supercode-harness 0.4.2

//! Inbound Agent Client Protocol adapter for the SDK-owned Supercode runtime.
//!
//! [`crate::runtime::AcpRuntimeBackend`] is the outbound half: it makes an ACP
//! agent look like a protocol-neutral SDK [`crate::RuntimeConnection`].  This
//! module is the deliberately symmetric inbound half: it makes one canonical
//! [`crate::server::RpcEngine`] look like an ACP agent.  The ACP adapter owns no
//! model loop, transcript, scheduler, or persistence state; it only translates
//! wire messages and subscribes to the runtime's canonical event stream.

use std::collections::{HashSet, VecDeque};
use std::sync::atomic::{AtomicBool, Ordering};
use std::sync::{Arc, Mutex};

use serde_json::{json, Value};
use tokio::io::{AsyncBufRead, AsyncBufReadExt, AsyncWrite, AsyncWriteExt};
use tokio::sync::{broadcast, mpsc};

use crate::server::{RuntimeSubmitError, SERVER_MAX_LINE_BYTES};
use crate::{
    ChatMessage, FrontendApprovalDecision, FrontendEvent, FrontendRequest, FrontendRequestKind,
    FrontendResponse, FrontendRuntimeError, Role, SdkRuntime, FRONTEND_REPLAY_CAPACITY,
};

const ACP_APPROVAL_REQUEST_ID_PREFIX: &str = "supercode-approval-";

/// ACP protocol version implemented by this adapter.
pub const ACP_PROTOCOL_VERSION: u64 = 1;

/// Versioned stock-client compatibility behavior layered over standard ACP.
///
/// The default remains donor-neutral ACP. A pinned profile may answer only
/// the client-local extension calls and ordering quirks proven by its stock
/// traffic corpus; it never changes the SDK runtime's model, tools, provider,
/// persistence, or session identity.
#[derive(Debug, Clone, Copy, Default, PartialEq, Eq)]
pub enum AcpCompatibilityProfile {
    /// Standard ACP with Supercode's typed frontend extensions.
    #[default]
    Standard,
    /// Stock Goose text UI at source commit `acd3c135cff7...`.
    GooseAcd3c135,
}

/// Compatibility name for the HTTP implementation of the canonical SDK
/// runtime contract. ACP no longer owns a separate HTTP client.
#[cfg(feature = "adapter-api")]
pub type HttpAcpRuntime = crate::HttpFrontendRuntime;

struct AcpRuntimeBridge {
    runtime: Arc<dyn SdkRuntime>,
    session_id: String,
    model: String,
    history: Vec<ChatMessage>,
    history_cursor: u64,
    initial_replay_cursor: u64,
    events: broadcast::Sender<FrontendEvent>,
    routing: Mutex<EventRoutingState>,
}

#[derive(Default)]
struct EventRoutingState {
    active: bool,
    pending: VecDeque<FrontendEvent>,
    failure: Option<String>,
}

impl EventRoutingState {
    fn buffer(&mut self, event: FrontendEvent) -> Result<(), ()> {
        if self.pending.len() >= FRONTEND_REPLAY_CAPACITY {
            self.pending.clear();
            self.failure = Some(format!(
                "ACP attachment received more than {FRONTEND_REPLAY_CAPACITY} events before session activation; reconnect required to preserve a gap-free stream"
            ));
            return Err(());
        }
        self.pending.push_back(event);
        Ok(())
    }

    fn activate(&mut self, acknowledged_cursor: u64) -> Result<Vec<FrontendEvent>, String> {
        if let Some(error) = &self.failure {
            return Err(error.clone());
        }
        self.active = true;
        Ok(self
            .pending
            .drain(..)
            .filter(|event| event.sequence > acknowledged_cursor)
            .collect())
    }
}

impl AcpRuntimeBridge {
    async fn connect(runtime: Arc<dyn SdkRuntime>) -> Result<Arc<Self>, FrontendRuntimeError> {
        let mut attachment = runtime.attach(200).await?;
        let session_id = attachment.descriptor.session_id.clone();
        let model = attachment.descriptor.model.clone();
        let history = std::mem::take(&mut attachment.history);
        let history_cursor = attachment.history_cursor;
        let initial_replay_cursor = attachment
            .replay
            .iter()
            .map(|event| event.sequence)
            .max()
            .unwrap_or(history_cursor);
        let (events, _) = broadcast::channel(1024);
        let bridge = Arc::new(Self {
            runtime,
            session_id,
            model,
            history,
            history_cursor,
            initial_replay_cursor,
            events,
            routing: Mutex::new(EventRoutingState::default()),
        });
        let weak = Arc::downgrade(&bridge);
        tokio::spawn(async move {
            loop {
                let event = match attachment.next_event().await {
                    Ok(event) => event,
                    Err(error) => FrontendEvent {
                        sequence: u64::MAX,
                        kind: "runtime_disconnected".into(),
                        payload: json!({
                            "type": "runtime_disconnected",
                            "message": error.to_string(),
                        }),
                    },
                };
                let terminal = disconnect_message(&event).is_some();
                let Some(bridge) = weak.upgrade() else {
                    return;
                };
                let mut routing = bridge
                    .routing
                    .lock()
                    .unwrap_or_else(std::sync::PoisonError::into_inner);
                if routing.active {
                    drop(routing);
                    let _ = bridge.events.send(event);
                } else if routing.buffer(event).is_err() {
                    return;
                }
                if terminal {
                    return;
                }
            }
        });
        Ok(bridge)
    }

    fn subscribe(&self) -> broadcast::Receiver<FrontendEvent> {
        self.events.subscribe()
    }

    fn session_id(&self) -> &str {
        &self.session_id
    }

    /// Atomically publish the history/replay/live boundary. The attachment
    /// reader buffers every event newer than `history_cursor` until this
    /// method has queued the history prefix and finite replay. Producers
    /// cannot overtake the boundary because they share `routing`.
    fn activate_and_route(
        &self,
        history: Vec<Value>,
        acknowledged_cursor: u64,
        tx: &mpsc::UnboundedSender<Value>,
    ) -> Result<(), String> {
        let mut routing = self
            .routing
            .lock()
            .unwrap_or_else(std::sync::PoisonError::into_inner);
        if routing.active {
            return Ok(());
        }
        let pending = routing.activate(acknowledged_cursor)?;
        for update in history {
            let _ = tx.send(update);
        }
        let mut terminal = None;
        for event in pending {
            let _ = route_event_projection(tx, self.session_id(), &event);
            if disconnect_message(&event).is_some() {
                terminal = Some(event);
                break;
            }
        }
        drop(routing);
        // Wake the connection lifecycle without projecting the terminal a
        // second time; the event task treats disconnect as control only.
        if let Some(event) = terminal {
            let _ = self.events.send(event);
        }
        Ok(())
    }

