feat: harden storage, schema persistence, fair benches, fix wire crash

Core storage: hash MemTable, WAL group commit, L0 compaction rebuild,
reader-writer lock, and a global StorageGate so HTTP workers and TCP
share the LSM safely under multi-thread access.

Schema: durable CREATE/ALTER/DROP under _schema:tables:* with full LSM
restore on open. Executor types/values/schema split into query/exec/.

Wire protocol: switch default MM to ARC — ORC cycle collector segfaulted
after ~20 async INSERTs. Fair multi-tier benchmarks (SQLite/HTTP/wire/PG)
and honesty docs for mixed-tier comparisons.

benchmarks/README.md

@@ -0,0 +1,80 @@
+# BaraDB Benchmarks
+
+## Tiers (read this first)
+
+| Tier | What is measured | Fair peers |
+|------|------------------|------------|
+| **embedded** | In-process storage API | BaraDB LSM ↔ SQLite |
+| **client_server** | Network + query protocol | BaraDB HTTP / **wire** ↔ PostgreSQL |
+
+**Never** quote “BaraDB is Nx faster than Postgres” using embedded LSM numbers.
+That comparison mixes tiers and is meaningless as a product claim.
+
+## Quick start
+
+```bash
+# 1) Embedded micro-benches (Nim, in-process)
+nimble bench
+# or: nim c -d:release -r benchmarks/bench_all.nim
+
+# 2) Optional: start server for client_server tier (HTTP + wire)
+./build/baradadb
+
+# 3) Fair multi-tier suite (Python)
+#    - always: SQLite embedded (+ batch)
+#    - optional: BaraDB HTTP (:9912), wire TCP (:9472), PostgreSQL
+python3 benchmarks/fair_bench.py
+
+# 3) Markdown report
+nimble bench_report
+# or: python3 benchmarks/generate_report.py --fair
+```
+
+Outputs:
+
+- `benchmark_results.json` — Nim embedded suite  
+- `fair_benchmark_results.json` — multi-tier fair suite  
+- `benchmarks/FAIR_COMPARISON.md` — human-readable fair report  
+- `pg_benchmark_results.json` — optional PG-only micro suite  
+
+## Environment
+
+| Variable | Default | Meaning |
+|----------|---------|---------|
+| `FAIR_N_KV` | 20000 | embedded KV ops |
+| `FAIR_N_SQL` | 5000 | SQL loops (HTTP/wire/PG) |
+| `FAIR_BATCH` | 100 | multi-row INSERT batch size |
+| `BARADB_HTTP_HOST` | 127.0.0.1 | HTTP host |
+| `BARADB_HTTP_PORT` | 9912 | HTTP port (`TCP+440`) |
+| `BARADB_WIRE_HOST` | 127.0.0.1 | wire protocol host |
+| `BARADB_WIRE_PORT` | 9472 | wire protocol TCP port |
+| `FAIR_SKIP_HTTP=1` | — | skip BaraDB HTTP |
+| `FAIR_SKIP_WIRE=1` | — | skip BaraDB wire |
+| `FAIR_SKIP_PG=1` | — | skip PostgreSQL |
+| `PGHOST` / `PGUSER` / `PGPASSWORD` / … | — | libpq-style |
+
+## Files
+
+| File | Role |
+|------|------|
+| `bench_all.nim` | Embedded: LSM, WAL modes, BTree, vector, FTS, graph |
+| `fair_bench.py` | Fair multi-tier runner + markdown |
+| `pg_bench.py` | PostgreSQL client-server micro suite |
+| `generate_report.py` | `--fair` report; legacy mixed report without flag |
+| `compare.nim` | **Synthetic** — do not publish |
+| `search_bench.nim` | Search-focused micro suite |
+
+## Durability knobs
+
+- BaraDB: `wal_sync_mode` = `none` \| `group` \| `every` (see WAL-* rows from `bench_all`)  
+- SQLite: `PRAGMA synchronous = OFF` vs `FULL`  
+- PostgreSQL: `synchronous_commit = off` vs `on`  
+
+Match durability stories when claiming write speedups.
+
+## Wire protocol note
+
+The Python wire client (`clients/python`) is exercised by `fair_bench.py`.
+Builds use **`--mm:arc`** (see `nim.cfg`) because Nim **ORC** cycle collection
+crashed under async wire INSERT load (`markGray` SIGSEGV). With ARC, sequential
+wire INSERTs + batch multi-row INSERT are stable.