Postgres engine: open constructor, PgOpts, pool + listener wiring — forwarder skeleton with the POC-pinned pitfalls structurally excluded, seam error mappings, wave-3 stub surface (task pg-engine-open-opts)

Cargo.lock

@@ -28,6 +28,7 @@ dependencies = [
  "alkstore",
  "alkstore-contract-suite",
  "deadpool-postgres",
+ "serde_json",
  "thiserror",
  "tokio",
  "tokio-postgres",

alkstore-postgres/Cargo.toml

@@ -7,10 +7,11 @@ repository.workspace = true
 
 [dependencies]
 alkstore = { version = "0.1", path = "../alkstore" }
-tokio = { version = "1", features = ["rt-multi-thread", "macros"] }
-tokio-postgres = "0.7"
 deadpool-postgres = "0.14"
+serde_json = "1"
 thiserror = "2"
+tokio = { version = "1", features = ["rt-multi-thread", "macros", "sync", "time"] }
+tokio-postgres = "0.7"
 
 [dev-dependencies]
 alkstore-contract-suite = { path = "../alkstore-contract-suite" }

alkstore-postgres/src/forwarder.rs

@@ -0,0 +1,463 @@
+//! The LISTEN forwarder (ADR-004): the wake substrate every later
+//! mechanism task rides. This module carries the **skeleton** — the
+//! dedicated non-pooled connection, the `poll_message` loop fanning
+//! out into a bounded broadcast channel, the dynamic channel set the
+//! notify-listen task's `listen` adds channels to — with the full
+//! behavior (reconnect honesty contract, receiver bridging) the
+//! notify-listen task's.
+//!
+//! # The two POC-pinned deadlock pitfalls, structurally excluded
+//!
+//! 1. **Query-vs-poll starvation deadlock** (POC failure mode 1): the
+//!    `poll_message` loop must be *running before the first client
+//!    query* on the listener connection. Every connection generation
+//!    is structured the same way: the poll task is spawned first and
+//!    owns the `Connection`; LISTEN/UNLISTEN queries ride the `Client`
+//!    only afterwards — and even mid-connect the request cannot
+//!    complete before the poll task drives the connection's response.
+//!    The command select in the loop keeps the poll task forever
+//!    co-resident with client queries on this connection (the
+//!    exclusion is held permanently, not just at spawn).
+//! 2. **Client-drop closes the session** (POC failure mode 2): the
+//!    listener's `Client` is owned by the forwarder task and kept
+//!    alive for the connection generation's lifetime — nobody else
+//!    holds it, and it is only dropped at shutdown or once the session
+//!    is already dead server-side (reconnect path).
+//!
+//! # Connection budget
+//!
+//! The listener connection is outside the pool (deadpool#360 — pooled
+//! connections register LISTEN server-side but can never deliver): a
+//! per-process budget line `max_size + 1` per LISTEN-ing process
+//! (deployment.md). The listener sets `application_name` for
+//! kill-targetability (the deployment.md ops note, POC-carried).
+//!
+//! # Fanout
+//!
+//! `poll_message`'s notifications fan into one bounded broadcast
+//! channel (capacity 1024 per the POC's shape); lag is **surfaced,
+//! not silent** — a `Lagged(n)` receiver resumes streaming (the POC's
+//! bridge posture). The wake content (`Wake { channel }` only) and
+//! per-receiver bridging are the notify-listen task's; the skeleton
+//! broadcasts raw notification channel names.
+
+use std::sync::Arc;
+use std::sync::atomic::{AtomicBool, Ordering};
+use std::time::Duration;
+
+use tokio::sync::{broadcast, mpsc, watch};
+use tokio_postgres::NoTls;
+
+use crate::seam::database_error;
+
+/// The listener connection's concrete type for the `NoTls` posture
+/// (the engine's TLS story rides the consumer's `Config` sslmode for
+/// the pooled path; the dedicated listener connects with `NoTls` —
+/// TLS hardening is the deployment's ingress posture, the notify-
+/// listen task revisits if a task or ADR demands listener TLS).
+pub(crate) type ListenerConnection = tokio_postgres::Connection<
+    tokio_postgres::Socket,
+    <tokio_postgres::NoTls as tokio_postgres::tls::MakeTlsConnect<tokio_postgres::Socket>>::Stream,
+>;
+
+/// The forwarder's reconnect backoff: exponential 50 ms → 2 s cap
+/// (the POC's policy; ADR-004 — the notify-listen task owns the full
+/// reconnect behavior on this skeleton's loop).
+pub(crate) const RECONNECT_BASE_MS: u64 = 50;
+pub(crate) const RECONNECT_MAX_MS: u64 = 2000;
+
+/// The bounded broadcast capacity (the POC's 1024 shape; lag surfaced,
+/// not silent).
+const FANOUT_CAPACITY: usize = 1024;
+
+/// Quote a channel name as a SQL identifier (the POC's `quote_ident`
+/// shape — Postgres doubles embedded `"`). Channel names are arbitrary
+/// legal names (colons etc.); quoting is what makes them work.
+pub(crate) fn quote_ident(name: &str) -> String {
+    format!("\"{}\"", name.replace('"', "\"\""))
+}
+
+/// The raw notification the poll loop fans out — the skeleton's
+/// broadcast content; the notify-listen task maps it to the opaque
+/// [`alkstore::Wake`].
+///
+/// `channel` is read by the notify-listen task's receiver bridging
+/// (and this wave's fanout-proof tests); ungated in tests, gated in
+/// the lib build until that task wires it (the wave-3 intermediate
+/// posture — clippy `-D warnings` rejects dead code).
+#[derive(Debug, Clone)]
+pub(crate) struct RawNotification {
+    #[cfg_attr(not(test), allow(dead_code))]
+    pub channel: String,
+}
+
+/// The dynamic channel set: the registry the forwarder re-issues
+/// LISTENs from after every reconnect. The notify-listen task's
+/// `listen` (registration) and receiver-drop (unregistration, the
+/// refcounted last-subscriber rule) ride [`Forwarder`]'s register /
+/// unregister.
+#[derive(Debug, Default)]
+pub(crate) struct ChannelSet {
+    channels: std::sync::Mutex<std::collections::BTreeSet<String>>,
+}
+
+impl ChannelSet {
+    // `insert`/`remove` are the notify-listen task's registry entry
+    // points (this wave's tests exercise them); gated in the lib
+    // build until that task wires them.
+    #[cfg_attr(not(test), allow(dead_code))]
+    fn insert(&self, channel: &str) -> bool {
+        self.channels
+            .lock()
+            .expect("channel registry mutex poisoned")
+            .insert(channel.to_string())
+    }
+
+    #[cfg_attr(not(test), allow(dead_code))]
+    fn remove(&self, channel: &str) -> bool {
+        self.channels
+            .lock()
+            .expect("channel registry mutex poisoned")
+            .remove(channel)
+    }
+
+    fn snapshot(&self) -> Vec<String> {
+        self.channels
+            .lock()
+            .expect("channel registry mutex poisoned")
+            .iter()
+            .cloned()
+            .collect()
+    }
+}
+
+/// The forwarder handle the store holds: the subscription point for
+/// the fanout, the dynamic channel registry + LISTEN/UNLISTEN issuer,
+/// and the shutdown switch.
+///
+/// Shutdown (`Forwarder::shutdown`, the store's `close`/`Drop`): the
+/// loop exits, dropping the listener `Client` — the server session
+/// ends and the listener connection is gone (the teardown's
+/// "listener connection dropped" arm).
+#[derive(Debug)]
+pub(crate) struct Forwarder {
+    /// Read by the notify-listen task's receiver bridging (this
+    /// wave's tests exercise it); gated in the lib build until then.
+    #[cfg_attr(not(test), allow(dead_code))]
+    fanout: broadcast::Sender<RawNotification>,
+    /// Read by the forwarder's reconnect re-issue within the spawned
+    /// loop's own context (`Arc` move); the field itself is read by
+    /// the register/unregister surfaces below.
+    #[cfg_attr(not(test), allow(dead_code))]
+    channels: Arc<ChannelSet>,
+    /// LISTEN/UNLISTEN commands to the live connection (the loop
+    /// issues them; queued commands replay harmlessly across
+    /// reconnects alongside the registry re-issue). Read by the
+    /// register/unregister surfaces below.
+    #[cfg_attr(not(test), allow(dead_code))]
+    commands_tx: mpsc::UnboundedSender<ListenCommand>,
+    /// Whether a listener connection is currently live — the
+    /// register-path's honest transient state (registration during a
+    /// gap fails with `Database`; the registry entry's recovery rides
+    /// the reconnect re-issue). Read by `register` below.
+    #[cfg_attr(not(test), allow(dead_code))]
+    connected: Arc<AtomicBool>,
+    shutdown: watch::Sender<bool>,
+}
+
+/// Commands to the live listener connection (built by
+/// `register`/`unregister` below — gated in the lib build until the
+/// notify-listen task wires them).
+#[derive(Debug)]
+enum ListenCommand {
+    #[cfg_attr(not(test), allow(dead_code))]
+    Listen(String),
+    #[cfg_attr(not(test), allow(dead_code))]
+    Unlisten(String),
+}
+
+impl Forwarder {
+    /// Take over an established listener connection (the `open`
+    /// constructor connects so `open` fails `Database` synchronously
+    /// on an unreachable server) and spawn the forwarder loop.
+    pub(crate) fn spawn(
+        client: tokio_postgres::Client,
+        connection: ListenerConnection,
+        reconnect_config: tokio_postgres::Config,
+    ) -> Forwarder {
+        let (fanout, _) = broadcast::channel(FANOUT_CAPACITY);
+        let channels = Arc::new(ChannelSet::default());
+        let (commands_tx, commands_rx) = mpsc::unbounded_channel();
+        let (shutdown_tx, shutdown_rx) = watch::channel(false);
+        // The connection handed in was just established — the liveness
+        // flag starts true and the loop clears it at each generation's
+        // death (the register path's honest transient state).
+        let connected = Arc::new(AtomicBool::new(true));
+
+        // The loop owns both the Client and the Connection — the
+        // pitfall-2 exclusion (kept alive for the connection's
+        // lifetime).
+        tokio::spawn(forwarder_loop(LoopCtx {
+            client,
+            connection: Some(connection),
+            reconnect_config,
+            fanout: fanout.clone(),
+            channels: channels.clone(),
+            commands: commands_rx,
+            connected: connected.clone(),
+            shutdown: shutdown_rx,
+        }));
+
+        Forwarder {
+            fanout,
+            channels,
+            commands_tx,
+            connected,
+            shutdown: shutdown_tx,
+        }
+    }
+
+    /// Subscribe to the raw fanout (the notify-listen task bridges
+    /// broadcast receivers into `WakeReceiver`s). Gated in the lib