    async fn submit(
        &self,
        prompt: String,
        image_urls: Vec<String>,
    ) -> Result<String, FrontendRuntimeError> {
        let mut events = self.subscribe();
        let reply = self.runtime.submit_with_images(prompt, image_urls).await?;
        let deadline = tokio::time::Instant::now() + std::time::Duration::from_secs(5);
        loop {
            match tokio::time::timeout_at(deadline, events.recv()).await {
                Ok(Ok(event)) if is_turn_boundary(&event) => return Ok(reply),
                Ok(Ok(event)) => {
                    if let Some(message) = disconnect_message(&event) {
                        return Err(FrontendRuntimeError::Transport(message.to_string()));
                    }
                }
                Ok(Err(broadcast::error::RecvError::Lagged(skipped))) => {
                    return Err(FrontendRuntimeError::Transport(format!(
                        "SDK event stream lagged by {skipped} event(s)"
                    )));
                }
                Ok(Err(broadcast::error::RecvError::Closed)) => {
                    return Err(FrontendRuntimeError::Closed);
                }
                Err(_) => {
                    return Err(FrontendRuntimeError::Transport(
                        "SDK event stream did not confirm turn completion".into(),
                    ));
                }
            }
        }
    }

    async fn interrupt(&self) -> bool {
        self.runtime.interrupt().await.unwrap_or(false)
    }
}

fn is_turn_boundary(event: &FrontendEvent) -> bool {
    matches!(
        event.payload.get("type").and_then(Value::as_str),
        Some("turn_succeeded" | "turn_failed" | "turn_interrupted")
    )
}

/// Inbound ACP projection of one SDK runtime.
pub struct AcpServer {
    runtime: Arc<AcpRuntimeBridge>,
    compatibility: AcpCompatibilityProfile,
    session_open: AtomicBool,
    history_replayed: AtomicBool,
    prompt_active: AtomicBool,
}

enum RouterCommand {
    Prompt {
        id: Value,
        prompt: String,
        image_urls: Vec<String>,
        frontend_reply: bool,
    },
}

async fn project_prompt(
    server: &AcpServer,
    events: &mut tokio::sync::broadcast::Receiver<FrontendEvent>,
    prompt: String,
    image_urls: Vec<String>,
    frontend_reply: bool,
    tx: &mpsc::UnboundedSender<Value>,
) -> (Result<Value, FrontendRuntimeError>, bool) {
    let runtime = server.runtime.clone();
    // A runtime approval handler may synchronously wait for the frontend's
    // answer. Keep that wait off this event-routing task so the outbound ACP
    // permission request can be delivered and its response read concurrently.
    let mut submit = tokio::spawn(async move { runtime.submit(prompt, image_urls).await });
    let mut streamed = String::new();
    let mut terminal = false;
    let submit_result = loop {
        tokio::select! {
            result = &mut submit => break match result {
                Ok(result) => result,
                Err(error) => Err(FrontendRuntimeError::Transport(format!(
                    "ACP runtime submit task failed: {error}"
                ))),
            },
            event = events.recv() => match event {
                Ok(event) => {
                    if let Some(message) = disconnect_message(&event) {
                        submit.abort();
                        terminal = true;
                        break Err(FrontendRuntimeError::Transport(message.to_string()));
                    }
                    if let Some(text) = assistant_event_text(&event) {
                        streamed.push_str(text);
                    }
                    if !route_event_projection(tx, server.runtime.session_id(), &event) {
                        submit.abort();
                        terminal = true;
                        break Err(FrontendRuntimeError::Closed);
                    }
                }
                Err(tokio::sync::broadcast::error::RecvError::Lagged(skipped)) => {
                    submit.abort();
                    terminal = true;
                    break Err(FrontendRuntimeError::Transport(format!(
                        "ACP event stream lagged by {skipped} events"
                    )));
                }
                Err(tokio::sync::broadcast::error::RecvError::Closed) => {
                    submit.abort();
                    terminal = true;
                    break Err(FrontendRuntimeError::Closed);
                }
            }
        }
    };

    // The SDK runtime publishes every event for the reply before submit
    // before submit resolves. This task is the sole subscriber, so draining
    // its queue is an ordering barrier: no assistant chunk can arrive after
    // the end_turn response.
    while !terminal {
        match events.try_recv() {
            Ok(event) => {
                if let Some(message) = disconnect_message(&event) {
                    terminal = true;
                    return (
                        Err(FrontendRuntimeError::Transport(message.to_string())),
                        terminal,
                    );
                }
                if let Some(text) = assistant_event_text(&event) {
                    streamed.push_str(text);
                }
                if !route_event_projection(tx, server.runtime.session_id(), &event) {
                    terminal = true;
                    return (Err(FrontendRuntimeError::Closed), terminal);
                }
            }
            Err(tokio::sync::broadcast::error::TryRecvError::Empty) => break,
            Err(tokio::sync::broadcast::error::TryRecvError::Lagged(skipped)) => {
                terminal = true;
                return (
                    Err(FrontendRuntimeError::Transport(format!(
                        "ACP event stream lagged by {skipped} events"
                    ))),
                    terminal,
                );
            }
            Err(tokio::sync::broadcast::error::TryRecvError::Closed) => {
                terminal = true;
                return (Err(FrontendRuntimeError::Closed), terminal);
            }
        }
    }

    let result = match submit_result {
        Ok(reply) if reply.starts_with(&streamed) => {
            let missing = &reply[streamed.len()..];
            if !missing.is_empty() {
                let _ = tx.send(session_update(
                    server.runtime.session_id(),
                    json!({
                        "sessionUpdate": "agent_message_chunk",
                        "content": {"type": "text", "text": missing}
                    }),
                ));
                streamed.push_str(missing);
            }
            if streamed.is_empty() {
                Err(FrontendRuntimeError::Execution {
                    operation: crate::SdkOperation::Input,
                    message: "runtime completed without assistant output".into(),
                })
            } else {
                if frontend_reply {
                    Ok(json!({"reply": reply}))
                } else {
                    Ok(json!({"stopReason": "end_turn"}))
                }
            }
        }
        Ok(reply) => Err(FrontendRuntimeError::Execution {
            operation: crate::SdkOperation::Input,
            message: format!(
                "runtime reply did not match streamed assistant output (reply {} bytes, stream {} bytes)",
                reply.len(),
                streamed.len()
            ),
        }),
        Err(FrontendRuntimeError::Submit(RuntimeSubmitError::Interrupted)) => {
            Ok(json!({"stopReason": "cancelled"}))
        }
        Err(error) => Err(error),
    };
    (result, terminal)
}

impl AcpServer {
    /// Wrap an existing SDK runtime.  Multiple frontends may wrap/subscribe to
    /// the same runtime; the runtime, not this adapter, remains authoritative.
    pub async fn new(runtime: Arc<dyn SdkRuntime>) -> Result<Arc<Self>, FrontendRuntimeError> {
        Self::new_with_profile(runtime, AcpCompatibilityProfile::Standard).await
    }

    /// Wrap an existing SDK runtime with one version-pinned stock-client
    /// compatibility profile. The profile affects only ACP projection; the
    /// supplied runtime remains the sole owner of continuation and state.
    pub async fn new_with_profile(
        runtime: Arc<dyn SdkRuntime>,
        compatibility: AcpCompatibilityProfile,
    ) -> Result<Arc<Self>, FrontendRuntimeError> {
        Ok(Arc::new(Self {
            runtime: AcpRuntimeBridge::connect(runtime).await?,
            compatibility,
            session_open: AtomicBool::new(false),
            history_replayed: AtomicBool::new(false),
            prompt_active: AtomicBool::new(false),
        }))
    }

