Postgres engine: transactional seam — begin_tx, PgTxHandle, all eleven *_tx methods with drop=rollback detached teardown, probe-pinned unknowable-state discard arms, engine-side resolution arithmetic (task pg-engine-seam-tx)

alkstore-postgres/src/lib.rs

@@ -34,9 +34,11 @@
 
 mod forwarder;
 mod opts;
+mod resolution;
 mod schema;
 mod seam;
 mod store;
+mod tx;
 
 pub use opts::{DEFAULT_MAX_SIZE, PgOpts};
 pub use schema::{
@@ -44,3 +46,4 @@ pub use schema::{
     tables,
 };
 pub use store::{PgStore, open};
+pub use tx::PgTxHandle;

alkstore-postgres/src/resolution.rs

@@ -0,0 +1,227 @@
+//! The engine-side opts-resolution arithmetic (ADR-020 §1–§3) and the
+//! derived stamp sets — the shared formulas the tx seam stamps rows
+//! with and the auto-commit mechanism tasks reuse, one owner per
+//! formula (ADR-012 §2 — the pg engine's own `resolution.rs`; the
+//! SQLite one is reference not dependency).
+//!
+//! # The clock posture
+//!
+//! `now` is the **one `std::time` read per enqueue** (the single clock
+//! read, second-precision) — not a SQL-side `EXTRACT(EPOCH …)`:
+//! the resolution arithmetic (delay-over-`run_at`, relative-`expires`)
+//! is owned here in Rust, so the same instant stamps `run_at`/
+//! `created_at`/`expires_at` without a second read, and the timestamps
+//! leave the engine as plain `i64` parameters the SQL binds. One
+//! read, one instant, every column resolved from it.
+
+use std::time::{SystemTime, UNIX_EPOCH};
+
+use alkstore::{EnqueueOpts, QueueOpts};
+
+/// The engine's second-precision clock — the single read the
+/// resolution and row write share (ADR-020 §1: "one enqueue, one
+/// clock read"). No SQL round trip: a plain `std::time` read.
+pub(crate) fn now_unix() -> i64 {
+    SystemTime::now()
+        .duration_since(UNIX_EPOCH)
+        .map(|d| d.as_secs() as i64)
+        .unwrap_or(0)
+}
+
+/// The plain queue's derived `QueueOpts` defaults (300/3/5/none,
+/// honker parities — ADR-010 §3) — the stamp source for the
+/// no-handle-open shapes (`enqueue_tx`, scheduler boundary fires,
+/// ADR-020 §3 / §3a note).
+///
+/// Named (not an inline `QueueOpts::default()` call) so the "derived
+/// defaults" formula has one owner: a future default change lands
+/// here, once, engine-wide.
+pub(crate) fn plain_queue_default_stamps() -> Stamps {
+    let QueueOpts {
+        visibility_timeout_s,
+        max_attempts,
+        backoff_base_s,
+        dead_letter_retention_s,
+    } = QueueOpts::default();
+    Stamps {
+        max_attempts,
+        visibility_timeout_s,
+        backoff_base_s,
+        dead_letter_retention_s,
+    }
+}
+
+/// The outbox backing queue's derived `QueueOpts` set (60/5/5 — ADR-010
+/// §3, visibility 60 s, max_attempts 5, backoff base 5 s, retention
+/// forever). The stamp source for `outbox_enqueue_tx` /
+/// `Outbox::enqueue`.
+pub(crate) fn outbox_default_stamps() -> Stamps {
+    Stamps {
+        visibility_timeout_s: 60,
+        max_attempts: 5,
+        backoff_base_s: 5,
+        dead_letter_retention_s: None,
+    }
+}
+
+/// The derived backing-queue name for an outbox (the reserved
+/// namespace — ADR-008 §4). Engine-internal derivation: the reserved
+/// prefix makes the name unreachable by `enqueue_tx` by design
+/// (ADR-014 §1) — outbox enqueue is the only path into it.
+pub(crate) fn outbox_backing_queue_name(outbox: &str) -> String {
+    format!("{}outbox:{outbox}", alkstore::RESERVED_PREFIX)
+}
+
+/// The one per-enqueue stamp override (ADR-010 §3a):
+/// `EnqueueOpts::max_attempts` is the only per-job override — the
+/// other stamps (visibility/backoff/retention) always take the base's.
+///
+/// One helper both enqueue shapes share: the tx paths (`enqueue_tx`
+/// over the plain-queue defaults, `outbox_enqueue_tx` over the
+/// outbox's 60/5/5 set) and the auto-commit `Queue::enqueue` over the
+/// handle's `QueueOpts` — resolved once, engine-wide (ADR-012 §2).
+pub(crate) fn stamps_with_override(base: Stamps, opts: &EnqueueOpts) -> Stamps {
+    Stamps {
+        max_attempts: opts.max_attempts.unwrap_or(base.max_attempts),
+        ..base
+    }
+}
+
+/// The enqueue-time stamp set a row carries (ADR-010 §3a) —
+/// column-bound primitives; the engine layer resolves
