ARCADIA-Studio/crates/oa-desktop/src/behavior/scenario.rs

//! Staged scenario authoring. UI picks semantic identities; the core validates
//! the complete transaction, including correlation, lifecycle and reuse rules.
use super::topology::{occurrence, unique_batch};
use super::*;
use iced::widget::{Column, column, text_input};
use std::{cell::RefCell, collections::BTreeSet};
mod camera;
pub(crate) mod focus;
pub(crate) mod spacing;
use super::scenario_layout::{
    Representation,
    presentation::{self, ScenarioPresentation},
};
#[cfg(test)]
mod presentation_tests;
mod usage;
mod workspace;
pub(crate) use workspace::NAME_INPUT;
pub use workspace::{Shelf, view};

#[cfg(test)]
#[path = "scenario_operation_tests.rs"]
mod operation_tests;

#[derive(Debug, Clone, Copy, PartialEq, Eq, serde::Serialize, serde::Deserialize)]
pub enum Tool {
    Lifeline,
    Message,
    Reuse,
    Action,
    Observation,
    Fragment,
}
impl Tool {
    pub(super) fn canvas_occurrence(self) -> bool {
        matches!(
            self,
            Self::Reuse | Self::Action | Self::Observation | Self::Fragment
        )
    }
    pub(super) fn uses_lifeline(self) -> bool {
        matches!(self, Self::Action | Self::Observation)
    }
    fn label(self) -> &'static str {
        match self {
            Self::Lifeline => "Add lifeline",
            Self::Message => "Add message",
            Self::Reuse => "Reuse scenario",
            Self::Action => "Add action",
            Self::Observation => "Observe state",
            Self::Fragment => "Add fragment",
        }
    }
}
#[derive(Debug, Clone, Copy, PartialEq, Eq, serde::Serialize, serde::Deserialize)]
pub enum MessageStyle {
    Asynchronous,
    Call,
    CallReply,
    Reply,
    Create,
    Delete,
    Timer,
}
impl std::fmt::Display for MessageStyle {
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        f.write_str(match self {
            Self::Asynchronous => "Asynchronous message",
            Self::Call => "Synchronous call",
            Self::CallReply => "Call + correlated reply",
            Self::Reply => "Reply to existing call",
            Self::Create => "Create participant",
            Self::Delete => "Delete participant",
            Self::Timer => "Local timer",
        })
    }
}
#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub struct Context {
    pub document: Id,
    pub scenario: Id,
    pub representation: Representation,
    pub visit: Id,
    pub revision: u64,
    pub epoch: u64,
}
#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub struct Slot {
    pub parent: Id,
    pub before: Option<Id>,
}
#[derive(Debug, Default, Clone, Copy, PartialEq, Eq)]
pub enum CanvasTool {
    #[default]
    Select,
    Message(MessageStyle),
    Add(Tool),
}
impl std::fmt::Display for CanvasTool {
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        match self {
            Self::Select => f.write_str("Select / reorder"),
            Self::Message(style) => write!(f, "{style}"),
            Self::Add(tool) => f.write_str(tool.label()),
        }
    }
}
#[derive(Debug, Clone)]
pub enum CanvasEvent {
    Spacing(spacing::Event),
    Scrolled(Context, ScrollArea, iced::Vector),
    Restored(Context, Id, ScrollArea, iced::Vector),
    Viewport(Context, Size),
    FormShown(Context, Id),
    Zoom(Context, Option<f32>),
    Camera(Context, u64, super::canvas_workspace::Event),
    Focus(Context),
    Shelf(Context, Shelf),
    OpenUse(Context, Id),
    Back(Context),
    Choose(Context, CanvasTool),
    Representation(Context, Representation),
    Select(Context, Id),
    Begin {
        context: Context,
        slot: Slot,
        sender: Id,
        receiver: Id,
        style: MessageStyle,
    },
    BeginOccurrence {
        context: Context,
        tool: Tool,
        slot: Slot,
        lifeline: Option<Id>,
    },
    Reorder {
        context: Context,
        occurrence: Id,
        slot: Slot,
    },
}
#[derive(Debug, Clone, Copy)]
pub enum ScrollArea {
    // The independent Details/outline scroller; viewport motion uses Camera.
    Page,
}
impl CanvasEvent {
    pub fn context(&self) -> Context {
        match self {
            Self::Spacing(event) => event.stamp().context,
            Self::Scrolled(context, _, _)
            | Self::Restored(context, ..)
            | Self::Viewport(context, _)
            | Self::FormShown(context, _)
            | Self::Zoom(context, _)
            | Self::Camera(context, ..)
            | Self::Focus(context)
            | Self::Shelf(context, _)
            | Self::OpenUse(context, _)
            | Self::Back(context)
            | Self::Choose(context, _)
            | Self::Representation(context, _)
            | Self::Select(context, _)
            | Self::Begin { context, .. }
            | Self::BeginOccurrence { context, .. }
            | Self::Reorder { context, .. } => *context,
        }
    }
}
#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub struct Operator(pub FragmentOperator);
impl std::fmt::Display for Operator {
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        f.write_str(match self.0 {
            FragmentOperator::Alternative => "ALT · alternatives",
            FragmentOperator::Parallel => "PAR · parallel",
            FragmentOperator::Loop => "LOOP · repetition",
            FragmentOperator::Optional => "OPT · optional",
        })
    }
}
#[derive(Debug, Clone)]
pub enum Event {
    Source(super::source_draft::Event),
    Start(Id, Tool),
    Cancel,
    Submit,
    Name(String),
    Target(Choice),
    Exchange(Choice),
    Sender(Choice),
    Receiver(Choice),
    Call(Choice),
    Style(MessageStyle),
    OperationIntent(bool),
    Operation(Choice),
    ClearOperation,
    Parent(Choice),
    Expression(String),
    SecondGuard(String),
    Operator(Operator),
    Binding(Id, Choice),
    Value(crate::data_values::FieldPathKey, String),
    ValueFocus(crate::data_values::FieldPathKey),
    ValueBrowse(Option<crate::data_values::FieldPathKey>),
    ValuePage(ValueSection, usize),
    ChoiceSearch(String),
    ChoicePage(usize),
    AppendInstead,
}
#[derive(Debug, Clone, Copy)]
pub enum ValueSection {
    Fields,
    Authored,
}
const VALUE_PAGE_SIZE: usize = 24;
#[derive(Default)]
pub struct State {
    spacing: Option<spacing::controller::Session>,
    draft: Option<Draft>,
    form_session: Id,
    form_mount: Id,
    form_focus_pending: bool,
    canvas_tool: Option<(Id, CanvasTool)>,
    call_choices: RefCell<Option<(CallChoiceContext, Vec<Choice>)>>,
    details_offset: iced::Vector,
    return_to: Vec<Caller>,
    restore: Option<DetailsRestore>,
    presentation: workspace::Presentation,
}
const CALLER_LIMIT: usize = 32;
pub(crate) struct Caller {
    document: Id,
    pub owner: Id,
    pub representation: Representation,
    pub occurrence: Id,
    target: Id,
    tool: CanvasTool,
    details_offset: iced::Vector,
    presentation: workspace::Presentation,
}
struct DetailsRestore {
    document: Id,
    owner: Id,
    representation: Representation,
    visit: Id,
    token: Id,
    offset: iced::Vector,
}
#[derive(Clone, Copy)]
pub(super) struct ScrollRestore {
    pub document: Id,
    pub owner: Id,
    pub representation: Representation,
    pub visit: Id,
    pub token: Id,
    pub offset: iced::Vector,
}
#[derive(PartialEq, Eq)]
struct CallChoiceContext {
    document: Id,
    revision: u64,
    owner: Id,
    parent: Id,
    before: Option<Id>,
    endpoints: Option<(Option<Id>, Option<Id>)>,
}
#[derive(Clone, serde::Serialize, serde::Deserialize)]
#[serde(deny_unknown_fields)]
struct Draft {
    #[serde(default)]
    source: super::source_draft::State,
    #[serde(default = "Id::new_v4")]
    invocation: Id,
    #[serde(default)]
    source_origin: Option<(Id, oa_core::Element)>,

    owner: Id,
    parent: Id,
    before: Option<Id>,
    fixed_endpoints: bool,
    tool: Tool,
    name: String,
    target: Option<Id>,
    exchange: Option<Id>,
    sender: Option<Id>,
    receiver: Option<Id>,
    call: Option<Id>,
    style: MessageStyle,
    #[serde(default)]
    operation: Option<OperationUse>,
    #[serde(default)]
    disabled_operation: Option<OperationUse>,
    expression: String,
    second_guard: String,
    operator: FragmentOperator,
    bindings: BTreeMap<Id, Id>,
    #[serde(with = "recovery_values")]
    values: BTreeMap<crate::data_values::FieldPathKey, String>,
    #[serde(with = "recovery_field_key")]
    value_focus: Option<crate::data_values::FieldPathKey>,
    #[serde(with = "recovery_field_key")]
    value_browse: Option<crate::data_values::FieldPathKey>,
    value_browse_page: usize,
    value_authored_page: usize,
    choice_search: String,
    choice_page: usize,
}
impl State {
    pub(crate) fn camera_boundary(&self) -> impl PartialEq + use<> {
        (
            self.canvas_tool,
            self.presentation.focused,
            self.presentation.shelf,
            self.presentation.viewport,
            self.presentation.pan,
            self.presentation.zoom,
            self.presentation.fit,
        )
    }

    pub(super) fn pending_name(&self) -> Option<&str> {
        self.draft.as_ref().map(|d| d.name.as_str())
    }
    pub(super) fn source_view<'a>(&'a self, p: &'a Project) -> Option<iced::Element<'a, Event>> {
        self.draft
            .as_ref()?
            .source
            .view(p)
            .map(|v| v.map(Event::Source))
    }

    pub fn source_active(&self) -> bool {
        self.draft.as_ref().is_some_and(|d| d.source.engaged())
    }

    pub fn source_open(&self) -> bool {
        self.draft.as_ref().is_some_and(|d| d.source.is_open())
    }
    pub fn source_back(&mut self) -> bool {
        let returned = self.draft.as_mut().is_some_and(|d| d.source.back());
        if returned {
            self.remount_form();
        }
        returned
    }

    pub(crate) fn enter(&mut self, document: Id, owner: Id) {
        self.enter_representation(document, owner, Representation::Derived { owner });
    }
    /// App validates requested identity with checked_owner before entering.
    pub(crate) fn enter_representation(
        &mut self,
        document: Id,
        owner: Id,
        representation: Representation,
    ) -> bool {
        if matches!(representation, Representation::Derived { owner: requested } if requested != owner)
        {
            return false;
        }
        let changed = self.presentation.identity != Some((document, owner))
            || self.presentation.representation != Some(representation);
        if changed {
            self.presentation = workspace::Presentation {
                identity: Some((document, owner)),
                representation: Some(representation),
                focused: self.presentation.focused,
                fit: matches!(representation, Representation::Saved { .. }),
                ..Default::default()
            };
            self.details_offset = iced::Vector::ZERO;
            self.canvas_tool = Some((owner, CanvasTool::Select));
        }
        if changed || self.presentation.visit.is_nil() {
            self.spacing = None;
            self.presentation.visit = Id::new_v4();
            self.restore = None;
            return true;
        }
        false
    }
    /// Suspend captured events while preserving this destination's camera state.
    pub(crate) fn leave(&mut self) {
        self.spacing = None;
        self.presentation.visit = Id::nil();
        self.restore = None;
    }
    pub(crate) fn forget_view(&mut self) {
        self.spacing = None;
        self.presentation.identity = None;
        self.presentation.representation = None;
        self.presentation.visit = Id::nil();
        self.restore = None;
    }
    pub(crate) fn representation(&self) -> Option<Representation> {
        self.presentation.representation
    }
    pub(crate) fn owner(&self) -> Option<Id> {
        self.presentation.identity.map(|(_, owner)| owner)
    }
    pub(crate) fn context(
        &self,
        document: Id,
        owner: Id,
        revision: u64,
        epoch: u64,
    ) -> Option<Context> {
        if self.presentation.identity != Some((document, owner)) || self.presentation.visit.is_nil()
        {
            return None;
        }
        Some(Context {
            document,
            scenario: owner,
            representation: self.representation()?,
            visit: self.presentation.visit,
            revision,
            epoch,
        })
    }
    pub(crate) fn display(
        &self,
        p: &Project,
        owner: Id,
        selected: Id,
    ) -> Option<ScenarioPresentation> {
        let (_, current_owner) = self.presentation.identity?;
        let representation = self.representation()?;
        (current_owner == owner).then(|| presentation::present(p, representation, selected))
    }
    pub(crate) fn coordinate_input(&self, p: &Project, context: Context) -> bool {
        self.context(
            context.document,
            context.scenario,
            context.revision,
            context.epoch,
        ) == Some(context)
            && self
                .display(p, context.scenario, context.scenario)
                .is_some_and(|shown| shown.capabilities().coordinate_input)
    }
    pub(crate) fn viewport(&mut self, size: Size) -> bool {
        self.presentation.viewport(size)
    }
    pub(crate) fn camera(
        &mut self,
        project: &Project,
        owner: Id,
        event: super::canvas_workspace::Event,
    ) -> bool {
        let Some(bounds) = self
            .display(project, owner, owner)
            .and_then(|shown| shown.bounds())
        else {
            return false;
        };
        let p = &mut self.presentation;
        camera::change(
            &mut p.pan,
            &mut p.zoom,
            &mut p.fit,
            p.viewport,
            bounds,
            event,
        )
    }
    pub(crate) fn zoom(&mut self, scale: Option<f32>) -> bool {
        self.presentation.zoom(scale)
    }
    pub(crate) fn camera_zoom(&mut self, p: &Project, owner: Id, zoom: Option<f32>) -> bool {
        let Some(bounds) = self
            .display(p, owner, owner)
            .and_then(|shown| shown.bounds())
        else {
            return false;
        };
        if let Some(next) = zoom {
            let current = self.presentation.camera(bounds);
            let viewport = self.presentation.viewport.unwrap_or(Size::new(500., 300.));
            self.camera(
                p,
                owner,
                super::canvas_workspace::Event::Zoom {
                    factor: next / current.scale,
                    at: Point::new(viewport.width / 2., viewport.height / 2.),
                    base: current.scale,
                },
            )
        } else {
            self.zoom(None)
        }
    }
    pub(crate) fn focused(&self) -> bool {
        self.presentation.focused
    }
    pub(crate) fn toggle_focus(&mut self) {
        self.presentation.focused = !self.presentation.focused;
    }
    pub(crate) fn toggle_shelf(&mut self, shelf: Shelf) {
        self.presentation.shelf = (self.presentation.shelf != Some(shelf)).then_some(shelf);
    }
    pub(crate) fn open_use(
        &mut self,
        p: &Project,
        context: Context,
        occurrence: Id,
    ) -> Result<Id, String> {
        let target = referenced_scenario(p, context.scenario, occurrence)
            .ok_or("Choose a scenario reference in the current scenario.")?;
        self.return_to
            .retain(|frame| frame.document == context.document);
        if self.return_to.len() == CALLER_LIMIT {
            self.return_to.remove(0);
        }
        self.return_to.push(Caller {
            document: context.document,
            owner: context.scenario,
            representation: context.representation,
            occurrence,
            target,
            tool: self.canvas_tool(context.scenario),
            details_offset: self.details_offset,
            presentation: self.presentation.clone(),
        });
        self.canvas_tool = Some((target, CanvasTool::Select));
        self.details_offset = iced::Vector::ZERO;
        self.restore = None;
        Ok(target)
    }
    fn valid_caller(p: &Project, context: Context, frame: &Caller) -> bool {
        frame.document == context.document
            && frame.target == context.scenario
            && presentation::checked_owner(p, frame.representation) == Some(frame.owner)
            && referenced_scenario(p, frame.owner, frame.occurrence) == Some(frame.target)
    }
    pub(super) fn can_back(&self, p: &Project, context: Context) -> bool {
        self.return_to
            .iter()
            .any(|frame| Self::valid_caller(p, context, frame))
    }
    pub(crate) fn back(&mut self, p: &Project, context: Context) -> Option<Caller> {
        while let Some(frame) = self.return_to.pop() {
            if Self::valid_caller(p, context, &frame) {
                return Some(frame);
            }
        }
        None
    }
    pub(crate) fn restore_caller(&mut self, context: Context, frame: Caller) {
        if context.document != frame.document
            || context.scenario != frame.owner
            || context.representation != frame.representation
        {
            return;
        }
        self.canvas_tool = Some((frame.owner, frame.tool));
        self.details_offset = frame.details_offset;
        self.presentation = frame.presentation;
        self.presentation.identity = Some((context.document, context.scenario));
        self.presentation.representation = Some(frame.representation);
        self.presentation.visit = context.visit;
        self.restore = Some(DetailsRestore {
            document: context.document,
            owner: frame.owner,
            representation: frame.representation,
            visit: context.visit,
            token: Id::new_v4(),
            offset: frame.details_offset,
        });
    }
    pub(super) fn scroll_restore(
        &self,
        context: Context,
        ScrollArea::Page: ScrollArea,
    ) -> Option<ScrollRestore> {
        let restore = self.restore.as_ref().filter(|r| {
            r.document == context.document
                && r.owner == context.scenario
                && r.representation == context.representation
                && r.visit == context.visit
        })?;
        Some(ScrollRestore {
            document: restore.document,
            owner: restore.owner,
            representation: restore.representation,
            visit: restore.visit,
            token: restore.token,
            offset: restore.offset,
        })
    }
    pub(crate) fn restored(
        &mut self,
        context: Context,
        token: Id,
        area: ScrollArea,
        offset: iced::Vector,
    ) -> bool {
        if !self.restore.as_ref().is_some_and(|r| {
            r.document == context.document
                && r.owner == context.scenario
                && r.representation == context.representation
                && r.visit == context.visit
                && r.token == token
        }) {
            return false;
        }
        self.restore = None;
        self.scrolled(area, offset)
    }
    pub(super) fn recovery_snapshot(&self) -> Result<Option<serde_json::Value>, String> {
        self.draft
            .as_ref()
            .map(serde_json::to_value)
            .transpose()
            .map_err(|e| e.to_string())
    }