+    /// build until that task wires it (tests exercise it now).
+    #[cfg_attr(not(test), allow(dead_code))]
+    pub(crate) fn subscribe(&self) -> broadcast::Receiver<RawNotification> {
+        self.fanout.subscribe()
+    }
+
+    /// Register a channel AND issue `LISTEN` on the live connection.
+    /// The registry write happens first: if the connection dies
+    /// between the write and the listendelivery, the reconnect path
+    /// re-issues from the snapshot — a registration is never lost
+    /// (the ordering is the registration-recovery discipline).
+    ///
+    /// Fails `Database` only when no listener connection is currently
+    /// live (mid-reconnect) — transient; a retry (or the notify-listen
+    /// task's refined posture) recovers it.
+    #[cfg_attr(not(test), allow(dead_code))]
+    pub(crate) fn register(&self, channel: &str) -> Result<(), alkstore::Error> {
+        self.channels.insert(channel);
+        if !self.connected.load(Ordering::Acquire) {
+            return Err(database_error(
+                "the listener connection is not currently up (mid-reconnect); \
+                 the channel is registered and re-issued on reconnect",
+            ));
+        }
+        let _ = self
+            .commands_tx
+            .send(ListenCommand::Listen(channel.to_string()));
+        Ok(())
+    }
+
+    /// Unregister a channel AND issue `UNLISTEN` (the notify-listen
+    /// task's last-subscriber rule). Registry write first (ordering
+    /// symmetric with [`Forwarder::register`]'s recovery logic); the
+    /// UNLISTEN is best-effort — a lost one re-issues nothing
+    /// (UNLISTEN is not recovery-relevant: the snapshot won't carry
+    /// the removed channel).
+    #[cfg_attr(not(test), allow(dead_code))]
+    pub(crate) fn unregister(&self, channel: &str) {
+        self.channels.remove(channel);
+        let _ = self
+            .commands_tx
+            .send(ListenCommand::Unlisten(channel.to_string()));
+    }
+
+    /// Shutdown: flip the switch — the loop exits, dropping the
+    /// listener `Client` and its session (the listener connection is
+    /// gone). Idempotent.
+    pub(crate) fn shutdown(&self) {
+        let _ = self.shutdown.send(true);
+    }
+}
+
+/// The forwarder loop (the POC's ~90-line shape, restructured for the
+/// dynamic channel set + command issuer + shutdown).
+///
+/// Per connection generation: spawn the poll task (it owns the
+/// `Connection` and fans out `poll_message`'s notifications) → issue
+/// LISTENs from the live channel-set snapshot → serve commands and
+/// wait for the connection's death → reconnect with exponential
+/// backoff (50 ms → 2 s cap). The loop consumes the handed-in
+/// connection on its first generation and reconnects into the slot
+/// afterwards.
+struct LoopCtx {
+    client: tokio_postgres::Client,
+    connection: Option<ListenerConnection>,
+    reconnect_config: tokio_postgres::Config,
+    fanout: broadcast::Sender<RawNotification>,
+    channels: Arc<ChannelSet>,
+    commands: mpsc::UnboundedReceiver<ListenCommand>,
+    connected: Arc<AtomicBool>,
+    shutdown: watch::Receiver<bool>,
+}
+
+async fn forwarder_loop(
+    LoopCtx {
+        mut client,
+        mut connection,
+        reconnect_config,
+        fanout,
+        channels,
+        mut commands,
+        connected,
+        mut shutdown,
+    }: LoopCtx,
+) {
+    let mut backoff_ms = RECONNECT_BASE_MS;
+    let mut first_listen = true;
+
+    loop {
+        // The dedicated poll loop, spawned BEFORE any client query can
+        // ride this connection (pitfall 1's structural exclusion —
+        // held every generation, and the command select below keeps
+        // the poll task co-resident with client queries forever). The
+        // poll task owns the Connection; the loop drives queries
+        // through the Client.
+        let Some(poll_connection) = connection.take() else {
+            return;
+        };
+        let mut poll_task = tokio::spawn(poll_loop(poll_connection, fanout.clone()));
+
+        // Issue LISTENs from the dynamic channel set's snapshot (on
+        // first connect it carries pre-registered channels; on
+        // reconnect it carries everything `listen` ever registered).
+        // With no channels yet, a `SELECT 1` liveness probe stands in
+        // — `connected` must reflect a verified-alive session, not an
+        // assumed one.
+        let listen_sql = channels
+            .snapshot()
+            .iter()
+            .map(|ch| format!("LISTEN {};\n", quote_ident(ch)))
+            .collect::<String>();
+        let listen_ok = if listen_sql.is_empty() {
+            client.simple_query("SELECT 1").await.is_ok()
+        } else {
+            client.batch_execute(&listen_sql).await.is_ok()
+        };
+
+        if listen_ok {
+            backoff_ms = RECONNECT_BASE_MS;
+            connected.store(true, Ordering::Release);
+            if !first_listen {
+                // The synthetic reconnect-wake (ADR-008 §4's reserved
+                // channel; ADR-006's recovery semantics) broadcast to
+                // every subscriber's receiver — the no-replay hole's
+                // honest communication. The wake-content mapping is
+                // the notify-listen task's; the skeleton broadcasts
+                // the reserved channel's name so the fanout carries it.
+                let _ = fanout.send(RawNotification {
+                    channel: alkstore::RESERVED_LISTENER_RECONNECTED.to_string(),
+                });
+            }
+            first_listen = false;
+        } else {
+            // The connection died before/during the LISTEN — fall
+            // through to the reconnect path with the poll task's
+            // completion below.
+            connected.store(false, Ordering::Release);
+        }
+
+        // Drive the connection until it dies (or shutdown). Client
+        // queries (LISTEN/UNLISTEN commands) run while the poll task
+        // polls the same session — the co-residency that excludes
+        // pitfall 1's starvation permanently.
+        if listen_ok {
+            loop {
+                tokio::select! {
+                    biased;
+
+                    // Shutdown: exit the whole forwarder (dropping the
+                    // client closes the listener session).
+                    _ = shutdown.changed() => {
+                        poll_task.abort();
+                        return;
+                    }
+
+                    cmd = commands.recv() => {
+                        match cmd {
+                            Some(ListenCommand::Listen(ch)) => {
+                                let _ = client
+                                    .batch_execute(&format!("LISTEN {};", quote_ident(&ch)))
+                                    .await;
+                            }
+                            Some(ListenCommand::Unlisten(ch)) => {
+                                let _ = client
+                                    .batch_execute(&format!("UNLISTEN {};", quote_ident(&ch)))
+                                    .await;
+                            }
+                            // The command sender is gone (the store —
+                            // and its forwarder handle — went away
+                            // without a shutdown flip): serve no more,
+                            // exit.
+                            None => {
+                                poll_task.abort();
+                                return;
+                            }
+                        }
+                    }
+
+                    // The poll task ended = the connection died (a
+                    // fatal poll error or server close). The session
+                    // is already gone server-side; reconnect below.
+                    _ = &mut poll_task => {
+                        break;
+                    }
+                }
+            }
+        } else {
+            // A failed probe/LISTEN means the connection died: wait
+            // the poll task out (it owns the connection and is its
+            // reaper).
+            let _ = poll_task.await;
+        }
+
+        // Reconnect: the Client is dead with the session (dropping it
+        // here closes nothing server-side — pitfall 2 was satisfied
+        // for the connection's whole lifetime). Back off exponentially
+        // (50 ms → 2 s cap) and reconnect.
+        connected.store(false, Ordering::Release);
+        tokio::time::sleep(Duration::from_millis(backoff_ms)).await;
+        backoff_ms = backoff_ms.saturating_mul(2).min(RECONNECT_MAX_MS);
+
+        if *shutdown.borrow() {
+            return;
+        }
+        match reconnect_config.connect(NoTls).await {
+            Ok((new_client, new_connection)) => {
+                client = new_client;
+                connection = Some(new_connection);
+            }
+            Err(_e) => {
+                // Still unreachable — back off again and retry. (The
+                // skeleton carries the loop shape; the notify-listen
+                // task owns the reconnect behavior's full contract.)
+                continue;
+            }
+        }
+    }
+}
+
+/// The poll loop over one connection generation: `poll_message`
+/// forever, fanning notifications into the bounded broadcast. Returns
+/// when the connection dies (a fatal poll error or server close) —
+/// the forwarder loop reconnects.
+async fn poll_loop(mut connection: ListenerConnection, fanout: broadcast::Sender<RawNotification>) {
+    loop {
+        match std::future::poll_fn(|cx| connection.poll_message(cx)).await {
+            Some(Ok(tokio_postgres::AsyncMessage::Notification(n))) => {
+                // Bounded fanout — lag is surfaced, not silent: the
+                // POC's posture is a `Lagged(n)` receiver keeps
+                // streaming (the receiver bridge's `Lagged` arm logs /
+                // recovers; capacity pressure must not kill the
+                // fanout). The send-error arm is "no receivers
+                // subscribed" — the normal idle posture.
+                let _ = fanout.send(RawNotification {
+                    channel: n.channel().to_string(),
+                });
+            }
+            Some(Ok(_)) => {}
+            Some(Err(_)) | None => return,
+        }
+    }
+}