+/// contract semantics into these (the substrate boundary posture,
+/// engine-owned here since there is no forked substrate).
+#[derive(Clone, Copy, Debug)]
+pub(crate) struct Stamps {
+    pub max_attempts: i64,
+    pub visibility_timeout_s: i64,
+    pub backoff_base_s: i64,
+    pub dead_letter_retention_s: Option<i64>,
+}
+
+/// Resolve [`EnqueueOpts`] against the enqueue instant: the row's ready
+/// time (`delay` → `now + delay`, wins over `run_at` (absolute);
+/// neither → `now`) and the absolute row expiry (`expires` relative
+/// seconds from enqueue; `None` = never) — ADR-020 §1/§2. One clock
+/// read per enqueue: the caller's `now` stamps everything.
+pub(crate) struct ResolvedEnqueue {
+    pub run_at: i64,
+    pub expires_at: Option<i64>,
+}
+
+pub(crate) fn resolve_enqueue_opts(now: i64, opts: &EnqueueOpts) -> ResolvedEnqueue {
+    let run_at = match opts.delay {
+        Some(delay) => now.saturating_add(delay),
+        None => opts.run_at.unwrap_or(now),
+    };
+    let expires_at = opts.expires.map(|s| now.saturating_add(s));
+    ResolvedEnqueue { run_at, expires_at }
+}
+
+#[cfg(test)]
+mod resolution_tests {
+    use super::*;
+
+    #[test]
+    fn plain_queue_default_stamps_are_300_3_5_none() {
+        let stamps = plain_queue_default_stamps();
+        assert_eq!(
+            (
+                stamps.visibility_timeout_s,
+                stamps.max_attempts,
+                stamps.backoff_base_s,
+                stamps.dead_letter_retention_s
+            ),
+            (300, 3, 5, None)
+        );
+    }
+
+    #[test]
+    fn outbox_default_stamps_are_60_5_5_forever() {
+        let stamps = outbox_default_stamps();
+        assert_eq!(
+            (
+                stamps.visibility_timeout_s,
+                stamps.max_attempts,
+                stamps.backoff_base_s,
+                stamps.dead_letter_retention_s
+            ),
+            (60, 5, 5, None)
+        );
+    }
+
+    #[test]
+    fn outbox_backing_queue_name_is_reserved_and_derived() {
+        assert_eq!(
+            outbox_backing_queue_name("billing"),
+            "__alkstore_outbox:billing"
+        );
+    }
+
+    #[test]
+    fn stamp_override_changes_only_max_attempts() {
+        let base = plain_queue_default_stamps();
+        let opts = EnqueueOpts {
+            max_attempts: Some(9),
+            ..Default::default()
+        };
+        let stamped = stamps_with_override(base, &opts);
+        assert_eq!(stamped.max_attempts, 9);
+        assert_eq!(
+            (
+                stamped.visibility_timeout_s,
+                stamped.backoff_base_s,
+                stamped.dead_letter_retention_s
+            ),
+            (300, 5, None)
+        );
+    }
+
+    #[test]
+    fn delay_wins_over_run_at() {
+        let opts = EnqueueOpts {
+            delay: Some(120),
+            run_at: Some(100_000_000),
+            ..Default::default()
+        };
+        let resolved = resolve_enqueue_opts(1_000, &opts);
+        assert_eq!(resolved.run_at, 1_120, "delay wins over run_at");
+        assert_eq!(resolved.expires_at, None);
+    }
+
+    #[test]
+    fn run_at_alone_is_literal_and_neither_is_now() {
+        let absolute = EnqueueOpts {
+            run_at: Some(1_500_000_000),
+            ..Default::default()
+        };
+        assert_eq!(resolve_enqueue_opts(1_000, &absolute).run_at, 1_500_000_000);
+        assert_eq!(
+            resolve_enqueue_opts(1_000, &Default::default()).run_at,
+            1_000
+        );
+    }
+
+    #[test]
+    fn expires_is_relative_resolved_to_absolute() {
+        let opts = EnqueueOpts {
+            expires: Some(90),
+            ..Default::default()
+        };
+        let resolved = resolve_enqueue_opts(1_000, &opts);
+        assert_eq!(resolved.expires_at, Some(1_090));
+    }
+
+    #[test]
+    fn saturating_resolution_never_panics() {
+        let opts = EnqueueOpts {
+            delay: Some(i64::MAX),
+            run_at: Some(i64::MAX),
+            expires: Some(i64::MAX),
+            ..Default::default()
+        };
+        let resolved = resolve_enqueue_opts(i64::MAX, &opts);
+        assert_eq!(resolved.run_at, i64::MAX);
+        assert_eq!(resolved.expires_at, Some(i64::MAX));
+    }
+}

