2) == ids[-3]

    def test_preserve_tail_ignores_existing_markers(self, storage_backend):
        # A compaction marker is saved as a NEW row but is not part of the
        # preserved in-memory tail, so it must not shift the (preserve_tail+1)
        # boundary — without the exclusion, this returns ids[-1] (the marker
        # consumes an offset slot) and resume would drop a real tail row.
        st = storage_backend
        ws = _register(st)
        ids = [st.save_message(ws, "user", f"m{i}") for i in range(5)]
        st.save_message(ws, "assistant", "SUM", source="compaction", meta=_marker_meta(max(ids)))
        st.save_message(ws, "user", "m5")
        # Real rows newest-first: m5, m4, m3, ... → 3rd-newest real row is m3.
        assert st.get_compaction_watermark(ws, 2) == ids[-2]

    def test_empty_workstream_is_none(self, storage_backend):
        st = storage_backend
        ws = _register(st)
        assert st.get_compaction_watermark(ws, 0) is None

    def test_preserve_tail_exceeding_row_count_is_none(self, storage_backend):
        # Fewer rows than the preserved tail → no boundary, so compaction skips
        # the marker rather than writing a watermark that points past the history.
        st = storage_backend
        ws = _register(st)
        st.save_message(ws, "user", "only")
        assert st.get_compaction_watermark(ws, 5) is None


# ---------------------------------------------------------------------------
# load_message_turns — checkpoint-aware resume
# ---------------------------------------------------------------------------


class TestCheckpointResume:
    def test_loads_summary_plus_tail_not_full_history(self, storage_backend):
        st = storage_backend
        ws = _register(st)
        for i in range(5):
            st.save_message(ws, "user" if i % 2 == 0 else "assistant", f"old{i}")
        watermark = st.get_compaction_watermark(ws, 0)
        st.save_message(
            ws, "assistant", "THE SUMMARY", source="compaction", meta=_marker_meta(watermark)
        )
        st.save_message(ws, "user", "new question")
        st.save_message(ws, "assistant", "new answer")

        texts = [t.text for t in st.load_message_turns(ws)]
        assert texts == ["[Conversation summary]", "THE SUMMARY", "new question", "new answer"]
        assert not any("old" in x for x in texts)  # summarized prefix is gone

    def test_preserved_tail_kept_after_summary(self, storage_backend):
        st = storage_backend
        ws = _register(st)
        ids = sorted(st.save_message(ws, "user", f"m{i}") for i in range(4))
        # Mid-turn compaction keeps the newest row (m3) verbatim.
        watermark = st.get_compaction_watermark(ws, 1)
        assert watermark == ids[-2]
        st.save_message(ws, "assistant", "SUM", source="compaction", meta=_marker_meta(watermark))

        texts = [t.text for t in st.load_message_turns(ws)]
        assert texts == ["[Conversation summary]", "SUM", "m3"]

    def test_latest_marker_wins(self, storage_backend):
        st = storage_backend
        ws = _register(st)
        st.save_message(ws, "user", "old")
        st.save_message(
            ws,
            "assistant",
            "SUMMARY 1",
            source="compaction",
            meta=_marker_meta(st.get_compaction_watermark(ws, 0)),
        )
        st.save_message(ws, "user", "mid")
        st.save_message(
            ws,
            "assistant",
            "SUMMARY 2",
            source="compaction",
            meta=_marker_meta(st.get_compaction_watermark(ws, 0)),
        )
        st.save_message(ws, "user", "after")

        texts = [t.text for t in st.load_message_turns(ws)]
        assert texts == ["[Conversation summary]", "SUMMARY 2", "after"]
        assert "SUMMARY 1" not in texts and "old" not in texts and "mid" not in texts

    def test_no_marker_loads_full_history(self, storage_backend):
        st = storage_backend
        ws = _register(st)
        for i in range(3):
            st.save_message(ws, "user", f"m{i}")
        assert [t.text for t in st.load_message_turns(ws)] == ["m0", "m1", "m2"]

    def test_malformed_marker_falls_back_to_full_history(self, storage_backend):
        # A marker with no watermark (legacy/corrupt) must NOT slice — losing
        # real messages is worse than reloading more than necessary.
        st = storage_backend
        ws = _register(st)
        st.save_message(ws, "user", "a")
        st.save_message(ws, "assistant", "SUMMARY", source="compaction", meta=None)
        st.save_message(ws, "user", "b")
        texts = [t.text for t in st.load_message_turns(ws)]
        assert "a" in texts and "b" in texts  # no real message dropped


