docs(plans): implementation plan — wave-based decomposition; wave 1 decomposed into tasks/

- docs/plans/implementation.md: the meta plan (alkstore pattern) — nine
  waves, dependency logic, decided points, review gates. Scope authority:
  v0.1.0 ships the full surface (all five engines, fleet GC, ops).
- Wave 1 decomposed: scaffold-crate-features, core-error-model,
  core-hashing-keys, core-trait-and-types, suite-scaffold,
  review-wave-1 (the one-way-door gate).
- Waves 2-9 shaped in the plan; each decomposes after the prior wave's
  review gate.

Verification: cargo test / clippy -D warnings / fmt --check green
(docs-only change).

tasks/scaffold-crate-features.md

@@ -0,0 +1,72 @@
+---
+id: scaffold-crate-features
+name: Crate scaffold — ADR-013 §4 feature graph and module skeleton
+status: pending
+depends_on: []
+scope: narrow
+risk: low
+impact: project
+level: implementation
+tags: [wave-1, workspace]
+---
+
+## Description
+
+Replace the placeholder crate body with the real skeleton, so every
+later task lands in an existing, compiling structure with the decided
+feature graph present from the first commit:
+
+- **Feature graph per ADR-013 §4** (backends-and-dispatch.md's table
+  is the spec home): `sqlite` (default-on, carries rusqlite with the
+  `bundled` feature — match alkstore's engine manifests as the family
+  baseline, verifying current compatible versions at implementation),
+  `postgres` (tokio-postgres + deadpool-postgres), `mem` (no driver —
+  dependency-free), `pg-lo` (the shared pg cluster: tokio-postgres +
+  deadpool-postgres; **must not** imply `postgres` — ADR-010 §1's
+  feature-graph consequence), `ops` (alkcall, default-off — published
+  crate, version dep per the sibling posture, `alkcall = "0.8.1"`).
+  `local` is ungated (no feature, no dependency). `default = ["sqlite"]`.
+- **Module skeleton** under `src/`: `lib.rs` re-export shape with
+  module stubs for the planned tree (keys/hashing, error, backend,
+  facade, dispatch, gc; engine modules behind `#[cfg(feature)]`).
+  Remove `pub fn placeholder()`. Modules are one per file, re-exported
+  from `lib.rs` (AGENTS convention 10); engine module files exist
+  gated and empty.
+- Base dependencies stay as-is (tokio, thiserror, parking_lot). Driver
+  deps declared now with no consuming code — unused optional deps are
+  inert, and the graph being a decided artifact (ADR-013 §4) is why it
+  lands whole.
+
+Family standards apply from this commit onward: tokio async runtime,
+`thiserror` errors, no panics in library code, no `unwrap()`/`expect()`
+outside tests, no comments in code (doc comments on public API fine).
+
+## Acceptance Criteria
+
+- [ ] `cargo test` green with the default build (sqlite feature on,
+      no engine code yet)
+- [ ] `cargo check --all-features` resolves the full feature graph
+      (sqlite, postgres, mem, pg-lo, ops) with their driver clusters
+- [ ] `pg-lo` alone (`cargo check --no-default-features --features pg-lo`)
+      resolves without pulling postgres-only machinery (the
+      no-implication rule, ADR-010 §1)
+- [ ] `cargo clippy --all-targets -- -D warnings` and
+      `cargo fmt --check` green
+- [ ] `lib.rs` carries the module re-export shape; no placeholder
+      function remains
+
+## References
+
+- docs/architecture/overview.md (dependency posture table)
+- docs/architecture/backends-and-dispatch.md (the engine/feature table)
+- docs/architecture/decisions/013-family-composition-reactive-boundary-and-feature-graph.md §4
+- docs/architecture/decisions/010-backend-io-seams-and-fleet-state-home.md §1 (pg-lo no-implication)
+- /workspace/@alkdev/alkstore/tasks/scaffold-workspace.md (the family scaffold precedent)
+
+## Notes
+
+> To be filled by implementation agent
+
+## Summary
+
+> To be filled on completion