alkstore-postgres/src/store.rs

@@ -231,7 +231,7 @@ impl Store for PgStore {
         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")) })
+        crate::tx::PgTxHandle::begin(self.pool.clone(), self.schema.clone())
     }
 
     fn notify<'a>(
@@ -340,3 +340,6 @@ impl Store for PgStore {
 
 #[cfg(test)]
 mod open_tests;
+
+#[cfg(test)]
+mod tx_tests;

alkstore-postgres/src/store/open_tests.rs

@@ -541,7 +541,10 @@ async fn close_and_drop_teardown_cleanly() {
         matches!(err, alkstore::Error::Database(_)),
         "post-close notify fails closed, got: {err:?}"
     );
-    let err = stub_err!(store.begin_tx().await);
+    let err = match store.begin_tx().await {
+        Err(e) => e,
+        Ok(_) => panic!("post-close begin_tx must fail closed"),
+    };
     assert!(
         matches!(err, alkstore::Error::Database(_)),
         "post-close begin_tx fails closed, got: {err:?}"
@@ -627,22 +630,15 @@ async fn store_trait_methods_are_wiring_stubs() {
     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"
-    );
+    // `begin_tx` is wired (the seam task's): the seam boots and
+    // commits — its full behavior the tx tests' scope.
+    let tx = store.begin_tx().await.unwrap();
+    tx.commit().await.unwrap();
+
     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"
-    );
+        .await;
+    assert!(err.is_ok(), "with_tx surfaces the wired begin_tx naturally");
     let err = store
         .notify("ch", serde_json::json!("x"))
         .await
@@ -686,7 +682,10 @@ async fn store_trait_methods_are_wiring_stubs() {
     // 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);
+    let err = store
+        .notify("ch", serde_json::json!("x"))
+        .await
+        .unwrap_err();
     match err {
         alkstore::Error::Database(source) => {
             let msg = source.to_string();
@@ -695,7 +694,7 @@ async fn store_trait_methods_are_wiring_stubs() {
                 "stub errors name their landing task, got: {msg}"
             );
         }
-        other => panic!("begin_tx stub must be Database, got {other:?}"),
+        other => panic!("notify stub must be Database, got {other:?}"),
     }
 
     drop(store);

