brep_render/

runner.rs

//! The history-run seam — the async RUN machine behind a trait, mirroring the
//! platform-seam shape of `brep-app/src/store.rs`'s `ModelStore` (a trait with
//! impls behind it, async surfaced via a poll idiom).
//!
//! A history run is split SUBMIT → POLL/APPLY: [`HistoryRunner::submit_run`]
//! kicks off a run tagged with a monotonic generation, and the completed
//! [`RunReply`] is drained later via [`HistoryRunner::poll_run`]. The runner OWNS
//! the [`SceneRunner`](crate::pipeline::SceneRunner) — so a future thread/worker
//! impl owns the resident registry that `execute_history` populates — and holds
//! the delta baseline across reruns.
//!
//! This slice ships the DEFAULT [`InlineRunner`]: it runs on `submit_run` and
//! stashes the reply for an immediate `poll_run`, so the run stays synchronous
//! and byte-identical to the pre-seam in-process run. A native-thread impl (M2b)
//! and a wasm-worker impl (M3) slot in behind the SAME trait — `submit_run`
//! defers the work and `poll_run` surfaces it a frame (or many) later, so the
//! `EngineState::pump` caller never changes.

/// A completed history run, tagged with the [`generation`](Self::generation) it
/// was submitted under so the applier can drop stale replies (a newer run that
/// finished first). The [`output`](Self::output) is the [`SceneRunner`] delta to
/// apply to the display scene.
///
/// [`SceneRunner`]: crate::pipeline::SceneRunner
#[derive(Debug, Clone, serde::Serialize, serde::Deserialize)]
pub struct RunReply {
    /// The monotonic generation this run was submitted under.
    pub generation: u64,
    /// The delta snapshot + report the run produced.
    pub output: crate::pipeline::RunOutput,
}

/// A feature about to EXECUTE inside an in-flight run (cached replays are
/// instant and are not reported): which one, of how many, under which
/// generation. Posted by the runner before the kernel starts the feature, so
/// the UI can name what it is waiting on — and, after a cancel, what it was
/// waiting on.
#[derive(Debug, Clone, PartialEq, Eq, serde::Serialize, serde::Deserialize)]
pub struct RunProgress {
    /// The generation of the run this belongs to (see [`RunReply::generation`]).
    pub generation: u64,
    /// Zero-based position of the feature in the request.
    pub index: usize,
    /// The request's feature count.
    pub total: usize,
    pub feature_id: String,
    pub feature_type: String,
}

/// A STEP text to PROBE for product structure on the runner — the parse that
/// `brep_kernel::read_step_assembly` performs, which builds every product's
/// bodies and takes seconds on a real assembly (8.3 s natively for a 5 MB,
/// 140-product file), so it must not run on the browser's main thread.
#[derive(Debug, Clone, serde::Serialize, serde::Deserialize)]
pub struct StepProbeRequest {
    pub id: u64,
    pub text: String,
}

/// The probe's answer: the parsed assembly (`Some`), no structure (`None`),
/// or a parse failure. The assembly crosses back to the main side whole — its
/// JSON is large (74 MB for the file above) but the trip costs a third of a
/// second against the seconds the parse took.
#[derive(Debug, Clone, serde::Serialize, serde::Deserialize)]
pub struct StepProbeReply {
    pub id: u64,
    pub result: Result<Option<brep_kernel::StepAssembly>, String>,
}

/// Which exact measurement a [`MeasureQuery`] wants, mirroring the object-info
/// kinds ([`crate::metadata`]): a whole solid, one named face, or one named edge.
#[derive(Debug, Clone, Copy, PartialEq, Eq, serde::Serialize, serde::Deserialize)]
pub enum MeasureKind {
    Solid,
    Face,
    Edge,
    /// A whole-solid CHECK for `model_inspect`: the kernel's topology
    /// validation issues and the exact volume, read from the runner's warm
    /// registry instead of a main-thread re-execution of the history.
    Inspect,
}

/// A per-object MEASUREMENT request routed to the runner (which owns the warm
/// registry). The runner resolves `owner` to its resident handle and measures by
/// [`kind`](Self::kind); the reply is the object-info JSON fragment MINUS the
/// main-injected `name`/`creatingFeature` fields. Tagged with a monotonic
/// [`id`](Self::id) so the main side can pair the reply with its pending request.
#[derive(Debug, Clone, serde::Serialize, serde::Deserialize)]
pub struct MeasureQuery {
    /// Monotonic request id (main pairs the reply back by it).
    pub id: u64,
    /// The measurement to run.
    pub kind: MeasureKind,
    /// The OWNING solid name (a solid is its own owner; a face/edge names its solid).
    pub owner: String,
    /// The face/edge NAME to measure (ignored for a whole-solid query).
    pub entity: String,
    /// The density (mass per mm³) to scale a solid's weight (ignored for face/edge).
    pub density: f64,
}

/// A completed [`MeasureQuery`]: the object-info measurement fields as a JSON
/// fragment (WITHOUT `name`/`creatingFeature`, which the main thread injects from
/// its eager provenance), tagged with the request [`id`](Self::id).
#[derive(Debug, Clone, serde::Serialize, serde::Deserialize)]
pub struct MeasureReply {
    /// The request id this answers.
    pub id: u64,
    /// The measurement JSON fragment (see `measure_json`).
    pub result: String,
}

/// A request for the B-rep TOPOLOGY of resident solids, by the handle each
/// display was tessellated from. The drawing sheet's exact hidden-line pass
/// reads faces and edges, and the resident registry that holds them is
/// thread-local to the runner, so the main side asks for exactly the solids a
/// placement draws and does not already hold. Nothing else ever asks, so a
/// document with no sheet never pays for the topology crossing.
#[derive(Debug, Clone, serde::Serialize, serde::Deserialize)]
pub struct TopologyRequest {
    /// Monotonic request id (main pairs the reply back by it).
    pub id: u64,
    /// `(solid name, resident handle)` per solid wanted.
    pub solids: Vec<(String, u32)>,
}

/// A completed [`TopologyRequest`]: a clone of every requested solid the
/// registry still holds, `(name, handle, solid)`. A handle the registry no
/// longer holds (a later run freed it) is left out.
#[derive(Debug, Clone, serde::Serialize, serde::Deserialize)]
pub struct TopologyReply {
    /// The request id this answers.
    pub id: u64,
    pub solids: Vec<(String, u32, brep_kernel::BrepSolid)>,
}

/// Answer a topology request against the resident registry of the thread this
/// runs on. Shared by every runner.
fn topology_reply(request: TopologyRequest) -> TopologyReply {
    let solids = request
        .solids
        .into_iter()
        .filter_map(|(name, handle)| {
            brep_kernel::registered_solid_clone(handle)
                .ok()
                .map(|solid| (name, handle, solid))
        })
        .collect();
    TopologyReply { id: request.id, solids }
}

/// A drawing sheet's exact hidden-line pass for ONE placement, handed to the
/// runner so the UI thread never runs it (see
/// [`crate::sheets::project::LinesJob`]). The job names the runner's own
/// resident solids by handle and content fingerprint, so nothing crosses the
/// seam but the question and the lines.
#[derive(Debug, Clone, serde::Serialize, serde::Deserialize)]
pub struct SheetLinesRequest {
    /// Monotonic request id (main pairs the reply back by it).
    pub id: u64,
    pub job: crate::sheets::project::LinesJob,
}

/// A completed [`SheetLinesRequest`]: the placement's lines relative to its
/// position, or why the runner could not draw them (a handle its registry no
/// longer holds, or holds different geometry under).
#[derive(Debug, Clone, serde::Serialize, serde::Deserialize)]
pub struct SheetLinesReply {
    /// The request id this answers.
    pub id: u64,
    pub key: String,
    pub lines: Result<crate::sheets::project::ExactLines, String>,
}

/// Answer a sheet-lines request against the resident registry of the thread
/// this runs on. Shared by every runner.
fn sheet_lines_reply(request: SheetLinesRequest) -> SheetLinesReply {
    SheetLinesReply {
        id: request.id,
        lines: crate::sheets::project::run_lines_job(&request.job),
        key: request.job.key,
    }
}

/// ONE CAM operation's generation, off the UI thread (the CAM workbench's
/// Generate). The job carries everything the generator reads as plain data:
/// the operation, its setup and the document's tools (the shared model, by
/// value), and the resident solids it machines by `(name, handle)`, which
/// the runner clones out of its registry and tessellates through the CAM
/// kernel adapter. The main side submits ONE operation per job and the next
/// when its reply lands, so a cancel between operations is immediate on
/// every platform; inside a job the native thread's cancel flag ends it at
/// the generator's next work chunk, and the browser worker — which cannot
/// read a message while it is inside a job — finishes the operation, whose
/// reply the main side then drops as cancelled. A document `Reset` drops
/// nothing here: the job holds no parked state across commands.
#[derive(Debug, Clone, serde::Serialize, serde::Deserialize)]
pub struct CamJob {
    /// Monotonic job id (main pairs the reply and the progress back by it).
    pub id: u64,
    pub operation: brep_cam::model::Operation,
    pub setup: brep_cam::model::Setup,
    pub tools: Vec<brep_cam::model::Tool>,
    /// The bodies the setup machines or protects: `(solid name, resident handle)`.
    pub solids: Vec<(String, u32)>,
    /// The chordal tolerance the bodies are tessellated at, in model units.
    pub chord_tolerance: f64,
    /// Work units per progress / cancel check (the generator's chunk).
    pub budget_chunk: u64,
    /// The sketch curves the operation's chains name, `(sketch id, geometry
    /// id, curve)` in model space, from the last history run (the runner's
    /// registry holds solids, not sketches).
    #[serde(default)]
    pub chain_curves: Vec<(String, String, brep_kernel::NurbsCurve)>,
    /// The sketch profiles the operation's chains name, `(sketch id, profile)`.
    #[serde(default)]
    pub chain_profiles: Vec<(String, brep_kernel::SketchProfile)>,
    /// The setup's machine, resolved (its id is `setup.machine`): the
    /// generator's kinematics context for rotary-capable strategies.
    #[serde(default)]
    pub machine: Option<brep_cam::model::Machine>,
    /// Exact automatically programmed geometry and associative feature identity.
    #[serde(default)]
    pub autoprogram: Option<brep_cam::autoprogram::binding::Binding>,
    /// The setup's operations BEFORE this one, in program order, each with
    /// its current toolpath (`None`: not generated, failed or stale): the
    /// runner replays them into the stock this operation starts from (lane C7).
    #[serde(default)]
    pub earlier: Vec<(brep_cam::model::Operation, Option<brep_cam::model::Toolpath>)>,
    /// The setups this one continues from (`Stock::FromRest`), oldest first.
    #[serde(default)]
    pub previous_setups: Vec<brep_cam::SetupHistory>,
    /// A multi-axis finish's designated three-axis source, generated and
    /// current (lane C17): the generator tilts this path.
    #[serde(default)]
    pub source: Option<brep_cam::program::OperationInput>,
    /// The designated source's definition when it has no current result: the
    /// worker generates it on this job's bodies first.
    #[serde(default)]
    pub source_operation: Option<brep_cam::model::Operation>,
}

/// A completed [`CamJob`]: the toolpath, or why the operation could not be
/// generated (the generator's own words), and how much work it took.
#[derive(Debug, Clone, serde::Serialize, serde::Deserialize)]
pub struct CamReply {
    /// Certified setup-Z meridian, carried with the generated result for axial replay.
    #[serde(default, skip_serializing_if = "Option::is_none")]
    pub turning_profile: Option<brep_cam::turning::profile::TurningProfile>,
    /// The stock the operation's setup starts from, as this job resolved it
    /// (the simulation loads it; absent when the job built no pre-operation stock).
    #[serde(default, skip_serializing_if = "Option::is_none")]
    pub setup_start: Option<brep_cam::SetupStart>,
    pub id: u64,
    pub operation: String,
    pub toolpath: Result<brep_cam::model::Toolpath, String>,
    pub work_units: u64,
    /// Whether the job ended on the cancel flag rather than on its own.
    pub cancelled: bool,
}

