Polyglot interop roadmap (Rust front, Swift)

This doc ties optional embedding work to concrete crates and repo paths. Nothing here is required for cargo install inauguration; it guides in-tree consolidation.

Boundaries today

Piece	Role	Today
Swift front	Tree-sitter bounded body extraction → `UnifiedModule` → Core IR → SIL	`compiler::tree_front` — same pipeline as all other languages
Protocol enums (`PatchType`)	Rust + Swift from JSON Schema	Rust `protocol-gen` (`cargo run --manifest-path in-cli/Cargo.toml --bin protocol-gen`) is canonical checked-in codegen; CI uses `scripts/check-protocol-models.sh`. V `shared/protocol/generate_models.v` is optional minor-tool parity (same outputs as `protocol-gen` aside from header comment).
Benchmark harness	Swift vs `in` timings + markdown/json reports	`./scripts/bench-swift.sh` runs `v -gc none run $ROOT/scripts/bench_swift.v` (sets `BENCH_ROOT`).
Preview pipeline	NDJSON over Unix socket	`in dev` defaults to Rust client; `--preview-client swift` runs SwiftPM `swift-preview-host-client`

swift-rs (macOS Swift linkage)

Add swift-rs + build-dependencies swift-rs with features = ["build"], then SwiftLinker in build.rs against an SPM static library with @_cdecl exports (see swift-rs README). Until then, in dev --preview-client swift shells swift run for the Swift bridge.

Suggested phases

Phase A — Contract freeze: JSON schema + frontend artifact JSON shape stay the cross-language contracts.
Phase B — Richer Tree-sitter extraction: deepen AST body extraction for all languages through the shared AstShape pattern.
Phase C — Preview bridge: SPM static lib + swift-rs for PreviewHost without subprocess.

Related paths

Core IR + parser IDs + front resolution: multi-frontend-ir.md.
Phased roadmap (Swift subset front → shared Core IR AST → SIL → hotreload): native-swift-master-plan.md.
Parser entry: in-cli/src/compiler/tree_front/extract.rs with per-language AstShape definitions.
Socket client reference: runtime/swift-preview-host/Sources/SwiftPreviewHostClient/main.swift.