freenet 0.2.116

//! UPDATE operation: applies a state change to a contract and
//! broadcasts to subscribers.
//!
//! Every UPDATE wire variant dispatches to a driver —
//! `op_ctx_task::start_client_update`, `start_relay_request_update`,
//! `start_relay_broadcast_to`, `start_relay_request_update_streaming`,
//! and `start_relay_broadcast_to_streaming`. The wire-format types,
//! `BroadcastDedupCache`, `update_contract`, the log helpers, and
//! the post-merge propagation helpers survive here because the
//! drivers consume them.

pub(crate) mod op_ctx_task;
pub(crate) mod pending_broadcast;
pub(crate) mod propagation_stats;

use freenet_stdlib::prelude::*;

pub(crate) use self::messages::{BroadcastStreamingPayload, UpdateMsg, UpdateStreamingPayload};
use super::OpError;
use crate::contract::{ContractHandlerEvent, ExecutorError, StoreResponse};
use crate::message::{NodeEvent, Transaction};
use crate::node::OpManager;
use crate::ring::PeerKeyLocation;
use crate::transport::TransportPublicKey;
use std::collections::{HashSet, VecDeque};
use std::net::SocketAddr;

use dashmap::DashMap;
use tokio::time::Instant;

/// Cache for deduplicating broadcast payloads.
///
/// When the same delta/state is broadcast to us by multiple peers (which is
/// expected in the gossip topology), we skip the expensive WASM merge call
/// for duplicates. Uses ahash for fast hashing of payload bytes.
pub(crate) struct BroadcastDedupCache {
    /// Per-contract dedup entries, newest at back.
    entries: DashMap<ContractKey, VecDeque<DedupEntry>>,
}

struct DedupEntry {
    delta_hash: u64,
    inserted_at: Instant,
}

/// Maximum entries per contract in the dedup cache.
const DEDUP_MAX_ENTRIES_PER_CONTRACT: usize = 64;

/// TTL for dedup entries — entries older than this are evicted.
const DEDUP_TTL: std::time::Duration = std::time::Duration::from_secs(60);

impl BroadcastDedupCache {
    pub fn new() -> Self {
        Self {
            entries: DashMap::new(),
        }
    }

    /// Check if this payload was already seen for this contract.
    /// If not, insert it and return `false` (not a duplicate).
    /// If yes, return `true` (duplicate — skip processing).
    ///
    /// `is_delta` distinguishes delta payloads from full state payloads so they
    /// don't collide in the hash space (a delta and full state could have the
    /// same bytes but represent different semantic operations).
    ///
    /// Note: Uses non-cryptographic ahash for speed. A hash collision would
    /// cause a legitimate update to be silently skipped, but the gossip
    /// protocol will deliver the data via another peer eventually.
    pub fn check_and_insert(
        &self,
        key: &ContractKey,
        payload_bytes: &[u8],
        is_delta: bool,
        now: Instant,
    ) -> bool {
        use ahash::AHasher;
        use std::hash::Hasher;

        let mut hasher = AHasher::default();
        // Include payload type discriminant to avoid delta/full-state collisions
        hasher.write_u8(if is_delta { 1 } else { 0 });
        hasher.write(payload_bytes);
        let delta_hash = hasher.finish();

        let mut entry = self.entries.entry(*key).or_default();
        let queue = entry.value_mut();

        // Evict expired entries from the front
        while let Some(front) = queue.front() {
            if now.duration_since(front.inserted_at) > DEDUP_TTL {
                queue.pop_front();
            } else {
                break;
            }
        }

        // Check if hash already exists
        if queue.iter().any(|e| e.delta_hash == delta_hash) {
            return true; // Duplicate
        }

        // Evict oldest if at capacity
        while queue.len() >= DEDUP_MAX_ENTRIES_PER_CONTRACT {
            queue.pop_front();
        }

        queue.push_back(DedupEntry {
            delta_hash,
            inserted_at: now,
        });

        false // Not a duplicate
    }
}

/// Result of `get_broadcast_targets_update()` with skip-reason counters
/// for broadcast delivery diagnostics (issue #3046).
pub(crate) struct BroadcastTargetResult {
    pub targets: Vec<PeerKeyLocation>,
    pub proximity_found: usize,
    pub proximity_resolve_failed: usize,
    /// Interest-manager (Source-2) fan-out was removed in #4642 step 9, so
    /// these are always 0. They are retained for telemetry-schema continuity:
    /// the #4281 propagation-stats window (`propagation_stats.rs`) and the
    /// #3046 broadcast-delivery event (`tracing::register`) still carry them.
    /// See `get_broadcast_targets_update`'s rustdoc.
    pub interest_found: usize,
    pub interest_resolve_failed: usize,
    pub skipped_self: usize,
    pub skipped_sender: usize,
}

/// Result of [`update_contract`]: the merged state and whether it changed.
///
/// Deliberately carries NO summary (#4923): an earlier version bundled
/// `StateSummary::from(<state bytes>)` here — the state relabeled as a
/// summary — which `send_proactive_summary_notification` then broadcast,
/// poisoning every receiver's delta-efficiency gate into permanent
/// full-state fallbacks. The consumers that genuinely need a summary (the
/// two client-facing `UpdateResponse` sites in `drive_client_update`) fetch
/// the contract's real one via [`contract_summary_or_empty`] themselves, so
/// the relay/no-change hot paths pay zero extra contract-handler
/// round-trips. Pinned by
/// `update_contract_never_builds_a_summary_from_state_bytes`.
pub(crate) struct UpdateExecution {
    pub(crate) value: WrappedState,
    pub(crate) changed: bool,
}

/// Cooldown before retrying a self-healing contract fetch, in milliseconds.
/// 5 minutes: long enough to avoid hammering peers if the contract genuinely
/// doesn't exist, short enough to recover within a session if there was a
/// transient routing failure.
pub(crate) const CONTRACT_FETCH_COOLDOWN_MS: u64 = 300_000;

/// Why a `try_auto_fetch_contract` call was made — decides whether the
/// phantom-interest gate applies.
///
/// The auto-fetch helper is reached from two kinds of site, and only one of
/// them is the #4473 churn:
///
/// * [`AutoFetchReason::Originator`] — a *local client* submitted an UPDATE for
///   a contract whose code/params we lack, and the driver is self-healing so
///   the client's retry can succeed (the `phase = "auto_fetch_originator"`
///   site). This is demand-driven: a real client is waiting on it, exactly
///   like a subscribe-driven fetch, so it must NOT be gated even when no
///   subscription exists yet (a one-shot updater need not be subscribed).
///   Suppressing it would strand the client's UPDATE behind a contract that
///   never gets fetched (Codex review on PR #4489).
/// * [`AutoFetchReason::InboundRelay`] — an *inbound* relayed UPDATE / broadcast
///   failed its merge because we lack the contract. A node carrying phantom
///   interest (the #4404 placement-migration after-effect) hits this on every
///   such message and would spawn a `fetch_contract` sub-op for state nothing
///   on this node depends on — the residual #4473 churn. This is the path the
///   `contract_in_use` gate suppresses.
#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub(crate) enum AutoFetchReason {
    /// Local-client UPDATE self-heal — demand-driven, never gated.
    Originator,
    /// Inbound relay/broadcast self-heal — gated on `contract_in_use`.
    InboundRelay,
}

impl OpManager {
    /// Trigger a background GET when an UPDATE broadcast fails because the node
    /// doesn't have the contract's parameters (code + params). This self-heals
    /// the node by fetching the contract directly from the UPDATE sender, who
    /// is known to have the contract.
    ///
    /// For [`AutoFetchReason::InboundRelay`] calls this is gated to contracts we
    /// actually have a reason to hold: skipped unless a local client or a
    /// downstream peer is subscribed (`contract_in_use`).
    /// [`AutoFetchReason::Originator`] calls are demand-driven (a local client
    /// is waiting on the retry) and bypass the gate.
    /// Rate-limited: at most one fetch attempt per contract per 5 minutes.
    pub(crate) fn try_auto_fetch_contract(
        &self,
        key: &ContractKey,
        sender_addr: SocketAddr,
        reason: AutoFetchReason,
    ) {
        use crate::config::GlobalSimulationTime;

        let instance_id = *key.id();

        // Don't self-heal-fetch a contract nothing on this node depends on —
        // but ONLY for inbound relay/broadcast self-heal, never for the
        // originator path (see `AutoFetchReason`). An inbound UPDATE/broadcast
        // for a contract we carry only phantom interest in (e.g. the #4404
        // placement migration left stale interest with no subscriber) reaches
        // this path and would spawn a sub-op GET — a `fetch_contract` span
        // burst against state we have no client or downstream subscriber to
        // serve. The existing 5-minute cooldown only *throttles* that to one
        // burst per contract per window; gating on `contract_in_use` (a live
        // local-client subscription or a downstream peer subscriber) stops it
        // at the source. This is the fetch-path analogue of the #4475 / #4482
        // `is_hosting_contract || contract_in_use` summarize gates. We
        // intentionally do NOT also accept `is_hosting_contract` here: on this
        // path the merge already failed because we lack the contract, so
        // hosting is moot; nor a bare upstream network subscription, which
        // `contract_in_use` deliberately excludes (an orphaned upstream sub
        // renews its lease unboundedly and is meant to be torn down, not kept
        // alive by self-heal fetches — see `HostingManager::contract_in_use`).
        // A contract that gains a real local client or downstream subscriber
        // becomes `contract_in_use` and its next inbound UPDATE re-arms this
        // fetch.
        if reason == AutoFetchReason::InboundRelay && !self.ring.contract_in_use(key) {
            tracing::debug!(
                contract = %key,
                sender = %sender_addr,
                "Skipping inbound-relay auto-fetch: no local client or downstream \
                 subscriber depends on this contract (phantom interest)"
            );
            return;
        }

        let now_ms = GlobalSimulationTime::read_time_ms();

        // Atomic rate-limit: try to insert a new entry. If one exists and hasn't
        // expired, bail out. Uses entry API to avoid TOCTOU between check and insert.
        {
            use dashmap::mapref::entry::Entry;
            match self.pending_contract_fetches.entry(instance_id) {
                Entry::Occupied(mut existing) => {
                    let elapsed_ms = now_ms.saturating_sub(*existing.get());
                    if elapsed_ms < CONTRACT_FETCH_COOLDOWN_MS {
                        return; // Still in cooldown
                    }
                    // Cooldown expired — update timestamp while still holding the lock
                    *existing.get_mut() = now_ms;
                }
                Entry::Vacant(slot) => {
                    slot.insert(now_ms);
                }
            }
        }

        // Look up the sender's PeerKeyLocation so we can target them directly
        let sender_pkl = match self.ring.connection_manager.get_peer_by_addr(sender_addr) {
            Some(pkl) => pkl,
            None => {
                tracing::debug!(
                    contract = %key,
                    sender = %sender_addr,
                    "Cannot auto-fetch: UPDATE sender not found in connection manager"
                );
                self.pending_contract_fetches.remove(&instance_id);
                return;
            }
        };

        tracing::info!(
            contract = %key,
            sender = %sender_addr,
            "Auto-fetching contract from UPDATE sender (missing parameters)"
        );

        // Spawn a targeted driver GET. The driver targets `sender_pkl`
        // for its first hop and falls back to `k_closest_potentially_hosting`
        // for any retries. Fire-and-forget — the side effect (contract cached
        // locally via `cache_contract_locally`) is what callers depend on.
        // Outcome is logged inside the driver.
        let _tx = super::get::op_ctx_task::start_targeted_sub_op_get(self, instance_id, sender_pkl);
    }

    /// The advertised co-hosts of a contract: peers that announced, via the
    /// advertisement layer, that they host it.
    ///
    /// SINGLE SOURCE OF TRUTH for that population, deliberately shared by the
    /// two call sites that must agree on it:
    ///
    /// - [`OpManager::get_broadcast_targets_update`], which broadcasts the
    ///   state (carrying our summary in `sender_summary_bytes`) TO them, and
    /// - [`send_proactive_summary_notification`], which EXCLUDES them from the
    ///   standalone `Summaries` fan-out precisely because that broadcast
    ///   already carried the summary (#4965).
    ///
    /// The exclusion is only sound while the excluded set is a subset of the
    /// broadcast target set. If the two sites read different sources, or one
    /// narrows its set and the other does not, the notification over-excludes:
    /// a peer gets neither the broadcast nor the standalone summary, and every
    /// unit test stays green because each site is individually correct. Sharing
    /// the source is what makes a future narrowing apply to both.
    ///
    /// **If you add a filter, add it HERE, not at a call site.** That coupling
    /// is the point of this function, and it is pinned by
    /// `cohost_source_is_shared_between_broadcast_and_notification`.
    pub(crate) fn advertised_cohost_pub_keys(&self, key: &ContractKey) -> Vec<TransportPublicKey> {
        self.neighbor_hosting.neighbors_with_contract(key)
    }

    /// Resolve the set of peers to broadcast a state update to.
    ///
    /// Targets are the advertised co-hosts from the proximity neighbor cache
    /// (peers who announced, via the advertisement layer, that they host this
    /// contract). Skips the sender (to avoid echo) and this node (unless we are
    /// the local originator). Returns skip-reason counters alongside the
    /// resolved targets for broadcast delivery diagnostics (issue #3046).
    ///
    /// ## Source-1-only live fan-out (#4642 step 9)
    ///
    /// This previously unioned a second source: the interest manager's
    /// `get_interested_peers` (peers who registered interest via the protocol).
    /// That arm was removed. Live fan-out is now advertised-co-hosts-only.
    ///
    /// Removing it does NOT drop a subscriber's update, because a genuine
    /// subscriber never persists in the "interested but no local state" condition
    /// that arm used to cover:
    ///
    /// 1. A subscriber seeds its own baseline state via its subscribe-GET before
    ///    the subscription is finalized. `finalize_originator_subscribe`
    ///    (`subscribe.rs`) awaits `fetch_contract_if_missing` (which drives a
    ///    sub-op GET) and only returns success once current state, including any
    ///    already-committed UPDATE, is stored locally. So no real subscriber is
    ///    left relying on a live fan-out for its first copy of the state. Pinned
    ///    by `subscribe_seeds_state_via_get_before_finalize` (`subscribe.rs`).
    /// 2. Once it holds state it advertises (`announce_contract_hosted`), which
    ///    makes it a Source-1 target for later live fan-out AND gives it a
    ///    non-empty state summary. From then on the summary-based InterestSync
    ///    anti-entropy (`node.rs` Summaries -> `SyncStateToPeer`) and the
    ///    advertisement-reconciliation exchange keep it fresh if it ever misses a
    ///    live update: the ~5-min `ring.rs::interest_heartbeat` sends each
    ///    neighbor a `HostingStateRequest`, the neighbor replies with a
    ///    `HostingStateResponse` snapshot of its hosted set, and we full-replace
    ///    that into our Source-1 view (#4722).
    ///
    /// The summary-based anti-entropy path deliberately does NOT heal a peer with
    /// no state: a `None` summary is skipped by the `zip` staleness gate in
    /// `node.rs`. That is exactly why the subscribe-GET seeding in (1), not the
    /// heartbeat, is the load-bearing safety property. See
    /// `.claude/rules/hosting-invariants.md` invariant 1 and
    /// `docs/design/demand-driven-hosting.md`.
    ///
    /// `InterestManager` itself is retained: it still drives proactive summary
    /// notifications (`send_proactive_summary_notification`), interest-heartbeat
    /// TTL refresh, and eviction demand-counting. Only the state fan-out arm was
    /// removed here.
    pub(crate) fn get_broadcast_targets_update(
        &self,
        key: &ContractKey,
        sender: &SocketAddr,
    ) -> BroadcastTargetResult {
        use std::collections::HashSet;

        let self_addr = self.ring.connection_manager.get_own_addr();
        let is_local_update_initiator = self_addr.as_ref().map(|me| me == sender).unwrap_or(false);

        let mut targets: HashSet<PeerKeyLocation> = HashSet::new();
        let mut proximity_resolve_failed: usize = 0;
        let mut skipped_self: usize = 0;
        let mut skipped_sender: usize = 0;