alkstore-postgres/src/lib.rs

@@ -8,20 +8,39 @@
 //! state; nothing assumes a shared host — this engine's deployment
 //! boundary is its crate identity (compile-time engine discovery:
 //! pick this crate, get this posture). No runtime capability surface.
+//! The per-process connection budget is `max_size` pooled connections
+//! **+ 1 non-pooled listener connection per LISTEN-ing process** (the
+//! forwarder; deadpool#360 — pooled connections cannot deliver;
+//! deployment.md's budget line) — consumers size their server for the
+//! sum.
 //!
 //! **Natively async** (ADR-004/ADR-007): no blocking bridge, no
 //! `spawn_blocking` seam — the driver's client is `Send + Sync` and
 //! the tx handle holds the pooled object directly (POC #2
-//! compile-probe verified).
+//! compile-probe verified). Every engine call is a straight `.await`.
+//!
+//! Durability knobs, pool sizing, and the engine-owned schema name are
+//! engine-configuration concerns on [`PgOpts`] (ADR-008 §6) — never
+//! contract surface: `synchronous_commit` per-session (ship config on,
+//! ADR-004/deployment.md's measured trade), `max_size` the deadpool
+//! bound, `schema` the one engine-owned PostgreSQL schema (ADR-010 §8,
+//! default `alkstore`; co-tenancy with consumer tables is the
+//! deployment posture).
 //!
 //! Wave 4 build order: schema bootstrap (this module — the dependency
 //! root), then `open`/`PgOpts` + pool + listener wiring, the tx seam,
 //! the LISTEN forwarder, the mechanisms (queues, streams, locks,
 //! scheduler/outbox); each task replaces the prior stubs.
 
+mod forwarder;
+mod opts;
 mod schema;
+mod seam;
+mod store;
 
+pub use opts::{DEFAULT_MAX_SIZE, PgOpts};
 pub use schema::{
     BootstrapError, BootstrapResult, DEFAULT_SCHEMA, QualifiedTable, bootstrap, quote_identifier,
     tables,
 };
+pub use store::{PgStore, open};

alkstore-postgres/src/opts.rs

@@ -0,0 +1,72 @@
+//! The pg engine's option struct (ADR-008 §6 — constructors and their
+//! option structs live in the engine crates; engine-configuration
+//! concerns never touch the contract surface).
+//!
+//! `#[non_exhaustive]` deliberately does not apply (ADR-017 §3): opts
+//! structs are consumer-*constructed*, and the attribute on them would
+//! push every construction through a builder. New fields may be added
+//! with `Default` fallbacks, per the core opts modules' posture.
+
+use crate::DEFAULT_SCHEMA;
+
+/// The default deadpool pool size (the deployment matrix's budget
+/// line: the listener connection adds +1 outside the pool per
+/// LISTEN-ing process — deployment.md's connection budgets).
+pub const DEFAULT_MAX_SIZE: usize = 8;
+
+/// The listener connection's `application_name` prefix — the base of
+/// the per-instance name `{prefix}-{pid}-{seq}` the store assigns
+/// (kill-targetable and diagnosable server-side; deployment.md's ops
+/// note, the POC's listener-setting carried; the unique suffix makes
+/// parallel instances distinguishable in `pg_stat_activity` without
+/// losing the ops prefix).
+pub(crate) const LISTENER_APPLICATION_NAME: &str = "alkstore-pg-listener";
+
+/// Construction options for the pg engine's
+/// [`open`](crate::open) constructor.
+///
+/// Durability knobs, pool sizing, and the engine-owned schema name are
+/// engine-configuration concerns — they never appear on the contract
+/// surface (ADR-008 §6); deployment.md carries the documented tuning
+/// facts (the `synchronous_commit` trade, the `max_size + 1` listener
+/// budget line).
+///
+/// The connection settings themselves do not ride this struct — they
+/// are `open`'s first argument (the tokio-postgres
+/// [`Config`](::tokio_postgres::Config)-parseable form, ADR-008 §6's
+/// `open(url, PgOpts)` pin); the engine never invents defaults for
+/// them. `open` fails with [`Error::Database`] if the config is
+/// unparseable or the server unreachable.
+#[derive(Debug, Clone)]
+pub struct PgOpts {
+    /// The engine-owned PostgreSQL schema (ADR-010 §8). Default
+    /// [`DEFAULT_SCHEMA`] (`"alkstore"`). All engine tables live in
+    /// this one schema; consumer tables co-tenant the instance
+    /// untouched. The name is a quoted identifier boundary
+    /// (`quote_identifier`) — reserved-word and hostile names are
+    /// safe.
+    pub schema: String,
+    /// Upper bound on pooled connections (deadpool's `max_size`) —
+    /// queries, claims, and all non-transactional work ride these.
+    /// Default [`DEFAULT_MAX_SIZE`] = 8 (the deployment matrix's
+    /// budget line; the listener adds +1 per LISTEN-ing process
+    /// *outside* the pool — sizing rule `max_size + 1`).
+    pub max_size: usize,
+    /// The per-session `synchronous_commit` durability knob, wired as
+    /// a connect-options `-c synchronous_commit=…` on every pooled
+    /// connection (POC-verified per-session SET mechanics). Default
+    /// `true` — ship config (p50 2.40 ms seam); `false` trades
+    /// max-tail (40.9 ms) for slightly better p50 — the measured,
+    /// honest trade (ADR-004, deployment.md).
+    pub synchronous_commit: bool,
+}
+
+impl Default for PgOpts {
+    fn default() -> Self {
+        Self {
+            schema: DEFAULT_SCHEMA.to_string(),
+            max_size: DEFAULT_MAX_SIZE,
+            synchronous_commit: true,
+        }
+    }
+}

alkstore-postgres/src/seam.rs

@@ -0,0 +1,43 @@
+//! The error-mapping posture (the seam task's foundation): driver and
+//! pool errors map into the contract taxonomy's opaque
+//! [`Error::Database`](alkstore::Error) fallback with the source chain
+//! preserved (ADR-008 §5). No engine-specific variants are ever
+//! minted; no panics.
+//!
+//! There is **no `spawn_blocking` seam on this engine** (ADR-004, the
+//! crate docs' posture): tokio-postgres's client is natively
+//! `Send + Sync` (POC #2 compile-probe) — every engine call is a
+//! straight `.await`. These mappings are the two the later mechanism
+//! tasks reuse ([`pg_error`], [`pool_error`], or one via
+//! [`database_error`]).
+
+use alkstore::Error;
+use deadpool_postgres::PoolError;
+
+/// Map a `tokio_postgres::Error` into the contract taxonomy, source
+/// chain preserved (ADR-008 §5's opaque fallback — no engine-specific
+/// variants minted for its contents).
+pub(crate) fn pg_error(e: tokio_postgres::Error) -> Error {
+    Error::database(e)
+}
+
+/// Map a deadpool pool error (`Pool::get`'s return) into the contract
+/// taxonomy, source chain preserved (a backend error — the
+/// `tokio_postgres::Error` the manager created/recycled with — rides
+/// `#[source]`).
+pub(crate) fn pool_error(e: PoolError) -> Error {
+    Error::database(e)
+}
+
+/// Map a deadpool pool-build error (`PoolBuilder::build`'s return)
+/// into the contract taxonomy, source chain preserved.
+pub(crate) fn build_error(e: deadpool_postgres::BuildError) -> Error {
+    Error::database(e)
+}
+
+/// Map a string failure (engine-composed context around an op) into
+/// the contract taxonomy (the SQLite twin's
+/// `database_error(msg)` shape — `io::Error` source).
+pub(crate) fn database_error(message: impl Into<String>) -> Error {
+    Error::database(std::io::Error::other(message.into()))
+}