alkstore-postgres/src/tx.rs

@@ -0,0 +1,661 @@
+//! The transactional seam's pg arm (ADR-007) — `begin_tx`, the
+//! [`PgTxHandle`] (the pooled-object handle), and all eleven `*_tx`
+//! methods (`pg-engine-seam-tx`).
+//!
+//! # No bridge, no `spawn_blocking`
+//!
+//! The handle holds the pooled object directly: tokio-postgres's
+//! client is `Send + Sync` (POC #2 compile-probe — ADR-007's pg arm),
+//! so every op is a straight `.await` through the held
+//! [`deadpool_postgres::Object`], no hop cost, no thread rigging.
+//! `begin_tx` checks the pooled client out, issues `BEGIN`, and hands
+//! the caller the boxed handle; `commit` and the drop path conclude
+//! the transaction and return (or, when the state is unknowable,
+//! discard) the object — the pool accounting stays exact on every
+//! arm.
+//!
+//! # The unknowable-state disposition
+//!
+//! A failed `BEGIN`/`COMMIT`/`ROLLBACK` leaves the client's session
+//! state unknowable: the object is **discarded, not re-pooled** —
+//! [`Object::take`](deadpool_postgres::Object::take) takes it from
+//! the pool permanently (the size accounting stays exact; the next
+//! checkout draws a fresh object). Same posture for an already-closed
+//! client (`is_closed`).
+//!
+//! # Drop = rollback (ADR-021 §4)
+//!
+//! A handle dropped without `commit` rolls back: `Drop` schedules the
+//! rollback on the construction runtime (async-native drop posture —
+//! `Drop` cannot `.await`; a detached task carries the `ROLLBACK`
+//! then re-pools the object, and a failed rollback discards it). The
+//! detached task never races ghosts: `tokio::spawn`'s failure arm
+//! (runtime shut down before the task runs — the one case the
+//! rollback does not run in) drops the held object, whose connection
+//! closes server-side and the server itself aborts the open
+//! transaction (POC ground: no ghost survives a closed session). Drop
+//! is panic-safe (`Handle::spawn` never panics — the handle is
+//! captured, not current-context resolved) and never blocks.
+//!
+//! Ops after `commit`/drop-consumption fail closed with
+//! [`Error::Closed`] (the wave-3 fail-closed guard shape) — one-shot
+//! handles cannot op past their terminal transition.
+//!
+//! # Entry-point validation + payload encoding
+//!
+//! Every name-bearing method validates via core's `validation`
+//! helpers (shared-namespace kinds vs consumer-local — ADR-008 §4)
+//! **before any round trip**; payloads encode through core's fallible
+//! [`alkstore::encode_payload`] with the typed `Codec` error `?`-ed
+//! at the seam (ADR-023 §1). `notify_tx` additionally checks the
+//! 8000-byte payload boundary client-side, before any round trip
+//! (`PayloadTooLarge { limit: 8000 }` — ADR-016 §5); the measured
+//! quantity is the serde_json serialization of the payload `Value` —
+//! the same byte string ADR-020 §4 pins as the stored row bytes —
+//! which is valid UTF-8 by construction.
+//!
+//! # Engine-side arithmetic
+//!
+//! The stamp/derivation arithmetic lives in [`crate::resolution`]
+//! (one owner per formula, ADR-012 §2) — the plain-queue 300/3/5/none
+//! set on `enqueue_tx`, the outbox's 60/5/5 set and the
+//! `__alkstore_outbox:{name}` derivation on `outbox_enqueue_tx`, and
+//! `resolve_enqueue_opts`' delay-over-`run_at` + relative-`expires`
+//! resolution on both enqueue shapes, one clock read per enqueue
+//! (the resolution's `now` is the std-time read, document there).
+
+use deadpool_postgres::Object;
+use serde_json::Value;
+use tokio::runtime::Handle;
+
+use alkstore::{
+    BoxedFuture, EnqueueOpts, Error, Job, JobState, Result, StreamEvent, TxHandle,
+    validate_local_name, validate_shared_name,
+};
+
+use crate::resolution::{
+    ResolvedEnqueue, outbox_backing_queue_name, outbox_default_stamps, plain_queue_default_stamps,
+    resolve_enqueue_opts, stamps_with_override,
+};
+use crate::schema::{QualifiedTable, tables};
+use crate::seam::{pg_error, pool_error};
+
+/// The notification payload boundary (the contract's pinned limit —
+/// client-side checked, typed before any round trip; the predicate
+/// rejects at `len >= limit`, the server's NUL-inclusive wire budget).
+pub(crate) const NOTIFY_PAYLOAD_LIMIT: usize = 8000;
+
+/// The caller-held pg transaction handle: the pooled-object handle.
+/// Constructed only through [`crate::PgStore`]'s `begin_tx` — never
+/// held across an engine `Store` trait object (the trait is what
+/// consumers see).
+pub struct PgTxHandle {
+    object: Option<Object>,
+    schema: String,
+    runtime: Handle,
+}
+
+impl std::fmt::Debug for PgTxHandle {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        f.debug_struct("PgTxHandle")
+            .field("open", &self.object.is_some())
+            .finish_non_exhaustive()
+    }
+}
+
+impl PgTxHandle {
+    /// `begin_tx`: pool checkout + `BEGIN`, returning the boxed
+    /// handle. Pool exhaustion blocks (deadpool's acquire semantics);
+    /// a closed pool (or store) fails its checkout. A failed `BEGIN`
+    /// discards the object (session state unknowable) — checkout +
+    /// begin fail as one typed `Database` error, no stranded slot.
