leviath_core/

output.rs

//! An agent's final output: the one value a run hands back to whoever asked.
//!
//! Every surface that reports a result reads this and nothing else:
//! `GET /api/agents/{id}/result`, the completion webhook's `result` field,
//! `wait_for_agent`'s answer to a parent, and a fan-out worker's contribution
//! to its merge stage. None of them has to guess at a log tail or at whatever
//! text sat in a last assistant message, which for a worker whose final turn
//! was a tool call is nothing at all.
//!
//! # The format rule
//!
//! **Nothing here interprets the format.** There is no enum of supported
//! formats, no per-format parser, and no branch on a format name anywhere in the
//! engine. [`OutputSpec::format`] is an opaque label; markdown, JSON, XML, CSV,
//! an [a2ui](https://a2ui.org/) document, and a house format invented next week
//! all travel the same path: describe it to the model, record what comes back
//! verbatim, hand it on unchanged.
//!
//! The single exception is opt-in and named as such. When an author supplies
//! [`OutputSpec::schema`], the submission is parsed as JSON and validated
//! against it. That is the only thing that ever looks inside the content, and it
//! happens because someone asked for it, never because a format string said
//! `"json"`.
//!
//! This is also why an unusual format needs no engine support. There is no
//! usual: every format is produced by the model from
//! [`OutputSpec::instructions`] and [`OutputSpec::example`].

use serde::{Deserialize, Serialize};

/// Largest final output kept, in bytes. Anything longer is cut at a character
/// boundary and flagged [`FinalOutput::truncated`].
///
/// Sits between the log tail the result endpoint already serves (64 KiB) and the
/// cap on reading a file the run wrote (1 MiB). A final output is meant to be an
/// answer, not a payload; an agent with megabytes to hand back should write a
/// file and say where it is.
pub const MAX_FINAL_OUTPUT_BYTES: usize = 256 * 1024;

/// What happens to a submission when its Rhai validator cannot run: the script
/// threw, exhausted its operation budget, or returned something that is neither
/// `()` nor a string.
///
/// Distinct from the validator *rejecting* the answer, which always refuses the
/// submission back to the model. This knob is only about the script itself
/// failing.
#[derive(Debug, Clone, Copy, Default, PartialEq, Eq, Serialize, Deserialize)]
#[serde(rename_all = "snake_case")]
pub enum OnValidatorError {
    /// Refuse the submission, sending the script's error text to the model as
    /// retry feedback. The default: an answer nothing checked must not ship as
    /// if it passed, and a `parse_json` throw on malformed output is something
    /// the model can act on.
    #[default]
    Reject,
    /// Record the submission unchecked, as if no validator were declared. For
    /// blueprints that would rather have an unchecked answer than a failed run.
    /// The broken script is still flagged on the run either way.
    Accept,
}

/// What shape an agent should return.
///
/// Declared by a blueprint (`[agent.output]`), narrowed by a stage
/// (`[stages.<name>.output]`), and overridable by whoever starts the run. See
/// [`resolve_output_spec`] for how the three combine.
///
/// Every field is optional, and an entirely empty spec is meaningful: it asks
/// for a final output without constraining its shape.
#[derive(Debug, Clone, Default, PartialEq, Eq, Serialize, Deserialize)]
pub struct OutputSpec {
    /// An opaque label for the shape, carried to the model and recorded beside
    /// the result. `"markdown"`, `"json"`, `"a2ui"`, and
    /// `"application/vnd.acme.report+xml"` are all equally valid and equally
    /// uninterpreted. Consumers that render differently per format (a browser
    /// UI, say) match on this string; the engine never does.
    #[serde(default, skip_serializing_if = "Option::is_none")]
    pub format: Option<String>,

    /// Free-form guidance folded into the `submit_output` tool description and
    /// the output stage's system prompt. This is where a format that the model
    /// has never seen gets explained.
    #[serde(default, skip_serializing_if = "Option::is_none")]
    pub instructions: Option<String>,

    /// A literal sample shown to the model verbatim. The most effective lever
    /// for an unusual format, and the reason one needs no code support.
    #[serde(default, skip_serializing_if = "Option::is_none")]
    pub example: Option<String>,

    /// A JSON Schema describing the answer's shape. When present, a submission
    /// is parsed as JSON and validated against it, and a failure is refused back
    /// to the model so it can correct itself.
    ///
    /// Separate from `format` because they answer different questions.
    /// `format = "json"` asks "does this parse as JSON"; a schema asks "does the
    /// parsed document have the fields I need". A format check comes free for
    /// the handful of formats the engine can parse; shape is only ever checked
    /// when someone writes a schema down.
    #[serde(default, skip_serializing_if = "Option::is_none")]
    pub schema: Option<serde_json::Value>,

    /// A `.rhai` script that decides whether an answer is valid, as a path
    /// relative to the blueprint directory.
    ///
    /// For a format the engine cannot parse and a shape a JSON Schema cannot
    /// describe. The script defines `fn validate(content)` and returns `()` when
    /// the answer is fine or a string saying what is wrong; the string goes back
    /// to the agent as the same refusal a schema failure produces.
    ///
    /// Written for the format it accompanies, so a caller who overrides the
    /// format retires it along with the schema.
    #[serde(default, skip_serializing_if = "Option::is_none")]
    pub validator: Option<String>,

    /// What to do when the validator itself cannot run. `None` means the
    /// default, [`OnValidatorError::Reject`]. Travels with the validator: a
    /// caller who retires the validator by overriding the format retires this
    /// setting along with it.
    #[serde(default, skip_serializing_if = "Option::is_none")]
    pub on_validator_error: Option<OnValidatorError>,

    /// Whether an artifact named after a part the run produced may replace a
    /// different file already at that path in the working directory. `None`
    /// defers to the user's `[mime] overwrite_artifacts`, which defaults to
    /// false: the existing file is left alone and the part is written beside
    /// it under a name carrying its hash.
    #[serde(default, skip_serializing_if = "Option::is_none")]
    pub overwrite_artifacts: Option<bool>,

    /// The files the stage hands back beside its answer, by name and type.
    /// A submission is checked against them: a `required` one must be
    /// present, and one that is present must be of the declared type.
    #[serde(default, skip_serializing_if = "Vec::is_empty")]
    pub artifacts: Vec<ArtifactSpec>,
}

impl OutputSpec {
    /// Whether this spec constrains anything at all. An empty spec still asks
    /// for an output, so this is about wording the request, not skipping it.
    pub fn is_empty(&self) -> bool {
        self.format.is_none()
            && self.instructions.is_none()
            && self.example.is_none()
            && self.schema.is_none()
            && self.validator.is_none()
            && self.on_validator_error.is_none()
            && self.overwrite_artifacts.is_none()
            && self.artifacts.is_empty()
    }
}

