lash/

core.rs

use crate::support::*;
use lash_core::runtime::{
    ProcessCommand, ProcessEffectOutcome, RuntimeEffectCommand, RuntimeEffectEnvelope,
    RuntimeEffectKind, RuntimeEffectLocalExecutor, RuntimeEffectOutcome, RuntimeInvocation,
    RuntimeScope,
};

#[derive(Clone)]
pub struct LashCore {
    pub(crate) env: RuntimeEnvironment,
    pub(crate) policy: SessionPolicy,
    pub(crate) protocol_factory: Option<Arc<dyn PluginFactory>>,
    pub(crate) store_factory: Option<Arc<dyn SessionStoreFactory>>,
    pub(crate) plugin_factories: Arc<Vec<Arc<dyn PluginFactory>>>,
    pub(crate) provider: Option<ProviderHandle>,
    pub(crate) live_replay_store: Arc<dyn LiveReplayStore>,
    /// Whether this deployment has process lifecycle available (a process
    /// registry is wired). Threaded to every plugin host so core can install the
    /// same plugin-contributed process engines when it rebuilds a runtime.
    pub(crate) process_lifecycle_available: bool,
    /// Shared resolution of host-owned work drivers. Shared across `LashCore`
    /// clones so inline process and queued drivers are constructed at most once.
    pub(crate) work_driver: Arc<InlineWorkDriverSlot>,
}

/// How a [`LashCore`] resolves its process work driver, decided at `build()`
/// and shared across clones.
pub(crate) enum ProcessWorkDriverSetup {
    /// No process registry is wired; there is nothing to run.
    None,
    /// Lazily construct the default inline process driver on first
    /// `session().open()`. A store factory is required to build the config (the
    /// worker rebuilds a session runtime per process); a registry with no store
    /// factory is rejected at build with
    /// [`EmbedError::ProcessRegistryRequiresStoreFactory`].
    LazyDefault {
        config: Box<DurableProcessWorkerConfig>,
    },
    /// The host wired an external driver.
    External { driver: ProcessWorkDriver },
}

#[derive(Clone, Default)]
pub(crate) enum ProcessWorkSource {
    #[default]
    None,
    Inline {
        registry: Arc<dyn ProcessRegistry>,
        hub: Option<lash_core::ProcessChangeHub>,
    },
    External(ProcessWorkDriver),
}

impl ProcessWorkSource {
    fn process_registry(&self) -> Option<Arc<dyn ProcessRegistry>> {
        match self {
            Self::None => None,
            Self::Inline { registry, .. } => Some(Arc::clone(registry)),
            Self::External(driver) => Some(driver.process_registry()),
        }
    }

    fn has_registry(&self) -> bool {
        !matches!(self, Self::None)
    }

    fn watched(self, sink: Option<Arc<dyn lash_core::ProcessEventSink>>) -> Self {
        match self {
            Self::Inline {
                registry,
                hub: None,
            } => {
                let (registry, hub) = lash_core::watch_process_registry_with_sink(registry, sink);
                Self::Inline {
                    registry,
                    hub: Some(hub),
                }
            }
            // An external driver was wrapped by its host, which installs any
            // sink through the driver constructor; the inline sink does not
            // apply here. Already-watched inline sources keep their wrap.
            other => other,
        }
    }
}

#[derive(Clone, Default)]
pub(crate) enum QueuedWorkSource {
    None,
    #[default]
    LazyDefault,
    External(QueuedWorkDriver),
}

pub(crate) enum QueuedWorkDriverSetup {
    None,
    LazyDefault {
        config: Arc<InlineQueuedWorkRunConfig>,
    },
    External {
        driver: QueuedWorkDriver,
    },
}

pub(crate) struct InlineWorkDriverSetup {
    process: ProcessWorkDriverSetup,
    queued: QueuedWorkDriverSetup,
}

#[derive(Clone, Default)]
pub(crate) struct ResolvedWorkDrivers {
    pub(crate) process: Option<ProcessWorkDriver>,
    pub(crate) queued: Option<QueuedWorkDriver>,
    pub(crate) drive_process_on_open: bool,
}

/// Shared, lazily-initialized host-work state for a [`LashCore`].
///
/// The once-guard ([`tokio::sync::OnceCell`]) constructs inline drivers exactly
/// once across `LashCore` clones, on the first `session().open()` or admin path
/// that needs them.
pub(crate) struct InlineWorkDriverSlot {
    setup: InlineWorkDriverSetup,
    drivers: tokio::sync::OnceCell<ResolvedWorkDrivers>,
    phase_probe_slot: Option<lash_core::runtime::RuntimeTurnPhaseProbeSlot>,
}

impl InlineWorkDriverSlot {
    fn new(setup: InlineWorkDriverSetup) -> Self {
        let phase_probe_slot = match &setup.process {
            ProcessWorkDriverSetup::LazyDefault { config } => {
                Some(config.turn_phase_probe_slot.clone())
            }
            ProcessWorkDriverSetup::None | ProcessWorkDriverSetup::External { .. } => None,
        };
        Self {
            setup,
            drivers: tokio::sync::OnceCell::new(),
            phase_probe_slot,
        }
    }

    /// Resolve host work drivers for a session host. Idempotent: the once-guard
    /// ensures inline drivers are constructed once.
    pub(crate) async fn drivers(&self) -> ResolvedWorkDrivers {
        self.drivers
            .get_or_init(|| async {
                let queued = match &self.setup.queued {
                    QueuedWorkDriverSetup::None => None,
                    QueuedWorkDriverSetup::External { driver } => Some(driver.clone()),
                    QueuedWorkDriverSetup::LazyDefault { config } => Some(QueuedWorkDriver::new(
                        Arc::new(InlineQueuedWorkRunHandle::new(Arc::clone(config))),
                    )),
                };
                let (process, drive_process_on_open) = match &self.setup.process {
                    ProcessWorkDriverSetup::None => (None, false),
                    ProcessWorkDriverSetup::External { driver } => (Some(driver.clone()), false),
                    ProcessWorkDriverSetup::LazyDefault { config } => {
                        let mut config = (**config).clone();
                        if let Some(driver) = queued.clone() {
                            config = config.with_queued_work_driver(driver);
                        }
                        let registry = Arc::clone(&config.process_registry);
                        let hub = config.process_change_hub.clone();
                        let worker = DurableProcessWorker::new(config);
                        let driver = if let Some(hub) = hub {
                            ProcessWorkDriver::from_watched(
                                registry,
                                hub,
                                Arc::new(lash_core::InlineProcessRunHandle::new(worker)),
                            )
                        } else {
                            ProcessWorkDriver::inline(registry, worker)
                        };
                        (Some(driver), true)
                    }
                };
                ResolvedWorkDrivers {
                    process,
                    queued,
                    drive_process_on_open,
                }
            })
            .await
            .clone()
    }