/// A generation's progress, posted from inside the job at its stage and
/// chunk boundaries.
#[derive(Debug, Clone, serde::Serialize, serde::Deserialize)]
pub struct CamProgress {
    pub id: u64,
    pub operation: String,
    pub phase: String,
    pub message: String,
    pub current: u64,
    pub total: u64,
}

/// A CAM SIMULATION request (lane C17b). The runner keeps ONE simulation
/// session resident (its stock and checkpoints live runner-side; a thread
/// local, so the native thread and the wasm worker hold it the same way);
/// the main side loads it once and then asks it to advance in bounded
/// chunks, so a cancel between chunks is immediate on every platform and a
/// chunk stops between two motions on the native thread.
#[derive(Debug, Clone, serde::Serialize, serde::Deserialize)]
pub enum CamSimRequest {
    /// Make `stock` the session's stock over `timeline`, each range cut by its cutter.
    Load {
        timeline: brep_cam::multiaxis::sim::Timeline,
        stock: brep_cam::multiaxis::sim::StockModel,
        ranges: Vec<brep_cam::multiaxis::sim::RangeCutter>,
        options: brep_cam::multiaxis::sim::DriverOptions,
        /// The machine whose chain applies rotary positioning (C7's
        /// `*_on_machine`); none refuses any nonzero rotary word.
        #[serde(default)]
        machine: Option<brep_cam::model::Machine>,
    },
    /// Advance (or rewind and replay) toward `target` applied motions, at
    /// most `budget` motions. `stock: true` returns the stock whenever its
    /// version differs from `known_version` (the one the caller holds), so
    /// a chunk whose reply the caller dropped is still made good.
    Advance { target: usize, budget: usize, stock: bool, known_version: u64 },
    /// Forget the session.
    Drop,
}

/// One simulation command, paired back by `(session, seq)`.
#[derive(Debug, Clone, serde::Serialize, serde::Deserialize)]
pub struct CamSimJob {
    pub session: u64,
    pub seq: u64,
    pub request: CamSimRequest,
}

/// The session's state after a [`CamSimJob`].
#[derive(Debug, Clone, serde::Serialize, serde::Deserialize)]
pub struct CamSimReply {
    pub session: u64,
    pub seq: u64,
    pub applied: usize,
    pub version: u64,
    pub removed_volume: f64,
    pub stock_volume: f64,
    pub unsupported: Vec<usize>,
    pub warnings: Vec<(usize, brep_cam::model::Diagnostic)>,
    /// The stock, when asked and it changed since the job started.
    pub stock: Option<brep_cam::multiaxis::sim::StockModel>,
    /// The target was reached (`false`: the budget ran out or it stopped).
    pub reached: bool,
    /// The chunk stopped on the cancel flag (between two motions).
    pub cancelled: bool,
    pub error: Option<String>,
}

/// A simulation chunk's progress, posted between motions.
#[derive(Debug, Clone, serde::Serialize, serde::Deserialize)]
pub struct CamSimProgress {
    pub session: u64,
    pub seq: u64,
    pub applied: usize,
    pub target: usize,
}

/// The runner-side simulation session.
struct CamSimSession {
    session: u64,
    timeline: brep_cam::multiaxis::sim::Timeline,
    ranges: Vec<brep_cam::multiaxis::sim::RangeCutter>,
    driver: brep_cam::multiaxis::sim::SimDriver,
}

thread_local! {
    static CAM_SIM: std::cell::RefCell<Option<CamSimSession>> = const { std::cell::RefCell::new(None) };
}

/// Forget the resident simulation (a document switch).
fn cam_sim_clear() {
    CAM_SIM.with(|c| *c.borrow_mut() = None);
}

thread_local! {
    /// Pre-operation stock states of this document session (lane C7): a
    /// regenerated operation replays only from the longest unchanged prefix.
    static PRE_OP_STOCK: std::cell::RefCell<brep_cam::PreOpStockCache> = std::cell::RefCell::new(brep_cam::PreOpStockCache::new(16));
}

/// Forget the pre-operation stock states (a document switch).
fn pre_op_stock_clear() {
    PRE_OP_STOCK.with(|c| c.borrow_mut().clear());
}

fn cam_sim_reply(job: CamSimJob, post: &mut dyn FnMut(Reply) -> bool) -> CamSimReply {
    let (session, seq) = (job.session, job.seq);
    let empty = |error: Option<String>| CamSimReply {
        session,
        seq,
        applied: 0,
        version: 0,
        removed_volume: 0.0,
        stock_volume: 0.0,
        unsupported: Vec::new(),
        warnings: Vec::new(),
        stock: None,
        reached: false,
        cancelled: false,
        error,
    };
    match job.request {
        CamSimRequest::Drop => {
            cam_sim_clear();
            empty(None)
        }
        CamSimRequest::Load { timeline, stock, ranges, options, machine } => match brep_cam::multiaxis::sim::SimDriver::new(stock, options) {
            Ok(driver) => {
                let driver = driver.with_chain(brep_cam::multiaxis::sim::sim_chain(machine.as_ref()));
                let reply = CamSimReply {
                    applied: driver.applied,
                    version: driver.version,
                    stock_volume: driver.stock.volume(),
                    reached: true,
                    ..empty(None)
                };
                CAM_SIM.with(|c| *c.borrow_mut() = Some(CamSimSession { session, timeline, ranges, driver }));
                reply
            }
            Err(e) => empty(Some(e.to_string())),
        },
        CamSimRequest::Advance { target, budget, stock, known_version } => CAM_SIM.with(|c| {
            let mut guard = c.borrow_mut();
            let Some(sim) = guard.as_mut().filter(|s| s.session == session) else {
                return empty(Some("no simulation session is loaded on the runner".into()));
            };
            let mut cancelled = false;
            let tolerance = brep_cam::Tolerance::default();
            let outcome = sim.driver.advance_ranges(&sim.timeline, &sim.ranges, target, budget, &tolerance, &mut |applied| {
                let keep = post(Reply::CamSimProgress(CamSimProgress { session, seq, applied, target }));
                if !keep {
                    cancelled = true;
                }
                keep
            });
            let d = &sim.driver;
            let (reached, error) = match outcome {
                Ok(o) => (o == brep_cam::multiaxis::sim::AdvanceOutcome::Reached, None),
                Err(e) => (false, Some(e.to_string())),
            };
            CamSimReply {
                session,
                seq,
                applied: d.applied,
                version: d.version,
                removed_volume: d.removed_volume,
                stock_volume: d.stock.volume(),
                unsupported: d.unsupported.clone(),
                warnings: d.warnings.clone(),
                stock: (stock && d.version != known_version).then(|| d.stock.clone()),
                reached,
                cancelled,
                error,
            }
        }),
    }
}

/// A progress sink that posts through the driver's reply channel and turns
/// a driver that says "stop" into the generator's cancel.
struct CamSink<'a> {
    id: u64,
    operation: String,
    token: brep_cam::CancelToken,
    post: &'a mut dyn FnMut(Reply) -> bool,
}

impl brep_cam::ProgressSink for CamSink<'_> {
    fn progress(&mut self, progress: &brep_cam::Progress) {
        if std::env::var_os("BREP_CAM_DEBUG").is_some() {
            eprintln!("cam job {} progress: {} {}/{}", self.operation, progress.phase, progress.current, progress.total);
        }
        let keep_going = (self.post)(Reply::CamProgress(CamProgress {
            id: self.id,
            operation: self.operation.clone(),
            phase: progress.phase.clone(),
            message: progress.message.clone(),
            current: progress.current,
            total: progress.total,
        }));
        if !keep_going {
            if std::env::var_os("BREP_CAM_DEBUG").is_some() {
                eprintln!("cam job {}: the driver said stop; cancelling", self.operation);
            }
            self.token.cancel();
        }
    }
}

/// The most triangles a CAM job's part mesh may have (the triangle index and
/// the drop-cutter queries scale with it).
pub const CAM_TRIANGLE_BUDGET: usize = 4_000_000;

