[M4] mxaccess: wire MxValue overloads + shutdown(timeout) shim

Replaces the lib.rs `Unsupported`-stub Session methods with real
implementations where the underlying primitives already exist in
session.rs, sharpens docstrings on the still-deferred ones, and
refreshes the stale "M0 stub" module preamble.

Wired (now functional):
- `Session::write(MxValue)` — converts via `mxvalue_to_writevalue` then
  delegates to `write_value`.
- `Session::write_with_timestamp(MxValue, SystemTime)` — same plus
  `system_time_to_filetime` then `write_value_at`.
- `Session::write_secured_at(MxValue, SystemTime, SecurityContext)` —
  same plus `write_value_secured_at`.
- `Session::shutdown(timeout)` — `tokio::time::timeout` wrapper around
  `shutdown_nmx`; on elapse returns `Error::Timeout` (the in-flight
  unregister is cancelled, mirroring the .NET `IDisposable` semantics
  at `MxNativeSession.cs:481`).

Still `Unsupported` (gating reasons documented in each docstring):
- `Session::connect` — needs F12 auto-resolve (gated on F6 windows-rs).
- `Session::write_with_completion` — needs per-token registry, gated
  on R15 long-lived task.
- `Session::write_secured` (no timestamp) — `NmxClient` only ports
  `WriteSecured2` (LMX 0x3A), not the unversioned `WriteSecured` (0x39).
- `Session::subscribe_many` — no atomic frame on the wire; canonical
  pattern is `examples/multi-tag.rs`.
- `Session::subscribe_buffered` — M6 `SetBufferedUpdateInterval` RPC.

`mxvalue_to_writevalue` consumes the `MxValue` and returns
`Error::Configuration(InvalidArgument)` for the three variants whose
re-encode is policy-dependent: `DateTime` / `ElapsedTime` /
`DateTimeArray`. The `non_exhaustive` MxValue catch-all preserves
forward compat.

Test count delta: 532 → 542 (+10; conversion happy paths for Boolean /
Int32 / Float64 / String / Int32Array / BoolArray / StringArray, plus
the three rejected variant errors).
Open followups touched: none resolved (F12, F16 still gating).

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

design/followups.md

@@ -6,6 +6,48 @@ move to `## Resolved` with a date + commit hash.
 
 ## Open
 
+### F18 — M5 plan of attack (ASB transport, parallel-safe sub-streams)
+**Severity:** P0 — milestone driver, blocks ASB consumers + V1 release
+**Source:** `design/dependencies.md:73-89` + `design/60-roadmap.md:84-91` + `design/70-risks-and-open-questions.md:5-25` (R1 estimates ~3000 LoC for framing+encoders).
+
+**Scope.** Build the ASB data-plane end-to-end:
+- `mxaccess-asb-nettcp` — `[MS-NMF]` framing + `[MC-NBFX]` binary-XML node codec + `[MC-NBFS]` static dictionary table + DH/HMAC/AES authentication crypto.
+- `mxaccess-asb` — `IASBIDataV2` client (Connect, RegisterItems, Read, Write, PublishWriteComplete, CreateSubscription, AddMonitoredItems, Publish, Disconnect) + `SecretProvider` trait + DPAPI default impl + ASB Variant codec port (currently a stub at `crates/mxaccess-codec/src/lib.rs:74,77,80`).
+- `mxaccess::Session` over an `AsbTransport` impl; capabilities surface ASB limits (no `subscribe_buffered`, no Activate/Suspend, no OperationComplete outside the proven write-completion frame — see `design/60-roadmap.md:88`).
+- `examples/asb-subscribe.rs` exercises the whole path against a live ASB endpoint with parity vs `dotnet run --project src\MxAsbClient.Probe`.
+
+**Sub-stream breakdown** (matches `design/dependencies.md:78-89`). Each sub-stream is a separate followup so it can be claimed by a separate agent in a worktree without merge conflict:
+
+| Sub-followup | Stream | Owns | Depends on |
+|---|---|---|---|
+| F19 | (workspace prereq) | Add the M5 dep set to `rust/Cargo.toml` workspace deps + per-crate `Cargo.toml`: `aes`, `hmac`, `md-5`, `sha1`, `sha2`, `pbkdf2`, `flate2`, `rand`, `crypto-bigint` (constant-time DH per `review.md` MAJOR), `quick-xml`, `tokio-util`. Pinned to the `digest 0.11`/`cipher 0.5` generation per `design/30-crate-topology.md:251-289`. Sequential prereq for the others. | M0 |
+| F20 | A — MS-NMF framing | `mxaccess-asb-nettcp::nmf` — preamble (`0x00 ver=1 mode=2 via=encoded-string`), preamble-ack, sized-envelope (`0x06 var-int len bytes`), end (`0x07`), fault (`0x08`), upgrade-request, known-encoding via lookup. Reliable-session ack handling. Round-trip against `analysis/proxy/mxasbclient-register-message.txt` and `mxasbclient-probe-stage*.txt` byte traces. | F19 |
+| F21 | B — MC-NBFX | `mxaccess-asb-nettcp::nbfx` — record types (`0x40` ShortElement, `0x41` Element, `0x44` ShortDictionaryAttribute, `0x04` PrefixDictionary*A-Z, `0x84` BoolText, `0x88` Int32Text, `0x86` BoolFalseText, etc., per `[MC-NBFX]` §2.2). Length-prefixed strings (var-int 7-bit groups). Read/write over `bytes::BytesMut`. | F19 |
+| F22 | C — MC-NBFS | `mxaccess-asb-nettcp::nbfs` — the static dictionary table. SOAP/WS-Addressing tokens + `IASBIDataV2`-action strings used by the operation set (`http://ASB.IDataV2:registerItemsIn`, `:readIn`, `:writeIn`, `:createSubscriptionIn`, `:publishIn`, etc., see `src/MxAsbClient/AsbContracts.cs:14-58`). Hand-rolled from the proven action set; the full WCF dictionary is much larger but only the action subset is on the wire. | F19 |
+| F23 | D — Auth crypto | `mxaccess-asb-nettcp::auth` — port `src/MxAsbClient/AsbSystemAuthenticator.cs` (167 LoC): DH key exchange with `crypto-bigint` constant-time `mod_exp` (review.md MAJOR finding — .NET `BigInteger.ModPow` is **not** constant-time and the DH private exponent is long-lived per `cs:153-166`); HMAC-MD5/SHA1/SHA512 (negotiated per `AsbSolutionCryptoParameters.HashAlgorithm`); AES-128 with PBKDF2-SHA1 1000-iteration key derivation; deflate-then-encrypt `EncryptBaktun` vs raw-encrypt `EncryptApollo` distinguished by `:V2` lifetime suffix (`cs:48`); ASCII salt `"ArchestrAService"`; UTF-16LE passphrase. Plus DPAPI shared-secret read on Windows behind the existing `dpapi` feature gate, with a `SecretProvider::shared_secret(&[u8])` escape hatch for tests/CI (`design/30-crate-topology.md:150`). | F19 |
+| F24 | (codec) | `mxaccess-codec::asb_variant` — fill in the stubbed `AsbVariant`, `AsbStatus`, `RuntimeValue` (`crates/mxaccess-codec/src/lib.rs:74,77,80`) per `docs/ASB-Variant-Wire-Format.md`. Decode/encode for the proven type matrix: `TypeBool`, `TypeInt32`, `TypeFloat`, `TypeDouble`, `TypeString`, `TypeDateTime`, `TypeDuration`, plus deployed array shapes (`work_remain.md:108-113`). Less-common scalars stay as raw bytes (matches .NET `DecodeVariant` fallback at `MxAsbDataClient.cs:748`). Independent of the framing/encoder work — separate crate. | M1 (envelope/status types) |
+| F25 | E — IASBIDataV2 client | `mxaccess-asb::client` — top-level `AsbClient` with `connect`, `register_items`, `read`, `write`, `publish_write_complete`, `create_subscription`, `add_monitored_items`, `publish`, `disconnect`. Wires the contract → NBFX-encoded SOAP envelope → NMF-framed TCP. `ConnectedRequest::ConnectionValidator` HMAC signing per `AsbSystemAuthenticator::Sign`. Receives `Publish` callbacks via a long-lived background task (mirrors the M4 NMX `callback_router` pattern). Depends on F20+F21+F22+F23+F24. | A+B+C+D+codec |
+| F26 | (session) | `mxaccess::Session` over `AsbTransport`. New transport impl alongside `NmxTransport`. Surface ASB capability flags so `subscribe_buffered`/`activate`/`suspend` return `Error::Unsupported(Capability::*)` rather than a runtime fallthrough. Update `examples/asb-subscribe.rs` to drive the path end-to-end. Live-probe DoD: round-trip parity with `dotnet run --project src\MxAsbClient.Probe`. | F25 |
+
+**Parallel-safety analysis.**
+- F19 (workspace deps) is the **single sequential bottleneck** — F20-F25 all reference workspace deps that don't exist yet, so they cannot start in parallel until F19 lands. Tight & small (~30 lines of TOML).
+- F20, F21, F22, F23, F24 are **fully parallel-safe** after F19: each owns a different module under a different crate (or different sibling module within `mxaccess-asb-nettcp`). No shared state, no cross-import — each can land in its own commit. Per `dependencies.md:88` "Peak agents in parallel: 4 in the framing/encoding wave (A+B+C+D)".
+- F25 is sequential after the four framing/encoder streams + F24 land — it composes them. The .NET `MxAsbDataClient` is monolithic enough that splitting F25 across agents costs more in coordination than it saves.
+- F26 is sequential after F25.
+- **Cross-milestone parallelism still holds.** M5 (this whole F18-F26 cluster) runs in parallel with M3+M4 per `design/60-roadmap.md:14-17` because the `Transport` trait was lifted into M0. M4's `Session` core landed (commits `4863c6d`, `2dc091d`, `a31237d`); the F26 `AsbTransport` plugs into the same trait without re-design.
+
+**Risk-driven sequencing inside the parallel wave.** R1 in `design/70-risks-and-open-questions.md:9` is the project-blocker. Of the four parallel streams, F23 (auth crypto) carries the most live-probe risk (DH handshake against the live VM is the first irreversible test of the spec port) but is the smallest in LoC. F22 (NBFS) is the largest unknown — the dictionary table size is bounded only by the action subset we exercise. Recommended order *if* agents are constrained: F23 (smallest, highest-leverage) → F20 (foundational for any wire test) → F21 (encoder) → F22 (dictionary) → F24 (codec, independent).
+
+**Definition of done** for F18 as a whole (= M5 DoD per `design/60-roadmap.md:91`):
+1. `cargo run -p mxaccess --example asb-subscribe -- --tag TestChildObject.TestInt` succeeds against a live ASB endpoint.
+2. Round-trip parity with `dotnet run --project src\MxAsbClient.Probe` (Frida/Wireshark diff is byte-identical for the proven type matrix).
+3. The `mxaccess-asb` type matrix covers what `work_remain.md:108-113` documents as proven: scalar Boolean, Int32, Float, Double, String, DateTime, Duration plus deployed array tags.
+4. `cargo build --workspace` and `cargo test --workspace` green; `cargo clippy --workspace -- -D warnings` clean.
+
+**Resolves when:** F19-F26 are all closed and the four DoD bullets above pass.
+
+**This-iteration execution slice.** Land F19 (workspace deps) sequentially first, then F23 (auth crypto port — smallest stream, fully self-contained, exercises the largest set of new deps in one place to validate the dep choice). F20/F21/F22/F24/F25/F26 stay open for follow-up iterations or parallel agent fan-out.
+
 ### F2 — NTLM verify_signature path + constant-time MAC compare (server-to-client direction)
 **Severity:** P2
 **Source:** M2 wave 1, `crates/mxaccess-rpc/src/ntlm.rs`
@@ -88,3 +130,6 @@ move to `## Resolved` with a date + commit hash.
 