    /// Canonical runtime shared by this ACP projection and other frontends.
    pub fn runtime(&self) -> &Arc<dyn SdkRuntime> {
        &self.runtime.runtime
    }

    fn initialize(&self) -> Value {
        let mut frontend_methods = crate::FrontendFacadeMethod::ALL
            .into_iter()
            .map(crate::FrontendFacadeMethod::wire_name)
            .collect::<Vec<_>>();
        frontend_methods.extend(["session/cancel", "session/steer", "session/respond"]);
        json!({
            "protocolVersion": ACP_PROTOCOL_VERSION,
            "agentCapabilities": {
                "loadSession": true,
                "sessionCapabilities": {"resume": {}},
                "promptCapabilities": {"image": false, "embeddedContext": false},
                "_meta": {
                    "supercode": {
                        "frontend": {
                            "schemaVersion": crate::frontend::FRONTEND_RUNTIME_SCHEMA_VERSION,
                            "contract": "supercode.frontend.contract.v2",
                            "eventMethod": "frontend.v2.event",
                            "runtimeOwnedByClient": false,
                            "methods": frontend_methods
                        }
                    }
                }
            },
            "authMethods": [],
            "agentInfo": {
                "name": "supercode",
                "title": "Supercode",
                "version": env!("CARGO_PKG_VERSION")
            }
        })
    }

    fn open_session(&self, requested: Option<&str>) -> Result<Value, String> {
        if let Some(requested) = requested {
            if requested != self.runtime.session_id() {
                return Err(format!(
                    "runtime `{}` is not session `{requested}`",
                    self.runtime.session_id()
                ));
            }
        }
        self.session_open.store(true, Ordering::SeqCst);
        Ok(json!({"sessionId": self.runtime.session_id()}))
    }

    fn goose_defaults(&self) -> Result<Value, String> {
        if self.compatibility != AcpCompatibilityProfile::GooseAcd3c135 {
            return Err("Goose defaults are unavailable on the standard ACP profile".into());
        }
        Ok(json!({
            "providerId": "supercode",
            "modelId": self.runtime.model,
        }))
    }

    fn validate_new_session(&self, params: &Value) -> Result<(), String> {
        if self.compatibility != AcpCompatibilityProfile::GooseAcd3c135 {
            return Ok(());
        }
        if params
            .get("mcpServers")
            .and_then(Value::as_array)
            .is_some_and(|servers| !servers.is_empty())
        {
            return Err("Goose frontend cannot mutate the selected runtime's MCP servers".into());
        }
        Ok(())
    }

    fn history_updates_once(&self) -> Vec<Value> {
        if self.compatibility != AcpCompatibilityProfile::GooseAcd3c135
            || self.history_replayed.swap(true, Ordering::SeqCst)
        {
            return Vec::new();
        }
        project_history(
            self.runtime.session_id(),
            &self.runtime.history,
            self.runtime.history_cursor,
        )
    }

    fn prompt_text(params: &Value) -> Result<String, String> {
        let prompt = params
            .get("prompt")
            .and_then(Value::as_array)
            .ok_or_else(|| "session/prompt requires a `prompt` content array".to_string())?;
        let text = prompt
            .iter()
            .filter(|part| part.get("type").and_then(Value::as_str) == Some("text"))
            .filter_map(|part| part.get("text").and_then(Value::as_str))
            .collect::<Vec<_>>()
            .join("\n");
        if text.is_empty() {
            Err("session/prompt contains no text content".into())
        } else {
            Ok(text)
        }
    }

    fn validate_session(&self, params: &Value) -> Result<(), String> {
        if !self.session_open.load(Ordering::SeqCst) {
            return Err("open a session before prompting".into());
        }
        let requested = params
            .get("sessionId")
            .and_then(Value::as_str)
            .ok_or_else(|| "request omitted `sessionId`".to_string())?;
        if requested != self.runtime.session_id() {
            return Err(format!(
                "runtime `{}` is not session `{requested}`",
                self.runtime.session_id()
            ));
        }
        Ok(())
    }
}

fn response(id: Value, result: Result<Value, String>) -> Value {
    match result {
        Ok(result) => json!({"jsonrpc": "2.0", "id": id, "result": result}),
        Err(message) => json!({
            "jsonrpc": "2.0",
            "id": id,
            "error": {"code": -32000, "message": message}
        }),
    }
}

fn sdk_response(id: Value, result: Result<Value, FrontendRuntimeError>) -> Value {
    match result {
        Ok(result) => json!({"jsonrpc": "2.0", "id": id, "result": result}),
        Err(error) => {
            let code = match error.code() {
                crate::SdkErrorCode::Busy => -32000,
                crate::SdkErrorCode::Unauthenticated => -32030,
                crate::SdkErrorCode::Unauthorized => -32031,
                crate::SdkErrorCode::ControllerRequired => -32032,
                crate::SdkErrorCode::LeaseExpired => -32033,
                _ => -32002,
            };
            let mut envelope = json!({
                "jsonrpc": "2.0",
                "id": id,
                "error": {
                    "code": code,
                    "name": error.code(),
                    "operation": error.operation(),
                    "message": error.to_string(),
                }
            });
            if let Some(detail) = envelope.get_mut("error").and_then(Value::as_object_mut) {
                match error {
                    FrontendRuntimeError::Unauthorized { permission } => {
                        detail.insert("permission".into(), Value::String(permission));
                    }
                    FrontendRuntimeError::ControllerRequired {
                        holder,
                        expires_at_ms,
                    } => {
                        if let Some(holder) = holder {
                            detail.insert("holder".into(), Value::String(holder));
                        }
                        if let Some(expires_at_ms) = expires_at_ms {
                            detail.insert("expiresAtMs".into(), json!(expires_at_ms));
                        }
                    }
                    _ => {}
                }
            }
            envelope
        }
    }
}

fn session_update(session_id: &str, update: Value) -> Value {
    json!({
        "jsonrpc": "2.0",
        "method": "session/update",
        "params": {"sessionId": session_id, "update": update}
    })
}

fn projected_session_update(session_id: &str, event: &FrontendEvent, mut update: Value) -> Value {
    if let Some(update) = update.as_object_mut() {
        update.insert(
            "_meta".into(),
            json!({
                "supercode": {
                    "sdkSequence": event.sequence,
                    "sdkKind": event.kind,
                }
            }),
        );
    }
    session_update(session_id, update)
}

fn frontend_event_notification(session_id: &str, event: &FrontendEvent) -> Value {
    json!({
        "jsonrpc": "2.0",
        "method": "frontend.v2.event",
        "params": {"sessionId": session_id, "event": event}
    })
}

fn approval_request_id(request_id: u64) -> String {
    format!("{ACP_APPROVAL_REQUEST_ID_PREFIX}{request_id}")
}

fn approval_request_id_from_wire(message: &Value) -> Option<u64> {
    let wire_id = message.get("id")?.as_str()?;
    let request_id = wire_id
        .strip_prefix(ACP_APPROVAL_REQUEST_ID_PREFIX)?
        .parse::<u64>()
        .ok()?;
    (approval_request_id(request_id) == wire_id).then_some(request_id)
}