# ---------------------------------------------------------------------------
# load_messages — display path keeps markers invisible
# ---------------------------------------------------------------------------


class TestDisplayPath:
    def test_history_excludes_marker(self, storage_backend):
        st = storage_backend
        ws = _register(st)
        st.save_message(ws, "user", "q")
        st.save_message(ws, "assistant", "a")
        st.save_message(
            ws,
            "assistant",
            "SUMMARY",
            source="compaction",
            meta=_marker_meta(st.get_compaction_watermark(ws, 0)),
        )

        contents = [m.get("content") for m in st.load_messages(ws)]
        assert "SUMMARY" not in contents
        assert contents == ["q", "a"]  # true transcript, no injected summary

    def test_include_compaction_projects_marker_as_system_row(self, storage_backend):
        """The /history display path (include_compaction=True) surfaces the
        marker IN PLACE as a first-class system row — source="compaction",
        meta = the marker's stored fields — so the UI re-renders its
        compaction card after a reload.  Export/search (default False)
        stay on the drop path pinned above."""
        st = storage_backend
        ws = _register(st)
        st.save_message(ws, "user", "q")
        st.save_message(ws, "assistant", "a")
        wm = st.get_compaction_watermark(ws, 0)
        st.save_message(
            ws,
            "assistant",
            "SUMMARY",
            source="compaction",
            meta=json.dumps(
                {"watermark": wm, "before_tokens": 900, "after_tokens": 80, "trigger": "manual"}
            ),
        )
        st.save_message(ws, "user", "later question")

        msgs = st.load_messages(ws, include_compaction=True)
        assert [m.get("content") for m in msgs] == ["q", "a", "SUMMARY", "later question"]
        marker = msgs[2]
        assert marker["role"] == "system"  # display row, not a fake assistant turn
        assert marker.get("_source") == "compaction"
        meta = marker.get("_source_meta")
        assert meta == {
            "watermark": wm,
            "before_tokens": 900,
            "after_tokens": 80,
            "trigger": "manual",
        }


# ---------------------------------------------------------------------------
# End-to-end: compaction writes the marker, resume is bounded
# ---------------------------------------------------------------------------


def test_compaction_persists_checkpoint_and_resume_is_bounded(tmp_db, mock_openai_client):
    """The deadlock-fix proof: a session compacts, a fresh session reopens it,
    and resume rehydrates [summary]+[tail] — never the full pre-compaction
    transcript that would overflow the window on reopen."""
    from unittest.mock import patch

    from turnstone.core.memory import register_workstream, save_message

    ws = "wsE2E"
    register_workstream(ws, user_id="u1", name="t")
    history = [
        {"role": "user" if i % 2 == 0 else "assistant", "content": f"turn {i}"} for i in range(6)
    ]
    for h in history:
        save_message(ws, h["role"], h["content"])

    sess = make_session(client=mock_openai_client, context_window=10_000, max_tokens=1_000)
    sess._ws_id = ws
    sess.messages = turns_from_dicts(history)
    sess._msg_tokens = [1] * len(history)
    with patch.object(
        sess,
        "_summarize_blocks",
        return_value=_SummaryResult(text="DENSE SUMMARY", producer="summary-producer"),
    ):
        assert sess._compact_messages(auto=False) is True

    # Conversation continues after the compaction.
    save_message(ws, "user", "after compaction")

    # A fresh session reopens the workstream.
    sess2 = make_session(client=mock_openai_client, context_window=10_000, max_tokens=1_000)
    assert sess2.resume(ws) is True
    texts = [t.text for t in sess2.messages]

    assert texts[:2] == ["[Conversation summary]", "DENSE SUMMARY"]
    assert "after compaction" in texts
    assert not any(t.startswith("turn ") for t in texts)  # full history NOT reloaded