 ### F9 — `ObjectExporterClient.cs` ResolveOxid wrapper methods
 **Resolved:** 2026-05-05. Both portable methods land in `crates/mxaccess-rpc/src/object_exporter_client.rs`: `resolve_oxid_unauthenticated` (mirrors `cs:14-30`) and `resolve_oxid_with_managed_ntlm_packet_integrity` (mirrors `cs:66-81`). Each opens a TCP connection, binds to `IObjectExporter`, calls opnum 0 with the encoded request, and decodes the response — preferring `parse_resolve_oxid_result` then falling back to `parse_resolve_oxid_failure` for short stubs. The two SSPI flavours (`ResolveOxidWithNtlmConnect`, `ResolveOxidWithNtlmPacketIntegrity`) wrap .NET's `System.Net.Security.SspiClientContext` and are explicitly out of scope for the Rust port — that's a permanent skip, not a deferral.
+
+### F17 — `Guid::parse_str` helper (dashed-hex string parser)
+**Resolved:** 2026-05-05. `Guid::parse_str(&str) -> Result<Guid, RpcError>` landed in `crates/mxaccess-rpc/src/guid.rs:65-112` as the inverse of the existing `Display` impl. Accepts the canonical dashed-hex form, optionally wrapped in `{}` braces (.NET `B` format), case-insensitive, and tolerant of bare 32-char hex without dashes. Single-pass char-by-char nibble accumulator avoids per-byte string allocation; the same byte-swap of groups 1-3 the Display impl does is applied after the raw hex pass. Eight new tests cover round-trip against the `Display` fixture (`b49f92f7-c748-4169-8eca-a0670b012746`), braces, uppercase, no-dashes, zero-GUID, too-short, too-long, and non-hex rejection. The five live-NMX examples (`connect-write-read`, `subscribe`, `recovery`, `multi-tag`, `secured-write`) lost their per-file 15-line `parse_guid` helpers in favour of the canonical implementation. Test count delta: 524 → 532 (+8).

rust/crates/mxaccess-rpc/src/guid.rs

@@ -46,6 +46,71 @@ impl Guid {
         Ok(Self(out))
     }
 
+    /// Parse a `12345678-1234-1234-1234-123456789012` style GUID string
+    /// into wire-byte form. Inverse of the [`std::fmt::Display`] impl.
+    ///
+    /// Accepts the canonical dashed-hex form, optionally wrapped in
+    /// `{...}` braces (the .NET `B` format). Case-insensitive. The
+    /// first three hex groups are stored little-endian on the wire (per
+    /// the module docstring) so the parser byte-swaps them after the
+    /// raw hex pass.
+    ///
+    /// There is no .NET reference to mirror here — the Display impl is
+    /// the spec, this is its inverse.
+    ///
+    /// # Errors
+    /// Returns [`crate::error::RpcError::Decode`] if the input is not
+    /// 32 hex chars (with 4 optional dashes and optional outer braces),
+    /// or contains a non-hex character.
+    pub fn parse_str(s: &str) -> Result<Self, crate::error::RpcError> {
+        let trimmed = s.trim_start_matches('{').trim_end_matches('}');
+        // Strip dashes; everything else must be a hex digit.
+        let mut bytes = [0u8; 16];
+        let mut nibble_count = 0usize;
+        let mut acc: u8 = 0;
+        for c in trimmed.chars() {
+            if c == '-' {
+                continue;
+            }
+            let digit = match c.to_digit(16) {
+                Some(d) => d as u8,
+                None => {
+                    return Err(crate::error::RpcError::Decode {
+                        offset: nibble_count / 2,
+                        reason: "non-hex character in guid",
+                        buffer_len: trimmed.len(),
+                    });
+                }
+            };
+            if nibble_count >= 32 {
+                return Err(crate::error::RpcError::Decode {
+                    offset: 16,
+                    reason: "guid hex too long",
+                    buffer_len: trimmed.len(),
+                });
+            }
+            if nibble_count % 2 == 0 {
+                acc = digit << 4;
+            } else {
+                bytes[nibble_count / 2] = acc | digit;
+            }
+            nibble_count += 1;
+        }
+        if nibble_count != 32 {
+            return Err(crate::error::RpcError::Decode {
+                offset: nibble_count / 2,
+                reason: "guid hex too short",
+                buffer_len: trimmed.len(),
+            });
+        }
+        // Byte-swap the first three groups so the resulting bytes match
+        // the wire layout the Display impl reads.
+        bytes[0..4].reverse();
+        bytes[4..6].reverse();
+        bytes[6..8].reverse();
+        Ok(Self(bytes))
+    }
+
     /// Write the 16 wire bytes into `dst[..16]`. Mirrors .NET
     /// `Guid.TryWriteBytes(span)`.
     ///
@@ -142,4 +207,80 @@ mod tests {
             "00000000-0000-0000-0000-000000000000"
         );
     }
+
+    #[test]
+    fn parse_str_round_trips_display() {
+        // The dashed-hex form from the display fixture above.
+        let g = Guid::parse_str("b49f92f7-c748-4169-8eca-a0670b012746").unwrap();
+        assert_eq!(
+            g.0,
+            [
+                0xF7, 0x92, 0x9F, 0xB4, 0x48, 0xC7, 0x69, 0x41, 0x8E, 0xCA, 0xA0, 0x67, 0x0B, 0x01,
+                0x27, 0x46,
+            ]
+        );
+        // Round-trip back via Display.
+        assert_eq!(g.to_string(), "b49f92f7-c748-4169-8eca-a0670b012746");
+    }
+
+    #[test]
+    fn parse_str_accepts_braces() {
+        // .NET "B" format wraps the dashed-hex form in `{}`.
+        let g = Guid::parse_str("{b49f92f7-c748-4169-8eca-a0670b012746}").unwrap();
+        assert_eq!(g.to_string(), "b49f92f7-c748-4169-8eca-a0670b012746");
+    }
+
+    #[test]
+    fn parse_str_accepts_uppercase() {
+        let g = Guid::parse_str("B49F92F7-C748-4169-8ECA-A0670B012746").unwrap();
+        assert_eq!(g.to_string(), "b49f92f7-c748-4169-8eca-a0670b012746");
+    }
+
+    #[test]
+    fn parse_str_accepts_no_dashes() {
+        let g = Guid::parse_str("b49f92f7c74841698ecaa0670b012746").unwrap();
+        assert_eq!(g.to_string(), "b49f92f7-c748-4169-8eca-a0670b012746");
+    }
+
+    #[test]
+    fn parse_str_round_trips_zero() {
+        let g = Guid::parse_str("00000000-0000-0000-0000-000000000000").unwrap();
+        assert_eq!(g, Guid::ZERO);
+    }
+
+    #[test]
+    fn parse_str_rejects_too_short() {
+        let err = Guid::parse_str("b49f92f7-c748-4169-8eca-a0670b0127").unwrap_err();
+        assert!(matches!(
+            err,
+            crate::error::RpcError::Decode {
+                reason: "guid hex too short",
+                ..
+            }
+        ));
+    }
+
+    #[test]
+    fn parse_str_rejects_too_long() {
+        let err = Guid::parse_str("b49f92f7-c748-4169-8eca-a0670b01274600").unwrap_err();
+        assert!(matches!(
+            err,
+            crate::error::RpcError::Decode {
+                reason: "guid hex too long",
+                ..
+            }
+        ));
+    }
+
+    #[test]
+    fn parse_str_rejects_non_hex() {
+        let err = Guid::parse_str("b49f92f7-c748-4169-8eca-a0670b01274z").unwrap_err();
+        assert!(matches!(
+            err,
+            crate::error::RpcError::Decode {
+                reason: "non-hex character in guid",
+                ..
+            }
+        ));
+    }
 }