/// A file a stage declares it hands back beside its answer.
#[derive(Debug, Clone, PartialEq, Eq, Serialize, Deserialize)]
pub struct ArtifactSpec {
    /// What the submission calls it: `final`, `scene`, `track`.
    pub name: String,
    /// The mime type it must be, or a pattern it must match (`video/*`).
    #[serde(rename = "type")]
    pub mime_type: String,
    /// Whether a submission without it is refused.
    #[serde(default)]
    pub required: bool,
    /// What it is for, shown to the model.
    #[serde(default, skip_serializing_if = "Option::is_none")]
    pub description: Option<String>,
}

/// A file a run produced, as recorded on its answer.
///
/// Every field but `path` is what the run could tell from the bytes: the
/// registry's type (or the declared one), the size, and the hash the run's
/// blob store holds the file under. An answer recorded before artifacts were
/// typed carried a bare path, and reads back as one with the rest unknown.
#[derive(Debug, Clone, PartialEq, Eq, Serialize, Deserialize)]
pub struct Artifact {
    /// The name the stage declared, or the file name when it declared none.
    pub name: String,
    /// The file, relative to the working directory. An answer emitted from
    /// routed parts alone never wrote a file, and carries the part's name here
    /// instead; its bytes are reachable only through `sha256`.
    pub path: String,
    /// The file's type.
    pub mime_type: crate::mime::MimeType,
    /// Size in bytes.
    #[serde(default)]
    pub size: u64,
    /// The sha256 the run's blob store holds the bytes under; empty when the
    /// file was too large to store, or the answer predates typed artifacts.
    #[serde(default, skip_serializing_if = "String::is_empty")]
    pub sha256: String,
}

impl Artifact {
    /// `name (type, size)`: how a produced file reads in a sentence.
    pub fn short_label(&self) -> String {
        format!(
            "{} ({}, {})",
            self.name,
            self.mime_type,
            crate::mime::human_size(self.size)
        )
    }

    /// The columns after the name in a listing: path, type, size, and the
    /// hash prefix when the bytes are stored.
    pub fn detail_columns(&self) -> String {
        let sha = match self.sha256.is_empty() {
            true => String::new(),
            false => format!(
                "  sha256:{}",
                self.sha256.chars().take(12).collect::<String>()
            ),
        };
        format!(
            "{}  {}  {}{sha}",
            self.path,
            self.mime_type,
            crate::mime::human_size(self.size)
        )
    }

    /// An artifact known only by its path: the shape every answer recorded
    /// before artifacts were typed carried.
    pub fn from_path(path: &str) -> Self {
        let name = path
            .rsplit(['/', '\\'])
            .find(|s| !s.is_empty())
            .unwrap_or(path)
            .to_string();
        Self {
            name,
            path: path.to_string(),
            mime_type: crate::mime::octet_stream(),
            size: 0,
            sha256: String::new(),
        }
    }
}

/// One artifact on the wire: the typed record, or the bare path older
/// answers wrote.
#[derive(Deserialize)]
#[serde(untagged)]
enum ArtifactWire {
    Full(Artifact),
    Path(String),
}

/// Read an artifacts list that may hold bare paths.
fn artifacts_from_wire<'de, D: serde::Deserializer<'de>>(d: D) -> Result<Vec<Artifact>, D::Error> {
    let listed: Vec<ArtifactWire> = Vec::deserialize(d)?;
    Ok(listed
        .into_iter()
        .map(|a| match a {
            ArtifactWire::Full(a) => a,
            ArtifactWire::Path(p) => Artifact::from_path(&p),
        })
        .collect())
}

/// What an agent actually produced, content included.
///
/// [`content`](Self::content) is stored exactly as submitted. Nothing in the
/// engine reformats, re-indents, or re-serializes it, so a consumer that asked
/// for a particular byte sequence receives that byte sequence.
///
/// This is the in-memory and one-shot form: the live ECS component, the
/// completion event, a webhook body, a reply to a waiting parent. What a run's
/// `meta.json` carries is the [`FinalOutputDescriptor`], because that file is
/// read for every run on every listing and must not carry a payload.
#[derive(Debug, Clone, PartialEq, Eq, Serialize, Deserialize)]
pub struct FinalOutput {
    /// The submission, verbatim (subject only to [`MAX_FINAL_OUTPUT_BYTES`]).
    pub content: String,

    /// The format label in effect when this was submitted, if any. Copied from
    /// the resolved spec rather than guessed from the content.
    #[serde(default, skip_serializing_if = "Option::is_none")]
    pub format: Option<String>,

    /// The stage that produced it. Read by the enforcement gate, which must
    /// tell "this stage submitted" from "some earlier stage did".
    pub stage: String,

    /// Unix seconds at submission.
    pub submitted_at: i64,

    /// Whether [`MAX_FINAL_OUTPUT_BYTES`] cut the content short.
    #[serde(default)]
    pub truncated: bool,

    /// Files the run produced, typed and hashed.
    ///
    /// An answer is one model response; anything larger is a file. A run that
    /// gathers two million rows writes them incrementally and names the file
    /// here, so a consumer can fetch it rather than parse the path out of prose.
    /// Validated to resolve inside the run's working directory, the same rule
    /// the files endpoint enforces when serving one.
    #[serde(
        default,
        skip_serializing_if = "Vec::is_empty",
        deserialize_with = "artifacts_from_wire"
    )]
    pub artifacts: Vec<Artifact>,
}

impl FinalOutput {
    /// Record a submission, truncating at a character boundary if it exceeds
    /// [`MAX_FINAL_OUTPUT_BYTES`].
    ///
    /// Truncation walks back to a boundary rather than slicing by byte index:
    /// this workspace denies `clippy::string_slice` because a byte cut through a
    /// multi-byte character once double-panicked and aborted the whole daemon.
    pub fn new(content: &str, format: Option<String>, stage: String, submitted_at: i64) -> Self {
        let truncated = content.len() > MAX_FINAL_OUTPUT_BYTES;
        let kept = crate::text::truncate_at_boundary(content, MAX_FINAL_OUTPUT_BYTES);
        Self {
            content: kept.to_string(),
            format,
            stage,
            submitted_at,
            truncated,
            artifacts: Vec::new(),
        }
    }

    /// The same submission with `artifacts` attached.
    pub fn with_artifacts(mut self, artifacts: Vec<Artifact>) -> Self {
        self.artifacts = artifacts;
        self
    }

    /// Everything about this answer except the bytes.
    pub fn descriptor(&self) -> FinalOutputDescriptor {
        FinalOutputDescriptor {
            format: self.format.clone(),
            stage: self.stage.clone(),
            submitted_at: self.submitted_at,
            bytes: self.content.len(),
            truncated: self.truncated,
            artifacts: self.artifacts.clone(),
        }
    }
}

