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/FAIR_COMPARISON.md

@@ -0,0 +1,93 @@
+# Fair Benchmark Results
+
+Generated: **2026-07-18 13:53:46 UTC**
+
+## Methodology
+
+- Tier `embedded`: in-process only (BaraDB LSM from nimble bench JSON; SQLite via Python sqlite3).
+- Tier `client_server`: network SQL (BaraDB HTTP /query; BaraDB binary wire TCP; PostgreSQL via psycopg2).
+- `sql_insert_row`: one INSERT statement per row (chatty).
+- `sql_insert_batch`: multi-row INSERT with batch size 50 (same SQL style across systems).
+- PostgreSQL: synchronous_commit=on|off; SQLite: PRAGMA synchronous FULL|OFF.
+- BaraDB WAL modes appear only if you ran benchmarks/bench_all.nim (WAL-* rows).
+- Never claim 'Nx faster than Postgres' using embedded BaraDB numbers.
+
+**Do not compare numbers across tiers.** Embedded storage is not the same
+workload as client-server SQL over the network.
+
+## Tier: `embedded`
+
+| Bench | System | ops/s | seconds | n | notes |
+|-------|--------|------:|--------:|--:|-------|
+| kv_write | `baradb_lsm_embedded` | 41.50K | 2.410 | 100000 | benchmark_results.json |
+| kv_read | `baradb_lsm_embedded` | 3.77M | 0.026 | 100000 | benchmark_results.json |
+| wal_none | `baradb_lsm_embedded` | 232.65K | 0.215 | 50000 | benchmark_results.json |
+| wal_group64 | `baradb_lsm_embedded` | 42.25K | 1.183 | 50000 | benchmark_results.json |
+| wal_group256 | `baradb_lsm_embedded` | 107.16K | 0.467 | 50000 | benchmark_results.json |
+| wal_every | `baradb_lsm_embedded` | 825.27 | 60.586 | 50000 | benchmark_results.json |
+| kv_write | `sqlite_off` | 402.61K | 0.002 | 1000 | PRAGMA synchronous=OFF |
+| kv_read | `sqlite_off` | 195.60K | 0.005 | 1000 |  |
+| sql_insert_batch | `sqlite_off` | 559.66K | 0.002 | 1000 | multi-row INSERT batch=50, sync=OFF |
+| kv_write | `sqlite_full` | 272.62K | 0.004 | 1000 | PRAGMA synchronous=FULL |
+| kv_read | `sqlite_full` | 196.16K | 0.005 | 1000 |  |
+| sql_insert_batch | `sqlite_full` | 370.18K | 0.003 | 1000 | multi-row INSERT batch=50, sync=FULL |
+
+### Same-bench ratios (`embedded`)
+
+**kv_read** (fastest: `baradb_lsm_embedded` @ 3.77M/s)
+
+| System | Relative to fastest |
+|--------|--------------------:|
+| `baradb_lsm_embedded` | 1.00x |
+| `sqlite_full` | 0.05x |
+| `sqlite_off` | 0.05x |
+
+**kv_write** (fastest: `sqlite_off` @ 402.61K/s)
+
+| System | Relative to fastest |
+|--------|--------------------:|
+| `sqlite_off` | 1.00x |
+| `sqlite_full` | 0.68x |
+| `baradb_lsm_embedded` | 0.10x |
+
+**sql_insert_batch** (fastest: `sqlite_off` @ 559.66K/s)
+
+| System | Relative to fastest |
+|--------|--------------------:|
+| `sqlite_off` | 1.00x |
+| `sqlite_full` | 0.66x |
+
+## Tier: `client_server`
+
+| Bench | System | ops/s | seconds | n | notes |
+|-------|--------|------:|--------:|--:|-------|
+| sql_insert_row | `baradb_http` | 979.31 | 0.511 | 500 |  |
+| sql_select_row | `baradb_http` | 235.20 | 2.126 | 500 |  |
+| sql_insert_batch | `baradb_http` | 10.19K | 0.049 | 500 | multi-row INSERT batch=50 |
+| sql_insert_row | `baradb_wire` | 4.65K | 0.108 | 500 | binary wire protocol |
+| sql_select_row | `baradb_wire` | 642.04 | 0.779 | 500 |  |
+| sql_insert_batch | `baradb_wire` | 20.47K | 0.024 | 500 | multi-row INSERT batch=50 |
+
+### Same-bench ratios (`client_server`)
+
+**sql_insert_batch** (fastest: `baradb_wire` @ 20.47K/s)
+
+| System | Relative to fastest |
+|--------|--------------------:|
+| `baradb_wire` | 1.00x |
+| `baradb_http` | 0.50x |
+
+**sql_insert_row** (fastest: `baradb_wire` @ 4.65K/s)
+
+| System | Relative to fastest |
+|--------|--------------------:|
+| `baradb_wire` | 1.00x |
+| `baradb_http` | 0.21x |
+
+**sql_select_row** (fastest: `baradb_wire` @ 642.04/s)
+
+| System | Relative to fastest |
+|--------|--------------------:|
+| `baradb_wire` | 1.00x |
+| `baradb_http` | 0.37x |
+