rust/crates/mxaccess/examples/asb-subscribe.rs

@@ -1,7 +1,44 @@
-//! `asb-subscribe` — subscribe via the ASB transport.
+//! `asb-subscribe` — subscribe via the ASB transport (M5 placeholder).
 //!
-//! M0 stub. See `design/60-roadmap.md` M5.
+//! ASB (`net.tcp` to MxDataProvider) is the M5 milestone — the
+//! `mxaccess-asb-nettcp` framing crate and `mxaccess-asb` operations crate
+//! are scaffolded but not yet wired into `Session`. Once M5 lands the demo
+//! body below becomes a ~30-line subscribe + drain identical in shape to
+//! `subscribe.rs`, just over the ASB transport.
+//!
+//! See `design/60-roadmap.md` M5 for the operations matrix and
+//! `docs/ASB-Native-Integration-Decision.md` for why ASB is the preferred
+//! data-plane.
 
-fn main() {
-    eprintln!("asb-subscribe: stubbed (M0). See design/60-roadmap.md M5.");
+use mxaccess::{ConnectionOptions, Session};
+
+#[tokio::main]
+async fn main() -> Result<(), Box<dyn std::error::Error>> {
+    if std::env::var_os("MX_LIVE").is_none() {
+        eprintln!(
+            "MX_LIVE not set — `asb-subscribe` is the M5 placeholder; \
+             run `. tools/Setup-LiveProbeEnv.ps1` once the ASB transport lands."
+        );
+        return Ok(());
+    }
+
+    match Session::connect(ConnectionOptions).await {
+        Ok(_) => {
+            eprintln!(
+                "Session::connect returned Ok unexpectedly — \
+                 update this example once M5 wires the ASB transport."
+            );
+        }
+        Err(mxaccess::Error::Unsupported {
+            operation,
+            transport,
+        }) => {
+            eprintln!(
+                "{operation} on {transport:?}: deferred to M5. See \
+                 design/60-roadmap.md M5 for the ASB transport operations matrix."
+            );
+        }
+        Err(e) => return Err(e.into()),
+    }
+    Ok(())
 }

rust/crates/mxaccess/examples/connect-write-read.rs

@@ -1,7 +1,156 @@
-//! `connect-write-read` — connect, write a value, read it back.
+//! `connect-write-read` — connect to NMX, write a value, read it back, shut down.
 //!
-//! M0 stub. Filled in as M4 lands. See `design/60-roadmap.md` M4 DoD.
+//! The 30-line consumer-experience target from `design/60-roadmap.md` M4 DoD.
+//!
+//! # Required env vars
+//!
+//! Populate via `tools/Setup-LiveProbeEnv.ps1` (dot-source it):
+//!
+//! - `MX_LIVE` (any non-empty value enables the live path)
+//! - `MX_NMX_HOST` — NMX endpoint host[:port]; defaults port 135 if omitted
+//! - `MX_NMX_SERVICE_IPID` — `INmxService2` IPID (UUID; auto-resolution is F12)
+//! - `MX_RPC_USER`, `MX_RPC_PASSWORD`, `MX_RPC_DOMAIN` — NTLM creds
+//! - `MX_TEST_TAG` — tag reference (default `TestChildObject.TestInt`)
+//!
+//! # Resolver shim
+//!
+//! Examples ship with an inline `StaticResolver` that returns canned metadata
+//! for the configured `MX_TEST_TAG`. Production consumers should plug in a
+//! `tiberius`-backed Galaxy SQL resolver (followup F14 in
+//! `design/followups.md`); the `Resolver` trait is `Send + Sync` so any
+//! concrete impl drops in.
 
-fn main() {
-    eprintln!("connect-write-read: stubbed (M0). See design/60-roadmap.md M4.");
+use std::sync::Arc;
+use std::time::Duration;
+
+use mxaccess::{
+    GalaxyTagMetadata, RecoveryPolicy, Resolver, ResolverError, Session, SessionOptions, WriteValue,
+};
+use mxaccess_rpc::guid::Guid;
+use mxaccess_rpc::ntlm::NtlmClientContext;
+
+#[tokio::main]
+async fn main() -> Result<(), Box<dyn std::error::Error>> {
+    let Some(env) = LiveEnv::from_process()? else {
+        eprintln!(
+            "MX_LIVE not set — skipping live demo. Run \
+             `. tools/Setup-LiveProbeEnv.ps1` to populate the required env vars."
+        );
+        return Ok(());
+    };
+
+    let session = Session::connect_nmx(
+        env.addr,
+        SessionOptions::default(),
+        NtlmClientContext::from_env()?,
+        env.service_ipid,
+        Arc::new(StaticResolver::new(&env.tag)),
+        RecoveryPolicy::default(),
+    )
+    .await?;
+
+    eprintln!("connected; writing {} = 123", env.tag);
+    session
+        .write_value(&env.tag, WriteValue::Int32(123))
+        .await?;
+
+    eprintln!("reading {}; timeout 5s", env.tag);
+    let dc = session.read(&env.tag, Duration::from_secs(5)).await?;
+    println!(
+        "{} = {:?} (quality 0x{:x})",
+        dc.reference, dc.value, dc.quality
+    );
+
+    session.shutdown_nmx().await?;
+    Ok(())
+}
+
+// ---- live-env wiring (duplicated across examples; see module docstring) -----
+
+struct LiveEnv {
+    addr: std::net::SocketAddr,
+    service_ipid: Guid,
+    tag: String,
+}
+
+impl LiveEnv {
+    fn from_process() -> Result<Option<Self>, Box<dyn std::error::Error>> {
+        if std::env::var_os("MX_LIVE").is_none() {
+            return Ok(None);
+        }
+        let host = std::env::var("MX_NMX_HOST")?;
+        let addr = parse_host_port(&host, 135)?;
+        let service_ipid = Guid::parse_str(&std::env::var("MX_NMX_SERVICE_IPID")?)?;
+        let tag = std::env::var("MX_TEST_TAG").unwrap_or_else(|_| "TestChildObject.TestInt".into());
+        Ok(Some(Self {
+            addr,
+            service_ipid,
+            tag,
+        }))
+    }
+}
+
+fn parse_host_port(
+    s: &str,
+    default_port: u16,
+) -> Result<std::net::SocketAddr, Box<dyn std::error::Error>> {
+    if let Ok(addr) = s.parse() {
+        return Ok(addr);
+    }
+    let with_port = if s.contains(':') {
+        s.to_string()
+    } else {
+        format!("{s}:{default_port}")
+    };
+    Ok(
+        std::net::ToSocketAddrs::to_socket_addrs(&with_port.as_str())?
+            .next()
+            .ok_or("no addrs resolved")?,
+    )
+}
+
+// ---- canned in-memory resolver ----------------------------------------------
+
+struct StaticResolver {
+    tag_reference: String,
+    metadata: GalaxyTagMetadata,
+}
+
+impl StaticResolver {
+    fn new(tag_reference: &str) -> Self {
+        let (object, attribute) = tag_reference
+            .split_once('.')
+            .unwrap_or((tag_reference, "TestInt"));
+        Self {
+            tag_reference: tag_reference.to_string(),
+            metadata: GalaxyTagMetadata {
+                object_tag_name: object.to_string(),
+                attribute_name: attribute.to_string(),
+                primitive_name: None,
+                platform_id: 1,
+                engine_id: 2,
+                object_id: 3,
+                primitive_id: 0,
+                attribute_id: 7,
+                property_id: GalaxyTagMetadata::VALUE_PROPERTY_ID,
+                mx_data_type: 2, // Integer (Int32)
+                is_array: false,
+                security_classification: 0,
+                attribute_source: "dynamic".into(),
+            },
+        }
+    }
+}
+
+#[async_trait::async_trait]
+impl Resolver for StaticResolver {
+    async fn resolve(&self, tag: &str) -> Result<GalaxyTagMetadata, ResolverError> {
+        if tag == self.tag_reference {
+            Ok(self.metadata.clone())
+        } else {
+            Err(ResolverError::NotFound {
+                tag_reference: tag.to_string(),
+            })
+        }
+    }
 }

rust/crates/mxaccess/examples/multi-tag.rs

@@ -1,8 +1,195 @@
-//! `multi-tag` — `subscribe_many` over several tags. Non-atomic per-tag
-//! advise loop matching `MxNativeSession.SubscribeAsync` (`MxNativeSession.cs:250-270`).
+//! `multi-tag` — subscribe to several tags in one session.
 //!
-//! M0 stub.
+//! Demonstrates the per-tag advise loop that mirrors
+//! `MxNativeSession.SubscribeAsync` (`MxNativeSession.cs:250-270`) — there
+//! is no atomic "subscribe-many" RPC on the LMX wire, so consumers
+//! issue one `AdviseSupervisory` per tag. The high-level
+//! `Session::subscribe_many` shim is currently `Unsupported` (it is
+//! reserved for a future atomic frame; per `wwtools/mxaccesscli/`
+//! research no such frame is documented) — the loop below is the
+//! consumer-side replacement.
+//!
+//! Streams are merged with `futures_util::stream::select_all`. The
+//! example takes a comma-separated `MX_TEST_TAGS` env var (default:
+//! two canned tags); both must be writable through the inline
+//! `StaticResolver`.
 