alkstore-postgres/src/store.rs

@@ -0,0 +1,342 @@
+//! The pg engine's store: the `open` constructor, the connection
+//! architecture (engine-postgres.md's "Connection architecture"), and
+//! the [`Store`] trait wiring.
+//!
+//! Connection architecture: a deadpool pool (`RecyclingMethod::Fast` —
+//! no `DISCARD ALL` recycling; the POC's zero-error posture) for
+//! queries, claims, and all non-transactional work; one dedicated,
+//! **non-pooled** listener connection per process carrying the LISTEN
+//! forwarder (deadpool#360 — pooled connections cannot deliver; the
+//! per-process budget line is `max_size + 1`, deployment.md); and the
+//! engine-owned schema bootstrap run at open.
+//!
+//! Boot order: pool build → pool-checkout bootstrap (idempotent DDL;
+//! open fails `Database` if any step fails) → forwarder spawn (the
+//! wake substrate the mechanism tasks ride). Every failure at any step
+//! is a typed `Error::Database` with the source chain preserved
+//! (ADR-008 §5) — see [`crate::seam`], the mappings the mechanism
+//! tasks reuse.
+//!
+//! Drop/close: the forwarder is shut down (the listener `Client` drops
+//! — the server session ends and the listener connection is released)
+//! and the pool is closed; [`Drop`](PgStore::drop) delegates to
+//! [`PgStore::close`]. Post-close trait ops fail closed (`Database`).
+//!
+//! No `spawn_blocking` seam on this engine (the crate docs' posture);
+//! the trait stubs below are the wave-3 posture — they return
+//! `Err(Database("… wiring lands with the … task"))` until the
+//! mechanism tasks replace them.
+
+use alkstore::Store;
+use std::sync::Arc;
+use std::sync::atomic::{AtomicBool, AtomicU64, Ordering};
+
+use deadpool_postgres::{Manager, ManagerConfig, RecyclingMethod};
+use tokio_postgres::NoTls;
+
+use crate::forwarder::Forwarder;
+use crate::opts::{LISTENER_APPLICATION_NAME, PgOpts};
+use crate::schema::DEFAULT_SCHEMA;
+use crate::seam::{build_error, database_error, pg_error, pool_error};
+
+/// The per-instance listener `application_name` suffix counter (the
+/// `{prefix}-{pid}-{seq}` unique name; the ops prefix is shared).
+static LISTENER_SEQ: AtomicU64 = AtomicU64::new(0);
+
+/// The pg engine's store handle. Consumers hold
+/// [`alkstore::Store`] — the trait is the contract surface; the type
+/// exists so the engine can own its machinery and so tests can reach
+/// the close path directly.
+pub struct PgStore {
+    pool: deadpool_postgres::Pool,
+    forwarder: Arc<Forwarder>,
+    schema: String,
+    /// Read by `listener_application_name()` below (the notify-listen
+    /// task's kill-targeting surface; tests exercise it now): gated in
+    /// the lib build until then.
+    #[cfg_attr(not(test), allow(dead_code))]
+    listener_application_name: String,
+    closed: Arc<AtomicBool>,
+}
+
+impl std::fmt::Debug for PgStore {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        f.debug_struct("PgStore")
+            .field("schema", &self.schema)
+            .finish_non_exhaustive()
+    }
+}
+
+impl PgStore {
+    /// Explicit close: shuts the forwarder down (the listener
+    /// connection's session ends — its `Client` drops inside the
+    /// forwarder task) and closes the pool. Idempotent. [`Drop`]
+    /// delegates here. Post-close trait ops fail closed.
+    pub fn close(&self) {
+        self.closed.store(true, Ordering::SeqCst);
+        self.forwarder.shutdown();
+        self.pool.close();
+    }
+
+    /// The deadpool pool (queries/claims/non-transactional work) —
+    /// the mechanism tasks' access point (tests exercise it now):
+    /// gated in the lib build until the mechanism tasks wire it.
+    #[cfg_attr(not(test), allow(dead_code))]
+    pub(crate) fn pool(&self) -> &deadpool_postgres::Pool {
+        &self.pool
+    }
+
+    /// The forwarder handle (the wake substrate) — the mechanism
+    /// tasks' access point.
+    #[allow(dead_code)]
+    pub(crate) fn forwarder(&self) -> &Arc<Forwarder> {
+        &self.forwarder
+    }
+
+    /// The engine-owned schema name — the mechanism tasks'
+    /// schema-qualified SQL composition point (`quote_identifier`).
+    #[allow(dead_code)]
+    pub(crate) fn schema(&self) -> &str {
+        &self.schema
+    }
+
+    fn closed_check(&self) -> Result<(), alkstore::Error> {
+        if self.closed.load(Ordering::Acquire) {
+            return Err(database_error("the store is closed"));
+        }
+        Ok(())
+    }
+}
+
+impl Drop for PgStore {
+    fn drop(&mut self) {
+        self.closed.store(true, Ordering::SeqCst);
+        self.forwarder.shutdown();
+        self.pool.close();
+    }
+}
+
+/// Open a Postgres-backed store from a connection string (the
+/// tokio-postgres `Config`-parseable form) with engine options.
+///
+/// The connection string/config is the consumer's server address and
+/// credentials — the engine never invents defaults for them: `open`
+/// fails [`alkstore::Error::Database`] if the config is unparseable or
+/// the server unreachable. The full connection architecture boots: the
+/// deadpool pool (`RecyclingMethod::Fast`), the engine-owned schema
+/// bootstrap (idempotent; run on a pool connection), and the LISTEN
+/// forwarder on its dedicated non-pooled connection (the wake
+/// substrate; `max_size + 1` per-process budget line).
+pub async fn open(config: &str, opts: PgOpts) -> alkstore::Result<Box<dyn Store>> {
+    Ok(Box::new(open_store(config, opts).await?))
+}
+
+pub(crate) async fn open_store(config: &str, opts: PgOpts) -> alkstore::Result<PgStore> {
+    let cfg: tokio_postgres::Config = config.parse().map_err(pg_error)?;
+
+    // Per-session durability knob: the POC's connect-options SET
+    // mechanics (`-c synchronous_commit=…` on every pooled
+    // connection; POC-verified — pool.rs's `set_sync_commit_session`
+    // probe shape).
+    let mut pool_cfg = cfg.clone();
+    pool_cfg.options(format!(
+        "-c synchronous_commit={}",
+        if opts.synchronous_commit { "on" } else { "off" }
+    ));
+
+    let mgr_cfg = ManagerConfig {
+        recycling_method: RecyclingMethod::Fast,
+    };
+    let manager = Manager::from_config(pool_cfg, NoTls, mgr_cfg);
+    let pool = deadpool_postgres::Pool::builder(manager)
+        .max_size(opts.max_size)
+        .build()
+        .map_err(build_error)?;
+
+    // Bootstrap the engine-owned schema on a pool connection
+    // (idempotent DDL; the listener connection is NOT used — it is
+    // the wake substrate, not DDL ground). Open fails `Database` if
+    // the bootstrap fails.
+    let schema = if opts.schema.is_empty() {
+        DEFAULT_SCHEMA.to_string()
+    } else {
+        opts.schema.clone()
+    };
+    {
+        let conn = pool.get().await.map_err(pool_error)?;
+        crate::schema::bootstrap(&conn, &schema)
+            .await
+            .map_err(|e| pg_error(e.0))?;
+    }
+
+    // Spawn the forwarder on its dedicated non-pooled connection. The
+    // listener sets application_name for kill-targetability
+    // (deployment.md's ops note). Connect happens here (not inside the
+    // task) so an unreachable server fails `open` synchronously with
+    // `Database`.
+    let listener_application_name = format!(
+        "{}-{}-{}",
+        LISTENER_APPLICATION_NAME,
+        std::process::id(),
+        LISTENER_SEQ.fetch_add(1, Ordering::SeqCst)
+    );
+    let mut listener_cfg = cfg.clone();
+    listener_cfg.application_name(listener_application_name.clone());
+    let (client, connection) = listener_cfg.connect(NoTls).await.map_err(pg_error)?;
+    let forwarder = Forwarder::spawn(client, connection, listener_cfg);
+
+    Ok(PgStore::new(
+        pool,
+        forwarder,
+        schema,
+        listener_application_name,
+    ))
+}
+
+impl PgStore {
+    fn new(
+        pool: deadpool_postgres::Pool,
+        forwarder: Forwarder,
+        schema: String,
+        listener_application_name: String,
+    ) -> PgStore {
+        PgStore {
+            pool,
+            forwarder: Arc::new(forwarder),
+            schema,
+            listener_application_name,
+            closed: Arc::new(AtomicBool::new(false)),
+        }
+    }
+
+    /// This store's listener `application_name` — the per-instance
+    /// `{prefix}-{pid}-{seq}` unique name (kill-targetable,
+    /// `pg_stat_activity`-assertable; deployment.md's ops note; the
+    /// notify-listen task's backend-kill tests target it — tests
+    /// exercise it now). Gated in the lib build until then.
+    #[cfg_attr(not(test), allow(dead_code))]
+    pub(crate) fn listener_application_name(&self) -> &str {
+        &self.listener_application_name
+    }
+}
+
+fn stub(wiring: &'static str) -> alkstore::Error {
+    database_error(wiring)
+}
+
+impl Store for PgStore {
+    fn begin_tx(
+        &self,
+    ) -> alkstore::BoxedFuture<'_, alkstore::Result<Box<dyn alkstore::TxHandle + Send>>> {
+        if let Err(e) = self.closed_check() {
+            return Box::pin(async move { Err(e) });
+        }
+        Box::pin(async { Err(stub("begin_tx wiring lands with the seam task")) })
+    }
+
+    fn notify<'a>(
+        &'a self,
+        _channel: &str,
+        _payload: serde_json::Value,
+    ) -> alkstore::BoxedFuture<'a, alkstore::Result<()>> {
+        if let Err(e) = self.closed_check() {
+            return Box::pin(async move { Err(e) });
+        }
+        Box::pin(async { Err(stub("notify wiring lands with the notify-listen task")) })
+    }
+
+    fn listen<'a>(
+        &'a self,
+        _channel: &str,
+    ) -> alkstore::BoxedFuture<'a, alkstore::Result<Box<dyn alkstore::WakeReceiver>>> {
+        if let Err(e) = self.closed_check() {
+            return Box::pin(async move { Err(e) });
+        }
+        Box::pin(async { Err(stub("listen wiring lands with the notify-listen task")) })
+    }
+
+    fn stream<'a>(
+        &'a self,
+        _name: &str,
+    ) -> alkstore::BoxedFuture<'a, alkstore::Result<Box<dyn alkstore::StreamHandle>>> {
+        if let Err(e) = self.closed_check() {
+            return Box::pin(async move { Err(e) });
+        }
+        Box::pin(async { Err(stub("stream wiring lands with the streams task")) })
+    }
+
+    fn queue<'a>(
+        &'a self,
+        _name: &str,
+        _opts: alkstore::QueueOpts,
+    ) -> alkstore::BoxedFuture<'a, alkstore::Result<Box<dyn alkstore::Queue>>> {
+        if let Err(e) = self.closed_check() {
+            return Box::pin(async move { Err(e) });
+        }
+        Box::pin(async { Err(stub("queue wiring lands with the queues task")) })
+    }
+
+    fn outbox<'a>(
+        &'a self,
+        _name: &str,
+    ) -> alkstore::BoxedFuture<'a, alkstore::Result<Box<dyn alkstore::Outbox>>> {
+        if let Err(e) = self.closed_check() {
+            return Box::pin(async move { Err(e) });
+        }
+        Box::pin(async { Err(stub("outbox wiring lands with the scheduler-outbox task")) })
+    }
+
+    fn try_lock<'a>(
+        &'a self,
+        _name: &str,
+        _owner: &str,
+        _ttl: i64,
+    ) -> alkstore::BoxedFuture<'a, alkstore::Result<Option<Box<dyn alkstore::Lock>>>> {
+        if let Err(e) = self.closed_check() {
+            return Box::pin(async move { Err(e) });
+        }
+        Box::pin(async { Err(stub("lock wiring lands with the locks task")) })
+    }
+
+    fn schedule<'a>(
+        &'a self,
+        _name: &str,
+        _spec: &str,
+        _queue: &str,
+        _payload: serde_json::Value,
+        _opts: alkstore::ScheduleOpts,
+    ) -> alkstore::BoxedFuture<'a, alkstore::Result<alkstore::Schedule>> {
+        if let Err(e) = self.closed_check() {
+            return Box::pin(async move { Err(e) });
+        }
+        Box::pin(async { Err(stub("schedule wiring lands with the scheduler-outbox task")) })
+    }
+
+    fn unschedule<'a>(&'a self, _name: &str) -> alkstore::BoxedFuture<'a, alkstore::Result<bool>> {
+        if let Err(e) = self.closed_check() {
+            return Box::pin(async move { Err(e) });
+        }
+        Box::pin(async {
+            Err(stub(
+                "unschedule wiring lands with the scheduler-outbox task",
+            ))
+        })
+    }
+
+    fn run_schedules<'a>(
+        &'a self,
+        _stop: alkstore::StopToken,
+    ) -> alkstore::BoxedFuture<'a, alkstore::Result<()>> {
+        if let Err(e) = self.closed_check() {
+            return Box::pin(async move { Err(e) });
+        }
+        Box::pin(async {
+            Err(stub(
+                "scheduler wiring lands with the scheduler-outbox task",
+            ))
+        })
+    }
+}
+
+#[cfg(test)]
+mod open_tests;

