docs: specify POC #1 — SQLite engine posture comparison (poc-sqlite-posture-spec.md)

Arm A: honker-core linked on our rusqlite (bridge per REQ-TTY-01, honker's watcher). Arm B: honker extension .so over sqlx-sqlite (natively async call path, own watcher, per-pool-connection extension + bootstrap — stress-testing what the CI proof script doesn't cover: pool wiring, lost connections, full surface). Option 2 (honker-rs-as-substrate) dropped from scope with reasoning: its mutex-pinned sync transaction model is subsumed by both other postures' trade space. Five probes (async seam, watcher, transactional contract, packaging, cross-process interop), a decision gate including a legitimate hybrid verdict, and out-of-scope boundaries (postgres side, full surface, extension-as-consumer-feature regardless of outcome). Phase-0: POC register added, plan/frontmatter updated; AGENTS.md: POC-register convention codified.

docs/research/phase-0.md

@@ -8,23 +8,25 @@ REQ-TTY-01's async-facing-trait + sync-bridge posture recorded as family
 precedent bearing on OQ-ST-03; OQ-ST-03's SQLite option space expanded
 to three named postures (honker-core on our rusqlite / honker-rs as
 substrate / honker extension over sqlx — the last CI-proven in the
-honker checkout's own ORM proof suite). OQ-ST-03/04/05 remain open
-research. Interface finding and driver tension from 2026-10-03 remain
-trusted-but-unverified working input.)
+honker checkout's own ORM proof suite) and POC #1 (the A-vs-B posture
+comparison) specified. OQ-ST-03/04/05 remain open
+research. Interface finding and driver tension from
+2026-10-03 remain trusted-but-unverified working input.)
 ---
 
 # alkstore — Phase 0 (Exploration)
 
 This document captures Phase 0 (Exploration) for the `alkstore` crate:
-vision, guiding principles, prior art, and the open-question register
-(OQ-ST-01..NN). Phase 0's objective per `docs/sdd_process.md`: *capture
+vision, guiding principles, prior art, the open-question register
+(OQ-ST-01..NN), and the POC register. Phase 0's objective per
+`docs/sdd_process.md`: *capture
 vision and guiding principles; research options; validate approaches;
 converge on a recommended approach.* The scope question (OQ-ST-01) has
 been answered per-feature from the consumers' documents
-(`consumer-inventory.md`); the driver and reactive-shape questions
-(OQ-ST-03/04) are the open research; there is no POC register yet
-(see `consumer-inventory.md` for the first cut candidates that keep its
-register small).
+(`consumer-inventory.md`); the driver question (OQ-ST-03) has a named
+SQLite option space with POC #1 specified against it; the reactive
+contract (OQ-ST-04) and ownership questions (OQ-ST-05/06) are the open
+work the research rounds feed.
 
 Context for why this crate starts now: **alkblobs**
 (`/workspace/@alkdev/alkblobs` — spec + POCs only, paused mid-planning)
@@ -589,6 +591,15 @@ to expose engine capabilities at all?
 Open; partially rides OQ-ST-04 (the trait's shape constrains where
 capability differences can surface).
 
+## POC register
+
+Proposals run as standalone crates in the global workspace; findings
+land in `docs/research/` here. Named per the OQ each feeds:
+
+| # | POC | Spec | Feeds |
+|---|---|---|---|
+| 1 | SQLite engine posture: honker-core-on-rusqlite vs honker-extension-over-sqlx (async seam, watcher, transactional contract, packaging, interop) | [poc-sqlite-posture-spec.md](poc-sqlite-posture-spec.md) | OQ-ST-03, OQ-ST-04, OQ-ST-06 |
+
 ## Phase 0 plan
 
 Iteration expected; this register grows as research rounds land.
@@ -603,13 +614,13 @@ Expected sequence (deliberately rough):
    decision)**: reactive-core + engine crates. Reasoning and the
    superseded inventory lean recorded at the OQ and in the inventory.
 2. Research rounds on OQ-ST-03/04 (drivers + reactive shape) — library
-   capability matrices, then a POC if the unified-trait shape needs
-   validation (likely, given the structural mismatch noted in OQ-ST-04).
-   The honker-rs surface (§Interface finding) is the concrete starting
+   capability matrices (**POC #1 specified**: the SQLite posture
+   comparison, [poc-sqlite-posture-spec.md](poc-sqlite-posture-spec.md);
+   the honker-rs surface (§Interface finding) is the concrete starting
    artifact for the OQ-ST-04 work: pinning its contract costs less and
    is more honest than inventing a parallel shape — now scoped against
    the inventory's confirmed features rather than the full honker menu,
-   and shaped as the core-crate trait surface per OQ-ST-02's split.
+   and shaped as the core-crate trait surface per OQ-ST-02's split).
 3. Ownership decisions (OQ-ST-05/06) — adopt/fork/derive per subsystem,
    after the driver and shape questions narrow the option space.
 4. Converge; Phase 1 opens with the ADR backlog this register becomes.