/// What a run's `meta.json` records about its answer: everything but the bytes.
///
/// The content lives beside it in a sidecar file
/// ([`FINAL_OUTPUT_FILE`]). `meta.json` is
/// parsed for every run on every `lev ps`, every `/api/runs` page, and every
/// restart scan, so a payload in it is paid for by operations that never wanted
/// it: a thousand answered runs would mean hundreds of megabytes of JSON per
/// listing. A descriptor is a couple of hundred bytes and stays that way.
#[derive(Debug, Clone, Default, PartialEq, Eq, Serialize, Deserialize)]
pub struct FinalOutputDescriptor {
    /// The format label the answer was produced under, if any.
    #[serde(default, skip_serializing_if = "Option::is_none")]
    pub format: Option<String>,
    /// The stage that produced it.
    pub stage: String,
    /// Unix seconds at submission.
    pub submitted_at: i64,
    /// Size of the answer in bytes, so a caller can decide whether to fetch it.
    #[serde(default)]
    pub bytes: usize,
    /// Whether [`MAX_FINAL_OUTPUT_BYTES`] cut the answer short.
    #[serde(default)]
    pub truncated: bool,
    /// Files the run produced, typed and hashed.
    #[serde(
        default,
        skip_serializing_if = "Vec::is_empty",
        deserialize_with = "artifacts_from_wire"
    )]
    pub artifacts: Vec<Artifact>,
}

/// The file, inside a run's directory, holding the answer's bytes.
///
/// Raw content with no wrapper, so serving it is a read and `lev result --raw`
/// is a copy.
pub const FINAL_OUTPUT_FILE: &str = "final_output";

/// Combine the blueprint's, the stage's, and the caller's output specs into the
/// one that governs a stage. Later levels win field by field, the way
/// [`resolve_nudge`](crate::blueprint::resolve_nudge) cascades.
///
/// Returns `None` when no level asks for an output at all, which is how a stage
/// that has nothing to hand back stays silent.
///
/// # The schema drop
///
/// A caller who names a `format` and supplies no `schema` **drops the declared
/// schema**. Validating an a2ui document against the agent's own JSON schema
/// would be nonsense: the caller asked for a different shape, so the check
/// written for the old shape no longer applies. A caller who wants validation
/// supplies a schema alongside the format. This is the one place where fields do
/// not cascade independently, and it is deliberate.
pub fn resolve_output_spec(
    agent: Option<&OutputSpec>,
    stage: Option<&OutputSpec>,
    request: Option<&OutputSpec>,
) -> Option<OutputSpec> {
    if agent.is_none() && stage.is_none() && request.is_none() {
        return None;
    }

    fn field<T: Clone>(
        agent: Option<&OutputSpec>,
        stage: Option<&OutputSpec>,
        request: Option<&OutputSpec>,
        get: impl Fn(&OutputSpec) -> Option<T>,
    ) -> Option<T> {
        request
            .and_then(&get)
            .or_else(|| stage.and_then(&get))
            .or_else(|| agent.and_then(&get))
    }

    // A shape check is written for one format. When a caller asks for a
    // different one, a check the blueprint declared no longer describes what is
    // being produced, so it is retired rather than applied to something it was
    // never about. A caller who wants their new shape checked supplies their own.
    let declared_format = field(agent, stage, None, |s| s.format.clone());
    let requested_format = request.and_then(|r| r.format.clone());
    let reshaped = requested_format.is_some() && requested_format != declared_format;

    let shape_field = |get: fn(&OutputSpec) -> Option<serde_json::Value>| match reshaped {
        true => request.and_then(get),
        false => field(agent, stage, request, get),
    };
    let validator = match reshaped {
        true => request.and_then(|r| r.validator.clone()),
        false => field(agent, stage, request, |s| s.validator.clone()),
    };
    // The error policy accompanies the validator it is about, so it follows the
    // validator's cascade: retired with it on a reshape, inherited otherwise.
    let on_validator_error = match reshaped {
        true => request.and_then(|r| r.on_validator_error),
        false => field(agent, stage, request, |s| s.on_validator_error),
    };

    // Declared artifacts describe the declared shape, so they go with the
    // schema and the validator when a caller reshapes. Otherwise the nearest
    // non-empty list wins whole: a stage that names its own files replaces
    // the agent's list rather than adding to it.
    let artifacts = match reshaped {
        true => request.map(|r| r.artifacts.clone()).unwrap_or_default(),
        false => field(agent, stage, request, |s| {
            (!s.artifacts.is_empty()).then(|| s.artifacts.clone())
        })
        .unwrap_or_default(),
    };

    Some(OutputSpec {
        format: field(agent, stage, request, |s| s.format.clone()),
        instructions: field(agent, stage, request, |s| s.instructions.clone()),
        example: field(agent, stage, request, |s| s.example.clone()),
        schema: shape_field(|s| s.schema.clone()),
        validator,
        on_validator_error,
        overwrite_artifacts: field(agent, stage, request, |s| s.overwrite_artifacts),
        artifacts,
    })
}

/// The warnings a caller's requested output shape earns at spawn: what
/// [`resolve_output_spec`] will retire, said out loud before it happens.
///
/// Retiring the declared Rhai validator and JSON schema when the request names
/// a different format is deliberate and stays: a check written for one shape
/// cannot judge another. These warnings say so out loud, so a caller who types
/// `--output-format json` over a blueprint with a validator does not go on
/// believing the run is still being checked.
///
/// One line per group of stages losing the same checks, so an agent-level
/// validator shared by four stages reads as one sentence naming four stages.
/// Empty when there is nothing to say: no request, no format in it, the
/// declared format re-stated (which retires nothing), or nothing declared that
/// could be retired. A declared schema the request *replaces* with its own is
/// also not warned about: supplying a schema for the new shape is exactly what
/// the warning would have asked for. A declared validator is always worth the
/// line, because no request can bring a replacement for it.
pub fn retired_check_warnings(
    blueprint: &crate::Blueprint,
    request: Option<&OutputSpec>,
) -> Vec<String> {
    let Some(requested) = request.and_then(|r| r.format.as_deref()) else {
        return Vec::new();
    };
    let request_has_schema = request.is_some_and(|r| r.schema.is_some());
    let mut groups: Vec<(RetiredChecks, Vec<String>)> = Vec::new();
    for stage in &blueprint.stages {
        let Some(retired) = retired_checks_for_stage(
            blueprint.output.as_ref(),
            stage.output.as_ref(),
            requested,
            request_has_schema,
        ) else {
            continue;
        };
        match groups.iter_mut().find(|(g, _)| *g == retired) {
            Some((_, stages)) => stages.push(stage.name.clone()),
            None => groups.push((retired, vec![stage.name.clone()])),
        }
    }
    groups
        .iter()
        .map(|(checks, stages)| checks.warning_line(requested, stages, request_has_schema))
        .collect()
}

