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

tasks/core-pin-offset-initial-value.md

@@ -1,7 +1,7 @@
 ---
 id: core-pin-offset-initial-value
 name: Verify and pin EventReceiver::offset()'s pre-yield value (review 004 item 12)
-status: pending
+status: completed
 depends_on: []
 scope: narrow
 risk: low
@@ -38,14 +38,14 @@ conversation, not a doc edit.
 
 ## Acceptance Criteria
 
-- [ ] The three engines' pre-yield `offset()` values verified equal by
+- [x] The three engines' pre-yield `offset()` values verified equal by
       live runs (the probe/leg recorded; green on all three columns —
       pg against the harness server)
-- [ ] core-contract.md's `EventReceiver::offset()` text pins the
+- [x] core-contract.md's `EventReceiver::offset()` text pins the
       pre-yield return with a dated annotation
 - [ ] If divergent instead: the divergence recorded and raised with
       the user (this AC replaces the doc pin, not supplements it)
-- [ ] Doc gate green; any new suite leg green on all three columns
+- [x] Doc gate green; any new suite leg green on all three columns
 
 ## References
 
@@ -58,8 +58,59 @@ conversation, not a doc edit.
 
 ## Notes
 
-> To be filled by implementation agent
+- **The engines were equal — the doc-pin branch applies, not the
+  divergence branch.** Read first (all three `offset()` bodies are
+  `self.position`, and all three constructors initialize
+  `position: 0` unconditionally — mem
+  `alkstore-mem/src/stream.rs:353`, sqlite
+  `alkstore-sqlite/src/stream.rs:399`, pg
+  `alkstore-postgres/src/stream.rs:620`), then verified live by the
+  new suite leg on all three columns: 0 on every pre-yield arm
+  (fresh, positive-checkpoint, negative-seed), no divergence to
+  raise.
+- **Probe home: the contract suite** (the task's first choice) — a
+  new row `receiver_offset_pre_yield_is_zero` in
+  `alkstore-contract-suite/src/properties.rs`, wired into all three
+  engines' `tests/contract_suite.rs` executors. Four arms: fresh
+  consumer, consumer with a stored positive checkpoint, consumer
+  with a stored negative checkpoint (the ADR-023 §2 totality seed —
+  the arm a checkpoint-seeded realization would surface on), and a
+  first-observation composition leg (the attach read prefetches
+  unobserved; the first `recv` moves `offset()` to the last-yielded
+  offset). Stamp per the `version_stamp` convention: ADR-008 §8's
+  `EventReceiver` shape + the core-contract.md pin (no ADR owns this
+  property's pre-yield arm — the review item is the pin's origin, so
+  the backlog row is the cited pin).
+- **Doc pin location**: the task said "core-contract.md's
+  `EventReceiver::offset()` paragraph" — no such standalone paragraph
+  exists; the receiver's contract text lives in the streams/
+  `subscribe(consumer)` bullet (ADR-008 §8 pins only the shape
+  comment "the receiver's current offset"). The pin landed there
+  (dated annotation), *and* on `offset()`'s own trait doc in
+  `alkstore/src/event_receiver.rs` (core's doc comments are contract
+  text per AGENTS.md; dated the same). ADR-008 §8's shape comment was
+  deliberately left untouched — a doc-only verification task takes no
+  ADR amendment.
+- **Verification-backlog bullet added** (core-contract.md), matching
+  the section's evolved role: the new bullet records the verified pin
+  with the row's name and the all-three-columns result, same posture
+  as the review-004 suite legs before it.
+- Frontmatter `last_updated` extended with the pin (dated), keeping
+  the freeze note intact.
 
 ## Summary
 
-> To be filled on completion
+The pre-yield `offset()` question closed: all three engines return 0
+before any yield regardless of stored checkpoint (positive, negative,
+or absent) — the no-yield sentinel, composing with the pinned
+pre-yield `save_offset()` no-op; the first `recv`/`try_recv`
+observation is the first move. Pinned in three places: the contract
+text (core-contract.md streams row + verification-backlog bullet,
+dated 2026-10-11), the core trait doc (`event_receiver.rs::offset()`),
+and the suite (new stamped row `receiver_offset_pre_yield_is_zero` on
+`alkstore-contract-suite`). Verified: the new row green on all three
+columns (pg against the harness server `pglo-poc` :15432), full pg
+column green (135+26+9), workspace tests green server-less, clippy `-D
+warnings`, `cargo fmt --check`, doc gate zero warnings, fuzz corpus
+replay 6/6, wasm32 mem check green. Contract-observation only — no
+engine code changed, no ADR amendment.