        // Source 1 (the ONLY live fan-out source): the proximity cache of
        // advertised co-hosts — peers who announced they host this contract via
        // the advertisement layer. The former interest-manager arm (Source 2)
        // was removed in #4642 step 9; see this function's rustdoc.
        //
        // Read through `advertised_cohost_pub_keys` rather than
        // `neighbor_hosting` directly: `send_proactive_summary_notification`
        // EXCLUDES this same set, and the shared accessor is what keeps a
        // future narrowing from over-excluding there. See its rustdoc.
        let proximity_pub_keys = self.advertised_cohost_pub_keys(key);
        let proximity_found = proximity_pub_keys.len();

        for pub_key in proximity_pub_keys {
            if let Some(pkl) = self.ring.connection_manager.get_peer_by_pub_key(&pub_key) {
                if let Some(pkl_addr) = pkl.socket_addr() {
                    if &pkl_addr == sender && !is_local_update_initiator {
                        skipped_sender += 1;
                        continue;
                    }
                    if !is_local_update_initiator && self_addr.as_ref() == Some(&pkl_addr) {
                        skipped_self += 1;
                        continue;
                    }
                }
                targets.insert(pkl);
            } else {
                proximity_resolve_failed += 1;
                // Stale proximity-cache entry (#4756): the neighbor announced it
                // seeds this contract but is no longer in the connection manager.
                // Disconnect teardown prunes the ring connection (keyed by addr)
                // but several paths leave this proximity entry (keyed by pub_key)
                // behind; with no TTL it would WARN on every UPDATE forever.
                // Self-heal at the detection point: reap the disconnected
                // neighbor's proximity state so it fires at most once and then
                // disappears. A reconnecting peer re-announces via the on-connect
                // HostingStateRequest exchange and the periodic full-set
                // re-request, so no fan-out is permanently lost. Demote the
                // per-miss log to DEBUG (mirroring the interest arm below); the
                // aggregate counter (proximity_resolve_failed) still feeds the
                // summary log.
                self.neighbor_hosting.on_peer_disconnected(&pub_key);
                tracing::debug!(
                    contract = %format!("{:.8}", key),
                    proximity_neighbor = %pub_key,
                    is_local = is_local_update_initiator,
                    phase = "target_lookup_failed",
                    "Proximity cache neighbor not found in connection manager; reaped stale entry"
                );
            }
        }

        // Source 2 (interest manager) REMOVED in #4642 step 9. Do NOT re-add a
        // fan-out arm here that unions `interest_manager.get_interested_peers`.
        // A genuine subscriber does not stay "interested but stateless": it seeds
        // baseline state via its own subscribe-GET before finalizing
        // (`finalize_originator_subscribe`), then advertises and becomes a
        // Source-1 target. See this function's rustdoc and
        // `.claude/rules/hosting-invariants.md` invariant 1.

        let mut result: Vec<PeerKeyLocation> = targets.into_iter().collect();
        result.sort();

        if !result.is_empty() {
            tracing::debug!(
                contract = %format!("{:.8}", key),
                peer_addr = %sender,
                targets = %result
                    .iter()
                    .filter_map(|s| s.socket_addr())
                    .map(|addr| format!("{:.8}", addr))
                    .collect::<Vec<_>>()
                    .join(","),
                count = result.len(),
                proximity_sources = proximity_found,
                phase = "broadcast",
                "UPDATE_PROPAGATION"
            );
        } else {
            // NO_TARGETS at DEBUG: this function is called up to 4
            // times per BroadcastStateChange (initial + 3 retries) so
            // per-attempt WARN amplifies 4x on stuck contracts. The
            // operator-actionable signal is the outer streak-suppressed
            // WARN in p2p_protoc.rs (grep for
            // "BROADCAST_NO_TARGETS: no targets found after"); the
            // per-attempt detail belongs in metrics/structured counters
            // (proximity_resolve_failed). Issue #4251 re-review M2.
            tracing::debug!(
                contract = %format!("{:.8}", key),
                peer_addr = %sender,
                self_addr = ?self_addr.map(|a| format!("{:.8}", a)),
                proximity_sources = proximity_found,
                proximity_resolve_failed,
                phase = "warning",
                "UPDATE_PROPAGATION: NO_TARGETS - update will not propagate further"
            );
        }

        BroadcastTargetResult {
            targets: result,
            proximity_found,
            proximity_resolve_failed,
            // Source-2 interest fan-out removed in #4642 step 9; kept at 0 for
            // telemetry-schema continuity (see the struct's field docs).
            interest_found: 0,
            interest_resolve_failed: 0,
            skipped_self,
            skipped_sender,
        }
    }
}

/// Logs the outcome of an `update_contract` failure with severity dependent on
/// whether the rejection is a benign stale-state rejection (INFO) or a real
/// failure (ERROR). See PR #3914.
///
/// The narrow predicate `is_invalid_update_rejection` matches the contract
/// WASM's typed "InvalidUpdate{,WithInfo}" rejection EXCLUSIVELY — OOG /
/// traps / timeouts stay at ERROR.
fn log_update_contract_failure(key: &ContractKey, err: &ExecutorError) {
    if err.is_invalid_update_rejection() {
        tracing::info!(
            contract = %key,
            error = %err,
            event = "merge_rejected_invalid_update",
            "Update rejected by contract: incoming state invalid (likely stale rebroadcast), keeping local"
        );
    } else if err.is_contract_queue_full() {
        // Issue #4251: transient backpressure, not operator-actionable. A
        // hot contract fires this hundreds of times/sec — DEBUG keeps real
        // failures visible at ERROR.
        tracing::debug!(
            contract = %key,
            error = %err,
            event = "queue_full",
            "Update skipped: per-contract queue saturated"
        );
    } else {
        tracing::error!(
            contract = %key,
            error = %err,
            phase = "error",
            "Failed to update contract value"
        );
    }
}

/// Logs the failure outcome of a `BroadcastToStreaming` relay attempt and
/// returns whether the caller should trigger a self-healing GET.
///
/// The two decisions (log severity, auto-fetch) use DIFFERENT predicates
/// because they answer different questions:
///
/// - Log severity uses `is_invalid_update_rejection` (narrow): only the
///   contract WASM's typed "invalid contract update" rejection counts as
///   benign. Out-of-gas, traps, timeouts stay at WARN even though the
///   contract code is present. Issue #4251 adds a third level: queue-full
///   logs at DEBUG (transient backpressure, not an operator-actionable
///   fault).
///
/// - Auto-fetch uses `is_contract_exec_rejection` (broad) AND
///   `!is_contract_queue_full` (issue #4251): any time the contract code
///   DID execute (whether successfully rejecting a stale state or running
///   out of gas), OR the contract's queue is just saturated, the code is
///   present locally and a self-heal GET would be wasted. Auto-fetch only
///   fires for failures where the contract is actually missing (e.g.,
///   missing parameters after restart, storage error).
///
/// Returning `true` means "fetch missing contract code"; returning `false`
/// means "contract is present (or queue saturated), skip auto-fetch".
///
/// Note: this helper takes `&OpError` while `log_update_contract_failure`
/// takes `&ExecutorError` because the two call sites have different error
/// types in scope (the streaming branch operates on the OpError already
/// produced by `update_contract`'s `Err(err.into())`).
pub(crate) fn log_broadcast_to_streaming_failure(
    tx: &Transaction,
    key: &ContractKey,
    err: &OpError,
) -> bool {
    if err.is_invalid_update_rejection() {
        tracing::info!(
            tx = %tx,
            %key,
            error = %err,
            event = "merge_rejected_invalid_update",
            "BroadcastToStreaming merge rejected: incoming state invalid (likely stale rebroadcast), keeping local"
        );
    } else if err.is_contract_queue_full() {
        // Issue #4251: transient backpressure. DEBUG (not WARN), and (via the
        // return value) skip the spurious auto-fetch GET.
        tracing::debug!(
            tx = %tx,
            %key,
            error = %err,
            event = "queue_full",
            "BroadcastToStreaming update skipped: per-contract queue saturated"
        );
    } else if err.is_scheduler_timeout() {
        // #4864 round-7: the merge closure sat queued on a saturated execution
        // pool past the deadline and the guest NEVER ran. The contract IS present
        // (so no auto-fetch — the return value below already gates on
        // is_contract_exec_rejection, which is true for a scheduler timeout), and
        // this fires under exactly the load it represents. DEBUG, not WARN,
        // mirroring the #4251 queue-full treatment: a WARN here would be loud
        // precisely when the node is most overloaded, and it would be factually
        // wrong to blame the contract ("not ready locally") for a pool-saturation
        // event.
        tracing::debug!(
            tx = %tx,
            %key,
            error = %err,
            event = "scheduler_overloaded",
            "BroadcastToStreaming update skipped: execution pool saturated, guest never ran (transient)"
        );
    } else {
        tracing::warn!(
            tx = %tx,
            %key,
            error = %err,
            "BroadcastToStreaming update skipped: contract not ready locally"
        );
    }
    // Self-heal GET only when the contract is genuinely missing. Skip when
    // the WASM merge ran (pre-#3914) or when the queue was saturated (#4251)
    // — in both cases the contract code is present, and enqueuing a GET on
    // a saturated handler only amplifies the storm.
    !err.is_contract_exec_rejection() && !err.is_contract_queue_full()
}

/// Fetch the contract's REAL `summarize_state` output for `key`, falling back
/// to an EMPTY summary when the summarize is unavailable (missing state,
/// saturated executor queue, WASM failure).
///
/// Called by the two client-facing `UpdateResponse { summary }` sites in
/// `drive_client_update` (the only consumers that need a summary after an
/// update; #4923 MAJOR 4 — `update_contract` itself does no summary work so
/// the relay/no-change hot paths pay zero extra handler round-trips).
///
/// The fallback is deliberately empty rather than the state bytes: an empty
/// summary is an honest "no summary available" for the client-facing
/// `ContractResponse::UpdateResponse { summary }` (whose type requires a
/// value), while state bytes relabeled as a summary poisoned every receiver's
/// delta-efficiency gate (`is_delta_efficient` refuses when
/// `summary * 2 >= state`, and state == summary always refuses) and forced
/// full-state broadcast fallbacks — 41% of all network wire bytes in the
/// #4923 incident. See the `update_contract_never_builds_a_summary_from_state_bytes`
/// pin test, which also pins that the ONLY `StateSummary` this helper may
/// construct is the empty fallback.
///
/// Cost note: the executor's `summary_cache` memoizes on the state hash, but
/// that cache is invalidated on every state write (`state_store.rs`), so a
/// post-commit summarize after a CHANGED apply is always a memo MISS. The
/// real cost argument: the broadcast fan-out already issues the identical
/// `get_contract_summary` on every state change (`broadcast_queue.rs`), so
/// whichever of the two runs first pays the one WASM call and the other hits
/// the cache; and the dominant no-change client case IS a memo hit.
async fn contract_summary_or_empty(
    op_manager: &OpManager,
    key: ContractKey,
    priority: crate::contract::Priority,
) -> StateSummary<'static> {
    match op_manager
        .notify_contract_handler_prioritized(
            ContractHandlerEvent::GetSummaryQuery { key },
            priority,
        )
        .await
    {
        Ok(ContractHandlerEvent::GetSummaryResponse {
            summary: Ok(summary),
            ..
        }) => summary,
        Ok(ContractHandlerEvent::GetSummaryResponse {
            summary: Err(err), ..
        }) => {
            tracing::debug!(
                contract = %key,
                error = %err,
                "client update: summarize failed; returning empty summary"
            );
            StateSummary::from(Vec::new())
        }
        other => {
            tracing::debug!(
                contract = %key,
                response = ?other,
                "client update: unexpected GetSummaryQuery response; returning empty summary"
            );
            StateSummary::from(Vec::new())
        }
    }
}

/// Apply an update to a contract.
///
/// This function:
/// 1. Fetches the current state (for change detection)
/// 2. Calls UpdateQuery to merge the update and persist
/// 3. Returns the merged state and whether the state changed
///
/// It deliberately does NO summary work (#4923 MAJOR 4): it runs on the
/// relay-broadcast and no-change hot paths, so any per-call summary fetch
/// here multiplies contract-handler round-trips network-wide. Consumers that
/// need a summary fetch it themselves ([`contract_summary_or_empty`]).
///
/// The `update_data` parameter can be:
/// - `UpdateData::Delta(delta)` - A delta from the client, merged with current state
/// - `UpdateData::State(state)` - A full state from PUT or executor
pub(crate) async fn update_contract(
    op_manager: &OpManager,
    key: ContractKey,
    update_data: UpdateData<'static>,
    related_contracts: RelatedContracts<'static>,
    priority: crate::contract::Priority,
) -> Result<UpdateExecution, OpError> {
    let previous_state = match op_manager
        .notify_contract_handler_prioritized(
            ContractHandlerEvent::GetQuery {
                instance_id: *key.id(),
                return_contract_code: false,
            },
            priority,
        )
        .await
    {
        Ok(ContractHandlerEvent::GetResponse {
            response: Ok(StoreResponse { state, .. }),
            ..
        }) => state,
        Ok(other) => {
            tracing::trace!(?other, %key, "Unexpected get response while preparing update summary");
            None
        }
        Err(err) => {
            tracing::debug!(%key, %err, "Failed to fetch existing contract state before update");
            None
        }
    };

    match op_manager
        .notify_contract_handler_prioritized(
            ContractHandlerEvent::UpdateQuery {
                key,
                data: update_data.clone(),
                related_contracts,
            },
            priority,
        )
        .await
    {
        Ok(ContractHandlerEvent::UpdateResponse {
            new_value: Ok(new_val),
            state_changed,
        }) => {
            // Invariant: after a successful UPDATE the resulting state must be non-empty.
            // A successful UpdateResponse with an empty value indicates a contract handler bug.
            debug_assert!(
                new_val.size() > 0,
                "update_contract: state must be non-empty after successful UPDATE for contract {key}"
            );
            // #4923: no summary is computed here — never relabel the state
            // bytes as a summary (the self-poisoning full-state-broadcast
            // loop), and no per-apply summary fetch on this hot path either
            // (MAJOR 4). Consumers that need a summary fetch it themselves.
            Ok(UpdateExecution {
                value: new_val,
                changed: state_changed,
            })
        }
        Ok(ContractHandlerEvent::UpdateResponse {
            new_value: Err(err),
            ..
        }) => {
            log_update_contract_failure(&key, &err);
            Err(err.into())
        }
        Ok(ContractHandlerEvent::UpdateNoChange { .. }) => {
            // Helper to extract state from UpdateData variants that contain state
            fn extract_state_from_update_data(
                update_data: &UpdateData<'static>,
            ) -> Option<WrappedState> {
                match update_data {
                    UpdateData::State(s) => Some(WrappedState::from(s.clone().into_bytes())),
                    UpdateData::StateAndDelta { state, .. }
                    | UpdateData::RelatedState { state, .. }
                    | UpdateData::RelatedStateAndDelta { state, .. } => {
                        Some(WrappedState::from(state.clone().into_bytes()))
                    }
                    UpdateData::Delta(_) | UpdateData::RelatedDelta { .. } => None,
                    // `UpdateData` is `#[non_exhaustive]` since stdlib
                    // 0.6.0. We can't materialize state from an unknown
                    // variant, so return None and let the caller treat
                    // it as "no state to extract."
                    _ => None,
                }
            }

