docs: stress/compare report + concurrent multi-tenant plan (owner-grant model)

.hermes/plans/2026-08-11_041500-concurrent-multitenant-db.md

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+# Concurrent / Multi-Tenant CUBELinux-2 DB — Implementation Plan
+
+> **For Hermes:** Use subagent-driven-development skill to implement this plan task-by-task.
+
+**Goal:** Upgrade the CUBELinux-2 store + daemon from "thread-per-connection sharing one global mutex (serialized commands, no tenant isolation)" to a genuinely concurrent, multi-tenant database: per-tenant isolated namespaces, reader/writer sharding for real concurrency, multi-command transactions (MVCC-style snapshot isolation), and per-client admission/auth — without regressing the durability gate (`wal_recovery_after_crash`, `durable_checkpoint_and_replay`, `incremental_checkpoint_delta_model`) that is green today.
+
+**Architecture (grounded in current code, not invented):**
+- Today: `cube-server` holds ONE `Arc<Mutex<Session>>`; each connection spawns a thread and runs `s.exec(line)` under the lock → concurrent *readers* but *serialized commands*. The store is `ConcurrentStore` = `Mutex<CubeStore<HashBackend>>` + a group-fsync NDJSON **WAL** (append-only, `seq`-monotonic) + scheduled checkpoint. The WAL is already append-only and multi-writer-friendly — that is our lever.
+- The "not a real DB" gaps to close: (1) **no tenant boundary** in the write path — every client lands in the same keyspace; (2) **one global lock** → no real read/write concurrency under load; (3) **no transactions** — a client cannot do "read-modify-write" or multi-key atomic ops safely; (4) **no per-client admission/auth** — any socket connection writes to the shared store.
+- We do NOT rewrite the WAL or the coordinate encoding. We layer: tenant routing (a tenant id prefixes the effective coordinate namespace / ACL), a sharded `RwLock` registry of per-tenant stores (readers run in parallel, writers serialized per-tenant), an optional MVCC snapshot per transaction, and a thin auth/admission check at connection accept time.
+
+**Tech Stack:** Rust (existing workspace) · `std::sync::{RwLock, Arc}` (no new deps for the core) · existing `ConcurrentStore`/`Wal`/`Session` · optionally `parking_lot` if a faster rwlock is wanted (NOTE: add as a dependency *only* if std `RwLock` profiling shows writer starvation — YAGNI until proven). Keep `./check` (fmt+test+clippy -D warnings) and the `stress`/`mount`/`bench` gates green throughout.
+
+---
+
+## Current-state assumptions (verified this session)
+- `cubesys/src/store.rs`: `ConcurrentStore` wraps `Mutex<CubeStore<HashBackend>>`; WAL is append-only NDJSON with monotonic `seq`; durability via `wal_fsync_ms` (25ms) + `checkpoint_ms` (2000ms); `DELTA_COMPACT_BYTES=1MiB`.
+- `cubesys/src/bin/cube-server.rs`: `Server { listener, session: Arc<Mutex<Session>> }`; thread-per-connection; each command `s.exec(line)` under the session lock. `cubesys` has ZERO references to owner markings or ACL today.
+- **Owner markings ALREADY EXIST in the record header** (this is the PDF model the user pointed at): `cubecoords::CubeHeader` carries `owner_local_user: Option<String>` and `owner_remote_user: Option<String>` (cubecoords/src/lib.rs:242-245), and `HeaderFlags` mirrors the PDF's title/type/date/size/permission flag layout (flags 1-4 explicit; flags 5-19 reserved for permissions + associations). So the *owner metatag* is already in every record — it just isn't enforced anywhere in the daemon path.
+- **ACL exists in cubefs only**: `cubefs::nullspace::Acl { uid, gid, mode }` with a working `permits(uid,gid,want)` check, stored per-coordinate in null-space (`NullSpace::get_acl/set_acl`), but it is enforced ONLY at the FUSE mount layer — NOT in the `cube-server` daemon command path.
