ridl_ir/

lib.rs

//! RIDL intermediate representation.
//!
//! The v2 schema (`proto/ridl/ir/v2/ir.proto`) is compiled from its protobuf
//! source by `build.rs` (protox + prost-build, ADR-0006 decision 3) and
//! exposed as [`v2`]. v2 is the typl surface plus the ridl interaction layer
//! (ridl language reference §3–§14) with exact decimal values — every numeric
//! value is a canonical decimal string, never a floating-point field (ADR-0007
//! decision 9, ADR-0008 decision 12). The v1 schema was removed when its last
//! consumer moved to v2 (task 6 of the E2 plan), mirroring the E1 v0→v1
//! retirement.

pub mod v2 {
    //! IR v2 — the typl surface plus the ridl interaction layer (ridl
    //! language reference §3–§14) with exact decimal values (ADR-0007
    //! decision 9, ADR-0008 decision 12).

    include!(concat!(env!("OUT_DIR"), "/ridl.ir.v2.rs"));
    // The canonical protobuf JSON serde impls, generated by pbjson-build in
    // `build.rs` from the same schema compilation as the types above
    // (ADR-0014 decision 14).
    //
    // The file holds only trait impls, so it sits in a private module to scope
    // one lint allowance to generated code: pbjson-build 0.9.0 writes
    // `write!(formatter, "…", &FIELDS)`, which clippy 1.98 reports as
    // `useless_borrows_in_formatting`. The build script writes the file into
    // `OUT_DIR`, so an edit to it does not last and the lint cannot be repaired
    // in source. A lint attribute on the `include!` itself is ignored by rustc.
    // `expect` rather than `allow`: when the lint no longer fires here, clippy
    // reports the expectation as unfulfilled. Then remove this module and
    // include the file directly in `v2` again.
    #[expect(clippy::useless_borrows_in_formatting)]
    mod serde_impls {
        use super::*;

        include!(concat!(env!("OUT_DIR"), "/ridl.ir.v2.serde.rs"));
    }

    /// The descriptor pool over the compiled IR schema — the reflection data
    /// the prototext encoding needs (ADR-0014 decision 7; since decision 14
    /// JSON goes through the pbjson-generated impls and no longer uses the
    /// pool). Binary needs none of it.
    /// `build.rs` writes the `FileDescriptorSet` to `OUT_DIR` from the same
    /// `protox` compilation that generates the types above, so the pool and
    /// the types cannot disagree; every `expect` on this path leans on that.
    static DESCRIPTOR_POOL: std::sync::LazyLock<prost_reflect::DescriptorPool> =
        std::sync::LazyLock::new(|| {
            prost_reflect::DescriptorPool::decode(
                include_bytes!(concat!(env!("OUT_DIR"), "/ir_descriptor.binpb")).as_slice(),
            )
            .expect("the embedded descriptor set decodes: build.rs wrote it from the schema compilation that generated these types")
        });

    /// The descriptor of one root message of the compiled schema, by its
    /// full name.
    fn descriptor(name: &str) -> prost_reflect::MessageDescriptor {
        DESCRIPTOR_POOL
            .get_message_by_name(name)
            .unwrap_or_else(|| panic!("{name} is declared by the compiled schema"))
    }

    /// The `Package` message descriptor — the entry point of the prototext
    /// encoder and decoder, the one reflection path left in this module.
    pub(crate) fn package_descriptor() -> prost_reflect::MessageDescriptor {
        descriptor("ridl.ir.v2.Package")
    }

    /// The `System` message descriptor (`system.proto`), the prototext entry
    /// point of the rsdl system layer.
    pub(crate) fn system_descriptor() -> prost_reflect::MessageDescriptor {
        descriptor("ridl.ir.v2.System")
    }

    /// The `ridl.codegen.v1.CodegenRequest` message descriptor — the entry
    /// point of the request reader that ignores unknown keys.
    pub(crate) fn codegen_request_descriptor() -> prost_reflect::MessageDescriptor {
        descriptor("ridl.codegen.v1.CodegenRequest")
    }

    /// The `ridl.codegen.v1.Model` message descriptor — the prototext entry
    /// point of the lowered codegen model, from the same pool, because
    /// `build.rs` compiles both schemas in one `protox` call.
    pub(crate) fn codegen_model_descriptor() -> prost_reflect::MessageDescriptor {
        descriptor("ridl.codegen.v1.Model")
    }

    /// Rebuilds a message as a `DynamicMessage` over its descriptor — the
    /// step `prost-reflect` needs before rendering a text encoding.
    /// Transcoding goes through the wire encoding, whose decoder enforces
    /// prost's fixed recursion limit, so a package whose composite nesting
    /// crosses that limit fails here — an input-dependent failure, not
    /// schema drift (ADR-0014 decision 12).
    fn transcode<M: prost::Message>(
        descriptor: prost_reflect::MessageDescriptor,
        message: &M,
    ) -> Result<prost_reflect::DynamicMessage, prost::DecodeError> {
        let mut dynamic = prost_reflect::DynamicMessage::new(descriptor);
        dynamic.transcode_from(message)?;
        Ok(dynamic)
    }

    /// Derives the synthesized transport identity of an inline `T | E`
    /// result union (ADR-0008 decision 4): the enclosing interface name plus
    /// the interaction ordinal plus the ordered arm references. The single
    /// derivation every consumer — backends and the diff classifier — calls,
    /// so the identity stays stable under compatible evolution.
    pub fn fallible_transport_identity(
        interface: &str,
        ordinal: u32,
        fallible: &FallibleType,
    ) -> String {
        format!(
            "{interface}#{ordinal}:{ok}|{err}",
            ok = fallible.ok,
            err = fallible.err
        )
    }

    /// The error [`to_json_pretty`] and [`to_text_format`] return. The
    /// serialization surface is fallible on purpose (ADR-0014 decisions 12
    /// and 14), and the two encodings now fail for different causes, so each
    /// carries its own variant — its `Display` names the encoding, so a
    /// build requesting several IR emits attributes each failure to its own
    /// artifact.
    #[derive(Debug)]
    pub enum SerializeError {
        /// Canonical protobuf JSON (ADR-0014 decision 14): the
        /// pbjson-generated `Serialize` impl writes the typed message
        /// directly — no transcode, so no message-level recursion limit —
        /// and its one error path is an `i32` enum field holding a
        /// discriminant outside the schema.
        Json(serde_json::Error),
        /// Prototext (ADR-0014 decision 12): the transcode into the dynamic
        /// message goes through the wire encoding, whose decoder enforces
        /// prost's fixed recursion limit, and legal source can nest
        /// composites past it.
        Text(prost::DecodeError),
        /// An interaction holds a (kind, family, shape) combination the IR
        /// does not admit (`ridl_ir::class`).
        Class(crate::class::InteractionClassError),
    }

    impl std::fmt::Display for SerializeError {
        fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
            match self {
                Self::Json(source) => write!(
                    f,
                    "cannot render the package as canonical protobuf JSON: {source}; the known \
                     cause is an enum field holding a discriminant outside the schema"
                ),
                Self::Text(source) => write!(
                    f,
                    "cannot render the package as prototext: {source}; the known cause \
                     is composite nesting deeper than the transcoding decoder's recursion limit"
                ),
                Self::Class(source) => write!(f, "{source}"),
            }
        }
    }

    impl std::error::Error for SerializeError {
        fn source(&self) -> Option<&(dyn std::error::Error + 'static)> {
            match self {
                Self::Json(source) => Some(source),
                Self::Text(source) => Some(source),
                Self::Class(source) => Some(source),
            }
        }
    }

    /// Renders a package as pretty-printed canonical protobuf JSON — the one
    /// dialect every IR surface carries: the `--emit ir-json` artifact, the
    /// baselines, and the goldens (ADR-0014 decision 1) — through the
    /// pbjson-generated `Serialize` impl (decision 14), byte-identical to
    /// what the retired reflection path rendered.
    ///
    /// A field holding its default is emitted rather than skipped (decision
    /// 2, `emit_fields()` in `build.rs`); an unset proto3 `optional` field
    /// is omitted entirely, never rendered as `null` (the answer to that
    /// decision's open item). 64-bit fields render as strings, the canonical
    /// mapping JavaScript consumers need (decision 8).
    ///
    /// Still fallible (ADR-0014 decision 14, amending decision 12), but the
    /// error path changed rather than survived: the generated impl writes
    /// the typed message directly, so the transcode's depth error is gone,
    /// and the one error path it has is new — an `i32` enum field holding a
    /// discriminant outside the schema, which the retired reflection path
    /// serialized successfully as its bare number. The checker never
    /// produces one, but the value is data, not schema, so the failure is
    /// returned rather than panicked on.
    pub fn to_json_pretty(package: &Package) -> Result<String, SerializeError> {
        crate::class::check_package(package).map_err(SerializeError::Class)?;
        render_json(package)
    }

    /// Renders a lowered system (`system.proto`, rsdl reference §13) as
    /// pretty-printed canonical protobuf JSON — the `<pkg.Name>.system.json`
    /// artifact, under the rules of [`to_json_pretty`].
    pub fn system_to_json_pretty(system: &System) -> Result<String, SerializeError> {
        render_json(system)
    }

    /// The one JSON writer behind [`to_json_pretty`] and
    /// [`system_to_json_pretty`]: the pbjson-generated `Serialize` impl of
    /// the message, pretty-printed.
    pub(crate) fn render_json<M: serde::Serialize>(message: &M) -> Result<String, SerializeError> {
        let mut buf = Vec::new();
        let mut serializer = serde_json::Serializer::pretty(&mut buf);
        serde::Serialize::serialize(message, &mut serializer).map_err(SerializeError::Json)?;
        Ok(String::from_utf8(buf).expect("serde_json emits UTF-8"))
    }

    /// The nesting ceiling `from_json` enforces, in JSON bracket levels.
    ///
    /// It cannot bind on IR this toolchain produces, and the bound is a
    /// measurement rather than a guess. The parser refuses type nesting past
    /// 128 levels (FORM-102, `MAX_TYPE_DEPTH` in `ridl-syntax`), and the
    /// deepest package that limit admits emits JSON **516 brackets** deep —
    /// so 1,000 leaves a factor of 1.9 over anything `ridlc` can write, and
    /// the deepest nesting in the corpus is single digits. The figure this
    /// comment carried until 2026-09-22, 262 brackets and a factor of 3.8,
    /// was the array shape; the tuple shape costs four brackets per source
    /// level rather than two and is the one that binds (the IR
    /// specification, "The nesting bound").
    ///
    /// It exists for input this toolchain did not write: a hand-edited
    /// baseline, or a snapshot from elsewhere. Past the stack ceiling the
    /// failure mode is a stack-overflow abort, which no caller can catch, so
    /// the cap turns an abort into a diagnostic (ADR-0014 decisions 12
    /// and 14).
    pub(crate) const MAX_JSON_NESTING: usize = 1_000;

    /// The stack `from_json` parses on, in bytes. An explicit size makes the
    /// depth that fits a constant of this crate rather than of the ambient
    /// stack, which differs between debug and release builds and between
    /// platforms — the same input parses everywhere or nowhere.
    const JSON_PARSE_STACK: usize = 16 * 1024 * 1024;

    /// The maximum bracket nesting of `text`: the largest number of `{` and
    /// `[` open at once, with string literals skipped — a bracket inside a
    /// string must not count, an escaped quote (`\"`) must not end the
    /// string, and an escaped backslash (`\\`) must not disarm the real
    /// closing quote after it. Runs before the parse in [`from_json`], so it
    /// tolerates input that is not valid JSON; a stray closer never
    /// underflows the running depth.
    pub(crate) fn max_json_nesting(text: &str) -> usize {
        let mut depth = 0usize;
        let mut deepest = 0usize;
        let mut in_string = false;
        let mut escaped = false;
        for byte in text.bytes() {
            if in_string {
                if escaped {
                    escaped = false;
                } else if byte == b'\\' {
                    escaped = true;
                } else if byte == b'"' {
                    in_string = false;
                }
            } else {
                match byte {
                    b'"' => in_string = true,
                    b'{' | b'[' => {
                        depth += 1;
                        deepest = deepest.max(depth);
                    }
                    b'}' | b']' => depth = depth.saturating_sub(1),
                    _ => {}
                }
            }
        }
        deepest
    }

    /// Reads a package from canonical protobuf JSON — the inverse of
    /// [`to_json_pretty`], through the pbjson-generated `Deserialize` impl
    /// (ADR-0014 decision 14). Unknown fields are rejected (the generated
    /// deserializer's default; `ignore_unknown_fields()` stays unset in
    /// `build.rs`), so a snapshot written against a different schema fails
    /// loudly rather than dropping fields silently.
    ///
    /// The generated impl recurses per JSON level, so `serde_json`'s own
    /// recursion limit of 128 levels is disabled — it would bind far below
    /// this crate's documented ceiling — and two guards replace it
    /// (ADR-0014 decision 14):
    ///
    /// - input nesting is measured first and refused past
    ///   `MAX_JSON_NESTING`, returning a diagnostic where unbounded
    ///   recursion would eventually abort on a stack overflow no caller can
    ///   catch;
    /// - the parse runs on a thread of `JSON_PARSE_STACK` bytes, so the
    ///   ceiling behaves identically across build profiles and platforms
    ///   instead of tracking the ambient stack. On the wasm family there is
    ///   no such thread — see the branch below — and the cap alone guards
    ///   the parse.
    ///
    /// After the parse, every interaction's (kind, family, shape) is checked
    /// against [`crate::class`]; an invalid combination is an error of this
    /// reader.
    pub fn from_json(text: &str) -> Result<Package, serde_json::Error> {
        let package: Package = read_json(text)?;
        crate::class::check_package(&package).map_err(serde::de::Error::custom)?;
        Ok(package)
    }

    /// An error loading an `.ir.json` snapshot with [`load_ir_json`].
    #[derive(Debug)]
    pub enum LoadError {
        /// The file could not be read.
        Io(std::io::Error),
        /// The file was not valid IR v2 JSON.
        Parse(String),
    }

    impl std::fmt::Display for LoadError {
        fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
            match self {
                LoadError::Io(err) => write!(f, "cannot read the IR snapshot: {err}"),
                LoadError::Parse(err) => {
                    write!(f, "the IR snapshot is not valid IR v2 JSON: {err}")
                }
            }
        }
    }

    impl std::error::Error for LoadError {}

    /// Loads an `.ir.json` snapshot written by `ridl build --emit ir-json` —
    /// canonical protobuf JSON, read through [`from_json`], the one reader
    /// every surface shares (ADR-0014 decision 1).
    pub fn load_ir_json(path: &std::path::Path) -> Result<Package, LoadError> {
        let text = std::fs::read_to_string(path).map_err(LoadError::Io)?;
        from_json(&text).map_err(|err| LoadError::Parse(err.to_string()))
    }

    /// Reads a lowered system from canonical protobuf JSON — the inverse of
    /// [`system_to_json_pretty`], under the rules and guards of
    /// [`from_json`].
    pub fn system_from_json(text: &str) -> Result<System, serde_json::Error> {
        read_json(text)
    }

    /// The one JSON reader behind [`from_json`] and [`system_from_json`]:
    /// the nesting cap, then the parse on its own stack.
    pub(crate) fn read_json<M>(text: &str) -> Result<M, serde_json::Error>
    where
        M: serde::de::DeserializeOwned + Send,
    {
        check_nesting(text)?;
        on_parse_stack(|| parse_json(text))
    }