/// Run one CAM job against the resident registry of this thread.
fn cam_generate_reply(job: CamJob, post: &mut dyn FnMut(Reply) -> bool) -> CamReply {
    use brep_cam::kernel_adapter::{machine_snapshot, revolved_faces, BodyInput};
    use brep_cam::{Runner, Tolerance, TreeIndex, TreeOptions, WorkBudget};
    let operation = job.operation.id.as_str().to_string();
    let token = brep_cam::CancelToken::new();
    let mut sink = CamSink { id: job.id, operation: operation.clone(), token: token.clone(), post };
    let mut certified_turning_profile = None;
    let mut setup_start = None;
    let mut outcome = || -> Result<(brep_cam::model::Toolpath, u64), String> {
        // The resident bodies, cloned out of the registry by handle.
        let mut bodies: Vec<(String, brep_kernel::BrepSolid)> = Vec::new();
        for (name, handle) in &job.solids {
            let solid = brep_kernel::registered_solid_clone(*handle)
                .map_err(|e| format!("body `{name}` is not resident on the runner ({e}); run the history again"))?;
            bodies.push((name.clone(), solid));
        }
        let diagonal = bodies
            .iter()
            .filter_map(|(_, s)| brep_cam::kernel_adapter::body_bounds(s, job.chord_tolerance).ok())
            .fold(brep_cam::model::Bounds3::empty(), |acc, b| acc.union(&b))
            .diagonal();
        let tolerance = if diagonal.is_finite() && diagonal > 0.0 { Tolerance::scaled_for_diagonal(diagonal) } else { Tolerance::default() };
        // The snapshot holds the SETUP's bodies and the operation's own: an
        // operation's target or protected body outside the setup's list is
        // still machined or avoided, so it joins the snapshot here.
        let mut snapshot_setup = job.setup.clone();
        for name in &job.operation.targets.target_solids {
            if !snapshot_setup.targets.iter().any(|t| &t.solid == name) {
                snapshot_setup.targets.push(brep_cam::model::TargetRef { solid: name.clone(), face: None });
            }
        }
        for name in &job.operation.targets.protected_solids {
            let listed = snapshot_setup.targets.iter().chain(snapshot_setup.protected.iter()).any(|t| &t.solid == name);
            if !listed {
                snapshot_setup.protected.push(brep_cam::model::TargetRef { solid: name.clone(), face: None });
            }
        }
        let (mesh, unresolved) = machine_snapshot(&snapshot_setup, job.chord_tolerance, tolerance, |name| bodies.iter().find(|(n, _)| n == name).map(|(_, s)| s))
            .map_err(|e| format!("{e}"))?;
        if !unresolved.is_empty() {
            return Err(format!("the setup names bodies the model does not have: {}", unresolved.join(", ")));
        }
        if std::env::var_os("BREP_CAM_DEBUG").is_some() {
            eprintln!("cam job {}: {} bodies, snapshot {} faces / {} triangles, bounds {:?}", operation, bodies.len(), mesh.faces.len(), mesh.triangles.len(), mesh.bounds);
        }
        // The mesh is tessellated at the operation's own tolerance (a quarter
        // of it); a part that needs more triangles than the generators can
        // carry is refused by name, never coarsened behind the user's back.
        if mesh.triangles.len() > CAM_TRIANGLE_BUDGET {
            return Err(format!(
                "the part mesh needs {} triangles at a chord of {}, over the budget of {CAM_TRIANGLE_BUDGET}; raise the operation's tolerance or machine fewer bodies at once",
                mesh.triangles.len(),
                job.chord_tolerance
            ));
        }
        let index = TreeIndex::build(&mesh, TreeOptions::default());
        let mut runner = Runner::new(token.clone(), &mut sink, WorkBudget::new(job.budget_chunk.max(1))).with_operation(operation.clone());
        // Drilling reads the recognised holes of the target bodies.
        let holes = if matches!(job.operation.strategy, brep_cam::model::Strategy::Drill(_)) {
            let mut carriers = Vec::new();
            for (name, solid) in &bodies {
                if job.setup.targets.iter().any(|t| t.solid == *name) || job.operation.targets.target_solids.contains(name) {
                    let body = BodyInput { name, solid, protected_only: false };
                    carriers.extend(revolved_faces(&body, &job.setup));
                }
            }
            brep_cam::holes::recognize(&carriers, &mesh, tolerance, &mut runner).map_err(|e| e.to_string())?.holes
        } else {
            Vec::new()
        };
        // Frozen geometry is valid only for the exact bodies it was planned
        // against. A body edit re-recognises by face identity and XY dimensions,
        // preserving depth associativity without choosing a different feature.
        let mut effective_operation = job.operation.clone();
        let mut automatic_geometry = None;
        let mut rebound = false;
        if let Some(binding) = &job.autoprogram {
            let tool = job.tools.iter().find(|t| t.id == job.operation.tool).ok_or("automatic programming tool is missing")?;
            binding.validate_inputs(&job.operation, &job.setup, tool)?;
            let fingerprints: std::collections::BTreeMap<_, _> = bodies.iter().map(|(name, solid)| (name.clone(), crate::scene::brep_fingerprint(solid))).collect();
            if fingerprints == binding.body_fingerprints {
                automatic_geometry = Some(binding.geometry.clone());
            } else {
                let recognized = brep_cam::autoprogram::binding::recognize_bodies(&bodies, &job.setup, &mesh, job.chord_tolerance, tolerance, &mut runner).map_err(|e| e.to_string())?;
                let model_bounds = bodies.iter().filter(|(name, _)| job.setup.targets.iter().any(|t| &t.solid == name))
                    .filter_map(|(_, s)| brep_cam::kernel_adapter::body_bounds(s, job.chord_tolerance).ok())
                    .fold(brep_cam::model::Bounds3::empty(), |a, b| a.union(&b));
                let stock_bounds = match &job.setup.stock {
                    brep_cam::model::Stock::FromSolid { solid } => bodies.iter().find(|(name, _)| name == solid).and_then(|(_, body)| brep_cam::kernel_adapter::body_bounds(body, job.chord_tolerance).ok()),
                    _ => job.setup.stock.model_bounds(&model_bounds),
                };
                let stock_top = stock_bounds.map(|b| job.setup.model_to_machine.apply_bounds(&b).max.z);
                let (op, geometry) = binding.rebind_with_mesh(&recognized, &mesh, &job.operation, &job.setup, &job.tools, job.machine.as_ref(), stock_top, tolerance)?;
                effective_operation = op;
                automatic_geometry = Some(geometry);
                rebound = true;
            }
        }
        let resolved_planar = match &automatic_geometry { Some(brep_cam::autoprogram::OperationGeometry::Planar(p)) => Some((&effective_operation.id, p)), _ => None };
        let holes = match &automatic_geometry { Some(brep_cam::autoprogram::OperationGeometry::Holes(h)) => h.as_slice(), _ => holes.as_slice() };
        // Lane C7: the stock as it stands before this operation (the setup's
        // earlier operations replayed; a FromRest setup carried from the one it
        // continues from). Unavailable: a named warning on the operation, and the
        // linkers keep above the conservative material top. Never the raw stock.
        let mut pre_op_warning = None;
        // Automatic axial live contouring uses conservative planar links and
        // does not consume the milling stock cache. Replaying a preceding
        // turning operation into that cache is both unused and inappropriate.
        let live_contour = matches!(job.operation.strategy, brep_cam::Strategy::Contour2D(_) | brep_cam::Strategy::Trace(_))
            && job.operation.live_tool.unwrap_or(true)
            && job.machine.as_ref().is_some_and(|m| matches!(m.kind, brep_cam::MachineKind::MillTurn { .. }));
        let pre_op = if !live_contour && brep_cam::uses_pre_op_stock(&job.operation.strategy, job.machine.as_ref()) {
            let fallback = job.operation.targets.target_solids.clone();
            let request = brep_cam::JobStock {
                setup: &job.setup,
                machine: job.machine.as_ref(),
                tools: &job.tools,
                mesh: &mesh,
                fallback_targets: &fallback,
                earlier: &job.earlier,
                previous: &job.previous_setups,
                tolerance,
            };
            match PRE_OP_STOCK.with(|c| brep_cam::job_stock(&mut c.borrow_mut(), &request, &mut runner)) {
                Ok(result) => Some(result),
                Err(brep_cam::PreOpStockError::Cancelled) => return Err("cancelled".to_string()),
                Err(error) => {
                    pre_op_warning = Some(brep_cam::unavailable_warning(&error));
                    None
                }
            }
        } else {
            None
        };
        let input = brep_cam::dispatch::GenerateInput {
            operation: &effective_operation,
            setup: &job.setup,
            tools: &job.tools,
            mesh: &mesh,
            index: Some(&index),
            tolerance,
            holes,
        };
        // Picked chains resolve by identity against the bodies, sketch curves
        // and profiles the job carries (C20's KernelChainGeometry).
        let solid_refs: Vec<(&str, &brep_kernel::BrepSolid)> = bodies.iter().map(|(n, s)| (n.as_str(), s)).collect();
        let curve_refs: Vec<(&str, &str, &brep_kernel::NurbsCurve)> = job.chain_curves.iter().map(|(s, g, c)| (s.as_str(), g.as_str(), c)).collect();
        let profile_refs: Vec<(&str, &brep_kernel::SketchProfile)> = job.chain_profiles.iter().map(|(s, p)| (s.as_str(), p)).collect();
        let chain_geometry = brep_cam::dispatch::chains::KernelChainGeometry { solids: &solid_refs, curves: &curve_refs, profiles: &profile_refs };
        let is_turning = matches!(job.operation.strategy, brep_cam::Strategy::TurnFace(_) | brep_cam::Strategy::TurnProfile(_));
        let mut turning_carriers = Vec::new();
        let turning_tool = if is_turning {
            let tool = job.tools.iter().find(|t| t.id == job.operation.tool).ok_or("turning tool is missing")?;
            if tool.turning_geometry.is_none() { return Err(format!("tool {} has no insert geometry", tool.id)); }
            if job.setup.turning_stick_out.is_none() { return Err("setup has no stick-out".into()); }
            let targets: std::collections::BTreeSet<_> = job.setup.targets.iter().map(|t| t.solid.as_str()).collect();
            if targets.len() != 1 || job.operation.targets.target_solids.iter().any(|n| !targets.contains(n.as_str())) {
                return Err("turning requires one exact setup solid and matching operation targets".into());
            }
            let name = *targets.iter().next().unwrap();
            let solid = bodies.iter().find(|(n, _)| n == name).map(|(_, s)| s).ok_or("turning setup solid is missing")?;
            if !job.machine.as_ref().is_some_and(|m| matches!(m.kind, brep_cam::MachineKind::Lathe | brep_cam::MachineKind::MillTurn { .. })) {
                return Err("turning envelope requires a defined lathe spindle axis".into());
            }
            certified_turning_profile = Some(match brep_cam::kernel_adapter::turning_faces(&BodyInput { name, solid, protected_only: false }, &job.setup, tolerance) {
                Ok(carriers) => {
                    turning_carriers = carriers;
                    brep_cam::turning::profile::extract(&turning_carriers, &mesh, job.operation.tolerance * 0.125, &mut runner)
                }
                Err(_) => brep_cam::turning::envelope::extract(&mesh, job.chord_tolerance, &mut runner),
            }.map_err(|e| e.to_string())?);
            Some(tool)
        } else { None };
        let turning = turning_tool.map(|tool| brep_cam::dispatch::TurningInput {
            tool_id: &tool.id, tool_geometry: tool.turning_geometry.as_ref().unwrap(),
            carriers: &turning_carriers, profile: certified_turning_profile.as_ref(), contour: None,
            stick_out: job.setup.turning_stick_out.unwrap(), groove_center_z: None, thread_radius: None,
        });
        let context = brep_cam::dispatch::GenerateContext {
            turning: turning.as_ref(),
            chain_geometry: Some(&chain_geometry),
            machine: job.machine.as_ref(),
            resolved_planar,
            rest_stock: pre_op.as_ref().map(|r| &r.stock.grid),
            pre_op_stock: pre_op.as_ref().map(|r| &r.stock.envelope),
            source: job.source.as_ref(),
            source_operation: job.source_operation.as_ref(),
            ..Default::default()
        };
        let mut path = brep_cam::dispatch::generate_with_context(&input, &context, &mut runner).map_err(|e| e.to_string())?;
        if rebound { path.report.warn(brep_cam::model::Diagnostic::new("autoprogram-re-recognised", "re-recognised after model change")); }
        if let Some(warning) = pre_op_warning {
            // First, so a reader finds it at warnings[0] whenever it is there.
            path.report.warn(warning);
            path.report.warnings.rotate_right(1);
        }
        if let Some(result) = pre_op {
            path.report.approximations.extend(result.limits);
            setup_start = Some(result.start);
        }
        Ok((path, runner.budget().used()))
    };
    match outcome() {
        Ok((toolpath, work_units)) => CamReply { turning_profile: certified_turning_profile, setup_start, id: job.id, operation, toolpath: Ok(toolpath), work_units, cancelled: false },
        Err(message) => {
            let cancelled = token.is_cancelled();
            CamReply { turning_profile: None, setup_start: None, id: job.id, operation, toolpath: Err(if cancelled { "cancelled".to_string() } else { message }), work_units: 0, cancelled }
        }
    }
}

pub use brep_reconstruction::stl_conversion::{
    ConversionBackend, ConversionPolicy, HybridDemotion, StlConversionOptions, StlConversionOutput,
    StlConversionReport,
};
pub use brep_reconstruction::import_session::{
    FitAttempt, FitKind, ImportRegion, ImportRegions, NurbsFaceChoice, NurbsFaceOutcome, NurbsFit, RegionFit,
    RegionFitRequest, RegionKind, UNASSIGNED as UNASSIGNED_REGION,
};

/// Mesh encoding accepted by the off-thread reconstruction channel.
#[derive(Debug, Clone, Copy, serde::Serialize, serde::Deserialize)]
pub enum MeshImportFormat {
    Stl,
    Obj,
    /// 3MF (core specification): a package whose build instances are flattened
    /// into one millimetre triangle soup before this common chain runs.
    ThreeMf,
}

/// A mesh reconstruction request. The byte payload moves to the native thread
/// or is serialized to the browser worker; no parsing or fitting happens on UI.
#[derive(Debug, serde::Serialize, serde::Deserialize)]
pub struct MeshImportRequest {
    pub id: u64,
    pub format: MeshImportFormat,
    pub bytes: Vec<u8>,
    pub options: StlConversionOptions,
    /// Stream the interactive import's phases ([`Reply::MeshImportPhase`])
    /// before the final reply: the parsed mesh, then its regions. The final
    /// reply is the same with or without them.
    #[serde(default)]
    pub phases: bool,
}

/// One phase of an interactive mesh import, posted from inside the
/// reconstruction before its [`MeshImportReply`].
#[derive(Debug, Clone, serde::Serialize, serde::Deserialize)]
pub enum MeshImportPhase {
    /// The parsed, welded triangle soup the reconstruction reads.
    Mesh { positions: Vec<f64>, indices: Vec<u32> },
    /// The regions the builder starts from, per source triangle.
    Regions(brep_reconstruction::import_session::ImportRegions),
    /// The regions could not be read (the reconstruction still runs).
    RegionsFailed(String),
}

#[derive(Debug, Clone, serde::Serialize, serde::Deserialize)]
pub struct MeshImportPhaseReply {
    pub id: u64,
    pub phase: MeshImportPhase,
}