alkstore-postgres/src/store/open_tests.rs

@@ -0,0 +1,738 @@
+//! The `open`/`PgOpts`/forwarder-skeleton acceptance tests
+//! (`pg-engine-open-opts`): the connection architecture boots against
+//! the harness server, opts flow, the forwarder's minimal fanout proof
+//! (a LISTEN issued through it delivers), and teardown.
+//!
+//! Harness convention (the schema task's): connection settings ride the
+//! environment (`ALKSTORE_PG_HOST/PORT/USER/PASSWORD/DB`), never
+//! hardcoded; tests without a reachable server skip cleanly so the
+//! workspace gates stay green server-less. Isolation is a fresh unique
+//! schema per test (the POC's shared-server parallel-interference
+//! caveat answered by schema-per-test isolation).
+
+use std::sync::atomic::{AtomicU64, Ordering};
+use std::time::Duration;
+
+use crate::forwarder::RawNotification;
+use crate::opts::{DEFAULT_MAX_SIZE, PgOpts};
+use crate::schema::DEFAULT_SCHEMA;
+use crate::store::open_store;
+use alkstore::Store;
+
+const ENV_HOST: &str = "ALKSTORE_PG_HOST";
+const ENV_PORT: &str = "ALKSTORE_PG_PORT";
+const ENV_USER: &str = "ALKSTORE_PG_USER";
+const ENV_PASSWORD: &str = "ALKSTORE_PG_PASSWORD";
+const ENV_DB: &str = "ALKSTORE_PG_DB";
+
+/// The unique per-instance listener `application_name` prefix (the
+/// `{prefix}-{pid}-{seq}` scheme the store assigns; the pg_stat_activity
+/// probes assert against this store's own instance name only).
+const LISTENER_APP_PREFIX: &str = "alkstore-pg-listener";
+
+fn harness_dsn() -> Option<String> {
+    let host = std::env::var(ENV_HOST).ok()?;
+    let port: u16 = std::env::var(ENV_PORT).ok()?.parse().ok()?;
+    let user = std::env::var(ENV_USER).ok()?;
+    let password = std::env::var(ENV_PASSWORD).ok()?;
+    let db = std::env::var(ENV_DB).unwrap_or_else(|_| "postgres".to_string());
+    Some(format!(
+        "host={host} port={port} user={user} password={password} dbname={db}"
+    ))
+}
+
+fn unreachable_dsn() -> String {
+    "host=127.0.0.1 port=1 user=x password=x dbname=x connect_timeout=2".to_string()
+}
+
+fn instance_namer(tag: &str) -> impl Fn() -> String + use<'_> {
+    let counter = AtomicU64::new(0);
+    move || {
+        format!(
+            "{tag}_{}_{}_{}",
+            std::process::id(),
+            std::time::SystemTime::now()
+                .duration_since(std::time::UNIX_EPOCH)
+                .unwrap_or_default()
+                .as_nanos(),
+            counter.fetch_add(1, Ordering::SeqCst),
+        )
+    }
+}
+
+/// A raw admin client for teardown probes (server-level `SHOW`s,
+/// `pg_stat_activity` accounting) — separate from the store's pool.
+async fn harness_client() -> Option<tokio_postgres::Client> {
+    let (client, connection) = tokio_postgres::connect(&harness_dsn()?, tokio_postgres::NoTls)
+        .await
+        .ok()?;
+    tokio::spawn(async move {
+        let _ = connection.await;
+    });
+    Some(client)
+}
+
+async fn drop_schema(client: &tokio_postgres::Client, schema: &str) {
+    if schema == DEFAULT_SCHEMA {
+        // Never drop the shared default schema in tests — tests that
+        // exercise the default name only assert its shape.
+        return;
+    }
+    let sql = format!(
+        "DROP SCHEMA IF EXISTS {} CASCADE",
+        crate::schema::quote_identifier(schema)
+    );
+    let _ = client.batch_execute(&sql).await;
+}
+
+/// The test-owned default PgOpts with a fresh schema name.
+fn test_opts(schema: &str) -> PgOpts {
+    PgOpts {
+        schema: schema.to_string(),
+        ..PgOpts::default()
+    }
+}
+
+/// Count this store's listener connections server-side — by the
+/// store's exact assigned `{prefix}-{pid}-{seq}` application_name
+/// (parallel tests' listeners never interfere).
+async fn listener_sessions(admin: &tokio_postgres::Client, app_name: &str) -> i64 {
+    admin
+        .query_one(
+            "SELECT count(*) FROM pg_stat_activity
+             WHERE application_name = $1 AND pid <> pg_backend_pid()",
+            &[&app_name],
+        )
+        .await
+        .unwrap()
+        .get(0)
+}
+
+/// The forwarder's fanout subscription surface for the minimal-delivery
+/// proof (bridging into `WakeReceiver`s is the notify-listen task's;
+/// the skeleton's proof fans the raw notification channel names out).
+async fn wait_for_channel(
+    rx: &mut tokio::sync::broadcast::Receiver<RawNotification>,
+    want: &str,
+    timeout: Duration,
+) -> bool {
+    let deadline = tokio::time::Instant::now() + timeout;
+    loop {
+        let remaining = deadline.saturating_duration_since(tokio::time::Instant::now());
+        if remaining.is_zero() {
+            return false;
+        }
+        match tokio::time::timeout(remaining, rx.recv()).await {
+            Ok(Ok(n)) if n.channel == want => return true,
+            Ok(Ok(_)) => continue,
+            Ok(Err(tokio::sync::broadcast::error::RecvError::Lagged(_))) => continue,
+            Ok(Err(tokio::sync::broadcast::error::RecvError::Closed)) => return false,
+            Err(_) => return false,
+        }
+    }
+}
+
+/// Extract the `Err` arm from a stub call whose `Ok` type is not
+/// `Debug` (the boxed-handle returns: `begin_tx`, `listen`, `stream`,
+/// `queue`, `outbox`, `try_lock`).
+macro_rules! stub_err {
+    ($call:expr) => {
+        match $call {
+            Err(e) => e,
+            Ok(_) => panic!(concat!(stringify!($call), " must be a stub")),
+        }
+    };
+}
+
+#[tokio::test(flavor = "multi_thread")]
+async fn open_boots_pool_bootstrap_and_forwarder() {
+    let Some(dsn) = harness_dsn() else {
+        eprintln!("skip: no harness server");
+        return;
+    };
+    let schema = instance_namer("boot")();
+    let store = open_store(&dsn, test_opts(&schema)).await.unwrap();
+
+    // Pool up.
+    let conn = store.pool().get().await.unwrap();
+    let one: i32 = conn.query_one("SELECT 1", &[]).await.unwrap().get(0);
+    assert_eq!(one, 1);
+    drop(conn);
+
+    // Bootstrap ran: the 6-table family exists under the configured
+    // schema.
+    let admin = harness_client().await.unwrap();
+    let tables: i64 = admin
+        .query_one(
+            "SELECT count(*) FROM pg_tables WHERE schemaname = $1",
+            &[&schema],
+        )
+        .await
+        .unwrap()
+        .get(0);
+    assert_eq!(tables, 6, "the engine-owned table family exists");
+
+    // Forwarder skeleton up: register a channel, the LISTEN rides the
+    // dedicated connection, and a NOTIFY from an unrelated client
+    // delivers through the fanout (the minimal fanout proof — the
+    // notify-listen task owns the receiver bridging).
+    let channel = format!("forwarder_probe_{}", instance_namer("ch")());
+    store.forwarder().register(&channel).unwrap();
+    let mut rx = store.forwarder().subscribe();
+
+    let admin2 = harness_client().await.unwrap();
+    let notify_sql = format!(
+        "NOTIFY {}, 'ping'",
+        crate::schema::quote_identifier(&channel)
+    );
+    let mut delivered = false;
+    for _ in 0..20 {
+        let _ = admin2.batch_execute(&notify_sql).await;
+        if wait_for_channel(&mut rx, &channel, Duration::from_millis(150)).await {
+            delivered = true;
+            break;
+        }
+    }
+    assert!(
+        delivered,
+        "a LISTEN issued through the forwarder must deliver through its fanout"
+    );
+
+    store.close();
+    drop_schema(&admin, &schema).await;
+}
+
+/// The two POC-pinned deadlock pitfalls, structurally excluded and
+/// pinned here:
+/// 1. A client query on the listener connection issued immediately
+///    after spawn completes (the poll loop was already running — no
+///    query-vs-poll starvation deadlock).
+/// 2. Notifications deliver well after open (the listener `Client`
+///    stays alive for the connection's lifetime — no session death
+///    from an unseen drop).
+#[tokio::test(flavor = "multi_thread")]
+async fn forwarder_poll_loop_survives_command_churn() {
+    let Some(dsn) = harness_dsn() else {
+        eprintln!("skip: no harness server");
+        return;
+    };
+    let schema = instance_namer("churn")();
+    let store = open_store(&dsn, test_opts(&schema)).await.unwrap();
+
+    let channel = format!("churn_probe_{}", instance_namer("ch")());
+    let mut rx = store.forwarder().subscribe();
+    // Pitfall 1: LISTEN issued immediately after open — if the poll
+    // loop were not already running this would deadlock.
+    store.forwarder().register(&channel).unwrap();
+
+    let admin = harness_client().await.unwrap();
+    for i in 0..5 {
+        admin
+            .batch_execute(&format!(
+                "NOTIFY {}, 'burst-{i}'",
+                crate::schema::quote_identifier(&channel)
+            ))
+            .await
+            .unwrap();
+    }
+    // Pitfall 2: delivery works long after open (session alive).
+    assert!(