    /// Reads a request-shaped message the way [`read_json`] does, except that
    /// an object key the schema does not declare is ignored at every nesting
    /// level. The same nesting cap and parse stack apply.
    ///
    /// The text is read once into a `serde_json::Value` that keeps only the
    /// keys `descriptor` declares at each point (by JSON name or proto name),
    /// including inside repeated and map message values, and the value is
    /// then read by the generated deserializer of `M`. That reader still
    /// rejects what it rejects for the strict path: a value of the wrong
    /// type, an unknown enum name, and a field written twice. Only an unknown
    /// key is dropped; an unknown enum name is an error, because it changes
    /// the meaning of a known field. A value of a `google.protobuf` message
    /// is left untouched.
    ///
    /// An error from the second phase, the generated deserializer reading the
    /// filtered value, carries no line and column, because the value no longer
    /// has a position in the text.
    pub(crate) fn read_json_ignoring_unknown<M>(
        descriptor: prost_reflect::MessageDescriptor,
        text: &str,
    ) -> Result<M, serde_json::Error>
    where
        M: serde::de::DeserializeOwned + Send,
    {
        use serde::de::DeserializeSeed as _;
        check_nesting(text)?;
        on_parse_stack(|| {
            let mut deserializer = serde_json::Deserializer::from_str(text);
            deserializer.disable_recursion_limit();
            let known = JsonShape::Message(descriptor).deserialize(&mut deserializer)?;
            deserializer.end()?;
            serde::Deserialize::deserialize(known)
        })
    }

    /// What a JSON value is expected to be, as far as dropping unknown keys
    /// needs to know.
    #[derive(Clone)]
    enum JsonShape {
        /// A message: an object whose unknown keys are dropped.
        Message(prost_reflect::MessageDescriptor),
        /// A repeated field: an array of the inner shape.
        List(Box<JsonShape>),
        /// A map field: an object whose values have the inner shape.
        Map(Box<JsonShape>),
        /// Anything else: kept as read.
        Opaque,
    }

    impl JsonShape {
        /// The shape of the value of one field.
        fn of(field: &prost_reflect::FieldDescriptor) -> JsonShape {
            use prost_reflect::Kind;
            if field.is_map() {
                let Kind::Message(entry) = field.kind() else {
                    return JsonShape::Opaque;
                };
                return JsonShape::Map(Box::new(JsonShape::of_kind(
                    &entry.map_entry_value_field().kind(),
                )));
            }
            let item = JsonShape::of_kind(&field.kind());
            if field.is_list() {
                JsonShape::List(Box::new(item))
            } else {
                item
            }
        }

        fn of_kind(kind: &prost_reflect::Kind) -> JsonShape {
            match kind {
                prost_reflect::Kind::Message(message)
                    if !message.full_name().starts_with("google.protobuf.") =>
                {
                    JsonShape::Message(message.clone())
                }
                _ => JsonShape::Opaque,
            }
        }
    }

    impl<'de> serde::de::DeserializeSeed<'de> for JsonShape {
        type Value = serde_json::Value;

        fn deserialize<D: serde::Deserializer<'de>>(
            self,
            deserializer: D,
        ) -> Result<Self::Value, D::Error> {
            match self {
                JsonShape::Opaque => serde::Deserialize::deserialize(deserializer),
                shape => deserializer.deserialize_any(ShapeVisitor(shape)),
            }
        }
    }

    struct ShapeVisitor(JsonShape);

    impl<'de> serde::de::Visitor<'de> for ShapeVisitor {
        type Value = serde_json::Value;

        fn expecting(&self, formatter: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
            formatter.write_str(match self.0 {
                JsonShape::List(_) => "an array",
                _ => "an object",
            })
        }

        // `null` is passed on: the generated reader decides what it means.
        fn visit_unit<E>(self) -> Result<Self::Value, E> {
            Ok(serde_json::Value::Null)
        }

        fn visit_seq<A: serde::de::SeqAccess<'de>>(
            self,
            mut seq: A,
        ) -> Result<Self::Value, A::Error> {
            let JsonShape::List(item) = self.0 else {
                return Err(serde::de::Error::invalid_type(
                    serde::de::Unexpected::Seq,
                    &self,
                ));
            };
            let mut items = Vec::new();
            while let Some(value) = seq.next_element_seed((*item).clone())? {
                items.push(value);
            }
            Ok(serde_json::Value::Array(items))
        }

        fn visit_map<A: serde::de::MapAccess<'de>>(
            self,
            mut map: A,
        ) -> Result<Self::Value, A::Error> {
            use serde::de::Error as _;
            let mut out = serde_json::Map::new();
            match &self.0 {
                JsonShape::Message(descriptor) => {
                    let mut seen = std::collections::HashSet::new();
                    while let Some(key) = map.next_key::<String>()? {
                        let field = descriptor
                            .get_field_by_json_name(&key)
                            .or_else(|| descriptor.get_field_by_name(&key));
                        match field {
                            Some(field) => {
                                if !seen.insert(field.number()) {
                                    return Err(A::Error::custom(format!(
                                        "duplicate field `{key}`"
                                    )));
                                }
                                let value = map.next_value_seed(JsonShape::of(&field))?;
                                out.insert(key, value);
                            }
                            None => {
                                map.next_value::<serde::de::IgnoredAny>()?;
                            }
                        }
                    }
                }
                JsonShape::Map(value_shape) => {
                    while let Some(key) = map.next_key::<String>()? {
                        let value = map.next_value_seed((**value_shape).clone())?;
                        if out.insert(key.clone(), value).is_some() {
                            return Err(A::Error::custom(format!("duplicate key `{key}`")));
                        }
                    }
                }
                JsonShape::List(_) | JsonShape::Opaque => {
                    return Err(A::Error::invalid_type(serde::de::Unexpected::Map, &self));
                }
            }
            Ok(serde_json::Value::Object(out))
        }
    }

    /// Refuses input that nests past `MAX_JSON_NESTING`.
    fn check_nesting(text: &str) -> Result<(), serde_json::Error> {
        if max_json_nesting(text) > MAX_JSON_NESTING {
            return Err(<serde_json::Error as serde::de::Error>::custom(format!(
                "the input nests deeper than {MAX_JSON_NESTING} JSON levels, the ceiling this \
                 reader enforces (ADR-0014 decision 14); real IR nests orders of magnitude \
                 shallower"
            )));
        }
        Ok(())
    }

    /// Runs a parse on its own stack of `JSON_PARSE_STACK` bytes, or in line
    /// on the wasm family.
    fn on_parse_stack<R: Send>(parse: impl FnOnce() -> R + Send) -> R {
        if cfg!(target_family = "wasm") {
            // The wasm family has no spawnable threads: `spawn_scoped`
            // returns `Err(Unsupported)` at run time on
            // `wasm32-unknown-unknown`, the `just wasm-check` target, so a
            // spawn here would turn every call into a panic. The parse runs
            // in line instead, on the caller's stack. What this path loses
            // is the deterministic stack — the ceiling is the ambient stack
            // — and the `MAX_JSON_NESTING` cap is the guard that matters: it
            // is what turns an abort into an error.
            parse()
        } else {
            std::thread::scope(|scope| {
                let handle = std::thread::Builder::new()
                    .stack_size(JSON_PARSE_STACK)
                    .spawn_scoped(scope, parse)
                    .expect("the JSON parse thread spawns");
                match handle.join() {
                    Ok(result) => result,
                    Err(payload) => std::panic::resume_unwind(payload),
                }
            })
        }
    }

    /// The parse both branches of [`from_json`] share; only the stack that
    /// carries it differs. `serde_json`'s own recursion limit is disabled
    /// here, so the caller must have applied the `MAX_JSON_NESTING` cap
    /// first.
    fn parse_json<M: serde::de::DeserializeOwned>(text: &str) -> Result<M, serde_json::Error> {
        let mut deserializer = serde_json::Deserializer::from_str(text);
        deserializer.disable_recursion_limit();
        let message: M = serde::Deserialize::deserialize(&mut deserializer)?;
        deserializer.end()?;
        Ok(message)
    }

    /// Renders a package in the protobuf text format — the inspection
    /// encoding (ADR-0014 decision 9): emittable, but not a recommended
    /// interchange form. Rendered `pretty`, with a field holding its default
    /// emitted rather than skipped (decision 2) and message fields printed
    /// in schema index order, so the output ordering is deterministic rather
    /// than incidental (decision 8).
    ///
    /// Fallible on purpose (ADR-0014 decision 12): the transcode into the
    /// dynamic message goes through the wire encoding, and a package whose
    /// composite nesting crosses prost's recursion limit fails there. That
    /// input is legal source, so the failure is returned rather than
    /// panicked on. JSON lost this failure mode when it moved off the
    /// transcode (decision 14); prototext keeps it.
    pub fn to_text_format(package: &Package) -> Result<String, SerializeError> {
        crate::class::check_package(package).map_err(SerializeError::Class)?;
        render_text_for(package_descriptor(), package)
    }

    /// Renders a lowered system in the protobuf text format — the
    /// `<pkg.Name>.system.txtpb` artifact, under the rules of
    /// [`to_text_format`].
    pub fn system_to_text_format(system: &System) -> Result<String, SerializeError> {
        render_text_for(system_descriptor(), system)
    }

    /// The one prototext writer behind [`to_text_format`] and
    /// [`system_to_text_format`].
    pub(crate) fn render_text_for<M: prost::Message>(
        descriptor: prost_reflect::MessageDescriptor,
        message: &M,
    ) -> Result<String, SerializeError> {
        let dynamic = transcode(descriptor, message).map_err(SerializeError::Text)?;
        Ok(dynamic.to_text_format_with_options(
            &prost_reflect::text_format::FormatOptions::new()
                .pretty(true)
                .skip_default_fields(false)
                .print_message_fields_in_index_order(true),
        ))
    }

    /// The error [`from_text_format`] returns: the input does not parse as
    /// prototext, or the parsed message does not transcode into the
    /// generated types. The transcode failure is the read direction of the
    /// recursion-limit failure mode (ADR-0014 decision 12) — input-dependent,
    /// so it is mapped into this return rather than expected on.
    #[cfg(test)]
    #[derive(Debug)]
    pub(crate) enum TextFormatError {
        /// The input is not valid prototext for the `Package` schema.
        Parse(prost_reflect::text_format::ParseError),
        /// The parsed message cannot be rebuilt as a typed `Package`.
        Transcode(prost::DecodeError),
    }

    #[cfg(test)]
    impl std::fmt::Display for TextFormatError {
        fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
            match self {
                Self::Parse(source) => {
                    write!(f, "cannot parse the text as an IR package: {source}")
                }
                Self::Transcode(source) => write!(
                    f,
                    "cannot rebuild the parsed prototext as a package: {source}; the known cause \
                     is composite nesting deeper than the transcoding decoder's recursion limit"
                ),
            }
        }
    }

    #[cfg(test)]
    impl std::error::Error for TextFormatError {
        fn source(&self) -> Option<&(dyn std::error::Error + 'static)> {
            match self {
                Self::Parse(source) => Some(source),
                Self::Transcode(source) => Some(source),
            }
        }
    }

    /// Reads a package from the protobuf text format — the inverse of
    /// [`to_text_format`], kept because without it the prototext emit has no
    /// round-trip test, and a write path with no read path is untested by
    /// construction (ADR-0014 decision 7).
    ///
    /// **Deliberately not public.** `prost-reflect`'s text parser recurses per
    /// message level with frames large enough that a debug build exhausts a
    /// 2 MiB stack at roughly 45 levels of nesting — *below* prost's recursion
    /// limit of 100, so on that path the error return below is unreachable and
    /// the process aborts instead. A stack overflow cannot be caught, so the
    /// hazard is contained by reach rather than handled: nothing in the
    /// toolchain reads prototext, `ridl diff` and `ridl check --baseline`
    /// refuse the encoding by name (ADR-0014 decision 5), and this function is
    /// compiled only for this crate's tests. The tests that exercise it run on an
    /// explicitly sized stack (see `with_sized_stack`). Making it public again
    /// means giving it a stack strategy first — driftsys/ridl#218.
    ///
    /// A package whose nesting crosses prost's limit *before* the stack runs
    /// out fails in the transcode out of the dynamic message; that failure is
    /// mapped into the error return, not expected on (ADR-0014 decision 12).
    #[cfg(test)]
    pub(crate) fn from_text_format(text: &str) -> Result<Package, TextFormatError> {
        parse_text(package_descriptor(), text)
    }

    /// Reads a lowered system from the protobuf text format — the inverse of
    /// [`system_to_text_format`], test-only for the reason
    /// [`from_text_format`] states.
    #[cfg(test)]
    pub(crate) fn system_from_text_format(text: &str) -> Result<System, TextFormatError> {
        parse_text(system_descriptor(), text)
    }

    #[cfg(test)]
    fn parse_text<M: prost::Message + Default>(
        descriptor: prost_reflect::MessageDescriptor,
        text: &str,
    ) -> Result<M, TextFormatError> {
        let dynamic = prost_reflect::DynamicMessage::parse_text_format(descriptor, text)
            .map_err(TextFormatError::Parse)?;
        dynamic.transcode_to().map_err(TextFormatError::Transcode)
    }

    /// Encodes a package in the protobuf binary wire format — a derived
    /// encoding since ADR-0014 decision 9's 2026-09-22 amendment, whose
    /// reader stops 100 message levels below the root where the canonical
    /// encoding has no such bound (the IR specification, "The derived
    /// encodings"). Binary needs no descriptors: prost's generated encoding
    /// is schema-faithful by construction.
    pub fn to_binary(package: &Package) -> Vec<u8> {
        prost::Message::encode_to_vec(package)
    }

    /// Decodes a package from the protobuf binary wire format — the inverse
    /// of [`to_binary`].
    pub fn from_binary(bytes: &[u8]) -> Result<Package, prost::DecodeError> {
        let package: Package = prost::Message::decode(bytes)?;
        crate::class::check_package(&package).map_err(|err| {
            // `DecodeError::new` is the only way to build one: prost exposes
            // no other constructor, and this reader's error type is prost's.
            #[allow(deprecated)]
            prost::DecodeError::new(err.to_string())
        })?;
        Ok(package)
    }

    /// Encodes a lowered system in the protobuf binary wire format — the
    /// `<pkg.Name>.system.binpb` artifact (ADR-0014 decision 9).
    pub fn system_to_binary(system: &System) -> Vec<u8> {
        prost::Message::encode_to_vec(system)
    }

    /// Decodes a lowered system from the protobuf binary wire format — the
    /// inverse of [`system_to_binary`].
    pub fn system_from_binary(bytes: &[u8]) -> Result<System, prost::DecodeError> {
        prost::Message::decode(bytes)
    }

    /// `pkg.Name` — how a system, a component or a distribution is referred
    /// to across the system layer (`system.proto`); a name with no package,
    /// the implicit component of a lone service (rsdl §6), is its own
    /// qualified name.
    fn qualified(package: &str, name: &str) -> String {
        if package.is_empty() {
            name.to_string()
        } else {
            format!("{package}.{name}")
        }
    }

    impl System {
        /// The system's qualified name, `pkg.Name` — the base name of its
        /// artifacts.
        pub fn qualified_name(&self) -> String {
            qualified(&self.package, &self.name)
        }
    }

    impl Component {
        /// The name every reference to this component uses: `pkg.Name` for a
        /// declared component, the service's dotted name for an implicit one.
        pub fn qualified_name(&self) -> String {
            qualified(&self.package, &self.name)
        }
    }

    impl Distribution {
        /// The name `Distribution.depends_on` and `Installation.distribution`
        /// use.
        pub fn qualified_name(&self) -> String {
            qualified(&self.package, &self.name)
        }
    }

