docs(tasks): correct the wave-5 pure-build gates — the literal kv-less pg-lo config is not a gate

The wave-5 engine task (d69d9a3) found the literal
--no-default-features --features pg-lo config cannot compile the whole
crate: with no kv feature enabled, KvEngine/KvCursor go empty (E0004)
and the facade's by-reference dispatch matches are non-exhaustive
(references are always considered inhabited). Structural, not a bug —
per ADR-011 §4 every constructor mode pairs a kv engine, so a build
with zero kv engines is not a supported configuration (ADR-013 §4's
supported non-default configurations all include one).

The meaningful pure builds, verified on this tree:
- --no-default-features --features "pg-lo,mem" — check/test/clippy
  green (115 tests ok server-less)
- --no-default-features --features "postgres,pg-lo" — check/clippy
  green, test target compiles

Amended: engine-pg-lo (description + acceptance + gates),
engine-pg-lo-window (acceptance), store-pg-lo-construction (the full
structural reading + acceptance), review-wave-5 (gates). The engine
task's Notes/Summary already recorded the finding; the criteria text
now matches what was verified.

Verification: cargo test 69/19/3 ok, fmt --check green (docs-only
change).

tasks/engine-pg-lo-window.md

@@ -88,7 +88,10 @@ engine-level contract tests.
 - [ ] `cargo test` (default) green; `cargo test --features pg-lo`
       green server-less (skipping); `cargo clippy --all-targets -- -D
       warnings` and `cargo fmt --check` green (default + `--features
-      pg-lo`); the pg-lo-pure check clean
+      pg-lo`); the pg-lo pure builds clean (`--no-default-features
+      --features "pg-lo,mem"` and `--features "postgres,pg-lo"` — the
+      literal kv-less config is not a gate, see
+      `store-pg-lo-construction`)
 
 ## References
 

tasks/engine-pg-lo.md

@@ -22,9 +22,15 @@ posture (pool, prepared statements, schema bootstrap, error mapping);
 the local engine (`src/local.rs`) is the structural twin for the
 large-tier bodies (streaming read cursor, staged put). **`pg-lo` does
 not imply `postgres`** (ADR-013 §4's consequence; the Cargo.toml
-feature carries its own driver deps) — every shared piece must
+feature carries its own driver deps) — every shared piece must compile
-compile under `--no-default-features --features pg-lo` (the pg-lo-pure
+under the **pg-lo pure builds**: `--no-default-features --features
-build).
+"pg-lo,mem"` and `--no-default-features --features "postgres,pg-lo"`.
+**The literal kv-less config (`--no-default-features --features
+pg-lo`) is not a gate and cannot compile the whole crate** — with no kv
+feature enabled, `KvEngine`/`KvCursor` go empty and the facade's
+by-reference dispatch matches are non-exhaustive (E0004; references
+are always considered inhabited) — see `store-pg-lo-construction` for
+the full reading.
 
 - **Engine shape (POC #7 C1 is the contract)** — two artifacts: LOs
   hold the bytes; the companion table
@@ -47,8 +53,8 @@ build).
   helpers) live behind `#[cfg(feature = "postgres")]` today — decide
   and record the sharing shape (the natural one: a crate-internal
   pg-common module gated `cfg(any(feature = "postgres",
-  feature = "pg-lo"))`, one module per file, so the pg-lo-pure build
+   feature = "pg-lo"))`, one module per file, so the pg-lo pure builds
-  compiles without duplication). The `PgOpts` question rides the same
+   compile without duplication). The `PgOpts` question rides the same
   point: it is `pub` and re-exported behind `postgres` (wave 4's
   constructor signature put it on the public surface) — widening its
   gate to `any(postgres, pg-lo)` (re-export gate widened with it) vs a
@@ -193,16 +199,18 @@ engine and its in-module unit tests only.
       returned + VACUUM FULL operator line + rel-size monitoring;
       autovacuum inherited; the cached-get capacity facts)
 - [ ] Shared-helper + PgOpts + LO-isolation design points decided and
-      recorded; the pg-lo-pure build (`--no-default-features
+      recorded; the pg-lo pure builds (`--no-default-features
-      --features pg-lo`) compiles clean
+      --features "pg-lo,mem"` and `--features "postgres,pg-lo"`)
+      compile clean (the literal kv-less config is not a gate — see
+      the Description)
 - [ ] Unit tests env-driven (`ALKBLOBS_PG_*`), skipping cleanly
       server-less; green against the harness server at acceptance;
       zero schema + LO residue on the shared db after runs
 - [ ] `cargo test` (default — pg-lo compiles out) green;
       `cargo test --features pg-lo` green server-less (skipping);
       `cargo clippy --all-targets -- -D warnings` and `cargo fmt
-      --check` green (default + `--features pg-lo` + the pg-lo-pure
+      --check` green (default + `--features pg-lo` + the pg-lo pure
-      check)
+      builds)
 