fn project_approval_request(session_id: &str, event: &FrontendEvent) -> Option<Value> {
    if event.payload.get("type").and_then(Value::as_str) != Some("request") {
        return None;
    }
    let request: FrontendRequest =
        serde_json::from_value(event.payload.get("request")?.clone()).ok()?;
    if request.kind != FrontendRequestKind::Approval {
        return None;
    }
    let tool = request
        .payload
        .get("tool")
        .and_then(Value::as_str)
        .unwrap_or("tool");
    let title = request
        .payload
        .get("subject")
        .and_then(Value::as_str)
        .filter(|subject| !subject.is_empty())
        .unwrap_or(tool);
    let raw_input = request
        .payload
        .get("raw_args")
        .cloned()
        .unwrap_or(Value::Null);
    Some(json!({
        "jsonrpc":"2.0",
        "id":approval_request_id(request.id),
        "method":"session/request_permission",
        "params":{
            "sessionId":session_id,
            "toolCall":{
                "toolCallId":format!("supercode-request-{}", request.id),
                "title":title,
                "kind":"other",
                "status":"pending",
                "rawInput":raw_input,
                "_meta":{"supercode":{"requestId":request.id, "tool":tool}},
            },
            "options":[
                {"optionId":"allow_once", "name":"Allow once", "kind":"allow_once"},
                {"optionId":"allow_for_session", "name":"Allow for session", "kind":"allow_always"},
                {"optionId":"deny", "name":"Deny", "kind":"reject_once"},
            ],
        },
    }))
}

fn decode_approval_response(message: &Value) -> Option<FrontendResponse> {
    let request_id = approval_request_id_from_wire(message)?;
    let result = message.get("result");
    let error = message.get("error");
    let exact_top_level = message.as_object().is_some_and(|object| {
        object.len() == 3
            && object.contains_key("jsonrpc")
            && object.contains_key("id")
            && (object.contains_key("result") ^ object.contains_key("error"))
    });
    let valid_envelope = message.get("jsonrpc").and_then(Value::as_str) == Some("2.0")
        && message.get("method").is_none()
        && exact_top_level
        && (result.is_some() ^ error.is_some());
    let decision =
        if valid_envelope && error.is_none() {
            match message.pointer("/result/outcome") {
                Some(outcome)
                    if result.and_then(Value::as_object).is_some_and(|object| {
                        object.len() == 1 && object.contains_key("outcome")
                    }) && outcome.as_object().is_some_and(|object| {
                        object.len() == 2
                            && object.contains_key("outcome")
                            && object.contains_key("optionId")
                    }) && outcome.get("outcome").and_then(Value::as_str) == Some("selected") =>
                {
                    match outcome.get("optionId").and_then(Value::as_str) {
                        Some("allow_once") => FrontendApprovalDecision::Allow,
                        Some("allow_for_session") => FrontendApprovalDecision::AllowForSession,
                        _ => FrontendApprovalDecision::Deny,
                    }
                }
                _ => FrontendApprovalDecision::Deny,
            }
        } else {
            FrontendApprovalDecision::Deny
        };
    Some(FrontendResponse::Approval {
        request_id,
        decision,
    })
}

fn route_event_projection(
    tx: &mpsc::UnboundedSender<Value>,
    session_id: &str,
    event: &FrontendEvent,
) -> bool {
    if tx
        .send(frontend_event_notification(session_id, event))
        .is_err()
    {
        return false;
    }
    if let Some(request) = project_approval_request(session_id, event) {
        if tx.send(request).is_err() {
            return false;
        }
    }
    if let Some(update) = project_event(session_id, event) {
        if tx.send(update).is_err() {
            return false;
        }
    }
    true
}

fn project_event(session_id: &str, event: &FrontendEvent) -> Option<Value> {
    let payload = &event.payload;
    match payload.get("type").and_then(Value::as_str)? {
        "text_delta" => Some(projected_session_update(
            session_id,
            event,
            json!({
                "sessionUpdate": "agent_message_chunk",
                "content": {"type": "text", "text": payload.get("text")?}
            }),
        )),
        "tool_call_started" => Some(projected_session_update(
            session_id,
            event,
            json!({
                "sessionUpdate": "tool_call",
                "toolCallId": payload.get("id")?,
                "title": payload.get("name")?,
                "kind": "other",
                "status": "in_progress",
                "rawInput": payload.get("arguments").cloned().unwrap_or(Value::Null)
            }),
        )),
        "tool_call_completed" => Some(projected_session_update(
            session_id,
            event,
            json!({
                "sessionUpdate": "tool_call_update",
                "toolCallId": payload.get("id")?,
                "status": if payload.get("is_error").and_then(Value::as_bool).unwrap_or(false) {
                    "failed"
                } else {
                    "completed"
                },
                "content": [{
                    "type": "content",
                    "content": {
                        "type": "text",
                        "text": payload.get("output").cloned().unwrap_or(Value::String(String::new()))
                    }
                }]
            }),
        )),
        "background_output" => Some(projected_session_update(
            session_id,
            event,
            json!({
                "sessionUpdate": "agent_message_chunk",
                "content": {"type": "text", "text": payload.get("chunk")?},
                "nativeEvent": payload
            }),
        )),
        // Usage/cache/round-trip completion remain available on the SDK event
        // bus but have no portable ACP v1 update shape.
        _ => Some(projected_session_update(
            session_id,
            event,
            json!({
                "sessionUpdate": "agent_thought_chunk",
                "content": {"type": "text", "text": ""},
                "nativeEvent": payload,
            }),
        )),
    }
}

fn canonical_content_blocks(message: &ChatMessage) -> Vec<Value> {
    if let Some(content) = &message.content {
        return if content.is_empty() {
            Vec::new()
        } else {
            vec![json!({"type":"text", "text":content})]
        };
    }
    message
        .content_parts
        .as_deref()
        .unwrap_or_default()
        .iter()
        .filter_map(|part| match part.get("type").and_then(Value::as_str) {
            Some("text") => part
                .get("text")
                .and_then(Value::as_str)
                .map(|text| json!({"type":"text", "text":text})),
            Some("image_url") => {
                let url = part.pointer("/image_url/url").and_then(Value::as_str)?;
                if let Some(data) = url.strip_prefix("data:") {
                    let (mime_type, data) = data.split_once(";base64,")?;
                    Some(json!({
                        "type":"image",
                        "data":data,
                        "mimeType":mime_type,
                    }))
                } else {
                    Some(json!({
                        "type":"resource_link",
                        "name":"image attachment",
                        "uri":url,
                    }))
                }
            }
            _ => None,
        })
        .collect()
}

fn history_update(
    session_id: &str,
    history_cursor: u64,
    history_index: usize,
    role: Role,
    update: Value,
) -> Value {
    let mut notification = session_update(session_id, update);
    notification["params"]["update"]["_meta"] = json!({
        "supercode": {
            "historyCursor": history_cursor,
            "historyIndex": history_index,
            "canonicalRole": match role {
                Role::System => "system",
                Role::User => "user",
                Role::Assistant => "assistant",
                Role::Tool => "tool",
            },
        }
    });
    notification
}