    /// One interface shape of a package (ridl §14.0): a declared `interface`,
    /// or the inline shape of a `service` (§14.5).
    ///
    /// **[`Package::interfaces`] is not the complete set.** A `service`
    /// declared with an inline body carries a full [`Interface`] inside its
    /// shape list (the single `INLINE` slot, ADR-0015 decision 14), which
    /// lives outside `interfaces`; a consumer that walks `interfaces` alone
    /// silently misses it. Six defects of exactly that shape were found
    /// independently across E2 — observer-stub lowering, both backends'
    /// transport identity, `ridl test`'s report, the Rust backend's collision
    /// check, and the desk check's span index.
    /// [`Package::shapes`] is the one walk that sees both, the way
    /// [`fallible_transport_identity`] is the one transport-identity
    /// derivation.
    ///
    /// This view is deliberately not a bare `&Interface`, because two of an
    /// inline shape's own fields are empty by construction and reading them
    /// is what produced two of those six defects:
    ///
    /// - [`Interface::name`] is `""` for an inline shape, so [`Self::name`]
    ///   carries the **identity** name instead — the interface's own name, or
    ///   the owning service's dotted global name. That is the name the diff
    ///   paths, the observer-stub scoping, and both backends' identity fields
    ///   already use.
    /// - [`Interface::visibility`] is `VISIBILITY_UNSPECIFIED` for an inline
    ///   shape; the owning [`Service`] carries the authoritative one, which
    ///   [`Self::visibility`] reads.
    ///
    /// The generated *type* name is not derived here on purpose: mangling is
    /// language-specific and stays with each backend.
    #[derive(Debug, Clone, Copy, PartialEq)]
    pub struct InterfaceShape<'a> {
        /// The name this shape is known by outside the package: an
        /// `interface` declaration's own name, or the owning service's dotted
        /// global name. Never `Interface::name` for an inline shape.
        pub name: &'a str,
        /// The interface body — its interactions and its doc envelope.
        pub interface: &'a Interface,
        /// The owning service, for an inline shape; `None` for a declared
        /// `interface`.
        pub service: Option<&'a Service>,
    }

    impl InterfaceShape<'_> {
        /// The authoritative visibility of this shape: the owning service's
        /// for an inline shape (an inline shape's own field is
        /// `VISIBILITY_UNSPECIFIED` by construction), the interface's own
        /// otherwise.
        pub fn visibility(&self) -> i32 {
            match self.service {
                Some(service) => service.visibility,
                None => self.interface.visibility,
            }
        }

        /// `true` when this shape is the inline body of a `service`.
        pub fn is_inline(&self) -> bool {
            self.service.is_some()
        }
    }

    impl Package {
        /// Every interface shape the package carries — the declared
        /// interfaces and the inline shapes of its services. See
        /// [`InterfaceShape`] for why walking [`Package::interfaces`] alone is
        /// a defect.
        ///
        /// The order is the one every consumer already walked: the declared
        /// interfaces in source order, then the services in source order. A
        /// shape-list entry that names an interface yields nothing — its
        /// target is a declared interface and is already in the sequence, so
        /// yielding it again would visit one shape twice; a service composing
        /// several interfaces (ADR-0015 decision 12) therefore contributes
        /// nothing at all. A tombstone slot names no shape. Only the `INLINE`
        /// slot of an inline-form service carries an interface of its own,
        /// and that is what this walk yields.
        pub fn shapes(&self) -> impl Iterator<Item = InterfaceShape<'_>> {
            let named = self.interfaces.iter().map(|interface| InterfaceShape {
                name: &interface.name,
                interface,
                service: None,
            });
            let inline = self.services.iter().flat_map(|service| {
                service
                    .shapes
                    .iter()
                    .filter_map(move |slot| match slot.kind.as_ref()? {
                        service_shape::Kind::Inline(interface) => Some(InterfaceShape {
                            name: &service.name,
                            interface,
                            service: Some(service),
                        }),
                        service_shape::Kind::InterfaceRef(_) => None,
                    })
            });
            named.chain(inline)
        }
    }

    /// The unit of `package`: its `unit` field when set, else its `name`.
    ///
    /// A snapshot written before the field existed carries an empty `unit`;
    /// for such a package the package name is the unit.
    pub fn unit_of(package: &Package) -> &str {
        if package.unit.is_empty() {
            &package.name
        } else {
            &package.unit
        }
    }

    /// The packages of `packages` that belong to `unit`, in their order.
    pub fn packages_of_unit<'a>(
        unit: &str,
        packages: &'a [Package],
    ) -> impl Iterator<Item = &'a Package> {
        select_unit(unit, packages.iter())
    }

    /// [`packages_of_unit`] over borrowed packages, the form the catalog
    /// hash and the codegen lowering hold.
    pub fn members_of_unit<'a>(
        unit: &str,
        packages: &[&'a Package],
    ) -> impl Iterator<Item = &'a Package> {
        select_unit(unit, packages.iter().copied())
    }

    /// The one selection behind [`packages_of_unit`] and
    /// [`members_of_unit`]: by [`unit_of`], never by a name prefix.
    fn select_unit<'a>(
        unit: &str,
        packages: impl Iterator<Item = &'a Package>,
    ) -> impl Iterator<Item = &'a Package> {
        let unit = unit.to_owned();
        packages.filter(move |p| unit_of(p) == unit)
    }

    /// The name of a declaration relative to its unit: `name` for a package
    /// that is the unit itself, else the package's path below the unit
    /// followed by `name`, joined with `.`.
    pub fn relative_name(unit: &str, package: &str, name: &str) -> String {
        if package == unit {
            return name.to_owned();
        }
        // A package outside the unit — a corrupt or hand-edited snapshot
        // read by `ridl diff` — keeps its full name, so no name is wrong and
        // nothing panics in a release build.
        match package
            .strip_prefix(unit)
            .and_then(|rest| rest.strip_prefix('.'))
        {
            Some(below) => format!("{below}.{name}"),
            None => format!("{package}.{name}"),
        }
    }

    impl Package {
        /// The name `shape` carries in the catalog of its unit: the global
        /// name for an inline shape, else the declared name relative to the
        /// unit (see [`relative_name`]).
        pub fn catalog_name(&self, shape: &InterfaceShape<'_>) -> String {
            if shape.is_inline() {
                shape.name.to_owned()
            } else {
                relative_name(unit_of(self), &self.name, shape.name)
            }
        }
    }

    /// The retired entries of the catalog of `unit`: every `retired` entry
    /// of every package of the unit (a package named twice is read once),
    /// as spelled, in number order. The checker spells each entry as its
    /// lock key, which is its catalog name (`cluster.Old`, `Old` for the
    /// root, `service:veh.x`), on the package the key names or on the
    /// unit's anchor package, so no entry is qualified here.
    pub fn unit_retired(unit: &str, packages: &[&Package]) -> Vec<RetiredInterface> {
        let mut seen: Vec<&str> = Vec::new();
        let mut retired: Vec<RetiredInterface> = members_of_unit(unit, packages)
            .filter(|package| {
                let first = !seen.contains(&package.name.as_str());
                if first {
                    seen.push(&package.name);
                }
                first
            })
            .flat_map(|package| package.retired.iter().cloned())
            .collect();
        retired.sort_by_key(|entry| entry.number);
        retired
    }

    /// Every package named by a type reference in `package`.
    ///
    /// A resolved type-reference string is the fully qualified `pkg.Name` for
    /// a cross-package reference and the bare `Name` for a same-package one,
    /// never an import alias — the canonical form stated in
    /// `proto/ridl/ir/v2/ir.proto`, which also enumerates the fields carrying
    /// one. **That enumeration and this walk are edited together.** A
    /// reference-bearing field added there and not read here makes the package
    /// it names invisible to every caller asking what a package depends on.
    ///
    /// Every `oneof` below is matched exhaustively with no wildcard arm, so a
    /// variant added later fails to compile here rather than going unread.
    pub fn referenced_packages(package: &Package) -> std::collections::BTreeSet<String> {
        let mut found = std::collections::BTreeSet::new();
        for decl in &package.decls {
            walk_decl(decl, &mut found);
        }
        for interface in &package.interfaces {
            for interaction in &interface.interactions {
                walk_decl(interaction, &mut found);
            }
        }
        for service in &package.services {
            for slot in &service.shapes {
                match &slot.kind {
                    Some(service_shape::Kind::InterfaceRef(reference)) => {
                        qualifier(reference, &mut found);
                    }
                    Some(service_shape::Kind::Inline(interface)) => {
                        for interaction in &interface.interactions {
                            walk_decl(interaction, &mut found);
                        }
                    }
                    None => {}
                }
            }
        }
        found
    }

    /// Records the package qualifier of a dotted reference. A bare reference
    /// is same-package and contributes nothing.
    fn qualifier(reference: &str, found: &mut std::collections::BTreeSet<String>) {
        if let Some((package, _)) = reference.rsplit_once('.') {
            found.insert(package.to_string());
        }
    }

    /// Records every reference in one declaration — a package-level one or an
    /// interaction inside an interface, which share the `Decl` envelope.
    fn walk_decl(decl: &Decl, found: &mut std::collections::BTreeSet<String>) {
        match &decl.kind {
            Some(decl::Kind::TypeDef(type_def)) => walk_type_def(type_def, found),
            Some(decl::Kind::ConstDef(const_def)) => {
                if let Some(reference) = &const_def.type_ref {
                    qualifier(reference, found);
                }
            }
            Some(decl::Kind::StructDef(struct_def)) => {
                for member in &struct_def.members {
                    match &member.member {
                        Some(struct_member::Member::Field(field)) => {
                            if let Some(field_type) = &field.r#type {
                                walk_field_type(field_type, found);
                            }
                        }
                        // A tombstone occupies an ordinal and names no type.
                        Some(struct_member::Member::Reserved(_)) | None => {}
                    }
                }
            }
            // An enum's variants are integers; it names no type.
            Some(decl::Kind::EnumDef(_)) => {}
            Some(decl::Kind::EnumSetDef(enum_set)) => {
                if let Some(reference) = &enum_set.backing_enum {
                    qualifier(reference, found);
                }
            }
            Some(decl::Kind::UnionDef(union_def)) => {
                for arm in &union_def.arms {
                    qualifier(&arm.type_ref, found);
                }
            }
            Some(decl::Kind::SignalDef(signal)) => qualifier(&signal.payload, found),
            Some(decl::Kind::EventDef(event)) => qualifier(&event.payload, found),
            Some(decl::Kind::CommandDef(command)) => {
                for param in &command.params {
                    if let Some(field_type) = &param.r#type {
                        walk_field_type(field_type, found);
                    }
                }
            }
            Some(decl::Kind::QueryDef(query)) => {
                for param in &query.params {
                    if let Some(field_type) = &param.r#type {
                        walk_field_type(field_type, found);
                    }
                }
                if let Some(return_type) = &query.return_type {
                    walk_return_type(return_type, found);
                }
            }
            Some(decl::Kind::FixedDef(fixed)) => {
                if let Some(field_type) = &fixed.payload {
                    walk_field_type(field_type, found);
                }
            }
            // A tombstone occupies an ordinal and names no type.
            Some(decl::Kind::ReservedSlot(_)) | None => {}
        }
    }

    /// The recursive half: a reference is reachable at arbitrary depth through
    /// tuples, arrays, maps, inline scalars, and streams.
    fn walk_field_type(field_type: &FieldType, found: &mut std::collections::BTreeSet<String>) {
        match &field_type.kind {
            Some(field_type::Kind::Named(reference)) => qualifier(reference, found),
            // A primitive names no package.
            Some(field_type::Kind::Primitive(_)) => {}
            Some(field_type::Kind::InlineScalar(type_def)) => walk_type_def(type_def, found),
            Some(field_type::Kind::Tuple(tuple)) => {
                for field in &tuple.fields {
                    if let Some(inner) = &field.r#type {
                        walk_field_type(inner, found);
                    }
                }
            }
            Some(field_type::Kind::Array(array)) => {
                if let Some(element) = &array.element {
                    walk_field_type(element, found);
                }
            }
            Some(field_type::Kind::Map(map)) => {
                if let Some(key) = &map.key {
                    walk_field_type(key, found);
                }
                if let Some(value) = &map.value {
                    walk_field_type(value, found);
                }
            }
            Some(field_type::Kind::Stream(stream)) => match &stream.element {
                Some(stream_type::Element::Named(reference)) => qualifier(reference, found),
                // STRING or BYTES only; names no package.
                Some(stream_type::Element::Primitive(_)) | None => {}
            },
            None => {}
        }
    }

    /// A `TypeDef`'s only reference is the constant a `match` bound names.
    fn walk_type_def(type_def: &TypeDef, found: &mut std::collections::BTreeSet<String>) {
        if let Some(constraint) = &type_def.constraint
            && let Some(reference) = &constraint.pattern_const
        {
            qualifier(reference, found);
        }
    }

    fn walk_return_type(return_type: &ReturnType, found: &mut std::collections::BTreeSet<String>) {
        match &return_type.kind {
            Some(return_type::Kind::Value(field_type)) => walk_field_type(field_type, found),
            Some(return_type::Kind::Fallible(fallible)) => {
                qualifier(&fallible.ok, found);
                qualifier(&fallible.err, found);
            }
            None => {}
        }
    }

    /// Whether a constraint leaves a generated constructor nothing to check.
    ///
    /// True when no bound, step or pattern is present. A step is an enforced
    /// quantization constraint, including when its origin defaults to zero.
    ///
    /// A pattern given by name counts as a pattern: `pattern_const` is read as
    /// well as `pattern`, because a pattern constant that did not resolve leaves
    /// `pattern` absent while the type still carries a match constraint.
    /// `ridl-sem` treats the two fields the same way in its derived-init rule
    /// (`init.rs`).
    ///
    /// Because the checker materializes the typl §4.4 default `[0..256]` into
    /// `len_min`/`len_max`, every string and bytes type is non-vacuous. In
    /// practice this reduces to `boolean`, and `integer`/`float` with no declared
    /// range.
    pub fn constraint_is_vacuous(constraint: Option<&Constraint>) -> bool {
        let Some(c) = constraint else { return true };
        c.min.is_none()
            && c.max.is_none()
            && c.step.is_none()
            && c.len_min.is_none()
            && c.len_max.is_none()
            && c.pattern.is_none()
            && c.pattern_const.is_none()
    }
}

pub mod catalog_hash;
pub mod class;
pub mod codegen;
pub mod name;
pub mod projection;
pub mod rules;
pub mod zero;

#[cfg(test)]
mod v2_round_trip {
    use crate::v2;

    /// Wraps an interaction kind in the shared `Decl` envelope. Visibility
    /// and `is_error` stay unset on interactions (ridl §14.1); the ordinal is
    /// the 1-based declaration order across all interactions of the
    /// enclosing interface (ridl §11).
    fn interaction(name: &str, ordinal: u32, kind: v2::decl::Kind) -> v2::Decl {
        v2::Decl {
            limit: None,
            name: name.to_string(),
            visibility: v2::Visibility::Unspecified as i32,
            is_error: false,
            doc: String::new(),
            labels: Vec::new(),
            deprecated: None,
            ordinal,
            kind: Some(kind),
            links: Vec::new(),
            see: Vec::new(),
            since: Vec::new(),
        }
    }

    fn named_type(name: &str) -> v2::FieldType {
        v2::FieldType {
            optional: false,
            kind: Some(v2::field_type::Kind::Named(name.to_string())),
        }
    }

    fn stream_of(element: v2::stream_type::Element) -> v2::FieldType {
        v2::FieldType {
            optional: false,
            kind: Some(v2::field_type::Kind::Stream(v2::StreamType {
                element: Some(element),
            })),
        }
    }

    /// A representative ridl package: one interface holding all five
    /// interaction kinds plus a reserved tombstone (ordinals 1–6, the
    /// tombstone counted, ridl §11), a strict-periodic and a defaulted
    /// range timing, a fallible query, and two services — a named
    /// reference and an inline shape holding a stream query.
    fn fixture() -> v2::Package {
        // signal speed : Speed @10ms — strict periodic stores the period
        // in both bounds (ADR-0008 decision 12).
        let speed = v2::SignalDef {
            payload: "Speed".to_string(),
            declared_init: None,
            init: Some(v2::InitValue {
                derivable: true,
                value: Some("0.0".to_string()),
            }),
            timing: Some(v2::Timing {
                mode: v2::TimingMode::StrictPeriodic as i32,
                min_us: Some("10000".to_string()),
                max_us: Some("10000".to_string()),
                default_applied: false,
            }),
            family: v2::Family::Dispatch as i32,
        };