+    pub(crate) fn begin(
+        pool: deadpool_postgres::Pool,
+        schema: String,
+    ) -> BoxedFuture<'static, Result<Box<dyn TxHandle + Send>>> {
+        Box::pin(async move {
+            let object = pool.get().await.map_err(pool_error)?;
+            let client: &tokio_postgres::Client = &object;
+            if let Err(e) = client.batch_execute("BEGIN").await {
+                drop(Object::take(object));
+                return Err(pg_error(e));
+            }
+            Ok(Box::new(PgTxHandle {
+                object: Some(object),
+                schema,
+                runtime: Handle::current(),
+            }) as Box<dyn TxHandle + Send>)
+        })
+    }
+
+    /// The concrete-typed constructor — the tests' fault-injection
+    /// surface (poisoning the tx server-side needs raw in-tx SQL, and
+    /// the boxed trait object cannot downcast, ADR-007). Never
+    /// consumer API.
+    #[cfg(test)]
+    pub(crate) fn begin_concrete(
+        pool: deadpool_postgres::Pool,
+        schema: String,
+    ) -> BoxedFuture<'static, Result<PgTxHandle>> {
+        Box::pin(async move {
+            let object = pool.get().await.map_err(pool_error)?;
+            let client: &tokio_postgres::Client = &object;
+            if let Err(e) = client.batch_execute("BEGIN").await {
+                drop(Object::take(object));
+                return Err(pg_error(e));
+            }
+            Ok(PgTxHandle {
+                object: Some(object),
+                schema,
+                runtime: Handle::current(),
+            })
+        })
+    }
+
+    /// The private op bridge: borrow the held object for one `.await`
+    /// op; ops after a terminal disposition fail closed with
+    /// [`Error::Closed`].
+    fn client(&self) -> Result<&tokio_postgres::Client> {
+        self.object
+            .as_ref()
+            .map(|o| {
+                let client: &tokio_postgres::Client = o;
+                client
+            })
+            .ok_or(Error::Closed)
+    }
+
+    /// The held pooled client — the fault-injection surface the
+    /// tests exercise (server-side tx poisoning); never consumer API.
+    #[cfg(test)]
+    pub(crate) fn pooled_client(&self) -> &tokio_postgres::Client {
+        self.client().expect("tests drive open handles")
+    }
+
+    /// Drain the held object, simulating a consumed (committed/dropped)
+    /// shell — the tests' entry into the fail-closed guard arm.
+    #[cfg(test)]
+    pub(crate) fn consume_shell(&mut self) {
+        self.object = None;
+    }
+
+    /// Schema-qualify a table reference for this handle's engine-owned
+    /// schema.
+    fn table(&self, name: &str) -> String {
+        QualifiedTable {
+            schema: &self.schema,
+            name,
+        }
+        .to_string()
+    }
+
+    fn enqueue_row_sql(&self) -> String {
+        format!(
+            "INSERT INTO {} (queue, payload, run_at, priority, max_attempts,
+               expires_at, created_at, visibility_timeout_s,
+               backoff_base_s, dead_letter_retention_s)
+             VALUES ($1, $2, $3, $4, $5, $6, $7, $8, $9, $10)
+             RETURNING id",
+            self.table(tables::JOB)
+        )
+    }
+
+    /// The plain-queue enqueue's shared write (the `enqueue_tx` /
+    /// `outbox_enqueue_tx` INSERT), called with this handle's
+    /// qualified job table.
+    async fn enqueue_row(
+        &self,
+        client: &tokio_postgres::Client,
+        queue: &str,
+        bytes: Vec<u8>,
+        opts: &EnqueueOpts,
+        base: crate::resolution::Stamps,
+    ) -> Result<i64> {
+        let now = crate::resolution::now_unix();
+        let ResolvedEnqueue { run_at, expires_at } = resolve_enqueue_opts(now, opts);
+        let stamps = stamps_with_override(base, opts);
+        let row = client
+            .query_one(
+                &self.enqueue_row_sql(),
+                &[
+                    &queue,
+                    &bytes,
+                    &run_at,
+                    &opts.priority,
+                    &stamps.max_attempts,
+                    &expires_at,
+                    &now,
+                    &stamps.visibility_timeout_s,
+                    &stamps.backoff_base_s,
+                    &stamps.dead_letter_retention_s,
+                ],
+            )
+            .await
+            .map_err(pg_error)?;
+        Ok(row.get(0))
+    }
+}
+
+/// Encode a trait-crossing payload `Value` into the exact stored bytes
+/// (the serde_json serialization — ADR-020 §4). The notify carriage
+/// reuses it: the JSON serialization is valid UTF-8 text by
+/// construction (ADR-016 §5).
+fn encode_payload_bytes(payload: &Value) -> Result<Vec<u8>> {
+    alkstore::encode_payload(payload)
+}
+
+impl TxHandle for PgTxHandle {
+    fn enqueue_tx<'a>(
+        &'a mut self,
+        queue: &str,
+        opts: EnqueueOpts,
+        payload: Value,
+    ) -> BoxedFuture<'a, Result<i64>> {
+        if let Err(e) = validate_shared_name(queue) {
+            return Box::pin(async move { Err(e) });
+        }
+        let queue = queue.to_string();
