docs(tasks): decompose wave 6 — the fleet GC mechanism, the architecture's most intricate state machine under concurrency

- store-fleet-construction: the fleet: true declaration slotting into
  the fleet-capable constructors (the recorded non-event), the
  composite fleet-validity predicate enforced at the constructor
  (kv=postgres AND pg-lo-same-instance OR local-on-declared-shared-
  media OR kv-only re-routing), the TTL/owner-id fleet state, the
  same-instance probe design point
- engine-pg-lo-joint: the pg-lo joint contribution — staged-put
  mechanics (512 KiB knee, CAS, transactional LO creation) into the
  store-held PgJointTx, the wave-5 deferred API-shape design point
- store-fleet-put: the joint entry+pin tx driver (amendment A1's
  drop discipline lands here — its recorded owner), the pin guard's
  TTL/3 renewal form, the dedup upsert-renewal, pin-first/
  publish-second for large=local, the consolidation one-tx put
- store-fleet-sweep: the SQL sweep lease (ADR-013 §2 semantics),
  SQL-level delete arbitration on the direct + window-execution
  paths, the expired-pin reaping clause (the seam as the named home
  for fleet-clause growth), the fleet liveness registration verb,
  the two-domain arbitration composition
- suite-column-fleet: the fleet column — two-instance factories over
  one schema, the exact-count fleet sweep rows (the wave's gate),
  lease contention, cross-instance arbitration, TTL/renewal rows,
  the fleet-validity predicate rows
- review-wave-6: the fleet gate per the plan, plus a standing
  code-smell/hygiene block — cargo doc --no-deps asserted clean
  (the twice-bitten PGLO-1 rustdoc private-link class), the
  allow(dead_code) scope notes audited against their remainder,
  stale wave-6 forward references, and task-Summary-vs-diff
  correctness

Harness server cited in every server-touching task: dockerized
pglo-poc (postgres:16-alpine) on :15432, db blobs, postgres/poc
(verified live 2026-10-12); env-driven ALKBLOBS_PG_* settings, clean
server-less skips, acceptance requires green against the server.

Dependency graph validated: two parallel roots (construction, pg-lo
joint), put merging them, sweep parallel to put, the fleet column
merging, the review gate last; no cycles.

docs/plans/implementation.md

@@ -1,6 +1,6 @@
 ---
 status: draft
-last_updated: "2026-10-12 (wave 5 decomposed into tasks/)"
+last_updated: "2026-10-12 (wave 6 decomposed into tasks/)"
 ---
 
 # alkblobs — Implementation plan
@@ -53,7 +53,7 @@ ops payload surfaces; release readiness is last.
 | [3](#wave-3--sqlite-engine) | sqlite kv engine (default): WAL posture, prepared statements, engine-state window family, suite column | wave 2 | decomposed (2026-10-11) |
 | [4](#wave-4--postgres-kv-engine) | postgres kv engine: schema, pool, CAS rows, stable-cursor list, full engine-state clause families, suite column | wave 2 | decomposed (2026-10-12) |
 | [5](#wave-5--pg-lo-large-engine) | pg-lo large engine: LO staged put, descriptorless lo_get windows, companion rows, window-family seam clauses, suite column | wave 4 | decomposed (2026-10-12) |
-| [6](#wave-6--fleet-gc) | Fleet GC mechanism: DB-backed pins, joint entry+pin tx, sweep lease, SQL delete arbitration, fleet-validity predicate + constructor declarations | waves 4 + 5 | pending |
+| [6](#wave-6--fleet-gc) | Fleet GC mechanism: DB-backed pins, joint entry+pin tx, sweep lease, SQL delete arbitration, fleet-validity predicate + constructor declarations | waves 4 + 5 | decomposed (2026-10-12) |
 | [7](#wave-7--ops-surface) | `ops` feature: alkcall-backed op family, ACL mapping, pin tokens + renewal, fanout seam | wave 6 | pending |
 | [8](#wave-8--fuzzing) | Fuzzing: family pattern targets (key encoding, ops payloads), corpus-replay gate | wave 7 | pending |
 | [9](#wave-9--release-readiness) | Crate docs, feature-graph verification, README, publish prep | wave 8 | pending |