        // event doorOpened : DoorEvent — untimed in source, so the
        // configured default range is resolved at compile time (ridl §9.1).
        let door_opened = v2::EventDef {
            payload: "DoorEvent".to_string(),
            timing: Some(v2::Timing {
                mode: v2::TimingMode::Range as i32,
                min_us: Some("20000".to_string()),
                max_us: Some("500000".to_string()),
                default_applied: true,
            }),
            family: v2::Family::Dispatch as i32,
        };

        // command setTarget(target : Speed) [ require target >= speed ]
        let set_target = v2::CommandDef {
            params: vec![v2::Param {
                name: "target".to_string(),
                r#type: Some(named_type("Speed")),
                doc: String::new(),
                links: Vec::new(),
                see: Vec::new(),
                since: Vec::new(),
            }],
            contracts: vec![v2::Contract {
                kind: v2::ContractKind::Require as i32,
                source: "target >= speed".to_string(),
                signal_refs: vec!["speed".to_string()],
                param_refs: vec!["target".to_string()],
                uses_result: false,
                observer_id: "VehicleStatus.setTarget.require[0]".to_string(),
            }],
            timing: None,
            family: v2::Family::Dispatch as i32,
            shape: v2::Shape::None as i32,
        };

        // query fetchFaults(page : PageSpec) : FaultPage | DiagError
        //   [ ensure result.count <= page.limit ]
        let fetch_faults = v2::QueryDef {
            params: vec![v2::Param {
                name: "page".to_string(),
                r#type: Some(named_type("PageSpec")),
                doc: String::new(),
                links: Vec::new(),
                see: Vec::new(),
                since: Vec::new(),
            }],
            return_type: Some(v2::ReturnType {
                kind: Some(v2::return_type::Kind::Fallible(v2::FallibleType {
                    ok: "FaultPage".to_string(),
                    err: "DiagError".to_string(),
                })),
            }),
            contracts: vec![v2::Contract {
                kind: v2::ContractKind::Ensure as i32,
                source: "result.count <= page.limit".to_string(),
                signal_refs: Vec::new(),
                param_refs: vec!["page".to_string()],
                uses_result: true,
                observer_id: "VehicleStatus.fetchFaults.ensure[0]".to_string(),
            }],
            timing: None,
            family: v2::Family::Dispatch as i32,
        };

        // fixed vin : Vin
        let vin = v2::FixedDef {
            payload: Some(named_type("Vin")),
        };

        let vehicle_status = v2::Interface {
            name: "VehicleStatus".to_string(),
            visibility: v2::Visibility::Public as i32,
            doc: "Vehicle status contract".to_string(),
            labels: Vec::new(),
            deprecated: None,
            interactions: vec![
                interaction("speed", 1, v2::decl::Kind::SignalDef(speed)),
                interaction("doorOpened", 2, v2::decl::Kind::EventDef(door_opened)),
                // reserved legacyMode — the tombstone keeps ordinal 3
                // occupied in the one interaction sequence (ridl §11).
                v2::Decl {
                    ordinal: 3,
                    kind: Some(v2::decl::Kind::ReservedSlot(v2::Reserved {
                        ordinal: 3,
                        name: Some("legacyMode".to_string()),
                        value: None,
                    })),
                    ..interaction("", 3, v2::decl::Kind::ReservedSlot(v2::Reserved::default()))
                },
                interaction("setTarget", 4, v2::decl::Kind::CommandDef(set_target)),
                interaction("fetchFaults", 5, v2::decl::Kind::QueryDef(fetch_faults)),
                interaction("vin", 6, v2::decl::Kind::FixedDef(vin)),
            ],
            number: 0,
            provisional: false,
            links: Vec::new(),
            see: Vec::new(),
            since: Vec::new(),
        };

        // query tailLogs(pattern : <string>) : <LogLine> — a stream param
        // and a stream return (ridl §12), inside the inline service shape.
        let tail_logs = v2::QueryDef {
            params: vec![v2::Param {
                name: "pattern".to_string(),
                r#type: Some(stream_of(v2::stream_type::Element::Primitive(
                    v2::PrimitiveType::String as i32,
                ))),
                doc: String::new(),
                links: Vec::new(),
                see: Vec::new(),
                since: Vec::new(),
            }],
            return_type: Some(v2::ReturnType {
                kind: Some(v2::return_type::Kind::Value(stream_of(
                    v2::stream_type::Element::Named("LogLine".to_string()),
                ))),
            }),
            contracts: Vec::new(),
            timing: None,
            family: v2::Family::Dispatch as i32,
        };

        // service veh.adas.status : VehicleStatus — one named reference in
        // the service's set (ADR-0015 decision 12).
        let status_service = v2::Service {
            name: "veh.adas.status".to_string(),
            visibility: v2::Visibility::Public as i32,
            doc: String::new(),
            labels: Vec::new(),
            deprecated: None,
            shapes: vec![v2::ServiceShape {
                kind: Some(v2::service_shape::Kind::InterfaceRef(
                    "VehicleStatus".to_string(),
                )),
            }],
            links: Vec::new(),
            see: Vec::new(),
            since: Vec::new(),
        };
        // service veh.adas.logs { … } — the inline shape as the one entry,
        // Interface.name == "" (ridl §14.5).
        let logs_service = v2::Service {
            name: "veh.adas.logs".to_string(),
            visibility: v2::Visibility::Public as i32,
            doc: String::new(),
            labels: Vec::new(),
            deprecated: None,
            shapes: vec![v2::ServiceShape {
                kind: Some(v2::service_shape::Kind::Inline(v2::Interface {
                    name: String::new(),
                    visibility: v2::Visibility::Unspecified as i32,
                    doc: String::new(),
                    labels: Vec::new(),
                    deprecated: None,
                    interactions: vec![interaction(
                        "tailLogs",
                        1,
                        v2::decl::Kind::QueryDef(tail_logs),
                    )],
                    number: 0,
                    provisional: false,
                    links: Vec::new(),
                    see: Vec::new(),
                    since: Vec::new(),
                })),
            }],
            links: Vec::new(),
            see: Vec::new(),
            since: Vec::new(),
        };

        v2::Package {
            name: "veh.adas".to_string(),
            // One typl declaration proves the verbatim v1 surface rides
            // along unchanged in v2; package-level declarations carry
            // ordinal 0.
            decls: vec![v2::Decl {
                limit: None,
                name: "Speed".to_string(),
                visibility: v2::Visibility::Public as i32,
                is_error: false,
                doc: String::new(),
                labels: Vec::new(),
                deprecated: None,
                ordinal: 0,
                kind: Some(v2::decl::Kind::TypeDef(v2::TypeDef {
                    backing: Some(v2::Backing {
                        kind: Some(v2::backing::Kind::Unit("km/h".to_string())),
                    }),
                    constraint: None,
                    declared_init: None,
                    init: None,
                    width: Some(v2::type_def::Width::FloatWidth(v2::FloatWidth::F32 as i32)),
                })),
                links: Vec::new(),
                see: Vec::new(),
                since: Vec::new(),
            }],
            interfaces: vec![vehicle_status],
            services: vec![status_service, logs_service],
            retired: Vec::new(),
            unit: "veh.adas".to_string(),
        }
    }

    /// The typl vocabulary surface the interaction fixture does not reach:
    /// the boxed `inlineScalar` oneof member, genuine 64-bit integer fields
    /// (array and map bounds, length bounds, `Reserved.value`,
    /// `EnumValue.value`), a tuple, a map, a union, an enum set, a constant,
    /// and a set `deprecated`. A second fixture, so each stays readable; the
    /// same round-trip tests drive both.
    fn vocabulary_fixture() -> v2::Package {
        fn decl(name: &str, kind: v2::decl::Kind) -> v2::Decl {
            v2::Decl {
                limit: None,
                name: name.to_string(),
                visibility: v2::Visibility::Public as i32,
                is_error: false,
                doc: String::new(),
                labels: Vec::new(),
                deprecated: None,
                ordinal: 0,
                kind: Some(kind),
                links: Vec::new(),
                see: Vec::new(),
                since: Vec::new(),
            }
        }

        fn field(name: &str, ordinal: u32, field_type: v2::FieldType) -> v2::Field {
            v2::Field {
                name: name.to_string(),
                ordinal,
                r#type: Some(field_type),
                declared_init: None,
                init: None,
                doc: String::new(),
                labels: Vec::new(),
                deprecated: None,
                links: Vec::new(),
                see: Vec::new(),
                since: Vec::new(),
            }
        }

        // const MAX_RETRY : integer = 24
        let max_retry = v2::ConstDef {
            type_ref: Some("integer".to_string()),
            value: "24".to_string(),
            regex: None,
        };

        // enum Gear { PARK = 1  DRIVE = 2  reserved 7 } — the tombstone
        // retires the integer value, a genuine int64 field.
        let gear = v2::EnumDef {
            values: vec![
                v2::EnumValue {
                    name: "PARK".to_string(),
                    value: 1,
                    doc: String::new(),
                    links: Vec::new(),
                    see: Vec::new(),
                    since: Vec::new(),
                },
                v2::EnumValue {
                    name: "DRIVE".to_string(),
                    value: 2,
                    doc: String::new(),
                    links: Vec::new(),
                    see: Vec::new(),
                    since: Vec::new(),
                },
            ],
            reserved: vec![v2::Reserved {
                ordinal: 0,
                name: None,
                value: Some(7),
            }],
            open: false,
        };

        // enumset Warnings { LOW_FUEL = 0  ICE_RISK = 33 } — the standalone
        // form; bit 33 forces the u64 width and is a genuine int64 value.
        let warnings = v2::EnumSetDef {
            backing_enum: None,
            bits: vec![
                v2::EnumValue {
                    name: "LOW_FUEL".to_string(),
                    value: 0,
                    doc: String::new(),
                    links: Vec::new(),
                    see: Vec::new(),
                    since: Vec::new(),
                },
                v2::EnumValue {
                    name: "ICE_RISK".to_string(),
                    value: 33,
                    doc: String::new(),
                    links: Vec::new(),
                    see: Vec::new(),
                    since: Vec::new(),
                },
            ],
            width: v2::IntWidth::U64 as i32,
            open: false,
        };

        // type PlateText : string [1..86] — character length bounds, two
        // genuine uint64 fields behind proto3 `optional`.
        let plate_text = v2::TypeDef {
            backing: Some(v2::Backing {
                kind: Some(v2::backing::Kind::Primitive(
                    v2::PrimitiveType::String as i32,
                )),
            }),
            constraint: Some(v2::Constraint {
                min: None,
                max: None,
                step: None,
                len_min: Some(1),
                len_max: Some(86),
                pattern: None,
                pattern_const: None,
            }),
            declared_init: None,
            init: None,
            width: None,
        };

        // union Sample { speed : Speed  gear : Gear }
        let sample = v2::UnionDef {
            arms: vec![
                v2::UnionArm {
                    name: "speed".to_string(),
                    ordinal: 1,
                    type_ref: "Speed".to_string(),
                    doc: String::new(),
                    links: Vec::new(),
                    see: Vec::new(),
                    since: Vec::new(),
                },
                v2::UnionArm {
                    name: "gear".to_string(),
                    ordinal: 2,
                    type_ref: "Gear".to_string(),
                    doc: String::new(),
                    links: Vec::new(),
                    see: Vec::new(),
                    since: Vec::new(),
                },
            ],
            is_result: false,
            reserved: Vec::new(),
        };

        // retries : integer [0..24] = 3 — the boxed `inlineScalar` oneof
        // member: the committed regression guard for ADR-0014 Open item 2,
        // which established that the Rust-side `Box` is invisible to the
        // reflection path. The enclosing field carries the init; the nested
        // TypeDef's stays unset.
        let retries = v2::Field {
            declared_init: Some("3".to_string()),
            init: Some(v2::InitValue {
                derivable: true,
                value: Some("3".to_string()),
            }),
            ..field(
                "retries",
                1,
                v2::FieldType {
                    optional: false,
                    kind: Some(v2::field_type::Kind::InlineScalar(Box::new(v2::TypeDef {
                        backing: Some(v2::Backing {
                            kind: Some(v2::backing::Kind::Primitive(
                                v2::PrimitiveType::Integer as i32,
                            )),
                        }),
                        constraint: Some(v2::Constraint {
                            min: Some("0".to_string()),
                            max: Some("24".to_string()),
                            step: None,
                            len_min: None,
                            len_max: None,
                            pattern: None,
                            pattern_const: None,
                        }),
                        declared_init: None,
                        init: None,
                        width: Some(v2::type_def::Width::IntWidth(v2::IntWidth::U8 as i32)),
                    }))),
                },
            )
        };

        // position : (x : Speed, y : Speed) — an anonymous named-field
        // composite (typl §11).
        let position = field(
            "position",
            2,
            v2::FieldType {
                optional: false,
                kind: Some(v2::field_type::Kind::Tuple(v2::TupleType {
                    fields: vec![
                        v2::TupleField {
                            name: "x".to_string(),
                            r#type: Some(named_type("Speed")),
                        },
                        v2::TupleField {
                            name: "y".to_string(),
                            r#type: Some(named_type("Speed")),
                        },
                    ],
                })),
            },
        );

        // gears : [Gear; 1..4096] — array bounds are genuine uint64 fields.
        let gears = field(
            "gears",
            3,
            v2::FieldType {
                optional: false,
                kind: Some(v2::field_type::Kind::Array(Box::new(v2::ArrayType {
                    element: Some(Box::new(named_type("Gear"))),
                    min: 1,
                    max: 4096,
                }))),
            },
        );

        // plates : { PlateText -> Gear } [0..53] — map bounds are genuine
        // uint64 fields. The field is deprecated, covering the optional
        // string on the Field envelope.
        let plates = v2::Field {
            deprecated: Some("superseded by gears".to_string()),
            ..field(
                "plates",
                4,
                v2::FieldType {
                    optional: false,
                    kind: Some(v2::field_type::Kind::Map(Box::new(v2::MapType {
                        key: Some(Box::new(named_type("PlateText"))),
                        value: Some(Box::new(named_type("Gear"))),
                        min: 0,
                        max: 53,
                    }))),
                },
            )
        };

        let snapshot = v2::StructDef {
            members: [retries, position, gears, plates]
                .into_iter()
                .map(|field| v2::StructMember {
                    member: Some(v2::struct_member::Member::Field(Box::new(field))),
                })
                .collect(),
            fixed_layout: false,
        };

        v2::Package {
            name: "veh.vocab".to_string(),
            decls: vec![
                decl("MAX_RETRY", v2::decl::Kind::ConstDef(max_retry)),
                decl("Gear", v2::decl::Kind::EnumDef(gear)),
                decl("Warnings", v2::decl::Kind::EnumSetDef(warnings)),
                decl("PlateText", v2::decl::Kind::TypeDef(plate_text)),
                // The union is deprecated — the optional string on the Decl
                // envelope.
                v2::Decl {
                    deprecated: Some("use Snapshot".to_string()),
                    ..decl("Sample", v2::decl::Kind::UnionDef(sample))
                },
                decl("Snapshot", v2::decl::Kind::StructDef(snapshot)),
            ],
            interfaces: Vec::new(),
            services: Vec::new(),
            retired: Vec::new(),
            unit: String::new(),
        }
    }

    #[test]
    fn protobuf_round_trip_preserves_package() {
        let package = fixture();

        let buf = v2::to_binary(&package);
        let decoded = v2::from_binary(buf.as_slice()).expect("decode must succeed");

        assert_eq!(package, decoded);