-fn main() {
-    eprintln!("multi-tag: stubbed (M0). See design/60-roadmap.md M4.");
+use std::sync::Arc;
+use std::time::Duration;
+
+use futures_util::stream::{StreamExt, select_all};
+use mxaccess::{
+    GalaxyTagMetadata, RecoveryPolicy, Resolver, ResolverError, Session, SessionOptions,
+    Subscription,
+};
+use mxaccess_rpc::guid::Guid;
+use mxaccess_rpc::ntlm::NtlmClientContext;
+
+#[tokio::main]
+async fn main() -> Result<(), Box<dyn std::error::Error>> {
+    let Some(env) = LiveEnv::from_process()? else {
+        eprintln!(
+            "MX_LIVE not set — skipping live demo. Run \
+             `. tools/Setup-LiveProbeEnv.ps1` to populate the required env vars."
+        );
+        return Ok(());
+    };
+
+    let session = Session::connect_nmx(
+        env.addr,
+        SessionOptions::default(),
+        NtlmClientContext::from_env()?,
+        env.service_ipid,
+        Arc::new(StaticResolver::new(&env.tags)),
+        RecoveryPolicy::default(),
+    )
+    .await?;
+
+    // Per-tag advise loop. This is the .NET cs:250-270 pattern lifted
+    // into Rust — one round-trip per tag, sequential to keep the wire
+    // ordering deterministic.
+    let mut subs: Vec<Subscription> = Vec::with_capacity(env.tags.len());
+    for tag in &env.tags {
+        eprintln!("subscribing to {tag}");
+        subs.push(session.subscribe(tag).await?);
+    }
+
+    // Merge the streams. select_all yields the first ready item across
+    // all subscriptions; we annotate each event with its source.
+    let labelled: Vec<_> = subs
+        .iter_mut()
+        .enumerate()
+        .map(|(i, s)| s.map(move |item| (i, item)))
+        .collect();
+    let mut merged = select_all(labelled);
+
+    let mut received = 0;
+    while received < 10 {
+        match tokio::time::timeout(Duration::from_secs(10), merged.next()).await {
+            Ok(Some((idx, Ok(dc)))) => {
+                println!("[{}] {} = {:?}", idx, dc.reference, dc.value);
+                received += 1;
+            }
+            Ok(Some((idx, Err(e)))) => {
+                eprintln!("[{idx}] subscription error: {e}");
+            }
+            Ok(None) => {
+                eprintln!("all streams ended");
+                break;
+            }
+            Err(_) => {
+                eprintln!("no update within 10s; exiting after {received} updates");
+                break;
+            }
+        }
+    }
+
+    // Drop the merged stream so we can hand the subscriptions back.
+    drop(merged);
+
+    // Best-effort cleanup. The merged drop above released the
+    // subscriptions; we re-subscribe just to get fresh handles for
+    // unsubscribe — except `select_all` consumed them. In real code
+    // structure subs in an Option<> or pull from `subs` before merging.
+    // Simplest demo path: just shutdown which fires UnregisterEngine and
+    // the server cleans up advises on its side.
+    session.shutdown_nmx().await?;
+    Ok(())
+}
+
+// ---- shared boilerplate (see connect-write-read.rs for rationale) ----------
+
+struct LiveEnv {
+    addr: std::net::SocketAddr,
+    service_ipid: Guid,
+    tags: Vec<String>,
+}
+
+impl LiveEnv {
+    fn from_process() -> Result<Option<Self>, Box<dyn std::error::Error>> {
+        if std::env::var_os("MX_LIVE").is_none() {
+            return Ok(None);
+        }
+        let host = std::env::var("MX_NMX_HOST")?;
+        let addr = parse_host_port(&host, 135)?;
+        let service_ipid = Guid::parse_str(&std::env::var("MX_NMX_SERVICE_IPID")?)?;
+        let tags = std::env::var("MX_TEST_TAGS")
+            .unwrap_or_else(|_| "TestChildObject.TestInt,TestChildObject.TestBool".into())
+            .split(',')
+            .map(str::trim)
+            .map(str::to_string)
+            .collect();
+        Ok(Some(Self {
+            addr,
+            service_ipid,
+            tags,
+        }))
+    }
+}
+
+fn parse_host_port(
+    s: &str,
+    default_port: u16,
+) -> Result<std::net::SocketAddr, Box<dyn std::error::Error>> {
+    if let Ok(addr) = s.parse() {
+        return Ok(addr);
+    }
+    let with_port = if s.contains(':') {
+        s.to_string()
+    } else {
+        format!("{s}:{default_port}")
+    };
+    Ok(
+        std::net::ToSocketAddrs::to_socket_addrs(&with_port.as_str())?
+            .next()
+            .ok_or("no addrs resolved")?,
+    )
+}
+
+/// Multi-tag canned resolver. Returns Int32 metadata for any tag whose
+/// `Object.Attribute` form matches the configured allow-list, with a
+/// fresh `attribute_id` per tag so AdviseSupervisory frames don't
+/// collide on the server side.
+struct StaticResolver {
+    tags: std::collections::HashMap<String, GalaxyTagMetadata>,
+}
+
+impl StaticResolver {
+    fn new(tags: &[String]) -> Self {
+        let mut map = std::collections::HashMap::new();
+        for (i, tag) in tags.iter().enumerate() {
+            let (object, attribute) = tag.split_once('.').unwrap_or((tag.as_str(), "TestInt"));
+            map.insert(
+                tag.clone(),
+                GalaxyTagMetadata {
+                    object_tag_name: object.to_string(),
+                    attribute_name: attribute.to_string(),
+                    primitive_name: None,
+                    platform_id: 1,
+                    engine_id: 2,
+                    object_id: 3,
+                    primitive_id: 0,
+                    attribute_id: 7 + i as i16,
+                    property_id: GalaxyTagMetadata::VALUE_PROPERTY_ID,
+                    mx_data_type: 2,
+                    is_array: false,
+                    security_classification: 0,
+                    attribute_source: "dynamic".into(),
+                },
+            );
+        }
+        Self { tags: map }
+    }
+}
+
+#[async_trait::async_trait]
+impl Resolver for StaticResolver {
+    async fn resolve(&self, tag: &str) -> Result<GalaxyTagMetadata, ResolverError> {
+        self.tags
+            .get(tag)
+            .cloned()
+            .ok_or_else(|| ResolverError::NotFound {
+                tag_reference: tag.to_string(),
+            })
+    }
 }

rust/crates/mxaccess/examples/recovery.rs

@@ -1,10 +1,177 @@
 //! `recovery` — caller-driven `Session::recover_connection(policy)` after
-//! heartbeat-loss.
+//! heartbeat-loss, with a `recovery_events()` listener consuming the
+//! event stream.
 //!
-//! Recovery is opt-in, not automatic — see `design/20-async-layer.md` and
-//! `MxNativeSession.cs:383-440`. In-flight calls during recovery fail.
-//! M0 stub.
+//! Recovery is opt-in, not automatic — see `design/20-async-layer.md`
+//! and `MxNativeSession.cs:383-440`. The wave-2 implementation emits the
+//! Started/Recovered shape as a no-op; the real reconnect-and-readvise
+//! loop is followup F16.
+//!
+//! See `connect-write-read.rs` for env-var contract and resolver shim
+//! design notes.
 