/// Project the bounded canonical attachment snapshot into standard ACP
/// history updates. These messages are a display replay only: the canonical
/// SDK history is neither copied into nor reconstructed from the client.
fn project_history(session_id: &str, history: &[ChatMessage], history_cursor: u64) -> Vec<Value> {
    let mut projected = Vec::new();
    for (index, message) in history.iter().enumerate() {
        match message.role {
            // System instructions are runtime authority, not transcript UI.
            Role::System => {}
            Role::User | Role::Assistant => {
                let session_update_kind = if message.role == Role::User {
                    "user_message_chunk"
                } else {
                    "agent_message_chunk"
                };
                for content in canonical_content_blocks(message) {
                    projected.push(history_update(
                        session_id,
                        history_cursor,
                        index,
                        message.role,
                        json!({
                            "sessionUpdate":session_update_kind,
                            "content":content,
                        }),
                    ));
                }
                if message.role == Role::Assistant {
                    for call in message.tool_calls() {
                        let raw_input = serde_json::from_str::<Value>(&call.function.arguments)
                            .unwrap_or_else(|_| Value::String(call.function.arguments.clone()));
                        projected.push(history_update(
                            session_id,
                            history_cursor,
                            index,
                            message.role,
                            json!({
                                "sessionUpdate":"tool_call",
                                "toolCallId":call.id,
                                "title":call.function.name,
                                "kind":"other",
                                "status":"in_progress",
                                "rawInput":raw_input,
                            }),
                        ));
                    }
                }
            }
            Role::Tool => {
                let Some(tool_call_id) = message.tool_call_id.as_deref() else {
                    continue;
                };
                let content = canonical_content_blocks(message)
                    .into_iter()
                    .map(|content| json!({"type":"content", "content":content}))
                    .collect::<Vec<_>>();
                projected.push(history_update(
                    session_id,
                    history_cursor,
                    index,
                    message.role,
                    json!({
                        "sessionUpdate":"tool_call_update",
                        "toolCallId":tool_call_id,
                        "status":"completed",
                        "content":content,
                    }),
                ));
            }
        }
    }
    projected
}

fn assistant_event_text(event: &FrontendEvent) -> Option<&str> {
    match event.payload.get("type").and_then(Value::as_str)? {
        "text_delta" => event.payload.get("text").and_then(Value::as_str),
        _ => None,
    }
}

fn disconnect_message(event: &FrontendEvent) -> Option<&str> {
    (event.payload.get("type").and_then(Value::as_str) == Some("runtime_disconnected"))
        .then(|| event.payload.get("message").and_then(Value::as_str))
        .flatten()
}

/// Serve ACP v1 JSON-RPC over a newline-delimited stream.
///
/// Requests are dispatched concurrently so `session/cancel` can interrupt a
/// running `session/prompt`.  A single writer task serializes responses and
/// notifications, preventing byte interleaving between event and request
/// tasks.
pub async fn run_stdio<R, W>(
    server: Arc<AcpServer>,
    mut reader: R,
    writer: W,
) -> std::io::Result<()>
where
    R: AsyncBufRead + Unpin + Send + 'static,
    W: AsyncWrite + Unpin + Send + 'static,
{
    let (out_tx, mut out_rx) = mpsc::unbounded_channel::<Value>();
    let pending_approvals = Arc::new(Mutex::new(HashSet::<u64>::new()));
    let writer_pending_approvals = pending_approvals.clone();
    let mut writer_task = tokio::spawn(async move {
        let mut writer = writer;
        while let Some(value) = out_rx.recv().await {
            if value.get("method").and_then(Value::as_str) == Some("session/request_permission") {
                if let Some(request_id) = approval_request_id_from_wire(&value) {
                    writer_pending_approvals
                        .lock()
                        .unwrap_or_else(std::sync::PoisonError::into_inner)
                        .insert(request_id);
                }
            }
            writer.write_all(format!("{value}\n").as_bytes()).await?;
            writer.flush().await?;
        }
        Ok::<(), std::io::Error>(())
    });

    let mut events = server.runtime.subscribe();
    let event_server = server.clone();
    let event_tx = out_tx.clone();
    let (router_tx, mut router_rx) = mpsc::unbounded_channel::<RouterCommand>();
    let (disconnect_tx, mut disconnect_rx) = mpsc::unbounded_channel::<()>();
    let event_task = tokio::spawn(async move {
        loop {
            tokio::select! {
                command = router_rx.recv() => match command {
                    Some(RouterCommand::Prompt { id, prompt, image_urls, frontend_reply }) => {
                        let (result, terminal) = project_prompt(
                            &event_server,
                            &mut events,
                            prompt,
                            image_urls,
                            frontend_reply,
                            &event_tx,
                        ).await;
                        event_server.prompt_active.store(false, Ordering::SeqCst);
                        let _ = event_tx.send(sdk_response(id, result));
                        if terminal {
                            let _ = disconnect_tx.send(());
                            break;
                        }
                    }
                    None => break,
                },
                event = events.recv() => match event {
                    Ok(event) if disconnect_message(&event).is_some() => {
                        let _ = disconnect_tx.send(());
                        break;
                    }
                    Ok(event) if event_server.session_open.load(Ordering::SeqCst) => {
                        if !route_event_projection(
                            &event_tx,
                            event_server.runtime.session_id(),
                            &event,
                        ) {
                            break;
                        }
                    }
                    Ok(_) => {}
                    Err(tokio::sync::broadcast::error::RecvError::Lagged(_))
                    | Err(tokio::sync::broadcast::error::RecvError::Closed) => {
                        let _ = disconnect_tx.send(());
                        break;
                    }
                },
            }
        }
    });

    let mut writer_finished = false;
    let mut terminal_error = None;
    loop {
        let mut line = String::new();
        let bytes = tokio::select! {
            bytes = reader.read_line(&mut line) => bytes?,
            _ = disconnect_rx.recv() => break,
            result = &mut writer_task => {
                writer_finished = true;
                terminal_error = match result {
                    Ok(Ok(())) => None,
                    Ok(Err(error)) => Some(error),
                    Err(error) => Some(std::io::Error::other(format!(
                        "ACP writer task failed: {error}"
                    ))),
                };
                break;
            }
        };
        if bytes == 0 {
            break;
        }
        if line.len() > SERVER_MAX_LINE_BYTES {
            let _ = out_tx.send(response(
                Value::Null,
                Err("ACP request exceeded size limit".into()),
            ));
            continue;
        }
        let request: Value = match serde_json::from_str(line.trim()) {
            Ok(request) => request,
            Err(error) => {
                let _ = out_tx.send(json!({
                    "jsonrpc": "2.0", "id": null,
                    "error": {"code": -32700, "message": error.to_string()}
                }));
                continue;
            }
        };
        if request.get("method").is_none() {
            if let Some(response) = decode_approval_response(&request) {
                pending_approvals
                    .lock()
                    .unwrap_or_else(std::sync::PoisonError::into_inner)
                    .remove(&response.request_id());
                let _ = server.runtime.runtime.respond(response).await;
            }
            // JSON-RPC responses never receive a response of their own.
            continue;
        }
        let method = request.get("method").and_then(Value::as_str).unwrap_or("");
        let id = request.get("id").cloned();
        let params = request.get("params").cloned().unwrap_or_else(|| json!({}));

