docs: open Phase 1 — architecture spec set over the Phase 0 evidence

docs/architecture/ now exists: README index, overview, five component
specs (core-contract, engine-sqlite, engine-postgres, queues,
deployment), ADR-001..007 carrying the Phase 0 resolved decisions
(crate split, feature scope, per-engine drivers, dependency
ownership, wake contract, tx seam), and the centralized
open-questions tracker promotion: OQ-ST-01..08 mirror to OQ-01..08
one-to-one with statuses/resolutions carried; new Phase 1 questions
append (OQ-09 scheduler collapse, OQ-10 contract versioning).
Open Phase 1 work: OQ-04 contract pinning (high), OQ-05 queue
semantics depth (high), OQ-06 honker-core quality read (high;
fork-trigger gate), OQ-08 capability surface, OQ-09, OQ-10.

Erratum fixed in phase-0 OQ-ST-04 (thread-affinity friction is
SQLite-side, previously garbled as pg-side) and a stale scheduler-
boundary pointer corrected in consumer-inventory.md. Two review
passes run (findings: OQ-promotion numbering faithfulness, ADR
back-reference sync) — all critical/warning findings resolved.

docs/architecture/README.md

@@ -0,0 +1,92 @@
+---
+status: draft
+last_updated: 2026-10-04
+---
+
+# alkstore — Architecture
+
+Architecture documentation for the alkstore project: one reactive
+store interface (notify, streams, queues, locks, scheduler, outbox)
+over SQLite and Postgres, with each engine native underneath
+(see [overview.md](overview.md)).
+
+## Current State
+
+**Phase 1 (Architecture) — in progress.** Phase 0 is complete
+(`docs/research/phase-0.md`): both POCs ran and passed, the scope
+inventory is confirmed, and the crate split, drivers, and ownership
+postures are decided. This directory carries the architecture spec
+build-out over that evidence base; all spec documents are `draft`
+pending architecture review and OQ resolution.
+
+## Architecture Documents
+
+| Doc | Status | Purpose | Key OQs |
+|---|---|---|---|
+| [overview.md](overview.md) | draft | Crate family, feature surface, non-goals, evidence base | — |
+| [core-contract.md](core-contract.md) | draft | The unified trait surface, delivery guarantees, tx seam | OQ-04, OQ-08, OQ-09, OQ-10 |
+| [engine-sqlite.md](engine-sqlite.md) | draft | SQLite engine: honker-core/rusqlite mapping | OQ-05, OQ-06, OQ-09 |
+| [engine-postgres.md](engine-postgres.md) | draft | Postgres engine: tokio-postgres/LISTEN mapping | OQ-05, OQ-08, OQ-09 |
+| [queues.md](queues.md) | draft | Queue/scheduler/outbox semantics depth frame | OQ-05, OQ-09 |
+| [deployment.md](deployment.md) | draft | Host semantics, connection budgets, knobs, matrix | OQ-04, OQ-08 |
+| [open-questions.md](open-questions.md) | draft | OQ tracker (promoted from OQ-ST register) | — |
+
+## Architecture Decision Records
+
+| ADR | Title | Status |
+|---|---|---|
+| [001](decisions/001-crate-split.md) | Reactive-core crate + per-engine crates | Accepted |
+| [002](decisions/002-feature-scope.md) | Feature scope — inventory-confirmed surface | Accepted |
+| [003](decisions/003-sqlite-driver.md) | SQLite engine — rusqlite + honker-core, bridged seam | Accepted |
+| [004](decisions/004-postgres-driver.md) | Postgres engine — tokio-postgres + deadpool, hand-rolled LISTEN | Accepted |
+| [005](decisions/005-dependency-ownership.md) | Published libraries by default, named fork triggers | Accepted |
+| [006](decisions/006-wake-and-delivery-contract.md) | Wake contract — opaque wake + re-read; notify-vs-streams split | Accepted |
+| [007](decisions/007-transactional-seam.md) | Transactional seam — caller-held `TxHandle`, `*_tx` methods | Accepted |
+
+## Open Questions
+
+Tracked in [open-questions.md](open-questions.md) (OQ-01..NN; the
+Phase 0 register's OQ-ST-01..08 promote one-to-one — OQ-NN mirrors
+OQ-ST-NN — with new Phase 1 questions appended after). Highlights,
+in suggested resolution order (OQ-04 first):
+
+- **OQ-04** (high): contract pinning — exact trait shape, handle
+  representation, error taxonomy, reserved strings, guarantee rows
+  for locks/scheduler.
+- **OQ-05** (high): queue semantics depth — retry/backoff/dead-letter/
+  sweep design.
+- **OQ-06** (high): honker-core quality read — fork-trigger gate.
+- **OQ-09** (medium): scheduler as first-class mechanism vs queues +
+  `schedule()`.
+- **OQ-08** (medium): capability-surface shape.
+- **OQ-10** (medium): contract versioning across engine crates.
+
+Resolved (Phase 0, kept with resolutions): OQ-01 (feature scope),
+OQ-02 (crate split), OQ-03 (drivers), OQ-07 (extension surface cut).
+
+No deferred OQs: all open questions are actionable Phase 1 work with
+complete evidence bases.
+
+## Document Lifecycle
+
+| Status | Meaning | Transitions |
+|---|---|---|
+| `draft` | Under active development; may change significantly | → `reviewed` when the doc's OQs are resolved |
+| `reviewed` | Architecture final; implementation may begin | → `stable` when implementation verified |
+| `stable` | Locked; changes need review, may warrant an ADR | → `deprecated` when superseded |
+| `deprecated` | Superseded; kept for reference | Removed when unreferenced |
+
+All spec documents carry YAML frontmatter (`status`, `last_updated`);
+ADRs carry a `## Status` section (Accepted/Proposed/Superseded).
+
+## Provenance of decisions
+
+Phase 1 inherits its decisions from Phase 0's evidence base — every
+Accepted ADR above cites its POC findings and register record. The
+research documents remain the deep background:
+
+- `docs/research/phase-0.md` — vision, prior art, OQ-ST register,
+  convergence.
+- `docs/research/consumer-inventory.md` — per-feature scope evidence.
+- `docs/research/poc-sqlite-posture-findings.md` /
+  `docs/research/poc-pg-posture-findings.md` — measured ground.