/// Refit one region of an interactive import. The caller sends the region's
/// own triangles (a small mesh), so the runner keeps no import state.
#[derive(Debug, Clone, serde::Serialize, serde::Deserialize)]
pub struct RegionFitJob {
    pub id: u64,
    pub positions: Vec<f64>,
    pub indices: Vec<u32>,
    pub request: brep_reconstruction::import_session::RegionFitRequest,
}

#[derive(Debug, Clone, serde::Serialize, serde::Deserialize)]
pub struct RegionFitReply {
    pub id: u64,
    pub fit: brep_reconstruction::import_session::RegionFit,
}

/// Run a region refit wherever the runner runs.
pub fn region_fit_reply(job: RegionFitJob) -> RegionFitReply {
    RegionFitReply {
        id: job.id,
        fit: brep_reconstruction::import_session::fit_region(&job.positions, &job.indices, &job.request),
    }
}

/// Rebuild an interactive import's chosen regions as NURBS faces: the
/// conversion's STEP, the welded mesh the regions index, and one choice per
/// region (`brep_reconstruction::import_session::apply_region_choices`).
#[derive(Debug, Clone, serde::Serialize, serde::Deserialize)]
pub struct ApplyRegionChoicesJob {
    pub id: u64,
    pub step_text: String,
    pub positions: Vec<f64>,
    pub indices: Vec<u32>,
    pub choices: Vec<NurbsFaceChoice>,
}

#[derive(Debug, Clone, serde::Serialize, serde::Deserialize)]
pub struct ApplyRegionChoicesReply {
    pub id: u64,
    /// The new STEP (unchanged when no choice applied) and one outcome per
    /// choice, in order.
    pub result: Result<(String, Vec<NurbsFaceOutcome>), String>,
}

/// Apply region choices wherever the runner runs.
pub fn apply_region_choices_reply(job: ApplyRegionChoicesJob) -> ApplyRegionChoicesReply {
    ApplyRegionChoicesReply {
        id: job.id,
        result: brep_reconstruction::import_session::apply_region_choices(&job.step_text, &job.positions, &job.indices, &job.choices),
    }
}

/// Completed off-thread reconstruction. Success carries validated STEP and
/// diagnostics for a preview or an ordinary IMPORT3D history insertion.
#[derive(Debug, serde::Serialize, serde::Deserialize)]
pub struct MeshImportReply {
    pub id: u64,
    pub result: Result<StlConversionOutput, String>,
}

/// Validate explicitly installed packages away from the UI thread.
#[derive(Debug, Clone, serde::Serialize, serde::Deserialize)]
pub struct PluginInstallRequest {
    pub id: u64,
    pub packages: serde_json::Value,
}
#[derive(Debug, Clone, serde::Serialize, serde::Deserialize)]
pub struct PluginInstallReply {
    pub id: u64,
    pub result: Result<brep_plugins::Registry, String>,
}
fn validate_plugins(request: PluginInstallRequest) -> PluginInstallReply {
    let result = serde_json::from_value(request.packages)
        .map_err(|e| format!("plugin packages: {e}"))
        .and_then(brep_plugins::Runtime::new)
        .map(|runtime| runtime.registry().clone());
    PluginInstallReply { id: request.id, result }
}

/// A callback request against an immutable document/selection snapshot.
#[derive(Debug, Clone, serde::Serialize, serde::Deserialize)]
pub struct PluginActionRequest {
    pub id: u64,
    pub pins: Vec<brep_plugins::PluginPin>,
    pub action: String,
    pub input: serde_json::Value,
    #[serde(default, skip_serializing_if = "Option::is_none")]
    pub script: Option<String>,
}

#[derive(Debug, Clone, serde::Serialize, serde::Deserialize)]
pub struct PluginActionReply {
    pub id: u64,
    pub result: Result<brep_plugins::ActionPlan, String>,
}

/// The history-run seam: SUBMIT a run, POLL for its completed reply, RESET the
/// delta baseline, plus a QUERY channel for per-object measurements (routed to the
/// runner so the warm registry answers them, never the cold main-side one). The
/// Inline impl runs everything synchronously; a later thread/worker impl defers
/// the work and surfaces the replies through the same poll idiom.
/// Where the main thread gets the assembly session of the run it applied
/// ([`HistoryRunner::session_for_main`]).
pub enum SessionOnMain {
    /// The run executed on the main thread and its session is still the
    /// thread's: nothing to do.
    Resident,
    /// An owned copy from the runner's thread, to import.
    Copied(brep_kernel::SessionTransfer),
    /// Not available (busy, replaced, or a runner that cannot copy): replay.
    Unavailable,
}

pub trait HistoryRunner {
    /// The assembly session the run of `generation` left, for the main
    /// thread's constraint actions. Blocking, but bounded. The default cannot
    /// provide one, and the caller replays the history instead.
    fn session_for_main(&mut self, _generation: u64) -> SessionOnMain {
        SessionOnMain::Unavailable
    }
    fn submit_plugin_install(&mut self, _request: PluginInstallRequest) -> bool { false }
    fn poll_plugin_install(&mut self) -> Option<PluginInstallReply> { None }
    /// Trusted installed content, separate from saved document dependency pins.
    fn sync_plugins(&mut self, _revision: u64, _fetch: &mut dyn FnMut() -> serde_json::Value) {}
    /// False explicitly reports a runner without action support.
    fn submit_plugin_action(&mut self, _request: PluginActionRequest) -> bool { false }
    fn poll_plugin_action(&mut self) -> Option<PluginActionReply> { None }

    /// Submit a history run tagged with a monotonic generation. The runner executes
    /// it (immediately for Inline; on a background thread later) and makes the reply
    /// available via [`poll_run`](Self::poll_run).
    fn submit_run(&mut self, request: brep_kernel::HistoryRequest, generation: u64);
    /// Non-blocking: the next completed run reply, if any (drained each frame).
    fn poll_run(&mut self) -> Option<RunReply>;
    /// Submit a per-object measurement query (answered against the runner's warm
    /// registry). Inline computes it immediately; a thread impl computes it on the
    /// runner thread and surfaces it via [`poll_query`](Self::poll_query).
    fn submit_query(&mut self, query: MeasureQuery);
    /// Non-blocking: the next completed measurement reply, if any.
    fn poll_query(&mut self) -> Option<MeasureReply>;
    /// Submit RANSAC mesh reconstruction to the runner's thread/worker.
    fn submit_mesh_import(&mut self, request: MeshImportRequest);
    /// Non-blocking: the next completed mesh reconstruction, if any.
    fn poll_mesh_import(&mut self) -> Option<MeshImportReply>;
    /// Non-blocking: the next phase of an interactive mesh import
    /// ([`MeshImportRequest::phases`]). The default posts none.
    fn poll_mesh_import_phase(&mut self) -> Option<MeshImportPhaseReply> {
        None
    }
    /// Submit a region refit; `false` when this runner cannot run one (the
    /// caller then fits on its own thread — a region is small).
    fn submit_region_fit(&mut self, _job: RegionFitJob) -> bool {
        false
    }
    /// Non-blocking: the next completed region refit, if any.
    fn poll_region_fit(&mut self) -> Option<RegionFitReply> {
        None
    }
    /// Submit region choices to apply; `false` when this runner cannot (the
    /// caller then applies them on its own thread).
    fn submit_apply_region_choices(&mut self, _job: ApplyRegionChoicesJob) -> bool {
        false
    }
    /// Non-blocking: the next applied region choices, if any.
    fn poll_apply_region_choices(&mut self) -> Option<ApplyRegionChoicesReply> {
        None
    }
    /// Submit a STEP product-structure probe (see [`StepProbeRequest`]).
    fn submit_step_probe(&mut self, request: StepProbeRequest);
    /// Non-blocking: the next completed STEP probe, if any.
    fn poll_step_probe(&mut self) -> Option<StepProbeReply>;
    /// Submit a topology request (see [`TopologyRequest`]). The default drops
    /// it: a runner that never answers leaves a sheet on its mesh
    /// approximation, which the drawing reports.
    fn submit_topology(&mut self, _request: TopologyRequest) {}
    /// Non-blocking: the next completed topology reply, if any.
    fn poll_topology(&mut self) -> Option<TopologyReply> {
        None
    }
    /// BLOCK up to `timeout` until a topology reply is ready to poll: `true`
    /// when one is. An export that needs the exact solids waits this way on a
    /// runner with a thread of its own; the default cannot wait (a worker
    /// answers through the page's event loop, which a blocked page never
    /// turns), so the export draws the mesh approximation and the file says
    /// so.
    fn wait_topology(&mut self, _timeout: std::time::Duration) -> bool {
        false
    }
    /// Submit a sheet placement's exact pass (see [`SheetLinesRequest`]).
    /// `false` when this runner cannot run one — the engine then runs it on
    /// its own thread, as every projection did before the pass moved off it.
    fn submit_sheet_lines(&mut self, _request: SheetLinesRequest) -> bool {
        false
    }
    /// Non-blocking: the next completed sheet-lines reply, if any.
    fn poll_sheet_lines(&mut self) -> Option<SheetLinesReply> {
        None
    }
    /// Submit ONE CAM operation's generation (see [`CamJob`]); `false` when
    /// this runner cannot run it.
    fn submit_cam(&mut self, _job: CamJob) -> bool {
        false
    }
    fn poll_cam(&mut self) -> Option<CamReply> {
        None
    }
    fn poll_cam_progress(&mut self) -> Option<CamProgress> {
        None
    }
    /// Cancel the CAM job in flight at its next work chunk, where the driver
    /// can reach it (the native thread); a driver that cannot lets the job
    /// finish and the main side drops its reply.
    fn cancel_cam(&mut self) {}
    /// TEST HOLD (automation only): while `hold`, finished CAM replies are
    /// kept back from `poll_cam`, so a job stays in flight on the main side
    /// however fast it ran — the one way a script can meet it with a cancel
    /// every time. Releasing delivers what was kept, in order. A driver
    /// without the hold ignores it.
    fn hold_cam_replies(&mut self, _hold: bool) {}
    /// Submit ONE CAM simulation command (see [`CamSimJob`]); `false` when
    /// this runner cannot simulate (the caller then simulates inline).
    fn submit_cam_sim(&mut self, _job: CamSimJob) -> bool {
        false
    }
    fn poll_cam_sim(&mut self) -> Option<CamSimReply> {
        None
    }
    fn poll_cam_sim_progress(&mut self) -> Option<CamSimProgress> {
        None
    }
    /// Stop the simulation chunk in flight between two motions where the
    /// driver can reach it (the native thread); elsewhere the chunk finishes
    /// and the caller drops its reply.
    fn cancel_cam_sim(&mut self) {}
    /// Drop the delta baseline (document switch → full rebuild).
    fn reset(&mut self);

    /// Bring the runner's resident PARTS LIBRARY up to `revision`, calling
    /// `fetch` ONLY when it is not already there. Called immediately before
    /// every [`submit_run`](Self::submit_run).
    ///
    /// This is the whole point of the library channel: the library is sent
    /// when it CHANGES (insert, document load, refresh), not on every run.
    /// Cheap to call — the revision comparison is an integer, and `fetch`
    /// (which clones the store) never runs in the steady state. The default is
    /// a no-op for [`InlineRunner`], which shares the caller's kernel store.
    fn sync_parts_library(
        &mut self,
        _revision: u64,
        _fetch: &mut dyn FnMut() -> brep_kernel::PartsLibraryMap,
    ) {
    }

    /// True when the runner REFUSED a run because its resident parts library
    /// could not serve it (see [`Reply::NeedPartsLibrary`]). It has already
    /// forgotten its copy, so the next `sync_parts_library` reinstalls; the
    /// caller must re-submit the run. Never true for a runner that shares the
    /// caller's store.
    fn poll_library_request(&mut self) -> bool {
        false
    }