        if method == "session/cancel" {
            let server = server.clone();
            tokio::spawn(async move {
                let _ = server.runtime.interrupt().await;
            });
            continue;
        }

        let Some(id) = id else {
            continue;
        };
        match method {
            "initialize" => {
                let version = params.get("protocolVersion").and_then(Value::as_u64);
                let result = if version == Some(ACP_PROTOCOL_VERSION) {
                    Ok(server.initialize())
                } else {
                    Err(format!("unsupported ACP protocol version {version:?}"))
                };
                let _ = out_tx.send(response(id, result));
            }
            "_goose/unstable/defaults/read"
                if server.compatibility == AcpCompatibilityProfile::GooseAcd3c135 =>
            {
                let _ = out_tx.send(response(id, server.goose_defaults()));
            }
            "session/new" => {
                let mut opened = server
                    .validate_new_session(&params)
                    .and_then(|()| server.open_session(None));
                if opened.is_ok() {
                    // The pinned stock Goose server sends session updates
                    // before resolving session/new, and its client accepts
                    // that ordering. Replaying at this exact boundary avoids
                    // inventing a client-side session-selection protocol.
                    let goose = server.compatibility == AcpCompatibilityProfile::GooseAcd3c135;
                    let acknowledged_cursor = if goose {
                        server.runtime.history_cursor
                    } else {
                        server.runtime.initial_replay_cursor
                    };
                    if let Err(error) = server.runtime.activate_and_route(
                        server.history_updates_once(),
                        acknowledged_cursor,
                        &out_tx,
                    ) {
                        server.session_open.store(false, Ordering::SeqCst);
                        opened = Err(error);
                    }
                }
                let _ = out_tx.send(response(id, opened));
            }
            "session/load" | "session/resume" => {
                let requested = params.get("sessionId").and_then(Value::as_str);
                let mut opened = server.open_session(requested);
                if opened.is_ok() {
                    if let Err(error) = server.runtime.activate_and_route(
                        Vec::new(),
                        server.runtime.initial_replay_cursor,
                        &out_tx,
                    ) {
                        server.session_open.store(false, Ordering::SeqCst);
                        opened = Err(error);
                    }
                }
                let _ = out_tx.send(response(id, opened));
            }
            "session/prompt" => {
                let validation = server
                    .validate_session(&params)
                    .and_then(|_| AcpServer::prompt_text(&params));
                let prompt = match validation {
                    Ok(prompt) => prompt,
                    Err(error) => {
                        let _ = out_tx.send(response(id, Err(error)));
                        continue;
                    }
                };
                if server
                    .prompt_active
                    .compare_exchange(false, true, Ordering::SeqCst, Ordering::SeqCst)
                    .is_err()
                {
                    let _ = out_tx.send(sdk_response(
                        id,
                        Err(FrontendRuntimeError::Submit(RuntimeSubmitError::Busy)),
                    ));
                    continue;
                }
                if let Err(error) = router_tx.send(RouterCommand::Prompt {
                    id,
                    prompt,
                    image_urls: Vec::new(),
                    frontend_reply: false,
                }) {
                    server.prompt_active.store(false, Ordering::SeqCst);
                    let RouterCommand::Prompt { id, .. } = error.0;
                    let _ = out_tx.send(response(
                        id,
                        Err("ACP runtime event router is unavailable".into()),
                    ));
                }
            }
            "session/steer" | "frontend.v2.steer" => {
                let result = match server.validate_session(&params) {
                    Ok(()) => match params.get("text").and_then(Value::as_str) {
                        Some(text) => server.runtime.runtime.steer(text.to_string()).await,
                        None => Err(FrontendRuntimeError::InvalidArgument {
                            operation: crate::SdkOperation::Steer,
                            message: "session/steer requires string `text`".into(),
                        }),
                    },
                    Err(message) => Err(FrontendRuntimeError::InvalidArgument {
                        operation: crate::SdkOperation::Steer,
                        message,
                    }),
                };
                let _ = out_tx.send(sdk_response(id, result.map(|()| json!({}))));
            }
            "session/respond" | "frontend.v2.respond" => {
                let result = match server.validate_session(&params) {
                    Ok(()) => serde_json::from_value::<FrontendResponse>(
                        params.get("response").cloned().unwrap_or(Value::Null),
                    )
                    .map_err(|error| FrontendRuntimeError::InvalidArgument {
                        operation: crate::SdkOperation::Respond,
                        message: error.to_string(),
                    }),
                    Err(message) => Err(FrontendRuntimeError::InvalidArgument {
                        operation: crate::SdkOperation::Respond,
                        message,
                    }),
                };
                let result = match result {
                    Ok(response) => server.runtime.runtime.respond(response).await,
                    Err(error) => Err(error),
                };
                let _ = out_tx.send(sdk_response(id, result.map(|()| json!({}))));
            }
            "frontend.v2.describe" | "supercode/frontend/describe" => {
                let result = match server.validate_session(&params) {
                    Ok(()) => server
                        .runtime
                        .runtime
                        .describe()
                        .await
                        .and_then(|descriptor| {
                            serde_json::to_value(descriptor)
                                .map_err(|error| FrontendRuntimeError::Transport(error.to_string()))
                        }),
                    Err(message) => Err(FrontendRuntimeError::InvalidArgument {
                        operation: crate::SdkOperation::Resume,
                        message,
                    }),
                };
                let _ = out_tx.send(sdk_response(id, result));
            }
            "frontend.v2.attach" | "supercode/frontend/attach" => {
                let limit = params
                    .get("limit")
                    .and_then(Value::as_u64)
                    .unwrap_or(50)
                    .clamp(1, crate::server::SERVER_HISTORY_CAPACITY as u64)
                    as usize;
                let after = params
                    .get("after_sequence")
                    .or_else(|| params.get("afterSequence"))
                    .and_then(Value::as_u64)
                    .unwrap_or_default();
                let result = match server.validate_session(&params) {
                    Ok(()) => match server.runtime.runtime.attach(limit).await {
                        Ok(attachment) => {
                            let mut snapshot = crate::FrontendAttachSnapshot {
                                descriptor: attachment.descriptor,
                                history: attachment.history,
                                history_cursor: attachment.history_cursor,
                                replay: attachment.replay,
                            };
                            snapshot.replay.retain(|event| event.sequence > after);
                            serde_json::to_value(snapshot)
                                .map_err(|error| FrontendRuntimeError::Transport(error.to_string()))
                        }
                        Err(error) => Err(error),
                    },
                    Err(message) => Err(FrontendRuntimeError::InvalidArgument {
                        operation: crate::SdkOperation::Events,
                        message,
                    }),
                };
                let _ = out_tx.send(sdk_response(id, result));
            }
            "frontend.v2.send_input" | "supercode/frontend/send_input" => {
                let result = match server.validate_session(&params) {
                    Ok(()) => match params.get("prompt").and_then(Value::as_str) {
                        Some(prompt) => {
                            server
                                .runtime
                                .runtime
                                .clone()
                                .send_input(prompt.to_string())
                                .await
                        }
                        None => Err(FrontendRuntimeError::InvalidArgument {
                            operation: crate::SdkOperation::Input,
                            message: "supercode/frontend/send_input requires string `prompt`"
                                .into(),
                        }),
                    },
                    Err(message) => Err(FrontendRuntimeError::InvalidArgument {
