perf: round 23 — Postgres query-shape pass: typed JSONB decode, drive-policy borrow-deserialize, user-profile join!, subject-group CTE reuse, dedup unzip

Benchmark-gated, same rule as ROUND2-22: BEFORE/AFTER with a value-equivalence
gate and rollback-on-regression. Two harnesses — bench_round23_micro (no
Postgres; deterministic allocation gate) and bench_round23_queries (live
Postgres; p50 latency + strict equivalence gate against seeded fixtures). See
benches/ROUND23.md.

- J1: contact_pg_repository::row_to_contact (+ the inlined contact_group sibling)
  decode the 3 JSONB columns via sqlx::types::Json<T> (one from_slice pass)
  instead of row.get::<serde_json::Value> + from_value (a throwaway Value DOM
  per column, walked a second time). Per contact row of every list / multiget /
  CardDAV sync. Micro 84 -> 33 allocs/op (2.15x); PG 3794 -> 2360 ns/contact
  (1.61x) on 500 real rows.
- J2: DrivePolicies::from_value deserializes straight from the borrow
  (T::deserialize(&Value)) instead of from_value(value.clone()) — dropping the
  full-DOM clone on every drive-policy read (move/copy, share, grant); one-line
  body change, all 7 callers unchanged. Micro 5 -> 0 allocs/op (11.51x).
- P1: get_user_profile overlaps the two independent caller+target reads with
  tokio::join! (self-case still a single fetch; caller-error precedence
  preserved via caller_res? first) instead of two serial round-trips. PG
  577 -> 312 us/call (1.85x).
- G1: subject_group remove_member computes the child's transitive-user recursive
  CTE once and reuses it for both the would-empty pre-check and the cache
  invalidation, instead of running the identical CTE twice (the edge delete is
  above the child, so its descendants can't change). PG 829 -> 412 us/removal
  (2.01x).
- U1: dedup_service (store_loose_chunks final registration + the ingest
  run_rollback) reshapes the owned, dead-after Vec<(String,i64)> via
  into_iter().unzip() instead of cloning every 64-byte hash for the
  sync_blobs(&[String]) + UNNEST bind. Micro 256 -> 0 hash clones.

Verified: cargo clippy --features bench --all-targets -D warnings clean, cargo
fmt --all --check clean, cargo test --lib --features bench = 529 passed / 0
failed. The PG benches run against a local PostgreSQL 16 (schema applied from
migrations/); every equivalence gate passes.

The download_zip per-item N+1 (the audit's highest raw-latency candidate) is
deferred to a dedicated pass: its fix moves the sole authorization inside the
stream call, so it needs an AuthZ-ordering + anti-enumeration proof, not a perf
banner.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01DKyQ4AnYtgp1JtjzweyMeo

Cargo.toml

@@ -354,6 +354,27 @@ name = "bench_micro_allocs"
 path = "examples/bench_micro_allocs.rs"
 required-features = ["bench"]
 
+# Round-23 battery ────────────────────────────────────────────────────────────
+
+# Round-23 CPU/alloc micro-pack (no Postgres) — deterministic alloc gates for
+# the decode/clone candidates: contact JSONB `Value`+`from_value` → typed
+# `sqlx::types::Json<T>` decode (J1); `DrivePolicies::from_value` DOM clone →
+# borrow-deserialize (J2); dedup hash reshape clone-collect → `into_iter().unzip()`
+# (U1). The PG latency/round-trip/equivalence evidence is bench_round23_queries.
+[[example]]
+name = "bench_round23_micro"
+path = "examples/bench_round23_micro.rs"
+required-features = ["bench"]
+
+# Round-23 PG query-shape pack — end-to-end latency + equivalence on the live
+# dev Postgres: contact JSONB typed decode on real rows (Q1); get_user_profile
+# 2 serial reads → tokio::join! (Q4); subject_group remove_member 2 recursive
+# CTEs → 1 reused (Q6). Needs the dev Postgres up (reads DATABASE_URL from .env).
+[[example]]
+name = "bench_round23_queries"
+path = "examples/bench_round23_queries.rs"
+required-features = ["bench"]
+
 # Round-22 battery ────────────────────────────────────────────────────────────
 
 # Round-22 CPU/alloc micro-pack — the deferred hot-GET-handler `HeaderMap`