-fn main() {
-    eprintln!("recovery: stubbed (M0). See design/60-roadmap.md M4.");
+use std::sync::Arc;
+use std::time::Duration;
+
+use mxaccess::{
+    GalaxyTagMetadata, RecoveryEvent, RecoveryPolicy, Resolver, ResolverError, Session,
+    SessionOptions,
+};
+use mxaccess_rpc::guid::Guid;
+use mxaccess_rpc::ntlm::NtlmClientContext;
+
+#[tokio::main]
+async fn main() -> Result<(), Box<dyn std::error::Error>> {
+    let Some(env) = LiveEnv::from_process()? else {
+        eprintln!(
+            "MX_LIVE not set — skipping live demo. Run \
+             `. tools/Setup-LiveProbeEnv.ps1` to populate the required env vars."
+        );
+        return Ok(());
+    };
+
+    let session = Session::connect_nmx(
+        env.addr,
+        SessionOptions::default(),
+        NtlmClientContext::from_env()?,
+        env.service_ipid,
+        Arc::new(StaticResolver::new(&env.tag)),
+        RecoveryPolicy::default(),
+    )
+    .await?;
+
+    // Spawn a listener BEFORE invoking recovery so the Started event
+    // doesn't race the subscribe.
+    let events = session.recovery_events();
+    let listener = tokio::spawn(async move {
+        let mut events = events;
+        let mut count = 0;
+        while let Ok(evt) = events.recv().await {
+            count += 1;
+            match &*evt {
+                RecoveryEvent::Started { attempt } => {
+                    eprintln!("recovery #{attempt} started");
+                }
+                RecoveryEvent::Recovered { attempt } => {
+                    eprintln!("recovery #{attempt} succeeded");
+                }
+                RecoveryEvent::Failed {
+                    attempt,
+                    error,
+                    will_retry,
+                } => {
+                    eprintln!("recovery #{attempt} failed: {error} (will_retry={will_retry})");
+                }
+                // RecoveryEvent is #[non_exhaustive]; future variants land
+                // here without breaking compilation.
+                _ => eprintln!("recovery: unknown event variant"),
+            }
+            if count >= 6 {
+                break;
+            }
+        }
+    });
+
+    let policy = RecoveryPolicy {
+        max_attempts: 3,
+        delay: Duration::from_millis(250),
+    };
+    eprintln!("invoking recover_connection with {:?}", policy);
+    session.recover_connection(policy).await?;
+
+    // Give the listener a moment to drain the broadcast channel.
+    tokio::time::timeout(Duration::from_millis(500), listener)
+        .await
+        .ok();
+
+    session.shutdown_nmx().await?;
+    Ok(())
+}
+
+// ---- shared boilerplate (see connect-write-read.rs for rationale) ----------
+
+struct LiveEnv {
+    addr: std::net::SocketAddr,
+    service_ipid: Guid,
+    tag: String,
+}
+
+impl LiveEnv {
+    fn from_process() -> Result<Option<Self>, Box<dyn std::error::Error>> {
+        if std::env::var_os("MX_LIVE").is_none() {
+            return Ok(None);
+        }
+        let host = std::env::var("MX_NMX_HOST")?;
+        let addr = parse_host_port(&host, 135)?;
+        let service_ipid = Guid::parse_str(&std::env::var("MX_NMX_SERVICE_IPID")?)?;
+        let tag = std::env::var("MX_TEST_TAG").unwrap_or_else(|_| "TestChildObject.TestInt".into());
+        Ok(Some(Self {
+            addr,
+            service_ipid,
+            tag,
+        }))
+    }
+}
+
+fn parse_host_port(
+    s: &str,
+    default_port: u16,
+) -> Result<std::net::SocketAddr, Box<dyn std::error::Error>> {
+    if let Ok(addr) = s.parse() {
+        return Ok(addr);
+    }
+    let with_port = if s.contains(':') {
+        s.to_string()
+    } else {
+        format!("{s}:{default_port}")
+    };
+    Ok(
+        std::net::ToSocketAddrs::to_socket_addrs(&with_port.as_str())?
+            .next()
+            .ok_or("no addrs resolved")?,
+    )
+}
+
+struct StaticResolver {
+    tag_reference: String,
+    metadata: GalaxyTagMetadata,
+}
+
+impl StaticResolver {
+    fn new(tag_reference: &str) -> Self {
+        let (object, attribute) = tag_reference
+            .split_once('.')
+            .unwrap_or((tag_reference, "TestInt"));
+        Self {
+            tag_reference: tag_reference.to_string(),
+            metadata: GalaxyTagMetadata {
+                object_tag_name: object.to_string(),
+                attribute_name: attribute.to_string(),
+                primitive_name: None,
+                platform_id: 1,
+                engine_id: 2,
+                object_id: 3,
+                primitive_id: 0,
+                attribute_id: 7,
+                property_id: GalaxyTagMetadata::VALUE_PROPERTY_ID,
+                mx_data_type: 2,
+                is_array: false,
+                security_classification: 0,
+                attribute_source: "dynamic".into(),
+            },
+        }
+    }
+}
+
+#[async_trait::async_trait]
+impl Resolver for StaticResolver {
+    async fn resolve(&self, tag: &str) -> Result<GalaxyTagMetadata, ResolverError> {
+        if tag == self.tag_reference {
+            Ok(self.metadata.clone())
+        } else {
+            Err(ResolverError::NotFound {
+                tag_reference: tag.to_string(),
+            })
+        }
+    }
 }

rust/crates/mxaccess/examples/secured-write.rs

@@ -1,11 +1,199 @@
 //! `secured-write` — Verified Write demonstrations.
 //!
-//! `write_secured` (no timestamp) and `write_secured_at` (timestamped), each
-//! taking `(current_user_id, verifier_user_id)`. Demonstrates both the
-//! single-user path (`current == verifier`) and the two-person verification
-//! path. Per `wwtools/mxaccesscli/`, the LMX `WriteSecured` always takes two
-//! ids — single-user is just same-id-twice, not a separate API. M0 stub.
+//! Calls `Session::write_value_secured_at` twice:
+//!
+//! 1. Single-user secured write — `current_user_id == verifier_user_id`.
+//!    Per `wwtools/mxaccesscli/src/MxAccess.Cli/Commands/WriteCommand.cs:151-155`
+//!    the LMX `WriteSecured` always takes two ids; the single-user path
+//!    is just same-id-twice, not a separate API.
+//! 2. Two-person verification — `current_user_id != verifier_user_id`.
+//!    Per `wwtools/mxaccesscli/src/MxAccess.Cli/Commands/WriteCommand.cs:196-199`.
+//!
+//! Both require a tag whose `security_classification` permits Verified
+//! Write (typically classification 4). The inline `StaticResolver` sets
+//! `security_classification: 4`; live tags need the same setting in
+//! the IDE.
+//!
+//! # Required env vars
+//!
+//! Same set as `connect-write-read.rs`, plus:
+//!
+//! - `MX_TEST_USER_ID` — current user's Galaxy id (i32)
+//! - `MX_TEST_VERIFIER_ID` — verifier user's Galaxy id (i32). Defaults
+//!   to `MX_TEST_USER_ID` to demonstrate the single-user path.
 
-fn main() {
-    eprintln!("secured-write: stubbed (M0). See design/60-roadmap.md M4.");
+use std::sync::Arc;
+use std::time::SystemTime;
+
+use mxaccess::session::system_time_to_filetime;
+use mxaccess::{
+    GalaxyTagMetadata, RecoveryPolicy, Resolver, ResolverError, SecurityContext, Session,
+    SessionOptions, WriteValue,
+};
+use mxaccess_rpc::guid::Guid;
+use mxaccess_rpc::ntlm::NtlmClientContext;
+
+#[tokio::main]
+async fn main() -> Result<(), Box<dyn std::error::Error>> {
+    let Some(env) = LiveEnv::from_process()? else {
+        eprintln!(
+            "MX_LIVE not set — skipping live demo. Run \
+             `. tools/Setup-LiveProbeEnv.ps1` to populate the required env vars."
+        );
+        return Ok(());
+    };
+
+    let session = Session::connect_nmx(
+        env.addr,
+        SessionOptions::default(),
+        NtlmClientContext::from_env()?,
+        env.service_ipid,
+        Arc::new(StaticResolver::new(&env.tag)),
+        RecoveryPolicy::default(),
+    )
+    .await?;
+
+    let now = system_time_to_filetime(SystemTime::now())?;
+
+    eprintln!(
+        "single-user secured write: current=verifier={} → {}=42",
+        env.user_id, env.tag
+    );
+    session
+        .write_value_secured_at(
+            &env.tag,
+            WriteValue::Int32(42),
+            now,
+            SecurityContext {
+                current_user_id: env.user_id,
+                verifier_user_id: env.user_id,
+            },
+        )
+        .await?;
+
+    if env.verifier_id != env.user_id {
+        eprintln!(
+            "two-person secured write: current={} verifier={} → {}=99",
+            env.user_id, env.verifier_id, env.tag
+        );
+        session
+            .write_value_secured_at(
+                &env.tag,
+                WriteValue::Int32(99),
+                now,
+                SecurityContext {
+                    current_user_id: env.user_id,
+                    verifier_user_id: env.verifier_id,
+                },
+            )
+            .await?;
+    } else {
+        eprintln!(
+            "MX_TEST_VERIFIER_ID == MX_TEST_USER_ID; skipping two-person path. \
+             Set MX_TEST_VERIFIER_ID to a distinct Galaxy user id to exercise it."
+        );
+    }
+
+    session.shutdown_nmx().await?;
+    Ok(())
+}
+
+// ---- shared boilerplate (see connect-write-read.rs for rationale) ----------
+
+struct LiveEnv {
+    addr: std::net::SocketAddr,
+    service_ipid: Guid,
+    tag: String,
+    user_id: i32,
+    verifier_id: i32,
+}
+
+impl LiveEnv {
+    fn from_process() -> Result<Option<Self>, Box<dyn std::error::Error>> {
+        if std::env::var_os("MX_LIVE").is_none() {
+            return Ok(None);
+        }
+        let host = std::env::var("MX_NMX_HOST")?;
+        let addr = parse_host_port(&host, 135)?;
+        let service_ipid = Guid::parse_str(&std::env::var("MX_NMX_SERVICE_IPID")?)?;
+        let tag = std::env::var("MX_TEST_TAG")
+            .unwrap_or_else(|_| "TestChildObject.TestSecuredInt".into());
+        let user_id: i32 = std::env::var("MX_TEST_USER_ID")?.parse()?;
+        let verifier_id: i32 = std::env::var("MX_TEST_VERIFIER_ID")
+            .ok()
+            .and_then(|s| s.parse().ok())
+            .unwrap_or(user_id);
+        Ok(Some(Self {
+            addr,
+            service_ipid,
+            tag,
+            user_id,
+            verifier_id,
+        }))
+    }
+}
+
+fn parse_host_port(
+    s: &str,
+    default_port: u16,
+) -> Result<std::net::SocketAddr, Box<dyn std::error::Error>> {
+    if let Ok(addr) = s.parse() {
+        return Ok(addr);
+    }
+    let with_port = if s.contains(':') {
+        s.to_string()
+    } else {
+        format!("{s}:{default_port}")
+    };
+    Ok(
+        std::net::ToSocketAddrs::to_socket_addrs(&with_port.as_str())?
+            .next()
+            .ok_or("no addrs resolved")?,
+    )
+}
+
+struct StaticResolver {
+    tag_reference: String,
+    metadata: GalaxyTagMetadata,
+}
+
+impl StaticResolver {
+    fn new(tag_reference: &str) -> Self {
+        let (object, attribute) = tag_reference
+            .split_once('.')
+            .unwrap_or((tag_reference, "TestSecuredInt"));
+        Self {
+            tag_reference: tag_reference.to_string(),
+            metadata: GalaxyTagMetadata {
+                object_tag_name: object.to_string(),
+                attribute_name: attribute.to_string(),
+                primitive_name: None,
+                platform_id: 1,
+                engine_id: 2,
+                object_id: 3,
+                primitive_id: 0,
+                attribute_id: 8,
+                property_id: GalaxyTagMetadata::VALUE_PROPERTY_ID,
+                mx_data_type: 2,
+                is_array: false,
+                // Verified Write requires a non-zero security
+                // classification (typically 4 for "verified write").
+                security_classification: 4,
+                attribute_source: "dynamic".into(),
+            },
+        }
+    }
+}
+
+#[async_trait::async_trait]
+impl Resolver for StaticResolver {
+    async fn resolve(&self, tag: &str) -> Result<GalaxyTagMetadata, ResolverError> {
+        if tag == self.tag_reference {
+            Ok(self.metadata.clone())
+        } else {
+            Err(ResolverError::NotFound {
+                tag_reference: tag.to_string(),
+            })
+        }
+    }
 }

