행은 재생에서 빠질 뿐, 기록에선 안 빠져

now = datetime.now(timezone.utc).isoformat()
removed = set(remove_ids)
kept_ids = {m.id for m in to_keep}

# Out of the replay, never out of the record (coop #351): the rows
# stay in ``messages``, flagged, so keys and pointers still find
# them and a conversation delete still takes them with it.
cursor = await db.execute(
    f"SELECT id, created_at FROM messages WHERE id IN ({placeholders})", remove_ids,
)
archived = [{"id": row[0], "created_at": row[1]} for row in await cursor.fetchall()]
await db.execute(
    f"UPDATE messages SET compacted_at = ?, compacted_by = ? WHERE id IN ({placeholders}) AND compacted_at IS NULL",
    (now, summary_id, *remove_ids),
)
# ... the summary row is inserted just before the first kept turn,
# and every kept row whose parent left is re-parented onto it.

clauses: list[dict] = []
if exclude_conversation_id:
    # The current conversation's replay is already in the prompt; its
    # compacted rows are not (coop #351), so they stay retrievable. A
    # conversation that never ends (Master Chief) recalls its own past.
    clauses.append({"$or": [
        {"conversation_id": {"$ne": exclude_conversation_id}},
        {"compacted": True},
    ]})

# A minimal sketch: compaction that flags rows out of the replay, against
# the first version's delete. Same rows, same retry key, two outcomes.
import sqlite3


def build() -> sqlite3.Connection:
    db = sqlite3.connect(":memory:")
    db.execute("CREATE TABLE messages (id TEXT PRIMARY KEY, seq REAL, role TEXT, content TEXT,"
               " external_request_id TEXT, compacted_at TEXT, compacted_by TEXT)")
    for i in range(6):
        db.execute("INSERT INTO messages VALUES (?, ?, ?, ?, ?, NULL, NULL)",
                   (f"m{i}", i, "user" if i % 2 == 0 else "assistant", f"turn {i}",
                    f"phone-{i}" if i % 2 == 0 else None))
    return db


def compact(db: sqlite3.Connection, old: list[str], *, delete: bool) -> None:
    marks = ",".join("?" * len(old))
    if delete:  # the first version: archived elsewhere, gone from messages
        db.execute(f"DELETE FROM messages WHERE id IN ({marks})", old)
    else:       # rows leave the replay, never the record
        db.execute(f"UPDATE messages SET compacted_at = 'now', compacted_by = 's1'"
                   f" WHERE id IN ({marks})", old)
    # The summary sorts just before the first kept row.
    db.execute("INSERT INTO messages VALUES ('s1', 3.5, 'assistant', '[summary of m0..m3]', NULL, NULL, NULL)")


for delete in (True, False):
    db = build()
    compact(db, ["m0", "m1", "m2", "m3"], delete=delete)
    replay = [r[0] for r in db.execute("SELECT id FROM messages WHERE compacted_at IS NULL ORDER BY seq")]
    retry = db.execute("SELECT id FROM messages WHERE external_request_id = 'phone-0'").fetchone()
    page = [r[0] for r in db.execute(
        "SELECT id FROM messages WHERE content NOT LIKE '[summary%' ORDER BY seq")]
    print("DELETE" if delete else "FLAG  ", "| replay:", replay,
          "| retry key phone-0 finds:", retry[0] if retry else "nothing, so 'may be sent'",
          "| page:", page)