        // The vocabulary fixture rides the same round trip.
        let vocabulary = vocabulary_fixture();
        let decoded_vocabulary =
            v2::from_binary(v2::to_binary(&vocabulary).as_slice()).expect("decode must succeed");
        assert_eq!(vocabulary, decoded_vocabulary);

        let interface = &decoded.interfaces[0];
        let ordinals: Vec<u32> = interface.interactions.iter().map(|d| d.ordinal).collect();
        assert_eq!(
            ordinals,
            [1, 2, 3, 4, 5, 6],
            "one ordinal sequence, tombstone counted (ridl §11)"
        );
        let Some(v2::decl::Kind::ReservedSlot(tombstone)) = &interface.interactions[2].kind else {
            panic!("ordinal 3 must decode as a reserved tombstone");
        };
        assert_eq!(tombstone.name.as_deref(), Some("legacyMode"));
        let Some(v2::service_shape::Kind::Inline(inline)) = decoded.services[1]
            .shapes
            .first()
            .and_then(|slot| slot.kind.as_ref())
        else {
            panic!("veh.adas.logs must decode as an inline shape");
        };
        assert_eq!(inline.name, "", "an inline shape carries no name");
        let references: Vec<&str> = decoded.services[0]
            .shapes
            .iter()
            .filter_map(|slot| match &slot.kind {
                Some(v2::service_shape::Kind::InterfaceRef(reference)) => Some(reference.as_str()),
                _ => None,
            })
            .collect();
        assert_eq!(
            references,
            ["VehicleStatus"],
            "a service's set carries its references and nothing else"
        );
    }

    /// A package with one interface `I` holding one command `c` of the given
    /// family and shape.
    fn package_with_command(family: v2::Family, shape: v2::Shape) -> v2::Package {
        v2::Package {
            name: "app".to_string(),
            interfaces: vec![v2::Interface {
                name: "I".to_string(),
                visibility: v2::Visibility::Public as i32,
                interactions: vec![v2::Decl {
                    name: "c".to_string(),
                    visibility: v2::Visibility::Public as i32,
                    ordinal: 1,
                    kind: Some(v2::decl::Kind::CommandDef(v2::CommandDef {
                        family: family as i32,
                        shape: shape as i32,
                        ..Default::default()
                    })),
                    ..Default::default()
                }],
                ..Default::default()
            }],
            ..Default::default()
        }
    }

    /// `(command, intent, none)` is refused where the IR is read, by both
    /// readers: ADR-0012 decision 5 admits no generic intent command.
    #[test]
    fn the_readers_reject_an_invalid_interaction_class() {
        let package = package_with_command(v2::Family::Intent, v2::Shape::None);
        let json = v2::render_json(&package).expect("the raw writer renders it");
        let err = v2::from_json(&json).expect_err("the JSON reader must refuse it");
        assert!(
            err.to_string().contains("invalid interaction class"),
            "{err}"
        );
        let bytes = prost::Message::encode_to_vec(&package);
        let err = v2::from_binary(&bytes).expect_err("the binary reader must refuse it");
        assert!(
            err.to_string().contains("invalid interaction class"),
            "{err}"
        );
    }

    #[test]
    fn the_json_writer_refuses_an_invalid_interaction_class() {
        let package = package_with_command(v2::Family::Intent, v2::Shape::None);
        let err = v2::to_json_pretty(&package).expect_err("the writer must refuse it");
        assert!(matches!(err, v2::SerializeError::Class(_)), "{err}");
    }

    #[test]
    fn a_valid_class_round_trips_through_both_readers() {
        let package = package_with_command(v2::Family::Intent, v2::Shape::Toggle);
        let json = v2::to_json_pretty(&package).expect("the writer renders it");
        assert_eq!(v2::from_json(&json).expect("the JSON parses"), package);
        assert_eq!(
            v2::from_binary(&v2::to_binary(&package)).expect("the binary decodes"),
            package
        );
    }

    /// An IR written before `family` existed has no such key and reads as
    /// dispatch.
    #[test]
    fn a_snapshot_without_family_reads_as_dispatch() {
        let package = package_with_command(v2::Family::Dispatch, v2::Shape::None);
        let json = v2::to_json_pretty(&package).expect("the writer renders it");
        let mut value: serde_json::Value =
            serde_json::from_str(&json).expect("the rendering is JSON");
        let command = value["interfaces"][0]["interactions"][0]["commandDef"]
            .as_object_mut()
            .expect("the command object");
        assert!(command.remove("family").is_some(), "`family` was rendered");
        assert!(command.remove("shape").is_some(), "`shape` was rendered");
        let stripped = serde_json::to_string(&value).expect("the stripped value renders");
        let read = v2::from_json(&stripped).expect("a 0.9 snapshot reads");
        assert_eq!(read, package);
    }

    #[test]
    fn json_round_trip_preserves_package() {
        for package in [fixture(), vocabulary_fixture()] {
            let json = v2::to_json_pretty(&package).expect("the fixture serializes as IR JSON");
            let decoded = v2::from_json(&json).expect("json deserialization must succeed");

            assert_eq!(package, decoded);
        }
    }

    /// The interface identity fields the lock design §9 adds — `number` and
    /// `provisional` on every `Interface`, an inline shape included, and the
    /// package's `retired` list — ride all three encodings unchanged, and the
    /// JSON writes them under their canonical names even when they hold their
    /// defaults (ADR-0014 decision 2), so a reader can tell `number` 0 from an
    /// absent field only by the schema, never by the text.
    #[test]
    fn number_provisional_and_retired_round_trip_through_json_text_and_binary() {
        let mut package = fixture();
        package.interfaces[0].number = 4;
        package.interfaces[0].provisional = true;
        let Some(v2::service_shape::Kind::Inline(inline)) =
            package.services[1].shapes[0].kind.as_mut()
        else {
            panic!("veh.adas.logs holds an inline shape in slot 1");
        };
        inline.number = 5;
        package.retired = vec![
            v2::RetiredInterface {
                name: "LaneAssist".to_string(),
                number: 2,
            },
            v2::RetiredInterface {
                name: "service:veh.hvac.cabin".to_string(),
                number: 3,
            },
        ];

        let json = v2::to_json_pretty(&package).expect("the package serializes as IR JSON");
        assert_eq!(v2::from_json(&json).expect("the JSON parses back"), package);
        let text = v2::to_text_format(&package).expect("the package serializes as prototext");
        assert_eq!(
            v2::from_text_format(&text).expect("the prototext parses back"),
            package
        );
        assert_eq!(
            v2::from_binary(v2::to_binary(&package).as_slice()).expect("the binary decodes"),
            package
        );

        for needle in [
            r#""number": 4"#,
            r#""provisional": true"#,
            r#""number": 5"#,
            r#""name": "LaneAssist""#,
            r#""name": "service:veh.hvac.cabin""#,
        ] {
            assert!(
                json.contains(needle),
                "the JSON must carry {needle}, got: {json}"
            );
        }

        // A default holds its place in the text (decision 2): an interface
        // that was never numbered writes `0` and `false`, and a package with
        // nothing retired writes an empty list.
        let unnumbered = v2::to_json_pretty(&fixture()).expect("the fixture serializes as IR JSON");
        for needle in [
            r#""number": 0"#,
            r#""provisional": false"#,
            r#""retired": []"#,
        ] {
            assert!(
                unnumbered.contains(needle),
                "a default field must still be written, expected {needle} in: {unnumbered}"
            );
        }
    }

    /// A baseline published before the lock existed carries no `number`, no
    /// `provisional` and no `retired` field. It still loads — a missing field
    /// reads as its default, which is the `number` 0 the lock design §7 names
    /// as the one transition case — while an unknown field is still rejected
    /// (`json_parse_rejects_an_unknown_field`).
    #[test]
    fn a_snapshot_lacking_the_number_fields_still_loads() {
        let package = v2::from_json(
            r#"{"name": "veh.x", "interfaces": [{"name": "LaneKeeping"}], "services": [{"name": "veh.x.s", "shapes": [{"inline": {"name": ""}}]}]}"#,
        )
        .expect("a pre-lock snapshot loads");

        assert_eq!(package.interfaces[0].number, 0);
        assert!(!package.interfaces[0].provisional);
        let Some(v2::service_shape::Kind::Inline(inline)) =
            package.services[0].shapes[0].kind.as_ref()
        else {
            panic!("the service holds an inline shape");
        };
        assert_eq!(inline.number, 0);
        assert!(!inline.provisional);
        assert_eq!(package.retired, Vec::new());
    }

    /// The prototext read path (ADR-0014 decision 7): both fixtures survive
    /// `to_text_format` then `from_text_format` unchanged. With the binary
    /// and JSON round trips above, this is what proves all three encodings
    /// carry the same IR.
    #[test]
    fn text_format_round_trip_preserves_package() {
        for package in [fixture(), vocabulary_fixture()] {
            let text = v2::to_text_format(&package).expect("the fixture serializes as prototext");
            let decoded = v2::from_text_format(&text).expect("prototext parsing must succeed");

            assert_eq!(package, decoded);
        }
    }

    /// The prototext options ADR-0014 decision 8 fixes — `pretty`,
    /// `skip_default_fields(false)`, `print_message_fields_in_index_order`.
    /// Any option set round-trips, which is why the round-trip test above
    /// cannot guard them.
    ///
    /// The first two are asserted through a visible consequence. The third is
    /// **not guarded here and cannot be on this schema**: every message in
    /// `ir.proto` declares its fields in ascending field-number order, and
    /// field-number order is also `prost-reflect`'s default, so index order
    /// and default order coincide everywhere and dropping the option would
    /// change no output. It is set because the schema's ordering is a
    /// property of the schema rather than a guarantee, and a message whose
    /// declaration order departs from its numbering would otherwise reorder
    /// every artifact it appears in.
    #[test]
    fn text_format_is_pretty_with_defaults_in_index_order() {
        let text = v2::to_text_format(&fixture()).expect("the fixture serializes as prototext");

        // pretty: nested messages are indented, one field per line.
        assert!(
            text.contains("\n  "),
            "pretty printing must indent nested fields, got: {text}"
        );
        // skip_default_fields(false): a field holding its default is present
        // (decision 2 — `ordinal: 0` is read, not inferred from absence).
        assert!(
            text.contains("is_error: false"),
            "a field holding its default must be emitted, got: {text}"
        );
        // print_message_fields_in_index_order: `name` is field 1 of
        // `Package`, so it opens the output.
        assert!(
            text.starts_with("name:"),
            "fields must print in schema index order, got: {text}"
        );
    }

    /// Parses emitted JSON the way ADR-0014 decision 11's conformance test
    /// requires: unknown fields rejected, trailing input rejected. Since
    /// decision 14 the strict parser is the pbjson-generated `Deserialize`
    /// impl, whose default already rejects unknown fields
    /// (`ignore_unknown_fields()` stays unset in `build.rs`), so the
    /// strictness needs no option to opt into.
    fn strict_parse(json: &str) -> v2::Package {
        let mut deserializer = serde_json::Deserializer::from_str(json);
        let package = <v2::Package as serde::Deserialize>::deserialize(&mut deserializer)
            .expect("a strict conformant parser must accept the emitted JSON");
        deserializer.end().expect("no trailing input");
        package
    }

    /// The conformance claim of ADR-0014 decision 11: a conformant protobuf
    /// JSON parser configured to reject unknown fields accepts the emitted
    /// JSON. Re-reading tests that claim itself; asserting on the rendered
    /// text would only restate the serializer's behaviour back to itself.
    #[test]
    fn emitted_json_survives_a_strict_conformant_parse() {
        for package in [fixture(), vocabulary_fixture()] {
            let json = v2::to_json_pretty(&package).expect("the fixture serializes as IR JSON");
            assert_eq!(package, strict_parse(&json));
        }
    }

    #[test]
    fn json_renders_timing_bounds_and_fallible_arms_exactly() {
        let json = v2::to_json_pretty(&fixture()).expect("the fixture serializes as IR JSON");

        // Exactness is visible: timing bounds are exact-decimal microsecond
        // strings, never floating-point numbers (ADR-0008 decision 12) —
        // under the canonical lowerCamelCase field name (ADR-0014 decision 1).
        assert!(
            json.contains(r#""minUs": "10000""#),
            "the timing bound must be a JSON string, got: {json}"
        );
        // Both arms of the inline T | E return are visible by name.
        assert!(
            json.contains(r#""ok": "FaultPage""#),
            "the ok arm must render, got: {json}"
        );
        assert!(
            json.contains(r#""err": "DiagError""#),
            "the err arm must render, got: {json}"
        );
    }

    /// ADR-0014 decision 8's stringification, tested on genuine 64-bit
    /// fields. The timing assertion above proves nothing about it —
    /// `Timing.min_us` is `optional string` in the schema — so the claim
    /// needs fields whose wire type actually is `uint64` or `int64`.
    #[test]
    fn json_renders_64_bit_integer_fields_as_strings() {
        let json = v2::to_json_pretty(&vocabulary_fixture())
            .expect("the vocabulary fixture serializes as IR JSON");

        // uint64: the array's upper bound.
        assert!(
            json.contains(r#""max": "4096""#),
            "an array bound must be a JSON string, got: {json}"
        );
        // uint64 behind proto3 `optional`: the character length bound.
        assert!(
            json.contains(r#""lenMax": "86""#),
            "a length bound must be a JSON string, got: {json}"
        );
        // int64: the retired enum value and the enum-set bit position.
        assert!(
            json.contains(r#""value": "7""#),
            "a retired enum value must be a JSON string, got: {json}"
        );
        assert!(
            json.contains(r#""value": "33""#),
            "an enum-set bit position must be a JSON string, got: {json}"
        );
    }

    #[test]
    fn fallible_transport_identity_follows_the_derivation_rule() {
        // The ADR-0008 decision 4 rule: interface + interaction ordinal +
        // both arm references, in that order.
        let fallible = v2::FallibleType {
            ok: "FaultPage".to_string(),
            err: "DiagError".to_string(),
        };
        assert_eq!(
            v2::fallible_transport_identity("VehicleStatus", 9, &fallible),
            "VehicleStatus#9:FaultPage|DiagError"
        );

        // Derived from the fixture: the fallible query sits at ordinal 5.
        let package = fixture();
        let interface = &package.interfaces[0];
        let query_decl = &interface.interactions[4];
        let Some(v2::decl::Kind::QueryDef(query)) = &query_decl.kind else {
            panic!("ordinal 5 must be the fallible query");
        };
        let Some(v2::return_type::Kind::Fallible(arms)) = &query.return_type.as_ref().unwrap().kind
        else {
            panic!("fetchFaults must return a fallible type");
        };
        assert_eq!(
            v2::fallible_transport_identity(&interface.name, query_decl.ordinal, arms),
            "VehicleStatus#5:FaultPage|DiagError"
        );
    }

    /// `Package::shapes` yields the named interfaces first, then the inline
    /// shapes of the services — and each shape carries the name it is known by
    /// OUTSIDE the package. The fixture's inline shape has `Interface.name ==
    /// ""` by construction, so a walk that yielded the interface bare would
    /// hand every consumer the empty string; two of the six E2 defects were
    /// exactly that.
    #[test]
    fn shapes_walks_named_interfaces_and_inline_service_shapes() {
        let package = fixture();
        let walk: Vec<(&str, bool, usize)> = package
            .shapes()
            .map(|shape| {
                (
                    shape.name,
                    shape.is_inline(),
                    shape.interface.interactions.len(),
                )
            })
            .collect();
        assert_eq!(
            walk,
            [("VehicleStatus", false, 6), ("veh.adas.logs", true, 1)],
            "the named interface, then the inline shape under the service's \
             dotted name",
        );

        // The fixture's third shape-bearing declaration is `service
        // veh.adas.status : VehicleStatus`, which names an interface already in
        // the walk. Yielding it too would visit `VehicleStatus` twice.
        assert_eq!(package.services.len(), 2, "one reference form, one inline");
        assert!(
            !package
                .shapes()
                .any(|shape| shape.name == "veh.adas.status"),
            "a service naming an interface contributes no shape of its own",
        );
    }