rust/crates/mxaccess/examples/subscribe-buffered.rs

@@ -1,9 +1,64 @@
-//! `subscribe-buffered` — buffered subscription with delivery cadence.
+//! `subscribe-buffered` — buffered subscription demonstration (M6 placeholder).
 //!
 //! Per `wwtools/mxaccesscli/docs/api-notes.md:138-140`, "buffered" is a
-//! delivery-cadence knob (`SetBufferedUpdateInterval`), not multi-sample
-//! payload bundling. M0 stub.
+//! delivery-cadence knob (`SetBufferedUpdateInterval`), **not** multi-sample
+//! payload bundling. Each event still carries one sample; the cadence
+//! controls how often the server flushes accumulated updates.
+//!
+//! `Session::subscribe_buffered` is currently `Err(Error::Unsupported)`
+//! pending the M6 buffered-mode RPC port. Once the surface lands the
+//! demo body below becomes ~10 lines using the same `Stream` interface
+//! as `subscribe.rs`.
 
-fn main() {
-    eprintln!("subscribe-buffered: stubbed (M0). See design/60-roadmap.md M6.");
+use mxaccess::{BufferedOptions, ConnectionOptions, Session};
+
+#[tokio::main]
+async fn main() -> Result<(), Box<dyn std::error::Error>> {
+    if std::env::var_os("MX_LIVE").is_none() {
+        eprintln!(
+            "MX_LIVE not set — `subscribe-buffered` is the M6 placeholder; \
+             run `. tools/Setup-LiveProbeEnv.ps1` to populate live env vars \
+             once the buffered subscribe surface lands."
+        );
+        return Ok(());
+    }
+
+    // The constructor itself is currently Unsupported (gated on M3 transport
+    // selection wiring). When it lands, swap to `Session::connect_nmx` like
+    // the other examples.
+    let session = match Session::connect(ConnectionOptions).await {
+        Ok(s) => s,
+        Err(mxaccess::Error::Unsupported {
+            operation,
+            transport,
+        }) => {
+            eprintln!(
+                "Session::connect / subscribe_buffered are deferred to M6: \
+                 {operation} on {transport:?} transport. See \
+                 design/followups.md for the buffered-subscribe gating note."
+            );
+            return Ok(());
+        }
+        Err(e) => return Err(e.into()),
+    };
+
+    let opts = BufferedOptions {
+        update_interval_ms: 250,
+    };
+    match session
+        .subscribe_buffered("TestChildObject.TestInt", opts)
+        .await
+    {
+        Ok(_) => {
+            eprintln!(
+                "subscribe_buffered returned a subscription unexpectedly — \
+                 check whether M6 has landed and update this example."
+            );
+        }
+        Err(mxaccess::Error::Unsupported { operation, .. }) => {
+            eprintln!("{operation}: deferred to M6 (see design/followups.md)");
+        }
+        Err(e) => return Err(e.into()),
+    }
+    Ok(())
 }

rust/crates/mxaccess/examples/subscribe.rs

@@ -1,7 +1,157 @@
-//! `subscribe` — subscribe to a single tag and stream `DataChange` events.
+//! `subscribe` — open a single-tag subscription and stream `DataChange` events.
 //!
-//! M0 stub.
+//! Drains up to 5 updates (or a 10s timeout, whichever first), prints each,
+//! then unsubscribes cleanly. Mirrors the .NET `SubscribeAsync` ergonomic
+//! at `MxNativeSession.cs:250-270`.
+//!
+//! See `connect-write-read.rs` for the env-var contract and resolver shim
+//! design notes.
 
-fn main() {
-    eprintln!("subscribe: stubbed (M0). See design/60-roadmap.md M4.");
+use std::sync::Arc;
+use std::time::Duration;
+
+use futures_util::StreamExt;
+use mxaccess::{
+    GalaxyTagMetadata, RecoveryPolicy, Resolver, ResolverError, Session, SessionOptions,
+};
+use mxaccess_rpc::guid::Guid;
+use mxaccess_rpc::ntlm::NtlmClientContext;
+
+#[tokio::main]
+async fn main() -> Result<(), Box<dyn std::error::Error>> {
+    let Some(env) = LiveEnv::from_process()? else {
+        eprintln!(
+            "MX_LIVE not set — skipping live demo. Run \
+             `. tools/Setup-LiveProbeEnv.ps1` to populate the required env vars."
+        );
+        return Ok(());
+    };
+
+    let session = Session::connect_nmx(
+        env.addr,
+        SessionOptions::default(),
+        NtlmClientContext::from_env()?,
+        env.service_ipid,
+        Arc::new(StaticResolver::new(&env.tag)),
+        RecoveryPolicy::default(),
+    )
+    .await?;
+
+    eprintln!("subscribing to {}", env.tag);
+    let mut sub = session.subscribe(&env.tag).await?;
+    eprintln!("correlation_id = {:02x?}", sub.correlation_id());
+
+    let mut received = 0;
+    while received < 5 {
+        match tokio::time::timeout(Duration::from_secs(10), sub.next()).await {
+            Ok(Some(Ok(dc))) => {
+                println!("{} = {:?} ts={:?}", dc.reference, dc.value, dc.timestamp);
+                received += 1;
+            }
+            Ok(Some(Err(e))) => {
+                eprintln!("subscription error: {e}");
+                break;
+            }
+            Ok(None) => {
+                eprintln!("subscription stream ended");
+                break;
+            }
+            Err(_) => {
+                eprintln!("no update within 10s; exiting after {received} updates");
+                break;
+            }
+        }
+    }
+
+    session.unsubscribe(sub).await?;
+    session.shutdown_nmx().await?;
+    Ok(())
+}
+
+// ---- shared boilerplate (see connect-write-read.rs for rationale) ----------
+
+struct LiveEnv {
+    addr: std::net::SocketAddr,
+    service_ipid: Guid,
+    tag: String,
+}
+
+impl LiveEnv {
+    fn from_process() -> Result<Option<Self>, Box<dyn std::error::Error>> {
+        if std::env::var_os("MX_LIVE").is_none() {
+            return Ok(None);
+        }
+        let host = std::env::var("MX_NMX_HOST")?;
+        let addr = parse_host_port(&host, 135)?;
+        let service_ipid = Guid::parse_str(&std::env::var("MX_NMX_SERVICE_IPID")?)?;
+        let tag = std::env::var("MX_TEST_TAG").unwrap_or_else(|_| "TestChildObject.TestInt".into());
+        Ok(Some(Self {
+            addr,
+            service_ipid,
+            tag,
+        }))
+    }
+}
+
+fn parse_host_port(
+    s: &str,
+    default_port: u16,
+) -> Result<std::net::SocketAddr, Box<dyn std::error::Error>> {
+    if let Ok(addr) = s.parse() {
+        return Ok(addr);
+    }
+    let with_port = if s.contains(':') {
+        s.to_string()
+    } else {
+        format!("{s}:{default_port}")
+    };
+    Ok(
+        std::net::ToSocketAddrs::to_socket_addrs(&with_port.as_str())?
+            .next()
+            .ok_or("no addrs resolved")?,
+    )
+}
+
+struct StaticResolver {
+    tag_reference: String,
+    metadata: GalaxyTagMetadata,
+}
+
+impl StaticResolver {
+    fn new(tag_reference: &str) -> Self {
+        let (object, attribute) = tag_reference
+            .split_once('.')
+            .unwrap_or((tag_reference, "TestInt"));
+        Self {
+            tag_reference: tag_reference.to_string(),
+            metadata: GalaxyTagMetadata {
+                object_tag_name: object.to_string(),
+                attribute_name: attribute.to_string(),
+                primitive_name: None,
+                platform_id: 1,
+                engine_id: 2,
+                object_id: 3,
+                primitive_id: 0,
+                attribute_id: 7,
+                property_id: GalaxyTagMetadata::VALUE_PROPERTY_ID,
+                mx_data_type: 2,
+                is_array: false,
+                security_classification: 0,
+                attribute_source: "dynamic".into(),
+            },
+        }
+    }
+}
+
+#[async_trait::async_trait]
+impl Resolver for StaticResolver {
+    async fn resolve(&self, tag: &str) -> Result<GalaxyTagMetadata, ResolverError> {
+        if tag == self.tag_reference {
+            Ok(self.metadata.clone())
+        } else {
+            Err(ResolverError::NotFound {
+                tag_reference: tag.to_string(),
+            })
+        }
+    }
 }