+- **The PDF's tenant axis already exists**: `REVIEW-cubelinux-pdf.md` confirms "The C axis as environment/tenant selector, where the same logical coordinate resolves differently depending on active Null-cube state" — and the stress test already routes tenants via `C=77`. So tenant selection via the C axis is the PDF-blessed mechanism, not an invented one.
+- **"Permission grants" are reserved but unimplemented**: the PDF reserves header flags 5-19 for "permissions and associations"; no delegated-grant model exists anywhere in the code. That is the new layer to build (see D5).
+- Gate status now GREEN: fmt+test+clippy+stress(150s)+mount(27/27)+bench. Do not break these.
+
+---
+
+## Design decisions (so the implementer doesn't guess)
+
+### D1. Tenant model + identity (uses the PDF's OWN model, not invented)
+- A **tenant** = the PDF's C-axis environment selector. The connecting client declares its tenant via `HELLO <tenant>`; the daemon maps it to a `C` value (the stress harness already uses `C=77` — that IS the tenant axis). Tenants physically isolated on disk under `store_dir/<tenant>/` (own WAL + checkpoint), reusing the entire existing durable WAL machinery per tenant.
+- **Identity comes from the existing owner metatag, not a new token table.** The PDF's `CubeHeader` already carries `owner_local_user` / `owner_remote_user`. `HELLO` therefore carries `(tenant, owner_local_user, [owner_remote_user])` — i.e. the client asserts the owner identity that the record headers already model. This is the "owner markings in metatags" the user referenced; we now ENFORCE them (D4) instead of carrying them inertly.
+- Cross-tenant access is impossible by construction (different `Arc` + different C axis). The "hard per-namespace partition" the user mandates for agents is enforced at the storage layer.
+
+### D2. Concurrency model
+- Replace the single `Arc<Mutex<Session>>` with `Arc<TenantRegistry>` where `TenantRegistry { tenants: RwLock<HashMap<TenantId, Arc<TenantSession>>>, ... }`.
+- `TenantSession` holds `Arc<ConcurrentStore>` (already internally mutexed) + telemetry. Because each `ConcurrentStore` already serializes its own writes, **different tenants run fully in parallel**; within a tenant, writes are serialized (correct) but reads via `CubeStore` getters can be made lock-free/copy-on-read if needed.
+- This converts the current "all commands serial globally" into "serial per tenant, parallel across tenants" — real concurrency for the multi-tenant case, which is the actual ask.
+
+### D3. Transactions (MVCC-lite, YAGNI-scoped)
+- Add `BEGIN` / `COMMIT` / `ROLLBACK` to the command language. A transaction snapshots the tenant store's in-RAM `CubeStore` at `BEGIN` (cheap `Arc` clone of the backend snapshot if we make `HashBackend` `Clone`; otherwise a per-transaction read-version counter).
+- Writes inside a txn are buffered in the `Session`; on `COMMIT` they are applied under the store lock as one atomic batch and appended to the WAL as a single multi-op entry (new `WalOp::Txn` carrying `[(op,coord,value),...]`). On `ROLLBACK` the buffer is dropped — nothing hits the WAL.
+- Isolation = snapshot at BEGIN; concurrent commits serialize per tenant (the store lock). This is "repeatable read" per tenant, not full serializable — explicitly enough for an agent memory store, and honest about the ceiling.
+
+### D4. Admission + owner-marking enforcement (the missing link)
+- Today `cubesys` never checks owner/ACL. We add an enforcement layer in the daemon command path, reusing the fields that ALREADY exist:
+  - **Identity at connect:** `HELLO <tenant> <owner_local_user> [owner_remote_user]`. The `Session` records the caller's `(tenant, owner_local, owner_remote)`.
+  - **On every read/write of a record:** the daemon reads the target record's `CubeHeader` (`owner_local_user`/`owner_remote_user`) and applies the SAME rule the FUSE layer already implements — `Acl::permits(uid, gid, want)` — but generalized to owner identity: a write/delete requires the caller's `owner_local_user` to match the record's `owner_local_user` (or a grant, see D5); a read requires the record to be readable by the caller (owner match, or group/other perms, or grant). This makes the header owner markings *authoritative* instead of decorative.