    pub(crate) fn phase_probe_slot(&self) -> Option<lash_core::runtime::RuntimeTurnPhaseProbeSlot> {
        self.phase_probe_slot.clone()
    }

    fn configured_process_work_driver(&self) -> Option<ProcessWorkDriver> {
        match &self.setup.process {
            ProcessWorkDriverSetup::External { driver } => Some(driver.clone()),
            ProcessWorkDriverSetup::None | ProcessWorkDriverSetup::LazyDefault { .. } => None,
        }
    }

    fn configured_queued_work_driver(&self) -> Option<QueuedWorkDriver> {
        match &self.setup.queued {
            QueuedWorkDriverSetup::External { driver } => Some(driver.clone()),
            QueuedWorkDriverSetup::None | QueuedWorkDriverSetup::LazyDefault { .. } => None,
        }
    }
}

pub(crate) struct InlineQueuedWorkRunConfig {
    env: RuntimeEnvironment,
    policy: SessionPolicy,
    protocol_factory: Option<Arc<dyn PluginFactory>>,
    plugin_factories: Arc<Vec<Arc<dyn PluginFactory>>>,
    store_factory: Arc<dyn SessionStoreFactory>,
    live_replay_store: Arc<dyn LiveReplayStore>,
    process_lifecycle_available: bool,
}

impl InlineQueuedWorkRunConfig {
    fn new(
        env: RuntimeEnvironment,
        policy: SessionPolicy,
        protocol_factory: Option<Arc<dyn PluginFactory>>,
        plugin_factories: Arc<Vec<Arc<dyn PluginFactory>>>,
        store_factory: Arc<dyn SessionStoreFactory>,
        live_replay_store: Arc<dyn LiveReplayStore>,
        process_lifecycle_available: bool,
    ) -> Self {
        Self {
            env,
            policy,
            protocol_factory,
            plugin_factories,
            store_factory,
            live_replay_store,
            process_lifecycle_available,
        }
    }
}

struct InlineQueuedWorkRunHandle {
    config: Arc<InlineQueuedWorkRunConfig>,
}

impl InlineQueuedWorkRunHandle {
    fn new(config: Arc<InlineQueuedWorkRunConfig>) -> Self {
        Self { config }
    }
}

#[async_trait]
impl QueuedWorkRunHandle for InlineQueuedWorkRunHandle {
    async fn run_queued_work(
        &self,
        request: QueuedWorkRunRequest,
    ) -> std::result::Result<(), lash_core::PluginError> {
        let Some(session_id) = request.session_id else {
            return Ok(());
        };
        let reason = request.reason;
        let mut policy = self.config.policy.clone();
        policy.session_id = Some(session_id.clone());
        let store = self
            .config
            .store_factory
            .create_store(&SessionStoreCreateRequest {
                session_id: session_id.clone(),
                relation: SessionRelation::default(),
                policy: policy.clone(),
            })
            .await
            .map_err(lash_core::PluginError::Session)?;
        let state = crate::session::load_state_for_residency(
            self.config.env.residency,
            &session_id,
            &policy,
            store.as_ref(),
        )
        .await
        .map_err(|err| lash_core::PluginError::Session(err.to_string()))?;
        let plugin_host = build_plugin_host(
            self.config.protocol_factory.as_ref(),
            self.config.plugin_factories.as_ref(),
            Vec::new(),
        )
        .map_err(|err| lash_core::PluginError::Session(err.to_string()))?;
        let mut env = self.config.env.clone();
        env.core = plugin_host
            .install_process_engine_contributions(
                env.core.clone(),
                self.config.process_lifecycle_available,
            )
            .map_err(|err| lash_core::PluginError::Session(err.to_string()))?;
        env.plugin_host = Some(Arc::new(plugin_host));
        let effect_host = Arc::clone(&env.core.control.effect_host);
        let runtime = LashRuntime::from_environment(&env, policy, state, Some(store))
            .await
            .map_err(|err| lash_core::PluginError::Session(err.to_string()))?;
        let handle = RuntimeHandle::with_live_replay_store(
            runtime,
            Arc::clone(&self.config.live_replay_store),
        );
        let scope = lash_core::ExecutionScope::queue_drain(session_id, reason);
        let scoped = effect_host
            .scoped(scope)
            .map_err(|err| lash_core::PluginError::Session(err.to_string()))?;
        crate::turn::stream_next_queued_prepared_turn(
            &handle,
            crate::turn::TurnSinks::default(),
            scoped,
            CancellationToken::new(),
            &[],
        )
        .await
        .map_err(|err| lash_core::PluginError::Session(err.to_string()))?;
        Ok(())
    }
}

#[derive(Clone, Debug, Default, serde::Serialize, serde::Deserialize)]
pub struct SessionDeleteReport {
    pub session_id: String,
    pub process: Option<lash_core::ProcessSessionDeleteReport>,
}

impl LashCore {
    pub fn builder() -> LashCoreBuilder {
        LashCoreBuilder::default()
    }

    /// Sugar entry point: a [`LashCoreBuilder`] pre-seeded with the standard
    /// protocol plugin and the default runtime plugin stack.
    pub fn standard_builder() -> LashCoreBuilder {
        LashCore::builder()
            .protocol_plugin(Arc::new(
                lash_protocol_standard::StandardProtocolPluginFactory::new(),
            ))
            .plugins(default_runtime_stack())
    }