    /// Whether a run reply (or a refusal asking for the parts library) is
    /// waiting for [`poll_run`](Self::poll_run): a caller may skip what only a
    /// landing needs while this is false. `true` when the runner cannot tell.
    fn run_reply_waiting(&mut self) -> bool {
        true
    }

    /// Non-blocking: the MOST RECENT progress report of the in-flight run, with
    /// any older ones discarded (only the latest feature matters). `None` for
    /// a synchronous runner — Inline has finished before anyone could ask.
    fn poll_progress(&mut self) -> Option<RunProgress> {
        None
    }

    /// ABANDON the in-flight work and start over with an EMPTY resident
    /// registry. Returns `false` when there is nothing this runner can abandon
    /// (Inline: the run already completed on the caller's thread). A `true`
    /// means every handle the caller holds is now invalid, no reply is coming
    /// for anything submitted so far, and the parts library must be re-sent —
    /// the caller reconciles its generations and pending sets accordingly
    /// (`EngineState::cancel_run`). Nothing inside a feature is interruptible:
    /// the thread runner lets its old thread finish the feature it is on and
    /// stop at the next boundary; the browser worker is terminated outright.
    fn cancel(&mut self) -> bool {
        false
    }
}

/// Measure `query` against `runner`'s resident geometry and emit the object-info
/// JSON FRAGMENT — EXACTLY the fields [`crate::metadata::EngineState::object_info_json`]
/// emits for that kind EXCEPT `name` and `creatingFeature` (the main thread injects
/// those from its eager provenance, so the merged output is byte-identical to the
/// pre-seam in-process result). Shared verbatim by the Inline and thread runners so
/// both produce the identical fragment. A missing handle / kernel error yields
/// `{ "ok": false, "message": .. }` (main injects `name`).
fn measure_json(runner: &crate::pipeline::SceneRunner, query: &MeasureQuery) -> String {
    let Some(handle) = runner.handle_of(&query.owner) else {
        return serde_json::json!({
            "ok": false,
            "message": format!("solid '{}' has no resident geometry", query.owner),
        })
        .to_string();
    };
    match query.kind {
        MeasureKind::Inspect => {
            let issues: Vec<serde_json::Value> = match brep_kernel::validate_handle_native(handle) {
                Ok(issues) => issues.into_iter().map(|(severity, message)| serde_json::json!({ "severity": severity, "message": message })).collect(),
                Err(error) => vec![serde_json::json!({ "severity": "error", "message": format!("validation unavailable: {error}") })],
            };
            let (volume, volume_error) = match brep_kernel::mass_measures_handle_native(handle) {
                Ok(properties) => (Some(properties.volume), None),
                Err(error) => (None, Some(error)),
            };
            serde_json::json!({ "ok": true, "kind": "inspect", "issues": issues, "volume": volume, "volumeError": volume_error }).to_string()
        }
        MeasureKind::Solid => {
            match brep_kernel::mass_properties_handle_native(handle, query.density) {
                Ok(properties) => {
                    let edge_total =
                        brep_kernel::solid_edge_length_total_native(handle).unwrap_or(0.0);
                    serde_json::json!({
                        "ok": true,
                        "kind": "solid",
                        "volume": properties.volume,
                        "surfaceArea": properties.surface_area,
                        "edgeLengthTotal": edge_total,
                        "density": properties.density,
                        "weight": properties.mass,
                    })
                    .to_string()
                }
                Err(error) => serde_json::json!({ "ok": false, "message": error }).to_string(),
            }
        }
        MeasureKind::Face => match brep_kernel::face_measurements_native(handle, &query.entity) {
            Ok((area, edge_total, surface_type)) => {
                let dimensions =
                    brep_kernel::face_carrier_dimensions_native(handle, &query.entity)
                        .ok()
                        .flatten();
                // A partial revolution of a straight line is a "Surface of
                // revolution" to the kernel and a cylinder to the user.
                let surface_type = dimensions.as_ref().map_or(surface_type, |d| d.label);
                let mut fragment = serde_json::json!({
                    "ok": true,
                    "kind": "face",
                    "solid": query.owner,
                    "surfaceType": surface_type,
                    "area": area,
                    "edgeLengthTotal": edge_total,
                });
                insert_dimensions(&mut fragment, dimensions.as_ref());
                fragment.to_string()
            }
            Err(error) => serde_json::json!({ "ok": false, "message": error }).to_string(),
        },
        MeasureKind::Edge => match brep_kernel::edge_length_native(handle, &query.entity) {
            Ok(length) => {
                let dimensions =
                    brep_kernel::edge_carrier_dimensions_native(handle, &query.entity)
                        .ok()
                        .flatten();
                let mut fragment = serde_json::json!({
                    "ok": true,
                    "kind": "edge",
                    "solid": query.owner,
                    "length": length,
                });
                if let Some(dimensions) = &dimensions {
                    fragment["curveType"] = serde_json::Value::from(dimensions.label);
                }
                insert_dimensions(&mut fragment, dimensions.as_ref());
                fragment.to_string()
            }
            Err(error) => serde_json::json!({ "ok": false, "message": error }).to_string(),
        },
    }
}

/// Add a carrier's named dimensions (`radius`, `diameter`, `halfAngleDeg`,
/// `majorRadius`, `minorRadius`, `sweepDeg`) to an object-info fragment.
fn insert_dimensions(
    fragment: &mut serde_json::Value,
    dimensions: Option<&brep_kernel::CarrierDimensions>,
) {
    let (Some(dimensions), Some(object)) = (dimensions, fragment.as_object_mut()) else {
        return;
    };
    for (key, value) in &dimensions.values {
        object.insert((*key).to_string(), serde_json::Value::from(*value));
    }
}

/// The default, SYNCHRONOUS runner: runs on submit, stashes the reply for an
/// immediate poll. Behavior-identical to the pre-seam in-process run.
pub struct InlineRunner {
    /// The scene-free history runner it owns (delta baseline lives here).
    runner: crate::pipeline::SceneRunner,
    /// Completed replies awaiting a poll. For Inline this holds exactly one entry
    /// between a `submit_run` and the immediately-following `poll_run`.
    pending: std::collections::VecDeque<RunReply>,
    /// Completed measurement replies awaiting a poll (computed synchronously on
    /// `submit_query`, popped on `poll_query`) — the synchronous mirror of the
    /// thread runner's query buffer, so the object-info path resolves same-call.
    query_pending: std::collections::VecDeque<MeasureReply>,
    mesh_import_pending: std::collections::VecDeque<MeshImportReply>,
    mesh_phase_pending: std::collections::VecDeque<MeshImportPhaseReply>,
    region_fit_pending: std::collections::VecDeque<RegionFitReply>,
    apply_choices_pending: std::collections::VecDeque<ApplyRegionChoicesReply>,
    step_probe_pending: std::collections::VecDeque<StepProbeReply>,
    topology_pending: std::collections::VecDeque<TopologyReply>,
    sheet_lines_pending: std::collections::VecDeque<SheetLinesReply>,
    plugin_action_pending: std::collections::VecDeque<PluginActionReply>,
    plugin_install_pending: std::collections::VecDeque<PluginInstallReply>,
}

impl InlineRunner {
    pub fn new() -> Self {
        Self {
            runner: crate::pipeline::SceneRunner::new(),
            pending: std::collections::VecDeque::new(),
            query_pending: std::collections::VecDeque::new(),
            mesh_import_pending: std::collections::VecDeque::new(),
            mesh_phase_pending: std::collections::VecDeque::new(),
            region_fit_pending: std::collections::VecDeque::new(),
            apply_choices_pending: std::collections::VecDeque::new(),
            step_probe_pending: std::collections::VecDeque::new(),
            topology_pending: std::collections::VecDeque::new(),
            sheet_lines_pending: std::collections::VecDeque::new(),
            plugin_action_pending: std::collections::VecDeque::new(),
            plugin_install_pending: std::collections::VecDeque::new(),
        }
    }
}

impl HistoryRunner for InlineRunner {
    fn submit_plugin_install(&mut self, request: PluginInstallRequest) -> bool {
        self.plugin_install_pending.push_back(validate_plugins(request));
        true
    }
    fn poll_plugin_install(&mut self) -> Option<PluginInstallReply> {
        self.plugin_install_pending.pop_front()
    }
    fn sync_plugins(&mut self, revision: u64, fetch: &mut dyn FnMut() -> serde_json::Value) {
        if self.runner.plugin_revision != Some(revision) {
            self.runner.set_plugins(revision, fetch());
        }
    }
    fn submit_plugin_action(&mut self, request: PluginActionRequest) -> bool {
        self.plugin_action_pending.push_back(self.runner.plugin_action(request));
        true
    }
    fn poll_plugin_action(&mut self) -> Option<PluginActionReply> {
        self.plugin_action_pending.pop_front()
    }

    fn submit_run(&mut self, request: brep_kernel::HistoryRequest, generation: u64) {
        let serial = brep_kernel::assembly_session_serial();
        let output = self.runner.run(&request);
        let after = brep_kernel::assembly_session_serial();
        self.runner.session_of = (after != serial).then_some((generation, after));
        self.pending.push_back(RunReply { generation, output });
    }

    /// The run executed on this (the caller's) thread: its session is already
    /// here unless something has replaced it since.
    fn session_for_main(&mut self, generation: u64) -> SessionOnMain {
        match self.runner.session_of {
            Some((ran, serial)) if ran == generation && serial == brep_kernel::assembly_session_serial() => {
                SessionOnMain::Resident
            }
            _ => SessionOnMain::Unavailable,
        }
    }

    /// Nothing to send: Inline runs on the CALLER's thread against the CALLER's
    /// kernel store, so the library the caller would hand over is already the
    /// one this run resolves against. (Which is also why Inline never needs the
    /// preflight — there is only one store, and the caller seeds it directly.)
    fn sync_parts_library(
        &mut self,
        _revision: u64,
        _fetch: &mut dyn FnMut() -> brep_kernel::PartsLibraryMap,
    ) {
    }

    fn poll_run(&mut self) -> Option<RunReply> {
        self.pending.pop_front()
    }

    fn submit_query(&mut self, query: MeasureQuery) {
        let result = measure_json(&self.runner, &query);
        self.query_pending.push_back(MeasureReply { id: query.id, result });
    }

    fn poll_query(&mut self) -> Option<MeasureReply> {
        self.query_pending.pop_front()
    }

    fn submit_mesh_import(&mut self, request: MeshImportRequest) {
        let phases = &mut self.mesh_phase_pending;
        let reply = reconstruct_mesh_phased(request, &mut |phase| {
            phases.push_back(phase);
            true
        });
        self.mesh_import_pending.push_back(reply);
    }

    fn poll_mesh_import(&mut self) -> Option<MeshImportReply> {
        self.mesh_import_pending.pop_front()
    }

    fn poll_mesh_import_phase(&mut self) -> Option<MeshImportPhaseReply> {
        self.mesh_phase_pending.pop_front()
    }

    fn submit_region_fit(&mut self, job: RegionFitJob) -> bool {
        self.region_fit_pending.push_back(region_fit_reply(job));
        true
    }

    fn poll_region_fit(&mut self) -> Option<RegionFitReply> {
        self.region_fit_pending.pop_front()
    }

    fn submit_apply_region_choices(&mut self, job: ApplyRegionChoicesJob) -> bool {
        self.apply_choices_pending.push_back(apply_region_choices_reply(job));
        true
    }

    fn poll_apply_region_choices(&mut self) -> Option<ApplyRegionChoicesReply> {
        self.apply_choices_pending.pop_front()
    }

    fn submit_step_probe(&mut self, request: StepProbeRequest) {
        self.step_probe_pending.push_back(probe_step(request));
    }

    fn poll_step_probe(&mut self) -> Option<StepProbeReply> {
        self.step_probe_pending.pop_front()
    }

    fn submit_topology(&mut self, request: TopologyRequest) {
        self.topology_pending.push_back(topology_reply(request));
    }

    fn poll_topology(&mut self) -> Option<TopologyReply> {
        self.topology_pending.pop_front()
    }

