decompose wave 5 — contract suite: audit-first split of the verification backlog (engines' columns already discharge most rows; map in review-wave-5's appendix), seven mechanism-grouped suite-row tasks (queue depth, scheduler, tx commit-atomicity, streams, locks, wakes, opts/backoff equivalence), two engine-side hardening tasks (sqlite commit-error arm, pg F-1 defense-in-depth), and the review-wave-5 gate that flips the engine specs to stable

tasks/suite-opts-backoff-rows.md

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+---
+id: suite-opts-backoff-rows
+name: Contract-suite rows — backoff-curve equivalence + the deferred enqueue-opts clock legs
+status: pending
+depends_on: []
+scope: narrow
+risk: low
+impact: phase
+level: implementation
+tags: [wave-5, contract-suite, queues]
+---
+
+## Description
+
+Complete the arithmetic-equivalence backlog rows
+(core-contract.md §Verification backlog): "Backoff-curve and
+stamp-resolution equivalence across engines" and the two
+wall-clock-adjacent legs the existing `enqueue_opts_resolution` row
+explicitly deferred ("The `run_at`-alone-literal and
+neither-field-resolves-to-now legs ... pin with wave 5's equivalence
+row").
+
+Work:
+
+- **Extend `enqueue_opts_resolution` in place** (one owner per
+  property — the row's own doc comment names this wave-5 completion;
+  stamps accumulate per the convention): the `run_at`-alone literal
+  leg (a future `run_at` is the row's ready time verbatim; a past
+  `run_at` resolves to ready-now — the boundary-total rule, ADR-023
+  §2) and the neither-field leg (ready now — tolerance-bounded
+  proximity, never a tight timing assert).
+- **Add `backoff_curve_equivalence`** — the equal-jitter exponential
+  curve (ADR-010 §3): `delay ∈ [base·2^(a−1)/2, base·2^(a−1)]` per
+  attempt, uniform jitter over the lower half — *the range, not a
+  jitter label, is the definition*. Drive claim → `retry(err, None)`
+  cycles on a queue with a small `backoff_base_s` stamp (2 s keeps
+  the integer-second row resolution honest: ranges [1,2], [2,4],
+  [4,8] across the first attempts; the inter-attempt waits stay
+  tolerance-bounded and sequential), reading the computed delay back
+  via `get_job`'s `run_at` minus now, asserting range membership per
+  attempt on both engines — identical bounds is the equivalence pin
+  (ADR-012 §2: engine-side arithmetic, suite-pinned identical
+  outputs). Include the explicit-delay override leg
+  (`retry(err, Some(d))` honored — a `Some(0)` resolves ready-now per
+  the boundary-total rule). **The 1-hour cap leg is not
+  suite-pinnable** (reaching capped attempts requires waiting out
+  minute-scale delays); it stays pinned engine-side (both engines'
+  unit tests already pin the curve against the ADR text — the
+  wave-3/4 reviews verified it) — record that disposition in Notes
+  for the review gate.
+
+## Acceptance Criteria
+
+- [ ] `enqueue_opts_resolution` extended with both clock legs; its
+      doc comment's deferral note updated (stamps accumulate)
+- [ ] `backoff_curve_equivalence` exists, version-stamped (ADR-010 §3,
+      ADR-020 §1–§3, ADR-012 §2, ADR-023 §2)
+- [ ] Rows wired into both engines' `contract_suite.rs` targets
+- [ ] SQLite column green server-less; pg column green against the
+      harness server
+- [ ] The cap-leg disposition recorded in Notes
+- [ ] `cargo test -p alkstore-sqlite -p alkstore-postgres` green
+      (pg rows skip cleanly server-less); clippy `-D warnings`; fmt clean
+
+## References
+
+- docs/architecture/core-contract.md §Verification backlog (backoff-curve
+  and stamp-resolution equivalence; enqueue-opts resolution equivalence)
+- docs/architecture/decisions/010-queue-semantics-depth.md §3
+- docs/architecture/decisions/020-enqueue-opt-semantics-and-bridges.md §1–§3
+- docs/architecture/decisions/012-forked-substrate-design.md §2
+- alkstore-contract-suite/src/properties.rs (`enqueue_opts_resolution`'s
+  deferral note)
+
+## Notes
+
+> To be filled by implementation agent
+
+## Summary
+
+> To be filled on completion