 ## References
 

tasks/review-wave-5.md

@@ -75,9 +75,12 @@ Gate checks:
   `#![allow(dead_code)]` scope notes matching their remaining scope.
 - **Gates green**: `cargo test` (default), `cargo test --features
   pg-lo` (server-less: skipping), `cargo test --features "pg-lo,mem"`,
-  `cargo test --all-features` (against the server), the pg-lo-pure
+  `cargo test --all-features` (against the server), the pg-lo pure
-  checks (`cargo check --no-default-features --features pg-lo` and
+  builds (`cargo check --no-default-features --features "pg-lo,mem"`
-  `--features "pg-lo,mem"`), `cargo clippy --all-targets -- -D
+  and `--features "postgres,pg-lo"` — the literal kv-less
+  `--features pg-lo` config is not a gate: with no kv engine the
+  facade's `KvEngine`/`KvCursor` go empty, E0004; see
+  `store-pg-lo-construction`), `cargo clippy --all-targets -- -D
   warnings` (default + the pg-lo variants + `--all-features`),
   `cargo fmt --check`, `cargo doc --no-deps`.
 

tasks/store-pg-lo-construction.md

@@ -103,12 +103,25 @@ the durable window gains its large-engine host arm.
   proof). Env-driven (`ALKBLOBS_PG_*`), skipping cleanly server-less
   (the engine tests' convention); the janitor discipline rides from
   the start (amendment A2).
-- **The pg-lo-pure builds** — `cargo check --no-default-features
+- **The pg-lo pure builds** — the supported non-default configurations
-  --features pg-lo` (engine + window family compile, constructors
+  are `cargo check/test --no-default-features --features "pg-lo,mem"`
-  cfg'd out where `mem` is absent) and
+  (the one-window-host topology's build; the mem-pglo constructor
-  `cargo test --no-default-features --features "pg-lo,mem"` (the
+  constructible) and `cargo check --no-default-features --features
-  mem-pglo constructor constructible): ADR-013 §4's supported
+  "postgres,pg-lo"` (ADR-013 §4's pg-pure consolidation build); verify
-  non-default configurations; verify both compile clean.
+  both compile clean. **The literal kv-less config
+  (`--no-default-features --features pg-lo`) is not a gate and cannot
+  compile the whole crate** — do not burn time on it: with no kv
+  feature enabled, `KvEngine`/`KvCursor` go empty (E0004) and the
+  facade's by-reference dispatch matches are non-exhaustive
+  (references are always considered inhabited, so an empty enum behind
+  `&` still requires arms). This is structural, not a bug: per ADR-011
+  §4 every constructor mode pairs a kv engine, so a build with zero kv
+  engines is not a supported configuration (ADR-013 §4's supported
+  non-default configurations all include one). The shared pieces
+  themselves (pg_common, the engines) compile in the literal config —
+  only store.rs errors. The finding is the wave-5 engine task's
+  (d69d9a3, recorded in its Notes); this task's verification uses the
+  two meaningful builds above.
 
 ## Acceptance Criteria
 
@@ -128,8 +141,10 @@ the durable window gains its large-engine host arm.
       branch keys off the engine representation, never a flag
 - [ ] The connection-settings design point (two DSN+opts pairs; the
       consolidation corollary) decided and recorded
-- [ ] The pg-lo-pure builds (`--no-default-features --features pg-lo`
+- [ ] The pg-lo pure builds (`--no-default-features --features
-      and `--features "pg-lo,mem"`) compile clean
+      "pg-lo,mem"` and `--features "postgres,pg-lo"`) compile clean
+      (the literal kv-less config is not a gate — see the Description
+      bullet)
 - [ ] `cargo test` (default) green; `cargo test --features pg-lo` and
       `--features "pg-lo,mem"` green server-less (skipping);
       `cargo clippy --all-targets -- -D warnings` and `cargo fmt