Initial project state: .NET reference, design, Rust port (M0+M1), evidence

Layout:
- src/                    .NET 10 x64 reference: MxNativeCodec, MxNativeClient,
                          MxAsbClient, probes, tests, harnesses. Executable spec.
- design/                 Architectural plan for the Rust port (M0–M6), error
                          model, protocol invariants, risks (R1–R16), adversarial
                          review log (review.md).
- rust/                   Rust workspace. M0 skeleton + M1 codec parity.
                          mxaccess-codec: 215 unit tests + 2 cross-implementation
                          parity tests (byte-identical against .NET reference).
                          Other crates are M0 stubs awaiting M2+.
- captures/               Frida + netsh + pcap evidence per CLAUDE.md
                          ("captures are evidence, not throwaway logs").
- analysis/               Decompiled C# (frida/proxy/decompiled-*),
                          Ghidra exports for native DLLs (`exports/` only —
                          working state at `projects/` and AVEVA's input
                          binaries at `input/` are gitignored).
- docs/                   Reverse-engineering reference docs.
- tools/                  Setup-LiveProbeEnv.ps1 (Infisical credential fetcher),
                          Compute-Crc.ps1 (.NET parity helper).
- .github/workflows/      Rust CI: fmt + build + test + clippy on Windows.
- LICENSE                 MIT (Joseph Doherty, 2026).

Verified:
- cargo test --workspace → 217 passed (215 unit + 2 .NET parity), 0 failed
- cargo clippy --workspace -- -D warnings → clean
- cargo fmt --all -- --check → clean
- cargo publish --dry-run -p mxaccess-codec → packages cleanly

Excluded from history (see .gitignore):
- **/bin, **/obj, **/target — build artifacts
- analysis/ghidra/projects/ — Ghidra working state (regenerable)
- analysis/ghidra/input/ — AVEVA proprietary DLLs (vendor IP)

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

rust/crates/mxaccess-codec/src/error.rs

@@ -0,0 +1,40 @@
+//! Codec-level errors. Used by [`MxReferenceHandle`](crate::MxReferenceHandle),
+//! [`NmxTransferEnvelope`](crate::NmxTransferEnvelope), and the M1+ message
+//! codecs.
+
+use thiserror::Error;
+
+#[derive(Debug, Error)]
+#[non_exhaustive]
+pub enum CodecError {
+    /// A buffer was shorter than required to decode the type.
+    #[error("short read: expected {expected} bytes, got {actual}")]
+    ShortRead { expected: usize, actual: usize },
+
+    /// `name.trim().is_empty()`. Mirrors `ArgumentException.ThrowIfNullOrWhiteSpace`
+    /// in `MxReferenceHandle.cs:49`.
+    #[error("name must not be empty or whitespace-only")]
+    InvalidName,
+
+    /// The `inner_length` field declared in an envelope did not match the
+    /// actual body size.
+    #[error("inner length {declared} does not match body size {actual}")]
+    InnerLengthMismatch { declared: i32, actual: usize },
+
+    #[error("unsupported version {actual} (expected {expected})")]
+    UnsupportedVersion { expected: u16, actual: u16 },
+
+    #[error("unsupported protocol marker {0:#010x}")]
+    UnsupportedProtocolMarker(i32),
+
+    #[error("unexpected opcode {0:#04x}")]
+    UnexpectedOpcode(u8),
+
+    /// Decoder failure with a position and human-readable reason.
+    #[error("decode at offset {offset} ({reason}); buffer len {buffer_len}")]
+    Decode {
+        offset: usize,
+        reason: &'static str,
+        buffer_len: usize,
+    },
+}