    /// Runs the pass at once, on the caller's thread: an inline runner's
    /// registry IS the caller's, so the answer is ready for the next poll.
    fn submit_sheet_lines(&mut self, request: SheetLinesRequest) -> bool {
        self.sheet_lines_pending.push_back(sheet_lines_reply(request));
        true
    }

    fn poll_sheet_lines(&mut self) -> Option<SheetLinesReply> {
        self.sheet_lines_pending.pop_front()
    }

    fn reset(&mut self) {
        self.runner.reset();
    }
}

impl Default for InlineRunner {
    fn default() -> Self {
        Self::new()
    }
}

// ===========================================================================
// Shared run/query PROTOCOL (M3b): the `Command`/`Reply` message pair and the
// `process_command` step. Both async runners speak it — the native `ThreadRunner`
// ships the enums over `mpsc` (no serialization), and the wasm `WorkerRunner`
// serializes them to JSON for `postMessage`. Hence the serde derives (the enums
// carry serde types: `HistoryRequest`/`MeasureQuery`/`RunReply`/`MeasureReply`)
// and `process_command` being un-gated + shared so both drivers do the SAME work.
// ===========================================================================

/// A command sent main → runner (thread channel OR worker `postMessage`) over one
/// ordered stream (so a `Reset` before a `Run` stays before it). `Run` carries the
/// whole request; the driver coalesces consecutive `Run`s to shed a slider drag's
/// backlog (the thread in `thread_main`, the worker's main side in `WorkerRunner`).
#[derive(serde::Serialize, serde::Deserialize)]
pub enum Command {
    ValidatePlugins(PluginInstallRequest),
    SetPlugins { revision: u64, packages: serde_json::Value },
    PluginAction(PluginActionRequest),
    Run {
        request: brep_kernel::HistoryRequest,
        generation: u64,
        /// The [`brep_kernel::parts_library_revision`] this run was built
        /// against. The runner refuses to execute a run stamped for a library
        /// it does not hold — see [`process_command`].
        #[serde(default)]
        parts_library_revision: u64,
    },
    /// Install the parts library on the runner's OWN kernel store. Sent only
    /// when the library actually changes (insert, document load, refresh),
    /// never per run: it carries the whole embedded-part payload, which for an
    /// imported STEP assembly is megabytes, and stringifying that on the
    /// browser's main thread once per edit is what froze the UI.
    ///
    /// Deliberately its OWN command rather than an optional field on `Run`:
    /// both drivers COALESCE consecutive runs (see `thread_main` and
    /// `WorkerRunner::submit_run`), so a library riding on a run could be
    /// dropped with it. A `SetPartsLibrary` is never coalesced away, and the
    /// stream is ordered, so it always lands before the run that needs it.
    SetPartsLibrary {
        library: brep_kernel::PartsLibraryMap,
        revision: u64,
    },
    Query(MeasureQuery),
    MeshImport(MeshImportRequest),
    RegionFit(RegionFitJob),
    ApplyRegionChoices(ApplyRegionChoicesJob),
    StepProbe(StepProbeRequest),
    Topology(TopologyRequest),
    SheetLines(SheetLinesRequest),
    /// Generate ONE CAM operation (never coalesced: every job answers).
    CamGenerate(CamJob),
    /// One CAM simulation command (never coalesced: every job answers).
    CamSimulate(CamSimJob),
    Reset,
    /// Copy the assembly session the run of `generation` left here (native
    /// thread only: the copy holds kernel solids and never crosses a worker).
    #[serde(skip)]
    ExportSession { generation: u64 },
}

/// A reply sent runner → main; the main side demuxes it into per-kind buffers.
#[derive(serde::Serialize, serde::Deserialize)]
pub enum Reply {
    ValidatedPlugins(PluginInstallReply),
    PluginAction(PluginActionReply),
    Run(RunReply),
    Query(MeasureReply),
    MeshImport(MeshImportReply),
    /// A phase of an interactive mesh import, posted before its `MeshImport`.
    MeshImportPhase(MeshImportPhaseReply),
    RegionFit(RegionFitReply),
    ApplyRegionChoices(ApplyRegionChoicesReply),
    StepProbe(StepProbeReply),
    Topology(TopologyReply),
    SheetLines(SheetLinesReply),
    CamGenerate(CamReply),
    /// A CAM job's progress, posted from inside the job.
    CamProgress(CamProgress),
    CamSimulate(CamSimReply),
    /// A simulation chunk's progress, posted between motions.
    CamSimProgress(CamSimProgress),
    /// The runner REFUSED a run because its resident parts library could not
    /// serve it (a part the request references is missing, or the run was
    /// stamped for a different library revision). No geometry was touched; the
    /// main side re-sends the library and re-submits. Refusing is the whole
    /// point — running with the wrong library would be silently wrong
    /// geometry, which is far worse than one extra round trip.
    NeedPartsLibrary,
    /// A feature of the in-flight run is about to execute (see
    /// [`RunProgress`]). Posted from INSIDE `process_command`, before its
    /// `Reply::Run`; the main side keeps only the latest.
    Progress(RunProgress),
    /// The answer to `Command::ExportSession` (native thread only).
    #[serde(skip)]
    SessionExport { generation: u64, transfer: Option<brep_kernel::SessionTransfer> },
}

/// The probe itself — the one parse of a structured STEP import (see
/// `EngineState::submit_step_probe`), run wherever the runner runs.
fn probe_step(request: StepProbeRequest) -> StepProbeReply {
    StepProbeReply {
        id: request.id,
        // The same probe answers an IGES file, whose structure is subfigure
        // instances; the app's choice and import consume either alike.
        result: if crate::engine_state::is_iges_text(&request.text) {
            brep_kernel::read_iges_assembly(&request.text)
        } else {
            brep_kernel::read_step_assembly(&request.text)
        },
    }
}

/// The import without its phase stream (every runner posts the phased one;
/// the runner's tests read the reply alone).
#[cfg_attr(not(test), allow(dead_code))]
fn reconstruct_mesh(request: MeshImportRequest) -> MeshImportReply {
    reconstruct_mesh_phased(request, &mut |_| true)
}

/// [`reconstruct_mesh`], posting each phase of an interactive import to
/// `phase` as it completes when the request asks for them.
fn reconstruct_mesh_phased(
    request: MeshImportRequest,
    phase: &mut dyn FnMut(MeshImportPhaseReply) -> bool,
) -> MeshImportReply {
    let id = request.id;
    let phases = request.phases;
    let result = (|| {
        use brep_reconstruction::stl_conversion::{
            binary_stl_coordinate_precision_tolerance, convert_stl_mesh_to_step_with_colors,
        };
        use brep_reconstruction::{Mesh, Vec3};

        // A 3MF build's placements, kept only to name each body afterwards.
        let mut instances = Vec::new();
        let mut reader_messages = Vec::new();
        // A 3MF's per-triangle colours (its base materials), parallel to the
        // soup's triangles; empty for STL and OBJ, which carry none.
        let mut triangle_colors: Vec<Option<[u8; 3]>> = Vec::new();
        let (mesh, positions, indices, coordinate_precision_tolerance) = match request.format {
            MeshImportFormat::Stl => {
                use brep_reconstruction::stl::{parse_stl_bytes, StlFormat, StlReadOptions};
                let read_options = StlReadOptions {
                    weld_tolerance: (request.options.weld_tolerance >= 0.0)
                        .then_some(request.options.weld_tolerance),
                };
                let imported = parse_stl_bytes(&request.bytes, &read_options)
                    .map_err(|error| format!("STL import failed: {error}"))?;
                let positions = imported
                    .mesh
                    .vertices
                    .iter()
                    .flat_map(|point| [point.x, point.y, point.z])
                    .collect::<Vec<_>>();
                let indices = imported
                    .mesh
                    .triangles
                    .iter()
                    .flatten()
                    .copied()
                    .collect::<Vec<_>>();
                let precision = if imported.format == StlFormat::Binary {
                    binary_stl_coordinate_precision_tolerance(&imported.mesh)
                } else {
                    0.0
                };
                if !imported.dropped_facets.is_empty() {
                    reader_messages.push(format!(
                        "the STL reader dropped {} of {} facet(s) with no area: {}",
                        imported.dropped_facets.len(),
                        imported.source_triangle_count,
                        imported.dropped_facets.iter().take(8).map(ToString::to_string).collect::<Vec<_>>().join("; ")
                    ));
                }
                (imported.mesh, positions, indices, precision)
            }
            MeshImportFormat::Obj => {
                let text = std::str::from_utf8(&request.bytes)
                    .map_err(|_| "OBJ import failed: file is not UTF-8 text".to_string())?;
                let obj = brep_kernel::read_obj(text)
                    .map_err(|error| format!("OBJ import failed: {error}"))?;
                let vertices = obj
                    .positions
                    .chunks_exact(3)
                    .map(|point| Vec3::new(point[0], point[1], point[2]))
                    .collect::<Vec<_>>();
                let triangles = obj
                    .indices
                    .chunks_exact(3)
                    .map(|triangle| [triangle[0], triangle[1], triangle[2]])
                    .collect::<Vec<_>>();
                (
                    Mesh::new(vertices, triangles),
                    obj.positions,
                    obj.indices,
                    0.0,
                )
            }
            // The 3MF reader has already applied the file's unit and every
            // build/component transform, so what arrives here is the same kind
            // of millimetre triangle soup an STL carries — including a build
            // that places SEVERAL instances, which is several bodies in that
            // one buffer. The chain splits a soup into its vertex-connected
            // components and reconstructs each as its own body, so the whole
            // build goes through in ONE call and the poses are already in the
            // coordinates.
            MeshImportFormat::ThreeMf => {
                let model = brep_kernel::read_3mf(&request.bytes)
                    .map_err(|error| format!("3MF import failed: {error}"))?;
                instances = model.instances;
                triangle_colors = model.triangle_colors;
                let vertices = model
                    .positions
                    .chunks_exact(3)
                    .map(|point| Vec3::new(point[0], point[1], point[2]))
                    .collect::<Vec<_>>();
                let triangles = model
                    .indices
                    .chunks_exact(3)
                    .map(|triangle| [triangle[0], triangle[1], triangle[2]])
                    .collect::<Vec<_>>();
                (
                    Mesh::new(vertices, triangles),
                    model.positions,
                    model.indices,
                    0.0,
                )
            }
        };
        let mut options = request.options;
        options.coordinate_precision_tolerance = options.coordinate_precision_tolerance
            .max(coordinate_precision_tolerance);
        if phases {
            // `false` back from a post: nobody is listening any more (a
            // cancelled preview on the native thread) — stop here.
            let listening = phase(MeshImportPhaseReply {
                id,
                phase: MeshImportPhase::Mesh { positions: positions.clone(), indices: indices.clone() },
            });
            if !listening {
                return Err("cancelled".to_string());
            }
            let regions = brep_reconstruction::import_session::analyze_regions(&positions, &indices, &options);
            let listening = phase(MeshImportPhaseReply {
                id,
                phase: match regions {
                    Ok(regions) => MeshImportPhase::Regions(regions),
                    Err(error) => MeshImportPhase::RegionsFailed(error),
                },
            });
            if !listening {
                return Err("cancelled".to_string());
            }
        }
        convert_stl_mesh_to_step_with_colors(
            &mesh,
            &positions,
            Some(&indices),
            (!triangle_colors.is_empty()).then_some(triangle_colors.as_slice()),
            &options,
            "Imported mesh",
            "MM",
            "",
        )
        .map(|mut output| {
            name_bodies(&mut output.report, &instances);
            output.report.messages.splice(0..0, reader_messages);
            output
        })
        .map_err(|error| format!("RANSAC reconstruction failed: {error}"))
    })();
    MeshImportReply { id, result }
}