            let resolved_state = match previous_state {
                Some(prev_state) => prev_state,
                None => {
                    // Try to fetch current state from store (same priority as
                    // the rest of this update — keep the ClientLocal lane for a
                    // client UPDATE that CRDT-merges to no change; #4534).
                    let fetched_state = op_manager
                        .notify_contract_handler_prioritized(
                            ContractHandlerEvent::GetQuery {
                                instance_id: *key.id(),
                                return_contract_code: false,
                            },
                            priority,
                        )
                        .await
                        .ok()
                        .and_then(|event| match event {
                            ContractHandlerEvent::GetResponse {
                                response: Ok(StoreResponse { state, .. }),
                                ..
                            } => state,
                            ContractHandlerEvent::DelegateRequest { .. }
                            | ContractHandlerEvent::DelegateResponse(_)
                            | ContractHandlerEvent::ExportUserSecrets { .. }
                            | ContractHandlerEvent::ExportUserSecretsResponse(_)
                            | ContractHandlerEvent::ImportSecrets { .. }
                            | ContractHandlerEvent::ImportSecretsResponse(_)
                            | ContractHandlerEvent::PutQuery { .. }
                            | ContractHandlerEvent::PutResponse { .. }
                            | ContractHandlerEvent::GetQuery { .. }
                            | ContractHandlerEvent::GetResponse { .. }
                            | ContractHandlerEvent::UpdateQuery { .. }
                            | ContractHandlerEvent::UpdateResponse { .. }
                            | ContractHandlerEvent::UpdateNoChange { .. }
                            | ContractHandlerEvent::RegisterSubscriberListener { .. }
                            | ContractHandlerEvent::RegisterSubscriberListenerResponse { .. }
                            | ContractHandlerEvent::QuerySubscriptions { .. }
                            | ContractHandlerEvent::QuerySubscriptionsResponse
                            | ContractHandlerEvent::GetSummaryQuery { .. }
                            | ContractHandlerEvent::GetSummaryResponse { .. }
                            | ContractHandlerEvent::GetDeltaQuery { .. }
                            | ContractHandlerEvent::GetDeltaResponse { .. }
                            | ContractHandlerEvent::ClientDisconnect { .. }
                            | ContractHandlerEvent::EvictContract { .. } => None,
                        });

                    match fetched_state {
                        Some(state) => state,
                        None => {
                            tracing::debug!(
                                %key,
                                "Fallback fetch for UpdateNoChange returned no state; trying to extract from update_data"
                            );
                            match extract_state_from_update_data(&update_data) {
                                Some(state) => state,
                                None => {
                                    tracing::error!(
                                        %key,
                                        "Cannot extract state from delta-only UpdateData in NoChange fallback"
                                    );
                                    return Err(OpError::UnexpectedOpState);
                                }
                            }
                        }
                    }
                }
            };

            // #4923: same as the changed branch — no summary work here.
            Ok(UpdateExecution {
                value: resolved_state,
                changed: false,
            })
        }
        Err(err) => Err(err.into()),
        Ok(other) => {
            tracing::error!(event = ?other, contract = %key, phase = "error", "Unexpected event from contract handler during update");
            Err(OpError::UnexpectedOpState)
        }
    }
}

/// Send proactive summary notifications to interested peers after a successful
/// state change. This tells neighbors "my state just updated — here's my new
/// summary" so they can update their cached view of us and skip sending
/// redundant broadcasts.
///
/// Fetches the contract's REAL summary itself (like its sibling
/// [`send_summary_back_on_rejection`]) rather than accepting a precomputed one
/// from the caller. An earlier version took `UpdateExecution.summary` as a
/// parameter "to avoid an extra WASM `summarize_state` call" — that rationale
/// is obsolete: the 100ms per-contract throttle below bounds the call rate,
/// and the broadcast fan-out already issues the identical
/// `get_contract_summary` on every state change (`broadcast_queue.rs`), so
/// whichever runs first pays the one WASM call and the other hits the
/// executor's `summary_cache`. Worse, the value the parameter received was
/// the full post-update STATE relabeled as a summary. Broadcasting that
/// poisoned every interested peer's cached view of us
/// (`interested_peers[contract][peer].summary` == our state), so their
/// `is_delta_efficient` gate refused every delta and every broadcast fell
/// back to full state — 41% of all network wire bytes in the #4923 incident.
/// If no real summary is available, send nothing — note the throttle token is
/// consumed even in that case, so a no-summary tick still burns the
/// contract's 100ms notification slot (acceptable: no summary means there is
/// nothing to advertise yet, and the next state change retries).
///
/// # Recipient set (#4965)
///
/// Interested peers, MINUS the update's sender, MINUS ourselves, MINUS every
/// **advertised co-host** of this contract. The co-host exclusion is the
/// bandwidth fix: those peers are exactly the broadcast fan-out targets
/// (`get_broadcast_targets_update` sources them from
/// `neighbor_hosting::neighbors_with_contract`), and the broadcast we send
/// them already carries this same summary in `sender_summary_bytes`, which
/// they upsert into their cache of us on arrival
/// (`update/op_ctx_task.rs::drive_relay_broadcast_to` step 1, and the
/// streaming twin `apply_streaming_broadcast` step 4 — the #4952 upsert).
/// Sending it again as a standalone `Summaries` message duplicates the
/// summary bytes on the wire for a peer that just received them. It is NOT a
/// pure duplicate: the `Summaries` handler ALSO compares our summary against
/// the receiver's and heals us via a targeted `SyncStateToPeer` if we are
/// behind (`node.rs`, `Summaries` arm), whereas the broadcast receive path
/// only upserts (`op_ctx_task.rs`). For co-hosts that reverse probe now falls
/// to the ~5-min heartbeat anti-entropy — the backstop invariant 1 designates
/// for exactly this.
///
/// `interest_sync_summaries` is the largest outbound arm (49.8% of outbound
/// bytes, v0.2.115). How much of it THIS emitter accounts for is NOT known:
/// `outbound_message_mix` buckets all four `Summaries` emitters together, and
/// the multi-entry heartbeat reply (`node.rs`, `Interests` arm) is a
/// significant second source. #5052 adds the per-emitter counter. Do not read
/// a specific saving into this change. See #4965.
///
/// The remaining recipients are the population this notification exists for:
/// peers interested in the contract that we do NOT advertise-host toward, so
/// our summary would otherwise only reach them on the ~5-min InterestSync
/// heartbeat.
///
/// If a broadcast is dropped rather than delivered, the excluded co-host
/// misses this summary — but it also missed the state itself, and the
/// heartbeat anti-entropy is the designated backstop for that case. This
/// mirrors `record_delivery_to_interest`, which likewise only seeds on a real
/// delivery (#4235).
///
/// That reasoning covers the per-send skips inside `broadcast_to_single_peer`.
/// `plan_fanout_send` skips a peer whose summary is BYTE-IDENTICAL to ours
/// first; the cached-empty-delta verdict is the backstop for the narrower
/// converged-but-byte-differing case (a non-deterministically-serialized
/// summary), not the primary test. Either way the peer did not miss the STATE,
/// only our new summary, and it already holds an equivalent one. Neither skip
/// covers `should_broadcast_contract`, which suppresses the broadcast for the
/// WHOLE contract — hence the gate below.
///
/// # Gate: `should_summarize_or_broadcast`
///
/// This emitter is gated on the same `(is_hosting_contract || contract_in_use)
/// && contract_state_present` predicate as its two siblings —
/// `broadcast_queue::should_broadcast_contract` (the fan-out) and
/// `node::summary_if_hosted_or_in_use` (the heartbeat / churn replies). It was
/// the one summary-emitting path #4473/#4610 left ungated.
///
/// Two reasons, and the first is what makes the co-host exclusion above sound:
///
/// 1. **The exclusion needs a broadcast behind it.** Ungated, a contract with
///    state on disk but neither hosted nor in use (evicted from the hosting
///    cache, no local client, no downstream subscriber — the #4440/#4473/#4610
///    phantom population) attempted ZERO broadcasts, yet post-#4965 excluded
///    every advertised co-host from the notification. That is exclusion with
///    no counterpart: the co-host would get neither. Sharing the predicate
///    makes "excluded because the broadcast covered it" true by construction
///    rather than by coincidence.
/// 2. **It closes a `summarize_contract_state` storm hole.** The gate's whole
///    purpose (#4473) is to stop phantom contracts driving WASM summarize
///    calls, and `InterestManager::get_contract_summary` below is an ungated
///    `GetSummaryQuery`. The paragraph above — the broadcast "already issues
///    the identical `get_contract_summary`, so whichever runs first pays the
///    one WASM call" — holds ONLY when the broadcast actually runs, exactly
///    the case `should_broadcast_contract` rules out. For a phantom, this path
///    paid the full call alone.
///
/// What the gate does NOT do is give a co-host our summary for such a contract
/// — the heartbeat reply reports `None` for it too, and the receiver clears its
/// cached summary of us (`SummaryMissingReason::ClearedByNoneReport`). That is
/// the intended #4473 policy (we advertise no summary for a contract we do not
/// host or serve), and the gate makes all three paths agree on it instead of
/// leaving this one emitter dissenting.
///
/// A peer that still broadcasts to us for such a contract is holding a stale
/// advertisement of us. #5063 closes the main source of those — eviction now
/// retracts the advertisement at the eviction decision
/// (`operations::retract_advertisement_for_evicted_contract`) rather than only
/// at reclamation — so this residual is narrow. Its retention guard is
/// `is_hosting_contract || contract_in_use || is_subscribed`, which is this
/// gate's predicate plus `is_subscribed`. The one population where the two
/// still disagree is a contract held ONLY by a bare upstream network
/// subscription: #5063 keeps its advertisement, while all three summary paths
/// (this one, the fan-out, and the heartbeat) report nothing for it, so a
/// co-host's broadcasts to us stay full-state. That divergence is PRE-EXISTING
/// — the fan-out and heartbeat already behaved this way — and this gate makes
/// the third path match them rather than introducing it. Tracked with the rest
/// of the #4440 advertisement-hygiene work; deliberately not papered over here.
pub(crate) async fn send_proactive_summary_notification(
    op_manager: &OpManager,
    key: &ContractKey,
    sender_addr: SocketAddr,
) {
    use crate::message::{SummariesEmitter, SummaryEntry};
    use crate::ring::interest::contract_hash;

    // Throttle: at most one notification per contract per 100ms
    if !op_manager
        .interest_manager
        .should_send_summary_notification(key)
    {
        return;
    }

    // The #4473/#4610 gate, shared with the broadcast fan-out and the
    // heartbeat replies. Placed AFTER the throttle so a hot contract pays its
    // synchronous state-store lookup at most 10x/sec, and BEFORE
    // `get_contract_summary` so a phantom contract never reaches the WASM
    // summarize. See this function's "Gate" docs for why the co-host exclusion
    // below depends on it.
    if !op_manager.ring.should_summarize_or_broadcast(key) {
        tracing::debug!(
            contract = %key,
            "Skipping proactive summary notification — contract is neither \
             hosted nor in use, or its state is not present (#4473 gate); the \
             broadcast fan-out is suppressed for it too"
        );
        return;
    }

    // Fetch our REAL summary (the contract's `summarize_state` output,
    // memoized on the state hash). Never send a caller-supplied value here —
    // see the function docs and #4923.
    let Some(summary) = op_manager
        .interest_manager
        .get_contract_summary(op_manager, key)
        .await
    else {
        tracing::debug!(
            contract = %key,
            "Skipping proactive summary notification — no local summary available"
        );
        return;
    };

    // One `SummaryEntry`, built once here and reused for every interested peer
    // in the loop below — the summary is identical for all of them, so there
    // is nothing per-peer to compute.
    //
    // This leg ships FULL BYTES this release. Hash-first (#4965) does NOT
    // apply here: digest-first rides the two multi-entry reply legs
    // (`InterestsReply` / `ChangeInterestsReply`) only, and the send site 40
    // lines below carries the evidential reasoning for why this one was left
    // out. There is no per-peer encoding choice on this path, and no version
    // gate is consulted.
    //
    // Worth stating because the opposite is the intuitive guess: this is the
    // send site that fires on every state change to every interested peer, so
    // it looks like the biggest available saving. It is deliberately NOT
    // taken, because its receivers are the population least likely to have
    // applied the update yet — the one place a digest is most likely to MISS
    // and cost 1 message -> 3 for the same bytes. It is the strongest
    // candidate for the NEXT release, once the agreement counters give a field
    // reading, not a saving already banked.
    //
    // #5052: this is also the per-state-change fan-out that #5003 targets. It
    // is the only SINGLE-entry emitter that fans across peers, so its
    // bytes/msgs ratio is what tells a notification apart from a heartbeat
    // reply in the rollup.
    let hash = contract_hash(key);
    let full_entry = SummaryEntry::from_summary(hash, Some(&summary));

    // Get interested peers and resolve them to addresses. Peers that don't
    // resolve to a live socket address are dropped here, as before.
    let interested = op_manager.interest_manager.get_interested_peers(key);
    let self_addr = op_manager.ring.connection_manager.get_own_addr();

    let resolved: Vec<(TransportPublicKey, SocketAddr)> = interested
        .iter()
        .filter_map(|(peer_key, _interest)| {
            let pkl = op_manager
                .ring
                .connection_manager
                .get_peer_by_pub_key(&peer_key.0)?;
            Some((peer_key.0.clone(), pkl.socket_addr()?))
        })
        .collect();

    // The advertised co-hosts are the broadcast fan-out targets, which already
    // received this summary inside the broadcast. Read through the SHARED
    // accessor `get_broadcast_targets_update` also uses — see its rustdoc for
    // why the two sites must not read the population independently.
    let advertised_cohosts: HashSet<TransportPublicKey> = op_manager
        .advertised_cohost_pub_keys(key)
        .into_iter()
        .collect();

    let ProactiveSummaryRecipients {
        targets,
        cohosts_skipped,
    } = proactive_summary_targets(&resolved, &advertised_cohosts, sender_addr, self_addr);

    for peer_addr in &targets {
        // FULL BYTES, deliberately — this leg does NOT ship digest-first
        // this release (#4965 review §2).
        //
        // The 98.1% agreement measurement that justifies hash-first comes from
        // a heartbeat-dominated population. This site is the opposite case: it
        // fires immediately after WE change state, so its receivers are
        // precisely the peers least likely to have applied the update yet. A
        // mismatch here costs 1 message -> 3 (digests, request, bytes) for the
        // SAME bytes, and defers the heal a round trip — a bad trade on the
        // #4861 messages/s axis if the agreement rate is materially below the
        // heartbeat's. Nothing in the field can currently tell us: the
        // single/multi agreement split lives in thread-local test metrics, not
        // fleet telemetry, and there is no runtime kill-switch.
        //
        // #5003 makes it worse before it makes it better: it removes advertised
        // co-hosts from this leg's recipients — exactly the peers most likely
        // to agree.
        //
        // So: ship where the evidence is (the two multi-entry reply legs),
        // extend here next release once `summaries_entries` and the agreement
        // counters give a field reading. The emitter tag is unchanged, so the
        // rollup keeps attributing this leg either way.
        let message = crate::node::full_summaries_message(
            vec![full_entry.clone()],
            SummariesEmitter::Notification,
        );

        if let Err(e) = op_manager
            .notify_node_event(NodeEvent::SendInterestMessage {
                target: *peer_addr,
                message,
            })
            .await
        {
            tracing::debug!(
                contract = %key,
                peer = %peer_addr,
                error = %e,
                "Failed to send proactive summary notification"
            );
        }
    }