                        operation: crate::SdkOperation::Input,
                        message,
                    }),
                };
                let _ = out_tx.send(sdk_response(id, result.map(|()| json!({"accepted":true}))));
            }
            "frontend.v2.submit" | "supercode/frontend/submit" => {
                let prompt = match server.validate_session(&params).and_then(|_| {
                    params
                        .get("prompt")
                        .and_then(Value::as_str)
                        .map(str::to_owned)
                        .ok_or_else(|| {
                            "supercode/frontend/submit requires string `prompt`".to_string()
                        })
                }) {
                    Ok(prompt) => prompt,
                    Err(error) => {
                        let _ = out_tx.send(sdk_response(
                            id,
                            Err(FrontendRuntimeError::InvalidArgument {
                                operation: crate::SdkOperation::Input,
                                message: error,
                            }),
                        ));
                        continue;
                    }
                };
                let image_urls = match params.get("image_urls") {
                    None => Vec::new(),
                    Some(Value::Array(values)) => {
                        match values.iter().map(Value::as_str).collect::<Option<Vec<_>>>() {
                            Some(values) => values.into_iter().map(str::to_owned).collect(),
                            None => {
                                let _ = out_tx.send(sdk_response(
                                id,
                                Err(FrontendRuntimeError::InvalidArgument {
                                    operation: crate::SdkOperation::Input,
                                    message: "supercode/frontend/submit requires string entries in `image_urls`".into(),
                                }),
                            ));
                                continue;
                            }
                        }
                    }
                    Some(_) => {
                        let _ = out_tx.send(sdk_response(
                            id,
                            Err(FrontendRuntimeError::InvalidArgument {
                                operation: crate::SdkOperation::Input,
                                message: "supercode/frontend/submit requires array `image_urls`"
                                    .into(),
                            }),
                        ));
                        continue;
                    }
                };
                if server
                    .prompt_active
                    .compare_exchange(false, true, Ordering::SeqCst, Ordering::SeqCst)
                    .is_err()
                {
                    let _ = out_tx.send(sdk_response(
                        id,
                        Err(FrontendRuntimeError::Submit(RuntimeSubmitError::Busy)),
                    ));
                    continue;
                }
                if let Err(error) = router_tx.send(RouterCommand::Prompt {
                    id,
                    prompt,
                    image_urls,
                    frontend_reply: true,
                }) {
                    server.prompt_active.store(false, Ordering::SeqCst);
                    let RouterCommand::Prompt { id, .. } = error.0;
                    let _ = out_tx.send(sdk_response(
                        id,
                        Err(FrontendRuntimeError::Transport(
                            "ACP runtime event router is unavailable".into(),
                        )),
                    ));
                }
            }
            "frontend.v2.interrupt" | "supercode/frontend/interrupt" => {
                let result = match server.validate_session(&params) {
                    Ok(()) => server
                        .runtime
                        .runtime
                        .interrupt()
                        .await
                        .map(|interrupted| json!({"interrupted":interrupted})),
                    Err(message) => Err(FrontendRuntimeError::InvalidArgument {
                        operation: crate::SdkOperation::Interrupt,
                        message,
                    }),
                };
                let _ = out_tx.send(sdk_response(id, result));
            }
            "frontend.v2.invoke" | "supercode/frontend/invoke" => {
                let operation = params
                    .get("operation")
                    .cloned()
                    .ok_or_else(|| FrontendRuntimeError::InvalidArgument {
                        operation: crate::SdkOperation::Input,
                        message: "supercode/frontend/invoke requires `operation`".into(),
                    })
                    .and_then(|value| {
                        serde_json::from_value(value).map_err(|error| {
                            FrontendRuntimeError::InvalidArgument {
                                operation: crate::SdkOperation::Input,
                                message: error.to_string(),
                            }
                        })
                    });
                let result = match (server.validate_session(&params), operation) {
                    (Ok(()), Ok(operation)) => server.runtime.runtime.invoke(operation).await,
                    (Err(message), _) => Err(FrontendRuntimeError::InvalidArgument {
                        operation: crate::SdkOperation::Input,
                        message,
                    }),
                    (_, Err(error)) => Err(error),
                };
                let result = result.and_then(|result| {
                    serde_json::to_value(result)
                        .map_err(|error| FrontendRuntimeError::Transport(error.to_string()))
                });
                let _ = out_tx.send(sdk_response(id, result));
            }
            "frontend.v2.lease" | "supercode/frontend/lease" => {
                let result = match server.validate_session(&params) {
                    Ok(()) => server.runtime.runtime.lease_snapshot().await,
                    Err(message) => Err(FrontendRuntimeError::InvalidArgument {
                        operation: crate::SdkOperation::Events,
                        message,
                    }),
                }
                .and_then(|snapshot| {
                    serde_json::to_value(snapshot)
                        .map_err(|error| FrontendRuntimeError::Transport(error.to_string()))
                });
                let _ = out_tx.send(sdk_response(id, result));
            }
            "frontend.v2.take_control" | "supercode/frontend/take_control" => {
                let result = match server.validate_session(&params) {
                    Ok(()) => server.runtime.runtime.take_control().await,
                    Err(message) => Err(FrontendRuntimeError::InvalidArgument {
                        operation: crate::SdkOperation::Input,
                        message,
                    }),
                }
                .and_then(|snapshot| {
                    serde_json::to_value(snapshot)
                        .map_err(|error| FrontendRuntimeError::Transport(error.to_string()))
                });
                let _ = out_tx.send(sdk_response(id, result));
            }
            "frontend.v2.heartbeat" | "supercode/frontend/heartbeat" => {
                let result = match server.validate_session(&params) {
                    Ok(()) => server.runtime.runtime.heartbeat().await,
                    Err(message) => Err(FrontendRuntimeError::InvalidArgument {
                        operation: crate::SdkOperation::Events,
                        message,
                    }),
                }
                .and_then(|snapshot| {
                    serde_json::to_value(snapshot)
                        .map_err(|error| FrontendRuntimeError::Transport(error.to_string()))
                });
                let _ = out_tx.send(sdk_response(id, result));
            }
            "frontend.v2.detach" | "supercode/frontend/detach" => {
                let result = match server.validate_session(&params) {
                    Ok(()) => server.runtime.runtime.detach().await,
                    Err(message) => Err(FrontendRuntimeError::InvalidArgument {
                        operation: crate::SdkOperation::Events,
                        message,
                    }),
                }
                .and_then(|snapshot| {
                    serde_json::to_value(snapshot)
                        .map_err(|error| FrontendRuntimeError::Transport(error.to_string()))
                });
                if result.is_ok() {
                    server.session_open.store(false, Ordering::SeqCst);
                }
                let _ = out_tx.send(sdk_response(id, result));
            }
            "frontend.v2.close" | "supercode/frontend/close" => {
                let result = match server.validate_session(&params) {
                    Ok(()) => server
                        .runtime
                        .runtime
                        .close()
                        .await
                        .map(|()| json!({"closed":true})),
                    Err(message) => Err(FrontendRuntimeError::InvalidArgument {
                        operation: crate::SdkOperation::Close,
                        message,
                    }),
                };
                let _ = out_tx.send(sdk_response(id, result));
            }
            other => {
                let _ = out_tx.send(json!({
                    "jsonrpc": "2.0", "id": id,
                    "error": {"code": -32601, "message": format!("unknown ACP method `{other}`")}
                }));
            }
        }
    }