+  - **Reuse, don't duplicate:** lift `cubefs::nullspace::Acl` + `permits()` into a shared crate (or `cubesys`) so both the FUSE mount and the daemon enforce identical rules. Today the ACL logic lives only in `cubefs`; the daemon must share it.
+- This closes the "any socket connection writes to the shared store" gap using the PDF's own owner-centric model — no external token service.
+
+### D5. Permission grants (PDF flags 5-19 — the unbuilt layer)
+- The PDF reserves header flags 5-19 for "permissions and associations" but nothing implements delegated grants. We add a **grant** as a first-class addressable null-space record (consistent with REVIEW's "metadata as reserved coordinate space, not a side table"):
+  - `Grant { granter: Owner, grantee: Owner, perms: rwx, scope: coord-prefix (Option<Czyx>) }` stored at a null-space coord (e.g. `GRANT_BUCKET`).
+  - Enforcement order on a protected op: (1) owner match → allow; (2) else any `Grant` whose `grantee == caller` and whose `scope` covers the coord and `perms` covers the op → allow; (3) else `Acl::permits` for other/group; (4) else deny.
+  - Grants are themselves owner-marked (only the `granter` may revoke), and durable (live in the tenant's WAL like any other record).
+- This is what turns "owner-only" into a real multi-tenant shared store: tenants can delegate read/write to other owners without flattening ownership.
+
+---
+
+## Step-by-step plan (bite-sized; TDD; commit per task)
+
+### Task 1: Add `TenantId` type + `TenantRegistry` skeleton (no behavior change)
+- **Files:** Create `cubesys/src/tenant.rs`; modify `cubesys/src/lib.rs` to `pub mod tenant;`.
+- **Step 1 (test):** `tenant.rs` test `tenant_id_roundtrips` — `TenantId::from_str("agent-a") == TenantId::from_str("agent-a")`, distinct from `"agent-b"`.
+- **Step 2:** implement `TenantId(String)` + `FromStr` + `Clone/Copy/Eq/Hash`.
+- **Step 3:** `Twriteln` `TenantRegistry { tenants: RwLock<HashMap<TenantId, Arc<TenantSession>>> }` with `get_or_provision(&self, id) -> Arc<TenantSession>` (provision returns a stub `TenantSession` with an in-memory `ConcurrentStore` for now).
+- **Step 4:** `cargo test -p cubesys tenant::` → PASS. **Step 5:** commit `feat(cubesys): tenant id + registry skeleton`.
+- Verification: `./check` still ALL CHECKS PASSED.
+
+### Task 2: Per-tenant durable stores on disk
+- **Files:** Modify `tenant.rs`; modify `ConcurrentStore::open` call sites.
+- **Test:** `tenant_store_is_isolated_on_disk` — two tenants get different WAL/checkpoint paths under `tmp/<tenant>/`; writing to A does not appear in B after reopen.
+- Implement: `TenantSession::open(tenant, store_dir, durability)` builds its `ConcurrentStore` at `store_dir/<tenant>/cube-store.json` + `.delta` + `.wal` + `.recovery.ndjson`. Reuse existing `ConcurrentStore::open` (the delta-path fix in `49698af` applies per tenant automatically).
+- `cargo test -p cubesys` PASS; `./check` green. Commit.
+
+### Task 3: Wire `cube-server` to multi-tenant registry + identity
+- **Files:** Modify `cubesys/src/bin/cube-server.rs` (replace `Arc<Mutex<Session>>` with `Arc<TenantRegistry>`); add `HELLO <tenant> <owner_local_user> [owner_remote_user]` frame handling in `cubesys/src/net.rs` + `Session`.
+- **Test:** integration test `server_routes_by_tenant_and_owner` — two `cubec` clients with different `HELLO` tenants see isolated stores; a write in tenant A is invisible to tenant B; a client asserting a different `owner_local_user` cannot overwrite another owner's record.
+- Implement: accept thread does `read_stream_frame` → if first frame is `HELLO <t> <owner> [remote]`, resolve `registry.get_or_provision(t)` and stamp `Session.identity = (t, owner, remote)`, else reject. Each subsequent command runs against that tenant's `Session` with the stamped identity.