    pub(super) fn from_recovery(value: serde_json::Value) -> Result<Self, String> {
        let draft = serde_json::from_value(value).map_err(|e| e.to_string())?;
        let session = Id::new_v4();
        Ok(Self {
            draft: Some(draft),
            form_session: session,
            form_mount: session,
            form_focus_pending: true,
            ..Default::default()
        })
    }

    pub(crate) fn form_session(&self) -> Option<Id> {
        self.draft.as_ref().map(|_| self.form_session)
    }

    pub(crate) fn form_mount(&self) -> Option<Id> {
        self.draft
            .as_ref()
            .filter(|d| !d.source.is_open())
            .map(|_| self.form_mount)
    }

    pub(crate) fn focus_stamp(&self, context: Context) -> Option<focus::Stamp> {
        (self.draft.as_ref()?.owner == context.scenario).then_some(focus::Stamp::new(
            context,
            self.form_session,
            self.form_mount()?,
        ))
    }

    fn remount_form(&mut self) {
        self.form_mount = Id::new_v4();
        self.form_focus_pending = true;
    }

    pub(crate) fn take_form_focus(&mut self, mount: Id) -> bool {
        if self.form_mount() == Some(mount) && self.form_focus_pending {
            self.form_focus_pending = false;
            true
        } else {
            false
        }
    }

    pub(crate) fn scrolled(&mut self, ScrollArea::Page: ScrollArea, offset: iced::Vector) -> bool {
        if !offset.x.is_finite() || !offset.y.is_finite() || offset.x < 0. || offset.y < 0. {
            return false;
        }
        let changed = self.details_offset != offset;
        self.details_offset = offset;
        changed
    }
    fn call_choices(&self, p: &Project, context: Context, draft: &Draft) -> Vec<Choice> {
        let key = CallChoiceContext {
            document: context.document,
            revision: context.revision,
            owner: draft.owner,
            parent: draft.parent,
            before: draft.before,
            endpoints: draft
                .fixed_endpoints
                .then_some((draft.sender, draft.receiver)),
        };
        let mut cached = self.call_choices.borrow_mut();
        if cached.as_ref().is_none_or(|(previous, _)| *previous != key) {
            *cached = Some((key, calls(p, draft)));
        }
        cached.as_ref().unwrap().1.clone()
    }
    pub(crate) fn created_selection(&self, p: &Project, command: &Command) -> Option<Id> {
        let draft = self.draft.as_ref()?;
        if self
            .draft
            .as_ref()
            .is_some_and(|d| d.source.label(d.target).is_some())
            && self.prepare_pending(p).ok().as_ref() != Some(command)
        {
            return None;
        }
        fn created(command: &Command, parent: Id) -> Option<Id> {
            match command {
                Command::CreateElement(element) if element.parent == Some(parent) => {
                    Some(element.id)
                }
                Command::Batch(commands) => {
                    commands.iter().find_map(|command| created(command, parent))
                }
                _ => None,
            }
        }
        created(command, draft.parent)
    }
    pub(super) fn canvas_tool(&self, owner: Id) -> CanvasTool {
        self.canvas_tool
            .filter(|(id, _)| *id == owner)
            .map(|(_, tool)| tool)
            .unwrap_or_default()
    }
    pub(crate) fn choose_tool(&mut self, owner: Id, tool: CanvasTool) {
        self.canvas_tool = Some((owner, tool));
    }
    pub(crate) fn begin_message(
        &mut self,
        p: &Project,
        context: Context,
        slot: Slot,
        sender: Id,
        receiver: Id,
        style: MessageStyle,
    ) -> Result<(), String> {
        slot_index(p, context.scenario, slot)?;
        for line in [sender, receiver] {
            if p.elements
                .get(&line)
                .is_none_or(|e| e.kind() != Kind::Lifeline || e.parent != Some(context.scenario))
                || represented(p, line).is_none()
            {
                return Err("Choose represented lifelines in this scenario.".into());
            }
        }
        self.update(p, Event::Start(context.scenario, Tool::Message))?;
        let draft = self.draft.as_mut().expect("Start installed the draft");
        draft.parent = slot.parent;
        draft.before = slot.before;
        draft.fixed_endpoints = true;
        draft.sender = Some(sender);
        draft.receiver = (style != MessageStyle::Timer).then_some(receiver);
        draft.style = style;
        Ok(())
    }
    pub(crate) fn begin_occurrence(
        &mut self,
        p: &Project,
        context: Context,
        tool: Tool,
        slot: Slot,
        lifeline: Option<Id>,
    ) -> Result<(), String> {
        if !tool.canvas_occurrence() {
            return Err(
                "Choose an action, state observation, scenario reference or fragment.".into(),
            );
        }
        slot_index(p, context.scenario, slot)?;
        if let Some(line) = lifeline
            && (!tool.uses_lifeline()
                || p.elements.get(&line).is_none_or(|e| {
                    e.kind() != Kind::Lifeline || e.parent != Some(context.scenario)
                })
                || represented(p, line).is_none())
        {
            return Err("Choose a represented lifeline in this scenario.".into());
        }
        self.update(p, Event::Start(context.scenario, tool))?;
        let draft = self.draft.as_mut().expect("Start installed the draft");
        draft.parent = slot.parent;
        draft.before = slot.before;
        draft.sender = lifeline;
        Ok(())
    }
    pub(super) fn pending_placement(&self, owner: Id) -> Option<(Slot, Option<Id>)> {
        let draft = self
            .draft
            .as_ref()
            .filter(|d| d.owner == owner && d.tool != Tool::Lifeline)?;
        Some((
            Slot {
                parent: draft.parent,
                before: draft.before,
            },
            draft.sender,
        ))
    }
    pub(super) fn pending_owner(&self) -> Option<Id> {
        self.draft.as_ref().map(|d| d.owner)
    }

    pub(super) fn prepare_pending(&self, p: &Project) -> Result<Command, String> {
        let command = self
            .draft
            .as_ref()
            .ok_or("Choose a scenario tool first.")?
            .command(p)?;
        execute_batch(p, std::slice::from_ref(&command)).map_err(|e| e.to_string())?;
        Ok(command)
    }

    pub(super) fn acknowledge_commit(&mut self) {
        self.draft = None;
        *self.call_choices.get_mut() = None;
    }

    pub fn update(&mut self, p: &Project, event: Event) -> Result<Option<Command>, String> {
        if let Event::Source(event) = event {
            if self
                .draft
                .as_mut()
                .ok_or("Start the consumer form first.")?
                .source
                .dismiss(&event)?
            {
                self.remount_form();
                return Ok(None);
            }
            let d = self
                .draft
                .as_ref()
                .ok_or("Start the consumer form first.")?;
            if d.tool != Tool::Lifeline {
                return Err("This reference does not support staged source creation.".into());
            }
            if d.source_origin.as_ref().is_some_and(|(document, owner)| {
                *document != p.id || p.elements.get(&d.owner) != Some(owner)
            }) {
                return Err("The original consumer changed. Cancel and reopen its form; the current draft is retained.".into());
            }
            if d.source_origin.is_none() && d.source.engaged() {
                return Err("The recovered source draft has no original document binding. Go Back or cancel it.".into());
            }
            let mut next = d.clone();
            if next.source_origin.is_none() && matches!(&event, super::source_draft::Event::Open(_))
            {
                next.source_origin = Some((
                    p.id,
                    p.elements
                        .get(&d.owner)
                        .ok_or("The consumer owner no longer exists.")?
                        .clone(),
                ));
            }
            if let Some(id) = next.source.update(
                p,
                super::source_draft::Scope::Lifeline {
                    owner: d.owner,
                    viewpoint: viewpoint(p, d.owner),
                },
                d.invocation,
                event,
            )? {
                next.target = Some(id);
                next.command(p)?;
            }
            let returned = d.source.is_open() && !next.source.is_open();
            self.draft = Some(next);
            if returned {
                self.remount_form();
            }
            return Ok(None);
        }
        if self.source_open() && !matches!(&event, Event::Cancel) {
            return Err("Use the new source or go Back before editing the parent form.".into());
        }

        if self.draft.is_some() && matches!(&event, Event::Start(..)) {
            return Err(PENDING_DRAFT.into());
        }
        match event {
            Event::Start(owner, tool) => {
                if p.elements.get(&owner).map(oa_core::Element::kind) != Some(Kind::Scenario) {
                    return Err("Choose a scenario.".into());
                }
                self.form_session = Id::new_v4();
                self.form_mount = self.form_session;
                self.form_focus_pending = true;
                self.draft = Some(Draft {
                    source: Default::default(),
                    invocation: Id::new_v4(),
                    source_origin: Some((p.id, p.elements[&owner].clone())),
                    owner,
                    parent: owner,
                    before: None,
                    fixed_endpoints: false,
                    tool,
                    name: String::new(),
                    target: None,
                    exchange: None,
                    sender: None,
                    receiver: None,
                    call: None,
                    style: MessageStyle::CallReply,
                    operation: None,
                    disabled_operation: None,
                    expression: String::new(),
                    second_guard: "else".into(),
                    operator: FragmentOperator::Alternative,
                    bindings: BTreeMap::new(),
                    values: BTreeMap::new(),
                    value_focus: None,
                    value_browse: None,
                    value_browse_page: 0,
                    value_authored_page: 0,
                    choice_search: String::new(),
                    choice_page: 0,
                });
            }
            Event::Cancel => self.acknowledge_commit(),
            Event::Submit => return self.prepare_pending(p).map(Some),
            other => {
                if let Some(d) = &mut self.draft {
                    match other {
                        Event::Name(s) => d.name = s,
                        Event::Expression(s) => d.expression = s,
                        Event::SecondGuard(s) => d.second_guard = s,
                        Event::OperationIntent(enabled) => {
                            if enabled {
                                d.operation = Some(
                                    d.operation
                                        .clone()
                                        .or_else(|| d.disabled_operation.take())
                                        .unwrap_or(OperationUse { allocation: None }),
                                );
                            } else {
                                d.disabled_operation =
                                    d.operation.take().or_else(|| d.disabled_operation.take());
                            }
                        }
                        Event::Operation(c) => {
                            d.operation = Some(OperationUse {
                                allocation: Some(c.id),
                            })
                        }
                        Event::ClearOperation => {
                            d.operation = Some(OperationUse { allocation: None })
                        }
                        Event::Target(c) => {
                            d.target = Some(c.id);
                            d.bindings.clear();
                        }
                        Event::Exchange(c) => {
                            if d.exchange != Some(c.id) {
                                d.exchange = Some(c.id);
                                if !d.has_operation_intent(p) {
                                    d.reset_values();
                                }
                                if !d.fixed_endpoints {
                                    d.sender = None;
                                    d.receiver = None;
                                }
                            }
                        }
                        Event::Sender(c) => d.sender = Some(c.id),
                        Event::Receiver(c) => d.receiver = Some(c.id),
                        Event::Parent(c) => {
                            if d.parent != c.id {
                                d.parent = c.id;
                                d.before = None;
                            }
                        }
                        Event::ChoiceSearch(value) => {
                            d.choice_search = value;
                            d.choice_page = 0;
                        }
                        Event::ChoicePage(page) => d.choice_page = page,
                        Event::AppendInstead => d.before = None,
                        Event::Style(style) => {
                            let previous = d.style;
                            d.style = style;
                            if previous != style {
                                if previous == MessageStyle::Timer || style == MessageStyle::Timer {
                                    d.exchange = None;
                                    d.sender = None;
                                    d.receiver = None;
                                    d.call = None;
                                } else if (previous == MessageStyle::Reply)
                                    != (style == MessageStyle::Reply)
                                {
                                    std::mem::swap(&mut d.sender, &mut d.receiver);
                                    d.call = None;
                                }
                                if !d.has_operation_intent(p) {
                                    d.retain_value_paths(p);
                                }
                            }
                        }
                        Event::Call(c) => {
                            d.call = Some(c.id);
                            if let Some(SharedBody::Occurrence {
                                body:
                                    OccurrenceBody::Exchange {
                                        exchange,
                                        sender,
                                        receiver,
                                        ..
                                    },
                                ..
                            }) = p.elements.get(&c.id).and_then(|e| e.shared())
                            {
                                if d.exchange != *exchange && !d.has_operation_intent(p) {
                                    d.reset_values();
                                }
                                d.exchange = *exchange;
                                d.sender = *receiver;
                                d.receiver = *sender;
                            }
                        }
                        Event::Operator(operator) => d.operator = operator.0,
                        Event::Binding(referenced, c) => {
                            d.bindings.insert(referenced, c.id);
                        }
                        Event::Value(id, s) => {
                            d.values.insert(id, s);
                        }
                        Event::ValueFocus(key)
                            if d.signature(p)
                                .ok()
                                .flatten()
                                .and_then(|r| {
                                    crate::data_values::resolve(p, &r, &d.value_kind(), &key)
                                })
                                .is_some() =>
                        {
                            d.value_focus = Some(key);
                        }
                        Event::ValueBrowse(key) => {
                            if key.as_ref().is_none_or(|key| {
                                d.signature(p)
                                    .ok()
                                    .flatten()
                                    .and_then(|r| {
                                        crate::data_values::resolve(p, &r, &d.value_kind(), key)
                                    })
                                    .is_some()
                            }) {
                                d.value_browse = key;
                                d.value_browse_page = 0;
                            }
                        }
                        Event::ValuePage(section, page) => match section {
                            ValueSection::Fields => d.value_browse_page = page,
                            ValueSection::Authored => d.value_authored_page = page,
                        },
                        _ => {}
                    }
                }
            }
        }
        Ok(None)
    }
}

mod recovery_values {
    use super::*;
    use serde::{Deserialize, Serialize};
    pub fn serialize<S: serde::Serializer>(
        values: &BTreeMap<crate::data_values::FieldPathKey, String>,
        serializer: S,
    ) -> Result<S::Ok, S::Error> {
        values
            .iter()
            .map(|(key, value)| (&key.path, key.field, value))
            .collect::<Vec<_>>()
            .serialize(serializer)
    }
    pub fn deserialize<'de, D: serde::Deserializer<'de>>(
        deserializer: D,
    ) -> Result<BTreeMap<crate::data_values::FieldPathKey, String>, D::Error> {
        let values = Vec::<(Vec<Id>, Id, String)>::deserialize(deserializer)?;
        let mut result = BTreeMap::new();
        for (path, field, value) in values {
            if result
                .insert(crate::data_values::FieldPathKey { path, field }, value)
                .is_some()
            {
                return Err(serde::de::Error::custom(
                    "Duplicate recovered scenario value path",
                ));
            }
        }
        Ok(result)
    }
}

