[F35] mxaccess-compat: LMXProxyServer-shaped facade (18 methods)

Replace the 8-line `mxaccess-compat` stub with a real `LmxClient`
struct exposing the 18 `ILMXProxyServer5` methods as Rust async fns
on top of `mxaccess::Session` (NMX) and `mxaccess::AsbSession` (ASB).

Handle-table approach
* `Mutex<HashMap<i32, ItemRef>>` for item handles, populated by
  `add_item` / `add_item_2` / `add_buffered_item`, drained by
  `remove_item` / `unregister`.
* `Mutex<HashMap<i32, UserRef>>` for user handles allocated by
  `authenticate_user` / `archestra_user_to_id`.
* `AtomicI32` monotonic counters for both, matching the .NET
  reference's `_nextItemHandle` / `_nextUserHandles` per
  `MxNativeCompatibilityServer.cs:62-63`.

Stream-based event surface (per Q4)
* `OnDataChange` / `OnBufferedDataChange` / `OnWriteComplete` /
  `OperationComplete` exposed as `EventStream<T>: Stream<Item=T>`,
  backed by `tokio::sync::broadcast` channels. Lag silently skips
  past `BroadcastStream::Lagged` to keep the public `Item` shape
  ergonomic. NOT COM events — that's the post-V1
  `mxaccess-compat-com` crate per design/70-risks-and-open-questions.md
  Q4. The `OperationComplete` channel is wired but no firing path
  is modelled (R3 deferred — no captured byte mapping yet).
* `Advise` / `AdviseSupervisory` spawn a background fan-out task
  that drains the `Subscription` stream and routes each
  `DataChange` to either `on_data_change` or
  `on_buffered_data_change` based on the item's `is_buffered` flag.
  `UnAdvise` / `RemoveItem` abort the task.

Pass-through methods
* `Write` / `Write2` -> `Session::write` / `write_with_timestamp`
  (`userId` ignored — the underlying surface uses engine identity).
* `WriteSecured2` -> `Session::write_secured_at` with both user ids
  always passed (R6: single-user secured = same id twice; never
  gated).
* `AdviseSupervisory` collapses onto `Session::subscribe` because
  the wire path is `AdviseSupervisory` already (`session.rs:1057`),
  matching the .NET reference's `cs:251-259` identical collapse.
* `SetBufferedUpdateInterval` rounds up to nearest 100 ms per
  `MxNativeCompatibilityServer.cs:638`.

Stubbed pass-throughs (mirror upstream `Error::Unsupported`)
* `WriteSecured` (no timestamp) — `Session::write_secured` is
  stubbed at `crates/mxaccess/src/lib.rs:472` (only
  `WriteSecured2`/`0x3A` is ported); workaround documented inline.
* `AddBufferedItem` allocates the handle but `Advise` for buffered
  items does not yet drive `Session::subscribe_buffered` cadence
  knob — TODO(F36) flagged inline at `add_buffered_item` and
  `set_buffered_update_interval`.

Tests (25 new, all green)
* Handle-table lifecycle: Add -> Advise -> UnAdvise -> Remove with
  a mocked subscription task.
* Monotonic handle allocation; context-prefix combination.
* `SetBufferedUpdateInterval` rounding (50 -> 100, 101 -> 200, etc.)
  + zero-rejection.
* Compile-time check that all 18 LMX methods are reachable on
  `LmxClient`.
* Each event stream yields published items; lag silently dropped.
* GUID-shape validation; server-handle mismatch errors.

Build hygiene
* `cargo build -p mxaccess-compat` clean.
* `cargo test -p mxaccess-compat` -> 25 passed.
* `cargo clippy -p mxaccess-compat --all-targets -- -D warnings` clean.
* `RUSTDOCFLAGS=-D warnings cargo doc -p mxaccess-compat --no-deps` clean.

Deferred / TODOs
* TODO(F36): wire `set_buffered_update_interval` cadence into the
  `advise` path for buffered items.
* TODO(R3): plumb a real trigger into `on_operation_complete` once
  the byte mapping lands.
* TODO(wave 2): live integration tests against AVEVA.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

rust/Cargo.lock

@@ -464,6 +464,16 @@ version = "2.8.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "f8ca58f447f06ed17d5fc4043ce1b10dd205e060fb3ce5b979b8ed8e59ff3f79"
 
+[[package]]
+name = "metrics"
+version = "0.24.5"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "ff56c2e7dce6bd462e3b8919986a617027481b1dcc703175b58cf9dd98a2f071"
+dependencies = [
+ "portable-atomic",
+ "rapidhash",
+]
+
 [[package]]
 name = "miniz_oxide"
 version = "0.8.9"
@@ -491,6 +501,7 @@ version = "0.0.0"
 dependencies = [
  "async-trait",
  "futures-util",
+ "metrics",
  "mxaccess-asb",
  "mxaccess-asb-nettcp",
  "mxaccess-callback",
@@ -563,7 +574,11 @@ dependencies = [
 name = "mxaccess-compat"
 version = "0.0.0"
 dependencies = [
+ "futures-util",
  "mxaccess",
+ "thiserror 2.0.18",
+ "tokio",
+ "tokio-stream",
 ]
 
 [[package]]
@@ -665,6 +680,12 @@ version = "0.2.17"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "a89322df9ebe1c1578d689c92318e070967d1042b512afbe49518723f4e6d5cd"
 
+[[package]]
+name = "portable-atomic"
+version = "1.13.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "c33a9471896f1c69cecef8d20cbe2f7accd12527ce60845ff44c153bb2a21b49"
+
 [[package]]
 name = "ppv-lite86"
 version = "0.2.21"
@@ -769,6 +790,15 @@ dependencies = [
  "rand_core 0.5.1",
 ]
 
+[[package]]
+name = "rapidhash"
+version = "4.4.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "b5e48930979c155e2f33aa36ab3119b5ee81332beb6482199a8ecd6029b80b59"
+dependencies = [
+ "rustversion",
+]
+
 [[package]]
 name = "rc4"
 version = "0.2.0"

rust/crates/mxaccess-compat/Cargo.toml

@@ -10,6 +10,13 @@ authors.workspace = true
 
 [dependencies]
 mxaccess = { path = "../mxaccess" }
+tokio = { workspace = true }
+tokio-stream = { version = "0.1", features = ["sync"] }
+futures-util = { workspace = true }
+thiserror = { workspace = true }
+
+[dev-dependencies]
+tokio = { workspace = true, features = ["macros", "rt", "rt-multi-thread", "sync", "time"] }
 
 [lints]
 workspace = true