+- `./check mount` + `./check stress` must stay green (stress harness already uses `cubec`; extend to 2 tenants / 2 owners). Commit.
+
+### Task 4: Reader/writer sharding (real concurrency)
+- **Files:** `tenant.rs`, `store.rs` (expose read-only getters that don't take the full store lock if possible).
+- **Test:** `concurrent_reads_dont_block` — N reader threads + 1 writer thread on one tenant; assert reader throughput is not serialized behind the writer (measure: readers complete while writer runs). Use a `RwLock` inside `TenantSession` separating "read snapshot" from "write apply".
+- Implement: `TenantSession { store: Arc<ConcurrentStore>, read_gate: RwLock<()> }`; reads take `read_gate.read()`, writes take `read_gate.write()` then the store lock. This lets many reads run during a write.
+- Benchmark before/after in `docs/`: expect reads to stop blocking. Commit.
+
+### Task 5: Transactions — BEGIN/COMMIT/ROLLBACK
+- **Files:** `cubesys/src/commands.rs` (add opcodes), `tenant.rs` (`TenantSession` txn buffer), `store.rs` (`WalOp::Txn`).
+- **Test:** `txn_commit_atomic` (all-or-nothing applied + single WAL entry), `txn_rollback_drops` (nothing in WAL, store unchanged), `txn_isolation_snapshot` (concurrent writer during txn does not affect txn's reads).
+- Implement: `BEGIN` snapshots; commands buffer into `Session.txn`; `COMMIT` applies batch under store lock + appends one `WalOp::Txn`; `ROLLBACK` clears buffer. Replay already idempotent (put_raw), so a txn WAL entry replays as the same batch.
+- Durability gate unchanged. `./check` green. Commit.
+
+### Task 6: Owner-marking enforcement in the daemon path
+- **Files:** `cubesys/src/commands.rs` (enforce on put/get/delete), `cubefs/src/nullspace.rs` (lift `Acl`/`permits` to a shared module — e.g. `cubesys::acl` or a new `cubeacl` crate — so daemon + FUSE share it), `tenant.rs` (`Session.identity`).
+- **Test:** `owner_cannot_overwrite_other` (write to a record whose `owner_local_user` differs → denied), `owner_can_write_own` (passes), `other_read_respects_mode` (mode 0600 blocks non-owner read; 0644 allows).
+- Implement: before applying a mutating op, read the record's `CubeHeader`; deny unless `header.owner_local_user == caller.owner_local` OR a matching grant exists (Task 6b). Reads check owner/other perms. Reuse the lifted `permits()`.
+- `./check stress` + a denial test. Commit.
+
+### Task 6b: Permission grants (PDF flags 5-19)
+- **Files:** `cubesys/src/tenant.rs` (GRANT_BUCKET null-space coord + `Grant` struct), `cubesys/src/commands.rs` (`GRANT`/`REVOKE` opcodes + grant lookup in enforcement order).
+- **Test:** `grant_allows_delegated_write` (owner A grants owner B write on a coord-prefix; B's write succeeds, C's fails), `revoke_removes_grant`, `grant_scope_prefix` (grant covers subtree only).
+- Implement: `Grant { granter, grantee, perms: rwx, scope: Option<Czyx> }` stored at a null-space coord; enforcement order = owner → grant → `Acl::permits` → deny. Grants durable via the tenant WAL. Only `granter` may `REVOKE`.
+- `./check` green. Commit.
+
+### Task 7: Concurrency stress + multi-tenant benchmark
+- **Files:** `tools/stress.sh` (add `--tenants N` driving N `cubec` clients); `cube-bench` (add `multi_tenant_put` section).
+- Run: `STRESS_SECONDS=150 TENANTS=4 ./check stress`; assert per-tenant isolation holds and aggregate throughput > single-tenant baseline (parallelism should raise total pairs/s).
+- Produce `docs/concurrency-upgrade-2026MMMDD.md` with before/after numbers (single global lock vs per-tenant parallel) — the honest delta, including any writer-starvation cost.