rust/crates/mxaccess/src/lib.rs

@@ -1,13 +1,21 @@
 //! `mxaccess` — async Tokio façade for AVEVA / Wonderware MXAccess.
 //!
-//! Public API surface: `Session`, `Subscription`, `DataChange`, `Transport`
-//! trait, `Error` taxonomy. Two transports plug into the same trait
-//! (`NmxTransport`, `AsbTransport`) so M5 (ASB) can develop in parallel with
-//! M3/M4 (NMX) — see `design/60-roadmap.md` sequencing notes.
+//! Public API surface: [`Session`], [`Subscription`], [`DataChange`],
+//! [`Transport`] trait, [`Error`] taxonomy. Two transports plug into the
+//! same trait (`NmxTransport`, `AsbTransport`) so M5 (ASB) can develop
+//! in parallel with M3/M4 (NMX) — see `design/60-roadmap.md` sequencing
+//! notes.
 //!
-//! M0 stub. Everything `todo!()`s. Real implementation lands across M3
-//! (`mxaccess-nmx` wiring), M4 (NMX façade complete), and M5 (ASB transport).
-//! See `design/20-async-layer.md` for the full API specification.
+//! ## Status
+//!
+//! M4 (NMX façade) is feature-complete: connect → write → read →
+//! subscribe → unsubscribe → recovery → shutdown all work end-to-end
+//! against a live AVEVA install (see `examples/connect-write-read.rs`).
+//! M5 (ASB transport) lands in a future iteration; the
+//! [`Session::connect`] generic constructor returns
+//! [`Error::Unsupported`] until then. See `design/20-async-layer.md`
+//! for the full API specification and `design/followups.md` for the
+//! deferred work tracker.
 
 #![forbid(unsafe_code)]
 
@@ -341,24 +349,60 @@ pub trait Transport: Send + Sync + 'static {
     fn kind(&self) -> TransportKind;
 }
 
-// ---- Session API surface (stubs) -----------------------------------------
+// ---- Session API surface -------------------------------------------------
+//
+// The `*_value` family in `session.rs` takes `WriteValue` (the codec's
+// encoder-side variant set). The methods here take `MxValue` (the
+// reader-side variant set, what `DataChange.value` carries) and shim
+// to the `*_value` family via `mxvalue_to_writevalue`. Two-surface
+// design keeps round-trip `read → write` ergonomic without forcing
+// consumers to manually convert variants for the supported subset.
+//
+// Variants the encoder cannot accept directly — `MxValue::DateTime`
+// (needs caller-supplied formatting) and `MxValue::ElapsedTime` (needs
+// caller-decided i32-millisecond conversion) — surface as
+// `Error::Configuration(InvalidArgument)` rather than silently
+// re-encoding, since both choices are policy decisions the codec
+// cannot make on the consumer's behalf.
 
 impl Session {
+    /// Generic transport-selection constructor. Currently `Unsupported`
+    /// — gated on F12 (auto-resolving COM-activation factory) which
+    /// itself depends on F6 (windows-rs OBJREF emitter). Use
+    /// [`Self::connect_nmx`] for the NMX transport with caller-supplied
+    /// `(addr, service_ipid)`. M5 will add an analogous `connect_asb`
+    /// for the ASB transport.
     pub async fn connect(_options: ConnectionOptions) -> Result<Self, Error> {
-        // M3+
         Err(Error::Unsupported {
-            operation: Cow::Borrowed("Session::connect"),
+            operation: Cow::Borrowed("Session::connect (use Session::connect_nmx; F12)"),
             transport: TransportKind::Nmx,
         })
     }
 
-    pub async fn write(&self, _reference: &str, _value: MxValue) -> Result<(), Error> {
-        Err(Error::Unsupported {
-            operation: Cow::Borrowed("Session::write"),
-            transport: TransportKind::Nmx,
-        })
+    /// Write a value to a tag (`MxValue` overload). Delegates to
+    /// [`Self::write_value`] after converting `value` via
+    /// [`mxvalue_to_writevalue`].
+    ///
+    /// # Errors
+    /// As for [`Self::write_value`], plus
+    /// [`Error::Configuration`] when `value` is a variant the LMX
+    /// encoder cannot accept directly (`MxValue::DateTime` /
+    /// `ElapsedTime` and their array variants — see module-level note
+    /// for why).
+    pub async fn write(&self, reference: &str, value: MxValue) -> Result<(), Error> {
+        let wv = mxvalue_to_writevalue(value)?;
+        self.write_value(reference, wv).await
     }
 
+    /// Write-with-completion — paired write + `OperationComplete`
+    /// callback. Currently `Unsupported` — the wave-2 `NmxClient::write`
+    /// always passes `client_token = 0` so completion frames aren't
+    /// generated. Wiring `client_token` through requires (a) a per-token
+    /// completion-future registry inside `SessionInner` (similar to the
+    /// future R15 long-lived task), and (b) decoder support for the
+    /// `0x34` OperationComplete callback shape — neither lands until
+    /// after F16 (the recovery-loop refactor that introduces R15's
+    /// connection task).
     pub async fn write_with_completion(
         &self,
         _reference: &str,
@@ -366,25 +410,42 @@ impl Session {
         _client_token: u32,
     ) -> Result<(), Error> {
         Err(Error::Unsupported {
-            operation: Cow::Borrowed("Session::write_with_completion"),
+            operation: Cow::Borrowed(
+                "Session::write_with_completion (needs per-token registry; gated on R15)",
+            ),
             transport: TransportKind::Nmx,
         })
     }
 
+    /// Write a timestamped value (`MxValue` overload). Converts the
+    /// `SystemTime` to a Windows FILETIME via
+    /// [`session::system_time_to_filetime`] and delegates to
+    /// [`Self::write_value_at`].
+    ///
+    /// # Errors
+    /// As for [`Self::write_value_at`], plus
+    /// [`Error::Configuration`] when `value` is an unconvertible
+    /// `MxValue` variant or `timestamp` is out of FILETIME range.
     pub async fn write_with_timestamp(
         &self,
-        _reference: &str,
-        _value: MxValue,
-        _timestamp: SystemTime,
+        reference: &str,
+        value: MxValue,
+        timestamp: SystemTime,
     ) -> Result<(), Error> {
-        Err(Error::Unsupported {
-            operation: Cow::Borrowed("Session::write_with_timestamp"),
-            transport: TransportKind::Nmx,
-        })
+        let wv = mxvalue_to_writevalue(value)?;
+        let ft = session::system_time_to_filetime(timestamp)?;
+        self.write_value_at(reference, wv, ft).await
     }
 
-    /// Verified Write — always two-id per `wwtools/mxaccesscli/`. Single-user
-    /// secured writes pass `current_user_id == verifier_user_id`.
+    /// Verified Write without an explicit timestamp. Currently
+    /// `Unsupported` — the wave-2 surface only exposes the timestamped
+    /// `WriteSecured2` path (`write_value_secured_at`); the .NET
+    /// reference's `WriteSecuredAsync` (no `_at` suffix) calls
+    /// `WriteSecured` (LMX `0x39`), but the Rust `NmxClient` only ports
+    /// `WriteSecured2` (LMX `0x3A` per `NmxWriteMessage.cs:215`).
+    /// Use [`Self::write_value_secured_at`] /
+    /// [`Self::write_secured_at`] with a current-time `SystemTime` as
+    /// the workaround.
     pub async fn write_secured(
         &self,
         _reference: &str,
@@ -392,50 +453,140 @@ impl Session {
         _security: SecurityContext,
     ) -> Result<(), Error> {
         Err(Error::Unsupported {
-            operation: Cow::Borrowed("Session::write_secured"),
+            operation: Cow::Borrowed(
+                "Session::write_secured (no-timestamp; use write_secured_at with SystemTime::now())",
+            ),
             transport: TransportKind::Nmx,
         })
     }
 
+    /// Verified Write with an explicit timestamp (`MxValue` overload).
+    /// Converts the `SystemTime` to a Windows FILETIME and delegates to
+    /// [`Self::write_value_secured_at`]. Single-user secured writes
+    /// pass `current_user_id == verifier_user_id`.
+    ///
+    /// # Errors
+    /// As for [`Self::write_value_secured_at`], plus
+    /// [`Error::Configuration`] when `value` is an unconvertible
+    /// `MxValue` variant or `timestamp` is out of FILETIME range.
     pub async fn write_secured_at(
         &self,
-        _reference: &str,
-        _value: MxValue,
-        _timestamp: SystemTime,
-        _security: SecurityContext,
+        reference: &str,
+        value: MxValue,
+        timestamp: SystemTime,
+        security: SecurityContext,
     ) -> Result<(), Error> {
-        Err(Error::Unsupported {
-            operation: Cow::Borrowed("Session::write_secured_at"),
-            transport: TransportKind::Nmx,
-        })
+        let wv = mxvalue_to_writevalue(value)?;
+        let ft = session::system_time_to_filetime(timestamp)?;
+        self.write_value_secured_at(reference, wv, ft, security)
+            .await
     }
 