    drop(out_tx);
    event_task.abort();
    let _ = event_task.await;
    if !writer_finished {
        terminal_error = match writer_task.await {
            Ok(Ok(())) => terminal_error,
            Ok(Err(error)) => Some(error),
            Err(error) => Some(std::io::Error::other(format!(
                "ACP writer task failed: {error}"
            ))),
        };
    }
    // The writer is now quiescent, so its projected-request inventory cannot
    // race this drain. Any unanswered approval belonged to this dead stdio
    // attachment and must resolve as Deny rather than block or execute.
    let unresolved = pending_approvals
        .lock()
        .unwrap_or_else(std::sync::PoisonError::into_inner)
        .drain()
        .collect::<Vec<_>>();
    for request_id in unresolved {
        let _ = server
            .runtime
            .runtime
            .respond(FrontendResponse::Approval {
                request_id,
                decision: FrontendApprovalDecision::Deny,
            })
            .await;
    }
    match terminal_error {
        Some(error) => Err(error),
        None => Ok(()),
    }
}

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

    #[test]
    fn projects_text_and_tool_events_without_transport_state() {
        let sdk_event = FrontendEvent {
            sequence: 41,
            kind: "text_delta".into(),
            payload: json!({"type": "text_delta", "text": "hello"}),
        };
        let text = project_event("s1", &sdk_event).unwrap();
        assert_eq!(
            text.pointer("/params/update/sessionUpdate")
                .and_then(Value::as_str),
            Some("agent_message_chunk")
        );
        assert_eq!(
            text.pointer("/params/update/content/text")
                .and_then(Value::as_str),
            Some("hello")
        );
        assert_eq!(
            text.pointer("/params/update/_meta/supercode/sdkSequence")
                .and_then(Value::as_u64),
            Some(41)
        );
        assert_eq!(
            text.pointer("/params/update/_meta/supercode/sdkKind")
                .and_then(Value::as_str),
            Some("text_delta")
        );

        let tool = project_event(
            "s1",
            &FrontendEvent {
                sequence: 42,
                kind: "tool_call_started".into(),
                payload: json!({
                    "type": "tool_call_started", "id": "call-1",
                    "name": "read_file", "arguments": "{}"
                }),
            },
        )
        .unwrap();
        assert_eq!(
            tool.pointer("/params/update/toolCallId")
                .and_then(Value::as_str),
            Some("call-1")
        );
    }

    #[test]
    fn preserves_named_sdk_errors_in_acp_responses() {
        let response = sdk_response(
            json!(7),
            Err(FrontendRuntimeError::Submit(RuntimeSubmitError::Busy)),
        );
        assert_eq!(response["error"]["name"], "busy");
        assert_eq!(response["error"]["operation"], "input");
    }

    #[test]
    fn approval_requests_and_responses_preserve_runtime_correlation() {
        let event = FrontendEvent {
            sequence: 43,
            kind: "request".into(),
            payload: json!({
                "type":"request",
                "request":{
                    "id":17,
                    "kind":"approval",
                    "payload":{
                        "tool":"bash",
                        "subject":"echo reviewed",
                        "raw_args":{"command":"echo reviewed"},
                    },
                },
            }),
        };
        let request = project_approval_request("s1", &event).unwrap();
        assert_eq!(request["id"], "supercode-approval-17");
        assert_eq!(request["method"], "session/request_permission");
        assert_eq!(request["params"]["sessionId"], "s1");
        assert_eq!(request["params"]["toolCall"]["title"], "echo reviewed");
        assert_eq!(request["params"]["options"][0]["optionId"], "allow_once");

        assert_eq!(
            decode_approval_response(&json!({
                "jsonrpc":"2.0",
                "id":"supercode-approval-17",
                "result":{"outcome":{"outcome":"selected", "optionId":"allow_for_session"}},
            })),
            Some(FrontendResponse::Approval {
                request_id: 17,
                decision: FrontendApprovalDecision::AllowForSession,
            })
        );
        assert_eq!(
            decode_approval_response(&json!({
                "jsonrpc":"2.0",
                "id":"supercode-approval-17",
                "result":{"outcome":{"outcome":"cancelled"}},
            })),
            Some(FrontendResponse::Approval {
                request_id: 17,
                decision: FrontendApprovalDecision::Deny,
            })
        );
        for malformed in [
            json!({
                "id":"supercode-approval-17",
                "result":{"outcome":{"outcome":"selected", "optionId":"allow_once"}},
            }),
            json!({
                "jsonrpc":"2.0",
                "id":"supercode-approval-17",
                "result":{"outcome":{"outcome":"selected", "optionId":"allow_once"}},
                "error":{"code":-32603, "message":"invalid"},
            }),
            json!({
                "jsonrpc":"2.0",
                "id":"supercode-approval-17",
                "result":{"outcome":{"outcome":"selected", "optionId":"unknown"}},
            }),
            json!({
                "jsonrpc":"2.0",
                "id":"supercode-approval-17",
                "result":{"outcome":{"outcome":"selected", "optionId":"allow_once"}},
                "params":{},
            }),
            json!({
                "jsonrpc":"2.0",
                "id":"supercode-approval-17",
                "result":{
                    "outcome":{"outcome":"selected", "optionId":"allow_once"},
                    "extra":true,
                },
            }),
        ] {
            assert_eq!(
                decode_approval_response(&malformed),
                Some(FrontendResponse::Approval {
                    request_id: 17,
                    decision: FrontendApprovalDecision::Deny,
                })
            );
        }
        assert!(decode_approval_response(&json!({
            "jsonrpc":"2.0",
            "id":"supercode-approval-017",
            "result":{"outcome":{"outcome":"selected", "optionId":"allow_once"}},
        }))
        .is_none());
        assert!(decode_approval_response(&json!({"jsonrpc":"2.0", "id":99})).is_none());
    }

    #[test]
    fn inactive_event_routing_is_bounded_and_fails_instead_of_truncating() {
        let mut routing = EventRoutingState::default();
        for sequence in 1..=FRONTEND_REPLAY_CAPACITY as u64 {
            routing
                .buffer(FrontendEvent {
                    sequence,
                    kind: "loop_tick".into(),
                    payload: json!({"type":"loop_tick", "sequence":sequence}),
                })
                .unwrap();
        }
        assert_eq!(routing.pending.len(), FRONTEND_REPLAY_CAPACITY);
        assert!(routing
            .buffer(FrontendEvent {
                sequence: FRONTEND_REPLAY_CAPACITY as u64 + 1,
                kind: "loop_tick".into(),
                payload: json!({"type":"loop_tick"}),
            })
            .is_err());
        assert!(routing.pending.is_empty(), "failed replay is never partial");

        let error = routing.activate(0).unwrap_err();
        assert!(error.contains(&FRONTEND_REPLAY_CAPACITY.to_string()));
        assert!(error.contains("reconnect required"));
        assert!(!routing.active, "a gapped attachment must never activate");
    }
}