+        Box::pin(async move {
+            let client = self.client()?;
+            let bytes = encode_payload_bytes(&payload)?;
+            self.enqueue_row(client, &queue, bytes, &opts, plain_queue_default_stamps())
+                .await
+        })
+    }
+
+    fn publish_tx<'a>(&'a mut self, stream: &str, payload: Value) -> BoxedFuture<'a, Result<i64>> {
+        let stream = stream.to_string();
+        Box::pin(async move { self.publish_with_key_tx(&stream, None, payload).await })
+    }
+
+    fn publish_with_key_tx<'a>(
+        &'a mut self,
+        stream: &str,
+        key: Option<String>,
+        payload: Value,
+    ) -> BoxedFuture<'a, Result<i64>> {
+        if let Err(e) = validate_shared_name(stream) {
+            return Box::pin(async move { Err(e) });
+        }
+        let key = match key {
+            Some(k) if k.is_empty() || k.trim().is_empty() => {
+                return Box::pin(async move { Err(Error::InvalidName { name: k }) });
+            }
+            other => other,
+        };
+        let stream = stream.to_string();
+        Box::pin(async move {
+            let client = self.client()?;
+            let bytes = encode_payload_bytes(&payload)?;
+            let created_at = crate::resolution::now_unix();
+            let row = client
+                .query_one(
+                    &format!(
+                        "INSERT INTO {} (stream, \"key\", payload, created_at)
+                         VALUES ($1, $2, $3, $4)
+                         RETURNING id",
+                        self.table(tables::EVENTS)
+                    ),
+                    &[&stream, &key, &bytes, &created_at],
+                )
+                .await
+                .map_err(pg_error)?;
+            Ok(row.get(0))
+        })
+    }
+
+    fn notify_tx<'a>(&'a mut self, channel: &str, payload: Value) -> BoxedFuture<'a, Result<()>> {
+        if let Err(e) = validate_shared_name(channel) {
+            return Box::pin(async move { Err(e) });
+        }
+        let channel = channel.to_string();
+        Box::pin(async move {
+            let bytes = encode_payload_bytes(&payload)?;
+            // The 8000-byte boundary: client-side, typed, before any
+            // round trip (ADR-016 §5). The pinned quantity is the
+            // serde_json serialization — the same byte string the
+            // stored-row bytes pin; the predicate mirrors the server
+            // exactly (the pg payload budget is the wire's 8000 bytes
+            // counting the NUL terminator — probe-pinned: ≤ 7999-byte
+            // texts deliver, 8000 is server-rejected) so every
+            // too-big payload stays typed, never an opaque
+            // server-side reject.
+            if bytes.len() >= NOTIFY_PAYLOAD_LIMIT {
+                return Err(Error::PayloadTooLarge {
+                    limit: NOTIFY_PAYLOAD_LIMIT,
+                });
+            }
+            let client = self.client()?;
+            let text = String::from_utf8(bytes)
+                .map_err(|e| Error::Codec(format!("notify payload must be utf-8 text: {e}")))?;
+            client
+                .query_one("SELECT pg_notify($1, $2)", &[&channel, &text])
+                .await
+                .map_err(pg_error)?;
+            Ok(())
+        })
+    }
+
+    fn save_offset_tx<'a>(
+        &'a mut self,
+        stream: &str,
+        consumer: &str,
+        offset: i64,
+    ) -> BoxedFuture<'a, Result<()>> {
+        if let Err(e) = validate_shared_name(stream) {
+            return Box::pin(async move { Err(e) });
+        }
+        if let Err(e) = validate_local_name(consumer) {
+            return Box::pin(async move { Err(e) });
+        }
+        let stream = stream.to_string();
+        let consumer = consumer.to_string();
+        Box::pin(async move {
+            let client = self.client()?;
+            // Monotone upsert (one owner): a first save seeds the
+            // checkpoint — clamped at 0, the absent-consumer=0 rule
+            // (ADR-019 §1) — and a save at-or-below the stored one
+            // updates nothing (ADR-019 §6's silent no-op).
+            client
+                .execute(
+                    &format!(
+                        "INSERT INTO {} AS o (stream, consumer, \"offset\")
+                         VALUES ($1, $2, GREATEST($3::bigint, 0))
+                         ON CONFLICT (stream, consumer) DO UPDATE
+                           SET \"offset\" = EXCLUDED.\"offset\"
+                         WHERE EXCLUDED.\"offset\" > o.\"offset\"",
+                        self.table(tables::OFFSETS)
+                    ),
+                    &[&stream, &consumer, &offset],
+                )
+                .await
+                .map_err(pg_error)?;
+            Ok(())
+        })
+    }
+
+    fn get_job_tx<'a>(
+        &'a mut self,
+        queue: &str,
+        job_id: i64,
+    ) -> BoxedFuture<'a, Result<Option<Job>>> {
+        if let Err(e) = validate_shared_name(queue) {
+            return Box::pin(async move { Err(e) });
+        }
+        let queue = queue.to_string();
+        Box::pin(async move {