/// Give each body the name of the 3MF object its first source triangle came
/// from, so a refusal can say WHICH object is missing. Bodies are found in the
/// flattened soup the reader laid out instance by instance.
fn name_bodies(
    report: &mut brep_reconstruction::stl_conversion::StlConversionReport,
    instances: &[brep_kernel::ThreeMfInstance],
) {
    for component in &mut report.components {
        component.source_name = instances
            .iter()
            .find(|instance| {
                (instance.first_triangle..instance.first_triangle + instance.triangle_count)
                    .contains(&component.first_triangle)
            })
            .and_then(|instance| instance.name.clone());
    }
}

/// The notice for bodies a multi-body import left out, one clause per body,
/// named by the source's own name when it has one; `None` when every body was
/// built.
pub(crate) fn refused_bodies_notice(
    report: &brep_reconstruction::stl_conversion::StlConversionReport,
) -> Option<String> {
    let refused = report
        .components
        .iter()
        .filter_map(|component| {
            component.refusal.as_ref().map(|reason| {
                let body = match &component.source_name {
                    Some(name) => format!("body {} \"{name}\"", component.index + 1),
                    None => format!(
                        "body {} (from source triangle {})",
                        component.index + 1,
                        component.first_triangle
                    ),
                };
                format!("{body}: {reason}")
            })
        })
        .collect::<Vec<_>>();
    (!refused.is_empty()).then(|| {
        format!(
            "mesh import: {} of {} bodies could not be reconstructed and are NOT in the model — {}",
            refused.len(),
            report.components.len(),
            refused.join("; ")
        )
    })
}

/// Execute ONE [`Command`] against `runner` and return the [`Reply`] it produces,
/// if any. The shared step both async drivers run: the native `thread_main`
/// calls it for each (post-coalescing) command on the runner thread; the wasm
/// `WorkerRunner`'s `worker_entry` calls it per `postMessage` on the worker.
/// `Run` → a [`Reply::Run`]; `Query` → a [`Reply::Query`]; `Reset` drops the delta
/// baseline AND the runner's OWN kernel history cache (the resident registry lives
/// with the runner — thread or worker — not on main) and yields no reply.
///
/// `progress` is called before every feature a `Run` actually executes, with
/// the report the driver should ship as [`Reply::Progress`]; returning `false`
/// stops the run at that boundary (the native thread's cooperative cancel —
/// the worker is terminated instead and always returns `true`).
pub fn process_command(
    runner: &mut crate::pipeline::SceneRunner,
    command: Command,
    progress: &mut dyn FnMut(Reply) -> bool,
) -> Option<Reply> {
    match command {
        Command::ValidatePlugins(request) => Some(Reply::ValidatedPlugins(validate_plugins(request))),
        Command::SetPlugins { revision, packages } => {
            runner.set_plugins(revision, packages);
            None
        }
        Command::PluginAction(request) => Some(Reply::PluginAction(runner.plugin_action(request))),
        Command::Run {
            request,
            generation,
            parts_library_revision,
        } => {
            // PREFLIGHT (see `Reply::NeedPartsLibrary`). Two independent
            // checks, because neither alone is enough:
            //
            // * the revision stamp catches CHANGED content the sender knows
            //   about but this store has not received;
            // * `missing_library_parts` catches content that is simply GONE
            //   here — the orphan GC at the end of every run drops entries no
            //   ACOMP in THAT run referenced, so an undo to zero components
            //   empties this store while the sender's (which never ran) keeps
            //   everything and its revision never moves. Only looking at the
            //   actual content sees that.
            let stale = match runner.parts_library_revision {
                Some(installed) => installed != parts_library_revision,
                // Nothing installed yet. Accept a run stamped 0 — that is
                // either an empty library or a caller driving `submit_run`
                // directly (the runner tests); the content preflight below is
                // what actually protects the run. A non-zero stamp with nothing
                // installed IS a gap: refuse it.
                None => parts_library_revision != 0,
            };
            // Only a part the sender DID send and this store has since lost is
            // worth asking for again. One it never sent is a dangling reference
            // in the document itself: run it, so the ACOMP feature reports it
            // the way it always has. (An install inserts every incoming name,
            // so right after one this set can only be empty — which is what
            // makes the ask-and-retry terminate.)
            let recoverable = brep_kernel::missing_library_parts(&request)
                .iter()
                .any(|name| runner.parts_library_names.contains(name));
            if stale || recoverable {
                runner.parts_library_revision = None;
                return Some(Reply::NeedPartsLibrary);
            }
            let serial = brep_kernel::assembly_session_serial();
            let output = runner.run_observed(&request, &mut |event| {
                progress(Reply::Progress(RunProgress {
                    generation,
                    index: event.index,
                    total: event.total,
                    feature_id: event.id.to_string(),
                    feature_type: event.feature_type.to_string(),
                }))
            });
            let after = brep_kernel::assembly_session_serial();
            runner.session_of = (after != serial).then_some((generation, after));
            Some(Reply::Run(RunReply { generation, output }))
        }
        Command::SetPartsLibrary { library, revision } => {
            runner.parts_library_names = library.keys().cloned().collect();
            brep_kernel::install_parts_library(&library);
            runner.parts_library_revision = Some(revision);
            None
        }
        Command::Query(query) => {
            let result = measure_json(runner, &query);
            Some(Reply::Query(MeasureReply { id: query.id, result }))
        }
        Command::MeshImport(request) => Some(Reply::MeshImport(reconstruct_mesh_phased(request, &mut |phase| {
            progress(Reply::MeshImportPhase(phase))
        }))),
        Command::RegionFit(job) => Some(Reply::RegionFit(region_fit_reply(job))),
        Command::ApplyRegionChoices(job) => Some(Reply::ApplyRegionChoices(apply_region_choices_reply(job))),
        Command::StepProbe(request) => Some(Reply::StepProbe(probe_step(request))),
        Command::Topology(request) => Some(Reply::Topology(topology_reply(request))),
        Command::SheetLines(request) => Some(Reply::SheetLines(sheet_lines_reply(request))),
        Command::CamGenerate(job) => Some(Reply::CamGenerate(cam_generate_reply(job, progress))),
        Command::CamSimulate(job) => Some(Reply::CamSimulate(cam_sim_reply(job, progress))),
        Command::Reset => {
            // A document switch: drop the delta baseline AND this runner's OWN kernel
            // history cache (the resident registry lives here, not on main), mirroring
            // `set_history_json`'s main-thread clear so a new model rebuilds fully and
            // the old model's handles are freed.
            runner.reset();
            brep_kernel::clear_history_cache();
            cam_sim_clear();
            pre_op_stock_clear();
            None
        }
        Command::ExportSession { generation } => {
            Some(Reply::SessionExport { generation, transfer: runner.export_session(generation) })
        }
    }
}

// ===========================================================================
// ThreadRunner (M2b): a persistent std::thread that OWNS the SceneRunner, so a
// history run — and per-object measurement queries — execute OFF the main thread
// and the native UI stays responsive during a run AND during selection. Native
// only: `std::thread` + `std::sync::mpsc` do not exist on wasm32 (M3b lands a
// worker impl behind this same trait), so the whole thing is cfg-gated out there.
// ===========================================================================

/// The persistent-thread runner. `submit_*`/`reset` push [`Command`]s down the
/// channel; `poll_*` first DRAIN every ready [`Reply`] into the two demux buffers,
/// then pop the matching one. The `SceneRunner` (and thus the kernel's resident
/// registry it warms) lives ENTIRELY on the thread — it is never shared — so the
/// only cross-thread traffic is the `Send` command/reply payloads.
/// Called after the runner thread posts a reply or a progress report, from
/// that thread: the app's event loop wakes and collects it at once instead of
/// at its next timed check (`set_reply_waker`). Process-wide, like the
/// thread's other plumbing; none installed is a no-op.
#[cfg(not(target_arch = "wasm32"))]
static REPLY_WAKER: std::sync::RwLock<Option<std::sync::Arc<dyn Fn() + Send + Sync>>> = std::sync::RwLock::new(None);

/// Install (or with `None` remove) the hook a runner thread calls after each
/// reply it posts. The desktop event loop installs its own waker here.
#[cfg(not(target_arch = "wasm32"))]
pub fn set_reply_waker(waker: Option<std::sync::Arc<dyn Fn() + Send + Sync>>) {
    *REPLY_WAKER.write().unwrap_or_else(|p| p.into_inner()) = waker;
}

#[cfg(not(target_arch = "wasm32"))]
fn wake_main() {
    let waker = REPLY_WAKER.read().unwrap_or_else(|p| p.into_inner()).clone();
    if let Some(waker) = waker {
        waker();
    }
}

#[cfg(not(target_arch = "wasm32"))]
pub struct ThreadRunner {
    /// Main → thread. `Option` so [`Drop`] can take + drop it, ending the thread's
    /// blocking `recv` after already-submitted work finishes.
    tx: Option<std::sync::mpsc::Sender<Command>>,
    /// Thread → main.
    rx: std::sync::mpsc::Receiver<Reply>,
    /// Dropped without joining so closing a busy preview never stalls the UI.
    handle: Option<std::thread::JoinHandle<()>>,
    /// Demuxed completed run replies awaiting `poll_run`.
    run_buf: std::collections::VecDeque<RunReply>,
    /// Demuxed completed measurement replies awaiting `poll_query`.
    query_buf: std::collections::VecDeque<MeasureReply>,
    mesh_import_buf: std::collections::VecDeque<MeshImportReply>,
    mesh_phase_buf: std::collections::VecDeque<MeshImportPhaseReply>,
    region_fit_buf: std::collections::VecDeque<RegionFitReply>,
    apply_choices_buf: std::collections::VecDeque<ApplyRegionChoicesReply>,
    step_probe_buf: std::collections::VecDeque<StepProbeReply>,
    topology_buf: std::collections::VecDeque<TopologyReply>,
    sheet_lines_buf: std::collections::VecDeque<SheetLinesReply>,
    cam_buf: std::collections::VecDeque<CamReply>,
    /// [`HistoryRunner::hold_cam_replies`]: `poll_cam` answers `None` while set.
    cam_hold: bool,
    cam_progress_buf: std::collections::VecDeque<CamProgress>,
    /// Set by [`HistoryRunner::cancel_cam`]; the thread reads it on every CAM
    /// progress post and the running job cancels at its next chunk.
    cam_cancel: std::sync::Arc<std::sync::atomic::AtomicBool>,
    cam_sim_buf: std::collections::VecDeque<CamSimReply>,
    cam_sim_progress_buf: std::collections::VecDeque<CamSimProgress>,
    /// Set by [`HistoryRunner::cancel_cam_sim`]; read between two motions.
    cam_sim_cancel: std::sync::Arc<std::sync::atomic::AtomicBool>,
    plugin_action_buf: std::collections::VecDeque<PluginActionReply>,
    plugin_install_buf: std::collections::VecDeque<PluginInstallReply>,
    sent_plugin_revision: Option<u64>,
    /// Progress reports of the in-flight run, oldest first (`poll_progress`
    /// keeps the newest).
    progress_buf: std::collections::VecDeque<RunProgress>,
    /// The parts-library revision last SENT down the channel (`None` = never,
    /// or the thread dropped it). Lives here rather than on the caller so
    /// "reset forgets the library" is a local property of this object.
    sent_library_revision: Option<u64>,
    /// The thread refused a run for want of its library (drained by
    /// [`HistoryRunner::poll_library_request`]).
    library_requested: bool,
    /// The cooperative stop flag THIS thread checks between features. Each
    /// spawn gets its own, so a cancelled thread keeps its raised flag while
    /// the replacement starts clean.
    stop: std::sync::Arc<std::sync::atomic::AtomicBool>,
}