/// The declared checks one stage loses to a format override. Two stages with
/// equal values lose the same thing and share one warning line.
#[derive(PartialEq, Eq)]
struct RetiredChecks {
    /// The format the retired checks were written for, when one was declared.
    declared_format: Option<String>,
    /// The retired Rhai validator's path, when one was declared.
    validator: Option<String>,
    /// Whether a declared JSON schema is retired with nothing in its place.
    schema: bool,
}

/// What `requested` retires for one stage, or `None` when it retires nothing.
///
/// Asks [`resolve_output_spec`]'s question ahead of time, with the same
/// cascade: the stage's declaration wins over the agent's, and re-stating the
/// declared format keeps every check. Kept beside it so the two cannot drift.
fn retired_checks_for_stage(
    agent: Option<&OutputSpec>,
    stage: Option<&OutputSpec>,
    requested: &str,
    request_has_schema: bool,
) -> Option<RetiredChecks> {
    let declared =
        |get: fn(&OutputSpec) -> Option<&str>| stage.and_then(get).or_else(|| agent.and_then(get));
    let declared_format = declared(|s| s.format.as_deref());
    if declared_format == Some(requested) {
        return None;
    }
    let validator = declared(|s| s.validator.as_deref());
    let schema = !request_has_schema
        && stage
            .and_then(|s| s.schema.as_ref())
            .or_else(|| agent.and_then(|a| a.schema.as_ref()))
            .is_some();
    if validator.is_none() && !schema {
        return None;
    }
    Some(RetiredChecks {
        declared_format: declared_format.map(str::to_string),
        validator: validator.map(str::to_string),
        schema,
    })
}

impl RetiredChecks {
    /// The warning itself, worded for a person on any spawn path: what was
    /// requested, what it retires, and how to get the new shape checked. The
    /// closing advice depends on the request: a caller who already brought a
    /// schema for the new shape has nothing further to supply.
    fn warning_line(&self, requested: &str, stages: &[String], request_has_schema: bool) -> String {
        let cause = match &self.declared_format {
            Some(declared) => format!(
                "requested output format '{requested}' differs from the declared '{declared}'"
            ),
            None => format!(
                "requested output format '{requested}' reshapes an output declared without a \
                 format"
            ),
        };
        let what = match (&self.validator, self.schema) {
            (Some(v), true) => format!("the Rhai validator '{v}' and the JSON schema"),
            (Some(v), false) => format!("the Rhai validator '{v}'"),
            (None, _) => "the JSON schema".to_string(),
        };
        let tail = match request_has_schema {
            true => "the schema supplied with the request is what checks the answer now",
            false => {
                "nothing checks the answer's shape; supply a schema with the request if the new \
                 shape needs one"
            }
        };
        format!(
            "{cause}: {what} declared for {} will not run, because a check written for one shape \
             cannot judge another. Instead, {tail}.",
            stage_phrase(stages)
        )
    }
}

/// `stage 'plan'`, `stages 'plan' and 'wrap'`, `stages 'a', 'b', and 'c'`.
/// Callers only group stages they saw, so the slice is never empty.
fn stage_phrase(stages: &[String]) -> String {
    let quoted: Vec<String> = stages.iter().map(|s| format!("'{s}'")).collect();
    match quoted.split_last() {
        Some((last, [])) => format!("stage {last}"),
        Some((last, [first])) => format!("stages {first} and {last}"),
        Some((last, head)) => format!("stages {}, and {last}", head.join(", ")),
        // Unreachable by construction; an empty phrase keeps the sentence
        // grammatical if a future caller ever passes one.
        None => "its stages".to_string(),
    }
}

/// Render a resolved spec as the guidance an agent reads.
///
/// Used twice for the same text: once in the `submit_output` tool description
/// and once in an output stage's system prompt. Saying it in both places matters
/// most for a format the model has no prior knowledge of, which is exactly the
/// case this module is built to support.
///
/// A constrained spec closes with a precedence sentence, because without one
/// this text and the stage's own system prompt are two peer instructions and
/// which wins is model-dependent: a stage prompt saying "lead with the
/// diagnosis" beats `--output-instructions "reply with only the integer"` on
/// some models and loses on others. By the time this runs, [`resolve_output_spec`]
/// has already picked one winner per field - a caller's flag replaces the
/// blueprint's line rather than joining it - so there is exactly one shape here
/// and it is the one that should govern. The sentence is scoped to presentation
/// so a bare `format` does not read as licence to drop content.
///
/// Returns an empty string for a spec that constrains nothing, so callers can
/// append it unconditionally.
pub fn describe_spec(spec: &OutputSpec) -> String {
    let mut parts = Vec::new();
    if let Some(format) = &spec.format {
        parts.push(format!("Return it in this format: {format}."));
    }
    if let Some(instructions) = &spec.instructions {
        parts.push(instructions.clone());
    }
    if let Some(schema) = &spec.schema {
        parts.push(format!(
            "It must be JSON valid against this schema:\n{schema}"
        ));
    }
    if let Some(example) = &spec.example {
        parts.push(format!(
            "Here is an example of the expected shape:\n{example}"
        ));
    }
    if !spec.artifacts.is_empty() {
        let listed: Vec<String> = spec
            .artifacts
            .iter()
            .map(|a| {
                let mut line = format!("- {} ({}", a.name, a.mime_type);
                if a.required {
                    line.push_str(", required");
                }
                line.push(')');
                if let Some(d) = &a.description {
                    line.push_str(": ");
                    line.push_str(d);
                }
                line
            })
            .collect();
        parts.push(format!(
            "Hand back these files in `artifacts`, each as {{ name, path }} with the name \
             given here and the path of the file you wrote:\n{}",
            listed.join("\n")
        ));
    }
    if !parts.is_empty() {
        parts.push(
            "This governs how the answer is presented. Where anything else you were told says \
             to present it differently - its length, its structure, what to lead with - follow \
             this."
                .to_string(),
        );
    }
    parts.join("\n\n")
}

#[cfg(test)]
mod tests {
    use super::*;
    use serde_json::json;

    fn spec(format: Option<&str>, schema: Option<serde_json::Value>) -> OutputSpec {
        OutputSpec {
            format: format.map(str::to_string),
            schema,
            ..OutputSpec::default()
        }
    }