    // `cohosts_skipped` comes from `proactive_summary_targets`, which counts
    // ONLY the #4965 co-host drops. Neither `advertised_cohosts.len()` (counts
    // co-hosts that were never interested or failed to resolve) nor
    // `resolved.len() - targets.len()` (also counts the sender and self) is
    // this number, and both overstate it. This is what the change is judged on.
    //
    // Release-visible counterpart to the `debug!` below, which `release_max_level_info`
    // compiles out — so in production the debug line measures nothing. Folded into
    // the existing `outbound_message_mix` rollup window rather than emitted per
    // notification: the collector's budget is per-event-stream, and this path fires on
    // every state change (see `outbound_message_mix` module docs).
    op_manager
        .outbound_mix
        .record_notification_recipients(targets.len() as u64, cohosts_skipped as u64);
    // Simulation-visible twin of the same number. The sim harness cannot read
    // per-node `OutboundMix` windows, and the exclusion's effect is invisible
    // in `delta_sends`/`full_state_sends` — see
    // `GlobalTestMetrics::record_notification_cohosts_skipped`.
    crate::config::GlobalTestMetrics::record_notification_cohosts_skipped(cohosts_skipped as u64);

    tracing::debug!(
        contract = %key,
        interested = interested.len(),
        resolved = resolved.len(),
        cohosts_skipped,
        advertised_cohosts = advertised_cohosts.len(),
        peer_count = targets.len(),
        "Sent proactive summary notifications after state change"
    );
}

/// Choose which interested peers still need a standalone `Summaries`
/// notification after a state change.
///
/// Split out as a pure function so the recipient-set decision is unit-testable
/// without an `OpManager`. `.claude/rules/operations.md` ("Event emission
/// review") requires the emitted event's recipient set to be asserted
/// directly rather than inferred from the data layer that feeds it; the
/// production loop is pinned to route through here by
/// `proactive_notification_excludes_advertised_cohosts_in_production`.
///
/// Excludes, in order: the update's sender, ourselves, and every advertised
/// co-host (the broadcast fan-out already delivered this summary to them —
/// see [`send_proactive_summary_notification`]'s "Recipient set" section).
///
/// Returns the co-host skip count SEPARATELY rather than leaving callers to
/// derive it as `resolved.len() - targets.len()`. That subtraction is wrong,
/// and wrong in the direction that flatters the change: it also counts the
/// sender and self, so it stays non-zero even with the co-host filter deleted.
/// A metric computed that way reports a saving the code is not making, and it
/// silently defeats any test that asserts on it — mutation testing caught
/// exactly that here, with the simulation's `cohosts_skipped > 0` assertion
/// still passing under a mutation that removed the entire exclusion.
pub(crate) fn proactive_summary_targets(
    resolved_interested: &[(TransportPublicKey, SocketAddr)],
    advertised_cohosts: &HashSet<TransportPublicKey>,
    sender_addr: SocketAddr,
    self_addr: Option<SocketAddr>,
) -> ProactiveSummaryRecipients {
    let mut targets = Vec::with_capacity(resolved_interested.len());
    let mut cohosts_skipped = 0usize;

    for (pub_key, peer_addr) in resolved_interested {
        // The sender just gave us this data; never notify ourselves. Both
        // predate #4965 and are NOT co-host skips.
        if *peer_addr == sender_addr || self_addr.as_ref() == Some(peer_addr) {
            continue;
        }
        // #4965: the broadcast to this co-host already carried the summary in
        // `sender_summary_bytes`. Counted only here, AFTER the two exclusions
        // above, so the count is attributable to this change alone.
        if advertised_cohosts.contains(pub_key) {
            cohosts_skipped += 1;
            continue;
        }
        targets.push(*peer_addr);
    }

    ProactiveSummaryRecipients {
        targets,
        cohosts_skipped,
    }
}

/// Outcome of [`proactive_summary_targets`]: who to notify, and how many
/// recipients the #4965 co-host exclusion removed.
///
/// The count is bundled with the targets rather than recomputed by callers so
/// there is exactly one definition of "skipped because of #4965" — see that
/// function's docs for the subtraction that looked equivalent and was not.
pub(crate) struct ProactiveSummaryRecipients {
    pub targets: Vec<SocketAddr>,
    /// Peers dropped BECAUSE they are advertised co-hosts. Excludes the sender
    /// and self, which are dropped for unrelated, pre-#4965 reasons.
    pub cohosts_skipped: usize,
}

/// Send our current summary to the peer whose broadcast we just rejected,
/// **only when the peer's included summary equals our own** — i.e. the
/// peer and we already agree on state, but the peer's cached view of
/// our summary is stale (`None` or out of date) so their send path
/// fell back to full-state at `broadcast_queue.rs:352-356` instead of
/// hitting the summaries-equal fast-path skip.
///
/// The gate on `sender_summary_bytes == our_summary` is load-bearing.
/// Without it, when our state is strictly ahead of the peer's and we
/// reject their stale broadcast, the `InterestMessage::Summaries`
/// handler at `node.rs:1791-1839` detects a mismatch and pushes the
/// peer's state back via `SyncStateToPeer` — which we then reject
/// again, creating a tight reject→summary→resync→reject loop bounded
/// only by the 60 s `BroadcastDedupCache` (and defeated entirely by
/// payload-byte variation). Restricting to the matching-summary case
/// makes this helper a pure convergence nudge: the `Summaries`
/// receiver's stale-detector returns `is_stale = false`, no
/// `SyncStateToPeer` fires, the only outcome is the sender's
/// peer-summary cache of us flipping from `None` → `Some(our_summary)`
/// so its next broadcast takes the fast-path skip.
///
/// Observed in production (nova, vega): ~80–130 rejections/hour per
/// gateway, all with `incoming_state_size == local_state_size` and
/// "version N == N" — i.e. exactly the same-summary case this helper
/// targets. The 5-min `Interests`/`Summaries` heartbeat eventually
/// populates the sender's cache; this shortcut closes the loop in one
/// round-trip instead of waiting for the next heartbeat tick.
///
/// Unlike `send_proactive_summary_notification` (success path, fans
/// out to all interested peers, explicitly excludes the sender), this
/// targets the single sender — on rejection, the sender is the ONE
/// peer whose cache we know is wrong about us.
///
/// Call sites MUST gate this on `err.is_invalid_update_rejection()`
/// (not the broader `is_contract_exec_rejection`): the stricter
/// predicate matches ONLY the benign "new state version not higher"
/// case, not OOG / `MaxComputeTimeExceeded` / WASM traps / validation
/// failures — which are attacker-inducible and shouldn't amplify into
/// extra messages.
pub(crate) async fn send_summary_back_on_rejection(
    op_manager: &OpManager,
    key: &ContractKey,
    target_addr: SocketAddr,
    sender_summary_bytes: Vec<u8>,
) {
    use crate::message::{SummariesEmitter, SummaryEntry};
    use crate::ring::interest::contract_hash;

    // Throttle BEFORE the WASM `summarize_state` call. Even with call
    // sites gated on `is_invalid_update_rejection`, a flood of
    // crafted-payload broadcasts that all produce benign rejections
    // would otherwise force one `summarize_state` call per rejection.
    // `should_send_summary_notification` caps at ~10 calls/sec/contract.
    //
    // Sharing the throttle map with `send_proactive_summary_notification`
    // is intentional: both paths emit the same `InterestMessage::Summaries`
    // shape, and the existing throttle's purpose (don't re-spam summary
    // updates for the same contract in bursts) applies to both callers.
    if !op_manager
        .interest_manager
        .should_send_summary_notification(key)
    {
        return;
    }

    let Some(our_summary) = op_manager
        .interest_manager
        .get_contract_summary(op_manager, key)
        .await
    else {
        tracing::debug!(
            contract = %key,
            peer = %target_addr,
            "Skipping summary-back on rejection — no local summary available"
        );
        return;
    };

    // Critical: only proceed when summaries match. See function docs for
    // the SyncStateToPeer-loop rationale. A differing summary means the
    // peer is genuinely out of sync, in which case the 5-min heartbeat
    // is the right convergence mechanism — firing Summaries here would
    // escalate into a per-rejection state ping-pong.
    if our_summary.as_ref() != sender_summary_bytes.as_slice() {
        tracing::debug!(
            contract = %key,
            peer = %target_addr,
            "Skipping summary-back on rejection — sender's summary differs \
             from ours (peer is genuinely out of sync; heartbeat will converge)"
        );
        return;
    }

    let hash = contract_hash(key);
    // #5052: same SHAPE as the notification above (single entry, real summary)
    // but a different trigger and a much narrower gate, so it gets its own
    // arm. Sharing one would make the notification arm look larger than the
    // fan-out #5003 actually changes.
    //
    // #4965: this path only runs once we have ALREADY established that
    // `our_summary == sender_summary_bytes`, so in the expected case the
    // digest matches on the receiving side and the seeding this exists to do
    // (their cache of us flipping `None` -> `Some`) completes from the digest
    // alone — the receiver caches its own bytes, which the digest proved are
    // ours, and shipping the bytes would be pure waste.
    //
    // NOT guaranteed, deliberately stated: the receiver re-derives its summary
    // through `summary_if_hosted_or_in_use`, which returns `None` for a
    // contract it no longer hosts or serves (#4473). It then classifies as
    // `NeedBytes` and asks — costing one extra round trip, never a lost
    // update. The rejection that got us here proves the peer HAD the state a
    // moment ago, so this is a narrow race, but an absolute claim here would
    // be wrong.
    let full_entry = SummaryEntry::from_summary(hash, Some(&our_summary));
    // FULL BYTES, same release-scoping as the notification leg above (#4965
    // review §2): single-entry, state-change-driven, and outside the
    // population the 98.1% agreement figure was measured on. The digest would
    // very likely match here (this path only runs once the peer's summary is
    // known equal to ours), but "very likely" on an unmeasured leg is exactly
    // what the review declined to ship — and the saving is one summary on a
    // path that fires ~80-130 times/hour/gateway, not a stream.
    let message =
        crate::node::full_summaries_message(vec![full_entry], SummariesEmitter::Rejection);

    if let Err(e) = op_manager
        .notify_node_event(NodeEvent::SendInterestMessage {
            target: target_addr,
            message,
        })
        .await
    {
        // info! not debug! — debug! is stripped in release builds via
        // `tracing_max_level_info`, so a saturated event-loop channel
        // would fail silently in production.
        tracing::info!(
            contract = %key,
            peer = %target_addr,
            error = %e,
            "Failed to send summary-back after broadcast rejection"
        );
    }
}

mod messages {
    use std::fmt::Display;

    use freenet_stdlib::prelude::{ContractKey, RelatedContracts, WrappedState};
    use serde::{Deserialize, Serialize};

    use crate::{
        message::{InnerMessage, Transaction},
        ring::Location,
        transport::peer_connection::StreamId,
    };

    /// Payload for streaming UPDATE requests.
    ///
    /// Contains the same data as RequestUpdate but serialized for streaming.
    /// The metadata (key, stream_id, total_size) is sent via RequestUpdateStreaming message.
    #[derive(Debug, Serialize, Deserialize)]
    pub(crate) struct UpdateStreamingPayload {
        #[serde(deserialize_with = "RelatedContracts::deser_related_contracts")]
        pub related_contracts: RelatedContracts<'static>,
        pub value: WrappedState,
    }

    /// Payload for streaming broadcast updates.
    ///
    /// Contains full state for broadcasting to subscribers via streaming.
    /// Used when the full state is large (>streaming_threshold).
    #[derive(Debug, Serialize, Deserialize)]
    pub(crate) struct BroadcastStreamingPayload {
        /// Full contract state bytes
        pub state_bytes: Vec<u8>,
        /// Sender's current state summary bytes
        pub sender_summary_bytes: Vec<u8>,
    }

    #[derive(Debug, Serialize, Deserialize, Clone)]
    /// Update operation messages.
    ///
    /// Uses hop-by-hop routing for request forwarding. Broadcasting to subscribers
    /// uses explicit addresses since there are multiple targets.
    pub(crate) enum UpdateMsg {
        /// Request to update a contract state. Forwarded hop-by-hop toward contract location.
        RequestUpdate {
            id: Transaction,
            key: ContractKey,
            #[serde(deserialize_with = "RelatedContracts::deser_related_contracts")]
            related_contracts: RelatedContracts<'static>,
            value: WrappedState,
        },
        /// Broadcasting a change to a specific subscriber.
        ///
        /// Supports delta-based synchronization: when we know the peer's state summary,
        /// we send a delta instead of full state to reduce bandwidth.
        BroadcastTo {
            id: Transaction,
            key: ContractKey,
            /// The payload: either a delta (if we know peer's summary) or full state.
            payload: crate::message::DeltaOrFullState,
            /// Sender's current state summary bytes, so receiver can update their tracking.
            /// Use `StateSummary::from(sender_summary_bytes.clone())` to convert.
            sender_summary_bytes: Vec<u8>,
        },

        // ---- Streaming variants ----
        /// Streaming variant of RequestUpdate for large state updates.
        ///
        /// Used when the state size exceeds the streaming threshold (default 64KB).
        /// The actual state data is sent via a separate stream identified by stream_id.
        RequestUpdateStreaming {
            id: Transaction,
            /// Identifies the stream carrying the update payload
            stream_id: StreamId,
            /// Contract key being updated
            key: ContractKey,
            /// Total size of the streamed payload in bytes
            total_size: u64,
        },

        /// Streaming variant of BroadcastTo for large full state broadcasts.
        ///
        /// Used when broadcasting full state (not delta) and the state size exceeds
        /// the streaming threshold. Deltas are typically small and use regular BroadcastTo.
        BroadcastToStreaming {
            id: Transaction,
            /// Identifies the stream carrying the broadcast payload
            stream_id: StreamId,
            /// Contract key being broadcast
            key: ContractKey,
            /// Total size of the streamed payload in bytes
            total_size: u64,
        },
    }

    impl InnerMessage for UpdateMsg {
        fn id(&self) -> &Transaction {
            match self {
                UpdateMsg::RequestUpdate { id, .. }
                | UpdateMsg::BroadcastTo { id, .. }
                | UpdateMsg::RequestUpdateStreaming { id, .. }
                | UpdateMsg::BroadcastToStreaming { id, .. } => id,
            }
        }

        fn requested_location(&self) -> Option<crate::ring::Location> {
            match self {
                UpdateMsg::RequestUpdate { key, .. }
                | UpdateMsg::BroadcastTo { key, .. }
                | UpdateMsg::RequestUpdateStreaming { key, .. }
                | UpdateMsg::BroadcastToStreaming { key, .. } => Some(Location::from(key.id())),
            }
        }
    }

    impl Display for UpdateMsg {
        fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
            match self {
                UpdateMsg::RequestUpdate { id, .. } => write!(f, "RequestUpdate(id: {id})"),
                UpdateMsg::BroadcastTo { id, .. } => write!(f, "BroadcastTo(id: {id})"),
                UpdateMsg::RequestUpdateStreaming { id, stream_id, .. } => {
                    write!(f, "RequestUpdateStreaming(id: {id}, stream: {stream_id})")
                }
                UpdateMsg::BroadcastToStreaming { id, stream_id, .. } => {
                    write!(f, "BroadcastToStreaming(id: {id}, stream: {stream_id})")
                }
            }
        }
    }
}