mod recovery_field_key {
    use super::*;
    use serde::{Deserialize, Serialize};
    pub fn serialize<S: serde::Serializer>(
        key: &Option<crate::data_values::FieldPathKey>,
        serializer: S,
    ) -> Result<S::Ok, S::Error> {
        key.as_ref()
            .map(|key| (&key.path, key.field))
            .serialize(serializer)
    }
    pub fn deserialize<'de, D: serde::Deserializer<'de>>(
        deserializer: D,
    ) -> Result<Option<crate::data_values::FieldPathKey>, D::Error> {
        Ok(Option::<(Vec<Id>, Id)>::deserialize(deserializer)?
            .map(|(path, field)| crate::data_values::FieldPathKey { path, field }))
    }
}
fn viewpoint(p: &Project, owner: Id) -> ScenarioViewpoint {
    match p.elements.get(&owner).and_then(|e| e.shared()) {
        Some(SharedBody::Scenario { viewpoint, .. }) => *viewpoint,
        _ => ScenarioViewpoint::MixedLegacy,
    }
}
pub(crate) fn referenced_scenario(p: &Project, owner: Id, occurrence: Id) -> Option<Id> {
    if p.elements.get(&owner)?.kind() != Kind::Scenario
        || validation::ancestor_of_kind(p, occurrence, Kind::Scenario) != Some(owner)
    {
        return None;
    }
    let SharedBody::Occurrence {
        body:
            OccurrenceBody::ScenarioUse {
                scenario: Some(target),
                ..
            },
        ..
    } = p.elements.get(&occurrence)?.shared()?
    else {
        return None;
    };
    p.elements
        .get(target)
        .filter(|e| e.kind() == Kind::Scenario)
        .map(|e| e.id)
}
fn represented(p: &Project, line: Id) -> Option<Id> {
    match p.elements.get(&line)?.shared()? {
        SharedBody::Lifeline { represented } => *represented,
        _ => None,
    }
}
fn named_choice(p: &Project, id: Id) -> Choice {
    Choice {
        id,
        label: format!(
            "{} · {}",
            p.named(id),
            p.elements
                .get(&id)
                .map(|e| e.alias.as_str())
                .or_else(|| p.relations.get(&id).map(|r| r.alias.as_str()))
                .unwrap_or("")
        ),
    }
}
fn lines(p: &Project, owner: Id) -> Vec<Choice> {
    p.children(owner)
        .filter(|e| e.kind() == Kind::Lifeline)
        .map(|e| named_choice(p, e.id))
        .collect()
}
fn parents(p: &Project, owner: Id) -> Vec<Choice> {
    let mut out = vec![Choice {
        id: owner,
        label: "Main scenario sequence".into(),
    }];
    out.extend(
        p.elements
            .values()
            .filter(|e| {
                matches!(
                    e.shared(),
                    Some(SharedBody::Occurrence {
                        body: OccurrenceBody::Branch { .. },
                        ..
                    })
                ) && validation::ancestor_of_kind(p, e.id, Kind::Scenario) == Some(owner)
            })
            .map(|e| named_choice(p, e.id)),
    );
    out
}
fn slot_index(p: &Project, owner: Id, slot: Slot) -> Result<usize, String> {
    if !parents(p, owner)
        .iter()
        .any(|choice| choice.id == slot.parent)
    {
        return Err("Choose an insertion slot in this scenario or one of its operands.".into());
    }
    let steps = p
        .elements
        .get(&slot.parent)
        .and_then(oa_core::Element::steps)
        .ok_or("This sequence no longer exists.")?;
    slot.before.map_or(Ok(steps.len()), |id| {
        steps
            .iter()
            .position(|step| *step == id)
            .ok_or_else(|| "The insertion slot changed. Choose its position again.".into())
    })
}
pub(super) fn slot_label(p: &Project, slot: Slot) -> String {
    match slot.before {
        Some(id) => format!(
            "{} · before {}",
            named_choice(p, slot.parent).label,
            named_choice(p, id).label
        ),
        None => format!("{} · append", named_choice(p, slot.parent).label),
    }
}
pub(crate) fn reorder(
    p: &Project,
    owner: Id,
    occurrence: Id,
    slot: Slot,
) -> Result<Command, String> {
    let to = slot_index(p, owner, slot)?;
    if p.elements.get(&occurrence).and_then(|e| e.parent) != Some(slot.parent) {
        return Err(
            "Reorder inside the occurrence's current sequence; dragging never changes its operand."
                .into(),
        );
    }
    let mut steps = p.elements[&slot.parent]
        .steps()
        .expect("slot validated")
        .clone();
    let from = steps
        .iter()
        .position(|id| *id == occurrence)
        .ok_or("This occurrence is not in the sequence.")?;
    steps.remove(from);
    steps.insert(to - usize::from(from < to), occurrence);
    let command = Command::SetSteps(slot.parent, steps);
    execute_batch(p, std::slice::from_ref(&command)).map_err(|error| error.to_string())?;
    Ok(command)
}
fn compatible_binding(p: &Project, referenced: Id, local: Id) -> bool {
    represented(p, referenced)
        .zip(represented(p, local))
        .is_some_and(|(a, b)| validation::semantic_representation_compatible(p, b, a) == Some(true))
}
fn valid_body_choice(p: &Project, owner: Id, body: OccurrenceBody) -> bool {
    let e = occurrence(p, owner, "Scenario selection preview", body);
    execute_batch(p, &[Command::CreateElement(e)]).is_ok()
}
fn sources(p: &Project, d: &Draft) -> Vec<Choice> {
    let Some(owner) = p
        .elements
        .get(&d.owner)
        .filter(|e| e.kind() == Kind::Scenario)
    else {
        return vec![];
    };
    let layer = owner.layer();
    let mut values: Vec<_> = p
        .elements
        .values()
        .filter(|e| {
            e.layer() == layer
                && match d.tool {
                    Tool::Lifeline => {
                        validation::viewpoint_represents(viewpoint(p, d.owner), e.kind())
                    }
                    Tool::Action => e.kind().is_work(),
                    Tool::Observation => e.kind().is_state(),
                    Tool::Reuse => {
                        e.kind() == Kind::Scenario
                            && valid_body_choice(
                                p,
                                d.owner,
                                OccurrenceBody::ScenarioUse {
                                    scenario: Some(e.id),
                                    bindings: vec![],
                                },
                            )
                    }
                    _ => false,
                }
        })
        .map(|e| named_choice(p, e.id))
        .collect();
    values.sort_by(|a, b| a.label.cmp(&b.label));
    values
}
fn exchanges(p: &Project, d: &Draft) -> Vec<Choice> {
    // Candidate browsing concerns the declared viewpoint and represented
    // endpoints. The complete transaction still validates the chosen slot,
    // lifecycle, payload and paired reply on Apply.
    let viewpoint = viewpoint(p, d.owner);
    p.relations
        .values()
        .filter(|r| {
            p.layer_of(r.id) == p.layer_of(d.owner)
                && matches!(
                    r.kind(),
                    RelationKind::Interaction
                        | RelationKind::CommunicationMean
                        | RelationKind::FunctionalExchange
                        | RelationKind::BoundaryExchange
                )
                && match viewpoint {
                    ScenarioViewpoint::OperationalActivity => r.kind() == RelationKind::Interaction,
                    ScenarioViewpoint::Functional => r.kind() == RelationKind::FunctionalExchange,
                    ScenarioViewpoint::ParticipantInteraction => matches!(
                        r.kind(),
                        RelationKind::Interaction
                            | RelationKind::CommunicationMean
                            | RelationKind::BoundaryExchange
                    ),
                    ScenarioViewpoint::BoundaryInterface => matches!(
                        r.kind(),
                        RelationKind::FunctionalExchange | RelationKind::BoundaryExchange
                    ),
                    ScenarioViewpoint::MixedLegacy => true,
                }
                && (!d.fixed_endpoints
                    || d.sender.zip(d.receiver).is_some_and(|(sender, receiver)| {
                        let mut body = d.message_body();
                        if let OccurrenceBody::Exchange { exchange, .. } = &mut body {
                            *exchange = Some(r.id);
                        }
                        validation::message_endpoints(p, &body).is_some_and(|(source, target)| {
                            validation::lifeline_matches_endpoint(p, sender, source) == Some(true)
                                && validation::lifeline_matches_endpoint(p, receiver, target)
                                    == Some(true)
                        })
                    }))
        })
        .map(|r| Choice {
            id: r.id,
            label: format!(
                "{} · {} {} {}",
                r.name,
                p.named(r.source()),
                if matches!(
                    r.body,
                    RelationBody::CommunicationMean {
                        oriented: false,
                        ..
                    } | RelationBody::BoundaryExchange {
                        oriented: false,
                        ..
                    }
                ) {
                    "↔"
                } else {
                    "→"
                },
                p.named(r.target())
            ),
        })
        .collect()
}
fn calls(p: &Project, d: &Draft) -> Vec<Choice> {
    p.elements
        .values()
        .filter(|e| validation::ancestor_of_kind(p, e.id, Kind::Scenario) == Some(d.owner))
        .filter_map(|e| {
            let Some(SharedBody::Occurrence {
                body:
                    OccurrenceBody::Exchange {
                        message_kind: MessageKind::Call,
                        exchange,
                        sender,
                        receiver,
                        ..
                    },
                ..
            }) = e.shared()
            else {
                return None;
            };
            if d.fixed_endpoints && (d.sender != *receiver || d.receiver != *sender) {
                return None;
            }
            let mut candidate = d.clone();
            candidate.style = MessageStyle::Reply;
            candidate.call = Some(e.id);
            // Candidate availability must not fluctuate while typing names or
            // expressions. These draft values are validated only on Apply.
            candidate.reset_values();
            candidate.name.clear();
            candidate.exchange = *exchange;
            candidate.sender = *receiver;
            candidate.receiver = *sender;
            candidate
                .command(p)
                .ok()
                .and_then(|command| execute_batch(p, &[command]).ok())
                .map(|_| named_choice(p, e.id))
        })
        .collect()
}
impl Draft {
    fn has_operation_intent(&self, p: &Project) -> bool {
        self.operation.is_some()
            || self
                .call
                .and_then(|id| p.elements.get(&id))
                .is_some_and(|e| {
                    matches!(
                        e.shared(),
                        Some(SharedBody::Occurrence {
                            body: OccurrenceBody::Exchange {
                                operation: Some(_),
                                ..
                            },
                            ..
                        })
                    )
                })
    }
    fn proposed_message(&self, p: &Project) -> oa_core::Element {
        let mut message = self.append(p, "Operation preview", self.message_body());
        // This is a transient resolver input; no generated identity reaches a command.
        message.id = Id::nil();
        message
    }
    fn signature(&self, p: &Project) -> Result<Option<Relation>, String> {
        crate::data_values::message_signature(p, &self.proposed_message(p))
    }
    fn reset_values(&mut self) {
        self.values.clear();
        self.value_focus = None;
        self.value_browse = None;
        self.value_browse_page = 0;
        self.value_authored_page = 0;
    }
    fn retain_value_paths(&mut self, p: &Project) {
        let kind = self.kind();
        let exchange = self.exchange.and_then(|id| p.relations.get(&id));
        self.values.retain(|key, _| {
            exchange
                .and_then(|r| crate::data_values::resolve(p, r, &kind, key))
                .is_some()
        });
        if self.value_focus.as_ref().is_some_and(|key| {
            exchange
                .and_then(|r| crate::data_values::resolve(p, r, &kind, key))
                .is_none()
        }) {
            self.value_focus = None;
        }
        if self.value_browse.as_ref().is_some_and(|key| {
            exchange
                .and_then(|r| crate::data_values::resolve(p, r, &kind, key))
                .is_none()
        }) {
            self.value_browse = None;
            self.value_browse_page = 0;
        }
    }
    fn browsed_values(
        &self,
        p: &Project,
        exchange: &Relation,
    ) -> Result<Vec<crate::data_values::FieldPathChoice>, String> {
        match &self.value_browse {
            Some(key) => crate::data_values::children(p, exchange, &self.value_kind(), key),
            None => Ok(crate::data_values::roots(p, exchange, &self.value_kind())),
        }
    }
    fn authored_values(&self) -> Vec<(&crate::data_values::FieldPathKey, &str)> {
        self.values
            .iter()
            .filter(|(_, value)| !value.trim().is_empty())
            .map(|(key, value)| (key, value.as_str()))
            .collect()
    }
    fn value_kind(&self) -> MessageKind {
        crate::data_values::operation_value_phase(&self.kind(), self.operation.as_ref())
    }
    fn kind(&self) -> MessageKind {
        match self.style {
            MessageStyle::Asynchronous => MessageKind::Asynchronous,
            MessageStyle::Call | MessageStyle::CallReply => MessageKind::Call,
            MessageStyle::Reply => MessageKind::Reply,
            MessageStyle::Create => MessageKind::Create,
            MessageStyle::Delete => MessageKind::Delete,
            MessageStyle::Timer => MessageKind::Timer {
                expression: self.expression.clone(),
            },
        }
    }
    fn message_body(&self) -> OccurrenceBody {
        OccurrenceBody::Exchange {
            exchange: if self.style == MessageStyle::Timer {
                None
            } else {
                self.exchange
            },
            sender: self.sender,
            receiver: if self.style == MessageStyle::Timer {
                None
            } else {
                self.receiver
            },
            message_kind: self.kind(),
            operation: if matches!(
                self.style,
                MessageStyle::Call | MessageStyle::CallReply | MessageStyle::Asynchronous
            ) {
                self.operation.clone()
            } else {
                None
            },
            reply_to: self.call,
            values: self
                .values
                .iter()
                .filter(|(_, v)| !v.trim().is_empty())
                .map(|(field, expression)| MessageValue {
                    path: field.path.clone(),
                    field: field.field,
                    expression: expression.clone(),
                })
                .collect(),
        }
    }
    fn line_choices(&self, p: &Project, sender: bool) -> Vec<Choice> {
        let endpoint = validation::message_endpoints(p, &self.message_body())
            .map(|(a, b)| if sender { a } else { b });
        lines(p, self.owner)
            .into_iter()
            .filter(|line| {
                if self
                    .exchange
                    .and_then(|id| p.relations.get(&id))
                    .is_some_and(|r| {
                        matches!(
                            r.body,
                            RelationBody::CommunicationMean { .. }
                                | RelationBody::BoundaryExchange {
                                    oriented: false,
                                    ..
                                }
                        )
                    })
                {
                    let mut body = self.message_body();
                    if let OccurrenceBody::Exchange {
                        sender: from,
                        receiver: to,
                        ..
                    } = &mut body
                    {
                        if sender {
                            *from = Some(line.id);
                        } else {
                            *to = Some(line.id);
                        }
                    }
                    return !matches!(
                        validation::resolve_message_endpoints(p, &body),
                        validation::MessageEndpointResolution::Conflict
                    );
                }
                endpoint.is_none_or(|endpoint| {
                    validation::lifeline_matches_endpoint(p, line.id, endpoint) == Some(true)
                })
            })
            .collect()
    }
    fn append(&self, p: &Project, name: &str, body: OccurrenceBody) -> oa_core::Element {
        let mut e = occurrence(p, self.owner, name, body);
        e.parent = Some(self.parent);
        e
    }
    fn command(&self, p: &Project) -> Result<Command, String> {
        if self.source.engaged()
            && self.source_origin.as_ref().is_none_or(|(document, owner)| {
                *document != p.id || p.elements.get(&self.owner) != Some(owner)
            })
        {
            return Err("The original consumer document or owner changed. Cancel and reopen its form; your draft is retained.".into());
        }
        self.source.check_scope(
            super::source_draft::Scope::Lifeline {
                owner: self.owner,
                viewpoint: viewpoint(p, self.owner),
            },
            self.target,
        )?;
        let preview = self.source.preview(p, self.target)?;
        let command = self.consumer_command(preview.as_ref().unwrap_or(p))?;
        self.source.combine(p, self.target, command)
    }
    fn consumer_command(&self, p: &Project) -> Result<Command, String> {
        if p.elements.get(&self.owner).map(oa_core::Element::kind) != Some(Kind::Scenario) {
            return Err("The scenario no longer exists. Cancel or restore its owner.".into());
        }
        if !parents(p, self.owner).iter().any(|c| c.id == self.parent) {
            return Err("Choose this scenario or one of its operands as destination.".into());
        }
        let default = self
            .target
            .or(self.exchange)
            .map(|id| p.named(id))
            .unwrap_or(self.tool.label());
        let name = if self.name.trim().is_empty() {
            default
        } else if self.source.label(self.target).is_some() {
            self.name.as_str()
        } else {
            self.name.trim()
        };
        let mut commands = vec![];
        match self.tool {
            Tool::Lifeline => {
                let target = self
                    .target
                    .ok_or("Choose the work or participant represented by this lifeline.")?;
                if !sources(p, self).iter().any(|c| c.id == target) {
                    return Err(
                        "Choose a representation compatible with the scenario viewpoint.".into(),
                    );
                }
                let mut e = p
                    .make_element(
                        Kind::Lifeline,
                        p.elements[&self.owner].layer(),
                        name,
                        Some(self.owner),
                    )
                    .unwrap();
                *e.shared_mut().unwrap() = SharedBody::Lifeline {
                    represented: Some(target),
                };
                commands.push(Command::CreateElement(e));
            }
            Tool::Message => {
                let sender = self.sender.ok_or("Choose the sending lifeline.")?;
                if !self.line_choices(p, true).iter().any(|c| c.id == sender) {
                    return Err("The sender must represent the exchange source.".into());
                }
                if self.style == MessageStyle::Timer {
                    if self.expression.trim().is_empty() {
                        return Err("Enter the timer duration or deadline.".into());
                    }
                } else {
                    if self.exchange.is_none() {
                        return Err("Choose the exchange carried by this message.".into());
                    }
                    let receiver = self.receiver.ok_or("Choose the receiving lifeline.")?;
                    if !self.line_choices(p, false).iter().any(|c| c.id == receiver) {
                        return Err("The receiver must represent the exchange target.".into());
                    }
                }
                if self.style == MessageStyle::Reply && self.call.is_none() {
                    return Err("Choose the earlier call answered by this reply.".into());
                }
                let call = self.append(p, name, self.message_body());
                let call_id = call.id;
                commands.push(Command::CreateElement(call));
                if self.style == MessageStyle::CallReply {
                    commands.push(Command::CreateElement(self.append(
                        p,
                        &format!("Reply · {name}"),
                        OccurrenceBody::Exchange {
                            exchange: self.exchange,
                            sender: self.receiver,
                            receiver: self.sender,
                            message_kind: MessageKind::Reply,
                            operation: None,
                            reply_to: Some(call_id),
                            values: vec![],
                        },
                    )));
                }
            }
            Tool::Reuse => {
                let target = self.target.ok_or("Choose a scenario to reuse.")?;
                if !sources(p, self).iter().any(|c| c.id == target) {
                    return Err("Choose a compatible scenario without recursive reuse.".into());
                }
                let mut used = BTreeSet::new();
                let mut bindings = vec![];
                for line in lines(p, target) {
                    let local = *self
                        .bindings
                        .get(&line.id)
                        .ok_or("Bind every referenced lifeline to a local lifeline.")?;
                    if !lines(p, self.owner).iter().any(|c| c.id == local)
                        || !compatible_binding(p, line.id, local)
                        || !used.insert(local)
                    {
                        return Err(
                            "Each binding needs a distinct compatible local lifeline.".into()
                        );
                    }
                    bindings.push(LifelineBinding {
                        referenced: line.id,
                        local,
                    });
                }
                commands.push(Command::CreateElement(self.append(
                    p,
                    name,
                    OccurrenceBody::ScenarioUse {
                        scenario: Some(target),
                        bindings,
                    },
                )));
            }
            Tool::Action | Tool::Observation => {
                let target = self
                    .target
                    .ok_or("Choose the action or state to observe.")?;
                if !sources(p, self).iter().any(|c| c.id == target) {
                    return Err("Choose compatible work or a state in this layer.".into());
                }
                let line = self.sender.ok_or("Choose the observed lifeline.")?;
                if !lines(p, self.owner).iter().any(|c| c.id == line) {
                    return Err("Choose a lifeline in this scenario.".into());
                }
                let body = if self.tool == Tool::Action {
                    OccurrenceBody::Action {
                        action: Some(target),
                        lifeline: Some(line),
                    }
                } else {
                    OccurrenceBody::State {
                        state: Some(target),
                        lifeline: Some(line),
                    }
                };
                commands.push(Command::CreateElement(self.append(p, name, body)));
            }
            Tool::Fragment => {
                let two = matches!(
                    self.operator,
                    FragmentOperator::Alternative | FragmentOperator::Parallel
                );
                if self.operator != FragmentOperator::Parallel && self.expression.trim().is_empty()
                {
                    return Err("Describe the operand condition or loop guard.".into());
                }
                let fragment = self.append(
                    p,
                    name,
                    OccurrenceBody::Fragment {
                        operator: self.operator,
                        branches: vec![],
                    },
                );
                let id = fragment.id;
                commands.push(Command::CreateElement(fragment));
                for (i, guard) in [&self.expression, &self.second_guard]
                    .into_iter()
                    .take(if two { 2 } else { 1 })
                    .enumerate()
                {
                    let mut branch = self.append(
                        p,
                        &format!("{} · operand {}", name, i + 1),
                        OccurrenceBody::Branch {
                            guard: if self.operator == FragmentOperator::Parallel {
                                String::new()
                            } else {
                                guard.clone()
                            },
                            occurrences: vec![],
                        },
                    );
                    branch.parent = Some(id);
                    commands.push(Command::CreateElement(branch));
                }
            }
        }
        if self.tool != Tool::Lifeline {
            let slot = Slot {
                parent: self.parent,
                before: self.before,
            };
            let index = slot_index(p, self.owner, slot)?;
            let added: Vec<_> = commands
                .iter()
                .filter_map(|command| match command {
                    Command::CreateElement(e)
                        if e.parent == Some(self.parent) && e.kind() == Kind::Occurrence =>
                    {
                        Some(e.id)
                    }
                    _ => None,
                })
                .collect();
            let mut steps = p.elements[&self.parent]
                .steps()
                .expect("slot validated")
                .clone();
            steps.splice(index..index, added);
            commands.push(Command::SetSteps(self.parent, steps));
        }
        Ok(unique_batch(p, commands))
    }
}
fn event(e: Event) -> Message {
    Message::Behavior(super::Event::Scenario(e))
}
fn value_page(len: usize, requested: usize) -> std::ops::Range<usize> {
    let start = requested.min(len.saturating_sub(1) / VALUE_PAGE_SIZE) * VALUE_PAGE_SIZE;
    start..(start + VALUE_PAGE_SIZE).min(len)
}
fn value_pager(len: usize, requested: usize, section: ValueSection) -> Element<'static, Message> {
    let range = value_page(len, requested);
    let page = range.start / VALUE_PAGE_SIZE;
    row![
        button("Previous")
            .on_press_maybe((page > 0).then(|| event(Event::ValuePage(section, page - 1)))),
        text(format!(
            "Page {} of {} · {} fields",
            page + 1,
            len.div_ceil(VALUE_PAGE_SIZE).max(1),
            len
        ))
        .size(11),
        button("Next")
            .on_press_maybe((range.end < len).then(|| event(Event::ValuePage(section, page + 1))))
    ]
    .spacing(6)
    .into()
}
fn value_panel<'a>(p: &Project, d: &'a Draft, exchange: &Relation) -> Element<'a, Message> {
    use crate::data_values;
    let mut out = column![text("Message values").size(14)].spacing(7);
    if let Some(browse) = &d.value_browse {
        let title = data_values::resolve(p, exchange, &d.value_kind(), browse)
            .map(|choice| format!("Fields inside {}", choice.label))
            .unwrap_or_else(|| "This record path is no longer available in this message.".into());
        out = out.push(text(title).size(11)).push(
            row![
                button("Root fields").on_press(event(Event::ValueBrowse(None))),
                button("Up one level")
                    .on_press(event(Event::ValueBrowse(data_values::parent(browse))))
            ]
            .spacing(6),
        );
    } else {
        out = out.push(text("Root fields · choose a record to browse its fields").size(11));
    }
    match d.browsed_values(p, exchange) {
        Ok(choices) if !choices.is_empty() => {
            let range = value_page(choices.len(), d.value_browse_page);
            let visible = choices[range].to_vec();
            let selected = visible
                .iter()
                .find(|choice| Some(&choice.key) == d.value_focus.as_ref())
                .cloned();
            out = out
                .push(value_pager(
                    choices.len(),
                    d.value_browse_page,
                    ValueSection::Fields,
                ))
                .push(
                    pick_list(visible, selected, |choice| {
                        event(Event::ValueFocus(choice.key))
                    })
                    .placeholder("Choose a field on this page…")
                    .text_size(12)
                    .padding(8)
                    .width(Fill),
                );
        }
        Ok(_) => {
            out = out.push(text("No fields at this level for this message phase.").size(11));
        }
        Err(error) => out = out.push(text(error).size(11).color(style::MUTED)),
    }
    match d
        .value_focus
        .as_ref()
        .map(|key| data_values::resolve(p, exchange, &d.value_kind(), key))
    {
        Some(Some(focus)) => {
            let key = focus.key;
            out = out
                .push(text(focus.label).size(12))
                .push(
                    text_input(
                        "Optional value expression",
                        d.values.get(&key).map(String::as_str).unwrap_or(""),
                    )
                    .on_input({
                        let key = key.clone();
                        move |value| event(Event::Value(key.clone(), value))
                    })
                    .padding(8)
                    .size(12),
                )
                .push(text("An empty expression omits this value.").size(11));
            let mut actions = row![
                button("Show enclosing fields")
                    .on_press(event(Event::ValueBrowse(data_values::parent(&key))))
            ]
            .spacing(6);
            if matches!(p.elements.get(&key.field).and_then(oa_core::Element::shared),
                Some(SharedBody::DataField { type_ref: TypeRef::Named(record),
                    storage: FieldStorage::Value, .. }) if data::is_record(p, *record))
            {
                actions = actions.push(
                    button("Browse record fields").on_press(event(Event::ValueBrowse(Some(key)))),
                );
            }
            out = out.push(actions);
        }
        Some(None) => {
            out = out.push(text("The selected path is unavailable in this message. Choose a compatible field; entered values remain in the draft.")
                .size(11).color(style::MUTED));
        }
        None => out = out.push(text("Choose a field to enter its value expression.").size(11)),
    }
    let authored = d.authored_values();
    out = out.push(text(format!("Authored values ({})", authored.len())).size(12));
    if authored.is_empty() {
        out = out.push(text("No value expressions entered.").size(11));
    } else {
        out = out.push(value_pager(
            authored.len(),
            d.value_authored_page,
            ValueSection::Authored,
        ));
        for (key, expression) in &authored[value_page(authored.len(), d.value_authored_page)] {
            let title = data_values::resolve(p, exchange, &d.value_kind(), key)
                .map(|choice| choice.label)
                .unwrap_or_else(|| format!("Unavailable field {} · review this value", key.field));
            out = out.push(
                button(
                    column![text(title).size(11), text(short(expression, 100)).size(11)].spacing(3),
                )
                .on_press(event(Event::ValueFocus((*key).clone())))
                .width(Fill),
            );
        }
    }
    out.into()
}
fn picker<'a>(
    choices: Vec<Choice>,
    selected: Option<Id>,
    placeholder: &'a str,
    change: impl Fn(Choice) -> Event + 'a,
) -> Element<'a, Message> {
    let selected = selected
        .and_then(|id| choices.iter().find(|c| c.id == id))
        .cloned();
    pick_list(choices, selected, move |c| event(change(c)))
        .placeholder(placeholder)
        .width(Fill)
        .padding(9)
        .text_size(12)
        .into()
}
fn bounded_picker<'a>(
    mut choices: Vec<Choice>,
    d: &'a Draft,
    selected: Option<Id>,
    placeholder: &'a str,
    change: impl Fn(Choice) -> Event + 'a,
) -> Element<'a, Message> {
    let current = choices
        .iter()
        .find(|choice| Some(choice.id) == selected)
        .cloned();
    let query = d.choice_search.trim().to_lowercase();
    choices.retain(|choice| choice.label.to_lowercase().contains(&query));
    choices.sort_by(|a, b| a.label.cmp(&b.label).then(a.id.cmp(&b.id)));
    let len = choices.len();
    let range = value_page(len, d.choice_page);
    let page = range.start / VALUE_PAGE_SIZE;
    let mut out = column![
        text_input("Search compatible exchanges / calls…", &d.choice_search)
            .on_input(|value| event(Event::ChoiceSearch(value)))
            .padding(8)
            .size(12)
    ]
    .spacing(6);
    if let Some(choice) = current.as_ref().filter(|choice| {
        !choices[range.clone()]
            .iter()
            .any(|visible| visible.id == choice.id)
    }) {
        out = out.push(label(format!("Selected: {}", choice.label)));
    }
    if len == 0 {
        out = out.push(label("No matching exchange or eligible earlier call. Change the search, endpoints or destination, or cancel."));
    } else {
        out = out
            .push(
                row![
                    button("Previous")
                        .on_press_maybe((page > 0).then(|| event(Event::ChoicePage(page - 1)))),
                    text(format!(
                        "{} choices · page {}/{}",
                        len,
                        page + 1,
                        len.div_ceil(VALUE_PAGE_SIZE)
                    ))
                    .size(11),
                    button("Next").on_press_maybe(
                        (range.end < len).then(|| event(Event::ChoicePage(page + 1)))
                    ),
                ]
                .spacing(6),
            )
            .push(
                pick_list(choices[range].to_vec(), current, move |choice| {
                    event(change(choice))
                })
                .placeholder(placeholder)
                .padding(9)
                .text_size(12)
                .width(Fill),
            );
    }
    out.into()
}