def test_marker_watermark_read_blip_recovers_on_retry(tmp_db, mock_openai_client):
    """Round-3 review pin: a transient watermark-read failure aborts that
    persist attempt — the journal classifies the marker row retrying with NO
    meta bytes memoized — so the healthy retry re-reads and commits WITH a
    watermark.  Memoizing the failed read as "absent" would durably commit a
    permanently checkpoint-less marker: full-history rehydration and an
    immediate re-compaction on every reopen."""
    from unittest.mock import patch

    from turnstone.core.memory import register_workstream, save_message
    from turnstone.core.storage._registry import get_storage

    ws = "wsBLIP"
    register_workstream(ws, user_id="u1", name="t")
    history = [
        {"role": "user" if i % 2 == 0 else "assistant", "content": f"turn {i}"} for i in range(6)
    ]
    for h in history:
        save_message(ws, h["role"], h["content"])

    sess = make_session(client=mock_openai_client, context_window=10_000, max_tokens=1_000)
    sess._ws_id = ws
    sess.messages = turns_from_dicts(history)
    sess._msg_tokens = [1] * len(history)

    st = get_storage()
    real_watermark = st.get_compaction_watermark
    reads: list[int] = []

    def _flaky_watermark(ws_id: str, preserve_tail: int = 0) -> int | None:
        reads.append(preserve_tail)
        if len(reads) == 1:
            raise RuntimeError("transient watermark blip")
        return real_watermark(ws_id, preserve_tail)

    from turnstone.core.session import ConversationPersistenceError

    with (
        patch.object(
            sess,
            "_summarize_blocks",
            return_value=_SummaryResult(text="DENSE SUMMARY", producer="summary-producer"),
        ),
        patch.object(st, "get_compaction_watermark", side_effect=_flaky_watermark),
    ):
        # The first persist attempt dies at the read and surfaces like any
        # initial durability failure; the in-memory compaction stays applied
        # and the marker row is retained in the journal, nothing durable yet.
        with pytest.raises(ConversationPersistenceError):
            sess._compact_messages(auto=False)
        assert sess.conversation_persistence_status()["state"] == "retrying"
        assert st.get_compaction_checkpoint(ws) is None
        sess._reconcile_pending_conversation_commits(_force_retry=True)

    assert sess.conversation_persistence_status()["state"] == "healthy"
    checkpoint = st.get_compaction_checkpoint(ws)
    assert checkpoint is not None
    assert checkpoint == real_watermark(ws, 0)


def test_compaction_summary_producer_survives_storage_round_trip(
    storage_backend, mock_openai_client
):
    """Final summary producer and model provenance are durable metadata.

    A compaction marker has no provider-native payload, so its producer belongs
    in the marker's ``summary_producer`` meta field.  Checkpoint reconstruction
    maps that object to the summary Turn's ``meta.extra["source_meta"]`` while
    retaining the accepted model alias/backend/generation/principal tuple in
    the well-known provenance envelope.
    """
    st = storage_backend
    ws = _register(st, "ws-summary-producer")
    history = [
        {"role": "user" if i % 2 == 0 else "assistant", "content": f"turn {i}"} for i in range(6)
    ]
    for message in history:
        st.save_message(ws, message["role"], message["content"])

    sess = make_session(client=mock_openai_client, context_window=10_000, max_tokens=1_000)
    sess._ws_id = ws
    sess.messages = turns_from_dicts(history)
    sess._msg_tokens = [1] * len(history)
    provenance = TurnProvenance(
        model_alias="summary-alias",
        backend_model_id="summary-kernel",
        registry_generation=12,
        acting_principal_id="user-alice",
    )
    with pytest.MonkeyPatch.context() as monkeypatch:
        monkeypatch.setattr(
            sess,
            "_summarize_blocks",
            lambda *_args, **_kwargs: _SummaryResult(
                text="DENSE SUMMARY",
                producer="final-summary-producer",
                provenance=provenance,
            ),
        )
        assert sess._compact_messages(auto=False) is True

    marker = next(
        message
        for message in st.load_messages(ws, include_compaction=True)
        if message.get("_source") == "compaction"
    )
    assert marker["_source_meta"]["summary_producer"] == "final-summary-producer"
    assert "_provenance" not in marker
    assert "user-alice" not in json.dumps(marker)

