core: verify and pin the receiver's pre-yield offset() value (review 004 item 12, core-pin-offset-initial-value) — the three engines verified equal live, so the doc-pin branch applies: offset() reads 0 before any yield on every receiver — fresh consumer, stored positive checkpoint, stored negative seed (ADR-023 §2's totality arm, the one a checkpoint-seeded realization would surface on) — the no-yield sentinel, never the stored checkpoint: the checkpoint gates the feed's attach-read start while the receiver's offset tracks the last-yielded event only, composing with the pinned pre-yield save_offset() no-op; the attach read's prefetches sit unobserved and the first recv/try_recv observation is the first move (then the post-yield value, receiver_close_and_save_arms' pin). Verified by code read first (all three offset() bodies are self.position, all three constructors seed position: 0 unconditionally — mem stream.rs:353, sqlite :399, pg :620) then live: new suite row receiver_offset_pre_yield_is_zero (alkstore-contract-suite, stamped ADR-008 §8 + the core-contract.md pin, four arms incl. the first-observation composition leg) green on all three columns, pg against the harness server (parked pglo-poc :15432); pinned in three places: core-contract.md streams/subscribe row (dated 2026-10-11 annotation) + a verification-backlog bullet recording the verified pin, the core trait doc on offset() (core's doc comments are contract text), and the suite row itself — ADR-008 §8's shape comment deliberately left untouched (doc-only verification takes no ADR amendment, noted in the task); no engine code changed, no divergence to raise; gates green: workspace build/tests server-less, full pg column vs harness (135+26+9), clippy -D warnings, fmt --check, doc gate zero warnings, fuzz corpus replay 6/6, wasm32 mem check, taskgraph validate (96); task -> completed

alkstore-postgres/tests/contract_suite.rs

@@ -170,9 +170,10 @@ mod rows {
         name_validation_rejects_empty_and_reserved, outbox_enqueue_tx_commit_atomicity,
         payload_round_trip_stores_exact_encoding, payload_too_large_produced_on_pg,
         publish_with_key_tx_commit_atomicity, queue_depth_reclaim_and_dead_letter,
-        receiver_close_and_save_arms, scheduler_boundary_fires, scheduler_bounded_catchup,
-        scheduler_leadership_discipline, stream_ordering_equivalence, sweep_no_stranded_rows,
-        trim_to_semantics, wake_receiver_shapes, with_tx_panicking_closure_rolls_back,
+        receiver_close_and_save_arms, receiver_offset_pre_yield_is_zero, scheduler_boundary_fires,
+        scheduler_bounded_catchup, scheduler_leadership_discipline, stream_ordering_equivalence,
+        sweep_no_stranded_rows, trim_to_semantics, wake_receiver_shapes,
+        with_tx_panicking_closure_rolls_back,
     };
 
     use super::PgFactory;
@@ -253,6 +254,11 @@ mod rows {
         receiver_close_and_save_arms,
         "row-receiver-arms"
     );
+    harness_row!(
+        row_receiver_offset_pre_yield_is_zero,
+        receiver_offset_pre_yield_is_zero,
+        "row-receiver-offset-preyield"
+    );
     harness_row!(
         row_job_handle_validity_predicate,
         job_handle_validity_predicate,