+            let client = self.client()?;
+            // Queue-scoped (the seam's scoping rule): the id
+            // namespace is global across queues — the queue column
+            // must match the argument or the row does not surface.
+            // Dead rows are get-job-visible too (the auto-commit
+            // `get_job` shape; the diagnosis columns ride).
+            let row = client
+                .query_opt(
+                    &format!(
+                        "SELECT id, queue, 'dead', payload, priority, run_at, attempts,
+                                max_attempts, worker_id, claimed_at, claim_expires_at,
+                                created_at, expires_at, visibility_timeout_s,
+                                backoff_base_s, dead_letter_retention_s,
+                                last_error, died_at
+                         FROM {} WHERE id = $1 AND queue = $2",
+                        self.table(tables::DEAD)
+                    ),
+                    &[&job_id, &queue],
+                )
+                .await
+                .map_err(pg_error)?;
+            if let Some(row) = row {
+                return Ok(Some(job_from_row(&row)?));
+            }
+            let row = client
+                .query_opt(
+                    &format!(
+                        "SELECT id, queue, state, payload, priority, run_at, attempts,
+                                max_attempts, worker_id, claimed_at, claim_expires_at,
+                                created_at, expires_at, visibility_timeout_s,
+                                backoff_base_s, dead_letter_retention_s,
+                                NULL::text, NULL::bigint
+                         FROM {} WHERE id = $1 AND queue = $2",
+                        self.table(tables::JOB)
+                    ),
+                    &[&job_id, &queue],
+                )
+                .await
+                .map_err(pg_error)?;
+            match row {
+                Some(row) => Ok(Some(job_from_row(&row)?)),
+                None => Ok(None),
+            }
+        })
+    }
+
+    fn get_offset_tx<'a>(
+        &'a mut self,
+        stream: &str,
+        consumer: &str,
+    ) -> BoxedFuture<'a, Result<i64>> {
+        if let Err(e) = validate_shared_name(stream) {
+            return Box::pin(async move { Err(e) });
+        }
+        if let Err(e) = validate_local_name(consumer) {
+            return Box::pin(async move { Err(e) });
+        }
+        let stream = stream.to_string();
+        let consumer = consumer.to_string();
+        Box::pin(async move {
+            let client = self.client()?;
+            let row = client
+                .query_opt(
+                    &format!(
+                        "SELECT \"offset\" FROM {} WHERE stream = $1 AND consumer = $2",
+                        self.table(tables::OFFSETS)
+                    ),
+                    &[&stream, &consumer],
+                )
+                .await
+                .map_err(pg_error)?;
+            Ok(row.map(|r| r.get(0)).unwrap_or(0))
+        })
+    }
+
+    fn read_since_tx<'a>(
+        &'a mut self,
+        stream: &str,
+        offset: i64,
+        limit: i64,
+    ) -> BoxedFuture<'a, Result<Vec<StreamEvent>>> {
+        if let Err(e) = validate_shared_name(stream) {
+            return Box::pin(async move { Err(e) });
+        }
+        let stream = stream.to_string();
+        Box::pin(async move {
+            // The extent guard (ADR-023 §2): `limit <= 0` reads
+            // nothing — a value, never an error — at trait-impl
+            // entry, before any round trip.
+            if limit <= 0 {
+                return Ok(Vec::new());
+            }
+            let client = self.client()?;
+            let rows = client
+                .query(
+                    &format!(
+                        "SELECT id, \"key\", payload, created_at
+                         FROM {}
+                         WHERE stream = $1 AND id > $2
+                         ORDER BY id ASC
+                         LIMIT $3",
+                        self.table(tables::EVENTS)
+                    ),
+                    &[&stream, &offset, &limit],
+                )
+                .await
+                .map_err(pg_error)?;
+            stream_events_from_rows(&rows, stream)
+        })
+    }
+
+    fn read_from_consumer_tx<'a>(
+        &'a mut self,
+        stream: &str,
+        consumer: &str,
+        limit: i64,
+    ) -> BoxedFuture<'a, Result<Vec<StreamEvent>>> {
+        if let Err(e) = validate_shared_name(stream) {
+            return Box::pin(async move { Err(e) });
+        }
+        if let Err(e) = validate_local_name(consumer) {
+            return Box::pin(async move { Err(e) });
+        }
+        let stream = stream.to_string();
+        let consumer = consumer.to_string();
+        Box::pin(async move {
+            if limit <= 0 {
+                return Ok(Vec::new());
+            }
+            let from = self.get_offset_tx(&stream, &consumer).await?;
+            self.read_since_tx(&stream, from, limit).await
+        })