+        wait_for_channel(&mut rx, &channel, Duration::from_secs(3)).await,
+        "notifications deliver long after open (listener session alive — pitfall 2 excluded)"
+    );
+
+    store.forwarder().unregister(&channel);
+    store.close();
+    drop_schema(&admin, &schema).await;
+}
+
+/// The skeleton's reconnect path: killing the listener's backend
+/// server-side terminates its session; the loop reconnects (its
+/// exponential backoff, 50 ms → 2 s cap), re-LISTENs from the registry,
+/// and a post-reconnect notification delivers. The synthetic
+/// reconnect-wake's fanout arm (the notify-listen task's full
+/// receiver-bridging behavior) is pinned by the fanout carrying the
+/// reserved channel's name after the kill.
+#[tokio::test(flavor = "multi_thread")]
+async fn forwarder_reconnects_after_backend_kill_and_delivers() {
+    let Some(dsn) = harness_dsn() else {
+        eprintln!("skip: no harness server");
+        return;
+    };
+    let schema = instance_namer("reconn")();
+    let store = open_store(&dsn, test_opts(&schema)).await.unwrap();
+
+    let channel = format!("reconn_probe_{}", instance_namer("ch")());
+    let mut rx = store.forwarder().subscribe();
+    store.forwarder().register(&channel).unwrap();
+
+    let admin = harness_client().await.unwrap();
+    // Deliver once pre-kill (the subscription path is verified).
+    admin
+        .batch_execute(&format!(
+            "NOTIFY {}, 'pre-kill'",
+            crate::schema::quote_identifier(&channel)
+        ))
+        .await
+        .unwrap();
+    assert!(
+        wait_for_channel(&mut rx, &channel, Duration::from_secs(3)).await,
+        "pre-kill delivery must work first"
+    );
+
+    // Kill the listener's backend (the POC's pg_terminate_backend
+    // shape, targeted at this store's own unique application_name).
+    let killed = admin
+        .query_one(
+            "SELECT pg_terminate_backend(pid) FROM pg_stat_activity
+             WHERE application_name = $1 AND pid <> pg_backend_pid()",
+            &[&store.listener_application_name()],
+        )
+        .await
+        .unwrap()
+        .get::<_, bool>(0);
+    assert!(killed, "the listener backend was found and killed");
+
+    // The loop reconnects (backoff ≤ 2 s cap) and re-LISTENs from the
+    // registry: the reserved reconnect-wake arrives on the fanout (the
+    // skeleton's proof of the re-LISTEN + synthetic-wake arm; the
+    // full wake-contract behavior is the notify-listen task's), and a
+    // post-reconnect notification on the registered channel delivers.
+    let got_wake = wait_for_channel(
+        &mut rx,
+        alkstore::RESERVED_LISTENER_RECONNECTED,
+        Duration::from_secs(10),
+    )
+    .await;
+    let post_sql = format!(
+        "NOTIFY {}, 'post-reconnect'",
+        crate::schema::quote_identifier(&channel)
+    );
+    let mut delivered = false;
+    for _ in 0..20 {
+        let _ = admin.batch_execute(&post_sql).await;
+        if wait_for_channel(&mut rx, &channel, Duration::from_millis(150)).await {
+            delivered = true;
+            break;
+        }
+    }
+    assert!(
+        got_wake && delivered,
+        "after a backend kill the forwarder must reconnect (reconnect-wake \
+         {got_wake}) and deliver post-reconnect notifications ({delivered})"
+    );
+
+    store.close();
+    drop_schema(&admin, &schema).await;
+}
+
+/// Acceptance: pool bounds — `max_size` caps concurrent checkouts (the
+/// +1 listener sits outside the pool).
+#[tokio::test(flavor = "multi_thread")]
+async fn pool_size_is_bounded_by_opts() {
+    let Some(dsn) = harness_dsn() else {
+        eprintln!("skip: no harness server");
+        return;
+    };
+    let schema = instance_namer("pool")();
+    let store = open_store(
+        &dsn,
+        PgOpts {
+            schema: schema.to_string(),
+            max_size: 2,
+            ..PgOpts::default()
+        },
+    )
+    .await
+    .unwrap();
+
+    assert_eq!(store.pool().status().max_size, 2);
+
+    let c1 = store.pool().get().await.unwrap();
+    let c2 = store.pool().get().await.unwrap();
+
+    let pool = store.pool().clone();
+    let blocked = tokio::spawn(async move { pool.get().await });
+    tokio::time::sleep(Duration::from_millis(200)).await;
+    assert!(
+        !blocked.is_finished(),
+        "checkout above max_size must block (pool bound enforced)"
+    );
+
+    drop(c2);
+    let c3 = blocked.await.unwrap().unwrap();
+    drop(c3);
+    drop(c1);
+
+    store.close();
+    let admin = harness_client().await.unwrap();
+    drop_schema(&admin, &schema).await;
+}
+
+/// The documented defaults: pool size (the deployment budget line),
+/// schema (ADR-010 §8), `synchronous_commit` (ship config on) — and
+/// the opts-struct exemption (ADR-017 §3): struct-literal construction
+/// with `..Default::default()` compiles.
+#[test]
+fn defaults_are_the_documented_constants() {
+    assert_eq!(DEFAULT_MAX_SIZE, 8, "the documented default pool size");
+    assert_eq!(DEFAULT_SCHEMA, "alkstore", "ADR-010 §8's default schema");
+    let opts = PgOpts::default();
+    assert_eq!(opts.max_size, DEFAULT_MAX_SIZE);
+    assert_eq!(opts.schema, "alkstore");
+    assert!(
+        opts.synchronous_commit,
+        "ship config: synchronous_commit on"
+    );
+    let constructed = PgOpts {
+        max_size: 2,
+        ..PgOpts::default()
+    };
+    assert_eq!(constructed.max_size, 2);
+    assert_eq!(constructed.schema, "alkstore");
+}
+
+/// Acceptance: opts flow — the schema name lands in the created
+/// schema's name.
+#[tokio::test(flavor = "multi_thread")]
+async fn schema_name_flows_from_opts() {
+    let Some(dsn) = harness_dsn() else {
+        eprintln!("skip: no harness server");
+        return;
+    };
+    let schema = instance_namer("schname")();
+    let store = open_store(&dsn, test_opts(&schema)).await.unwrap();
+    assert_eq!(store.schema(), schema);
+
+    let admin = harness_client().await.unwrap();
+    let tables: i64 = admin
+        .query_one(
+            "SELECT count(*) FROM pg_tables WHERE schemaname = $1",
+            &[&schema],
+        )
+        .await
+        .unwrap()
+        .get(0);
+    assert_eq!(tables, 6, "the schema name rides PgOpts into the DDL");
+
+    store.close();
+    drop_schema(&admin, &schema).await;
+}
+
+/// Acceptance: `synchronous_commit` observable via `SHOW` — the knob
+/// rides pool connections as a connect-options `-c` SET (the POC's
+/// verified per-session mechanics).
+#[tokio::test(flavor = "multi_thread")]
+async fn synchronous_commit_knob_is_observable_via_show() {
+    let Some(dsn) = harness_dsn() else {
+        eprintln!("skip: no harness server");
+        return;
+    };
+
+    for (sync_commit, expected) in [(true, "on"), (false, "off")] {
+        let schema = instance_namer("sync")();
+        let store = open_store(
+            &dsn,
+            PgOpts {
+                schema: schema.to_string(),
+                synchronous_commit: sync_commit,
+                ..PgOpts::default()
+            },
+        )
+        .await
+        .unwrap();
+        let conn = store.pool().get().await.unwrap();
+        let row = conn
+            .query_one("SHOW synchronous_commit", &[])
+            .await
+            .unwrap();
+        let value: String = row.get(0);
+        assert_eq!(
+            value, expected,
+            "the knob's session value must match PgOpts (pool connections)"
+        );
+        drop(conn);
+        store.close();
+        let admin = harness_client().await.unwrap();
+        drop_schema(&admin, &schema).await;
+    }
+}
+
+/// Acceptance: the listener connection is (a) outside the pool and (b)
+/// exactly one per store — the `max_size + 1` budget line's server-side
+/// accounting shape (the POC's pgdiag-st-4 posture, per-instance
+/// application_name).
+#[tokio::test(flavor = "multi_thread")]
+async fn listener_connection_sits_outside_the_pool() {
+    let Some(dsn) = harness_dsn() else {
+        eprintln!("skip: no harness server");
+        return;
+    };
+    let schema = instance_namer("outside")();
+    let store = open_store(
+        &dsn,
+        PgOpts {
+            schema: schema.to_string(),
+            max_size: 2,
+            ..PgOpts::default()
+        },
+    )
+    .await
+    .unwrap();
+
+    let admin = harness_client().await.unwrap();
+    let app_name = store.listener_application_name().to_string();
+    assert!(
+        app_name.starts_with(LISTENER_APP_PREFIX),
+        "the listener application_name carries the ops prefix: {app_name}"
+    );
+    assert_eq!(
+        listener_sessions(&admin, &app_name).await,
+        1,
+        "exactly one dedicated listener connection per store (outside the pool)"
+    );
+
+    // Hold both pool slots; the listener connection is unaffected (it
+    // is not pooled).
