Function derive_session_id_v2

uncommon_route/session.py:125–174

Robust session id derivation. Priority: 1. previous_response_id chain hit (OpenAI Responses) 2. msg_hashes strict-prefix match in registry 3. fresh id seeded by (first_user_v2, system_hash, metadata_uid, now) `now` is included in the fresh-id seed so two parallel conversa

(
    *,
    msg_hashes: list[str],
    first_user_v2: str,
    system_hash: str,
    metadata_uid: str,
    prev_response: str,
    registry: RecentSessions,
    now: float,
)

def derive_session_id_v2(
    *,
    msg_hashes: list[str],
    first_user_v2: str,
    system_hash: str,
    metadata_uid: str,
    prev_response: str,
    registry: RecentSessions,
    now: float,
) -> str:
    """Robust session id derivation.

    Priority:
      1. previous_response_id chain hit (OpenAI Responses)
      2. msg_hashes strict-prefix match in registry
      3. fresh id seeded by (first_user_v2, system_hash, metadata_uid, now)

    `now` is included in the fresh-id seed so two parallel conversations
    starting with identical first messages still get distinct ids.
    """
    hashes = tuple(msg_hashes)

    # Eagerly evict stale records before any lookup so TTL is respected.
    registry.evict_expired(now)

    # 1. Response-chain rescue.
    if prev_response:
        chained = registry.find_by_response_id(prev_response)
        if chained is not None and chained in registry._records:
            rec = registry._records[chained]
            rec.msg_hashes = hashes
            rec.last_seen_ts = now
            registry.upsert(rec)
            return chained

    # 2. Prefix match.
    match = registry.find_prefix_match(hashes)
    if match is not None:
        match.msg_hashes = hashes
        match.last_seen_ts = now
        registry.upsert(match)
        return match.session_id

    # 3. Fresh id.
    seed = f"{first_user_v2}|{system_hash}|{metadata_uid}".encode("utf-8")
    new_sid = hashlib.sha256(seed + str(now).encode("utf-8")).hexdigest()[:8]
    registry.upsert(
        _SessionRecord(session_id=new_sid, msg_hashes=hashes, last_seen_ts=now)
    )
    return new_sid