#[cfg(test)]
pub(crate) mod direct_tests {
    use super::*;
    pub struct Fixture {
        pub project: Project,
        pub owner: Id,
        pub exchange: Id,
        pub sender: Id,
        pub receiver: Id,
        pub call: Id,
        pub reply: Id,
    }
    pub fn fixture() -> Fixture {
        let f = crate::data_values::tests::payload();
        let mut p = f.project;
        let mut lines = vec![];
        for (name, represented) in [
            ("Caller", p.relations[&f.exchange].source()),
            ("Callee", p.relations[&f.exchange].target()),
        ] {
            let id = p
                .add_element(Kind::Lifeline, Layer::Oa, name, Some(f.scenario))
                .unwrap();
            *p.elements.get_mut(&id).unwrap().shared_mut().unwrap() = SharedBody::Lifeline {
                represented: Some(represented),
            };
            lines.push(id);
        }
        let mut state = State::default();
        for event in [
            Event::Start(f.scenario, Tool::Message),
            Event::Exchange(named_choice(&p, f.exchange)),
            Event::Sender(named_choice(&p, lines[0])),
            Event::Receiver(named_choice(&p, lines[1])),
        ] {
            state.update(&p, event).unwrap();
        }
        p = execute_batch(&p, &[state.prepare_pending(&p).unwrap()]).unwrap();
        let steps = p.elements[&f.scenario].steps().unwrap();
        let (call, reply) = (steps[0], steps[1]);
        Fixture {
            project: p,
            owner: f.scenario,
            exchange: f.exchange,
            sender: lines[0],
            receiver: lines[1],
            call,
            reply,
        }
    }
    pub fn context(owner: Id) -> Context {
        Context {
            document: Id::new_v4(),
            scenario: owner,
            representation: Representation::Derived { owner },
            visit: Id::new_v4(),
            revision: 0,
            epoch: 0,
        }
    }
    pub(super) fn placement_fixture() -> (Fixture, Id, Id, Id, Id, Id) {
        let mut f = fixture();
        let p = &mut f.project;
        let machine = p
            .add_element(Kind::StateMachine, Layer::Oa, "Context", None)
            .unwrap();
        let region = p
            .add_element(Kind::Region, Layer::Oa, "Main region", Some(machine))
            .unwrap();
        let state = p
            .add_element(Kind::State, Layer::Oa, "Ready", Some(region))
            .unwrap();
        let reused = p
            .add_element(Kind::Scenario, Layer::Oa, "Reusable check", None)
            .unwrap();
        let remote = p
            .add_element(Kind::Lifeline, Layer::Oa, "Reused caller", Some(reused))
            .unwrap();
        let represented = represented(p, f.sender);
        *p.elements.get_mut(&remote).unwrap().shared_mut().unwrap() =
            SharedBody::Lifeline { represented };
        let fragment = occurrence(
            p,
            f.owner,
            "Outer alternative",
            OccurrenceBody::Fragment {
                operator: FragmentOperator::Alternative,
                branches: vec![],
            },
        );
        let fragment_id = fragment.id;
        *p = execute_batch(p, &[Command::CreateElement(fragment)]).unwrap();
        let branch = occurrence(
            p,
            fragment_id,
            "Chosen operand",
            OccurrenceBody::Branch {
                guard: "ready".into(),
                occurrences: vec![],
            },
        );
        let branch_id = branch.id;
        *p = execute_batch(p, &[Command::CreateElement(branch)]).unwrap();
        let anchor = occurrence(
            p,
            branch_id,
            "Existing check",
            OccurrenceBody::Action {
                action: represented,
                lifeline: Some(f.sender),
            },
        );
        let anchor_id = anchor.id;
        *p = execute_batch(p, &[Command::CreateElement(anchor)]).unwrap();
        (f, branch_id, anchor_id, state, reused, remote)
    }
    fn canvas_mouse(
        scene: &Scene,
        input: &mut SequenceInput,
        event: mouse::Event,
        point: Point,
        bounds: Rectangle,
    ) -> Option<Message> {
        canvas::Program::update(
            scene,
            input,
            &canvas::Event::Mouse(event),
            bounds,
            mouse::Cursor::Available(point),
        )
        .and_then(|action| action.into_inner().0)
    }
    fn form(app: &mut App, event: Event) {
        let _ = app.update(Message::Behavior(super::super::Event::Scenario(event)));
    }
    pub fn navigation_fixture() -> (Project, [Id; 3], [Id; 3]) {
        let mut p = Project::empty();
        let owners = ["A caller", "B definition", "C definition"].map(|name| {
            p.add_element(Kind::Scenario, Layer::Oa, name, None)
                .unwrap()
        });
        let uses = [
            (owners[0], owners[1]),
            (owners[0], owners[1]),
            (owners[1], owners[2]),
        ]
        .map(|(owner, target)| {
            let element = occurrence(
                &p,
                owner,
                "Reference",
                OccurrenceBody::ScenarioUse {
                    scenario: Some(target),
                    bindings: vec![],
                },
            );
            let id = element.id;
            p = execute_batch(&p, &[Command::CreateElement(element)]).unwrap();
            id
        });
        (p, owners, uses)
    }
    pub fn navigation_event(app: &mut App, event: impl FnOnce(Context) -> CanvasEvent) {
        let context = app.scenario_context().unwrap();
        let _ = app.update(Message::ScenarioCanvas(event(context)));
    }
    #[test]
    fn direct_scenario_reference_navigation_retains_each_exact_caller_without_history() {
        let (p, [a, b, c], [first, second, nested]) = navigation_fixture();
        let mut app = App::with_project(p.clone());
        let _ = app.update(Message::Select(a));
        let _ = app.update(Message::Page(crate::app::Page::Behavior));
        let source = app.document.bundle().clone();
        let revision = app.document.revision();
        for caller in [second, first] {
            navigation_event(&mut app, |ctx| {
                CanvasEvent::Choose(ctx, CanvasTool::Add(Tool::Reuse))
            });
            navigation_event(&mut app, |ctx| CanvasEvent::Zoom(ctx, None));
            let camera_epoch = app.camera_epoch;
            navigation_event(&mut app, |ctx| {
                CanvasEvent::Camera(
                    ctx,
                    camera_epoch,
                    super::super::canvas_workspace::Event::Pan(iced::Vector::new(25., 170.)),
                )
            });
            navigation_event(&mut app, |ctx| {
                CanvasEvent::Scrolled(ctx, ScrollArea::Page, iced::Vector::new(0., 80.))
            });
            navigation_event(&mut app, |ctx| CanvasEvent::OpenUse(ctx, caller));
            assert_eq!(app.selected, b);
            assert_eq!(app.behavior.scenario.presentation.pan, iced::Vector::ZERO);
            navigation_event(&mut app, |ctx| {
                CanvasEvent::Choose(ctx, CanvasTool::Message(MessageStyle::Timer))
            });
            let camera_epoch = app.camera_epoch;
            navigation_event(&mut app, |ctx| {
                CanvasEvent::Camera(
                    ctx,
                    camera_epoch,
                    super::super::canvas_workspace::Event::Pan(iced::Vector::new(0., 115.)),
                )
            });
            navigation_event(&mut app, |ctx| CanvasEvent::OpenUse(ctx, nested));
            assert_eq!(app.selected, c);
            navigation_event(&mut app, CanvasEvent::Back);
            assert_eq!(app.selected, nested);
            assert_eq!(
                app.behavior.scenario.canvas_tool(b),
                CanvasTool::Message(MessageStyle::Timer)
            );
            assert_eq!(
                app.behavior.scenario.presentation.pan,
                iced::Vector::new(0., 115.)
            );
            navigation_event(&mut app, CanvasEvent::Back);
            assert_eq!(app.selected, caller);
            assert_eq!(app.scenario_context().unwrap().scenario, a);
            assert_eq!(
                app.behavior.scenario.canvas_tool(a),
                CanvasTool::Add(Tool::Reuse)
            );
            assert_eq!(
                app.behavior.scenario.presentation.pan,
                iced::Vector::new(25., 170.)
            );
            assert_eq!(
                app.behavior.scenario.details_offset,
                iced::Vector::new(0., 80.),
                "The caller's independent outline scroll is restored separately"
            );
            assert!(
                !app.behavior
                    .scenario
                    .can_back(app.project(), app.scenario_context().unwrap())
            );
            assert_eq!(app.project(), &p);
            assert_eq!(app.document.bundle(), &source);
            assert_eq!(app.document.revision(), revision);
            assert!(!app.document.can_undo());
            assert!(!app.document.can_redo());
        }
    }
    #[test]
    fn direct_scenario_reference_navigation_blocks_pending_drafts_and_stale_contexts() {
        let (p, [a, b, _], [first, _, _]) = navigation_fixture();
        for back in [false, true] {
            for pending in 0..3 {
                let mut app = App::with_project(p.clone());
                let _ = app.update(Message::Select(a));
                let _ = app.update(Message::Page(crate::app::Page::Behavior));
                if back {
                    navigation_event(&mut app, |ctx| CanvasEvent::OpenUse(ctx, first));
                }
                match pending {
                    0 => {
                        let _ = app.update(Message::Field("/name".into(), "".into()));
                    }
                    1 => {
                        let _ = app.update(Message::SourceEdit(
                            iced::widget::text_editor::Action::Edit(
                                iced::widget::text_editor::Edit::Insert('?'),
                            ),
                        ));
                    }
                    _ => {
                        navigation_event(&mut app, |context| CanvasEvent::BeginOccurrence {
                            context,
                            tool: Tool::Action,
                            slot: Slot {
                                parent: context.scenario,
                                before: None,
                            },
                            lifeline: None,
                        });
                        form(&mut app, Event::Name("  Unfinished action  ".into()));
                    }
                }
                let selected = app.selected;
                let source = app.document.bundle().clone();
                let raw_source = app.source_editor.text();
                let property_snapshot = |app: &App| {
                    app.draft
                        .as_ref()
                        .map(|d| serde_json::to_value(d.recovery_snapshot()).unwrap())
                };
                let raw_properties = property_snapshot(&app);
                let raw_behavior = app.behavior.scenario.recovery_snapshot().unwrap();
                navigation_event(&mut app, |ctx| {
                    if back {
                        CanvasEvent::Back(ctx)
                    } else {
                        CanvasEvent::OpenUse(ctx, first)
                    }
                });
                assert_eq!(app.selected, selected);
                assert_eq!(app.source_editor.text(), raw_source);
                assert_eq!(property_snapshot(&app), raw_properties);
                assert_eq!(
                    app.behavior.scenario.recovery_snapshot().unwrap(),
                    raw_behavior
                );
                assert_eq!(app.document.bundle(), &source);
                assert_eq!(app.project(), &p);
                assert!(!app.document.can_undo());
                assert!(app.status.contains("Apply or cancel"), "{}", app.status);
                if back {
                    assert_eq!(selected, b);
                }
            }
        }
        let mut app = App::with_project(p.clone());
        let _ = app.update(Message::Select(a));
        let _ = app.update(Message::Page(crate::app::Page::Behavior));
        for dimension in 0..4 {
            let mut stale = app.scenario_context().unwrap();
            match dimension {
                0 => stale.document = Id::new_v4(),
                1 => stale.scenario = b,
                2 => stale.revision += 1,
                _ => stale.epoch += 1,
            }
            let _ = app.update(Message::ScenarioCanvas(CanvasEvent::OpenUse(stale, first)));
            assert_eq!(app.selected, a);
            assert!(app.behavior.scenario.return_to.is_empty());
        }
        navigation_event(&mut app, |ctx| CanvasEvent::OpenUse(ctx, b));
        assert_eq!(
            app.selected, a,
            "a definition is not a local reference occurrence"
        );
    }
    #[test]
    fn direct_scenario_reference_return_survives_rename_and_rejects_deleted_or_changed_use() {
        let (p, [a, b, c], [first, _, _]) = navigation_fixture();
        for edit in 0..4 {
            let mut app = App::with_project(p.clone());
            let _ = app.update(Message::Select(a));
            let _ = app.update(Message::Page(crate::app::Page::Behavior));
            navigation_event(&mut app, |ctx| CanvasEvent::OpenUse(ctx, first));
            let command = match edit {
                0 => Command::Batch(vec![
                    Command::Rename(a, "Renamed caller".into()),
                    Command::Rename(first, "Renamed reference".into()),
                ]),
                1 => Command::Delete(first),
                2 => Command::Delete(a),
                _ => {
                    let mut changed = p.elements[&first].clone();
                    if let Some(SharedBody::Occurrence {
                        body: OccurrenceBody::ScenarioUse { scenario, .. },
                        ..
                    }) = changed.shared_mut()
                    {
                        *scenario = Some(c);
                    }
                    Command::EditElement(first, changed)
                }
            };
            let _ = app.update(Message::Command(command));
            let source = app.document.bundle().clone();
            let project = app.project().clone();
            let revision = app.document.revision();
            assert!(app.document.can_undo(), "{}", app.status);
            navigation_event(&mut app, CanvasEvent::Back);
            assert_eq!(app.selected, if edit == 0 { first } else { b });
            assert_eq!(
                app.scenario_context().unwrap().scenario,
                if edit == 0 { a } else { b },
                "Back must restore the caller workspace even if a rename already selected its UUID"
            );
            assert_eq!(app.project(), &project);
            assert_eq!(app.document.bundle(), &source);
            assert_eq!(app.document.revision(), revision);
            assert!(app.document.can_undo());
            assert!(!app.document.can_redo());
        }
    }
    #[test]
    fn direct_clicked_occurrences_use_root_and_operand_slots_with_exact_source_history() {
        let (f, branch, anchor, observed, reused, remote) = placement_fixture();
        for tool in [Tool::Action, Tool::Observation, Tool::Reuse, Tool::Fragment] {
            for slot in [
                Slot {
                    parent: f.owner,
                    before: Some(f.reply),
                },
                Slot {
                    parent: branch,
                    before: Some(anchor),
                },
            ] {
                for on_lifeline in [true, false] {
                    let mut app = App::with_project(f.project.clone());
                    let _ = app.update(Message::Select(f.owner));
                    let _ = app.update(Message::Page(crate::app::Page::Behavior));
                    let context = app.scenario_context().unwrap();
                    let _ = app.update(Message::ScenarioCanvas(CanvasEvent::Choose(
                        context,
                        CanvasTool::Add(tool),
                    )));
                    let context = app.scenario_context().unwrap();
                    let before = app.document.bundle().clone();
                    let mut scene = Scene::sequence(app.project(), f.owner, f.call);
                    scene.interaction = Some((context, CanvasTool::Add(tool), true));
                    scene.camera_pan = iced::Vector::new(23., 80.);
                    let bounds = Rectangle::new(
                        Point::new(20., 40.),
                        Size::new(scene.size.width + 46., scene.size.height + 160.),
                    );
                    let y = scene.slots.iter().find(|s| s.slot == slot).unwrap().y;
                    let x = if on_lifeline {
                        scene.lanes[&f.sender]
                    } else {
                        scene.size.width - 35.
                    };
                    let point = Point::new(bounds.x + x, bounds.y + y) + scene.camera_pan;
                    assert!(bounds.contains(point));
                    let mut input = SequenceInput::default();
                    canvas_mouse(
                        &scene,
                        &mut input,
                        mouse::Event::CursorMoved { position: point },
                        point,
                        bounds,
                    );
                    assert!(
                        canvas_mouse(
                            &scene,
                            &mut input,
                            mouse::Event::ButtonPressed(mouse::Button::Left),
                            point,
                            bounds
                        )
                        .is_none()
                    );
                    let message = canvas_mouse(
                        &scene,
                        &mut input,
                        mouse::Event::ButtonReleased(mouse::Button::Left),
                        point,
                        bounds,
                    )
                    .unwrap();
                    let line = (tool.uses_lifeline() && on_lifeline).then_some(f.sender);
                    assert!(
                        matches!(&message, Message::ScenarioCanvas(CanvasEvent::BeginOccurrence { tool: actual, slot: captured, lifeline, .. }) if *actual == tool && *captured == slot && *lifeline == line)
                    );
                    assert!(
                        canvas_mouse(
                            &scene,
                            &mut input,
                            mouse::Event::ButtonReleased(mouse::Button::Left),
                            point,
                            bounds
                        )
                        .is_none(),
                        "one click publishes once"
                    );
                    let _ = app.update(message);
                    assert_eq!(
                        app.behavior.scenario.pending_placement(f.owner),
                        Some((slot, line))
                    );
                    assert_eq!(app.document.bundle(), &before);
                    assert!(!app.document.can_undo());
                    form(&mut app, Event::Name(format!("Placed {tool:?}")));
                    match tool {
                        Tool::Action => form(
                            &mut app,
                            Event::Target(named_choice(
                                &f.project,
                                represented(&f.project, f.sender).unwrap(),
                            )),
                        ),
                        Tool::Observation => {
                            form(&mut app, Event::Target(named_choice(&f.project, observed)))
                        }
                        Tool::Reuse => {
                            form(&mut app, Event::Target(named_choice(&f.project, reused)));
                            form(
                                &mut app,
                                Event::Binding(remote, named_choice(&f.project, f.sender)),
                            );
                        }
                        Tool::Fragment => form(&mut app, Event::Expression("ready".into())),
                        _ => unreachable!(),
                    }
                    if tool.uses_lifeline() && !on_lifeline {
                        form(&mut app, Event::Submit);
                        assert!(
                            app.behavior.has_pending(),
                            "off-lifeline creation requires an explicit lifeline"
                        );
                        assert_eq!(app.document.bundle(), &before);
                        form(&mut app, Event::Sender(named_choice(&f.project, f.sender)));
                    }
                    form(&mut app, Event::Submit);
                    assert!(!app.behavior.has_pending(), "{tool:?}: {}", app.status);
                    let created = app.selected;
                    assert_eq!(app.project().elements[&created].parent, Some(slot.parent));
                    let mut expected = f.project.elements[&slot.parent].steps().unwrap().clone();
                    let index = expected
                        .iter()
                        .position(|id| Some(*id) == slot.before)
                        .unwrap();
                    expected.insert(index, created);
                    assert_eq!(
                        app.project().elements[&slot.parent].steps().unwrap(),
                        &expected
                    );
                    let untouched = if slot.parent == f.owner {
                        branch
                    } else {
                        f.owner
                    };
                    assert_eq!(
                        app.project().elements[&untouched],
                        f.project.elements[&untouched]
                    );
                    assert_eq!(app.project().relations, f.project.relations);
                    assert_eq!(app.project().elements[&reused], f.project.elements[&reused]);
                    assert_eq!(
                        language::parse(&language::format(app.project())).unwrap(),
                        *app.project()
                    );
                    let after = app.document.bundle().clone();
                    let result = app.project().clone();
                    let _ = app.update(Message::Undo);
                    assert_eq!(app.document.bundle(), &before);
                    assert_eq!(app.project(), &f.project);
                    assert!(!app.document.can_undo());
                    let _ = app.update(Message::Redo);
                    assert_eq!(app.document.bundle(), &after);
                    assert_eq!(app.project(), &result);
                    assert!(!app.document.can_redo());
                }
            }
        }
    }
    #[test]
    fn direct_clicked_occurrence_rejects_stale_slots_and_retains_recoverable_drafts() {
        let (f, branch, anchor, _, _, remote) = placement_fixture();
        let slot = Slot {
            parent: branch,
            before: Some(anchor),
        };
        let mut state = State::default();
        for (tool, slot, line) in [
            (Tool::Lifeline, slot, None),
            (
                Tool::Action,
                Slot {
                    parent: f.owner,
                    before: Some(anchor),
                },
                Some(f.sender),
            ),
            (
                Tool::Action,
                Slot {
                    parent: Id::new_v4(),
                    before: None,
                },
                Some(f.sender),
            ),
            (Tool::Action, slot, Some(remote)),
            (Tool::Reuse, slot, Some(f.sender)),
        ] {
            assert!(
                state
                    .begin_occurrence(&f.project, context(f.owner), tool, slot, line)
                    .is_err()