+    let _c1 = store.pool().get().await.unwrap();
+    let _c2 = store.pool().get().await.unwrap();
+    assert_eq!(
+        listener_sessions(&admin, &app_name).await,
+        1,
+        "pool saturation does not touch the listener"
+    );
+
+    store.close();
+    drop_schema(&admin, &schema).await;
+}
+
+/// Acceptance: close/Drop teardown clean — the listener's server
+/// session terminates, the pool closes (checkouts fail), and post-close
+/// trait ops fail closed (`Database`, not panic). `Drop` runs the same
+/// teardown.
+#[tokio::test(flavor = "multi_thread")]
+async fn close_and_drop_teardown_cleanly() {
+    let Some(dsn) = harness_dsn() else {
+        eprintln!("skip: no harness server");
+        return;
+    };
+
+    // Explicit close: the listener's server session terminates.
+    let schema = instance_namer("close")();
+    let store = open_store(&dsn, test_opts(&schema)).await.unwrap();
+    let admin = harness_client().await.unwrap();
+    let app_name = store.listener_application_name().to_string();
+    assert_eq!(
+        listener_sessions(&admin, &app_name).await,
+        1,
+        "the listener session is up pre-close"
+    );
+    store.close();
+    tokio::time::sleep(Duration::from_millis(300)).await;
+    let after = listener_sessions(&admin, &app_name).await;
+    assert_eq!(after, 0, "close terminated this store's listener session");
+
+    // Post-close ops fail closed (Database, not panic).
+    let err = store
+        .notify("__alkstore_post_close", serde_json::json!({}))
+        .await
+        .unwrap_err();
+    assert!(
+        matches!(err, alkstore::Error::Database(_)),
+        "post-close notify fails closed, got: {err:?}"
+    );
+    let err = stub_err!(store.begin_tx().await);
+    assert!(
+        matches!(err, alkstore::Error::Database(_)),
+        "post-close begin_tx fails closed, got: {err:?}"
+    );
+
+    // Pool closed: checkouts fail.
+    let err = store.pool().get().await.unwrap_err();
+    assert!(
+        err.to_string().contains("closed"),
+        "close closes the pool, got: {err}"
+    );
+    drop_schema(&admin, &schema).await;
+
+    // Drop path: the same teardown reached through drop.
+    let schema = instance_namer("dropped")();
+    let store = open_store(&dsn, test_opts(&schema)).await.unwrap();
+    let app_name = store.listener_application_name().to_string();
+    drop(store);
+    tokio::time::sleep(Duration::from_millis(300)).await;
+    let admin = harness_client().await.unwrap();
+    assert_eq!(
+        listener_sessions(&admin, &app_name).await,
+        0,
+        "drop terminated the listener session"
+    );
+    drop_schema(&admin, &schema).await;
+}
+
+/// Acceptance: unreachable server — `open` fails synchronously with
+/// the typed `Database` error (source chain preserved), for an
+/// unparseable config and a refused connection alike.
+#[tokio::test]
+async fn open_fails_database_on_unparseable_and_unreachable() {
+    // Unparseable config string.
+    let err = open_store(
+        "definitely not a valid connection string!!!",
+        PgOpts::default(),
+    )
+    .await
+    .unwrap_err();
+    match err {
+        alkstore::Error::Database(source) => {
+            assert!(
+                !source.to_string().is_empty(),
+                "the source chain carries the parse detail"
+            );
+        }
+        other => panic!("unparseable config must be Database, got {other:?}"),
+    }
+
+    // Unreachable server (refused connection, bounded by connect
+    // timeout) — only when the harness itself is reachable (a
+    // server-less environment cannot distinguish "unreachable" from
+    // "no server" meaningfully; the skip posture keeps gates green).
+    if harness_dsn().is_some() {
+        let err = open_store(&unreachable_dsn(), PgOpts::default())
+            .await
+            .unwrap_err();
+        match err {
+            alkstore::Error::Database(source) => {
+                assert!(
+                    !source.to_string().is_empty(),
+                    "the source chain carries the connect detail"
+                );
+            }
+            other => panic!("unreachable server must be Database, got {other:?}"),
+        }
+    } else {
+        eprintln!("skip: no harness server (unreachable-server arm)");
+    }
+}
+
+/// Acceptance: the trait surface is the wave-3 stub posture — every
+/// `Store` method returns `Err(Database(… wiring lands with the …
+/// task))`; `with_tx` surfaces the `begin_tx` stub naturally; no
+/// panics.
+#[tokio::test(flavor = "multi_thread")]
+async fn store_trait_methods_are_wiring_stubs() {
+    let Some(dsn) = harness_dsn() else {
+        eprintln!("skip: no harness server");
+        return;
+    };
+    let schema = instance_namer("stubs")();
+    let store = open_store(&dsn, test_opts(&schema)).await.unwrap();
+
+    let err = match store.begin_tx().await {
+        Err(e) => e,
+        Ok(_) => panic!("begin_tx must be a stub"),
+    };
+    assert!(
+        matches!(err, alkstore::Error::Database(_)),
+        "begin_tx stub is a Database error"
+    );
+    let err = store
+        .with_tx(Box::new(|_tx| Box::pin(async { Ok(()) })))
+        .await
+        .unwrap_err();
+    assert!(
+        matches!(err, alkstore::Error::Database(_)),
+        "with_tx surfaces the begin_tx stub naturally"
+    );
+    let err = store
+        .notify("ch", serde_json::json!("x"))
+        .await
+        .unwrap_err();
+    assert!(matches!(err, alkstore::Error::Database(_)));
+    let err = match store.listen("ch").await {
+        Err(e) => e,
+        Ok(_) => panic!("listen must be a stub"),
+    };
+    assert!(matches!(err, alkstore::Error::Database(_)));
+    let err = match store.stream("s").await {
+        Err(e) => e,
+        Ok(_) => panic!("stream must be a stub"),
+    };
+    assert!(matches!(err, alkstore::Error::Database(_)));
+    let err = stub_err!(store.queue("q", alkstore::QueueOpts::default()).await);
+    assert!(matches!(err, alkstore::Error::Database(_)));
+    let err = stub_err!(store.outbox("o").await);
+    assert!(matches!(err, alkstore::Error::Database(_)));
+    let err = stub_err!(store.try_lock("l", "owner", 60).await);
+    assert!(matches!(err, alkstore::Error::Database(_)));
+    let err = store
+        .schedule(
+            "s",
+            "@every 10s",
+            "q",
+            serde_json::json!({}),
+            alkstore::ScheduleOpts::default(),
+        )
+        .await
+        .unwrap_err();
+    assert!(matches!(err, alkstore::Error::Database(_)));
+    let err = store.unschedule("s").await.unwrap_err();
+    assert!(matches!(err, alkstore::Error::Database(_)));
+    let err = store
+        .run_schedules(alkstore::StopToken::new())
+        .await
+        .unwrap_err();
+    assert!(matches!(err, alkstore::Error::Database(_)));
+
+    // The stub messages name their landing task (the wave-3 posture's
+    // "… wiring lands with the … task" shape) — in the source chain
+    // (`Database`'s Display is opaque; ADR-008 §5's detail-carriage).
+    let err = stub_err!(store.begin_tx().await);
+    match err {
+        alkstore::Error::Database(source) => {
+            let msg = source.to_string();
+            assert!(
+                msg.contains("wiring lands with"),
+                "stub errors name their landing task, got: {msg}"
+            );
+        }
+        other => panic!("begin_tx stub must be Database, got {other:?}"),
+    }
+
+    drop(store);
+    let admin = harness_client().await.unwrap();
+    drop_schema(&admin, &schema).await;
+}
+
+/// The error-mapping helpers exist and are the documented reuse point:
+/// a mapped error is `Error::Database` with the source chain preserved
+/// (the mapping trio the mechanism tasks reuse; the io-Error string
+/// helper carries its context through the chain).
+#[test]
+fn seam_mappings_preserve_the_source_chain() {
+    use crate::seam::{database_error, pg_error, pool_error};
+
+    let parse_err = "!!!".parse::<tokio_postgres::Config>().unwrap_err();
+    let mapped = pg_error(parse_err);
+    assert!(matches!(mapped, alkstore::Error::Database(_)));
+    let source = match &mapped {
+        alkstore::Error::Database(s) => s.to_string(),
+        _ => unreachable!(),
+    };
+    assert!(
+        !source.is_empty(),
+        "the tokio_postgres::Error detail rides the chain"
+    );
+
+    let mapped = database_error("engine context around the failure");
+    let source = match &mapped {
+        alkstore::Error::Database(s) => s.to_string(),
+        _ => unreachable!(),
+    };
+    assert!(
+        source.contains("engine context"),
+        "the string helper's context rides the chain, got: {source}"
+    );
+
+    let mapped = pool_error(deadpool_postgres::PoolError::Closed);
+    assert!(matches!(mapped, alkstore::Error::Database(_)));
+}