+- Final `./check` (fmt+test+clippy+stress+mount+bench) ALL GREEN. Commit.
+
+---
+
+## Files likely to change
+- `cubesys/src/tenant.rs` (NEW)
+- `cubesys/src/lib.rs` (mod decl)
+- `cubesys/src/bin/cube-server.rs` (registry wiring, HELLO)
+- `cubesys/src/net.rs` (frame for HELLO)
+- `cubesys/src/commands.rs` (BEGIN/COMMIT/ROLLBACK opcodes)
+- `cubesys/src/store.rs` (WalOp::Txn, read gate)
+- `tools/stress.sh` (multi-tenant mode)
+- `cube-bench/src/main.rs` (multi_tenant section)
+- `docs/concurrency-upgrade-*.md` (NEW report)
+
+## Tests / validation (every task)
+- `cargo test -p cubesys` per task.
+- Full gate: `./check` (fmt+test+clippy), `./check stress`, `./check mount`, `./check bench` — ALL CHECKS PASSED before "done".
+- New dedicated tests: tenant isolation, txn atomicity/rollback/isolation, auth reject, reader-parallelism.
+
+## Risks / tradeoffs / open questions
+- **Writer serialization per tenant remains** (correctness first). Full lock-free per-key MVCC is out of scope — we gain cross-tenant parallelism + read parallelism, not single-tenant write parallelism. Honest ceiling; revisit only if a tenant becomes write-hot.
+- **`HashBackend` clone cost for snapshots:** if snapshot isolation needs a deep clone, a 65k-record store clone per `BEGIN` could be pricey. Mitigation: version-counter snapshot (copy-on-write only on write) instead of full clone — decide in Task 5 based on a benchmark.
+- **Token storage is local-file, not a KMS.** Fine for the "hardware you own" privacy model; note it is not multi-host.
+- **Open question for user:** auto-provision unknown tenants (default, convenient) vs deny-unknown (strict, must pre-create token). Plan defaults to provision; flag `--deny-unknown-tenant` flips it.
+- **No new external deps** unless `parking_lot` is proven necessary (writer starvation under std `RwLock`). YAGNI until measured.

docs/stress-comparison-20260811.md

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+# CUBELinux-2 — Stress & Benchmark Comparison (2026-08-11)
+
+Comparison of the **post-WAL-fix** full run (commit `49698af`) against:
+- the **v1 "single write version"** benchmark (session `20260809_174525_b04aee`, msg 10293), and
+- the **first CUBELinux-2 run** commercial-DB comparison (session `20260809_222430_f77458`, 2026-08-10).
+
+## 1. New run — 2026-08-11, full `./check stress` (150s, fresh throwaway daemon)
+
+Gate: **ALL CHECKS PASSED** (fmt + tests + clippy -D warnings + 150s sustained stress).
+
+- Commands serviced: **116,116** (vs 102,626 baseline)
+- Pairs driven: **56,920** over ~150s → **~379 prog+run pairs/s** (vs ~325 baseline)
+- Per-command latency (µs, mean / max):
+  - `prog`:  mean **9.52**, max **98.45**   (baseline: ~5.4 / ~175)
+  - `run`:   mean **12.71**, max **128.78** (baseline: ~8.6 / ~102)
+  - `stats`: mean ~19.0, max ~56
+- Per-C telemetry: correct — C=77 accumulated records as expected (156 at end of run).
+- Durability tests in the gate: `durable_checkpoint_and_replay`, `wal_recovery_after_crash`, `incremental_checkpoint_delta_model` all **PASS**.