    #[test]
    fn relative_name_strips_the_unit_prefix() {
        assert_eq!(v2::relative_name("u", "u", "Session"), "Session");
        assert_eq!(
            v2::relative_name("u", "u.cluster", "Speed"),
            "cluster.Speed"
        );
        assert_eq!(
            v2::relative_name("com.example.hmi", "com.example.hmi.cluster.front", "A"),
            "cluster.front.A"
        );
    }

    /// A package that is not inside the unit keeps its full name: no slice
    /// past the unit's length, whatever the snapshot says.
    #[test]
    fn relative_name_keeps_the_full_name_of_a_package_outside_the_unit() {
        assert_eq!(
            v2::relative_name("u", "w.cluster", "Speed"),
            "w.cluster.Speed"
        );
        assert_eq!(v2::relative_name("u", "ux", "A"), "ux.A");
        assert_eq!(v2::relative_name("u.cluster", "u", "Session"), "u.Session");
    }

    /// A package named twice in the slice contributes the retired entries
    /// of its first occurrence only: two distinct values with the same name
    /// are not merged, and the later one is not read.
    #[test]
    fn unit_retired_reads_a_package_named_twice_once() {
        let first = v2::Package {
            name: "u.cluster".to_string(),
            unit: "u".to_string(),
            retired: vec![v2::RetiredInterface {
                name: "cluster.Old".to_string(),
                number: 3,
            }],
            ..Default::default()
        };
        let second = v2::Package {
            retired: vec![v2::RetiredInterface {
                name: "cluster.Older".to_string(),
                number: 4,
            }],
            ..first.clone()
        };
        assert_eq!(
            v2::unit_retired("u", &[&first, &second]),
            first.retired,
            "the first package of a name is the one read"
        );
    }

    #[test]
    fn an_inline_shape_keeps_its_global_name() {
        let mut package = fixture();
        package.name = "u.cluster".to_string();
        package.unit = "u".to_string();
        let inline = package
            .shapes()
            .find(|shape| shape.is_inline())
            .expect("the fixture has an inline shape");
        assert_eq!(package.catalog_name(&inline), "veh.adas.logs");
        let named = package
            .shapes()
            .find(|shape| !shape.is_inline())
            .expect("the fixture has a declared interface");
        assert_eq!(package.catalog_name(&named), "cluster.VehicleStatus");
    }

    #[test]
    fn catalog_name_treats_an_empty_unit_as_the_package_name() {
        let mut package = fixture();
        package.unit = String::new();
        let named = package
            .shapes()
            .find(|shape| !shape.is_inline())
            .expect("the fixture has a declared interface");
        assert_eq!(package.catalog_name(&named), "VehicleStatus");
    }

    #[test]
    fn unit_of_falls_back_to_the_name() {
        let bare = v2::Package {
            name: "p".to_string(),
            ..Default::default()
        };
        assert_eq!(v2::unit_of(&bare), "p");
        let member = v2::Package {
            name: "u.a".to_string(),
            unit: "u".to_string(),
            ..Default::default()
        };
        assert_eq!(v2::unit_of(&member), "u");
    }

    #[test]
    fn packages_of_unit_selects_by_unit_of() {
        let package = |name: &str, unit: &str| v2::Package {
            name: name.to_string(),
            unit: unit.to_string(),
            ..Default::default()
        };
        let packages = [
            package("u", "u"),
            package("u.a", "u"),
            package("w", ""),
            package("other.b", "other"),
        ];
        let names: Vec<&str> = v2::packages_of_unit("u", &packages)
            .map(|p| p.name.as_str())
            .collect();
        assert_eq!(names, ["u", "u.a"]);
        let legacy: Vec<&str> = v2::packages_of_unit("w", &packages)
            .map(|p| p.name.as_str())
            .collect();
        assert_eq!(legacy, ["w"]);
    }

    /// The owning service is carried because `Service.visibility` is the
    /// authoritative one: an inline shape's own field is
    /// `VISIBILITY_UNSPECIFIED` by construction, which is not "internal" and
    /// not "public".
    #[test]
    fn shape_visibility_reads_the_owning_service_for_an_inline_shape() {
        let package = fixture();
        let shapes: Vec<v2::InterfaceShape<'_>> = package.shapes().collect();

        let named = shapes[0];
        assert!(named.service.is_none());
        assert_eq!(named.visibility(), v2::Visibility::Public as i32);
        assert_eq!(named.visibility(), named.interface.visibility);

        let inline = shapes[1];
        assert_eq!(
            inline.interface.visibility,
            v2::Visibility::Unspecified as i32,
            "the trap: an inline shape's own visibility field is unset",
        );
        assert_eq!(
            inline.service.expect("an inline shape has an owner").name,
            "veh.adas.logs",
        );
        assert_eq!(
            inline.visibility(),
            v2::Visibility::Public as i32,
            "the accessor reads the owning service's, never the unset field",
        );
    }

    /// A package with no service at all still walks its interfaces, and a
    /// package with neither yields nothing — the emptiness both backends test
    /// for before emitting any interaction vocabulary.
    #[test]
    fn shapes_is_empty_only_when_the_package_declares_no_shape() {
        let mut package = fixture();
        package.services.clear();
        assert_eq!(package.shapes().count(), 1);

        package.interfaces.clear();
        assert_eq!(package.shapes().count(), 0);
    }

    /// A dotted reference contributes its qualifier; a bare one contributes
    /// nothing. Every recursive path through `walk_field_type` — array
    /// element, tuple field, map key, map value, stream element — carries a
    /// distinct qualifier, so no path's absence can hide behind another
    /// path's presence: deleting any one arm's body changes the expected set
    /// this test compares against, rather than leaving it unchanged.
    #[test]
    fn referenced_packages_finds_qualifiers_at_depth() {
        fn named(reference: &str) -> v2::FieldType {
            v2::FieldType {
                kind: Some(v2::field_type::Kind::Named(reference.to_string())),
                ..Default::default()
            }
        }

        fn fixed(payload: v2::FieldType) -> v2::decl::Kind {
            v2::decl::Kind::FixedDef(v2::FixedDef {
                payload: Some(payload),
            })
        }

        let package = v2::Package {
            name: "veh.cluster".to_string(),
            decls: vec![
                v2::Decl {
                    name: "Local".to_string(),
                    kind: Some(v2::decl::Kind::SignalDef(v2::SignalDef {
                        payload: "Speed".to_string(),
                        ..Default::default()
                    })),
                    ..Default::default()
                },
                v2::Decl {
                    name: "Stamped".to_string(),
                    kind: Some(v2::decl::Kind::SignalDef(v2::SignalDef {
                        payload: "ridl.std.Timestamp".to_string(),
                        ..Default::default()
                    })),
                    ..Default::default()
                },
                v2::Decl {
                    name: "ArrLabels".to_string(),
                    kind: Some(fixed(v2::FieldType {
                        kind: Some(v2::field_type::Kind::Array(Box::new(v2::ArrayType {
                            element: Some(Box::new(named("veh.arr.Label"))),
                            min: 0,
                            max: 32,
                        }))),
                        ..Default::default()
                    })),
                    ..Default::default()
                },
                v2::Decl {
                    name: "TupThing".to_string(),
                    kind: Some(fixed(v2::FieldType {
                        kind: Some(v2::field_type::Kind::Tuple(v2::TupleType {
                            fields: vec![v2::TupleField {
                                name: "x".to_string(),
                                r#type: Some(named("veh.tup.X")),
                            }],
                        })),
                        ..Default::default()
                    })),
                    ..Default::default()
                },
                v2::Decl {
                    name: "MapThing".to_string(),
                    kind: Some(fixed(v2::FieldType {
                        kind: Some(v2::field_type::Kind::Map(Box::new(v2::MapType {
                            key: Some(Box::new(named("veh.key.X"))),
                            value: Some(Box::new(named("veh.val.X"))),
                            min: 0,
                            max: 8,
                        }))),
                        ..Default::default()
                    })),
                    ..Default::default()
                },
                v2::Decl {
                    name: "StreamThing".to_string(),
                    kind: Some(fixed(v2::FieldType {
                        kind: Some(v2::field_type::Kind::Stream(v2::StreamType {
                            element: Some(v2::stream_type::Element::Named(
                                "veh.strm.X".to_string(),
                            )),
                        })),
                        ..Default::default()
                    })),
                    ..Default::default()
                },
            ],
            ..Default::default()
        };

        let found = v2::referenced_packages(&package);
        let expected: std::collections::BTreeSet<String> = [
            "ridl.std", "veh.arr", "veh.tup", "veh.key", "veh.val", "veh.strm",
        ]
        .into_iter()
        .map(str::to_string)
        .collect();
        assert_eq!(
            found, expected,
            "each recursive path must contribute its own distinct qualifier"
        );
        assert!(
            !found.contains("Speed") && !found.contains("veh.cluster"),
            "a bare reference contributes no package: {found:?}",
        );
    }

    /// An empty package references nothing — the negative case the emit rule in
    /// `ridlc` depends on.
    #[test]
    fn referenced_packages_is_empty_without_references() {
        let package = v2::Package {
            name: "veh.solo".to_string(),
            ..Default::default()
        };
        assert!(v2::referenced_packages(&package).is_empty());
    }

    /// Below prost's recursion limit at two message levels per nesting level
    /// — the depth ADR-0014 decision 12 measured as round-tripping correctly.
    /// Since decision 14 these two constants bound the prototext transcode
    /// alone: JSON no longer transcodes and carries its own read-side
    /// ceiling, tested separately below.
    const NESTING_BELOW_LIMIT: usize = 45;
    /// Past the limit today. The tests assert the outcome — an error, never a
    /// panic — not the exact threshold, so a prost release that moves the
    /// limit moves these constants, not the assertions.
    const NESTING_PAST_LIMIT: usize = 60;

    /// One declaration whose payload nests `depth` levels of inline arrays —
    /// each level costs two message levels on the wire (`FieldType` plus
    /// `ArrayType`), the arithmetic ADR-0014 decision 12 records against
    /// prost's recursion limit.
    fn nested_package(depth: usize) -> v2::Package {
        let mut payload = v2::FieldType {
            optional: false,
            kind: Some(v2::field_type::Kind::Primitive(
                v2::PrimitiveType::Integer as i32,
            )),
        };
        for _ in 0..depth {
            payload = v2::FieldType {
                optional: false,
                kind: Some(v2::field_type::Kind::Array(Box::new(v2::ArrayType {
                    element: Some(Box::new(payload)),
                    min: 1,
                    max: 1,
                }))),
            };
        }
        v2::Package {
            name: "veh.deep".to_string(),
            decls: vec![v2::Decl {
                name: "deep".to_string(),
                kind: Some(v2::decl::Kind::FixedDef(v2::FixedDef {
                    payload: Some(payload),
                })),
                ..Default::default()
            }],
            ..Default::default()
        }
    }

    /// One package whose nesting sits exactly `levels` message levels below
    /// the `Package` root — the unit the derived binary encoding's bound is
    /// stated in (the IR specification, "The derived encodings").
    ///
    /// The chain under a `FixedDef` costs three levels before any nesting
    /// (`Decl`, `FixedDef`, the outermost `FieldType`) and two per array level
    /// (`ArrayType`, `FieldType`), so an array-only chain reaches the odd
    /// depths alone. One tuple level costs three (`FieldType`, `TupleType`,
    /// `TupleField`, then the `FieldType` the next level counts), which is what
    /// reaches the even depths. Both shapes are what the front end lowers, so
    /// neither is a construction the schema would not otherwise see.
    fn package_at_message_depth(levels: usize) -> v2::Package {
        assert!(levels >= 3, "the chain costs three levels before nesting");
        let (arrays, tuple) = if levels % 2 == 1 {
            ((levels - 3) / 2, false)
        } else {
            assert!(levels >= 6, "one tuple level costs three");
            ((levels - 6) / 2, true)
        };

        let mut payload = v2::FieldType {
            optional: false,
            kind: Some(v2::field_type::Kind::Primitive(
                v2::PrimitiveType::Integer as i32,
            )),
        };
        for _ in 0..arrays {
            payload = v2::FieldType {
                optional: false,
                kind: Some(v2::field_type::Kind::Array(Box::new(v2::ArrayType {
                    element: Some(Box::new(payload)),
                    min: 1,
                    max: 1,
                }))),
            };
        }
        if tuple {
            payload = v2::FieldType {
                optional: false,
                kind: Some(v2::field_type::Kind::Tuple(v2::TupleType {
                    fields: vec![v2::TupleField {
                        name: "f0".to_string(),
                        r#type: Some(payload),
                    }],
                })),
            };
        }
        v2::Package {
            name: "veh.deep".to_string(),
            decls: vec![v2::Decl {
                name: "deep".to_string(),
                kind: Some(v2::decl::Kind::FixedDef(v2::FixedDef {
                    payload: Some(payload),
                })),
                ..Default::default()
            }],
            ..Default::default()
        }
    }

    /// The nesting of JSON objects in a canonical artifact, which in the
    /// protobuf JSON mapping is the nesting of messages: every message is an
    /// object, a repeated field is an array of them, and the schema declares no
    /// `map<>` field. The root `Package` object is included, so a caller
    /// counting levels *below* the root subtracts one. Brackets inside a string
    /// literal do not count.
    fn message_nesting(json: &str) -> usize {
        let (mut depth, mut max) = (0usize, 0usize);
        let (mut in_string, mut escaped) = (false, false);
        for byte in json.bytes() {
            if in_string {
                if escaped {
                    escaped = false;
                } else if byte == b'\\' {
                    escaped = true;
                } else if byte == b'"' {
                    in_string = false;
                }
                continue;
            }
            match byte {
                b'"' => in_string = true,
                b'{' => {
                    depth += 1;
                    max = max.max(depth);
                }
                b'}' => depth = depth.saturating_sub(1),
                _ => {}
            }
        }
        max
    }

    /// [`package_at_message_depth`] builds what it claims, on both parities.
    /// Without this the two bound tests below would pin a depth nobody
    /// measured.
    #[test]
    fn package_at_message_depth_builds_the_depth_it_names() {
        with_sized_stack(|| {
            for levels in [3, 6, 7, 99, 100, 101] {
                let json = v2::to_json_pretty(&package_at_message_depth(levels))
                    .expect("the writer is unrestricted at these depths");
                assert_eq!(
                    message_nesting(&json) - 1,
                    levels,
                    "the chain must nest {levels} message levels below the root"
                );
            }
        });
    }

    /// The derived binary encoding's bound, stated by the IR specification and
    /// pinned here: 100 message levels below the root round-trip.
    ///
    /// `to_binary` writes any depth; it is `from_binary` that stops, at prost's
    /// `RECURSION_LIMIT` of 100, decremented once per nested message on decode
    /// and not consulted on encode. The test asserts the outcome, not prost's
    /// constant: a prost release that moves the limit moves these two tests and
    /// the specification's paragraph together.
    #[test]
    fn binary_round_trip_at_100_message_levels_succeeds() {
        let package = package_at_message_depth(100);
        let bytes = v2::to_binary(&package);
        let decoded = v2::from_binary(&bytes).expect("100 message levels decode");
        assert_eq!(package, decoded);
    }

    /// One level past that bound the binary reader refuses — an error, never a
    /// panic — while the canonical encoding carries the same package. This is
    /// the asymmetry the specification states as the reason binary is derived
    /// rather than canonical (driftsys/ridl#231).
    #[test]
    fn binary_decode_at_101_message_levels_returns_an_error() {
        let package = package_at_message_depth(101);
        let bytes = v2::to_binary(&package);
        let error = v2::from_binary(&bytes).expect_err("101 message levels must fail, not panic");
        assert!(
            error.to_string().contains("recursion limit reached"),
            "the error must name the limit, got: {error}"
        );

        let json = v2::to_json_pretty(&package).expect("the canonical encoding has no such bound");
        assert_eq!(
            package,
            v2::from_json(&json).expect("the canonical encoding round-trips the same package")
        );
    }