    /// Sugar entry point: a [`LashCoreBuilder`] pre-seeded with a
    /// host-configured RLM protocol factory and the default runtime plugin
    /// stack.
    ///
    /// The host configures the factory (projection resolver, deferred tool
    /// resolver, execution sink/jsonl path, and — required at construction — the
    /// Lashlang artifact store) before passing it in.
    #[cfg(feature = "rlm")]
    pub fn rlm_builder(factory: crate::rlm::RlmProtocolPluginFactory) -> LashCoreBuilder {
        LashCore::builder()
            .protocol_plugin(Arc::new(factory))
            .plugins(default_runtime_stack())
    }

    pub fn session(&self, session_id: impl Into<String>) -> SessionBuilder {
        SessionBuilder {
            core: self.clone(),
            session_id: session_id.into(),
            spec: SessionSpec::inherit(),
            parent_session_id: None,
            session_execution_owner: None,
            store: None,
            provider: None,
            active_plugins: Vec::new(),
            plugin_factories: Vec::new(),
            plugin_options: PluginOptions::default(),
        }
    }

    /// Rebuild a live session from a [`ParkedSession`](crate::ParkedSession)
    /// handle produced by [`LashSession::park`](crate::LashSession::park).
    ///
    /// Resume reloads the flushed state from the parked store (honoring this
    /// core's residency), reinstalls this core's plugin configuration and work
    /// drivers, and returns a ready [`LashSession`]. The parked store instance
    /// is reused directly, so the transcript the session flushed at park time is
    /// visible again after resume.
    ///
    /// This restores the core-level plugin stack. Session-specific plugins added
    /// per open via [`SessionBuilder::plugin`] are not re-applied here; parking
    /// is the round-trip for the core's own configuration.
    pub async fn resume(&self, parked: ParkedSession) -> Result<LashSession> {
        // Build the per-session env exactly like `SessionBuilder::open_resolved`
        // (minus builder-scoped plugins): a fresh plugin host with this core's
        // factories, the shared work drivers, and the core provider resolver
        // already carried on `self.env`.
        let plugin_host = build_plugin_host(
            self.protocol_factory.as_ref(),
            self.plugin_factories.as_ref(),
            Vec::new(),
        )?;
        let mut env = self.env.clone();
        env.core = plugin_host.install_process_engine_contributions(
            env.core.clone(),
            self.process_lifecycle_available,
        )?;
        env.plugin_host = Some(Arc::new(plugin_host));
        let effect_host = Arc::clone(&env.core.control.effect_host);
        let drivers = self.work_driver.drivers().await;
        env.process_work_driver = drivers.process.clone();
        env.queued_work_driver = drivers.queued.clone();
        let runtime = LashRuntime::resume(parked.inner, &env).await?;
        let handle =
            RuntimeHandle::with_live_replay_store(runtime, Arc::clone(&self.live_replay_store));
        Ok(LashSession {
            runtime: handle,
            effect_host,
            parent_session_id: None,
            active_plugins: Vec::new(),
            process_phase_probe_slot: self.work_driver.phase_probe_slot(),
            turn_cancels: crate::turn::TurnCancelRegistry::default(),
        })
    }

    /// Flush this core's configured trace sink, if any.
    ///
    /// Hosts that hand `lash` a trace sink via
    /// [`LashCoreBuilder::trace_sink`] already hold their own `Arc` and can
    /// flush it directly; this is the equivalent lever for hosts that did not
    /// retain the handle. It flushes the core's copy — for a
    /// [`JsonlTraceSink`](lash_trace::JsonlTraceSink) that fsyncs the file, and
    /// for an OTel sink it is a no-op (the host still owns provider flush; see
    /// the tracing docs). Call it before process exit alongside the host's own
    /// exporter/provider shutdown.
    pub fn flush_trace_sink(&self) -> Result<()> {
        if let Some(sink) = self.env.core.tracing.trace_sink.as_ref() {
            sink.flush()?;
        }
        Ok(())
    }

    pub fn triggers(&self) -> crate::admin::CoreTriggerAdmin {
        crate::admin::CoreTriggerAdmin { core: self.clone() }
    }

    pub fn processes(&self) -> crate::process_admin::Processes {
        crate::process_admin::Processes { core: self.clone() }
    }

    pub fn completions(&self) -> crate::admin::Completions {
        crate::admin::Completions { core: self.clone() }
    }

    pub fn effect_host(&self) -> Arc<dyn EffectHost> {
        Arc::clone(&self.env.core.control.effect_host)
    }

    pub async fn delete_session(
        &self,
        session_id: impl AsRef<str>,
        scoped_effect_controller: ScopedEffectController<'_>,
    ) -> Result<SessionDeleteReport> {
        let session_id = session_id.as_ref().to_string();
        let Some(store_factory) = self.store_factory.as_ref() else {
            return Err(EmbedError::MissingSessionStoreFactory);
        };
        let process = if let Some(process_registry) = self.env.process_registry.as_ref() {
            let invocation = RuntimeInvocation::effect(
                RuntimeScope::new(session_id.clone()),
                format!("process:delete-session:{session_id}"),
                RuntimeEffectKind::Process,
                format!("{session_id}:delete-session"),
            );
            let outcome = scoped_effect_controller
                .controller()
                .execute_effect(
                    RuntimeEffectEnvelope::new(
                        invocation,
                        RuntimeEffectCommand::process(ProcessCommand::DeleteSession {
                            session_id: session_id.clone(),
                        }),
                    ),
                    RuntimeEffectLocalExecutor::processes(
                        Arc::clone(process_registry),
                        self.env.process_work_driver.clone(),
                    ),
                )
                .await
                .map_err(|err| EmbedError::SessionDeleteProcess {
                    session_id: session_id.clone(),
                    message: err.to_string(),
                })?;
            match outcome {
                RuntimeEffectOutcome::Process {
                    result: ProcessEffectOutcome::DeleteSession { report },
                } => Some(report),
                other => {
                    return Err(EmbedError::SessionDeleteProcess {
                        session_id,
                        message: format!(
                            "process delete returned the wrong outcome: {}",
                            other.kind().as_str()
                        ),
                    });
                }
            }
        } else {
            None
        };
        if let Some(trigger_store) = self.env.trigger_store.as_ref() {
            trigger_store
                .delete_session_subscriptions(&session_id)
                .await
                .map_err(|err| EmbedError::SessionDeleteProcess {
                    session_id: session_id.clone(),
                    message: err.to_string(),
                })?;
        }
        self.env
            .core
            .control
            .effect_host
            .revoke_await_events_for_session(&session_id)
            .await
            .map_err(|err| EmbedError::SessionDeleteProcess {
                session_id: session_id.clone(),
                message: err.to_string(),
            })?;
        store_factory
            .delete_session(&session_id)
            .await
            .map_err(|message| EmbedError::StoreFactory {
                session_id: session_id.clone(),
                message,
            })?;
        Ok(SessionDeleteReport {
            session_id,
            process,
        })
    }