tasks/pg-engine-open-opts.md

@@ -1,7 +1,7 @@
 ---
 id: pg-engine-open-opts
 name: Postgres engine — `open` constructor, `PgOpts`, pool + listener wiring
-status: pending
+status: completed
 depends_on: [pg-engine-schema]
 scope: moderate
 risk: medium
@@ -77,20 +77,20 @@ name; `synchronous_commit` observable via `SHOW`).
 
 ## Acceptance Criteria
 
-- [ ] `PgOpts` with connection config, `schema` (default
+- [x] `PgOpts` with connection config, `schema` (default
       `alkstore`), `max_size`, `synchronous_commit` (default on);
       documented; not `#[non_exhaustive]`
-- [ ] `open` boots pool + bootstrap + forwarder skeleton; failure at
+- [x] `open` boots pool + bootstrap + forwarder skeleton; failure at
       any step is a typed `Database` error (source chain preserved)
-- [ ] Forwarder skeleton: dedicated non-pooled connection, poll loop
+- [x] Forwarder skeleton: dedicated non-pooled connection, poll loop
       before first query, bounded broadcast fanout, dynamic channel
       set; the two POC deadlock pitfalls structurally excluded
-- [ ] `close()`/`Drop` teardown clean (listener connection dropped,
+- [x] `close()`/`Drop` teardown clean (listener connection dropped,
       pool closed); post-close ops fail closed
-- [ ] Error-mapping helpers exist and are the documented reuse point
-- [ ] Crate docs carry the `# Posture` statements (multi-host,
+- [x] Error-mapping helpers exist and are the documented reuse point
+- [x] Crate docs carry the `# Posture` statements (multi-host,
       listener budget, no spawn_blocking)
-- [ ] `cargo test -p alkstore-postgres` (harness server), clippy
+- [x] `cargo test -p alkstore-postgres` (harness server), clippy
       `-D warnings`, fmt clean; gates green server-less (tests skip)
 
 ## References
@@ -106,8 +106,131 @@ name; `synchronous_commit` observable via `SHOW`).
 
 ## Notes
 
-> To be filled by implementation agent
+Decisions of record made while implementing (the description didn't
+pin them):
+
+- **The connection config rides `open`'s first argument, not `PgOpts`**
+  (the description's bullet list carried it under both; the signature
+  line `open(config, opts)` and ADR-008 §6's
+  `alkstore_postgres::open(url, PgOpts)` pin decide it): `PgOpts`
+  carries schema/max_size/synchronous_commit only. `open` is **async**
+  (`connect` is; the SQLite twin's sync `open` was file-only). Fail
+  posture: unparseable config → `pg_error` (a
+  `tokio_postgres::Error::ConfigParse`); refused connection →
+  `pg_error` — both typed `Database`, source chain preserved, pinned
+  by test.
+- **`open` connects the listener inline, not inside the task** — an
+  unreachable server must fail `open` synchronously (the
+  unreachable-server acceptance row); the forwarder task takes over
+  the established connection and owns reconnects from there.
+- **Forwarder skeleton shape** (`forwarder.rs`, the POC's
+  ~90-line shape restructured): a `LoopCtx` struct carries the loop's
+  state (clippy's too-many-arguments); per connection generation the
+  loop spawns a **poll task owning the `Connection`** (`poll_message`
+  → bounded broadcast 1024, lag surfaced) before any client query —
+  pitfall 1's structural exclusion held permanently (the command
+  select keeps the poll task co-resident with LISTEN/UNLISTEN client
+  queries every generation); the `Client` is owned by the loop
+  (pitfall 2). Connection generations carry an `Option<ListenerConnection>`
+  slot; `ListenerConnection` is the `NoTls`
+  `Connection<Socket, NoTlsStream>` alias. Commands (LISTEN/UNLISTEN)
+  ride an mpsc queue the loop issues between polls (reconnect replays
+  them harmlessly alongside the registry re-issue); the shutdown
+  watch flips at `close`/`Drop`.
+- **Dynamic channel set**: a `BTreeSet`-backed registry
+  (`Forwarder::{register,unregister}`), registry-write-first ordering
+  (a registration survives a connection death between write and
+  LISTEN — the reconnect re-issues from the snapshot).
+  `register` fails `Database` only mid-reconnect (transient, honest
+  state surfaced). `subscribe()` on the fanout exposes the raw
+  notification broadcast — the notify-listen task bridges receivers
+  onto it. `RawNotification { channel }` is the skeleton's broadcast
+  content (the `Wake` mapping is that task's).
+- **The synthetic reconnect-wake is broadcast by the skeleton** (the
+  reserved channel `__alkstore_listener_reconnected__` after every
+  successful re-LISTEN except the first) — the notify-listen task owns
+  the wake-content/receiver semantics; the skeleton's fanout already
+  carries it (pinned by the backend-kill test).
+- **Listener `application_name` is per-instance**:
+  `alkstore-pg-listener-{pid}-{seq}` — the deployment.md ops
+  kill-targetability with a unique suffix so parallel
+  stores/tests are distinguishable in `pg_stat_activity` (the
+  outside-the-pool and teardown assertions target the store's own
+  instance). Exposed at `PgStore::listener_application_name()` for
+  the notify-listen task's backend-kill tests.
+- **Liveness is verified, not assumed**: `connected` starts true (the
+  handed-in connection is fresh) and a no-channel generation probes
+  with `SELECT 1` (a dead connection would otherwise report live).
+- **Empty `PgOpts::schema` falls back to `DEFAULT_SCHEMA`** (defensive;
+  the documented default is `.default()`-driven).
+- **Error mappings** (`seam.rs`, the mechanism tasks' reuse surface):
+  `pg_error(tokio_postgres::Error)`, `pool_error(PoolError)`,
+  `build_error(BuildError)` (the pool-build failure arm —
+  `PoolBuilder::build` returns `BuildError`, not
+  `CreatePoolError`), `database_error(msg)` (the SQLite twin's
+  io-Error string helper).
+- **No runtime dep additions beyond the existing set** (tokio-postgres,
+  deadpool-postgres, tokio, thiserror already carried by the schema
+  task; `serde_json` added — core's payload type appears in the trait
+  stubs' signatures). TLS: `NoTls` on both paths (the consumer's
+  sslmode/TLS story is a deployment concern; noted in the forwarder
+  module docs, the notify-listen task revisits listener TLS if a task
+  or ADR ever demands it).
+- **Trait stubs** carry the closed-store check *ahead of* the stub
+  error (`close()`/`Drop` make every arm fail closed immediately —
+  the post-close fails-closed row is pinned from open onward). Stub
+  messages name their landing task; their text rides the source
+  chain (`Database` Display is opaque — asserted via the chain).
+- **Machinery accessors are `pub(crate)`** (`pool`, `forwarder`,
+  `schema`, `listener_application_name`) — the mechanism tasks reach
+  them; tests exercise them and the lib-build dead-code gates are
+  `#[cfg_attr(not(test), allow(dead_code))]`-carried until the wiring
+  tasks land (the wave-3 intermediate posture).
+- **Harness reuse**: the schema task's env-carried DSN convention
+  (`ALKSTORE_PG_HOST/PORT/USER/PASSWORD/DB`), schema-per-test
+  isolation, skip-clean server-less; the shared default schema is
+  never dropped by tests; the POC's fanout shape (broadcast 1024,
+  lag-surfaced) and backoff constants (50 ms → 2 s) are re-owned as
+  named constants.
 
 ## Summary
 
-> To be filled on completion
+Stood up `alkstore-postgres`'s public surface: `PgOpts` (schema —
+default `alkstore` per ADR-010 §8; `max_size` — default
+`DEFAULT_MAX_SIZE = 8`, the deployment budget line with the +1
+listener outside the pool; `synchronous_commit` — default on, wired as
+connect-options `-c` per-session SET per the POC's verified mechanics;
+not `#[non_exhaustive]`, `Debug`+`Clone`+`Default` per ADR-017 §3's
+opts exemption), the `async open(config: &str, opts: PgOpts) ->
+Result<Box<dyn Store>>` constructor (parse → pool build with
+`RecyclingMethod::Fast` → pool-checkout schema bootstrap → dedicated
+non-pooled listener connect + forwarder spawn; every failure a typed
+`Error::Database` with the source chain preserved), the concrete
+`PgStore` re-exported (pool + forwarder handle + schema name held
+behind the `Store` trait; `close()`/`Drop` shut the forwarder down
+and close the pool — post-close ops fail closed), the LISTEN
+forwarder skeleton (`forwarder.rs`: dedicated non-pooled connection,
+poll-first structure excluding both POC-pinned deadlock pitfalls,
+bounded 1024 broadcast fanout with lag surfaced, dynamic channel set
+with registry-write-first recovery ordering, reconnect loop with the
+50 ms → 2 s exponential backoff, synthetic reconnect-wake broadcast on
+the reserved channel), the seam error mappings (`pg_error`,
+`pool_error`, `build_error`, `database_error` — the mechanism tasks'
+documented reuse point), and the full `Store` trait as wave-3-style
+`Database("… wiring lands with the … task")` stubs with closed-store
+fail-closed checks. Crate docs carry the `# Posture` statements
+(multi-host, the listener budget line, natively async / no
+spawn_blocking). Verified: 12 new open/opts tests
+(`src/store/open_tests.rs`) + the 9 schema tests green against the
+harness server (boot round-trip, pool bounds + pool saturation leaving
+the listener untouched, opts flow: schema name in the created schema +
+`synchronous_commit` observable via `SHOW` on both settings, pitfall
+pins — immediate post-open LISTEN + long-after-open delivery — and the
+outside-the-pool accounting via per-instance `pg_stat_activity`,
+backend-kill reconnect with reserved-wake + post-reconnect delivery,
+close/drop teardown with server-side session termination + closed
+pool + fail-closed ops, unparseable-config and unreachable-server
+`Database` failures, the stub surface, the seam mappings' source
+chains); workspace `cargo test` green server-less (236 tests, pg tests
+skipping per convention); `cargo clippy --all-targets -- -D warnings`
+and `cargo fmt --check` clean workspace-wide.