    /// The artifacts list is how an answer points at what it could never
    /// contain: a dataset, a report, a directory of generated files. It travels
    /// with the descriptor so a caller can fetch them without parsing paths back
    /// out of prose.
    #[test]
    fn artifacts_attach_to_a_submission_and_reach_the_descriptor() {
        let output = FinalOutput::new(
            "the summary",
            Some("markdown".to_string()),
            "present".to_string(),
            42,
        )
        .with_artifacts(vec![
            Artifact::from_path("data/dataset.csv"),
            Artifact::from_path("report.pdf"),
        ]);

        assert_eq!(output.artifacts[0].path, "data/dataset.csv");
        assert_eq!(output.artifacts[0].name, "dataset.csv");
        assert_eq!(output.artifacts[1].name, "report.pdf");
        assert_eq!(output.descriptor().artifacts, output.artifacts);
        // An answer recorded before artifacts were typed carried bare paths.
        let old: FinalOutputDescriptor = serde_json::from_str(
            "{\"stage\":\"s\",\"submitted_at\":1,\"artifacts\":[\"a/b.csv\",{\"name\":\"final\",\"path\":\"out.mp4\",\"mime_type\":\"video/mp4\",\"size\":9}]}",
        )
        .unwrap();
        assert_eq!(old.artifacts[0].name, "b.csv");
        assert_eq!(
            old.artifacts[0].mime_type.as_str(),
            "application/octet-stream"
        );
        assert_eq!(old.artifacts[1].name, "final");
        assert_eq!(old.artifacts[1].size, 9);
        assert_eq!(Artifact::from_path("").name, "");
        assert!(
            serde_json::from_str::<FinalOutputDescriptor>(
                "{\"stage\":\"s\",\"submitted_at\":1,\"artifacts\":5}"
            )
            .is_err()
        );
        assert_eq!(Artifact::from_path("dir\\x.png").name, "x.png");
        // The bytes stay out of the descriptor: it goes in `meta.json`, which is
        // read for every run in a listing.
        assert_eq!(output.descriptor().bytes, "the summary".len());
    }

    #[test]
    fn a_submission_carries_no_artifacts_unless_given_some() {
        assert!(
            FinalOutput::new("x", None, "present".to_string(), 0)
                .artifacts
                .is_empty()
        );
    }

    #[test]
    fn declared_artifacts_cascade_whole_and_retire_on_a_reshape() {
        let art = |name: &str| ArtifactSpec {
            name: name.to_string(),
            mime_type: "video/*".to_string(),
            required: true,
            description: None,
        };
        let agent = OutputSpec {
            format: Some("markdown".to_string()),
            artifacts: vec![art("agent-file")],
            ..OutputSpec::default()
        };
        let stage = OutputSpec {
            artifacts: vec![art("stage-file")],
            ..OutputSpec::default()
        };
        // The nearest non-empty list, whole.
        let resolved = resolve_output_spec(Some(&agent), Some(&stage), None).unwrap();
        assert_eq!(resolved.artifacts[0].name, "stage-file");
        let resolved = resolve_output_spec(Some(&agent), None, None).unwrap();
        assert_eq!(resolved.artifacts[0].name, "agent-file");
        // A reshaping request retires them with the schema and validator.
        let request = OutputSpec {
            format: Some("json".to_string()),
            ..OutputSpec::default()
        };
        let resolved = resolve_output_spec(Some(&agent), Some(&stage), Some(&request)).unwrap();
        assert!(resolved.artifacts.is_empty());
        // Unless it brings its own.
        let request = OutputSpec {
            format: Some("json".to_string()),
            artifacts: vec![art("request-file")],
            ..OutputSpec::default()
        };
        let resolved = resolve_output_spec(Some(&agent), Some(&stage), Some(&request)).unwrap();
        assert_eq!(resolved.artifacts[0].name, "request-file");
        assert!(!agent.is_empty());
    }

    #[test]
    fn empty_spec_constrains_nothing() {
        assert!(OutputSpec::default().is_empty());
        assert!(!spec(Some("json"), None).is_empty());
        assert!(!spec(None, Some(json!({}))).is_empty());
        assert!(
            !OutputSpec {
                instructions: Some("be brief".to_string()),
                ..OutputSpec::default()
            }
            .is_empty()
        );
        assert!(
            !OutputSpec {
                example: Some("<doc/>".to_string()),
                ..OutputSpec::default()
            }
            .is_empty()
        );
        assert!(
            !OutputSpec {
                on_validator_error: Some(OnValidatorError::Accept),
                ..OutputSpec::default()
            }
            .is_empty()
        );
    }

    #[test]
    fn no_level_asking_for_output_resolves_to_none() {
        assert_eq!(resolve_output_spec(None, None, None), None);
    }

    #[test]
    fn later_levels_win_field_by_field() {
        let agent = OutputSpec {
            format: Some("markdown".to_string()),
            instructions: Some("agent guidance".to_string()),
            example: Some("agent example".to_string()),
            schema: None,
            validator: None,
            on_validator_error: None,
            overwrite_artifacts: None,
            artifacts: Vec::new(),
        };
        let stage = OutputSpec {
            instructions: Some("stage guidance".to_string()),
            ..OutputSpec::default()
        };
        let resolved = resolve_output_spec(Some(&agent), Some(&stage), None)
            .expect("some level asked for an output");
        // The stage narrows one field; the rest fall through to the agent.
        assert_eq!(resolved.instructions.as_deref(), Some("stage guidance"));
        assert_eq!(resolved.format.as_deref(), Some("markdown"));
        assert_eq!(resolved.example.as_deref(), Some("agent example"));
    }

    /// The listing columns every surface prints: the hash prefix rides along
    /// only when the bytes were stored.
    #[test]
    fn an_artifact_lists_its_columns_with_the_hash_only_when_stored() {
        let mut artifact = Artifact::from_path("out/hero.png");
        assert!(
            artifact
                .short_label()
                .starts_with("hero.png (application/octet-stream, ")
        );
        let bare = artifact.detail_columns();
        assert!(
            bare.starts_with("out/hero.png  application/octet-stream  "),
            "{bare}"
        );
        assert!(!bare.contains("sha256"));
        artifact.sha256 = "abcdef0123456789".repeat(4);
        assert!(artifact.detail_columns().ends_with("  sha256:abcdef012345"));
    }

    #[test]
    fn a_stage_alone_can_ask_for_an_output() {
        let stage = spec(Some("a2ui"), None);
        let resolved =
            resolve_output_spec(None, Some(&stage), None).expect("the stage asked for one");
        assert_eq!(resolved.format.as_deref(), Some("a2ui"));
    }

    /// Naming the format the blueprint already declared keeps its schema: a
    /// caller who asks for exactly what is on offer must not lose the check
    /// that comes with it.
    #[test]
    fn re_stating_the_declared_format_keeps_its_shape_checks() {
        let agent = OutputSpec {
            format: Some("json".to_string()),
            schema: Some(json!({"type": "object"})),
            validator: Some("v.rhai".to_string()),
            ..OutputSpec::default()
        };
        let request = spec(Some("json"), None);
        let resolved = resolve_output_spec(Some(&agent), None, Some(&request))
            .expect("the agent asked for one");
        assert_eq!(resolved.schema, Some(json!({"type": "object"})));
        assert_eq!(resolved.validator.as_deref(), Some("v.rhai"));
    }