            );
            assert!(state.draft.is_none());
        }
        let mut app = App::with_project(f.project.clone());
        let _ = app.update(Message::Select(f.owner));
        let _ = app.update(Message::Page(crate::app::Page::Behavior));
        let original = app.document.bundle().clone();
        let event = |context| CanvasEvent::BeginOccurrence {
            context,
            tool: Tool::Action,
            slot,
            lifeline: Some(f.sender),
        };
        for dimension in 0..4 {
            let mut stale = app.scenario_context().unwrap();
            match dimension {
                0 => stale.document = Id::new_v4(),
                1 => stale.scenario = Id::new_v4(),
                2 => stale.revision += 1,
                _ => stale.epoch += 1,
            }
            let _ = app.update(Message::ScenarioCanvas(event(stale)));
            assert!(!app.behavior.has_pending());
        }
        let old_context = app.scenario_context().unwrap();
        let _ = app.update(Message::ScenarioCanvas(CanvasEvent::Camera(
            old_context,
            app.camera_epoch,
            super::super::canvas_workspace::Event::Pan(iced::Vector::new(0., 100.)),
        )));
        let _ = app.update(Message::ScenarioCanvas(event(old_context)));
        assert!(!app.behavior.has_pending());
        let current = app.scenario_context().unwrap();
        let _ = app.update(Message::ScenarioCanvas(event(current)));
        form(&mut app, Event::Name("  Λ phase — retained  ".into()));
        let raw = app.behavior.scenario.recovery_snapshot().unwrap().unwrap();
        form(&mut app, Event::Submit);
        assert!(
            app.behavior.has_pending(),
            "missing action source rejects without losing the clicked slot"
        );
        let _ = app.update(Message::Escape);
        let current = app.scenario_context().unwrap();
        let _ = app.update(Message::ScenarioCanvas(CanvasEvent::Scrolled(
            current,
            ScrollArea::Page,
            iced::Vector::new(0., 200.),
        )));
        assert_eq!(
            app.behavior.scenario.recovery_snapshot().unwrap(),
            Some(raw.clone())
        );
        assert_eq!(app.document.bundle(), &original);
        assert!(!app.document.can_undo());
        let recovered = State::from_recovery(raw.clone()).unwrap();
        assert_eq!(
            recovered.pending_placement(f.owner),
            Some((slot, Some(f.sender)))
        );
        assert_eq!(recovered.recovery_snapshot().unwrap(), Some(raw));
        assert!(recovered.prepare_pending(&f.project).is_err());
        form(
            &mut app,
            Event::Target(named_choice(
                &f.project,
                represented(&f.project, f.sender).unwrap(),
            )),
        );
        form(&mut app, Event::Submit);
        assert!(!app.behavior.has_pending(), "{}", app.status);
        let _ = app.update(Message::Undo);
        assert_eq!(app.document.bundle(), &original);
    }
    #[test]
    fn direct_middle_pair_insertion_is_one_exact_source_and_model_undo() {
        let f = fixture();
        let mut state = State::default();
        let slot = Slot {
            parent: f.owner,
            before: Some(f.reply),
        };
        state
            .begin_message(
                &f.project,
                context(f.owner),
                slot,
                f.sender,
                f.receiver,
                MessageStyle::CallReply,
            )
            .unwrap();
        assert!(
            exchanges(&f.project, state.draft.as_ref().unwrap())
                .iter()
                .any(|choice| choice.id == f.exchange)
        );
        state
            .update(
                &f.project,
                Event::Exchange(named_choice(&f.project, f.exchange)),
            )
            .unwrap();
        assert_eq!(state.draft.as_ref().unwrap().sender, Some(f.sender));
        assert_eq!(state.draft.as_ref().unwrap().receiver, Some(f.receiver));
        let mut document =
            crate::document::Document::from_project(f.project.clone(), Default::default()).unwrap();
        let source = document.bundle().clone();
        document
            .execute(state.prepare_pending(&f.project).unwrap())
            .unwrap();
        let p = document.project();
        let steps = p.elements[&f.owner].steps().unwrap();
        assert_eq!(steps.len(), 4);
        assert_eq!((steps[0], steps[3]), (f.call, f.reply));
        assert!(
            matches!(p.elements[&steps[2]].shared(), Some(SharedBody::Occurrence { body: OccurrenceBody::Exchange {
            reply_to: Some(call), message_kind: MessageKind::Reply, exchange: Some(exchange), .. }, .. }) if *call == steps[1] && *exchange == f.exchange)
        );
        assert_eq!(p.relations, f.project.relations);
        assert_eq!(language::parse(&language::format(p)).unwrap(), *p);
        assert!(document.undo());
        assert_eq!(document.project(), &f.project);
        assert_eq!(document.bundle(), &source);
        assert!(!document.undo());
    }
    #[test]
    fn direct_reply_choices_validate_the_actual_slot_and_reorder_rejects_reverse_order() {
        let f = fixture();
        let p = execute_batch(&f.project, &[Command::Delete(f.reply)]).unwrap();
        let mut state = State::default();
        state
            .begin_message(
                &p,
                context(f.owner),
                Slot {
                    parent: f.owner,
                    before: Some(f.call),
                },
                f.receiver,
                f.sender,
                MessageStyle::Reply,
            )
            .unwrap();
        assert!(calls(&p, state.draft.as_ref().unwrap()).is_empty());
        state.update(&p, Event::AppendInstead).unwrap();
        assert!(
            calls(&p, state.draft.as_ref().unwrap())
                .iter()
                .any(|choice| choice.id == f.call)
        );
        state
            .update(&p, Event::Call(named_choice(&p, f.call)))
            .unwrap();
        let result = execute_batch(&p, &[state.prepare_pending(&p).unwrap()]).unwrap();
        let reply = *result.elements[&f.owner].steps().unwrap().last().unwrap();
        assert!(
            reorder(
                &result,
                f.owner,
                reply,
                Slot {
                    parent: f.owner,
                    before: Some(f.call)
                }
            )
            .unwrap_err()
            .contains("call")
        );
        assert_eq!(result.elements[&f.owner].steps().unwrap(), &[f.call, reply]);
    }
    #[test]
    fn direct_operand_pair_keeps_parent_sequence_and_cannot_reorder_across_operands() {
        let f = fixture();
        let mut state = State::default();
        state
            .update(&f.project, Event::Start(f.owner, Tool::Fragment))
            .unwrap();
        state
            .update(&f.project, Event::Expression("ready".into()))
            .unwrap();
        let p = execute_batch(&f.project, &[state.prepare_pending(&f.project).unwrap()]).unwrap();
        let fragment = *p.elements[&f.owner].steps().unwrap().last().unwrap();
        let branches: Vec<_> = p.children(fragment).map(|e| e.id).collect();
        let root_steps = p.elements[&f.owner].steps().unwrap().clone();
        let mut state = State::default();
        state
            .begin_message(
                &p,
                context(f.owner),
                Slot {
                    parent: branches[0],
                    before: None,
                },
                f.sender,
                f.receiver,
                MessageStyle::CallReply,
            )
            .unwrap();
        state
            .update(&p, Event::Exchange(named_choice(&p, f.exchange)))
            .unwrap();
        let result = execute_batch(&p, &[state.prepare_pending(&p).unwrap()]).unwrap();
        assert_eq!(result.elements[&f.owner].steps().unwrap(), &root_steps);
        let branch_steps = result.elements[&branches[0]].steps().unwrap();
        assert_eq!(branch_steps.len(), 2);
        assert!(
            reorder(
                &result,
                f.owner,
                branch_steps[0],
                Slot {
                    parent: branches[1],
                    before: None
                }
            )
            .is_err()
        );
    }
    #[test]
    fn direct_busy_save_keeps_details_current_and_camera_for_the_next_pointer_gesture() {
        let f = fixture();
        let mut app = App::with_project(f.project.clone());
        let _ = app.update(Message::Select(f.owner));
        let _ = app.update(Message::Page(crate::app::Page::Behavior));
        let context = app.scenario_context().unwrap();
        let _ = app.update(Message::ScenarioCanvas(CanvasEvent::Camera(
            context,
            app.camera_epoch,
            super::super::canvas_workspace::Event::Pan(iced::Vector::new(-25., -100.)),
        )));
        let context = app.scenario_context().unwrap();
        let original = app.document.snapshot();
        app.busy = true;
        let _ = app.update(Message::ScenarioCanvas(CanvasEvent::Scrolled(
            context,
            ScrollArea::Page,
            iced::Vector::new(0., 40.),
        )));
        assert!(app.busy);
        assert_eq!(
            app.behavior.scenario.details_offset,
            iced::Vector::new(0., 40.)
        );
        assert_ne!(
            app.scenario_context(),
            Some(context),
            "scroll invalidates the pre-save pointer context even while busy"
        );
        let mut stale = context;
        stale.document = Id::new_v4();
        let _ = app.update(Message::ScenarioCanvas(CanvasEvent::Scrolled(
            stale,
            ScrollArea::Page,
            iced::Vector::new(0., 900.),
        )));
        assert_eq!(
            app.behavior.scenario.details_offset,
            iced::Vector::new(0., 40.)
        );
        let root = std::path::PathBuf::from("scenario-details-save-fixture");
        let receipt = crate::app::FileSnapshot {
            document: context.document,
            revision: context.revision,
            snapshot: original.clone(),
            path: root.join(&original.bundle.entry),
            disk: Some(oa_core::source_files::DiskProject {
                root,
                bundle: original.bundle.clone(),
                expectations: BTreeMap::new(),
                reachable: original.bundle.files.keys().cloned().collect(),
                diagnostics: vec![],
            }),
        };
        let _ = app.update(Message::Saved(Ok(Some(receipt))));
        assert!(!app.busy);
        assert_eq!(app.project(), &original.decoded.project);
        assert!(!app.document.can_undo());
        let context = app.scenario_context().unwrap();
        let mut scene = Scene::sequence(app.project(), f.owner, f.call);
        scene.interaction = Some((context, CanvasTool::Message(MessageStyle::CallReply), true));
        assert_eq!(
            app.behavior.scenario.presentation.pan,
            iced::Vector::new(-25., -100.)
        );
        scene.camera_pan = app.behavior.scenario.presentation.pan;
        let slot = scene.slots.last().unwrap().slot;
        let bounds = Rectangle::new(Point::new(20., 250.), scene.size);
        let y = bounds.y + scene.slots.last().unwrap().y;
        let a = Point::new(bounds.x + scene.lanes[&f.sender], y) + scene.camera_pan;
        let b = Point::new(bounds.x + scene.lanes[&f.receiver], y) + scene.camera_pan;
        assert!(bounds.contains(a) && bounds.contains(b));
        let mut input = super::super::SequenceInput::default();
        let mut published = vec![];
        for event in [
            mouse::Event::CursorMoved { position: a },
            mouse::Event::ButtonPressed(mouse::Button::Left),
            mouse::Event::CursorMoved { position: b },
            mouse::Event::ButtonReleased(mouse::Button::Left),
        ] {
            if let Some(message) = canvas::Program::update(
                &scene,
                &mut input,
                &canvas::Event::Mouse(event),
                bounds,
                mouse::Cursor::Available(b),
            )
            .and_then(|action| action.into_inner().0)
            {
                published.push(message);
            }
        }
        assert_eq!(published.len(), 1);
        assert!(
            matches!(&published[0], Message::ScenarioCanvas(CanvasEvent::Begin { sender, receiver, slot: actual, .. }) if *sender == f.sender && *receiver == f.receiver && *actual == slot)
        );
        let _ = app.update(published.pop().unwrap());
        assert_eq!(
            app.behavior.scenario.draft.as_ref().unwrap().before,
            slot.before
        );
        assert_eq!(
            app.behavior.scenario.draft.as_ref().unwrap().sender,
            Some(f.sender)
        );
        assert_eq!(
            app.behavior.scenario.draft.as_ref().unwrap().receiver,
            Some(f.receiver)
        );
    }
    #[test]
    fn direct_reply_choices_cache_keeps_typing_fast_and_revalidates_changed_contexts() {
        let f = fixture();
        let mut p = execute_batch(&f.project, &[Command::Delete(f.reply)]).unwrap();
        let mut commands = vec![];
        for index in 1..100 {
            commands.push(Command::CreateElement(occurrence(
                &p,
                f.owner,
                &format!("Call {index}"),
                OccurrenceBody::Exchange {
                    operation: None,
                    exchange: Some(f.exchange),
                    sender: Some(f.sender),
                    receiver: Some(f.receiver),
                    message_kind: MessageKind::Call,
                    reply_to: None,
                    values: vec![],
                },
            )));
        }
        p = execute_batch(&p, &commands).unwrap();
        let mut state = State::default();
        let mut context = context(f.owner);
        state
            .begin_message(
                &p,
                context,
                Slot {
                    parent: f.owner,
                    before: None,
                },
                f.receiver,
                f.sender,
                MessageStyle::Reply,
            )
            .unwrap();
        let start = std::time::Instant::now();
        let expected: BTreeSet<_> = state
            .call_choices(&p, context, state.draft.as_ref().unwrap())
            .into_iter()
            .map(|c| c.id)
            .collect();
        assert_eq!(expected.len(), 100);
        eprintln!(
            "100 exact-slot earlier-call choices cold: {:?}",
            start.elapsed()
        );
        for event in [
            Event::Name("unfinished name".into()),
            Event::ChoiceSearch("Call".into()),
            Event::ChoicePage(2),
            Event::Value(
                crate::data_values::FieldPathKey {
                    path: vec![],
                    field: Id::new_v4(),
                },
                "unfinished expression".into(),
            ),
        ] {
            state.update(&p, event).unwrap();
            let start = std::time::Instant::now();
            assert_eq!(
                state
                    .call_choices(&p, context, state.draft.as_ref().unwrap())
                    .into_iter()
                    .map(|c| c.id)
                    .collect::<BTreeSet<_>>(),
                expected
            );
            eprintln!(
                "100 earlier-call choices after draft edit: {:?}",
                start.elapsed()
            );
        }
        state.draft.as_mut().unwrap().before = Some(f.call);
        assert!(
            state
                .call_choices(&p, context, state.draft.as_ref().unwrap())
                .is_empty(),
            "changed insertion invalidates cached reply order"
        );
        state.update(&p, Event::AppendInstead).unwrap();
        assert_eq!(
            state
                .call_choices(&p, context, state.draft.as_ref().unwrap())
                .len(),
            100
        );
        let deleted = *expected.iter().find(|id| **id != f.call).unwrap();
        p = execute_batch(&p, &[Command::Delete(deleted)]).unwrap();
        context.revision += 1;
        assert_eq!(
            state
                .call_choices(&p, context, state.draft.as_ref().unwrap())
                .len(),
            99
        );
        let deleted = *expected
            .iter()
            .find(|id| **id != f.call && **id != deleted)
            .unwrap();
        p = execute_batch(&p, &[Command::Delete(deleted)]).unwrap();
        context.document = Id::new_v4();
        assert_eq!(
            state
                .call_choices(&p, context, state.draft.as_ref().unwrap())
                .len(),
            98,
            "another document with the same IDs and revision still invalidates cached choices"
        );
    }
    #[test]
    fn direct_exchange_compatibility_browsing_preserves_final_slot_validation() {
        let f = fixture();
        let mut state = State::default();
        state
            .begin_message(
                &f.project,
                context(f.owner),
                Slot {
                    parent: f.owner,
                    before: Some(f.call),
                },
                f.sender,
                f.receiver,
                MessageStyle::Delete,
            )
            .unwrap();
        assert!(
            exchanges(&f.project, state.draft.as_ref().unwrap())
                .iter()
                .any(|c| c.id == f.exchange)
        );
        state
            .update(
                &f.project,
                Event::Exchange(named_choice(&f.project, f.exchange)),
            )
            .unwrap();
        assert!(
            state.prepare_pending(&f.project).is_err(),
            "deleting the callee before the existing call fails exact-slot lifecycle validation"
        );
        state.update(&f.project, Event::AppendInstead).unwrap();
        assert!(state.prepare_pending(&f.project).is_ok());
        state.draft.as_mut().unwrap().sender = Some(f.receiver);
        state.draft.as_mut().unwrap().receiver = Some(f.sender);
        assert!(
            !exchanges(&f.project, state.draft.as_ref().unwrap())
                .iter()
                .any(|c| c.id == f.exchange),
            "reversed represented endpoints are not offered"
        );
    }
    #[test]
    fn direct_five_hundred_exchange_choice_render_probe() {
        let mut f = fixture();
        let template = f.project.relations[&f.exchange].clone();
        for index in 1..500 {
            let id = f.project.relate(
                RelationKind::Interaction,
                &format!("Contract {index:03}"),
                template.source(),
                template.target(),
            );
            f.project.relations.get_mut(&id).unwrap().body = template.body.clone();
        }
        let mut state = State::default();
        state
            .begin_message(
                &f.project,
                context(f.owner),
                Slot {
                    parent: f.owner,
                    before: None,
                },
                f.sender,
                f.receiver,
                MessageStyle::CallReply,
            )
            .unwrap();
        let started = std::time::Instant::now();
        assert_eq!(
            exchanges(&f.project, state.draft.as_ref().unwrap()).len(),
            500
        );
        eprintln!("500 compatible exchange choices: {:?}", started.elapsed());
        state
            .update(&f.project, Event::Name("Draft name changed".into()))
            .unwrap();
        let started = std::time::Instant::now();
        assert_eq!(
            exchanges(&f.project, state.draft.as_ref().unwrap()).len(),
            500
        );
        eprintln!("500 choices after name keystroke: {:?}", started.elapsed());
    }
    #[test]
    fn direct_exchange_picker_is_bounded_and_browsing_keeps_pending_values() {
        let mut f = fixture();
        let template = f.project.relations[&f.exchange].clone();
        for index in 0..70 {
            let id = f.project.relate(
                RelationKind::Interaction,
                &format!("Other contract {index:02}"),
                template.source(),
                template.target(),
            );
            f.project.relations.get_mut(&id).unwrap().body = template.body.clone();
        }
        let mut state = State::default();
        state
            .begin_message(
                &f.project,
                context(f.owner),
                Slot {
                    parent: f.owner,
                    before: None,
                },
                f.sender,
                f.receiver,
                MessageStyle::CallReply,
            )
            .unwrap();
        state
            .update(
                &f.project,
                Event::Exchange(named_choice(&f.project, f.exchange)),
            )
            .unwrap();
        let key = crate::data_values::roots(
            &f.project,
            &f.project.relations[&f.exchange],
            &MessageKind::Call,
        )[0]
        .key
        .clone();
        state
            .update(&f.project, Event::Value(key.clone(), "pending(".into()))
            .unwrap();
        let choices = exchanges(&f.project, state.draft.as_ref().unwrap());
        assert_eq!(choices.len(), 71);
        let mut visited = BTreeSet::new();
        for page in 0..choices.len().div_ceil(VALUE_PAGE_SIZE) {
            state.update(&f.project, Event::ChoicePage(page)).unwrap();
            let d = state.draft.as_ref().unwrap();
            for choice in &choices[value_page(choices.len(), d.choice_page)] {
                visited.insert(choice.id);
            }
            let view = bounded_picker(choices.clone(), d, d.exchange, "Choose", Event::Exchange);
            let tree = iced::advanced::widget::Tree::new(view.as_widget());
            fn count(tree: &iced::advanced::widget::Tree) -> usize {
                1 + tree.children.iter().map(count).sum::<usize>()
            }
            assert!(count(&tree) < 20);
        }
        assert_eq!(visited.len(), 71);
        state
            .update(&f.project, Event::ChoiceSearch("Other contract 69".into()))
            .unwrap();
        assert_eq!(state.draft.as_ref().unwrap().choice_page, 0);
        assert_eq!(state.draft.as_ref().unwrap().values[&key], "pending(");
        assert_eq!(state.draft.as_ref().unwrap().exchange, Some(f.exchange));
    }
    #[test]
    fn direct_form_keeps_the_same_canvas_in_the_widget_tree() {
        let f = fixture();
        let mut app = App::with_project(f.project.clone());
        let _ = app.update(Message::Select(f.owner));
        let _ = app.update(Message::Page(crate::app::Page::Behavior));
        let canvas: Element<'_, Message> =
            canvas::Canvas::new(Scene::sequence(app.project(), f.owner, f.call)).into();
        let tag = iced::advanced::widget::Tree::new(canvas.as_widget()).tag;
        fn count(
            tree: &iced::advanced::widget::Tree,
            tag: iced::advanced::widget::tree::Tag,
        ) -> usize {
            usize::from(tree.tag == tag)
                + tree
                    .children
                    .iter()
                    .map(|child| count(child, tag))
                    .sum::<usize>()
        }
        for pending in [false, true] {
            if pending {
                let context = app.scenario_context().unwrap();
                let _ = app.update(Message::ScenarioCanvas(CanvasEvent::Begin {
                    context,
                    slot: Slot {
                        parent: f.owner,
                        before: None,
                    },
                    sender: f.sender,
                    receiver: f.receiver,
                    style: MessageStyle::CallReply,
                }));
                assert!(app.behavior.has_pending());
            }
            let view = view(&app, f.owner, Column::new());
            let tree = iced::advanced::widget::Tree::new(view.as_widget());
            assert_eq!(count(&tree, tag), 1);
        }
    }
}