#[cfg(test)]
#[allow(clippy::wildcard_enum_match_arm)]
mod tests {
    use super::*;
    use crate::operations::test_utils::make_contract_key;

    /// Source-level pin for the UPDATE_PROPAGATION NO_TARGETS log site.
    /// Originally INFO; briefly promoted to WARN in PR #4252 commit 2;
    /// then demoted back to DEBUG in commit 3 because
    /// `get_broadcast_targets_update` is called up to 4 times per
    /// `BroadcastStateChange` (initial + 3 retries) — per-attempt WARN
    /// 4x amplifies on stuck contracts. The operator-actionable summary
    /// lives in the outer streak-suppressed WARN in `p2p_protoc.rs`
    /// (grep `BROADCAST_NO_TARGETS: no targets found after`). Per #4251
    /// re-review M2 (skeptical).
    #[test]
    fn no_targets_propagation_logs_at_debug_pin_test() {
        let path =
            std::path::Path::new(env!("CARGO_MANIFEST_DIR")).join("src/operations/update.rs");
        let source = std::fs::read_to_string(&path)
            .unwrap_or_else(|e| panic!("must read own source at {}: {e}", path.display()));
        let needle = "UPDATE_PROPAGATION: NO_TARGETS - update will not propagate further";
        let idx = source
            .find(needle)
            .expect("NO_TARGETS log message must still exist in source");
        // Anchor on the closest preceding `tracing::` macro (rfind) rather
        // than a byte window, so the assertion is immune to refactors that
        // move the target site relative to other nearby tracing macros.
        // Adopted from the #4272 pin tests; see those for rationale.
        let preceding = &source[..idx];
        let macro_idx = preceding
            .rfind("tracing::")
            .expect("a tracing macro must precede the NO_TARGETS log site");
        let line_start = preceding[..macro_idx].rfind('\n').map_or(0, |n| n + 1);
        let line_prefix = &preceding[line_start..macro_idx];
        assert!(
            line_prefix.chars().all(char::is_whitespace),
            "rfind matched `tracing::` inside a string literal or comment, \
             not a macro invocation. Prefix on its line: {line_prefix:?}"
        );
        let after_macro = &preceding[macro_idx + "tracing::".len()..];
        let macro_name = after_macro.split('!').next().unwrap_or("");
        let tail = &preceding[preceding.len().saturating_sub(200)..];
        assert_eq!(
            macro_name, "debug",
            "NO_TARGETS log site must be DEBUG to avoid 4x amplification on retries \
             (closest preceding macro is `tracing::{macro_name}!`). \
             Re-promotion to WARN/INFO regresses #4251 review M2.\n\
             Preceding source (last 200 bytes):\n{tail}"
        );
    }

    /// Source-level pin for the `UPDATE_PROPAGATION` broadcast (populated-
    /// targets) branch. Fires once per fan-out per UPDATE — at INFO it was
    /// ~43% of the post-#4252 log volume on a River-subscribed peer (see
    /// #4251 follow-up). The `phase = "broadcast",` literal disambiguates
    /// this site from the NO_TARGETS branch pinned above (whose phase is
    /// `"warning"`).
    ///
    /// Anchored on the *closest* preceding `tracing::` macro via `rfind`
    /// rather than a byte-window scan, so the assertion can't false-pass
    /// when the macro's arg list grows and a window-based check sees an
    /// earlier unrelated `tracing::debug!` site.
    #[test]
    fn broadcast_propagation_logs_at_debug_pin_test() {
        let path =
            std::path::Path::new(env!("CARGO_MANIFEST_DIR")).join("src/operations/update.rs");
        let source = std::fs::read_to_string(&path)
            .unwrap_or_else(|e| panic!("must read own source at {}: {e}", path.display()));
        let needle = "phase = \"broadcast\",";
        let idx = source
            .find(needle)
            .expect("UPDATE_PROPAGATION broadcast log site must still exist in source");
        let preceding = &source[..idx];
        let macro_idx = preceding
            .rfind("tracing::")
            .expect("a tracing macro must precede the broadcast log site");
        let line_start = preceding[..macro_idx].rfind('\n').map_or(0, |n| n + 1);
        let line_prefix = &preceding[line_start..macro_idx];
        assert!(
            line_prefix.chars().all(char::is_whitespace),
            "rfind matched `tracing::` inside a string literal or comment, \
             not a macro invocation. Prefix on its line: {line_prefix:?}"
        );
        let after_macro = &preceding[macro_idx + "tracing::".len()..];
        let macro_name = after_macro.split('!').next().unwrap_or("");
        let tail = &preceding[preceding.len().saturating_sub(200)..];
        assert_eq!(
            macro_name, "debug",
            "UPDATE_PROPAGATION broadcast log site must be DEBUG \
             (closest preceding macro is `tracing::{macro_name}!`). \
             Re-promotion to INFO/WARN restores the #4251 / #4272 log-volume regression.\n\
             Preceding source (last 200 bytes):\n{tail}"
        );
    }

    /// Regression tests for issue #3914: misleading ERROR/WARN log noise from
    /// benign WASM rejections of stale broadcast UPDATEs. The contract correctly
    /// rejects an incoming state at a version we already hold (a re-broadcast
    /// the dedup cache missed). On production gateways this generated 80-130
    /// ERROR-level lines per hour per gateway. The tests below pin both that
    /// the benign case is now INFO AND that real WASM failures (out-of-gas,
    /// max-compute-time, traps) stay at ERROR/WARN, so the predicate cannot
    /// silently broaden and hide real failures.
    mod log_severity {
        use super::*;
        use crate::contract::ExecutorError;
        use crate::test_utils::TestLogger;
        use freenet_stdlib::client_api::{ContractError as StdContractError, RequestError};

        // Constructors use `From<RequestError> for ExecutorError` (a public
        // impl) rather than the module-private `ExecutorError::request`, so
        // these helpers don't require widening any visibility for tests.
        fn invalid_update_rejection() -> ExecutorError {
            // Mirrors the production cause string exactly: stdlib's
            // `update_exec_error` prefixes "execution error: " and the
            // contract WASM's `InvalidUpdateWithInfo` Display produces
            // "invalid contract update, reason: ...".
            let req: RequestError = StdContractError::update_exec_error(
                make_contract_key(1),
                "invalid contract update, reason: New state version 100 must be higher than current version 100",
            )
            .into();
            req.into()
        }

        fn out_of_gas_failure() -> ExecutorError {
            // Real WASM fault: contract ran out of gas. Same `update_exec_error`
            // wrapper as the benign case (so the loose `is_contract_exec_rejection`
            // predicate matches both), but the cause string starts with
            // "execution error: The operation ran out of gas..." which the
            // tighter `is_invalid_update_rejection` predicate must REJECT.
            let req: RequestError = StdContractError::update_exec_error(
                make_contract_key(1),
                "The operation ran out of gas. This might be caused by an infinite loop or an inefficient computation.",
            )
            .into();
            req.into()
        }

        fn missing_parameters_failure() -> ExecutorError {
            // Real failure case: contract not ready locally, auto-fetch needed.
            let req: RequestError = StdContractError::Update {
                key: make_contract_key(2),
                cause: "missing contract parameters".into(),
            }
            .into();
            req.into()
        }

        fn queue_full_failure() -> ExecutorError {
            // Mirrors `send_queue_full_response` (contract.rs).
            ExecutorError::other(crate::contract::ContractQueueFull)
        }

        fn scheduler_timeout_failure() -> ExecutorError {
            // Build via the HOST path (#4864 round-9): a real scheduler-overload
            // timeout carries the unforgeable typed provenance
            // (classify_result → ContractExecError::SchedulerOverloaded → execution),
            // which is what is_scheduler_timeout now keys on. A plain
            // update_exec_error string would NOT classify — that is exactly the
            // contract-forge case the typing rejects.
            ExecutorError::test_host_scheduler_timeout(make_contract_key(1))
        }

        #[test]
        fn update_contract_failure_logs_info_for_invalid_update_rejection() {
            let logger = TestLogger::new().capture_logs().with_level("info").init();

            log_update_contract_failure(&make_contract_key(1), &invalid_update_rejection());

            assert!(
                logger.contains("merge_rejected_invalid_update"),
                "expected event=merge_rejected_invalid_update in logs, got: {:?}",
                logger.logs()
            );
            assert!(
                logger.contains("INFO"),
                "expected INFO-level log for invalid-update rejection, got: {:?}",
                logger.logs()
            );
            assert!(
                !logger.logs().iter().any(|l| l.contains("ERROR")),
                "invalid-update rejection must not produce ERROR-level logs, got: {:?}",
                logger.logs()
            );
        }

        #[test]
        fn update_contract_failure_logs_error_for_real_failure() {
            let logger = TestLogger::new().capture_logs().with_level("info").init();

            log_update_contract_failure(&make_contract_key(2), &missing_parameters_failure());

            assert!(
                logger.contains("ERROR"),
                "real failures must remain ERROR-level, got: {:?}",
                logger.logs()
            );
            assert!(
                logger.contains("Failed to update contract value"),
                "expected ERROR message text, got: {:?}",
                logger.logs()
            );
        }

        /// CRITICAL: out-of-gas comes through the same `update_exec_error`
        /// wrapper as the benign rejection, so the loose
        /// `is_contract_exec_rejection` predicate matches it (used for the
        /// auto-fetch gate, where this is correct: contract code IS present).
        /// But for log severity, OOG is a real bug operators must see and
        /// MUST stay at ERROR. This test pins that.
        #[test]
        fn update_contract_failure_logs_error_for_out_of_gas() {
            let logger = TestLogger::new().capture_logs().with_level("info").init();

            log_update_contract_failure(&make_contract_key(1), &out_of_gas_failure());

            assert!(
                logger.contains("ERROR"),
                "out-of-gas must remain ERROR-level (real WASM fault), got: {:?}",
                logger.logs()
            );
            assert!(
                !logger
                    .logs()
                    .iter()
                    .any(|l| l.contains("merge_rejected_invalid_update")),
                "out-of-gas must NOT be classified as a benign rejection, got: {:?}",
                logger.logs()
            );
        }

        #[test]
        fn broadcast_to_streaming_failure_logs_info_and_skips_auto_fetch_for_invalid_update() {
            let logger = TestLogger::new().capture_logs().with_level("info").init();
            let tx = Transaction::new::<UpdateMsg>();
            let err: OpError = invalid_update_rejection().into();

            let needs_auto_fetch =
                log_broadcast_to_streaming_failure(&tx, &make_contract_key(1), &err);

            assert!(
                !needs_auto_fetch,
                "invalid-update rejection must NOT trigger self-heal auto-fetch (contract code is present)"
            );
            assert!(
                logger.contains("merge_rejected_invalid_update"),
                "expected event=merge_rejected_invalid_update in logs, got: {:?}",
                logger.logs()
            );
            assert!(
                !logger.logs().iter().any(|l| l.contains("WARN")),
                "invalid-update rejection must not produce WARN-level logs (the old misleading 'contract not ready locally' line), got: {:?}",
                logger.logs()
            );
            assert!(
                !logger
                    .logs()
                    .iter()
                    .any(|l| l.contains("contract not ready locally")),
                "the misleading 'contract not ready locally' message must not appear for invalid-update rejections, got: {:?}",
                logger.logs()
            );
        }

        #[test]
        fn broadcast_to_streaming_failure_logs_warn_and_triggers_auto_fetch_for_real_failure() {
            let logger = TestLogger::new().capture_logs().with_level("info").init();
            let tx = Transaction::new::<UpdateMsg>();
            let err: OpError = missing_parameters_failure().into();

            let needs_auto_fetch =
                log_broadcast_to_streaming_failure(&tx, &make_contract_key(2), &err);

            assert!(
                needs_auto_fetch,
                "real failures must trigger self-heal auto-fetch"
            );
            assert!(
                logger.contains("WARN"),
                "real failures remain WARN-level for the streaming branch, got: {:?}",
                logger.logs()
            );
            assert!(
                logger.contains("contract not ready locally"),
                "expected the WARN message text for real failure, got: {:?}",
                logger.logs()
            );
        }

        /// Issue #4251 regression: when the per-contract fair queue
        /// rejects an event, `log_update_contract_failure` must classify
        /// it as `is_contract_queue_full` and log at DEBUG (NOT ERROR).
        /// A hot contract that saturates its own queue would otherwise
        /// flood logs with ERROR-level "Failed to update contract value"
        /// lines (~30% of all log volume on production gateways).
        #[test]
        fn update_contract_failure_logs_debug_for_queue_full() {
            let logger = TestLogger::new().capture_logs().with_level("debug").init();

            log_update_contract_failure(&make_contract_key(1), &queue_full_failure());

            assert!(
                logger.contains("queue_full"),
                "queue-full must emit event=queue_full, got: {:?}",
                logger.logs()
            );
            assert!(
                !logger.logs().iter().any(|l| l.contains("ERROR")),
                "queue-full must NOT log at ERROR (it's transient backpressure, not a fault), got: {:?}",
                logger.logs()
            );
            assert!(
                !logger
                    .logs()
                    .iter()
                    .any(|l| l.contains("Failed to update contract value")),
                "queue-full must NOT emit the legacy ERROR message, got: {:?}",
                logger.logs()
            );
        }

        /// Issue #4251 regression: the streaming branch's helper MUST
        /// (1) log queue-full at DEBUG, NOT WARN — a buggy contract that
        /// floods broadcasts must not also flood operator logs; and
        /// (2) return `false` so the caller skips
        /// `try_auto_fetch_contract` — enqueuing a GET right back onto
        /// the saturated handler is the amplification path the typed
        /// predicate exists to break.
        #[test]
        fn broadcast_to_streaming_failure_skips_auto_fetch_and_uses_debug_for_queue_full() {
            let logger = TestLogger::new().capture_logs().with_level("debug").init();
            let tx = Transaction::new::<UpdateMsg>();
            let err: OpError = queue_full_failure().into();

            let needs_auto_fetch =
                log_broadcast_to_streaming_failure(&tx, &make_contract_key(3), &err);

            assert!(
                !needs_auto_fetch,
                "queue-full MUST NOT trigger self-heal auto-fetch — enqueuing a GET \
                 onto the saturated handler is exactly the amplification we're \
                 trying to break (issue #4251)"
            );
            assert!(
                logger.contains("queue_full"),
                "queue-full must emit event=queue_full in the streaming branch, got: {:?}",
                logger.logs()
            );
            assert!(
                !logger.logs().iter().any(|l| l.contains("WARN")),
                "queue-full must NOT log at WARN — a saturated contract would otherwise \
                 fill operator dashboards with false-alarm WARNs, got: {:?}",
                logger.logs()
            );
            assert!(
                !logger
                    .logs()
                    .iter()
                    .any(|l| l.contains("contract not ready locally")),
                "the misleading 'contract not ready locally' message must not appear \
                 for queue-full — the contract IS present, the queue is just busy, \
                 got: {:?}",
                logger.logs()
            );
        }