    /// A Rhai validator is written for one format, so it retires with the schema
    /// when a caller asks for a different one - and its error policy, which is
    /// about that validator, retires with it.
    #[test]
    fn reshaping_retires_the_validator_too() {
        let agent = OutputSpec {
            format: Some("a2ui".to_string()),
            validator: Some("a2ui.rhai".to_string()),
            on_validator_error: Some(OnValidatorError::Accept),
            ..OutputSpec::default()
        };
        let request = spec(Some("xml"), None);
        let resolved = resolve_output_spec(Some(&agent), None, Some(&request))
            .expect("the agent asked for one");
        assert_eq!(resolved.format.as_deref(), Some("xml"));
        assert_eq!(resolved.validator, None);
        assert_eq!(resolved.on_validator_error, None);
    }

    /// The error policy cascades the way the validator does: a stage's setting
    /// beats the agent's.
    #[test]
    fn the_stage_error_policy_overrides_the_agents() {
        let agent = OutputSpec {
            format: Some("a2ui".to_string()),
            validator: Some("a2ui.rhai".to_string()),
            on_validator_error: Some(OnValidatorError::Reject),
            ..OutputSpec::default()
        };
        let stage = OutputSpec {
            on_validator_error: Some(OnValidatorError::Accept),
            ..OutputSpec::default()
        };
        let resolved =
            resolve_output_spec(Some(&agent), Some(&stage), None).expect("the agent asked for one");
        assert_eq!(resolved.on_validator_error, Some(OnValidatorError::Accept));
        assert_eq!(
            resolved.validator.as_deref(),
            Some("a2ui.rhai"),
            "the validator itself still falls through from the agent"
        );
    }

    /// The artifact overwrite policy cascades on its own, reshape or not: a
    /// stage beats the agent, a request beats both, and unset stays unset so
    /// the user's config can decide.
    #[test]
    fn the_overwrite_policy_cascades_field_by_field() {
        let agent = OutputSpec {
            format: Some("markdown".to_string()),
            overwrite_artifacts: Some(true),
            ..OutputSpec::default()
        };
        let stage = OutputSpec {
            overwrite_artifacts: Some(false),
            ..OutputSpec::default()
        };
        let resolved = resolve_output_spec(Some(&agent), None, None).unwrap();
        assert_eq!(resolved.overwrite_artifacts, Some(true));
        let resolved = resolve_output_spec(Some(&agent), Some(&stage), None).unwrap();
        assert_eq!(resolved.overwrite_artifacts, Some(false));
        let request = OutputSpec {
            format: Some("json".to_string()),
            overwrite_artifacts: Some(true),
            ..OutputSpec::default()
        };
        let resolved = resolve_output_spec(Some(&agent), Some(&stage), Some(&request)).unwrap();
        assert_eq!(resolved.overwrite_artifacts, Some(true));
        let resolved = resolve_output_spec(None, Some(&OutputSpec::default()), None).unwrap();
        assert_eq!(resolved.overwrite_artifacts, None);
        assert!(
            !OutputSpec {
                overwrite_artifacts: Some(false),
                ..OutputSpec::default()
            }
            .is_empty()
        );
    }

    /// A caller who reshapes and brings their own validator can bring their own
    /// error policy with it.
    #[test]
    fn a_reshaping_caller_can_supply_their_own_error_policy() {
        let agent = OutputSpec {
            format: Some("a2ui".to_string()),
            validator: Some("a2ui.rhai".to_string()),
            ..OutputSpec::default()
        };
        let request = OutputSpec {
            format: Some("xml".to_string()),
            validator: Some("xml.rhai".to_string()),
            on_validator_error: Some(OnValidatorError::Accept),
            ..OutputSpec::default()
        };
        let resolved = resolve_output_spec(Some(&agent), None, Some(&request))
            .expect("the agent asked for one");
        assert_eq!(resolved.validator.as_deref(), Some("xml.rhai"));
        assert_eq!(resolved.on_validator_error, Some(OnValidatorError::Accept));
    }

    /// A caller that brings its own checks keeps them.
    #[test]
    fn a_caller_can_supply_shape_checks_with_its_own_format() {
        let agent = OutputSpec {
            format: Some("a2ui".to_string()),
            validator: Some("a2ui.rhai".to_string()),
            ..OutputSpec::default()
        };
        let request = OutputSpec {
            format: Some("json".to_string()),
            schema: Some(json!({"type": "array"})),
            ..OutputSpec::default()
        };
        let resolved = resolve_output_spec(Some(&agent), None, Some(&request))
            .expect("the agent asked for one");
        assert_eq!(resolved.schema, Some(json!({"type": "array"})));
        assert_eq!(resolved.validator, None, "the agent's own is still retired");
    }

    #[test]
    fn a_caller_reshaping_the_output_drops_the_declared_schema() {
        let agent = spec(Some("json"), Some(json!({"type": "object"})));
        // Caller names a different format and supplies no schema of its own:
        // the schema written for the old shape no longer applies.
        let request = spec(Some("a2ui"), None);
        let resolved = resolve_output_spec(Some(&agent), None, Some(&request))
            .expect("the agent asked for one");
        assert_eq!(resolved.format.as_deref(), Some("a2ui"));
        assert_eq!(resolved.schema, None);
    }

    #[test]
    fn a_caller_supplying_its_own_schema_keeps_it() {
        let agent = spec(Some("json"), Some(json!({"type": "object"})));
        let request = spec(Some("json"), Some(json!({"type": "array"})));
        let resolved = resolve_output_spec(Some(&agent), None, Some(&request))
            .expect("the agent asked for one");
        assert_eq!(resolved.schema, Some(json!({"type": "array"})));
    }

    #[test]
    fn a_caller_that_names_no_format_leaves_the_schema_alone() {
        let agent = spec(Some("json"), Some(json!({"type": "object"})));
        // Only instructions differ, so the declared shape still stands.
        let request = OutputSpec {
            instructions: Some("keep it short".to_string()),
            ..OutputSpec::default()
        };
        let resolved = resolve_output_spec(Some(&agent), None, Some(&request))
            .expect("the agent asked for one");
        assert_eq!(resolved.format.as_deref(), Some("json"));
        assert_eq!(resolved.schema, Some(json!({"type": "object"})));
    }

    /// A parsed blueprint whose agent-level output is `agent`, over stages
    /// named and shaped by `stages`. Both take TOML output tables (or `None`),
    /// because a manifest is where these declarations really come from.
    fn blueprint_with(agent: Option<&str>, stages: &[(&str, Option<&str>)]) -> crate::Blueprint {
        let mut manifest =
            String::from("[agent]\nname = \"checked\"\nversion = \"1.0.0\"\ndescription = \"d\"\n");
        if let Some(fields) = agent {
            manifest.push_str(&format!("\n[agent.output]\n{fields}\n"));
        }
        for (name, output) in stages {
            manifest.push_str(&format!("\n[stages.{name}]\nsystem_prompt = \"p\"\n"));
            if let Some(fields) = output {
                manifest.push_str(&format!("\n[stages.{name}.output]\n{fields}\n"));
            }
        }
        crate::manifest::parse_manifest(&manifest).expect("the test manifest parses")
    }