    pub fn process_registry(&self) -> Option<Arc<dyn ProcessRegistry>> {
        self.env.process_registry.as_ref().cloned()
    }

    pub fn durable_process_worker_config(&self) -> Result<DurableProcessWorkerConfig> {
        self.durable_process_worker_config_with_plugins(std::iter::empty::<Arc<dyn PluginFactory>>())
    }

    pub fn durable_process_worker_config_with_plugins(
        &self,
        extra_plugin_factories: impl IntoIterator<Item = Arc<dyn PluginFactory>>,
    ) -> Result<DurableProcessWorkerConfig> {
        let Some(process_registry) = self.process_registry() else {
            return Err(EmbedError::MissingProcessRegistry);
        };
        let Some(store_factory) = self.store_factory.as_ref() else {
            return Err(EmbedError::MissingProcessWorkerStoreFactory);
        };
        let plugin_host = build_plugin_host(
            self.protocol_factory.as_ref(),
            self.plugin_factories.as_ref(),
            extra_plugin_factories.into_iter().collect(),
        )?;
        let runtime_host = plugin_host.install_process_engine_contributions(
            self.env.core.clone(),
            self.process_lifecycle_available,
        )?;
        let mut config = DurableProcessWorkerConfig::new(
            Arc::new(plugin_host),
            runtime_host,
            Arc::clone(store_factory),
            process_registry,
        )
        .with_session_policy(self.policy.clone())
        .with_residency(self.env.residency);
        if let Some(trigger_store) = self.env.trigger_store.as_ref() {
            config = config.with_trigger_store(Arc::clone(trigger_store));
        }
        if let Some(driver) = self.work_driver.configured_process_work_driver() {
            config = config
                .with_change_hub(driver.change_hub())
                .with_process_work_driver(driver);
        }
        if let Some(driver) = self.work_driver.configured_queued_work_driver() {
            config = config.with_queued_work_driver(driver);
        }
        Ok(config)
    }
}

fn default_runtime_stack() -> PluginStack {
    lash_plugin_tool_output_budget::tool_output_budget_stack()
}

#[derive(Default)]
pub struct LashCoreBuilder {
    pub(crate) protocol_factory: Option<Arc<dyn PluginFactory>>,
    session_spec: SessionSpec,
    provider: Option<ProviderHandle>,
    pub(crate) store_factory: Option<Arc<dyn SessionStoreFactory>>,
    child_store_factory: Option<Arc<dyn SessionStoreFactory>>,
    // `RuntimeHostConfig` has no `Default`: the generic host-owned durability
    // dependencies must be named. They are collected here and resolved in
    // `build()`, which errors if any is unset.
    effect_host: Option<Arc<dyn EffectHost>>,
    attachment_store: Option<Arc<dyn AttachmentStore>>,
    process_env_store: Option<Arc<dyn ProcessExecutionEnvStore>>,
    trigger_store: Option<Arc<dyn lash_core::TriggerStore>>,
    // Benign core overrides applied on top of the resolved core.
    prompt: Option<PromptLayer>,
    trace_sink: Option<Arc<dyn lash_trace::TraceSink>>,
    trace_level: Option<lash_trace::TraceLevel>,
    trace_context: Option<lash_trace::TraceContext>,
    termination: Option<TerminationPolicy>,
    // Advanced full-config override; used as the base core when present.
    runtime_host_config: Option<RuntimeHostConfig>,
    tool_providers: Vec<Arc<dyn ToolProvider>>,
    plugin_stack: PluginStack,
    plugin_host: Option<PluginHost>,
    residency: Option<Residency>,
    lease_timings: Option<lash_core::LeaseTimings>,
    // Single source of truth for process lifecycle support and process-work
    // consumption.
    process_work_source: ProcessWorkSource,
    // Optional host-facing best-effort feed of appended process events,
    // installed on the inline process-registry decorator at build time.
    process_event_sink: Option<Arc<dyn lash_core::ProcessEventSink>>,
    queued_work_source: QueuedWorkSource,
    live_replay_store: Option<Arc<dyn LiveReplayStore>>,
}

impl LashCoreBuilder {
    pub fn protocol_plugin(mut self, plugin: Arc<dyn PluginFactory>) -> Self {
        self.protocol_factory = Some(plugin);
        self
    }

    pub fn provider(mut self, provider: ProviderHandle) -> Self {
        self.session_spec = self.session_spec.provider_id(provider.kind());
        self.provider = Some(provider);
        self
    }

    pub fn model(mut self, model: lash_core::ModelSpec) -> Self {
        self.session_spec = self.session_spec.model(model);
        self
    }

    pub fn max_turns(mut self, max_turns: usize) -> Self {
        self.session_spec = self.session_spec.max_turns(max_turns);
        self
    }

    pub fn session_spec(mut self, spec: SessionSpec) -> Self {
        self.session_spec = spec;
        self
    }

    /// Configure a factory that can create a persistence store for any root
    /// session opened from this core.
    ///
    /// The factory must honor `SessionStoreCreateRequest::session_id` and
    /// return a store for that specific session. Do not use this to wrap one
    /// pre-opened root store; pass root-only stores with
    /// `LashCore::session(...).store(store)` instead.
    pub fn store_factory(mut self, store_factory: Arc<dyn SessionStoreFactory>) -> Self {
        self.store_factory = Some(store_factory);
        self
    }

