feat(rust): #259 slice 2 — own-lowered, typed Layer 2 replay/emitter

rust/Cargo.toml

@@ -8,7 +8,7 @@
 
 [workspace]
 resolver = "2"
-members = ["crates/own-ir", "crates/own-syntax", "crates/own-cfg", "crates/own-diagnostics", "crates/own-analysis"]
+members = ["crates/own-ir", "crates/own-syntax", "crates/own-cfg", "crates/own-diagnostics", "crates/own-analysis", "crates/own-lowered"]
 
 [workspace.package]
 edition = "2021"

rust/crates/own-diagnostics/tests/dag.rs

@@ -33,6 +33,13 @@ fn allowed_edges() -> HashMap<&'static str, BTreeSet<&'static str>> {
     m.insert("own-cfg", ["own-ir", "own-syntax"].into_iter().collect());
     // The invariant #214 is about: only the span leaf, never the solver/parser.
     m.insert("own-diagnostics", std::iter::once("own-ir").collect());
+    // The Layer 2 parity surface (#259): a DATA leaf like own-diagnostics —
+    // the typed model + canonical emitter of the normalized lowered
+    // representation. It deliberately depends on NO workspace crate: the
+    // future own-bridge will CONSTRUCT these types (own-bridge → own-lowered),
+    // never the reverse, and the surface must stay implementable without the
+    // lowering that fills it.
+    m.insert("own-lowered", BTreeSet::new());
     // own-analysis CONSTRUCTS diagnostics and consumes the cfg lowering. It reads
     // the effect type through `own_cfg::Effect`, NOT the parser — so there is no
     // production own-syntax edge (own-syntax is a dev-only edge for its tests).

rust/crates/own-lowered/Cargo.toml

@@ -0,0 +1,22 @@
+[package]
+name = "own-lowered"
+description = "Layer 2 normalized-lowered-representation surface: typed model + canonical emitter replaying the Python-authored goldens (tests/fixtures/lowered, LOWERED_VERSION 1) — the data half of the own-bridge parity contract (P-022 #259); no lowering, no MOS, no analysis wiring"
+edition.workspace = true
+rust-version.workspace = true
+license.workspace = true
+publish.workspace = true
+version = "0.1.0"
+
+# A LEAF data crate, like own-diagnostics: it models the Layer 2 JSON surface
+# (spec/Bridge.md §6, ownlang/lowered.py is the authoritative Python twin) and
+# re-emits it byte-for-byte. It deliberately depends on NO other own-* crate —
+# the future own-bridge will construct these types from real lowering; this
+# crate must stay implementable without it (typed replay first, derivation
+# later). serde_json is a REGULAR dependency: the canonical emitter is the
+# crate's purpose, not a test aid.
+[dependencies]
+serde = { workspace = true }
+serde_json = { workspace = true }
+
+[lints]
+workspace = true

rust/crates/own-lowered/src/lib.rs

@@ -0,0 +1,27 @@
+//! The Layer 2 parity surface, typed (P-022 #259, spec/Bridge.md §6).
+//!
+//! `ownlang/lowered.py` is the authoritative Python emitter of the normalized
+//! lowered representation; `tests/fixtures/lowered/` holds its frozen
+//! facts/golden pairs under `manifest.json`. This crate is the **typed Rust
+//! half of that contract**: a strict (`deny_unknown_fields`) data model of the
+//! surface plus the canonical emitter that re-serializes it **byte-for-byte**
+//! (2-space indent, fixed field order, raw UTF-8, trailing newline).
+//!
+//! Deliberately NOT here (next slices, gated separately): deriving these
+//! documents from `OwnIR` facts (the lowering itself), `OwnIR` validation,
+//! MOS inference, and any analysis wiring. A `rust_replay: false` manifest
+//! case is a Python-only behavior snapshot pinning an open decision (#294)
+//! and is not replayed by this crate's parity suite.
+//!
+//! Every shape here mirrors the frozen normalization decisions in the Python
+//! emitter's docstring; a field added there without a matching change here (or
+//! vice-versa) fails the replay suite, and `LOWERED_VERSION` must move in
+//! lockstep on both sides.
+
+mod model;
+
+pub use model::{
+    parse_document, to_canonical_json, Extern, ExternParam, Function, HandleEntry, Lifetime,
+    LoweredDocument, Manifest, ManifestCase, Maybe, Param, Rejected, Resource, ResourceMember,
+    Stmt, Surface, TypeShape, LOWERED_VERSION,
+};