    /// The headline: a differing format retires the declared validator, and
    /// the warning names the stage, the script, and both formats.
    #[test]
    fn a_differing_format_earns_a_warning_naming_the_retired_validator() {
        let bp = blueprint_with(
            Some("format = \"markdown\"\nvalidator = \"checks/report.rhai\""),
            &[("plan", None)],
        );
        let request = spec(Some("json"), None);
        let warnings = retired_check_warnings(&bp, Some(&request));
        assert_eq!(warnings.len(), 1, "{warnings:?}");
        let line = &warnings[0];
        assert!(line.contains("'json'"), "{line}");
        assert!(line.contains("'markdown'"), "{line}");
        assert!(
            line.contains("the Rhai validator 'checks/report.rhai'"),
            "{line}"
        );
        assert!(line.contains("stage 'plan'"), "{line}");
    }

    /// Re-stating the declared format keeps the checks (see
    /// `re_stating_the_declared_format_keeps_its_shape_checks`), so it earns
    /// no warning - and neither does a request with no format in it, nor no
    /// request at all.
    #[test]
    fn nothing_retired_means_nothing_warned() {
        let bp = blueprint_with(
            Some("format = \"markdown\"\nvalidator = \"v.rhai\"\nschema = { type = \"object\" }"),
            &[("plan", None)],
        );
        let restated = spec(Some("markdown"), None);
        assert!(retired_check_warnings(&bp, Some(&restated)).is_empty());
        let formatless = OutputSpec {
            instructions: Some("keep it short".to_string()),
            ..OutputSpec::default()
        };
        assert!(retired_check_warnings(&bp, Some(&formatless)).is_empty());
        assert!(retired_check_warnings(&bp, None).is_empty());
        // And a blueprint with nothing retirable has nothing to lose.
        let unchecked = blueprint_with(Some("format = \"markdown\""), &[("plan", None)]);
        let reshaped = spec(Some("json"), None);
        assert!(retired_check_warnings(&unchecked, Some(&reshaped)).is_empty());
    }

    /// A schema alone, a validator alone, and the two together each word the
    /// loss precisely.
    #[test]
    fn the_warning_names_exactly_what_is_lost() {
        let request = spec(Some("json"), None);
        let schema_only = blueprint_with(
            Some("format = \"markdown\"\nschema = { type = \"object\" }"),
            &[("plan", None)],
        );
        let warnings = retired_check_warnings(&schema_only, Some(&request));
        assert!(
            warnings[0].contains("the JSON schema declared"),
            "{warnings:?}"
        );
        let both = blueprint_with(
            Some("format = \"markdown\"\nvalidator = \"v.rhai\"\nschema = { type = \"object\" }"),
            &[("plan", None)],
        );
        let warnings = retired_check_warnings(&both, Some(&request));
        assert!(
            warnings[0].contains("the Rhai validator 'v.rhai' and the JSON schema"),
            "{warnings:?}"
        );
    }

    /// A caller who brings a schema for the new shape replaced the declared
    /// one on purpose, so only the validator - which nothing can replace - is
    /// still worth a warning.
    #[test]
    fn a_replacement_schema_is_not_warned_about() {
        let bp = blueprint_with(
            Some("format = \"markdown\"\nvalidator = \"v.rhai\"\nschema = { type = \"object\" }"),
            &[("plan", None)],
        );
        let request = spec(Some("json"), Some(json!({"type": "array"})));
        let warnings = retired_check_warnings(&bp, Some(&request));
        assert_eq!(warnings.len(), 1, "{warnings:?}");
        assert!(
            warnings[0].contains("the Rhai validator 'v.rhai'"),
            "{warnings:?}"
        );
        assert!(
            !warnings[0].contains("JSON schema declared"),
            "{warnings:?}"
        );
        // And the advice acknowledges the schema they brought rather than
        // asking for one.
        assert!(
            warnings[0].contains("the schema supplied with the request"),
            "{warnings:?}"
        );
        // With nothing but the schema declared, the replacement leaves nothing
        // retired at all.
        let schema_only = blueprint_with(
            Some("format = \"markdown\"\nschema = { type = \"object\" }"),
            &[("plan", None)],
        );
        assert!(retired_check_warnings(&schema_only, Some(&request)).is_empty());
    }

    /// An agent-level validator shared by several stages is one line naming
    /// them all, and a stage with its own distinct declaration gets its own.
    #[test]
    fn stages_losing_the_same_checks_share_one_line() {
        let bp = blueprint_with(
            Some("format = \"markdown\"\nvalidator = \"shared.rhai\""),
            &[
                ("plan", None),
                ("draft", None),
                ("wrap", Some("format = \"a2ui\"\nvalidator = \"a2ui.rhai\"")),
            ],
        );
        let request = spec(Some("json"), None);
        let warnings = retired_check_warnings(&bp, Some(&request));
        assert_eq!(warnings.len(), 2, "{warnings:?}");
        assert!(
            warnings[0].contains("stages 'plan' and 'draft'"),
            "{warnings:?}"
        );
        assert!(warnings[1].contains("stage 'wrap'"), "{warnings:?}");
        assert!(warnings[1].contains("'a2ui'"), "{warnings:?}");
    }

    /// A declaration that lives only on a stage retires the same way: the
    /// warning does not need an agent-level `[agent.output]` to exist.
    #[test]
    fn a_stage_level_declaration_retires_without_an_agent_one() {
        let bp = blueprint_with(
            None,
            &[(
                "plan",
                Some("format = \"markdown\"\nvalidator = \"v.rhai\""),
            )],
        );
        let request = spec(Some("json"), None);
        let warnings = retired_check_warnings(&bp, Some(&request));
        assert_eq!(warnings.len(), 1, "{warnings:?}");
        assert!(
            warnings[0].contains("the Rhai validator 'v.rhai'"),
            "{warnings:?}"
        );
    }

    /// A stage that re-declares the requested format keeps its checks even
    /// while its siblings lose theirs, because the cascade is per stage.
    #[test]
    fn a_stage_already_in_the_requested_format_keeps_its_checks() {
        let bp = blueprint_with(
            Some("format = \"markdown\"\nvalidator = \"shared.rhai\""),
            &[("plan", None), ("emit", Some("format = \"json\""))],
        );
        let request = spec(Some("json"), None);
        let warnings = retired_check_warnings(&bp, Some(&request));
        assert_eq!(warnings.len(), 1, "{warnings:?}");
        assert!(warnings[0].contains("stage 'plan'"), "{warnings:?}");
    }