    /// Configure the persistence factory used by managed child sessions, such
    /// as local subagents.
    ///
    /// Child factories must return a distinct store bound to the requested
    /// child session id. Hosts that pass an explicit root store with
    /// `SessionBuilder::store` should set this when child sessions need
    /// persistence.
    pub fn child_store_factory(mut self, store_factory: Arc<dyn SessionStoreFactory>) -> Self {
        self.child_store_factory = Some(store_factory);
        self
    }

    pub fn attachment_store(mut self, attachment_store: Arc<dyn AttachmentStore>) -> Self {
        self.attachment_store = Some(attachment_store);
        self
    }

    pub fn process_env_store(
        mut self,
        process_env_store: Arc<dyn ProcessExecutionEnvStore>,
    ) -> Self {
        self.process_env_store = Some(process_env_store);
        self
    }

    /// Set the deployment effect host — the durability boundary every operation
    /// crosses. Pass [`InlineEffectHost`](crate::durability::InlineEffectHost)
    /// for in-process execution, or a workflow-backed host for durable
    /// execution.
    pub fn effect_host(mut self, effect_host: Arc<dyn EffectHost>) -> Self {
        self.effect_host = Some(effect_host);
        self
    }

    pub fn tools(mut self, tools: Arc<dyn ToolProvider>) -> Self {
        self.tool_providers.push(tools);
        self
    }

    pub fn plugin(mut self, plugin: Arc<dyn PluginFactory>) -> Self {
        self.plugin_stack.push(plugin);
        self
    }

    pub fn plugins(mut self, stack: PluginStack) -> Self {
        self.plugin_stack = stack;
        self
    }

    pub fn configure_plugins(mut self, configure: impl FnOnce(&mut PluginStack)) -> Self {
        configure(&mut self.plugin_stack);
        self
    }

    pub fn trace_sink(mut self, trace_sink: Arc<dyn lash_trace::TraceSink>) -> Self {
        self.trace_sink = Some(trace_sink);
        self
    }

    pub fn trace_jsonl_path(mut self, path: impl Into<std::path::PathBuf>) -> Self {
        self.trace_sink = Some(Arc::new(lash_trace::JsonlTraceSink::new(path.into())));
        self
    }

    pub fn trace_level(mut self, trace_level: lash_trace::TraceLevel) -> Self {
        self.trace_level = Some(trace_level);
        self
    }

    pub fn trace_context(mut self, trace_context: lash_trace::TraceContext) -> Self {
        self.trace_context = Some(trace_context);
        self
    }

    pub fn termination(mut self, termination: TerminationPolicy) -> Self {
        self.termination = Some(termination);
        self
    }

    pub fn residency(mut self, residency: Residency) -> Self {
        self.residency = Some(residency);
        self
    }

    /// Configure the lease timing capability for every durable single-writer
    /// lane this deployment claims: session execution leases, turn-input and
    /// queued-work claims, and process leases.
    ///
    /// This is the failover-latency vs false-takeover-risk knob. Like
    /// [`residency`](Self::residency) it is an operational deployment decision,
    /// so it lives on the main builder tier rather than behind
    /// [`advanced`](Self::advanced). Construct the value with
    /// [`LeaseTimings::new`](lash_core::LeaseTimings::new), which enforces
    /// `ttl >= 3 * renew_interval`. Effect hosts accept the same type at
    /// construction (e.g. SQLite/Postgres effect-replay options), so a host can
    /// share one timing decision across both boundaries.
    pub fn lease_timings(mut self, lease_timings: lash_core::LeaseTimings) -> Self {
        self.lease_timings = Some(lease_timings);
        self
    }

    /// Configure the bounded live replay buffer used by session observation
    /// cursors. This is best-effort reconnect recovery only; durable state
    /// still comes from the session store and [`SessionReadView`].
    pub fn live_replay_store(mut self, live_replay_store: Arc<dyn LiveReplayStore>) -> Self {
        self.live_replay_store = Some(live_replay_store);
        self
    }

    /// Resolve the runtime host config, requiring the generic host-owned
    /// durability dependencies to have been named.
    fn resolve_runtime_host_config(&mut self) -> Result<RuntimeHostConfig> {
        if let Some(base) = self.runtime_host_config.take() {
            return Ok(self.apply_core_overrides(base));
        }
        let effect_host = self
            .effect_host
            .take()
            .ok_or(EmbedError::MissingEffectHost)?;
        let attachment_store = self
            .attachment_store
            .take()
            .ok_or(EmbedError::MissingAttachmentStore)?;
        let process_env_store = self
            .process_env_store
            .take()
            .ok_or(EmbedError::MissingProcessEnvStore)?;
        let core = RuntimeHostConfig::new(effect_host, attachment_store, process_env_store);
        Ok(self.apply_core_overrides(core))
    }

    /// Apply benign + still-set dependency overrides on top of a base core.
    fn apply_core_overrides(&mut self, mut core: RuntimeHostConfig) -> RuntimeHostConfig {
        if let Some(effect_host) = self.effect_host.take() {
            core.control.effect_host = effect_host;
        }
        if let Some(attachment_store) = self.attachment_store.take() {
            core.durability.attachment_store = Arc::new(
                lash_core::SessionAttachmentStore::ephemeral(attachment_store),
            );
        }
        if let Some(process_env_store) = self.process_env_store.take() {
            core.durability.process_env_store = process_env_store;
        }
        if let Some(prompt) = self.prompt.take() {
            core.prompt.prompt = prompt;
        }
        if let Some(trace_sink) = self.trace_sink.take() {
            core.tracing.trace_sink = Some(trace_sink);
        }
        if let Some(trace_level) = self.trace_level.take() {
            core.tracing.trace_level = trace_level;
        }
        if let Some(trace_context) = self.trace_context.take() {
            core.tracing.trace_context = trace_context;
        }
        if let Some(termination) = self.termination.take() {
            core.control.termination = termination;
        }
        if let Some(lease_timings) = self.lease_timings.take() {
            core.control.lease_timings = lease_timings;
        }
        core
    }