#[cfg(test)]
mod tests {
    use super::*;
    #[test]
    fn reverse_communication_canvas_choices_and_correlated_reply_share_core_direction() {
        let mut p = Project::empty();
        let a = p
            .add_element(Kind::Entity, Layer::Oa, "Crew", None)
            .unwrap();
        let b = p
            .add_element(Kind::Actor, Layer::Oa, "Station", None)
            .unwrap();
        let exchange = p.relate(RelationKind::CommunicationMean, "Radio", a, b);
        let owner = scenario(&mut p, "Participant dialogue");
        if let Some(SharedBody::Scenario { viewpoint, .. }) =
            p.elements.get_mut(&owner).unwrap().shared_mut()
        {
            *viewpoint = ScenarioViewpoint::ParticipantInteraction;
        }
        let la = lifeline(&mut p, owner, a);
        let lb = lifeline(&mut p, owner, b);
        let mut state = State::default();
        state
            .begin_message(
                &p,
                direct_tests::context(owner),
                Slot {
                    parent: owner,
                    before: None,
                },
                lb,
                la,
                MessageStyle::CallReply,
            )
            .unwrap();
        assert!(
            exchanges(&p, state.draft.as_ref().unwrap())
                .iter()
                .any(|c| c.id == exchange)
        );
        state
            .update(&p, Event::Exchange(named_choice(&p, exchange)))
            .unwrap();
        let mut document =
            crate::document::Document::from_project(p.clone(), Default::default()).unwrap();
        let original = document.bundle().clone();
        document
            .execute(state.prepare_pending(&p).unwrap())
            .unwrap();
        let accepted = document.project();
        let steps = accepted.elements[&owner].steps().unwrap();
        assert_eq!(steps.len(), 2);
        for (id, expected) in [(steps[0], (b, a)), (steps[1], (a, b))] {
            let Some(SharedBody::Occurrence { body, .. }) = accepted.elements[&id].shared() else {
                unreachable!()
            };
            assert_eq!(
                validation::message_endpoints(accepted, body),
                Some(expected)
            );
        }
        let after = document.bundle().clone();
        assert!(document.undo());
        assert_eq!(document.bundle(), &original);
        assert!(document.redo());
        assert_eq!(document.bundle(), &after);
        let mut directed = p.clone();
        if let RelationBody::CommunicationMean { oriented, .. } =
            &mut directed.relations.get_mut(&exchange).unwrap().body
        {
            *oriented = true;
        }
        assert!(
            !exchanges(&directed, state.draft.as_ref().unwrap())
                .iter()
                .any(|c| c.id == exchange)
        );
    }
    fn scenario(p: &mut Project, name: &str) -> Id {
        let mut e = p
            .make_element(Kind::Scenario, Layer::Oa, name, None)
            .unwrap();
        let id = e.id;
        if let Some(SharedBody::Scenario { viewpoint, .. }) = e.shared_mut() {
            *viewpoint = ScenarioViewpoint::OperationalActivity;
        }
        *p = execute_batch(p, &[Command::CreateElement(e)]).unwrap();
        id
    }
    fn lifeline(p: &mut Project, owner: Id, represented: Id) -> Id {
        let mut state = State::default();
        state
            .update(p, Event::Start(owner, Tool::Lifeline))
            .unwrap();
        state
            .update(p, Event::Target(named_choice(p, represented)))
            .unwrap();
        let command = state.update(p, Event::Submit).unwrap().unwrap();
        *p = execute_batch(p, &[command]).unwrap();
        p.children(owner).find(|e|matches!(e.shared(),Some(SharedBody::Lifeline {represented:Some(id)}) if *id==represented)).unwrap().id
    }
    fn fixture() -> (Project, Id, Id, Id, Id) {
        let mut p = Project::demo();
        let relation = p
            .relations
            .values()
            .find(|r| r.kind() == RelationKind::Interaction)
            .unwrap();
        let (exchange, a, b) = (relation.id, relation.source(), relation.target());
        let owner = scenario(&mut p, "Scenario authoring test");
        let sender = lifeline(&mut p, owner, a);
        let receiver = lifeline(&mut p, owner, b);
        (p, owner, exchange, sender, receiver)
    }
    fn message(p: &Project, owner: Id, exchange: Id, sender: Id, receiver: Id) -> State {
        let mut state = State::default();
        state.update(p, Event::Start(owner, Tool::Message)).unwrap();
        state
            .update(p, Event::Exchange(named_choice(p, exchange)))
            .unwrap();
        state
            .update(p, Event::Sender(named_choice(p, sender)))
            .unwrap();
        state
            .update(p, Event::Receiver(named_choice(p, receiver)))
            .unwrap();
        state
    }
    #[test]
    fn graphical_call_reply_is_atomic_correlated_and_source_equivalent() {
        let (p, owner, exchange, sender, receiver) = fixture();
        let mut state = message(&p, owner, exchange, sender, receiver);
        let command = state.update(&p, Event::Submit).unwrap().unwrap();
        let mut session = Session::new(p.clone());
        session.execute(command).unwrap();
        let result = session.project();
        let steps = result.elements[&owner].steps().unwrap();
        assert_eq!(steps.len(), 2);
        assert!(
            matches!(result.elements[&steps[1]].shared(),Some(SharedBody::Occurrence {body:OccurrenceBody::Exchange {message_kind:MessageKind::Reply,reply_to:Some(call),sender:Some(from),receiver:Some(to),..},..}) if *call==steps[0]&&*from==receiver&&*to==sender)
        );
        assert_eq!(language::parse(&language::format(result)).unwrap(), *result);
        let scene = Scene::sequence(result, owner, owner);
        assert!(
            scene
                .lines
                .iter()
                .any(|l| l.id == steps[1] && l.dashed && l.label.contains("reply"))
        );
        assert_eq!(
            scene.activations,
            vec![super::super::scenario_activation::Segment {
                call: steps[0],
                receiver,
                scope: owner,
                rect: Rectangle::new(
                    Point::new(scene.lanes[&receiver] - 6., 148.),
                    Size::new(12., 92.),
                ),
                column: 0,
                finish: super::super::scenario_activation::Finish::Reply(steps[1]),
            }]
        );
        let call_line = scene.lines.iter().find(|line| line.id == steps[0]).unwrap();
        let reply_line = scene.lines.iter().find(|line| line.id == steps[1]).unwrap();
        assert_eq!(call_line.points.last().unwrap().y, 148.);
        assert_eq!(reply_line.points.first().unwrap().y, 240.);
        let mut reply = State::default();
        reply
            .update(result, Event::Start(owner, Tool::Message))
            .unwrap();
        reply
            .update(result, Event::Style(MessageStyle::Reply))
            .unwrap();
        assert!(calls(result, reply.draft.as_ref().unwrap()).is_empty());
        session.undo();
        assert_eq!(session.project(), &p);
    }
    #[test]
    fn scenario_reuse_requires_explicit_compatible_bindings() {
        let (mut p, owner, _, sender, receiver) = fixture();
        let a = represented(&p, sender).unwrap();
        let b = represented(&p, receiver).unwrap();
        let target = scenario(&mut p, "Reusable scenario");
        let remote_a = lifeline(&mut p, target, a);
        let remote_b = lifeline(&mut p, target, b);
        let mut state = State::default();
        state.update(&p, Event::Start(owner, Tool::Reuse)).unwrap();
        state
            .update(&p, Event::Target(named_choice(&p, target)))
            .unwrap();
        assert!(state.update(&p, Event::Submit).is_err());
        assert!(state.draft.is_some());
        state
            .update(&p, Event::Binding(remote_a, named_choice(&p, receiver)))
            .unwrap();
        state
            .update(&p, Event::Binding(remote_b, named_choice(&p, sender)))
            .unwrap();
        assert!(state.update(&p, Event::Submit).is_err());
        assert!(state.draft.is_some());
        state
            .update(&p, Event::Binding(remote_a, named_choice(&p, sender)))
            .unwrap();
        state
            .update(&p, Event::Binding(remote_b, named_choice(&p, receiver)))
            .unwrap();
        let result =
            execute_batch(&p, &[state.update(&p, Event::Submit).unwrap().unwrap()]).unwrap();
        let use_id = result.elements[&owner].steps().unwrap()[0];
        assert!(
            matches!(result.elements[&use_id].shared(),Some(SharedBody::Occurrence {body:OccurrenceBody::ScenarioUse {scenario:Some(id),bindings},..}) if *id==target&&bindings.len()==2)
        );
        assert_eq!(result.children(target).count(), 2);
        assert_eq!(language::parse(&language::format(&result)).unwrap(), result);
    }
    #[test]
    fn fragment_operands_accept_paired_messages_through_normal_destination_picker() {
        let (mut p, owner, exchange, sender, receiver) = fixture();
        let mut state = State::default();
        state
            .update(&p, Event::Start(owner, Tool::Fragment))
            .unwrap();
        state
            .update(&p, Event::Name("Choose outcome".into()))
            .unwrap();
        state
            .update(&p, Event::Expression("accepted".into()))
            .unwrap();
        p = execute_batch(&p, &[state.update(&p, Event::Submit).unwrap().unwrap()]).unwrap();
        let fragment = p.elements[&owner].steps().unwrap()[0];
        let branches = p.children(fragment).map(|e| e.id).collect::<Vec<_>>();
        assert_eq!(branches.len(), 2);
        let mut state = message(&p, owner, exchange, sender, receiver);
        state
            .update(&p, Event::Parent(named_choice(&p, branches[0])))
            .unwrap();
        p = execute_batch(&p, &[state.update(&p, Event::Submit).unwrap().unwrap()]).unwrap();
        assert_eq!(p.elements[&branches[0]].steps().unwrap().len(), 2);
        assert_eq!(
            Scene::sequence(&p, owner, owner)
                .lines
                .iter()
                .filter(|l| !l.label.is_empty())
                .count(),
            2
        );
    }
    #[test]
    fn invalid_lifecycle_edit_keeps_draft_and_timer_has_no_global_exchange() {
        let (mut p, owner, exchange, sender, receiver) = fixture();
        let mut state = message(&p, owner, exchange, sender, receiver);
        p = execute_batch(&p, &[state.update(&p, Event::Submit).unwrap().unwrap()]).unwrap();
        let mut state = message(&p, owner, exchange, sender, receiver);
        state.draft.as_mut().unwrap().style = MessageStyle::Create;
        assert!(state.update(&p, Event::Submit).is_err());
        assert!(state.draft.is_some());
        state.update(&p, Event::Style(MessageStyle::Timer)).unwrap();
        state
            .update(&p, Event::Sender(named_choice(&p, sender)))
            .unwrap();
        state.update(&p, Event::Expression("30 s".into())).unwrap();
        p = execute_batch(&p, &[state.update(&p, Event::Submit).unwrap().unwrap()]).unwrap();
        let timer = *p.elements[&owner].steps().unwrap().last().unwrap();
        assert!(
            matches!(p.elements[&timer].shared(),Some(SharedBody::Occurrence {body:OccurrenceBody::Exchange {exchange:None,receiver:None,message_kind:MessageKind::Timer {expression},..},..}) if expression=="30 s")
        );
        assert!(
            Scene::sequence(&p, owner, owner)
                .lines
                .iter()
                .any(|l| l.id == timer && l.label.contains("30 s"))
        );
    }
    #[test]
    fn tagged_scenario_commit_is_not_redirected_by_other_editor_events() {
        let (p, owner, exchange, sender, receiver) = fixture();
        let mut state = crate::behavior::State::default();
        for e in [
            Event::Start(owner, Tool::Message),
            Event::Exchange(named_choice(&p, exchange)),
            Event::Sender(named_choice(&p, sender)),
            Event::Receiver(named_choice(&p, receiver)),
        ] {
            state
                .update(&p, crate::behavior::Event::Scenario(e))
                .unwrap();
        }
        state
            .update(
                &p,
                crate::behavior::Event::Topology(super::super::topology::Event::Cancel),
            )
            .unwrap();
        let submit = crate::behavior::Event::Scenario(Event::Submit);
        assert!(submit.is_submit());
        let command = state.update(&p, submit).unwrap().unwrap();
        let result = execute_batch(&p, &[command]).unwrap();
        assert_eq!(result.elements[&owner].steps().unwrap().len(), 2);
    }
    #[test]
    fn lifeline_picker_uses_core_viewpoint_contract() {
        let (p, owner, ..) = fixture();
        let mut state = State::default();
        state
            .update(&p, Event::Start(owner, Tool::Lifeline))
            .unwrap();
        let choices = sources(&p, state.draft.as_ref().unwrap());
        assert!(!choices.is_empty());
        assert!(
            choices
                .iter()
                .all(|c| p.elements[&c.id].kind() == Kind::Activity)
        );
    }
}