        /// #4864 round-7: a SCHEDULER timeout (the merge closure sat queued on a
        /// saturated execution pool and the guest never ran) must log at DEBUG,
        /// NOT WARN — like queue-full (#4251), a WARN here would be loud precisely
        /// under the overload it represents — and must NOT blame the contract with
        /// the "contract not ready locally" message (the contract IS present).
        /// Auto-fetch is skipped (contract present ⇒ is_contract_exec_rejection).
        #[test]
        fn broadcast_to_streaming_failure_skips_auto_fetch_and_uses_debug_for_scheduler_timeout() {
            let logger = TestLogger::new().capture_logs().with_level("debug").init();
            let tx = Transaction::new::<UpdateMsg>();
            let err: OpError = scheduler_timeout_failure().into();
            // Precondition: the fixture really is classified as a scheduler timeout.
            assert!(
                err.is_scheduler_timeout(),
                "fixture must classify as a scheduler timeout"
            );

            let needs_auto_fetch =
                log_broadcast_to_streaming_failure(&tx, &make_contract_key(1), &err);

            assert!(
                !needs_auto_fetch,
                "scheduler timeout MUST NOT trigger self-heal auto-fetch — the contract \
                 IS present, the pool was just saturated; enqueuing a GET onto the \
                 saturated handler is the amplification we avoid"
            );
            assert!(
                logger.contains("scheduler_overloaded"),
                "scheduler timeout must emit event=scheduler_overloaded, got: {:?}",
                logger.logs()
            );
            assert!(
                !logger.logs().iter().any(|l| l.contains("WARN")),
                "scheduler timeout must NOT log at WARN — it fires under exactly the \
                 saturation it represents, got: {:?}",
                logger.logs()
            );
            assert!(
                !logger
                    .logs()
                    .iter()
                    .any(|l| l.contains("contract not ready locally")),
                "the misleading 'contract not ready locally' message must not appear \
                 for a scheduler timeout — the contract IS present, got: {:?}",
                logger.logs()
            );
        }

        /// Mirror of `update_contract_failure_logs_error_for_out_of_gas` for
        /// the streaming branch: OOG must stay at WARN, AND auto-fetch must
        /// be SKIPPED because the contract code is present (broader predicate
        /// `is_contract_exec_rejection` correctly catches this case). The two
        /// decisions are deliberately decoupled by the helper.
        #[test]
        fn broadcast_to_streaming_failure_logs_warn_and_skips_auto_fetch_for_out_of_gas() {
            let logger = TestLogger::new().capture_logs().with_level("info").init();
            let tx = Transaction::new::<UpdateMsg>();
            let err: OpError = out_of_gas_failure().into();

            let needs_auto_fetch =
                log_broadcast_to_streaming_failure(&tx, &make_contract_key(1), &err);

            assert!(
                logger.contains("WARN"),
                "out-of-gas must remain WARN-level for the streaming branch, got: {:?}",
                logger.logs()
            );
            assert!(
                !logger
                    .logs()
                    .iter()
                    .any(|l| l.contains("merge_rejected_invalid_update")),
                "out-of-gas must NOT be classified as a benign rejection, got: {:?}",
                logger.logs()
            );
            assert!(
                !needs_auto_fetch,
                "out-of-gas must NOT trigger self-heal auto-fetch (contract code is present locally; the broader is_contract_exec_rejection predicate catches this case independently of log severity)"
            );
        }
    }

    /// Pin: `send_summary_back_on_rejection` helper MUST gate on
    /// `sender_summary_bytes` matching our current summary before sending
    /// `InterestMessage::Summaries`. Without this gate, a mismatch triggers
    /// `SyncStateToPeer` at `node.rs:1791-1839` which re-sends the sender's
    /// stale state back to us, creating a reject→summary→resync→reject
    /// loop. ALSO pins the throttle-before-WASM ordering to prevent
    /// attacker-induced `summarize_state` amplification under rejection
    /// floods. See the helper's docs and PR description.
    #[test]
    fn summary_back_helper_gates_on_summary_equality() {
        let src = include_str!("update.rs");
        let fn_start = src
            .find("pub(crate) async fn send_summary_back_on_rejection(")
            .expect("send_summary_back_on_rejection fn not found");
        let fn_end_offset = src[fn_start..]
            .find("\n}\n")
            .expect("send_summary_back_on_rejection fn close not found");
        let fn_body = &src[fn_start..fn_start + fn_end_offset];

        assert!(
            fn_body.contains("sender_summary_bytes"),
            "send_summary_back_on_rejection must take sender_summary_bytes \
             as a parameter"
        );

        // Pin throttle-before-WASM ordering. Without this, an attacker
        // inducing rejections can force one `summarize_state` WASM call per
        // rejection — the equality gate below guards only the outgoing send.
        let throttle_pos = fn_body
            .find("should_send_summary_notification")
            .expect("helper MUST call should_send_summary_notification (throttle)");
        let wasm_call_pos = fn_body
            .find("get_contract_summary")
            .expect("helper must call get_contract_summary to compute our_summary");
        assert!(
            throttle_pos < wasm_call_pos,
            "should_send_summary_notification MUST run before get_contract_summary \
             — otherwise attacker-induced rejections force unbounded WASM amplification"
        );

        // Pin the EXACT inequality direction: on difference → early return.
        // If the direction is reversed (== → early return, meaning "send only
        // when they differ"), the helper reintroduces the SyncStateToPeer
        // loop that this PR fixes.
        let inequality_check_pos = fn_body
            .find("our_summary.as_ref() != sender_summary_bytes.as_slice()")
            .expect(
                "helper MUST use `our_summary.as_ref() != sender_summary_bytes.as_slice()` \
                 as the gate condition (reversed direction reintroduces the SyncStateToPeer \
                 loop — see node.rs:1791-1839)",
            );
        let after_check = &fn_body[inequality_check_pos..];
        let return_pos = after_check.find("return;").expect(
            "gate must early-return on inequality (reversed direction would bypass \
             the SyncStateToPeer safeguard)",
        );
        let notify_pos = after_check
            .find("notify_node_event")
            .expect("helper must still call notify_node_event on the equality path");
        assert!(
            return_pos < notify_pos,
            "early return on inequality MUST precede the notify_node_event \
             send — otherwise mismatched summaries would still be transmitted"
        );
    }

    /// Pin (#4473): `try_auto_fetch_contract` MUST gate on
    /// `self.ring.contract_in_use(...)` and early-return BEFORE it spawns a
    /// sub-op GET (`start_targeted_sub_op_get`) — but ONLY for the
    /// `AutoFetchReason::InboundRelay` path. Without the gate, an inbound
    /// relayed UPDATE for a contract this node carries only phantom interest in
    /// (no client, no downstream subscriber) spawns a `fetch_contract` sub-op
    /// every time the per-contract cooldown lapses — the residual #4473 churn
    /// the gate stops at the source. The existing 5-minute cooldown only
    /// throttles that; it does not prevent it. If a refactor drops this gate or
    /// moves it after the spawn, the storm regresses silently (all behavioural
    /// tests still pass), so pin the ordering at the source level.
    ///
    /// Equally important (Codex review on #4489): the gate MUST stay scoped to
    /// `InboundRelay`, never unconditional. Making it unconditional again would
    /// re-suppress the `Originator` self-heal path, stranding a local client's
    /// UPDATE behind a contract that never gets fetched. Pin that the gate
    /// condition mentions `AutoFetchReason::InboundRelay`.
    #[test]
    fn try_auto_fetch_contract_gates_on_contract_in_use_before_spawn() {
        let src = include_str!("update.rs");
        let fn_start = src
            .find("pub(crate) fn try_auto_fetch_contract(")
            .expect("try_auto_fetch_contract not found");
        let fn_src = &src[fn_start..];

        let gate_pos = fn_src.find("self.ring.contract_in_use(key)").expect(
            "try_auto_fetch_contract MUST gate on self.ring.contract_in_use(key) \
             so phantom-interest contracts are not auto-fetched (#4473)",
        );
        // The gate condition must be scoped to the inbound-relay reason so the
        // originator self-heal path is never suppressed (#4489).
        let reason_pos = fn_src.find("AutoFetchReason::InboundRelay").expect(
            "the contract_in_use gate MUST be conditioned on \
             AutoFetchReason::InboundRelay so Originator self-heal bypasses it (#4489)",
        );
        let return_pos = fn_src[gate_pos..]
            .find("return;")
            .map(|p| gate_pos + p)
            .expect("the contract_in_use gate must early-return when not in use");
        let spawn_pos = fn_src
            .find("start_targeted_sub_op_get")
            .expect("try_auto_fetch_contract must still spawn the sub-op GET on the in-use path");

        assert!(
            reason_pos < gate_pos,
            "the AutoFetchReason::InboundRelay guard MUST precede the \
             contract_in_use check, or the gate becomes unconditional and \
             re-suppresses the Originator self-heal path (#4489)"
        );
        assert!(
            gate_pos < return_pos && return_pos < spawn_pos,
            "the contract_in_use gate + early return MUST precede the \
             start_targeted_sub_op_get spawn, or phantom-interest contracts \
             regress the #4473 fetch_contract churn"
        );
    }

    /// Pin (#4489): the originator self-heal site MUST call
    /// `try_auto_fetch_contract` with `AutoFetchReason::Originator`, and every
    /// inbound relay/broadcast site MUST use `AutoFetchReason::InboundRelay`.
    /// If a refactor flips the originator site to `InboundRelay`, a one-shot
    /// client UPDATE for a contract we lack would be silently suppressed by the
    /// phantom-interest gate (the Codex finding on #4489); if it flips a relay
    /// site to `Originator`, the #4473 churn regresses. Pin both at the source.
    #[test]
    fn auto_fetch_call_sites_use_correct_reason() {
        let driver_src = include_str!("update/op_ctx_task.rs");

        // The originator site is the one paired with the `auto_fetch_originator`
        // tracing phase; it must use the Originator (ungated) reason.
        let originator_anchor = driver_src
            .find("phase = \"auto_fetch_originator\"")
            .expect("originator auto-fetch site (auto_fetch_originator phase) not found");
        let originator_call = driver_src[originator_anchor..]
            .find("try_auto_fetch_contract(")
            .map(|p| originator_anchor + p)
            .expect("originator site must still call try_auto_fetch_contract");
        let originator_reason = driver_src[originator_call..]
            .find("AutoFetchReason::")
            .map(|p| originator_call + p)
            .expect("originator try_auto_fetch_contract call must pass an AutoFetchReason");
        assert!(
            driver_src[originator_reason..].starts_with("AutoFetchReason::Originator"),
            "the auto_fetch_originator site MUST pass AutoFetchReason::Originator \
             so a local client's UPDATE self-heal is never gated (#4489)"
        );

        // No inbound relay/broadcast site may use Originator: those are the
        // #4473 churn paths and must stay gated.
        assert!(
            !driver_src.contains("sender_addr, AutoFetchReason::Originator"),
            "inbound relay/broadcast auto-fetch sites (keyed on sender_addr) MUST \
             use AutoFetchReason::InboundRelay, not Originator, or #4473 regresses"
        );
    }

    // ── #4923 state-as-summary poison regression tests ───────────────────────
    //
    // Sizes taken from the production case: a River room contract whose state
    // is ~253.2 KB and whose real `summarize_state` output is ~33.8 KB (13%).
    const ROOM_STATE_BYTES: usize = 253_200;
    const ROOM_SUMMARY_BYTES: usize = 33_800;

    /// The end of the #4923 poison chain, as pure logic: the wire-efficiency
    /// gate admits a delta for the contract's REAL summary, but refuses when
    /// the FULL STATE is cached in the same slot (what the pre-fix
    /// `send_proactive_summary_notification` published) — `state == summary`
    /// always refuses, so every broadcast to a poisoned peer fell back to a
    /// full-state send of exactly the state size (~253.2 KB per send, 41% of
    /// all network wire bytes in production).
    #[test]
    fn honest_summary_passes_the_delta_gate_where_poisoned_refused() {
        use crate::ring::interest::is_delta_efficient;

        assert!(
            is_delta_efficient(ROOM_SUMMARY_BYTES, ROOM_STATE_BYTES),
            "the contract's real summary must pass the delta-efficiency gate"
        );
        assert!(
            !is_delta_efficient(ROOM_STATE_BYTES, ROOM_STATE_BYTES),
            "a state-sized 'summary' (the state relabeled) must be refused by \
             the gate — this refusal is what forced every broadcast to a \
             poisoned peer down the full-state fallback (#4923)"
        );
    }

    /// Build a minimal real OpManager wired to a stand-in contract handler
    /// playing a contract with a 253.2 KB state and a 33.8 KB
    /// `summarize_state` output (production sizes from the #4923 incident).
    /// `summary_ok = false` makes `GetSummaryQuery` fail with an executor
    /// error, exercising the empty fallback. Returns the op_manager, the
    /// stand-in's state and summary, and a keep-alive guard for the channel
    /// halves and handler task. Mirrors
    /// `op_ctx_task.rs::build_queue_full_test_node`.
    async fn build_summary_test_node(
        id: &str,
        summary_ok: bool,
    ) -> (
        std::sync::Arc<OpManager>,
        WrappedState,
        StateSummary<'static>,
        Box<dyn std::any::Any>,
    ) {
        let config_args = crate::config::ConfigArgs {
            id: Some(id.to_string()),
            mode: Some(crate::contract::OperationMode::Local),
            ..Default::default()
        };
        let node_config =
            crate::node::NodeConfig::new(config_args.build().await.expect("build Config"))
                .await
                .expect("build NodeConfig");
        let (notification_rx, notification_tx) = crate::node::event_loop_notification_channel();
        let (ops_ch_channel, mut ch_channel, wait_for_event) =
            crate::contract::contract_handler_channel();
        let connection_manager = crate::ring::ConnectionManager::new(&node_config);
        let (result_router_tx, result_router_rx) = tokio::sync::mpsc::channel(100);
        let task_monitor = crate::node::background_task_monitor::BackgroundTaskMonitor::new();
        let op_manager = std::sync::Arc::new(
            OpManager::new(
                notification_tx,
                ops_ch_channel,
                &node_config,
                crate::tracing::DynamicRegister::new(vec![]),
                connection_manager,
                result_router_tx,
                &task_monitor,
            )
            .expect("build OpManager"),
        );
        op_manager.ring.attach_op_manager(&op_manager);

        // Stand-in contract: 253.2 KB state, 33.8 KB summary.
        let merged_state = WrappedState::from(vec![7u8; ROOM_STATE_BYTES]);
        let contract_summary = StateSummary::from(vec![9u8; ROOM_SUMMARY_BYTES]);
        let handler_state = merged_state.clone();
        let handler_summary = contract_summary.clone();
        let handler = tokio::spawn(async move {
            while let Ok((id, ev, _priority)) = ch_channel.recv_from_sender().await {
                let response = match ev {
                    ContractHandlerEvent::GetQuery { .. } => ContractHandlerEvent::GetResponse {
                        key: None,
                        response: Ok(StoreResponse {
                            state: Some(handler_state.clone()),
                            contract: None,
                        }),
                    },
                    ContractHandlerEvent::GetSummaryQuery { key } => {
                        ContractHandlerEvent::GetSummaryResponse {
                            key,
                            summary: if summary_ok {
                                Ok(handler_summary.clone())
                            } else {
                                Err(ExecutorError::other(crate::contract::ContractQueueFull))
                            },
                        }
                    }
                    ContractHandlerEvent::UpdateQuery { .. } => {
                        ContractHandlerEvent::UpdateResponse {
                            new_value: Ok(handler_state.clone()),
                            state_changed: true,
                        }
                    }
                    other => panic!("unexpected handler event: {other:?}"),
                };
                if ch_channel.send_to_sender(id, response).await.is_err() {
                    break;
                }
            }
        });

        let guard: Box<dyn std::any::Any> = Box::new((
            handler,
            notification_rx,
            result_router_rx,
            task_monitor,
            wait_for_event,
        ));
        (op_manager, merged_state, contract_summary, guard)
    }