+    }
+
+    fn outbox_enqueue_tx<'a>(
+        &'a mut self,
+        outbox: &str,
+        opts: EnqueueOpts,
+        payload: Value,
+    ) -> BoxedFuture<'a, Result<i64>> {
+        if let Err(e) = validate_shared_name(outbox) {
+            return Box::pin(async move { Err(e) });
+        }
+        let outbox = outbox.to_string();
+        Box::pin(async move {
+            let client = self.client()?;
+            let bytes = encode_payload_bytes(&payload)?;
+            let queue = outbox_backing_queue_name(&outbox);
+            self.enqueue_row(client, &queue, bytes, &opts, outbox_default_stamps())
+                .await
+        })
+    }
+
+    /// Commit: `COMMIT` + re-pool. A failed COMMIT discards the object
+    /// — its state is unknowable (the wave-3 review's finding (c),
+    /// pre-empted here; the pool accounting stays exact either way).
+    /// One-shot; later ops on the consumed shell fail `Closed`.
+    fn commit(mut self: Box<Self>) -> BoxedFuture<'static, Result<()>> {
+        let Some(object) = self.object.take() else {
+            return Box::pin(async { Err(Error::Closed) });
+        };
+        Box::pin(async move {
+            let client: &tokio_postgres::Client = &object;
+            match client.batch_execute("COMMIT").await {
+                Ok(()) => {
+                    drop(object);
+                    Ok(())
+                }
+                Err(e) => {
+                    drop(Object::take(object));
+                    Err(pg_error(e))
+                }
+            }
+        })
+    }
+}
+
+impl Drop for PgTxHandle {
+    /// Drop = rollback (ADR-021 §4): the rollback runs on the
+    /// construction runtime as a detached task — `ROLLBACK`, then
+    /// re-pool; a failed rollback (or an already-closed client)
+    /// discards the object (unknowable state). Panic-safe: no panic
+    /// escapes drop (`Handle::spawn` is captured-handle-bound, never
+    /// current-context-bound), never blocking; the dropped-future arm
+    /// (runtime shut down before the task runs) closes the session —
+    /// the server aborts the open transaction, so no ghost survives
+    /// even there.
+    fn drop(&mut self) {
+        let Some(object) = self.object.take() else {
+            return;
+        };
+        self.runtime.spawn(async move {
+            if object.is_closed() {
+                drop(Object::take(object));
+                return;
+            }
+            let client: &tokio_postgres::Client = &object;
+            if let Err(e) = client.batch_execute("ROLLBACK").await {
+                drop(Object::take(object));
+                eprintln!(
+                    "alkstore: pg tx handle dropped with a failed ROLLBACK; \
+                     the pooled client is discarded (state unknowable): {e}"
+                );
+                return;
+            }
+            drop(object);
+        });
+    }
+}
+
+/// Decode a job row (the uniform 18-column shape — the dead-table
+/// select carries `last_error`/`died_at`; the live one binds NULLs)
+/// into the contract value (`Job::from_row` — the `#[doc(hidden)]`
+/// constructor, ADR-021 §2's field list of record). Malformed rows map
+/// to `Error::Codec` (the decode-side posture guard).
+fn job_from_row(row: &tokio_postgres::Row) -> Result<Job> {
+    let state = match row.get::<_, Option<&str>>(2) {
+        Some("pending") => JobState::Pending,
+        Some("processing") => JobState::Processing,
+        Some("dead") => JobState::Dead,
+        other => {
+            return Err(Error::Codec(format!(
+                "job row state must be pending|processing|dead, got {other:?}"
+            )));
+        }
+    };
+    let payload: Option<Vec<u8>> = row
+        .try_get(3)
+        .map_err(|e| Error::Codec(format!("job row payload must be bytea: {e}")))?;
+    Ok(Job::from_row(
+        row.get(0),
+        row.get(1),
+        state,
+        payload.unwrap_or_default(),
+        row.get(4),
+        row.get(5),
+        row.get(6),
+        row.get(7),
+        row.get(8),
+        row.get(9),
+        row.get(10),
+        row.get(11),
+        row.get(12),
+        row.get(13),
+        row.get(14),
+        row.get(15),
+        row.get(16),
+        row.get(17),
+    ))
+}
+
+/// Decode a read page into the contract's [`StreamEvent`] values (the
+/// core constructor's `from_row`). Malformed rows map to `Error::Codec`.
+fn stream_events_from_rows(
+    rows: &[tokio_postgres::Row],
+    stream: String,
+) -> Result<Vec<StreamEvent>> {
+    let mut out = Vec::with_capacity(rows.len());
+    for row in rows {
+        let key: Option<String> = row
+            .try_get(1)
+            .map_err(|e| Error::Codec(format!("stream row key must be text: {e}")))?;
+        let payload: Option<Vec<u8>> = row
+            .try_get(2)
+            .map_err(|e| Error::Codec(format!("stream row payload must be bytea: {e}")))?;
+        out.push(StreamEvent::from_row(
+            row.get(0),
+            stream.clone(),
+            key,
+            payload.unwrap_or_default(),
+            row.get(3),
+        ));
+    }
+    Ok(out)
+}