    loaded = st.load_message_turns(ws)
    assert [turn.text for turn in loaded[:2]] == ["[Conversation summary]", "DENSE SUMMARY"]
    assert "source_meta" not in loaded[0].meta.extra
    assert loaded[1].meta.extra["source_meta"]["summary_producer"] == "final-summary-producer"
    assert loaded[1].meta.extra[PROVENANCE_META_KEY] == provenance.to_meta()
    fork_row, _attachment_ids = _fork_turn_insert_row(
        loaded[1],
        "compaction-provenance-fork",
        "2026-08-09T00:00:00",
    )
    fork_meta = json.loads(fork_row["meta"])
    assert fork_meta["summary_producer"] == "final-summary-producer"
    assert fork_meta[PROVENANCE_META_KEY] == provenance.to_meta()

    reopened = make_session(client=mock_openai_client, context_window=10_000, max_tokens=1_000)
    assert reopened.resume(ws) is True
    assert reopened.messages[1].text == "DENSE SUMMARY"
    assert (
        reopened.messages[1].meta.extra["source_meta"]["summary_producer"]
        == "final-summary-producer"
    )
    assert reopened.messages[1].meta.extra[PROVENANCE_META_KEY] == provenance.to_meta()


# ---------------------------------------------------------------------------
# Malformed / edge-case markers — the watermark guards and the empty tail
# ---------------------------------------------------------------------------


class TestMarkerEdges:
    @pytest.mark.parametrize(
        "meta",
        [
            json.dumps({"watermark": "5"}),  # non-int (string)
            json.dumps({"watermark": True}),  # bool — True is an int subclass
            json.dumps({}),  # key absent
            json.dumps({"watermark": None}),  # null
        ],
    )
    def test_non_int_watermark_falls_back_to_full_history(self, storage_backend, meta):
        # A watermark that isn't a real int must NOT slice (a True watermark
        # would otherwise cut at id 1 and drop real history).
        st = storage_backend
        ws = _register(st)
        st.save_message(ws, "user", "a")
        st.save_message(ws, "assistant", "b")
        st.save_message(ws, "assistant", "SUMMARY", source="compaction", meta=meta)
        st.save_message(ws, "user", "c")
        texts = [t.text for t in st.load_message_turns(ws)]
        assert "a" in texts and "b" in texts and "c" in texts  # nothing sliced away
        # ...and the malformed marker is DROPPED, not leaked as a stray summary turn.
        assert "SUMMARY" not in texts

    def test_marker_as_final_row_yields_empty_tail(self, storage_backend):
        # watermark == max id, marker is the last row → resume is just the summary.
        st = storage_backend
        ws = _register(st)
        for i in range(3):
            st.save_message(ws, "user", f"old{i}")
        wm = st.get_compaction_watermark(ws, 0)
        st.save_message(ws, "assistant", "SUMMARY", source="compaction", meta=_marker_meta(wm))
        assert [t.text for t in st.load_message_turns(ws)] == ["[Conversation summary]", "SUMMARY"]


# ---------------------------------------------------------------------------
# checkpointed=False — export/audit gets the FULL transcript (markers dropped)
# ---------------------------------------------------------------------------


class TestFullHistoryLoad:
    def test_checkpointed_false_returns_full_history_without_marker(self, storage_backend):
        st = storage_backend
        ws = _register(st)
        for i in range(4):
            st.save_message(ws, "user" if i % 2 == 0 else "assistant", f"old{i}")
        wm = st.get_compaction_watermark(ws, 0)
        st.save_message(ws, "assistant", "SUMMARY", source="compaction", meta=_marker_meta(wm))
        st.save_message(ws, "user", "after")

        # Resume (default) is bounded; export (checkpointed=False) is full + marker-free.
        assert [t.text for t in st.load_message_turns(ws)] == [
            "[Conversation summary]",
            "SUMMARY",
            "after",
        ]
        full = [t.text for t in st.load_message_turns(ws, checkpointed=False)]
        assert full == ["old0", "old1", "old2", "old3", "after"]
        assert "SUMMARY" not in full and "[Conversation summary]" not in full