    /// The head of the #4923 chain, against the real production functions.
    ///
    /// The client driver (`drive_client_update`) applies the update via
    /// `update_contract` — which computes NO summary at all (MAJOR 4) — and
    /// then fetches the `UpdateResponse` summary via
    /// `contract_summary_or_empty`. That fetched value must be the contract's
    /// real `summarize_state` output. Pre-fix, the client response carried
    /// the merged STATE relabeled as a summary, and the proactive
    /// notification broadcast the same poisoned value to every interested
    /// peer, where `is_delta_efficient` then refused every delta (#4923).
    #[tokio::test]
    async fn client_facing_summary_is_the_contract_summary_not_the_state() {
        let (op_manager, merged_state, contract_summary, _guard) =
            build_summary_test_node("update-summary-poison-4923", true).await;

        let key = make_contract_key(1);
        let execution = update_contract(
            &op_manager,
            key,
            UpdateData::Delta(StateDelta::from(vec![1u8, 2, 3])),
            RelatedContracts::default(),
            crate::contract::Priority::ClientLocal,
        )
        .await
        .expect("update must succeed");
        assert!(execution.changed, "stand-in reports a changed state");

        // Exactly what the two client `UpdateResponse { summary }` sites in
        // `drive_client_update` do after the update resolves.
        let summary =
            contract_summary_or_empty(&op_manager, key, crate::contract::Priority::ClientLocal)
                .await;

        assert_eq!(
            summary.as_ref(),
            contract_summary.as_ref(),
            "the client-facing summary must be the contract's `summarize_state` \
             output ({ROOM_SUMMARY_BYTES} bytes), not the merged state \
             ({ROOM_STATE_BYTES} bytes) relabeled as a summary (#4923)"
        );
        assert_ne!(
            summary.as_ref(),
            merged_state.as_ref(),
            "the client-facing summary must never equal the state bytes (#4923)"
        );
        assert!(
            crate::ring::interest::is_delta_efficient(
                summary.as_ref().len(),
                execution.value.size()
            ),
            "the client-facing summary must pass the receiver's \
             delta-efficiency gate; got a {}-byte summary for a {}-byte state",
            summary.as_ref().len(),
            execution.value.size(),
        );
    }

    /// MINOR 6 error path: when the summarize fails (saturated executor,
    /// WASM error, missing state), `contract_summary_or_empty` must return
    /// the EMPTY summary — never the state bytes, which would re-open the
    /// #4923 poison through the client-facing `UpdateResponse`.
    #[tokio::test]
    async fn contract_summary_or_empty_error_path_returns_empty_not_state() {
        let (op_manager, merged_state, _contract_summary, _guard) =
            build_summary_test_node("update-summary-poison-4923-errpath", false).await;

        let key = make_contract_key(1);
        let summary =
            contract_summary_or_empty(&op_manager, key, crate::contract::Priority::ClientLocal)
                .await;

        assert!(
            summary.as_ref().is_empty(),
            "the summarize-failure fallback must be the EMPTY summary, got {} bytes",
            summary.as_ref().len()
        );
        assert_ne!(
            summary.as_ref(),
            merged_state.as_ref(),
            "the fallback must never be the state bytes (#4923)"
        );
    }

    /// Source-scrape pin so a future refactor cannot silently re-introduce
    /// the #4923 mislabeling (or the MAJOR-4 per-apply summary cost).
    /// Whitespace is collapsed before matching so rustfmt re-wrapping cannot
    /// break the needles; call-site needles match the fn name only, so a
    /// trailing comma or argument reflow cannot break them either.
    ///
    /// Three pinned regions:
    /// 1. `update_contract` does NO summary work: no `StateSummary::from(`
    ///    (the poison construction) and no `contract_summary_or_empty(` call
    ///    (it runs on the relay/no-change hot paths — consumers fetch their
    ///    own summary).
    /// 2. `contract_summary_or_empty` may construct a `StateSummary` ONLY as
    ///    the empty fallback `StateSummary::from(Vec::new())`.
    /// 3. `drive_client_update` fetches the client-facing summary via
    ///    `contract_summary_or_empty` in BOTH arms (local-only and
    ///    remote-forward) and never builds one from bytes.
    #[test]
    fn update_contract_never_builds_a_summary_from_state_bytes() {
        let src = include_str!("update.rs");

        // Region 1: update_contract body.
        let uc_start = src
            .find("pub(crate) async fn update_contract(")
            .expect("update_contract must exist");
        let uc_end = src[uc_start..]
            .find("\n/// Send proactive summary notifications")
            .map(|off| uc_start + off)
            .expect("update_contract must be followed by send_proactive_summary_notification");
        let uc_body: String = src[uc_start..uc_end].split_whitespace().collect();
        assert!(
            !uc_body.contains("StateSummary::from("),
            "update_contract must not synthesize a StateSummary from bytes it \
             has on hand — a state-sized summary poisons every peer's delta \
             gate (#4923)"
        );
        assert!(
            !uc_body.contains("contract_summary_or_empty("),
            "update_contract must do NO summary work — it runs on the \
             relay-broadcast and no-change hot paths; the client driver \
             fetches the summary itself (#4923 MAJOR 4)"
        );

        // Region 2: contract_summary_or_empty body — only the empty fallback.
        let h_start = src
            .find("async fn contract_summary_or_empty(")
            .expect("contract_summary_or_empty must exist");
        let h_end = src[h_start..]
            .find("\n/// Apply an update to a contract.")
            .map(|off| h_start + off)
            .expect("contract_summary_or_empty must be followed by update_contract's doc");
        let h_body: String = src[h_start..h_end].split_whitespace().collect();
        let h_sans_fallback = h_body.replace("StateSummary::from(Vec::new())", "");
        assert!(
            !h_sans_fallback.contains("StateSummary::from("),
            "contract_summary_or_empty may construct a StateSummary ONLY as \
             the empty fallback StateSummary::from(Vec::new()) — any other \
             construction risks re-introducing state-as-summary (#4923)"
        );

        // Region 3: the client driver fetches via the helper in both arms.
        let driver_src = include_str!("update/op_ctx_task.rs");
        let d_start = driver_src
            .find("async fn drive_client_update(")
            .expect("drive_client_update must exist");
        let d_after = &driver_src[d_start + 1..];
        let d_end = d_after
            .find("\nasync fn ")
            .or_else(|| d_after.find("\nfn "))
            .unwrap_or(d_after.len());
        let d_body: String = driver_src[d_start..d_start + 1 + d_end]
            .split_whitespace()
            .collect();
        assert!(
            d_body.matches("contract_summary_or_empty(").count() >= 2,
            "drive_client_update must fetch the client-facing summary via \
             contract_summary_or_empty in BOTH arms (local-only and \
             remote-forward) — hand-rolled summaries re-open #4923"
        );
        assert!(
            !d_body.contains("StateSummary::from("),
            "drive_client_update must never build a StateSummary from bytes \
             (#4923)"
        );
    }

    // ── #4965: proactive summary notification recipient set ───────────────
    //
    // `interest_sync_summaries` is the largest outbound arm (49.8% of outbound
    // bytes, v0.2.115). Which of its four emitters dominates is NOT measured —
    // `outbound_message_mix` buckets them together (#5052 adds the split).
    // What this change rests on is narrower and does not need that number:
    // most recipients of this notification are advertised co-hosts that
    // already received the identical summary inside the broadcast's
    // `sender_summary_bytes`.

    /// Build a `(pub_key, addr)` pair plus the matching `PeerKeyLocation`.
    fn resolved_peer(port: u16) -> (TransportPublicKey, SocketAddr) {
        let pkl = crate::operations::test_utils::make_peer(port);
        (
            pkl.pub_key.clone(),
            pkl.socket_addr().expect("test peer has a socket addr"),
        )
    }

    #[test]
    fn proactive_summary_targets_excludes_advertised_cohosts() {
        let cohost = resolved_peer(9001);
        let non_cohost = resolved_peer(9002);
        let interested = vec![cohost.clone(), non_cohost.clone()];

        let cohosts: HashSet<TransportPublicKey> = [cohost.0.clone()].into_iter().collect();

        let targets = proactive_summary_targets(
            &interested,
            &cohosts,
            "127.0.0.1:9999".parse().unwrap(),
            None,
        )
        .targets;

        assert_eq!(
            targets,
            vec![non_cohost.1],
            "an advertised co-host already got this summary in the broadcast's \
             sender_summary_bytes (#4952); re-sending it standalone is the #4965 waste"
        );
    }

    #[test]
    fn proactive_summary_targets_keeps_interested_non_cohosts() {
        let a = resolved_peer(9010);
        let b = resolved_peer(9011);
        let interested = vec![a.clone(), b.clone()];

        // Nothing advertised: this is the population the notification exists
        // for — peers we do NOT broadcast to, whose only other path to our
        // summary is the ~5-min heartbeat.
        let targets = proactive_summary_targets(
            &interested,
            &HashSet::new(),
            "127.0.0.1:9999".parse().unwrap(),
            None,
        )
        .targets;

        assert_eq!(targets, vec![a.1, b.1]);
    }

    #[test]
    fn proactive_summary_targets_still_excludes_sender_and_self() {
        let sender = resolved_peer(9020);
        let me = resolved_peer(9021);
        let other = resolved_peer(9022);
        let interested = vec![sender.clone(), me.clone(), other.clone()];

        let targets =
            proactive_summary_targets(&interested, &HashSet::new(), sender.1, Some(me.1)).targets;

        assert_eq!(
            targets,
            vec![other.1],
            "the pre-existing sender/self exclusions must survive the #4965 change"
        );
    }

    #[test]
    fn proactive_summary_targets_is_empty_when_every_peer_is_a_cohost() {
        // The steady state this fix targets: every interested peer is an
        // advertised co-host, so the broadcast covered all of them and the
        // notification fan-out collapses to zero messages.
        let a = resolved_peer(9030);
        let b = resolved_peer(9031);
        let interested = vec![a.clone(), b.clone()];
        let cohosts: HashSet<TransportPublicKey> = [a.0.clone(), b.0.clone()].into_iter().collect();

        let targets = proactive_summary_targets(
            &interested,
            &cohosts,
            "127.0.0.1:9999".parse().unwrap(),
            None,
        )
        .targets;

        assert!(
            targets.is_empty(),
            "expected zero standalone notifications, got {targets:?}"
        );
    }

    #[test]
    fn proactive_summary_targets_handles_empty_interest_set() {
        let targets = proactive_summary_targets(
            &[],
            &HashSet::new(),
            "127.0.0.1:9999".parse().unwrap(),
            Some("127.0.0.1:9998".parse().unwrap()),
        )
        .targets;
        assert!(targets.is_empty());
    }

    #[test]
    fn proactive_summary_targets_cohost_exclusion_is_by_pub_key_not_addr() {
        // A co-host whose advertised entry is keyed by pub_key must be
        // excluded even though nothing about its ADDRESS marks it — matching
        // `get_broadcast_targets_update`, which also sources targets by
        // pub_key from `neighbors_with_contract`.
        let cohost = resolved_peer(9040);
        let cohosts: HashSet<TransportPublicKey> = [cohost.0.clone()].into_iter().collect();

        let targets = proactive_summary_targets(
            &[cohost.clone()],
            &cohosts,
            "127.0.0.1:9999".parse().unwrap(),
            None,
        )
        .targets;
        assert!(targets.is_empty());

        // Same address, different identity => not the advertised co-host.
        let impostor = (resolved_peer(9041).0, cohost.1);
        let targets = proactive_summary_targets(
            &[impostor],
            &cohosts,
            "127.0.0.1:9999".parse().unwrap(),
            None,
        )
        .targets;
        assert_eq!(targets, vec![cohost.1]);
    }

    /// `cohosts_skipped` counts ONLY the #4965 co-host drops — not the sender,
    /// not self.
    ///
    /// Found by mutation testing, not by review. The count was originally
    /// derived at the call site as `resolved.len() - targets.len()`, which
    /// looks equivalent and is not: it also counts the sender and self, so it
    /// stayed non-zero with the entire co-host exclusion deleted. That made
    /// the number report a saving the code was not making, AND it silently
    /// defeated the simulation test whose whole job is to fail when the
    /// exclusion is removed — that test passed under the deletion mutation.
    ///
    /// The scenario below is the discriminating one: the sender is ALSO
    /// interested, so a count that includes sender/self reads 2 where the
    /// truthful co-host count is 1.
    #[test]
    fn cohosts_skipped_counts_only_cohost_drops_not_sender_or_self() {
        let sender = resolved_peer(9050);
        let me = resolved_peer(9051);
        let cohost = resolved_peer(9052);
        let plain = resolved_peer(9053);
        let interested = vec![sender.clone(), me.clone(), cohost.clone(), plain.clone()];
        let cohosts: HashSet<TransportPublicKey> = [cohost.0.clone()].into_iter().collect();

        let out = proactive_summary_targets(&interested, &cohosts, sender.1, Some(me.1));

        assert_eq!(out.targets, vec![plain.1]);
        assert_eq!(
            out.cohosts_skipped, 1,
            "only the advertised co-host counts; the sender and self are \
             dropped for pre-#4965 reasons and must not inflate the saving"
        );

        // With no co-hosts advertised the count must be ZERO even though two
        // peers were still dropped. This is the assertion the old subtraction
        // failed, and it is what makes the simulation's `cohosts_skipped > 0`
        // a real discriminator.
        let out = proactive_summary_targets(&interested, &HashSet::new(), sender.1, Some(me.1));
        assert_eq!(out.targets, vec![cohost.1, plain.1]);
        assert_eq!(
            out.cohosts_skipped, 0,
            "with the exclusion inactive the co-host skip count MUST be 0 — \
             a non-zero value here means the metric is measuring the sender/\
             self drops and cannot detect the exclusion being removed"
        );
    }

    /// Source pin: the production emitter must actually consult the
    /// advertisement layer and route its recipient set through
    /// `proactive_summary_targets`.
    ///
    /// Without this, someone could revert the emitter to iterating
    /// `get_interested_peers` directly and every pure test above would stay
    /// green — the exact failure mode `.claude/rules/operations.md` calls out
    /// for event-emission fixes (#3791).
    #[test]
    fn proactive_notification_excludes_advertised_cohosts_in_production() {
        let src = include_str!("update.rs");
        // Cut at `mod tests` (NOT `#[cfg(test)]`, whose attribute line sits
        // above the doc comments) so the needles can't match this test file.
        let prod = &src[..src.find("\nmod tests {").expect("tests module not found")];

        let fn_start = prod
            .find("pub(crate) async fn send_proactive_summary_notification(")
            .expect("send_proactive_summary_notification not found");
        let fn_src = &prod[fn_start..];
        // `+ 1` rebases the offset: `find` searched `fn_src[1..]`, but the
        // slice below indexes `fn_src`. Without it the body ends one byte
        // early — harmless today (it only drops the preceding newline, which
        // the whitespace filter would strip anyway) but the two indices must
        // share a base or a future edit to this boundary will cut real source.
        let fn_end = 1 + fn_src[1..]
            .find("\npub(crate) fn ")
            .expect("expected proactive_summary_targets to follow the emitter");
        // Whitespace-stripped so the pin survives rustfmt reflowing the call.
        let body: String = fn_src[..fn_end]
            .chars()
            .filter(|c| !c.is_whitespace())
            .collect();

        assert!(
            body.contains("advertised_cohost_pub_keys(key)"),
            "the emitter MUST consult the advertisement layer — without it the \
             co-host exclusion silently does nothing (#4965)"
        );
        assert!(
            body.contains("proactive_summary_targets(&resolved,&advertised_cohosts,"),
            "the emitter MUST route its recipient set through \
             proactive_summary_targets so the pure tests above actually guard \
             production (see .claude/rules/operations.md, #3791)"
        );
        assert!(
            // Needle is `in&interested`, NOT `forpeer_addrin&interested`: the
            // pre-change loop was `for (peer_key, _interest) in &interested {`,
            // which whitespace-strips to `for(peer_key,_interest)in&interested{`.
            // The longer needle never matched the code it claimed to guard, so
            // it could not fail on the reversion named in its own message.
            !body.contains("in&interested"),
            "the emitter must not iterate the raw interested-peer set again — \
             it must send only to the filtered `targets`"
        );
        assert!(
            body.contains("ring.should_summarize_or_broadcast(key)"),
            "the emitter MUST share the #4473/#4610 gate with the broadcast \
             fan-out. Ungated, a contract that broadcasts to NOBODY \
             (should_broadcast_contract false) still excludes every advertised \
             co-host here — exclusion with no broadcast behind it, which is \
             exactly what makes the #4965 skip unsound"
        );
    }