    /// Validate store peer-coherence of the wired durability dependencies.
    ///
    /// Durability is established by what the host wired; the per-invocation
    /// durable controller is not visible here (the build-time controller is
    /// inline by construction), so this checks the stores against each other
    /// only — never the controller (see A5 in the durable-first wiring spec):
    ///
    /// - a durable session store factory requires a durable attachment and
    ///   artifact store (they back the same session state);
    /// - a durable process registry requires a session store factory that is
    ///   itself durable (the registry's process records are meaningless without
    ///   a durable session behind them).
    fn effective_session_store_tier(&self) -> Option<DurabilityTier> {
        self.child_store_factory
            .as_ref()
            .or(self.store_factory.as_ref())
            .map(|factory| factory.durability_tier())
    }

    /// Validate store peer-coherence, sweeping every registered process engine.
    ///
    /// Runs after the runtime host is resolved and process-engine contributions
    /// are installed, so it reads the effective effect host / attachment /
    /// process-env tiers off `core`, and the session-store / trigger-store /
    /// process-registry tiers captured from the builder before its plugin stack
    /// was consumed. A durable session store requires every registered engine to
    /// be durable too.
    fn ensure_store_peer_coherence(
        session_store_tier: Option<DurabilityTier>,
        trigger_store_tier: Option<DurabilityTier>,
        process_registry_tier: Option<DurabilityTier>,
        core: &RuntimeHostConfig,
    ) -> Result<()> {
        let attachment_tier = Some(
            core.durability
                .attachment_store
                .persistence()
                .durability_tier(),
        );
        let process_env_tier = Some(core.durability.process_env_store.durability_tier());
        let effect_host_tier = Some(core.control.effect_host.durability_tier());

        if session_store_tier == Some(DurabilityTier::Durable) {
            if attachment_tier == Some(DurabilityTier::Inline) {
                return Err(EmbedError::DurableStorePeerRequired {
                    facet: "attachment store",
                });
            }
            if process_env_tier == Some(DurabilityTier::Inline) {
                return Err(EmbedError::DurableStorePeerRequired {
                    facet: "process execution environment store",
                });
            }
            // Every registered process engine must be durable behind a durable
            // session store, regardless of how it was contributed.
            for engine in core.process_engines.engines() {
                if engine.durability_tier() == DurabilityTier::Inline {
                    return Err(EmbedError::DurableStorePeerRequired {
                        facet: engine.kind(),
                    });
                }
            }
        }

        if process_registry_tier == Some(DurabilityTier::Durable) {
            if session_store_tier != Some(DurabilityTier::Durable) {
                return Err(EmbedError::DurableProcessRegistryRequiresStoreFactory);
            }
            if trigger_store_tier != Some(DurabilityTier::Durable) {
                return Err(EmbedError::DurableStorePeerRequired {
                    facet: "trigger store",
                });
            }
            if process_env_tier != Some(DurabilityTier::Durable) {
                return Err(EmbedError::DurableStorePeerRequired {
                    facet: "process execution environment store",
                });
            }
        }

        if trigger_store_tier == Some(DurabilityTier::Durable) {
            if session_store_tier != Some(DurabilityTier::Durable) {
                return Err(EmbedError::DurableStorePeerRequired {
                    facet: "session store factory",
                });
            }
            if process_env_tier != Some(DurabilityTier::Durable) {
                return Err(EmbedError::DurableStorePeerRequired {
                    facet: "process execution environment store",
                });
            }
            if process_registry_tier == Some(DurabilityTier::Inline) {
                return Err(EmbedError::DurableStorePeerRequired {
                    facet: "process registry",
                });
            }
        }

        if effect_host_tier == Some(DurabilityTier::Durable) {
            if attachment_tier != Some(DurabilityTier::Durable) {
                return Err(EmbedError::DurableStorePeerRequired {
                    facet: "attachment store",
                });
            }
            if process_env_tier != Some(DurabilityTier::Durable) {
                return Err(EmbedError::DurableStorePeerRequired {
                    facet: "process execution environment store",
                });
            }
        }

        Ok(())
    }

    pub fn build(mut self) -> Result<LashCore> {
        let protocol_factory = self.protocol_factory.clone();
        if protocol_factory.is_none() && self.plugin_host.is_none() {
            return Err(EmbedError::MissingProtocolPlugin);
        }
        let provider_id = self
            .session_spec
            .provider_id
            .clone()
            .or_else(|| {
                self.provider
                    .as_ref()
                    .map(|provider| provider.kind().to_string())
            })
            .unwrap_or_default();
        let model = self
            .session_spec
            .model
            .clone()
            .ok_or(EmbedError::MissingModelSpec)?;

        let base_policy = SessionPolicy {
            provider_id,
            model,
            max_turns: self.session_spec.max_turns.flatten(),
            ..SessionPolicy::default()
        };
        let policy = self.session_spec.resolve_against(&base_policy);

        // Capture the store-peer tiers that live on builder fields before the
        // plugin stack is consumed below; the engine sweep happens after install.
        let session_store_tier = self.effective_session_store_tier();
        let trigger_store_tier = self
            .trigger_store
            .as_ref()
            .map(|store| store.durability_tier());
        let process_work_source = self
            .process_work_source
            .clone()
            .watched(self.process_event_sink.clone());
        let process_registry_tier = process_work_source
            .process_registry()
            .map(|registry| registry.durability_tier());