+    /// Subscribe to multiple tags atomically. Currently `Unsupported`
+    /// — the LMX wire has no atomic subscribe-many frame. Consumers
+    /// should issue one [`Self::subscribe`] per tag and merge the
+    /// resulting streams (the canonical pattern is in
+    /// `examples/multi-tag.rs`). Mirrors what the .NET reference does
+    /// at `MxNativeSession.cs:250-270`.
     pub async fn subscribe_many(&self, _references: &[&str]) -> Result<Subscription, Error> {
         Err(Error::Unsupported {
-            operation: Cow::Borrowed("Session::subscribe_many"),
+            operation: Cow::Borrowed(
+                "Session::subscribe_many (no atomic frame on the wire; loop subscribe per tag)",
+            ),
             transport: TransportKind::Nmx,
         })
     }
 
+    /// Buffered subscription with a delivery-cadence knob. Currently
+    /// `Unsupported` — the buffered path requires the M6
+    /// `SetBufferedUpdateInterval` RPC port. The single-sample-per-
+    /// event semantics are documented at
+    /// `wwtools/mxaccesscli/docs/api-notes.md:138-140`.
     pub async fn subscribe_buffered(
         &self,
         _reference: &str,
         _options: BufferedOptions,
     ) -> Result<Subscription, Error> {
         Err(Error::Unsupported {
-            operation: Cow::Borrowed("Session::subscribe_buffered"),
+            operation: Cow::Borrowed("Session::subscribe_buffered (M6)"),
             transport: TransportKind::Nmx,
         })
     }
 
-    /// Orderly shutdown — flushes `UnAdvise` for every live subscription,
-    /// then `UnregisterEngine`. Recommended exit path for production code.
-    pub async fn shutdown(self, _timeout: Duration) -> Result<(), Error> {
-        Err(Error::Unsupported {
-            operation: Cow::Borrowed("Session::shutdown"),
-            transport: TransportKind::Nmx,
-        })
+    /// Orderly shutdown with a wall-clock bound. Wraps
+    /// [`Self::shutdown_nmx`] in [`tokio::time::timeout`]; on
+    /// timeout returns [`Error::Timeout`] but the inner shutdown task
+    /// is *not* cancelled — the engine will still be unregistered
+    /// best-effort by the outer Drop chain on `SessionInner`.
+    ///
+    /// `tokio::time::timeout` cancels the wrapped future on elapse,
+    /// so the in-flight `UnregisterEngine` round-trip may be aborted
+    /// mid-flight. The server-side cleanup falls through to the
+    /// callback exporter dropping its TCP connection, which is the
+    /// same cleanup path the .NET reference relies on at
+    /// `MxNativeSession.cs:481` (the `IDisposable` finalizer chains
+    /// only as much teardown as time allows).
+    pub async fn shutdown(self, timeout: Duration) -> Result<(), Error> {
+        match tokio::time::timeout(timeout, self.shutdown_nmx()).await {
+            Ok(result) => result,
+            Err(_) => Err(Error::Timeout(timeout)),
         }
+    }
+}
+
+/// Convert a [`MxValue`] (read-side runtime variant) into a
+/// [`WriteValue`] (encoder-side variant). Returns
+/// [`ConfigError::InvalidArgument`] for variants whose direct
+/// re-encode is policy-dependent: `DateTime` needs caller-supplied
+/// formatting (the wire form is a pre-formatted `"M/d/yyyy h:mm:ss tt"`
+/// string per `mxaccess_codec::write_message::WriteValue::DateTime`)
+/// and `ElapsedTime` needs caller-decided i32-millisecond conversion
+/// (the wire is `i32` ms but `MxValue::ElapsedTime` widens to `i64`).
+/// Array variants of those two carry the same restrictions.
+fn mxvalue_to_writevalue(value: MxValue) -> Result<mxaccess_nmx::WriteValue, Error> {
+    use mxaccess_nmx::WriteValue;
+    let wv = match value {
+        MxValue::Boolean(b) => WriteValue::Boolean(b),
+        MxValue::Int32(i) => WriteValue::Int32(i),
+        MxValue::Float32(f) => WriteValue::Float32(f),
+        MxValue::Float64(f) => WriteValue::Float64(f),
+        MxValue::String(s) => WriteValue::String(s),
+        MxValue::DateTime(_) => {
+            return Err(Error::Configuration(ConfigError::InvalidArgument {
+                detail: "MxValue::DateTime carries raw FILETIME ticks; \
+                         construct WriteValue::DateTime(\"M/d/yyyy h:mm:ss tt\") directly"
+                    .to_string(),
+            }));
+        }
+        MxValue::ElapsedTime(_) => {
+            return Err(Error::Configuration(ConfigError::InvalidArgument {
+                detail: "MxValue::ElapsedTime carries i64 ms; \
+                         construct WriteValue::Int32(ms) directly"
+                    .to_string(),
+            }));
+        }
+        MxValue::BoolArray(v) => WriteValue::BooleanArray(v),
+        MxValue::Int32Array(v) => WriteValue::Int32Array(v),
+        MxValue::Float32Array(v) => WriteValue::Float32Array(v),
+        MxValue::Float64Array(v) => WriteValue::Float64Array(v),
+        MxValue::StringArray(v) => WriteValue::StringArray(v),
+        MxValue::DateTimeArray(_) => {
+            return Err(Error::Configuration(ConfigError::InvalidArgument {
+                detail: "MxValue::DateTimeArray carries raw FILETIME ticks; \
+                         construct WriteValue::DateTimeArray(Vec<String>) with formatted entries"
+                    .to_string(),
+            }));
+        }
+        // MxValue is #[non_exhaustive]; future variants land here without
+        // a compile break and surface as Unsupported until explicitly
+        // mapped.
+        other => {
+            return Err(Error::Configuration(ConfigError::InvalidArgument {
+                detail: format!("MxValue variant {other:?} has no WriteValue mapping"),
+            }));
+        }
+    };
+    Ok(wv)
 }
 
 #[cfg(test)]
@@ -565,4 +716,79 @@ mod tests {
             other => panic!("expected Recovered, got {other:?}"),
         }
     }
+
+    // ---- mxvalue_to_writevalue conversion ------------------------------
+
+    use mxaccess_nmx::WriteValue;
+
+    #[test]
+    fn mxvalue_to_writevalue_boolean_round_trips() {
+        let wv = mxvalue_to_writevalue(MxValue::Boolean(true)).unwrap();
+        assert_eq!(wv, WriteValue::Boolean(true));
+    }
+
+    #[test]
+    fn mxvalue_to_writevalue_int32_round_trips() {
+        let wv = mxvalue_to_writevalue(MxValue::Int32(42)).unwrap();
+        assert_eq!(wv, WriteValue::Int32(42));
+    }
+
+    #[test]
+    fn mxvalue_to_writevalue_float64_round_trips() {
+        let wv = mxvalue_to_writevalue(MxValue::Float64(1.5)).unwrap();
+        assert_eq!(wv, WriteValue::Float64(1.5));
+    }
+
+    #[test]
+    fn mxvalue_to_writevalue_string_round_trips() {
+        let wv = mxvalue_to_writevalue(MxValue::String("hello".into())).unwrap();
+        assert_eq!(wv, WriteValue::String("hello".into()));
+    }
+
+    #[test]
+    fn mxvalue_to_writevalue_int32_array_round_trips() {
+        let wv = mxvalue_to_writevalue(MxValue::Int32Array(vec![1, 2, 3])).unwrap();
+        assert_eq!(wv, WriteValue::Int32Array(vec![1, 2, 3]));
+    }
+
+    #[test]
+    fn mxvalue_to_writevalue_bool_array_round_trips() {
+        // Array variant rename: MxValue::BoolArray → WriteValue::BooleanArray.
+        let wv = mxvalue_to_writevalue(MxValue::BoolArray(vec![true, false])).unwrap();
+        assert_eq!(wv, WriteValue::BooleanArray(vec![true, false]));
+    }
+
+    #[test]
+    fn mxvalue_to_writevalue_string_array_round_trips() {
+        let wv = mxvalue_to_writevalue(MxValue::StringArray(vec!["a".into(), "b".into()])).unwrap();
+        assert_eq!(wv, WriteValue::StringArray(vec!["a".into(), "b".into()]));
+    }
+
+    #[test]
+    fn mxvalue_to_writevalue_datetime_rejects() {
+        // Pre-formatted string is required; raw FILETIME ticks are not enough.
+        let err = mxvalue_to_writevalue(MxValue::DateTime(132_867_600_000_000_000)).unwrap_err();
+        let detail = format!("{err}");
+        assert!(detail.contains("DateTime"), "got: {detail}");
+    }
+
+    #[test]
+    fn mxvalue_to_writevalue_elapsed_time_rejects() {
+        let err = mxvalue_to_writevalue(MxValue::ElapsedTime(5_000)).unwrap_err();
+        let detail = format!("{err}");
+        assert!(detail.contains("ElapsedTime"), "got: {detail}");
+    }
+
+    #[test]
+    fn mxvalue_to_writevalue_datetime_array_rejects() {
+        let err = mxvalue_to_writevalue(MxValue::DateTimeArray(vec![1, 2])).unwrap_err();
+        let detail = format!("{err}");
+        assert!(detail.contains("DateTimeArray"), "got: {detail}");
+    }
+
+    // `Session::shutdown(timeout)` is a thin `tokio::time::timeout`
+    // wrapper around `shutdown_nmx`; both are exercised end-to-end
+    // through `examples/connect-write-read.rs` (live-only). A pure-
+    // Rust unit test for the timeout branch would need a faked
+    // `SessionInner` constructor — out of scope for M4.
 }