    /// The write side after ADR-0014 decision 14: the pbjson-generated
    /// writer recurses the typed message directly — no transcode, so no
    /// message-level recursion limit — and 400 levels of array nesting,
    /// roughly eight times the ceiling decision 12 recorded, serialize and
    /// round-trip. Run on an explicitly sized stack: the writer recurses on
    /// the caller's stack, and debug-build frames at this depth overflow the
    /// default test-thread stack (the reader sizes its own thread inside
    /// `from_json`).
    #[test]
    fn json_round_trip_at_400_nested_levels_succeeds() {
        with_sized_stack(|| {
            let package = nested_package(400);
            let json = v2::to_json_pretty(&package).expect("the writer has no message-level limit");
            let decoded = v2::from_json(&json).expect("the reader parses within its ceiling");
            assert_eq!(package, decoded);
        });
    }

    /// The one error path on the JSON write side (ADR-0014 decision 14),
    /// and it is new with the generated impl, not a survivor of the
    /// transcode's: an `i32` enum field holding a discriminant outside the
    /// schema — data, not depth — which the retired reflection path
    /// serialized successfully as its bare number. The checker never
    /// produces one, so there is no CLI route to this failure; it is pinned
    /// here at the crate surface.
    #[test]
    fn json_serialization_of_an_out_of_schema_discriminant_returns_an_error() {
        let mut package = fixture();
        package.decls[0].visibility = 999;
        let err = v2::to_json_pretty(&package)
            .expect_err("an out-of-schema discriminant must fail, not panic");
        let message = err.to_string();
        assert!(
            message.contains("canonical protobuf JSON"),
            "the error must name the encoding that failed, got: {message}"
        );
        assert!(
            message.contains("discriminant outside the schema"),
            "the error must name the known cause, got: {message}"
        );
    }

    /// The strictness ADR-0014 decision 11 relies on is the generated
    /// deserializer's default: `ignore_unknown_fields()` is the opt-out and
    /// stays unset, so a field the schema does not declare is an error,
    /// never silently dropped.
    #[test]
    fn json_parse_rejects_an_unknown_field() {
        let error = v2::from_json(r#"{"name": "veh.deep", "notAField": 1}"#)
            .expect_err("an unknown field must be rejected");
        assert!(
            error.to_string().contains("unknown field"),
            "the error must name the defect, got: {error}"
        );
    }

    /// A reader narrowing ADR-0014 decision 14 records: the proto3 JSON
    /// mapping expects parsers to accept numeric enum values, and the
    /// generated deserializer does — within the schema's range. A
    /// discriminant outside it (`"visibility": 77`) is rejected, where the
    /// retired reflection reader accepted it — and the retired *writer*
    /// emitted exactly such a number for an out-of-schema discriminant.
    /// Pinned so the narrowing stays a decision rather than an accident: a
    /// future mechanism change must confront this test.
    #[test]
    fn json_parse_rejects_an_out_of_range_numeric_enum_value() {
        let with_visibility =
            |value: &str| format!(r#"{{"name": "veh.x", "decls": [{{"visibility": {value}}}]}}"#);
        v2::from_json(&with_visibility("1"))
            .expect("an in-range numeric enum value parses, as the mapping expects");
        let error = v2::from_json(&with_visibility("77"))
            .expect_err("an out-of-range numeric enum value must be rejected");
        assert!(
            error.to_string().contains("invalid value: integer `77`"),
            "the error must name the value, got: {error}"
        );
    }

    /// A reader narrowing ADR-0014 decision 14 records: the mapping accepts
    /// float and exponent notation for integer fields (`"min": 1.0`), and
    /// the retired reflection reader did; the generated deserializer
    /// rejects both. Pinned for the same reason as the numeric-enum case
    /// above.
    #[test]
    fn json_parse_rejects_a_float_form_integer() {
        for spelling in ["1.0", "1e0"] {
            let error = v2::from_json(&format!(
                r#"{{"name": "veh.x", "decls": [{{"fixedDef": {{"payload": {{"array": {{"min": {spelling}}}}}}}}}]}}"#,
            ))
            .expect_err("a float-form integer must be rejected");
            assert!(
                error.to_string().contains("did not match any variant"),
                "the integer field's deserializer must be the one refusing `{spelling}`, \
                 got: {error}"
            );
        }
    }

    /// A reader narrowing ADR-0014 decision 14 records: `null` for a
    /// repeated field (`"decls": null`), which the retired reflection
    /// reader read as empty, is rejected. `null` for an optional scalar or
    /// message field is still accepted — parity with the retired reader,
    /// asserted alongside so the narrowing's edge is pinned from both
    /// sides.
    #[test]
    fn json_parse_rejects_null_for_a_repeated_field() {
        let error = v2::from_json(r#"{"name": "veh.x", "decls": null}"#)
            .expect_err("null for a repeated field must be rejected");
        assert!(
            error.to_string().contains("invalid type: null"),
            "the error must name the null, got: {error}"
        );
        v2::from_json(r#"{"name": "veh.x", "decls": [{"deprecated": null}]}"#)
            .expect("null for an optional scalar field still parses");
    }

    /// A reader narrowing ADR-0014 decision 14 records: a duplicate JSON
    /// key, which the retired reflection reader resolved last-wins, is
    /// rejected.
    #[test]
    fn json_parse_rejects_a_duplicate_key() {
        let error = v2::from_json(r#"{"name": "a", "name": "b"}"#)
            .expect_err("a duplicate key must be rejected");
        assert!(
            error.to_string().contains("duplicate field `name`"),
            "the error must name the duplicated field, got: {error}"
        );
    }

    /// The read-side ceiling (ADR-0014 decision 14): nesting past 1,000
    /// bracket levels returns an error before the parse begins — a
    /// diagnostic, where unbounded recursion would eventually abort on a
    /// stack overflow no caller can catch. The input is real writer output:
    /// past the ceiling the asymmetry is deliberate — the writer is
    /// unrestricted, the reader is not.
    #[test]
    fn json_parse_past_the_nesting_ceiling_returns_an_error() {
        with_sized_stack(|| {
            let json = v2::to_json_pretty(&nested_package(500))
                .expect("the writer is unrestricted at this depth");
            let error = v2::from_json(&json).expect_err("the reader must refuse past its ceiling");
            assert!(
                error.to_string().contains("1000 JSON levels"),
                "the error must name the ceiling, got: {error}"
            );
        });
    }

    /// The ceiling is exact: 1,000 open brackets pass the scan and reach the
    /// parser — which then rejects the input as not a package — and 1,001 do
    /// not. The scan runs before the parse, so the over-ceiling probe needs
    /// no valid JSON behind its brackets.
    #[test]
    fn json_nesting_ceiling_binds_exactly_at_1000() {
        let at = v2::from_json(&"[".repeat(1_000)).expect_err("an array is not a package");
        assert!(
            !at.to_string().contains("JSON levels"),
            "at the ceiling the parser, not the scan, must be the one refusing, got: {at}"
        );

        let past = v2::from_json(&"[".repeat(1_001)).expect_err("past the ceiling, the scan");
        assert!(
            past.to_string().contains("1000 JSON levels"),
            "past the ceiling the error must name it, got: {past}"
        );
    }

    /// The nesting scan behind the ceiling: brackets count only outside
    /// string literals, an escaped quote does not end a literal, an escaped
    /// backslash does not disarm the real closing quote after it, and a
    /// stray closer never underflows the running depth.
    #[test]
    fn nesting_scan_counts_brackets_outside_string_literals_only() {
        // Plain structural nesting counts every open bracket.
        assert_eq!(v2::max_json_nesting(r#"{"a": [{"b": []}]}"#), 4);
        // Brackets inside a string literal do not count.
        assert_eq!(v2::max_json_nesting(r#"{"doc": "{[[[{"}"#), 1);
        // An escaped quote does not end the literal, so the brackets after
        // it are still inside it.
        assert_eq!(v2::max_json_nesting(r#"{"doc": "a\"[[[", "x": []}"#), 2);
        // An escaped backslash does not escape the closing quote: the
        // literal ends, and the brackets after it count.
        assert_eq!(v2::max_json_nesting(r#"{"doc": "a\\", "x": [[]]}"#), 3);
        // A stray closer saturates at zero rather than underflowing.
        assert_eq!(v2::max_json_nesting("]]]{"), 1);
    }

    /// The prototext form of [`nested_package`], built by hand for the same
    /// reason [`nested_json`] is: past the limit the serializer rejects the
    /// package, so its prototext cannot come from [`v2::to_text_format`].
    fn nested_text(depth: usize) -> String {
        let mut payload = "primitive: PRIMITIVE_TYPE_INTEGER".to_string();
        for _ in 0..depth {
            payload = format!("array {{ element {{ {payload} }} min: 1 max: 1 }}");
        }
        format!(
            r#"name: "veh.deep" decls {{ name: "deep" fixed_def {{ payload {{ {payload} }} }} }}"#
        )
    }

    /// The prototext write path carries the same recursion-limit failure mode
    /// as JSON — both go through the one transcode (ADR-0014 decision 12) —
    /// and reports it as an error naming its own encoding, never a panic.
    #[test]
    fn text_serialization_past_the_nesting_limit_returns_an_error() {
        let err = v2::to_text_format(&nested_package(NESTING_PAST_LIMIT))
            .expect_err("serialization past the recursion limit must fail, not panic");
        let message = err.to_string();
        assert!(
            message.contains("recursion limit"),
            "the error must name the nesting limit as the known cause, got: {message}"
        );
        assert!(
            message.contains("prototext"),
            "the error must name the encoding that failed, got: {message}"
        );
    }

    /// Runs `test` on a thread whose stack fits the recursion the test
    /// drives on its own thread. Two groups need one. The prototext parser
    /// recurses once per message level with debug-build frames large enough
    /// that the default 2 MiB test-thread stack overflows near 45 array
    /// levels — under prost's own recursion limit, so the depths
    /// [`NESTING_BELOW_LIMIT`] and [`NESTING_PAST_LIMIT`] pin are
    /// unreachable on that stack; the production paths are unaffected, since
    /// the toolchain writes prototext and never parses it (`ridl diff` and
    /// the baselines stay `.ir.json`, ADR-0014 decision 5). And the deep
    /// JSON tests drive the pbjson-generated writer, which recurses on the
    /// caller's stack (ADR-0014 decision 14 — only the reader sizes a
    /// thread of its own, inside `from_json`).
    fn with_sized_stack(test: impl FnOnce() + Send + 'static) {
        let outcome = std::thread::Builder::new()
            .stack_size(16 * 1024 * 1024)
            .spawn(test)
            .expect("spawn the large-stack test thread")
            .join();
        if let Err(payload) = outcome {
            std::panic::resume_unwind(payload);
        }
    }

    /// The read direction: the text-format parser itself has no depth limit,
    /// so the failure is the transcode out of the dynamic message, mapped
    /// into the error return instead of expected on (ADR-0014 decision 12).
    #[test]
    fn text_parse_past_the_nesting_limit_returns_an_error() {
        with_sized_stack(|| {
            let error = v2::from_text_format(&nested_text(NESTING_PAST_LIMIT))
                .expect_err("parsing past the recursion limit must fail, not panic");

            // Assert *which* stage failed: prost's transcoding decoder says
            // "recursion limit reached", and a parse-stage failure would
            // render through the `Parse` variant instead.
            let message = error.to_string();
            assert!(
                message.contains("recursion limit reached"),
                "the transcode out of the dynamic message must be the failing \
                 stage, got: {message}"
            );
        });
    }

    /// The prototext bound must not tighten silently either: below the limit
    /// the package still serializes and round-trips.
    #[test]
    fn text_round_trip_below_the_nesting_limit_succeeds() {
        with_sized_stack(|| {
            let package = nested_package(NESTING_BELOW_LIMIT);
            let text = v2::to_text_format(&package)
                .expect("below the recursion limit, serialization succeeds");
            let decoded =
                v2::from_text_format(&text).expect("below the recursion limit, parsing succeeds");
            assert_eq!(package, decoded);
        });
    }
}

#[cfg(test)]
mod vacuous_constraint {
    use crate::v2;

    /// A constraint with every field absent. Each test sets only the field it
    /// is about, so no assertion can pass through a neighbouring field.
    fn constraint() -> v2::Constraint {
        v2::Constraint {
            min: None,
            max: None,
            step: None,
            len_min: None,
            len_max: None,
            pattern: None,
            pattern_const: None,
        }
    }

    #[test]
    fn an_absent_or_empty_constraint_is_vacuous() {
        assert!(v2::constraint_is_vacuous(None));
        assert!(v2::constraint_is_vacuous(Some(&constraint())));
    }

    #[test]
    fn a_step_constraint_is_non_vacuous() {
        let stepped = v2::Constraint {
            step: Some("0.5".to_string()),
            ..constraint()
        };
        assert!(!v2::constraint_is_vacuous(Some(&stepped)));
    }

    /// Every constrained field on its own. A fixture setting a pair — `min`
    /// with `max`, or `len_min` with `len_max` — cannot tell a predicate that
    /// reads both from one that reads either, so each bound here is one-sided.
    /// The paired shapes are pinned separately by
    /// [`a_bound_pair_set_together_is_non_vacuous`], which a one-sided fixture
    /// cannot do.
    #[test]
    fn any_single_constrained_field_is_non_vacuous() {
        let cases = [
            (
                "min",
                v2::Constraint {
                    min: Some("0.0".to_string()),
                    ..constraint()
                },
            ),
            (
                "max",
                v2::Constraint {
                    max: Some("250.0".to_string()),
                    ..constraint()
                },
            ),
            (
                "len_min",
                v2::Constraint {
                    len_min: Some(1),
                    ..constraint()
                },
            ),
            (
                "len_max",
                v2::Constraint {
                    len_max: Some(256),
                    ..constraint()
                },
            ),
            (
                "pattern",
                v2::Constraint {
                    pattern: Some("^[a-z]+$".to_string()),
                    ..constraint()
                },
            ),
            (
                "pattern_const",
                v2::Constraint {
                    pattern_const: Some("NAME_PATTERN".to_string()),
                    ..constraint()
                },
            ),
        ];
        for (field, case) in cases {
            assert!(
                !v2::constraint_is_vacuous(Some(&case)),
                "`{field}` alone must be non-vacuous"
            );
        }
    }

    /// The two shapes the checker actually emits: a declared range, and the
    /// typl §4.4 default `[0..256]` every string and bytes type carries.
    ///
    /// A one-sided fixture cannot pin these. A predicate reading each bound as
    /// a pair — `(c.min.is_none() == c.max.is_none())` and the same for the
    /// length bounds — passes every one-sided case and still reports both
    /// shapes below as vacuous, which would drop the range check from every
    /// bounded number and every string.
    #[test]
    fn a_bound_pair_set_together_is_non_vacuous() {
        let ranged = v2::Constraint {
            min: Some("0.0".to_string()),
            max: Some("250.0".to_string()),
            ..constraint()
        };
        assert!(!v2::constraint_is_vacuous(Some(&ranged)));

        let default_length = v2::Constraint {
            len_min: Some(0),
            len_max: Some(256),
            ..constraint()
        };
        assert!(!v2::constraint_is_vacuous(Some(&default_length)));
    }
}