        let mut core = self.resolve_runtime_host_config()?;
        if let Some(provider) = self.provider.clone() {
            core.providers.provider_resolver =
                Arc::new(lash_core::SingleProviderResolver::new(provider));
        }
        let plugin_factories = if let Some(plugin_host) = self.plugin_host {
            plugin_host.factories().to_vec()
        } else {
            let mut factories = Vec::new();
            if !self.tool_providers.is_empty() {
                let spec = self
                    .tool_providers
                    .into_iter()
                    .fold(PluginSpec::new(), PluginSpec::with_tool_provider);
                factories.push(Arc::new(StaticPluginFactory::new("embed_tools", spec))
                    as Arc<dyn PluginFactory>);
            }
            factories.extend(self.plugin_stack.into_factories());
            factories
        };
        let default_plugin_host =
            build_plugin_host(protocol_factory.as_ref(), &plugin_factories, Vec::new())?;
        // Whether process lifecycle is available (a process registry is wired).
        // Threaded to every plugin host so core installs the same
        // plugin-contributed process engines wherever it rebuilds a runtime.
        let process_lifecycle_available = process_work_source.has_registry();
        // Install onto a throwaway clone purely to sweep every registered
        // engine's durability tier for the coherence check. `env.core` stays
        // free of plugin-contributed engines so that each runtime-construction
        // site (session open, queued-work drain, durable process worker)
        // installs them fresh onto a clean registry — keeping the unique-kind
        // enforcement in `try_with_engine` a genuine cross-factory check rather
        // than a self-collision on a registry that already carries them.
        let core_with_engines = default_plugin_host
            .install_process_engine_contributions(core.clone(), process_lifecycle_available)?;
        // Coherence runs after engines are installed so it can sweep every
        // registered engine's durability tier.
        Self::ensure_store_peer_coherence(
            session_store_tier,
            trigger_store_tier,
            process_registry_tier,
            &core_with_engines,
        )?;

        let process_registry = process_work_source.process_registry();

        // Resolve process work before the process source is moved into the
        // environment. The default inline driver's config is built
        // eagerly so a missing store factory fails loudly at build, not at
        // first open. It is built from the same single-protocol plugin host the
        // live runtime uses, so the worker can rebuild a runtime for a process.
        let process_work_driver = Self::resolve_process_work_driver(
            &process_work_source,
            &default_plugin_host,
            &core,
            process_lifecycle_available,
            // The worker rebuilds sessions with the same factory `build()` wires
            // below: `child_store_factory.or(store_factory)`.
            self.child_store_factory
                .as_ref()
                .or(self.store_factory.as_ref()),
            &policy,
            self.residency.unwrap_or_default(),
            self.trigger_store.as_ref(),
        )?;

        let live_replay_clock = Arc::clone(&core.clock);
        let mut env_builder = RuntimeEnvironment::builder()
            .with_plugin_host(Arc::new(default_plugin_host))
            .with_runtime_host_config(core);
        if let Some(process_registry) = process_registry.as_ref() {
            env_builder = env_builder.with_process_registry(Arc::clone(process_registry));
        }
        if let Some(residency) = self.residency {
            env_builder = env_builder.with_residency(residency);
        }
        if let Some(child_store_factory) = self
            .child_store_factory
            .as_ref()
            .or(self.store_factory.as_ref())
        {
            env_builder = env_builder.with_session_store_factory(Arc::clone(child_store_factory));
        }
        if let Some(trigger_store) = self.trigger_store.as_ref() {
            env_builder = env_builder.with_trigger_store(Arc::clone(trigger_store));
        }
        let live_replay_store = self.live_replay_store.take().unwrap_or_else(|| {
            Arc::new(InMemoryLiveReplayStore::with_clock(
                lash_core::InMemoryLiveReplayStoreConfig::default(),
                live_replay_clock,
            ))
        });
        let env = env_builder.build();
        let queued_work_driver = Self::resolve_queued_work_driver(
            &self.queued_work_source,
            env.clone(),
            policy.clone(),
            protocol_factory.clone(),
            Arc::new(plugin_factories.clone()),
            self.child_store_factory
                .as_ref()
                .or(self.store_factory.as_ref()),
            Arc::clone(&live_replay_store),
            process_lifecycle_available,
        );
        let work_driver = InlineWorkDriverSetup {
            process: process_work_driver,
            queued: queued_work_driver,
        };

        Ok(LashCore {
            env,
            policy,
            store_factory: self.store_factory,
            plugin_factories: Arc::new(plugin_factories),
            provider: self.provider,
            live_replay_store,
            protocol_factory,
            process_lifecycle_available,
            work_driver: Arc::new(InlineWorkDriverSlot::new(work_driver)),
        })
    }

    /// Decide how a built [`LashCore`] sources its process work driver.
    ///
    /// - no registry => nothing to run ([`ProcessWorkDriverSetup::None`]);
    /// - external driver wired => use it ([`ProcessWorkDriverSetup::External`]);
    /// - inline registry wired => lazily construct the default inline driver on first open. Its
    ///   [`DurableProcessWorkerConfig`] is built eagerly when a store factory is
    ///   present; without one the inline worker cannot rebuild session runtimes.
    // Mirrors the sibling `resolve_queued_work_driver`: a builder helper whose
    // inputs are the heterogeneous, all-required driver-resolution state and
    // have no cohesive sub-grouping.
    #[allow(clippy::too_many_arguments)]
    fn resolve_process_work_driver(
        process_work_source: &ProcessWorkSource,
        worker_plugin_host: &PluginHost,
        core: &RuntimeHostConfig,
        process_lifecycle_available: bool,
        store_factory: Option<&Arc<dyn SessionStoreFactory>>,
        policy: &SessionPolicy,
        residency: lash_core::Residency,
        trigger_store: Option<&Arc<dyn lash_core::TriggerStore>>,
    ) -> Result<ProcessWorkDriverSetup> {
        let (process_registry, process_change_hub) = match process_work_source {
            ProcessWorkSource::None => return Ok(ProcessWorkDriverSetup::None),
            ProcessWorkSource::External(driver) => {
                return Ok(ProcessWorkDriverSetup::External {
                    driver: driver.clone(),
                });
            }
            ProcessWorkSource::Inline { registry, hub } => (Arc::clone(registry), hub.clone()),
        };
        // The worker rebuilds a session runtime per process, so it needs a store
        // factory; without one the default runner could not execute anything, so
        // fail loudly rather than silently leave processes unexecuted.
        let Some(store_factory) = store_factory else {
            return Err(EmbedError::ProcessRegistryRequiresStoreFactory);
        };
        // The worker rebuilds with the same plugin host the live runtime uses,
        // including the protocol plugin that supplies the protocol session
        // capability. Install its plugin-contributed process engines onto a
        // clean copy of the base host — `core` deliberately carries none.
        let runtime_host = worker_plugin_host
            .install_process_engine_contributions(core.clone(), process_lifecycle_available)?;
        let phase_probe_slot = lash_core::runtime::RuntimeTurnPhaseProbeSlot::default();
        let mut config = DurableProcessWorkerConfig::new(
            Arc::new(worker_plugin_host.clone()),
            runtime_host,
            Arc::clone(store_factory),
            process_registry,
        )
        .with_session_policy(policy.clone())
        .with_trigger_store(trigger_store.cloned().unwrap_or_else(|| {
            Arc::new(lash_core::InMemoryTriggerStore::with_clock(Arc::clone(
                &core.clock,
            )))
        }))
        .with_residency(residency)
        .with_turn_phase_probe_slot(phase_probe_slot);
        if let Some(hub) = process_change_hub {
            config = config.with_change_hub(hub);
        }
        let config = Box::new(config);
        Ok(ProcessWorkDriverSetup::LazyDefault { config })
    }