#[cfg(test)]
mod data_contract_tests {
    use super::*;

    #[test]
    fn scenario_form_commits_two_reused_record_values_and_correlated_reply_atomically() {
        let mut f = crate::data_values::tests::payload();
        if let Some(SharedBody::DataField { direction, .. }) = f
            .project
            .elements
            .get_mut(&f.destination)
            .unwrap()
            .shared_mut()
        {
            *direction = ParameterDirection::InOut;
        }
        let source = f.project.relations[&f.exchange].source();
        let target = f.project.relations[&f.exchange].target();
        let mut lines = vec![];
        for (name, represented) in [("Requester", source), ("Performer", target)] {
            let id = f
                .project
                .add_element(Kind::Lifeline, Layer::Oa, name, Some(f.scenario))
                .unwrap();
            *f.project
                .elements
                .get_mut(&id)
                .unwrap()
                .shared_mut()
                .unwrap() = SharedBody::Lifeline {
                represented: Some(represented),
            };
            lines.push(id);
        }
        let mut state = State::default();
        for event in [
            Event::Start(f.scenario, Tool::Message),
            Event::Name("Move coordinates".into()),
            Event::Exchange(named_choice(&f.project, f.exchange)),
            Event::Sender(named_choice(&f.project, lines[0])),
            Event::Receiver(named_choice(&f.project, lines[1])),
        ] {
            state.update(&f.project, event).unwrap();
        }
        assert!(
            exchanges(&f.project, state.draft.as_ref().unwrap())
                .iter()
                .any(|c| c.id == f.exchange)
        );
        for (parameter, expression) in [(f.origin, "45.0"), (f.destination, "46.0")] {
            state
                .update(
                    &f.project,
                    Event::Value(
                        crate::data_values::FieldPathKey {
                            path: vec![parameter],
                            field: f.leaf,
                        },
                        expression.into(),
                    ),
                )
                .unwrap();
        }
        let before = state.draft.as_ref().unwrap().values.clone();
        state
            .update(&f.project, Event::Style(MessageStyle::Call))
            .unwrap();
        state
            .update(
                &f.project,
                Event::Exchange(named_choice(&f.project, f.exchange)),
            )
            .unwrap();
        assert_eq!(state.draft.as_ref().unwrap().values, before);
        assert_eq!(state.draft.as_ref().unwrap().sender, Some(lines[0]));
        assert_eq!(state.draft.as_ref().unwrap().receiver, Some(lines[1]));
        state
            .update(&f.project, Event::Style(MessageStyle::CallReply))
            .unwrap();
        assert_eq!(state.draft.as_ref().unwrap().values, before);
        let command = state.prepare_pending(&f.project).unwrap();
        let mut document =
            crate::document::Document::from_project(f.project.clone(), Default::default()).unwrap();
        document.execute(command).unwrap();
        let messages = document
            .project()
            .children(f.scenario)
            .filter_map(|e| match e.shared()? {
                SharedBody::Occurrence {
                    body:
                        OccurrenceBody::Exchange {
                            message_kind,
                            values,
                            ..
                        },
                    ..
                } => Some((message_kind, values)),
                _ => None,
            })
            .collect::<Vec<_>>();
        let call = messages
            .iter()
            .find(|(kind, _)| **kind == MessageKind::Call)
            .unwrap()
            .1;
        assert_eq!(call.len(), 2);
        assert_eq!(
            call.iter().map(|v| v.field).collect::<BTreeSet<_>>(),
            BTreeSet::from([f.leaf])
        );
        assert_eq!(
            call.iter().map(|v| v.path.clone()).collect::<BTreeSet<_>>(),
            BTreeSet::from([vec![f.origin], vec![f.destination]])
        );
        assert!(
            messages
                .iter()
                .find(|(kind, _)| **kind == MessageKind::Reply)
                .unwrap()
                .1
                .is_empty()
        );
        assert!(document.undo());
        assert_eq!(document.project(), &f.project);
        assert!(!document.undo());
    }
    #[test]
    fn recursive_value_focus_exposes_authored_leaf_and_phase_changes_retain_surviving_keys() {
        let (f, next) = crate::data_values::tests::recursive_payload();
        let mut state = State::default();
        state
            .update(&f.project, Event::Start(f.scenario, Tool::Message))
            .unwrap();
        state
            .update(
                &f.project,
                Event::Exchange(named_choice(&f.project, f.exchange)),
            )
            .unwrap();
        let key = crate::data_values::FieldPathKey {
            path: vec![f.origin, next],
            field: f.leaf,
        };
        state
            .update(
                &f.project,
                Event::ValueBrowse(crate::data_values::parent(&key)),
            )
            .unwrap();
        state
            .update(&f.project, Event::ValueFocus(key.clone()))
            .unwrap();
        assert!(
            state
                .draft
                .as_ref()
                .unwrap()
                .browsed_values(&f.project, &f.project.relations[&f.exchange])
                .unwrap()
                .iter()
                .any(|c| c.key == key)
        );
        state
            .update(
                &f.project,
                Event::Value(key.clone(), "recursive expression".into()),
            )
            .unwrap();
        state
            .update(&f.project, Event::Style(MessageStyle::Call))
            .unwrap();
        assert_eq!(
            state.draft.as_ref().unwrap().values[&key],
            "recursive expression"
        );
        state
            .update(&f.project, Event::Style(MessageStyle::Asynchronous))
            .unwrap();
        assert_eq!(
            state.draft.as_ref().unwrap().values[&key],
            "recursive expression"
        );
        state
            .update(&f.project, Event::Style(MessageStyle::Reply))
            .unwrap();
        assert!(
            state.draft.as_ref().unwrap().values.is_empty(),
            "In parameters do not become reply values"
        );
        let out = crate::data_values::FieldPathKey {
            path: vec![f.destination],
            field: f.leaf,
        };
        state
            .update(&f.project, Event::Value(out.clone(), "reply value".into()))
            .unwrap();
        state
            .update(&f.project, Event::Style(MessageStyle::Asynchronous))
            .unwrap();
        assert_eq!(state.draft.as_ref().unwrap().values[&out], "reply value");
    }