# ---------------------------------------------------------------------------
# search — compaction markers stay out of search results
# ---------------------------------------------------------------------------


class TestSearchExclusion:
    def test_search_history_excludes_markers(self, storage_backend):
        st = storage_backend
        ws = _register(st)
        st.save_message(ws, "user", "findme apple")
        st.save_message(
            ws,
            "assistant",
            "findme SUMMARY banana",
            source="compaction",
            meta=_marker_meta(st.get_compaction_watermark(ws, 0)),
        )
        contents = [r[3] for r in st.search_history("findme")]
        assert any("apple" in (c or "") for c in contents)  # real row matched
        assert not any("SUMMARY" in (c or "") for c in contents)  # marker excluded
        # ...and normal rows (whose _source is NULL) are NOT dropped by the filter.
        assert contents

    def test_search_history_recent_excludes_markers(self, storage_backend):
        st = storage_backend
        ws = _register(st)
        st.save_message(ws, "user", "real")
        st.save_message(
            ws,
            "assistant",
            "SUMMARY",
            source="compaction",
            meta=_marker_meta(st.get_compaction_watermark(ws, 0)),
        )
        recent = [r[3] for r in st.search_history_recent(10)]
        assert "real" in recent and "SUMMARY" not in recent


# ---------------------------------------------------------------------------
# rewind / retry — compaction-safe truncation (never delete the summary backing)
# ---------------------------------------------------------------------------


class TestCompactionFloor:
    def test_floor_and_count(self, storage_backend):
        st = storage_backend
        ws = _register(st)
        for i in range(3):
            st.save_message(ws, "user", f"old{i}")  # summarized prefix
        wm = st.get_compaction_watermark(ws, 0)
        st.save_message(ws, "assistant", "SUMMARY", source="compaction", meta=_marker_meta(wm))
        st.save_message(ws, "user", "tail1")
        st.save_message(ws, "assistant", "tail2")
        assert st.get_compaction_floor(ws) == 4  # 3 prefix + 1 marker
        assert st.count_messages(ws) == 6

    def test_floor_zero_without_marker(self, storage_backend):
        st = storage_backend
        ws = _register(st)
        st.save_message(ws, "user", "x")
        assert st.get_compaction_floor(ws) == 0


def test_rewind_after_compaction_never_deletes_summary_backing(tmp_db, mock_openai_client):
    """The review's major rewind finding: after a compaction, a tail-trim must
    delete from the storage TAIL and floor at the marker, not keep the oldest
    summarized rows and drop the marker."""
    from turnstone.core.memory import get_storage, register_workstream, save_message

    ws = "wsRW"
    register_workstream(ws, user_id="u1", name="t")
    for i in range(3):
        save_message(ws, "user", f"old{i}")  # prefix
    st = get_storage()
    wm = st.get_compaction_watermark(ws, 0)
    save_message(
        ws, "assistant", "SUMMARY", source="compaction", meta=json.dumps({"watermark": wm})
    )
    save_message(ws, "user", "q1")  # tail
    save_message(ws, "assistant", "a1")  # tail
    assert st.get_compaction_floor(ws) == 4 and st.count_messages(ws) == 6

    sess = make_session(client=mock_openai_client, context_window=10_000, max_tokens=1_000)
    sess._ws_id = ws

    # Trim one tail turn → keep = max(floor 4, total 6 - 1) = 5 → deletes only "a1".
    sess._persist_truncation(1)
    assert st.count_messages(ws) == 5
    survived = [t.text for t in st.load_message_turns(ws)]
    assert survived[:2] == ["[Conversation summary]", "SUMMARY"]  # marker + prefix intact
    assert "q1" in survived

    # Over-deep trim → clamps at the floor; the marker + prefix still survive.
    sess._persist_truncation(100)
    assert st.count_messages(ws) == 4  # floored at prefix + marker
    after = [t.text for t in st.load_message_turns(ws)]
    assert after == ["[Conversation summary]", "SUMMARY"]  # summary backing never deleted


def test_persist_truncation_uncompacted_matches_plain_tail_delete(tmp_db, mock_openai_client):
    """With no compaction (floor 0), the new path is identical to the old
    keep=len(self.messages) tail delete."""
    from turnstone.core.memory import get_storage, register_workstream, save_message

    ws = "wsPlain"
    register_workstream(ws, user_id="u1", name="t")
    for i in range(5):
        save_message(ws, "user", f"m{i}")
    st = get_storage()
    assert st.get_compaction_floor(ws) == 0