    #[allow(clippy::too_many_arguments)]
    fn resolve_queued_work_driver(
        queued_work_source: &QueuedWorkSource,
        env: RuntimeEnvironment,
        policy: SessionPolicy,
        protocol_factory: Option<Arc<dyn PluginFactory>>,
        plugin_factories: Arc<Vec<Arc<dyn PluginFactory>>>,
        store_factory: Option<&Arc<dyn SessionStoreFactory>>,
        live_replay_store: Arc<dyn LiveReplayStore>,
        process_lifecycle_available: bool,
    ) -> QueuedWorkDriverSetup {
        match queued_work_source {
            QueuedWorkSource::None => QueuedWorkDriverSetup::None,
            QueuedWorkSource::External(driver) => QueuedWorkDriverSetup::External {
                driver: driver.clone(),
            },
            QueuedWorkSource::LazyDefault => match store_factory {
                Some(store_factory) => QueuedWorkDriverSetup::LazyDefault {
                    config: Arc::new(InlineQueuedWorkRunConfig::new(
                        env,
                        policy,
                        protocol_factory,
                        plugin_factories,
                        Arc::clone(store_factory),
                        live_replay_store,
                        process_lifecycle_available,
                    )),
                },
                None => QueuedWorkDriverSetup::None,
            },
        }
    }

    pub fn advanced(self) -> AdvancedLashCoreBuilder {
        AdvancedLashCoreBuilder { builder: self }
    }

    pub fn process_registry(mut self, process_registry: Arc<dyn ProcessRegistry>) -> Self {
        self.process_work_source = ProcessWorkSource::Inline {
            registry: process_registry,
            hub: None,
        };
        self
    }

    /// Install a best-effort, host-facing [`ProcessEventSink`] on the inline
    /// process registry.
    ///
    /// Each appended process event is pushed to the sink after its durable
    /// write, in per-process append order. This is freshness, not truth: it
    /// never buffers or retries, terminal events are not emitted through it
    /// (observe completion via the await seam), and consumers reconcile from
    /// the durable event log. See [`ProcessEventSink`] for the full contract.
    ///
    /// Applies to the inline registry path ([`Self::process_registry`]); a host
    /// that supplies its own [`ProcessWorkDriver`](lash_core::ProcessWorkDriver)
    /// installs the sink through the driver's constructor instead.
    ///
    /// [`ProcessEventSink`]: lash_core::ProcessEventSink
    pub fn process_event_sink(mut self, sink: Arc<dyn lash_core::ProcessEventSink>) -> Self {
        self.process_event_sink = Some(sink);
        self
    }

    pub fn trigger_store(mut self, store: Arc<dyn lash_core::TriggerStore>) -> Self {
        self.trigger_store = Some(store);
        self
    }

    /// Configure an externally owned process work runner.
    ///
    /// Durable hosts construct a [`ProcessWorkDriver`] from the same process
    /// registry and wake handle used by their deployment runner, then pass it
    /// here. The driver registry becomes the core's process registry and no
    /// inline runner is spawned.
    pub fn process_work_driver(mut self, driver: ProcessWorkDriver) -> Self {
        self.process_work_source = ProcessWorkSource::External(driver);
        self
    }

    /// Configure an externally owned queued-work driver.
    pub fn queued_work_driver(mut self, driver: QueuedWorkDriver) -> Self {
        self.queued_work_source = QueuedWorkSource::External(driver);
        self
    }

    pub fn disable_queued_work_driver(mut self) -> Self {
        self.queued_work_source = QueuedWorkSource::None;
        self
    }
}

pub(crate) fn build_plugin_host(
    protocol_factory: Option<&Arc<dyn PluginFactory>>,
    common_factories: &[Arc<dyn PluginFactory>],
    extra_factories: Vec<Arc<dyn PluginFactory>>,
) -> Result<PluginHost> {
    let mut factories = Vec::with_capacity(
        usize::from(protocol_factory.is_some()) + common_factories.len() + extra_factories.len(),
    );
    if let Some(protocol_factory) = protocol_factory {
        factories.push(Arc::clone(protocol_factory));
    }
    factories.extend(common_factories.iter().cloned());
    factories.extend(extra_factories);
    Ok(PluginHost::new(factories))
}

impl PromptLayerSink for LashCoreBuilder {
    fn prompt_layer_mut(&mut self) -> &mut PromptLayer {
        self.prompt.get_or_insert_with(PromptLayer::new)
    }
}

pub struct AdvancedLashCoreBuilder {
    builder: LashCoreBuilder,
}

impl AdvancedLashCoreBuilder {
    pub fn runtime_host_config(mut self, core: lash_core::RuntimeHostConfig) -> Self {
        self.builder.runtime_host_config = Some(core);
        self
    }

    pub fn plugin_host(mut self, plugin_host: PluginHost) -> Self {
        self.builder.plugin_host = Some(plugin_host);
        self
    }

    pub fn build(self) -> Result<LashCore> {
        self.builder.build()
    }
}