# Conformance — xyz-rust
Specification target: [xyz-spec](https://github.com/ejfkdev/xyz-spec) **v0.4.2**.
Status: **conformant (baseline anchor)** — xyz-rust is one of the two
reference implementations the specification was written from.
Deviations register: see
[deviations.md](https://github.com/ejfkdev/xyz-spec/blob/main/deviations.md),
entries `D-rust-01` … `D-rust-13`.
## Checklist
Every Class A item (conformance.md) is implemented and covered by the
following evidence:
| `cargo test -p xyz-rust --lib` (104 tests: errors/logx/registry/spec/cli/dispatch/httpapi/mcp) | A.1–A.53 pipeline, taxonomy, rendering, dispatcher semantics, rich errors, formats, headers, unions, blocks |
| `.github/workflows/test.yml` — six combination matrix (`default`, no-mcp, no-cli, no-http, cli-only, embedding-only) + fmt/clippy + MSRV 1.88 | A.38–A.39 trim invariants |
| `examples/example` (11 commands), `examples/tour`, `examples/clap` | showcase fixture §3.1, invocation matrix §3.2 |
| `docs/adapters.md` | A.41 embedding surfaces, §15.2 documentation |
Golden outputs (conformance.md §3.3) were diff-verified byte-for-byte
against the Rust binary — and the byte-exact segments (`file hash`, `math
sum`, `math div`, `/healthz`) additionally cross-checked against xyz-go
(identical bytes across SDKs).
## Showcase evidence
The fixture program runs with
`cargo run -p xyz-example -- <command>`; all commands of the §3.2 matrix
behave as specified, including `search query --query golang` (CLI default
k=25), the SHA-256 `file hash` answer, the rejection of `mcp sse`
(codified by spec §12.3 — see D-rust-06), and the default-subcommand
forwarding of §10.1 (`cli::cli_test::default_subcommand_forwards_all_args`),
plus the custom help blocks of §10.4/§13.2
(`dispatch_test::overview_help_blocks`, `cli::cli_test::help_blocks_on_leaf_only`)
and the language catalog of §15.5 (`lang::tests`,
`dispatch_test::lang_resolution_and_catalog`), plus §4.5a/§13.9/§6.1/
§10.4 (`cli::cli_test::channel_skip_and_help_types`,
`cli::cli_test::daemon_style_command`, `dispatch_test::try_run_composability`,
`dispatch_test::channel_defaults_flag`).
## v0.3.x → v0.4.2 additions
The clauses landed between the v0.3.0 anchor and v0.4.2, each with the
evidence that locks it:
- **§4.5a/§6.1/§13.9 (gs needs, v0.3.1–v0.3.2)** — channel skips, daemon
marker, `--default`, bare-flag passthrough, `try_run`:
`cli::cli_test::channel_skip_and_help_types`,
`cli::cli_test::daemon_style_command`, `dispatch_test::try_run_composability`,
`dispatch_test::channel_defaults_flag`.
- **§12.4a MCP tool-name override (v0.3.3)** — `MCPHints.name`, grammar-checked
at registration: `mcp::mcp_test::mcp_name_override`.
- **§4.7 tagged unions (v0.4.0)** — adjacent-tag enums → `oneOf` with `const`
discriminators, exactly-one-branch decode, per-frontend skip policy:
`spec::spec_test::tagged_union_schema_and_decode`,
`spec::spec_test::tagged_union_variant_rename_matches_serde`,
`cli::cli_test::union_field_degrades_not_fatals`.
- **§12.7 content-block results (v0.4.0)** — reserved `content` envelope,
MCP verbatim blocks, CLI temp-file projection:
`blocks::tests`, `mcp::mcp_test::block_envelope_passes_through`,
`cli::cli_test::block_envelope_spills_binary_to_files`.
- **§8.5/§8.6 rich errors (v0.4.2)** — `with_code/with_detail/with_status`
builders, shared error body on HTTP/CLI-machine/MCP:
`errors` unit tests, `httpapi::httpapi_test::rich_error_body_and_status_override`,
`mcp::mcp_test::result_meta_shape`.
- **§10.7 `--format` (v0.4.2)** — text/json/jsonl/markdown, `--json` alias,
bare-flag yield rule, `--xyz.format`:
`cli::format::tests`, `cli::cli_test::format_dispatch_and_conflict_yield`,
`cli::cli_test::format_flag_yields_to_command_field`.
- **§11.6 server-context headers (v0.4.2)** —
`httpapi::httpapi_test::server_context_headers_on_all_responses`; app
identity vs SDK version split is in `version` module docs and README §差异.
- **§12.6/§12.8 MCP identity & result `_meta.xyz` (v0.4.2)** —
`mcp::mcp_test::result_meta_shape`.
Known remaining gaps are in the deviations register: D-rust-12 closed by
this release (MCPHints.name), D-go-01 (tagged unions in Go) is the Go
side's open item.
## Deviations
All deviations are filed in the spec repository's
[deviations.md](https://github.com/ejfkdev/xyz-spec/blob/main/deviations.md)
with section references and classes (language-forced / SDK limitation /
extension); this document only points there to keep a single source of
truth.