    sess = make_session(client=mock_openai_client, context_window=10_000, max_tokens=1_000)
    sess._ws_id = ws
    sess._persist_truncation(2)  # remove the last 2
    assert st.count_messages(ws) == 3


def test_persist_truncation_propagates_atomic_storage_failure(tmp_db, mock_openai_client):
    """The strict backend error must reach the failure-atomic session caller."""
    from unittest.mock import patch

    import pytest

    from turnstone.core.memory import get_storage, register_workstream, save_message

    ws = "wsCnt"
    register_workstream(ws, user_id="u1", name="t")
    for i in range(4):
        save_message(ws, "user", f"m{i}")
    st = get_storage()
    sess = make_session(client=mock_openai_client)
    sess._ws_id = ws
    with (
        patch.object(
            st,
            "truncate_messages_tail",
            side_effect=RuntimeError("injected atomic truncation failure"),
        ),
        pytest.raises(RuntimeError, match="injected atomic truncation failure"),
    ):
        sess._persist_truncation(2)
    assert st.count_messages(ws) == 4  # nothing deleted


def test_persist_truncation_zero_is_a_storage_noop(tmp_db, mock_openai_client):
    """A no-op plan never opens the strict backend transaction."""
    from unittest.mock import patch

    from turnstone.core.memory import get_storage, register_workstream

    ws = "wsFloor"
    register_workstream(ws, user_id="u1", name="t")
    st = get_storage()
    sess = make_session(client=mock_openai_client)
    sess._ws_id = ws
    with patch.object(st, "truncate_messages_tail") as truncate:
        assert sess._persist_truncation(0) == 0
    truncate.assert_not_called()


def test_watermark_reads_inside_the_marker_persist_not_before_the_commit(
    tmp_db, mock_openai_client
):
    """The boundary is cut in the ordered durable batch, at persist time.

    A pre-commit snapshot can undercount the durable prefix whenever accepted
    rows are still pending in the journal when compaction is admitted (they
    land, FIFO, before the marker's persist executes). Reading inside the
    persist closure names exactly the summarized prefix; memoization keeps a
    keyed lost-ACK retry byte-identical.
    """
    from unittest.mock import patch

    from turnstone.core.memory import register_workstream, save_message
    from turnstone.core.storage._registry import get_storage

    ws = "wsWatermarkOrder"
    register_workstream(ws, user_id="u1", name="t")
    history = [
        {"role": "user" if i % 2 == 0 else "assistant", "content": f"turn {i}"} for i in range(6)
    ]
    for h in history:
        save_message(ws, h["role"], h["content"])

    sess = make_session(client=mock_openai_client, context_window=10_000, max_tokens=1_000)
    sess._ws_id = ws
    sess.messages = turns_from_dicts(history)
    sess._msg_tokens = [1] * len(history)

    order: list[str] = []
    real_journal = sess._journal_conversation_row_locked
    # The persist closure reads the backend directly (bypassing the memory
    # wrapper's error-to-None coercion), so the spy sits on the storage method.
    st = get_storage()
    real_watermark = st.get_compaction_watermark

    def _journal_spy(**kwargs):
        order.append("journal")
        return real_journal(**kwargs)

    def _watermark_spy(ws_id, preserve_tail=0):
        order.append("watermark")
        return real_watermark(ws_id, preserve_tail)

    with (
        patch.object(sess, "_journal_conversation_row_locked", side_effect=_journal_spy),
        patch.object(st, "get_compaction_watermark", side_effect=_watermark_spy),
        patch.object(
            sess,
            "_summarize_blocks",
            return_value=_SummaryResult(text="DENSE SUMMARY", producer="summary-producer"),
        ),
    ):
        assert sess._compact_messages(auto=False) is True

    assert order == ["journal", "watermark"], order

    # The durable marker's boundary covers every row persisted before it.
    from turnstone.core.storage import get_storage

    rows = get_storage().load_messages(ws, repair=False, include_compaction=True)
    marker = next(r for r in rows if r.get("_source") == "compaction")
    watermark = (marker.get("_source_meta") or {}).get("watermark")
    plain_ids = [r["id"] for r in rows if r.get("_source") != "compaction" if "id" in r]
    assert isinstance(watermark, int)
    if plain_ids:
        assert watermark >= max(plain_ids)