    /// A validator declared without any format is still retired by naming one
    /// (the request reshapes an output that never named its shape), and the
    /// warning says so without inventing a declared format.
    #[test]
    fn a_formatless_declaration_is_reshaped_by_any_request() {
        let bp = blueprint_with(Some("validator = \"v.rhai\""), &[("plan", None)]);
        let request = spec(Some("json"), None);
        let warnings = retired_check_warnings(&bp, Some(&request));
        assert_eq!(warnings.len(), 1, "{warnings:?}");
        assert!(
            warnings[0].contains("declared without a format"),
            "{warnings:?}"
        );
    }

    /// The three list shapes, plus the guard for a slice no caller produces.
    #[test]
    fn stage_phrases_read_as_prose() {
        let names = |names: &[&str]| names.iter().map(|n| n.to_string()).collect::<Vec<_>>();
        assert_eq!(stage_phrase(&names(&["a"])), "stage 'a'");
        assert_eq!(stage_phrase(&names(&["a", "b"])), "stages 'a' and 'b'");
        assert_eq!(
            stage_phrase(&names(&["a", "b", "c"])),
            "stages 'a', 'b', and 'c'"
        );
        assert_eq!(stage_phrase(&[]), "its stages");
    }

    #[test]
    fn short_content_is_stored_verbatim() {
        let out = FinalOutput::new(
            "done: 3 files",
            Some("markdown".to_string()),
            "wrap".into(),
            7,
        );
        assert_eq!(out.content, "done: 3 files");
        assert_eq!(out.format.as_deref(), Some("markdown"));
        assert_eq!(out.stage, "wrap");
        assert_eq!(out.submitted_at, 7);
        assert!(!out.truncated);
    }

    #[test]
    fn oversized_content_is_cut_at_a_char_boundary_and_flagged() {
        // A multi-byte character straddling the cap: slicing by byte index here
        // is what once aborted the daemon, so the cut must walk back.
        let mut content = "a".repeat(MAX_FINAL_OUTPUT_BYTES - 1);
        content.push('\u{1f600}');
        let out = FinalOutput::new(&content, None, "wrap".into(), 0);
        assert!(out.truncated);
        assert_eq!(out.content.len(), MAX_FINAL_OUTPUT_BYTES - 1);
        assert!(out.format.is_none());
    }

    #[test]
    fn describe_spec_is_empty_when_nothing_is_constrained() {
        assert_eq!(describe_spec(&OutputSpec::default()), "");
    }

    #[test]
    fn describe_spec_renders_every_field_it_has() {
        let described = describe_spec(&OutputSpec {
            format: Some("a2ui".to_string()),
            instructions: Some("One card per finding.".to_string()),
            example: Some("{\"root\": {}}".to_string()),
            schema: Some(json!({"type": "object"})),
            validator: None,
            on_validator_error: None,
            overwrite_artifacts: None,
            artifacts: Vec::new(),
        });
        assert!(described.contains("Return it in this format: a2ui."));
        assert!(described.contains("One card per finding."));
        assert!(described.contains("valid against this schema"));
        assert!(described.contains("{\"root\": {}}"));
        let with_files = describe_spec(&OutputSpec {
            artifacts: vec![
                ArtifactSpec {
                    name: "final".to_string(),
                    mime_type: "video/mp4".to_string(),
                    required: true,
                    description: Some("the cut".to_string()),
                },
                ArtifactSpec {
                    name: "notes".to_string(),
                    mime_type: "text/*".to_string(),
                    required: false,
                    description: None,
                },
            ],
            ..OutputSpec::default()
        });
        assert!(
            with_files.contains("- final (video/mp4, required): the cut\n- notes (text/*)"),
            "{with_files}"
        );
    }

    /// Without this the spec and the stage's own system prompt are two peer
    /// instructions, and a strongly-shaped stage prompt wins on some models
    /// and loses on others.
    #[test]
    fn a_constrained_spec_says_it_outranks_the_stage_prompt() {
        let described = describe_spec(&OutputSpec {
            instructions: Some("Reply with only the integer.".to_string()),
            ..OutputSpec::default()
        });
        assert!(
            described.contains("Where anything else you were told"),
            "{described}"
        );
        // Last, so it is read as governing what precedes it rather than as one
        // more line the next paragraph can override.
        assert!(
            described.trim_end().ends_with("follow this."),
            "{described}"
        );
    }

    /// A format on its own is still a shape, so it still outranks a prompt that
    /// describes a different one.
    #[test]
    fn a_format_only_spec_claims_precedence_too() {
        let described = describe_spec(&OutputSpec {
            format: Some("text".to_string()),
            ..OutputSpec::default()
        });
        assert!(
            described.contains("Where anything else you were told"),
            "{described}"
        );
    }

    /// The claim is scoped to presentation. A spec that constrains nothing must
    /// not tell a model to disregard its stage prompt.
    #[test]
    fn an_unconstrained_spec_claims_nothing() {
        assert!(!describe_spec(&OutputSpec::default()).contains("follow this"));
    }

    #[test]
    fn a_spec_round_trips_through_serde() {
        let original = spec(Some("a2ui"), Some(json!({"type": "object"})));
        let text = serde_json::to_string(&original).expect("a spec serializes");
        let back: OutputSpec = serde_json::from_str(&text).expect("and deserializes");
        assert_eq!(back, original);
        // Unset fields stay off the wire rather than serializing as nulls.
        assert!(!text.contains("instructions"));
        assert!(!text.contains("on_validator_error"));
    }

    /// The wire spelling is the manifest spelling: `accept` and `reject`,
    /// nothing else. A request naming a third policy is refused rather than
    /// quietly mapped to either behaviour.
    #[test]
    fn the_error_policy_uses_the_manifest_spelling_on_the_wire() {
        let original = OutputSpec {
            on_validator_error: Some(OnValidatorError::Accept),
            ..OutputSpec::default()
        };
        let text = serde_json::to_string(&original).expect("a spec serializes");
        assert!(text.contains(r#""on_validator_error":"accept""#), "{text}");
        let back: OutputSpec = serde_json::from_str(&text).expect("and deserializes");
        assert_eq!(back, original);

        let rejected = serde_json::from_str::<OutputSpec>(r#"{"on_validator_error":"sometimes"}"#);
        assert!(rejected.is_err(), "an unknown policy must not deserialize");
    }

    #[test]
    fn a_final_output_round_trips_through_serde() {
        let original = FinalOutput::new("answer", None, "wrap".into(), 1);
        let text = serde_json::to_string(&original).expect("an output serializes");
        let back: FinalOutput = serde_json::from_str(&text).expect("and deserializes");
        assert_eq!(back, original);
    }
}