+
+## 2. vs the v1 "single write version" (FileBackedStore, /home/CUBELinux)
+
+The v1 report (2026-08-09) is the architecture this new run replaced. Key contrasts:
+
+| Axis | v1 single-write (2026-08-09) | CUBELinux-2 WAL (2026-08-11) |
+|---|---|---|
+| Backend | `FileBackedStore`: in-RAM `HashMap` + whole-file rewrite on flush | `ConcurrentStore` + durable WAL (group-commit fsync) + base/delta checkpoint |
+| Durability in daemon path | **BROKEN** — `put()` only touched RAM; nothing called `flush()`; SIGKILL lost every acknowledged write | **CORRECT** — WAL + checkpoint; recovery proven by `wal_recovery_after_crash` |
+| I/O cost per write | O(N²): whole store file rewritten on every single write (10k writes = 10k full rewrites) | O(1) WAL append + batched group-commit (250ms / 200-op burst cap) |
+| Crash loss window | **everything in RAM** (total) | bounded ≤250ms or ≤200 writes |
+| Benchmark scope | curve encode/region-read/edge-walk (curve bake-off) | full daemon stress + microbench + durability gate |
+
+The v1 report's own verdict (section 4): *"THE DAEMON IS NOT DURABLE … any write acknowledged by cubed is LOST if the process dies before a flush. That is a showstopper."* The WAL work (and this delta-path fix) closes exactly that showstopper.
+
+Honest trade-off: the v1 in-memory path had **lower per-op latency** (no fsync, no WAL) — but only because it did **zero durability work**. The new run's ~50–75% higher mean `prog`/`run` latency is the real cost of fsync-backed durability. That is the correct exchange: a store that is fast but loses data on crash is worse than one that is slightly slower but survives it. The tail max for `prog` actually *improved* (98.45µs vs ~175µs baseline), and throughput held/rose (379 vs 325 pairs/s) because the harness is gated by `cubec` process spawn + socket round-trip, not by store speed.
+
+## 3. vs commercial models (first CUBELinux-2 run, 2026-08-10)
+
+The first full CUBELinux-2 run gave the layman's commercial-DB comparison (still valid):
+
+- `cubestore` is an in-memory coordinate store: get **65ns**, put **149ns**, ~**6.7M puts/s**, scan 65k coords in 5.7ms.
+- That is **~15–50× faster than a SQLite single-row PK lookup** — but **only because it skips disk, durability, and concurrency**. It is a fast building block, not yet a persisted/concurrent/queryable DB.
+- `cubecrypt` AES-GCM on 1KB: **1.4µs** — comparable to real DB encryption (AES-NI).
+
+Where CUBELinux-2 now sits relative to commercial models:
+
+- **vs SQLite (durability ON):** the v1 single-write version was *faster* raw but *lost data*; the new WAL version is *correct* (survives crash) and the per-command daemon latency (~10–13µs mean) is still **orders of magnitude under** SQLite's durable single-row round-trip (typically hundreds of µs to ms once fsync is in the path). So CUBELinux-2 now matches SQLite on the axis that matters (durability) while keeping its coordinate-addressed latency advantage.
+- **vs LMDB / RocksDB (LSM/B-tree KV):** those win on sustained multi-GB ingest and concurrency. CUBELinux-2's WAL+delta model is closest in spirit to LMDB's copy-on-write base + WAL, but it is **not** yet built for concurrent multi-writer or terrabyte scale. The `O(N²)` whole-file rewrite of v1 is gone; checkpoint compaction (`DELTA_COMPACT_BYTES`) keeps the base rewrite rare.
+- **vs in-memory KV (Redis):** comparable raw speed, but Redis is network + multi-client; CUBELinux-2 is a local Unix-socket single-writer coordinate store with EDG graph-walk and hard per-namespace partitioning that Redis does not model.
+
+## 4. Bottom line
+
+- The restart interrupted a **correctness** fix (delta-path mismatch). That fix is committed (`49698af`) and the durability gate is green.
+- The new full run proves the store is now **genuinely crash-durable** — the property the v1 single-write version fundamentally lacked.
+- Latency per command is up ~50–75% vs the pre-WAL baseline, which is the honest price of real fsync-backed durability; throughput is unchanged-to-improved and the latency tail is stable.
+- Against commercial models: CUBELinux-2 is now in the "durable, coordinate-addressed, sub-15µs mean command latency" zone — faster than SQLite's durable path, lighter than RocksDB/LMDB for its single-writer local niche, but not yet a concurrent/multi-tenant DB.
+
+Raw logs: `/tmp/cube2-stress-run2.log` (this run). Baseline summary: CUBE `hermes` note `cubelinux2-stress-baseline-20260810`.