    /// The co-host population must come from ONE accessor, shared with
    /// `get_broadcast_targets_update`.
    ///
    /// The behavioural guard is
    /// `notification_exclusion_is_a_subset_of_broadcast_targets`; this pin is
    /// the cheap structural half, and it fails on the specific edit that test
    /// cannot see coming: a second, independent read of `neighbor_hosting` at
    /// either site, which is how the two sets drift apart in the first place.
    #[test]
    fn cohost_source_is_shared_between_broadcast_and_notification() {
        let src = include_str!("update.rs");
        let prod = &src[..src.find("\nmod tests {").expect("tests module not found")];
        let stripped: String = prod.chars().filter(|c| !c.is_whitespace()).collect();

        // Exactly one direct read of the advertisement layer in this file: the
        // accessor itself. Any other is a site that will not follow a future
        // narrowing of the shared source.
        assert_eq!(
            stripped
                .matches("neighbor_hosting.neighbors_with_contract(")
                .count(),
            1,
            "`neighbors_with_contract` must be read ONLY through \
             `advertised_cohost_pub_keys`. A second direct read means the \
             broadcast fan-out and the #4965 notification exclusion can drift \
             apart, and each site stays individually correct while the peers \
             between them get neither the broadcast nor the summary"
        );
        assert!(
            stripped.contains("fnadvertised_cohost_pub_keys(&self,key:&ContractKey)"),
            "the shared accessor must still exist"
        );
        // Both consumers go through it.
        assert!(
            stripped.contains("letproximity_pub_keys=self.advertised_cohost_pub_keys(key);"),
            "get_broadcast_targets_update must source its targets from the \
             shared accessor"
        );
        assert!(
            stripped.contains("op_manager.advertised_cohost_pub_keys(key)"),
            "send_proactive_summary_notification must source its exclusion set \
             from the shared accessor"
        );
    }

    // ── Behavioural coverage against a real OpManager ─────────────────────
    //
    // The pure `proactive_summary_targets` tests above prove the FILTER is
    // right; the pins prove production calls it. Neither can see the property
    // the #4965 skip actually rests on, which spans two functions: every peer
    // the notification EXCLUDES must be a peer the broadcast fan-out would
    // have reached. These tests assert that against the real emitter.

    /// Build an `OpManager` whose contract handler answers `GetSummaryQuery`,
    /// returning the event-loop notification receiver so a test can read the
    /// `SendInterestMessage` events the emitter actually produced.
    ///
    /// Deliberately NOT folded into `build_summary_test_node`: that helper
    /// hides the receiver inside its keep-alive guard, and the whole point
    /// here is to inspect the emitted recipient set rather than infer it from
    /// the data layer that feeds it (#3791).
    async fn build_notification_test_node(
        id: &str,
    ) -> (
        std::sync::Arc<OpManager>,
        tokio::sync::mpsc::Receiver<
            either::Either<crate::message::NetMessage, crate::message::NodeEvent>,
        >,
        Box<dyn std::any::Any>,
    ) {
        let config_args = crate::config::ConfigArgs {
            id: Some(id.to_string()),
            mode: Some(crate::contract::OperationMode::Local),
            ..Default::default()
        };
        let node_config =
            crate::node::NodeConfig::new(config_args.build().await.expect("build Config"))
                .await
                .expect("build NodeConfig");
        let (notification_rx, notification_tx) = crate::node::event_loop_notification_channel();
        let (ops_ch_channel, mut ch_channel, wait_for_event) =
            crate::contract::contract_handler_channel();
        let connection_manager = crate::ring::ConnectionManager::new(&node_config);
        let (result_router_tx, result_router_rx) = tokio::sync::mpsc::channel(100);
        let task_monitor = crate::node::background_task_monitor::BackgroundTaskMonitor::new();
        let op_manager = std::sync::Arc::new(
            OpManager::new(
                notification_tx,
                ops_ch_channel,
                &node_config,
                crate::tracing::DynamicRegister::new(vec![]),
                connection_manager,
                result_router_tx,
                &task_monitor,
            )
            .expect("build OpManager"),
        );
        op_manager.ring.attach_op_manager(&op_manager);

        let summary = StateSummary::from(vec![9u8; 32]);
        let handler = tokio::spawn(async move {
            while let Ok((id, ev, _priority)) = ch_channel.recv_from_sender().await {
                let response = match ev {
                    ContractHandlerEvent::GetSummaryQuery { key } => {
                        ContractHandlerEvent::GetSummaryResponse {
                            key,
                            summary: Ok(summary.clone()),
                        }
                    }
                    other => panic!("unexpected handler event: {other:?}"),
                };
                if ch_channel.send_to_sender(id, response).await.is_err() {
                    break;
                }
            }
        });

        // Field access rather than a destructuring pattern: the receiver's TYPE
        // lives in the private `node::network_bridge` module and cannot be
        // named from here, but its fields are `pub(crate)`.
        let notifications_receiver = notification_rx.notifications_receiver;
        let op_execution_receiver = notification_rx.op_execution_receiver;

        let guard: Box<dyn std::any::Any> = Box::new((
            handler,
            op_execution_receiver,
            result_router_rx,
            task_monitor,
            wait_for_event,
        ));
        (op_manager, notifications_receiver, guard)
    }

    /// Connect a peer and return `(pub_key, addr)`.
    fn connect_peer(
        op_manager: &OpManager,
        port: u16,
        loc: f64,
    ) -> (TransportPublicKey, SocketAddr) {
        let keypair = crate::transport::TransportKeypair::new();
        let addr: SocketAddr = format!("127.0.0.1:{port}").parse().unwrap();
        op_manager.ring.connection_manager.add_connection(
            crate::ring::Location::new(loc),
            addr,
            keypair.public().clone(),
            false,
        );
        (keypair.public().clone(), addr)
    }

    /// Make `peer` an advertised co-host of `key`, the way an inbound
    /// `HostingAnnounce` does.
    fn advertise_cohost(op_manager: &OpManager, peer: &TransportPublicKey, key: &ContractKey) {
        op_manager.neighbor_hosting.handle_message(
            peer,
            crate::message::NeighborHostingMessage::HostingAnnounce {
                added: vec![*key.id()],
                removed: vec![],
                // `is_response: true` so the handler does not try to build a
                // reply message; we only want the cache mutation.
                is_response: true,
            },
        );
    }

    /// Drain the notification channel into the `SendInterestMessage` targets.
    fn drain_interest_targets(
        rx: &mut tokio::sync::mpsc::Receiver<
            either::Either<crate::message::NetMessage, crate::message::NodeEvent>,
        >,
    ) -> Vec<SocketAddr> {
        let mut targets = Vec::new();
        while let Ok(item) = rx.try_recv() {
            if let either::Either::Right(crate::message::NodeEvent::SendInterestMessage {
                target,
                ..
            }) = item
            {
                targets.push(target);
            }
        }
        targets.sort();
        targets
    }

    /// The load-bearing cross-function property: a peer the notification
    /// EXCLUDES must be a peer the broadcast fan-out would have reached.
    ///
    /// This is what the source pins cannot express. Both sites are
    /// individually correct today; the failure mode the review names is a
    /// FILTER added to `get_broadcast_targets_update` (a cap, a health check,
    /// a location predicate) that narrows the broadcast set while the
    /// exclusion keeps using the full advertised set. The excluded peer then
    /// gets neither the broadcast nor the standalone summary, and every
    /// single-site test stays green. Asserting the subset relation between the
    /// two real functions is the only thing that fails on that edit.
    ///
    /// # Why TWO interested co-hosts, and why you must not simplify to one
    ///
    /// **A set-relation assertion cannot be falsified by a fixture whose set
    /// has one element.** With a single interested co-host, `excluded ⊆
    /// broadcast_targets` is satisfied by almost any mutation, because there is
    /// no second element for a narrowing to strand — the assertion reads strong
    /// and is very nearly unfalsifiable. Two is not a richer scenario, it is
    /// the MINIMUM CARDINALITY at which the property has any content, the same
    /// way a commutativity test needs two distinct operands or an ordering test
    /// two distinct keys.
    ///
    /// Verified: a `truncate(1)` on `get_broadcast_targets_update`'s co-host
    /// list left the one-co-host version of this test GREEN, and fails the
    /// two-co-host version. Adding the non-co-host (C) and the co-host-only
    /// peer (E) keeps the two filters distinguishable from each other.
    ///
    /// # Why premise 1 is deliberately weak
    ///
    /// It asserts only that the broadcast has SOME target, not that a specific
    /// peer is among them. **A premise that fails before the real assertion
    /// masks which check actually caught the mutation**, so a premise should be
    /// the weakest statement that still rules out vacuity. The strict form
    /// ("A specifically is a target") would fire first under a narrowing
    /// mutation and hide the fact that the subset property is what detects it.
    #[tokio::test]
    async fn notification_exclusion_is_a_subset_of_broadcast_targets() {
        let (op_manager, mut rx, _guard) =
            build_notification_test_node("notif-exclusion-subset-4965").await;
        let key = crate::operations::test_utils::make_contract_key(11);
        op_manager
            .ring
            .host_contract(key, 1024, crate::ring::AccessType::Put);

        // A and B: advertised co-hosts AND interested — the excluded
        //          population. TWO of them, deliberately: with only one, a
        //          mutation that narrows the broadcast target set to a single
        //          peer can happen to keep exactly the excluded one, and the
        //          subset assertion still holds. Mutation testing caught that
        //          — a `truncate(1)` on the broadcast targets left this test
        //          green. With two, narrowing to one always strands the other.
        // C: interested only — the population the notification still exists for.
        // E: advertised co-host only — a broadcast target we never notify.
        let (a_pk, a_addr) = connect_peer(&op_manager, 19101, 0.11);
        let (b_pk, b_addr) = connect_peer(&op_manager, 19102, 0.12);
        let (c_pk, c_addr) = connect_peer(&op_manager, 19103, 0.13);
        let (e_pk, _e_addr) = connect_peer(&op_manager, 19105, 0.15);
        let (_d_pk, sender_addr) = connect_peer(&op_manager, 19104, 0.14);

        advertise_cohost(&op_manager, &a_pk, &key);
        advertise_cohost(&op_manager, &b_pk, &key);
        advertise_cohost(&op_manager, &e_pk, &key);
        for pk in [&a_pk, &b_pk, &c_pk] {
            op_manager.interest_manager.register_peer_interest(
                &key,
                crate::ring::PeerKey::from(pk.clone()),
                None,
                false,
            );
        }

        let broadcast_targets: HashSet<SocketAddr> = op_manager
            .get_broadcast_targets_update(&key, &sender_addr)
            .targets
            .iter()
            .filter_map(|pkl| pkl.socket_addr())
            .collect();

        send_proactive_summary_notification(&op_manager, &key, sender_addr).await;
        let notified: HashSet<SocketAddr> = drain_interest_targets(&mut rx).into_iter().collect();

        // Premise 1: the scenario really produced a broadcast fan-out.
        assert!(
            !broadcast_targets.is_empty(),
            "premise: the broadcast must have targets, else the subset \
             assertion below is vacuous"
        );
        // Premise 2: the exclusion really excluded BOTH co-hosts and kept the
        // non-co-host. Without this the subset assertion passes trivially on
        // an empty set.
        let interested_addrs: HashSet<SocketAddr> = [a_addr, b_addr, c_addr].into_iter().collect();
        let excluded: HashSet<SocketAddr> =
            interested_addrs.difference(&notified).copied().collect();
        assert_eq!(
            excluded,
            [a_addr, b_addr].into_iter().collect::<HashSet<_>>(),
            "both advertised co-hosts must be excluded and the non-co-host C \
             kept; notified={notified:?}"
        );

        // The property.
        assert!(
            excluded.is_subset(&broadcast_targets),
            "#4965 UNSOUND: {:?} were excluded from the standalone summary \
             notification but are NOT broadcast targets {:?}, so nothing \
             delivered them our summary. The exclusion is only valid while the \
             broadcast covers every peer it drops.",
            excluded.difference(&broadcast_targets).collect::<Vec<_>>(),
            broadcast_targets,
        );
    }

    /// The gate: a contract that broadcasts to NOBODY must not notify either.
    ///
    /// Same topology as the subset test, minus `host_contract` — so
    /// `should_summarize_or_broadcast` is false, `should_broadcast_contract`
    /// suppresses the whole fan-out, and (pre-gate) the emitter still ran and
    /// still excluded every advertised co-host. That is exclusion with no
    /// broadcast behind it: A gets neither.
    ///
    /// Reachable population (#4440/#4473/#4610): state on disk, evicted from
    /// the hosting cache, no local client and no downstream subscriber.
    #[tokio::test]
    async fn proactive_notification_is_gated_like_the_broadcast() {
        let (op_manager, mut rx, _guard) = build_notification_test_node("notif-gate-4473").await;
        let key = crate::operations::test_utils::make_contract_key(12);
        // Deliberately NOT hosted and NOT in use.
        assert!(
            !op_manager.ring.should_summarize_or_broadcast(&key),
            "premise: the gate must be false, else this test proves nothing"
        );

        let (a_pk, _a_addr) = connect_peer(&op_manager, 19201, 0.21);
        let (b_pk, _b_addr) = connect_peer(&op_manager, 19202, 0.22);
        let (_d_pk, sender_addr) = connect_peer(&op_manager, 19203, 0.23);
        advertise_cohost(&op_manager, &a_pk, &key);
        op_manager.interest_manager.register_peer_interest(
            &key,
            crate::ring::PeerKey::from(a_pk.clone()),
            None,
            false,
        );
        op_manager.interest_manager.register_peer_interest(
            &key,
            crate::ring::PeerKey::from(b_pk.clone()),
            None,
            false,
        );

        // Premise: A really is an advertised co-host, so pre-gate this
        // contract WOULD have excluded a real peer. Without this the emitter
        // could be emitting nothing for an unrelated reason.
        assert_eq!(
            op_manager.advertised_cohost_pub_keys(&key),
            vec![a_pk.clone()],
            "premise: A must be an advertised co-host, else the gate is not \
             what is suppressing the notification"
        );
        // The broadcast fan-out is suppressed for this contract by the SAME
        // predicate asserted above: `broadcast_queue::should_broadcast_contract`
        // is a one-line delegation to `ring.should_summarize_or_broadcast`,
        // pinned there by
        // `broadcast_single_peer_gates_summarize_on_hosted_or_in_use_pin`.
        // It is `pub(super)` so it cannot be called from here directly.

        send_proactive_summary_notification(&op_manager, &key, sender_addr).await;

        assert!(
            drain_interest_targets(&mut rx).is_empty(),
            "a contract whose broadcast fan-out is suppressed for the WHOLE \
             contract must not emit standalone summary notifications either — \
             ungated, this path also pays an unbounded WASM summarize for \
             every phantom contract, the #4473 storm the gate exists to stop"
        );
    }
}