#[cfg(test)]
mod system_round_trip {
    use crate::v2;

    fn attribute(namespace: &str, key: &str, value: Option<v2::AttributeValue>) -> v2::Attribute {
        v2::Attribute {
            namespace: namespace.to_string(),
            key: key.to_string(),
            value,
        }
    }

    fn scalar(text: &str) -> v2::AttributeValue {
        v2::AttributeValue {
            kind: Some(v2::attribute_value::Kind::Scalar(text.to_string())),
        }
    }

    fn list(items: Vec<v2::AttributeValue>) -> v2::AttributeValue {
        v2::AttributeValue {
            kind: Some(v2::attribute_value::Kind::List(v2::AttributeList { items })),
        }
    }

    fn interface(catalog: &str, name: &str, inline: bool) -> Option<v2::InterfaceRef> {
        Some(v2::InterfaceRef {
            catalog: catalog.to_string(),
            name: name.to_string(),
            inline,
        })
    }

    fn endpoint(component: &str, instance: &str, machine: &str) -> v2::Endpoint {
        v2::Endpoint {
            component: component.to_string(),
            instance: instance.to_string(),
            machine: machine.to_string(),
        }
    }

    /// A reduced rsdl reference Appendix A: `Cruise` with two instances
    /// offering `veh.adas.cruise` and requiring `LaneAssist`, the implicit
    /// component of `veh.diag.access`, one distribution and one deployment.
    /// Every message of `system.proto` appears at least once, with every
    /// scalar set to a value other than its default — a flag and a nested-list
    /// attribute value included — so a round trip that drops a field is
    /// caught.
    fn doc_link() -> v2::DocLink {
        v2::DocLink {
            text: "Cruise".to_string(),
            offset: 16,
            len: 6,
            target: "veh.topology.Cruise".to_string(),
        }
    }

    fn fixture() -> v2::System {
        let link = v2::Link {
            interface: interface("veh.diag", "veh.diag.access", true),
            service: "veh.diag.access".to_string(),
            consumer: Some(endpoint("veh.topology.Backend", "Unit", "Cloud")),
            producer: Some(endpoint("veh.diag.access", "Unit", "AdasHpc")),
            crossing: v2::Crossing::OffBoard as i32,
        };
        v2::System {
            name: "Vehicle".to_string(),
            package: "veh.topology".to_string(),
            labels: vec!["ASIL_B".to_string()],
            attributes: vec![attribute("rust", "crate", Some(scalar("\"vehicle\"")))],
            members: vec![
                v2::MemberLine {
                    component: "veh.topology.Cruise".to_string(),
                    attributes: vec![attribute("linux", "pinned", None)],
                    doc: "Documented, see [Cruise].".to_string(),
                    links: vec![doc_link()],
                    see: vec![doc_link()],
                    since: vec!["1.2".to_string()],
                },
                v2::MemberLine {
                    component: "veh.diag.access".to_string(),
                    attributes: vec![],
                    doc: "Documented, see [Cruise].".to_string(),
                    links: vec![doc_link()],
                    see: vec![doc_link()],
                    since: vec!["1.2".to_string()],
                },
            ],
            components: vec![
                v2::Component {
                    name: "Cruise".to_string(),
                    package: "veh.topology".to_string(),
                    implicit: false,
                    external: true,
                    instances: vec!["primary".to_string(), "backup".to_string()],
                    numbers: vec![
                        v2::InstanceNumber {
                            instance: "primary".to_string(),
                            number: 1,
                            provisional: false,
                        },
                        v2::InstanceNumber {
                            instance: "backup".to_string(),
                            number: 2,
                            provisional: true,
                        },
                    ],
                    offers: vec![v2::Offer {
                        service: "veh.adas.cruise".to_string(),
                        attributes: vec![attribute("someip", "serviceId", Some(scalar("4097")))],
                        doc: "Documented, see [Cruise].".to_string(),
                        links: vec![doc_link()],
                        see: vec![doc_link()],
                        since: vec!["1.2".to_string()],
                    }],
                    requires: vec![v2::Require {
                        interface: interface("veh.adas", "LaneAssist", false),
                        service: "veh.adas.lane".to_string(),
                        producer: "veh.topology.Lane".to_string(),
                        attributes: vec![attribute(
                            "linux",
                            "cpuset",
                            Some(list(vec![scalar("2"), list(vec![scalar("3")])])),
                        )],
                        doc: "Documented, see [Cruise].".to_string(),
                        links: vec![doc_link()],
                        see: vec![doc_link()],
                        since: vec!["1.2".to_string()],
                    }],
                    labels: vec!["ASIL_B".to_string()],
                    attributes: vec![attribute("rust", "crate", None)],
                    doc: "Documented, see [Cruise].".to_string(),
                    links: vec![doc_link()],
                    see: vec![doc_link()],
                    since: vec!["1.2".to_string()],
                    deprecated: Some("superseded".to_string()),
                },
                v2::Component {
                    name: "veh.diag.access".to_string(),
                    package: String::new(),
                    implicit: true,
                    external: false,
                    instances: vec!["Unit".to_string()],
                    numbers: vec![v2::InstanceNumber {
                        instance: "Unit".to_string(),
                        number: 3,
                        provisional: false,
                    }],
                    offers: vec![v2::Offer {
                        service: "veh.diag.access".to_string(),
                        attributes: vec![],
                        doc: "Documented, see [Cruise].".to_string(),
                        links: vec![doc_link()],
                        see: vec![doc_link()],
                        since: vec!["1.2".to_string()],
                    }],
                    requires: vec![],
                    labels: vec![],
                    attributes: vec![],
                    doc: "Documented, see [Cruise].".to_string(),
                    links: vec![doc_link()],
                    see: vec![doc_link()],
                    since: vec!["1.2".to_string()],
                    deprecated: Some("superseded".to_string()),
                },
            ],
            producers: vec![v2::Producer {
                service: "veh.adas.cruise".to_string(),
                component: "veh.topology.Cruise".to_string(),
                instances: vec!["primary".to_string(), "backup".to_string()],
                not_yet_realizable: true,
            }],
            grants: vec![v2::Grant {
                component: "veh.topology.Backend".to_string(),
                external: true,
                regions: vec!["veh.adas".to_string(), "veh.diag".to_string()],
            }],
            regions: vec![v2::Region {
                catalog: "veh.diag".to_string(),
                hash: vec![0xab; 32],
                interfaces: vec![v2::RegionInterface {
                    name: "veh.diag.access".to_string(),
                    inline: true,
                    number: 2,
                    provisional: true,
                    service: "veh.diag.access".to_string(),
                }],
            }],
            distributions: vec![v2::Distribution {
                name: "Adas".to_string(),
                package: "veh.topology".to_string(),
                members: vec![v2::MemberLine {
                    component: "veh.topology.Cruise".to_string(),
                    attributes: vec![],
                    doc: "Documented, see [Cruise].".to_string(),
                    links: vec![doc_link()],
                    see: vec![doc_link()],
                    since: vec!["1.2".to_string()],
                }],
                depends_on: vec!["veh.topology.Base".to_string()],
                labels: vec!["PLATFORM_BUNDLE".to_string()],
                attributes: vec![attribute("deb", "section", Some(scalar("net")))],
                doc: "Documented, see [Cruise].".to_string(),
                links: vec![doc_link()],
                see: vec![doc_link()],
                since: vec!["1.2".to_string()],
                tier: v2::Tier::Platform as i32,
                deprecated: Some("superseded".to_string()),
            }],
            deployments: vec![v2::Deployment {
                name: "Production".to_string(),
                package: "veh.topology".to_string(),
                labels: vec!["FLEET".to_string()],
                attributes: vec![attribute("ota", "channel", Some(scalar("stable")))],
                machines: vec![v2::Machine {
                    name: "Cloud".to_string(),
                    external: true,
                    labels: vec!["OFF_BOARD".to_string()],
                    attributes: vec![attribute("net", "zone", Some(scalar("wan")))],
                    doc: "Documented, see [Cruise].".to_string(),
                    links: vec![doc_link()],
                    see: vec![doc_link()],
                    since: vec!["1.2".to_string()],
                    deprecated: Some("superseded".to_string()),
                }],
                placements: vec![v2::Placement {
                    component: "veh.topology.Cruise".to_string(),
                    instance: "backup".to_string(),
                    machine: "Cockpit".to_string(),
                    attributes: vec![attribute("linux", "cpuset", Some(list(vec![])))],
                    sizing: Some(v2::Sizing {
                        depth: Some(4_294_967_295),
                        slots: Some(65_536),
                        budget: Some(18_446_744_073_709_551_615),
                    }),
                }],
                links: vec![link.clone()],
                routes: vec![v2::Route {
                    catalog: "veh.adas".to_string(),
                    interface_number: 2,
                    member_ordinal: 1,
                    interface: "LaneAssist".to_string(),
                    member: "active".to_string(),
                    service: "veh.adas.lane".to_string(),
                    producers: vec![endpoint("veh.topology.Lane", "Unit", "AdasHpc")],
                }],
                surface: vec![v2::Surface {
                    link: Some(link),
                    direction: v2::SurfaceDirection::ExternalConsumes as i32,
                }],
                installations: vec![v2::Installation {
                    distribution: "veh.topology.Adas".to_string(),
                    machines: vec!["AdasHpc".to_string(), "Cockpit".to_string()],
                }],
                doc: "Documented, see [Cruise].".to_string(),
                doc_links: vec![doc_link()],
                see: vec![doc_link()],
                since: vec!["1.2".to_string()],
                sizing: Some(v2::Sizing {
                    depth: Some(3),
                    slots: Some(8),
                    budget: Some(4096),
                }),
                deprecated: Some("superseded".to_string()),
            }],
            doc: "Documented, see [Cruise].".to_string(),
            see: vec![doc_link()],
            since: vec!["1.2".to_string()],
            links: vec![doc_link()],
            deprecated: Some("superseded".to_string()),
        }
    }

    #[test]
    fn system_binary_round_trip_preserves_system() {
        let system = fixture();
        let decoded = v2::system_from_binary(v2::system_to_binary(&system).as_slice())
            .expect("decode must succeed");
        assert_eq!(system, decoded);
    }

    /// The canonical JSON of the system artifact re-reads through the same
    /// strict pbjson-generated impl the package uses (ADR-0014 decisions 11
    /// and 14): unknown fields rejected, the catalog hash as base64, enums by
    /// name, the nested attribute list intact.
    #[test]
    fn system_json_round_trip_preserves_system() {
        let system = fixture();
        let json = v2::system_to_json_pretty(&system).expect("the fixture serializes as JSON");
        assert!(
            json.contains("\"hash\": \"q6urq6urq6urq6urq6urq6urq6urq6urq6urq6urq6s=\""),
            "bytes render as base64, got:\n{json}"
        );
        assert!(
            json.contains("\"crossing\": \"CROSSING_OFF_BOARD\""),
            "enums render by name, got:\n{json}"
        );
        assert!(
            json.contains("\"notYetRealizable\": true"),
            "fields render in lowerCamelCase, got:\n{json}"
        );
        assert!(
            json.contains("\"budget\": \"18446744073709551615\""),
            "a 64-bit value renders as a string, got:\n{json}"
        );
        assert_eq!(
            system,
            v2::system_from_json(&json).expect("the JSON parses")
        );
        assert!(
            v2::system_from_json(&json.replacen("\"name\"", "\"nam\"", 1)).is_err(),
            "an unknown field is rejected"
        );
    }

    /// An absent `sizing` and an empty one are different on the wire: a plugin
    /// reads "nothing declared" and "declared nothing" apart, in the binary and
    /// the JSON encodings.
    #[test]
    fn an_absent_sizing_and_an_empty_one_stay_distinct_through_the_encodings() {
        let mut absent = fixture();
        absent.deployments[0].sizing = None;
        absent.deployments[0].placements[0].sizing = None;
        let mut empty = absent.clone();
        empty.deployments[0].sizing = Some(v2::Sizing::default());
        empty.deployments[0].placements[0].sizing = Some(v2::Sizing::default());
        for system in [&absent, &empty] {
            let binary = v2::system_from_binary(v2::system_to_binary(system).as_slice())
                .expect("decode must succeed");
            assert_eq!(system, &binary);
            let json = v2::system_to_json_pretty(system).expect("serializes as JSON");
            assert_eq!(
                system,
                &v2::system_from_json(&json).expect("the JSON parses")
            );
        }
        assert_ne!(
            v2::system_to_binary(&absent),
            v2::system_to_binary(&empty),
            "the binary encodings differ"
        );
    }

    #[test]
    fn system_text_format_round_trip_preserves_system() {
        let system = fixture();
        let text = v2::system_to_text_format(&system).expect("the fixture serializes as prototext");
        assert!(
            text.starts_with("name:"),
            "fields print in schema index order, got: {text}"
        );
        assert_eq!(
            system,
            v2::system_from_text_format(&text).expect("prototext parsing must succeed")
        );
    }

    /// `pkg.Name` for a declared name; the implicit component of a lone
    /// service, which no package declares, is its own qualified name.
    #[test]
    fn qualified_names_follow_the_one_derivation() {
        let system = fixture();
        assert_eq!(system.qualified_name(), "veh.topology.Vehicle");
        assert_eq!(system.components[0].qualified_name(), "veh.topology.Cruise");
        assert_eq!(system.components[1].qualified_name(), "veh.diag.access");
        assert_eq!(
            system.distributions[0].qualified_name(),
            "veh.topology.Adas"
        );
    }
}

#[cfg(test)]
mod load_ir_json {
    use crate::v2::{self, LoadError, MAX_JSON_NESTING, load_ir_json};

    /// A snapshot written by `to_json_pretty` loads back as the same package.
    #[test]
    fn a_snapshot_file_loads() {
        let dir = tempfile::tempdir().unwrap();
        let package = v2::Package {
            name: "veh.cabin".to_string(),
            ..v2::Package::default()
        };
        let path = dir.path().join("cabin.ir.json");
        std::fs::write(&path, v2::to_json_pretty(&package).unwrap()).unwrap();
        assert_eq!(load_ir_json(&path).unwrap(), package);
    }

    /// A missing file is an `Io` error and a file that is not IR v2 JSON is a
    /// `Parse` error, each with the message `ridl diff` prints, inner error
    /// included.
    #[test]
    fn a_missing_file_is_io_and_bad_json_is_parse() {
        let dir = tempfile::tempdir().unwrap();

        let missing = dir.path().join("missing.ir.json");
        let io = std::fs::read_to_string(&missing).unwrap_err();
        let error = load_ir_json(&missing).unwrap_err();
        assert!(matches!(error, LoadError::Io(_)), "{error:?}");
        assert_eq!(
            error.to_string(),
            format!("cannot read the IR snapshot: {io}")
        );

        // The leading newline puts the error on line 2, so a loader that
        // trimmed the text first would report a different position.
        let bad = dir.path().join("bad.ir.json");
        std::fs::write(&bad, "\n{").unwrap();
        let parse = v2::from_json("\n{").unwrap_err();
        let error = load_ir_json(&bad).unwrap_err();
        assert!(matches!(error, LoadError::Parse(_)), "{error:?}");
        assert_eq!(
            error.to_string(),
            format!("the IR snapshot is not valid IR v2 JSON: {parse}")
        );
    }

    /// The loader reads through `from_json`: input nested past its cap draws
    /// the cap's own message, which a plain `serde_json` parse would not.
    #[test]
    fn input_past_the_nesting_cap_draws_from_json_s_refusal() {
        let dir = tempfile::tempdir().unwrap();
        let deep = format!(
            "{}{}",
            "[".repeat(MAX_JSON_NESTING + 1),
            "]".repeat(MAX_JSON_NESTING + 1)
        );
        let path = dir.path().join("deep.ir.json");
        std::fs::write(&path, &deep).unwrap();
        let refusal = v2::from_json(&deep).unwrap_err().to_string();
        assert!(
            refusal.contains("the ceiling this reader enforces"),
            "{refusal}"
        );
        let error = load_ir_json(&path).unwrap_err();
        assert!(matches!(error, LoadError::Parse(_)), "{error:?}");
        assert_eq!(
            error.to_string(),
            format!("the IR snapshot is not valid IR v2 JSON: {refusal}")
        );
    }
}