    fn panel_counts(p: &Project, d: &Draft, exchange: Id) -> (usize, usize) {
        let input: Element<'_, Message> = text_input("", "").into();
        let input_tag = iced::advanced::widget::Tree::new(input.as_widget()).tag;
        let panel = value_panel(p, d, &p.relations[&exchange]);
        let tree = iced::advanced::widget::Tree::new(panel.as_widget());
        fn count(
            tree: &iced::advanced::widget::Tree,
            tag: iced::advanced::widget::tree::Tag,
        ) -> (usize, usize) {
            tree.children.iter().fold(
                (1, usize::from(tree.tag == tag)),
                |(nodes, inputs), child| {
                    let (child_nodes, child_inputs) = count(child, tag);
                    (nodes + child_nodes, inputs + child_inputs)
                },
            )
        }
        count(&tree, input_tag)
    }

    #[test]
    fn large_payload_has_one_editor_with_reachable_field_and_authored_pages() {
        let f = crate::data_values::tests::wide_payload();
        let p = &f.project;
        let exchange = &p.relations[&f.exchange];
        let mut state = State::default();
        state
            .update(p, Event::Start(f.scenario, Tool::Message))
            .unwrap();
        state
            .update(p, Event::Exchange(named_choice(p, f.exchange)))
            .unwrap();
        let roots = crate::data_values::roots(p, exchange, &MessageKind::Call);
        assert_eq!(roots.len(), 96);
        assert_eq!(
            panel_counts(p, state.draft.as_ref().unwrap(), f.exchange).1,
            0
        );
        let mut visited = BTreeSet::new();
        for page in 0..roots.len().div_ceil(VALUE_PAGE_SIZE) {
            state
                .update(p, Event::ValuePage(ValueSection::Fields, page))
                .unwrap();
            let d = state.draft.as_ref().unwrap();
            let choices = d.browsed_values(p, exchange).unwrap();
            let visible = choices[value_page(choices.len(), d.value_browse_page)].to_vec();
            assert!(visible.len() <= VALUE_PAGE_SIZE);
            for choice in visible {
                visited.insert(choice.key.clone());
                state
                    .update(p, Event::ValueFocus(choice.key.clone()))
                    .unwrap();
                state
                    .update(p, Event::Value(choice.key, format!("draft {page}")))
                    .unwrap();
            }
            let (nodes, inputs) = panel_counts(p, state.draft.as_ref().unwrap(), f.exchange);
            assert_eq!(
                inputs, 1,
                "one input for over twelve thousand carried paths"
            );
            assert!(nodes < 200, "{nodes} widgets for the bounded value panel");
        }
        assert_eq!(
            visited,
            roots.iter().map(|choice| choice.key.clone()).collect()
        );

        state
            .update(p, Event::ValueBrowse(Some(roots[0].key.clone())))
            .unwrap();
        assert_eq!(state.draft.as_ref().unwrap().value_browse_page, 0);
        let children = state
            .draft
            .as_ref()
            .unwrap()
            .browsed_values(p, exchange)
            .unwrap();
        assert_eq!(children.len(), 128);
        let mut visited_children = BTreeSet::new();
        for page in 0..children.len().div_ceil(VALUE_PAGE_SIZE) {
            state
                .update(p, Event::ValuePage(ValueSection::Fields, page))
                .unwrap();
            let d = state.draft.as_ref().unwrap();
            let choices = d.browsed_values(p, exchange).unwrap();
            for choice in &choices[value_page(choices.len(), d.value_browse_page)] {
                assert_eq!(choice.key.path, [roots[0].key.field]);
                visited_children.insert(choice.key.clone());
            }
        }
        assert_eq!(
            visited_children,
            children.iter().map(|choice| choice.key.clone()).collect()
        );

        let nested = children[0].key.clone();
        state.update(p, Event::ValueFocus(nested.clone())).unwrap();
        state
            .update(p, Event::Value(nested.clone(), "unfinished(\"".into()))
            .unwrap();
        let before = state.draft.as_ref().unwrap().values.clone();
        let before_browse = state.draft.as_ref().unwrap().value_browse.clone();
        let before_page = state.draft.as_ref().unwrap().value_browse_page;
        for event in [
            Event::Style(MessageStyle::Call),
            Event::Exchange(named_choice(p, f.exchange)),
            Event::Style(MessageStyle::CallReply),
        ] {
            state.update(p, event).unwrap();
        }
        let d = state.draft.as_ref().unwrap();
        assert_eq!(d.values, before);
        assert_eq!(d.value_browse, before_browse);
        assert_eq!(d.value_browse_page, before_page);
        assert_eq!(d.value_focus, Some(nested));

        let mut authored = BTreeSet::new();
        for page in 0..before.len().div_ceil(VALUE_PAGE_SIZE) {
            state
                .update(p, Event::ValuePage(ValueSection::Authored, page))
                .unwrap();
            let d = state.draft.as_ref().unwrap();
            let values = d.authored_values();
            for (key, _) in &values[value_page(values.len(), d.value_authored_page)] {
                authored.insert((*key).clone());
            }
            let (nodes, inputs) = panel_counts(p, d, f.exchange);
            assert_eq!(inputs, 1);
            assert!(nodes < 200, "{nodes} widget nodes");
        }
        assert_eq!(authored, before.keys().cloned().collect());
        state.update(p, Event::ValueBrowse(None)).unwrap();
        state
            .update(p, Event::ValuePage(ValueSection::Fields, usize::MAX))
            .unwrap();
        let d = state.draft.as_ref().unwrap();
        assert_eq!(
            d.values, before,
            "browsing and page clamping never remove drafts"
        );
        let OccurrenceBody::Exchange { values, .. } = d.message_body() else {
            panic!()
        };
        assert_eq!(
            values.len(),
            before.len(),
            "commit includes every authored page"
        );
        assert_eq!(panel_counts(p, d, f.exchange).1, 1);
    }

    #[test]
    fn recursive_browsing_up_and_root_keep_values_and_report_the_depth_limit() {
        let (f, next) = crate::data_values::tests::recursive_payload();
        let p = &f.project;
        let exchange = &p.relations[&f.exchange];
        let mut state = State::default();
        state
            .update(p, Event::Start(f.scenario, Tool::Message))
            .unwrap();
        state
            .update(p, Event::Exchange(named_choice(p, f.exchange)))
            .unwrap();
        let root = crate::data_values::FieldPathKey {
            path: vec![],
            field: f.origin,
        };
        state.update(p, Event::ValueFocus(root.clone())).unwrap();
        state
            .update(p, Event::ValueBrowse(Some(root.clone())))
            .unwrap();
        let inner = state
            .draft
            .as_ref()
            .unwrap()
            .browsed_values(p, exchange)
            .unwrap()
            .into_iter()
            .find(|choice| choice.key.field == next)
            .unwrap()
            .key;
        state.update(p, Event::ValueFocus(inner.clone())).unwrap();
        state
            .update(p, Event::ValueBrowse(Some(inner.clone())))
            .unwrap();
        let leaf = state
            .draft
            .as_ref()
            .unwrap()
            .browsed_values(p, exchange)
            .unwrap()
            .into_iter()
            .find(|choice| choice.key.field == f.leaf)
            .unwrap()
            .key;
        assert_eq!(leaf.path, [f.origin, next]);
        state.update(p, Event::ValueFocus(leaf.clone())).unwrap();
        state
            .update(p, Event::Value(leaf.clone(), "keep this draft".into()))
            .unwrap();
        state
            .update(p, Event::ValueBrowse(crate::data_values::parent(&inner)))
            .unwrap();
        assert_eq!(state.draft.as_ref().unwrap().value_browse, Some(root));
        state.update(p, Event::ValueBrowse(None)).unwrap();
        assert_eq!(
            state.draft.as_ref().unwrap().values[&leaf],
            "keep this draft"
        );
        assert_eq!(
            panel_counts(p, state.draft.as_ref().unwrap(), f.exchange).1,
            1
        );
        let deepest = crate::data_values::FieldPathKey {
            path: std::iter::once(f.origin)
                .chain(std::iter::repeat_n(next, data::MAX_VALUE_PATH_DEPTH - 1))
                .collect(),
            field: next,
        };
        state.update(p, Event::ValueBrowse(Some(deepest))).unwrap();
        assert!(
            state
                .draft
                .as_ref()
                .unwrap()
                .browsed_values(p, exchange)
                .unwrap_err()
                .contains("128")
        );
        assert_eq!(
            panel_counts(p, state.draft.as_ref().unwrap(), f.exchange).1,
            1
        );
        assert_eq!(
            state.draft.as_ref().unwrap().values[&leaf],
            "keep this draft"
        );
        state
            .update(p, Event::Value(leaf.clone(), String::new()))
            .unwrap();
        let d = state.draft.as_ref().unwrap();
        assert!(d.authored_values().is_empty());
        assert_eq!(d.values[&leaf], "", "empty input remains an editable draft");
    }

    #[test]
    fn reply_call_picker_previews_the_same_value_reset_as_selecting_another_exchange() {
        let mut f = crate::data_values::tests::payload();
        let p = &mut f.project;
        let source = p.relations[&f.exchange].source();
        let target = p.relations[&f.exchange].target();
        let mut lifelines = vec![];
        for (name, represented) in [("Caller", source), ("Callee", target)] {
            let id = p
                .add_element(Kind::Lifeline, Layer::Oa, name, Some(f.scenario))
                .unwrap();
            *p.elements.get_mut(&id).unwrap().shared_mut().unwrap() = SharedBody::Lifeline {
                represented: Some(represented),
            };
            lifelines.push(id);
        }
        let other_item = p
            .add_element(Kind::ExchangeItem, Layer::Oa, "Other operation", None)
            .unwrap();
        *p.elements
            .get_mut(&other_item)
            .unwrap()
            .shared_mut()
            .unwrap() = p.elements[&f.item].shared().unwrap().clone();
        let other_field = p
            .add_element(Kind::DataField, Layer::Oa, "Result", Some(other_item))
            .unwrap();
        *p.elements
            .get_mut(&other_field)
            .unwrap()
            .shared_mut()
            .unwrap() = SharedBody::DataField {
            type_ref: TypeRef::Real,
            direction: ParameterDirection::Out,
            minimum: 1,
            maximum: Some(1),
            unit: String::new(),
            storage: FieldStorage::Value,
            default: None,
        };
        let other_exchange = p.relate(RelationKind::Interaction, "Other exchange", source, target);
        p.relations.get_mut(&other_exchange).unwrap().body = RelationBody::Interaction {
            source,
            target,
            items: vec![other_item],
        };
        let mut call_ids = vec![];
        for (name, exchange) in [("First call", f.exchange), ("Other call", other_exchange)] {
            let call = occurrence(
                p,
                f.scenario,
                name,
                OccurrenceBody::Exchange {
                    operation: None,
                    exchange: Some(exchange),
                    sender: Some(lifelines[0]),
                    receiver: Some(lifelines[1]),
                    message_kind: MessageKind::Call,
                    reply_to: None,
                    values: vec![],
                },
            );
            call_ids.push(call.id);
            *p = execute_batch(p, &[Command::CreateElement(call)]).unwrap();
        }
        let mut state = State::default();
        state
            .update(p, Event::Start(f.scenario, Tool::Message))
            .unwrap();
        state.update(p, Event::Style(MessageStyle::Reply)).unwrap();
        state
            .update(p, Event::Call(named_choice(p, call_ids[0])))
            .unwrap();
        let key = crate::data_values::FieldPathKey {
            path: vec![f.destination],
            field: f.leaf,
        };
        state.update(p, Event::ValueFocus(key.clone())).unwrap();
        state
            .update(p, Event::Value(key.clone(), "reply expression".into()))
            .unwrap();
        state
            .update(p, Event::ValueBrowse(crate::data_values::parent(&key)))
            .unwrap();
        let offered = calls(p, state.draft.as_ref().unwrap());
        assert!(
            offered.iter().any(|choice| choice.id == call_ids[1]),
            "a different exchange remains selectable after entering a value"
        );
        assert_eq!(
            state.draft.as_ref().unwrap().values[&key],
            "reply expression",
            "preview is read-only"
        );
        state
            .update(p, Event::Call(named_choice(p, call_ids[0])))
            .unwrap();
        assert_eq!(
            state.draft.as_ref().unwrap().values[&key],
            "reply expression"
        );
        state
            .update(p, Event::Call(named_choice(p, call_ids[1])))
            .unwrap();
        let d = state.draft.as_ref().unwrap();
        assert!(d.values.is_empty());
        assert!(d.value_focus.is_none());
        assert!(d.value_browse.is_none());
        assert_eq!(d.exchange, Some(other_exchange));
        assert!(state.prepare_pending(p).is_ok());
    }
}