#[cfg(not(target_arch = "wasm32"))]
impl ThreadRunner {
    pub fn new() -> Self {
        let (tx, cmd_rx) = std::sync::mpsc::channel::<Command>();
        let (reply_tx, rx) = std::sync::mpsc::channel::<Reply>();
        let stop = std::sync::Arc::new(std::sync::atomic::AtomicBool::new(false));
        let thread_stop = stop.clone();
        let cam_cancel = std::sync::Arc::new(std::sync::atomic::AtomicBool::new(false));
        let thread_cam_cancel = cam_cancel.clone();
        let cam_sim_cancel = std::sync::Arc::new(std::sync::atomic::AtomicBool::new(false));
        let thread_cam_sim_cancel = cam_sim_cancel.clone();
        let handle = std::thread::Builder::new()
            .name("brep-history-runner".to_string())
            .spawn(move || thread_main(cmd_rx, reply_tx, thread_stop, thread_cam_cancel, thread_cam_sim_cancel))
            .expect("spawn brep-history-runner thread");
        Self {
            tx: Some(tx),
            rx,
            handle: Some(handle),
            run_buf: std::collections::VecDeque::new(),
            query_buf: std::collections::VecDeque::new(),
            mesh_import_buf: std::collections::VecDeque::new(),
            mesh_phase_buf: std::collections::VecDeque::new(),
            region_fit_buf: std::collections::VecDeque::new(),
            apply_choices_buf: std::collections::VecDeque::new(),
            step_probe_buf: std::collections::VecDeque::new(),
            topology_buf: std::collections::VecDeque::new(),
            sheet_lines_buf: std::collections::VecDeque::new(),
            cam_buf: std::collections::VecDeque::new(),
            cam_hold: false,
            cam_progress_buf: std::collections::VecDeque::new(),
            cam_cancel,
            cam_sim_buf: std::collections::VecDeque::new(),
            cam_sim_progress_buf: std::collections::VecDeque::new(),
            cam_sim_cancel,
            plugin_action_buf: std::collections::VecDeque::new(),
            plugin_install_buf: std::collections::VecDeque::new(),
            sent_plugin_revision: None,
            progress_buf: std::collections::VecDeque::new(),
            sent_library_revision: None,
            library_requested: false,
            stop,
        }
    }

    /// Pull every ready reply off the channel and demux it into the run/query
    /// buffers (so a `poll_run` never swallows a query reply and vice versa).
    fn drain(&mut self) {
        while let Ok(reply) = self.rx.try_recv() {
            self.file(reply);
        }
    }

    /// Demux one reply into its buffer. A session export is handed back (only
    /// [`HistoryRunner::session_for_main`] waits for one; a late one is dropped).
    fn file(&mut self, reply: Reply) -> Option<(u64, Option<brep_kernel::SessionTransfer>)> {
        match reply {
            Reply::SessionExport { generation, transfer } => return Some((generation, transfer)),
            Reply::ValidatedPlugins(reply) => self.plugin_install_buf.push_back(reply),
            Reply::PluginAction(reply) => self.plugin_action_buf.push_back(reply),
            Reply::Run(run) => self.run_buf.push_back(run),
            Reply::Query(query) => self.query_buf.push_back(query),
            Reply::MeshImport(reply) => self.mesh_import_buf.push_back(reply),
            Reply::MeshImportPhase(reply) => self.mesh_phase_buf.push_back(reply),
            Reply::RegionFit(reply) => self.region_fit_buf.push_back(reply),
            Reply::ApplyRegionChoices(reply) => self.apply_choices_buf.push_back(reply),
            Reply::StepProbe(reply) => self.step_probe_buf.push_back(reply),
            Reply::Topology(reply) => self.topology_buf.push_back(reply),
            Reply::SheetLines(reply) => self.sheet_lines_buf.push_back(reply),
            Reply::CamGenerate(reply) => self.cam_buf.push_back(reply),
            Reply::CamProgress(progress) => self.cam_progress_buf.push_back(progress),
            Reply::CamSimulate(reply) => self.cam_sim_buf.push_back(reply),
            Reply::CamSimProgress(progress) => self.cam_sim_progress_buf.push_back(progress),
            Reply::Progress(progress) => self.progress_buf.push_back(progress),
            Reply::NeedPartsLibrary => {
                // The thread dropped (or never had) the library this run
                // needs. Forget what we believe it holds so the next
                // `sync_parts_library` re-installs, and flag the refused
                // run for the caller to re-submit.
                self.sent_library_revision = None;
                self.library_requested = true;
            }
        }
        None
    }
}

/// How long the main thread waits for the runner's session copy before it
/// replays the history instead (the copy of l500 takes ~8 ms).
#[cfg(not(target_arch = "wasm32"))]
const SESSION_EXPORT_WAIT: std::time::Duration = std::time::Duration::from_millis(250);

#[cfg(not(target_arch = "wasm32"))]
impl Default for ThreadRunner {
    fn default() -> Self {
        Self::new()
    }
}

/// The runner thread's whole life: block on the next command, batch it with every
/// other command already queued, COALESCE consecutive `Run`s (a `Run` immediately
/// followed by another `Run` — with no `Query`/`Reset` between — is dropped; only
/// the last of each consecutive group runs), then process the batch IN ORDER so a
/// `Reset` or a `Query` interleaved between two runs keeps its place. Exits when
/// the command sender is dropped (`recv` errors) or the reply receiver is gone (a
/// `send` errors — the main side went away).
///
/// `stop` is the cooperative cancel: raised by [`ThreadRunner::cancel`] on a
/// thread that has already been abandoned, it is checked before every feature
/// a run executes, so the abandoned thread finishes the feature it is on and
/// exits at the next boundary instead of running the rest of the history for
/// a receiver that is gone.
#[cfg(not(target_arch = "wasm32"))]
fn thread_main(
    cmd_rx: std::sync::mpsc::Receiver<Command>,
    reply_tx: std::sync::mpsc::Sender<Reply>,
    stop: std::sync::Arc<std::sync::atomic::AtomicBool>,
    cam_cancel: std::sync::Arc<std::sync::atomic::AtomicBool>,
    cam_sim_cancel: std::sync::Arc<std::sync::atomic::AtomicBool>,
) {
    let mut runner = crate::pipeline::SceneRunner::new();
    while let Ok(first) = cmd_rx.recv() {
        if stop.load(std::sync::atomic::Ordering::Relaxed) {
            return;
        }
        // Gather this command plus everything else already waiting.
        let mut batch = vec![first];
        loop {
            match cmd_rx.try_recv() {
                Ok(command) => batch.push(command),
                Err(_) => break, // Empty or Disconnected — process what we have.
            }
        }
        // A Run immediately followed by another Run is coalesced away (its result
        // would be overwritten before anything observed it); a Run followed by a
        // Query/Reset/end still runs, so interleaved work sees the right geometry.
        let mut run_here: Vec<bool> = vec![true; batch.len()];
        for i in 0..batch.len() {
            if matches!(batch[i], Command::Run { .. })
                && matches!(batch.get(i + 1), Some(Command::Run { .. }))
            {
                run_here[i] = false;
            }
        }
        // Process the KEPT commands in order through the SHARED `process_command`
        // (byte-identical work to the wasm worker's per-message step), sending each
        // reply it produces; a coalesced-away Run is skipped without touching the
        // runner, so interleaved Query/Reset still see the right geometry.
        for (i, command) in batch.into_iter().enumerate() {
            if !run_here[i] {
                continue;
            }
            // A CAM job's progress post also reads the cancel flag: `false`
            // back to the job is its cancel (see `CamSink`).
            let is_cam = matches!(command, Command::CamGenerate(_));
            if is_cam {
                cam_cancel.store(false, std::sync::atomic::Ordering::SeqCst);
            }
            let is_sim = matches!(command, Command::CamSimulate(_));
            let mut progress = |reply: Reply| {
                // A lost receiver means the main side abandoned this thread:
                // stop at this boundary rather than finishing for nobody.
                let sent = reply_tx.send(reply).is_ok();
                if sent {
                    wake_main();
                }
                sent
                    && !stop.load(std::sync::atomic::Ordering::Relaxed)
                    && !(is_cam && cam_cancel.load(std::sync::atomic::Ordering::SeqCst))
                    && !(is_sim && cam_sim_cancel.load(std::sync::atomic::Ordering::SeqCst))
            };
            if let Some(reply) = process_command(&mut runner, command, &mut progress) {
                if reply_tx.send(reply).is_err() {
                    return; // The reply receiver is gone — the main side went away.
                }
                wake_main();
            }
        }
    }
}

#[cfg(not(target_arch = "wasm32"))]
impl HistoryRunner for ThreadRunner {
    fn session_for_main(&mut self, generation: u64) -> SessionOnMain {
        let Some(tx) = &self.tx else { return SessionOnMain::Unavailable };
        if tx.send(Command::ExportSession { generation }).is_err() {
            return SessionOnMain::Unavailable;
        }
        let deadline = std::time::Instant::now() + SESSION_EXPORT_WAIT;
        loop {
            let left = deadline.saturating_duration_since(std::time::Instant::now());
            let Ok(reply) = self.rx.recv_timeout(left) else { return SessionOnMain::Unavailable };
            if let Some((answered, transfer)) = self.file(reply) {
                if answered != generation {
                    continue; // a late answer to an earlier ask
                }
                return transfer.map_or(SessionOnMain::Unavailable, SessionOnMain::Copied);
            }
        }
    }
    fn submit_plugin_install(&mut self, request: PluginInstallRequest) -> bool {
        self.tx.as_ref().is_some_and(|tx| tx.send(Command::ValidatePlugins(request)).is_ok())
    }
    fn poll_plugin_install(&mut self) -> Option<PluginInstallReply> {
        self.drain();
        self.plugin_install_buf.pop_front()
    }
    fn sync_plugins(&mut self, revision: u64, fetch: &mut dyn FnMut() -> serde_json::Value) {
        if self.sent_plugin_revision != Some(revision) {
            if let Some(tx) = &self.tx {
                if tx.send(Command::SetPlugins { revision, packages: fetch() }).is_ok() {
                    self.sent_plugin_revision = Some(revision);
                }
            }
        }
    }
    fn submit_plugin_action(&mut self, request: PluginActionRequest) -> bool {
        self.tx.as_ref().is_some_and(|tx| tx.send(Command::PluginAction(request)).is_ok())
    }
    fn poll_plugin_action(&mut self) -> Option<PluginActionReply> {
        self.drain();
        self.plugin_action_buf.pop_front()
    }

    fn submit_run(&mut self, request: brep_kernel::HistoryRequest, generation: u64) {
        if let Some(tx) = &self.tx {
            let _ = tx.send(Command::Run {
                request,
                generation,
                parts_library_revision: self.sent_library_revision.unwrap_or(0),
            });
        }
    }

    fn sync_parts_library(
        &mut self,
        revision: u64,
        fetch: &mut dyn FnMut() -> brep_kernel::PartsLibraryMap,
    ) {
        if self.sent_library_revision == Some(revision) {
            return;
        }
        if let Some(tx) = &self.tx {
            let _ = tx.send(Command::SetPartsLibrary {
                library: fetch(),
                revision,
            });
            self.sent_library_revision = Some(revision);
        }
    }

    fn poll_library_request(&mut self) -> bool {
        self.drain();
        std::mem::take(&mut self.library_requested)
    }

    fn poll_run(&mut self) -> Option<RunReply> {
        self.drain();
        self.run_buf.pop_front()
    }

    fn run_reply_waiting(&mut self) -> bool {
        self.drain();
        !self.run_buf.is_empty() || self.library_requested
    }

    fn submit_query(&mut self, query: MeasureQuery) {
        if let Some(tx) = &self.tx {
            let _ = tx.send(Command::Query(query));
        }
    }

    fn poll_query(&mut self) -> Option<MeasureReply> {
        self.drain();
        self.query_buf.pop_front()
    }

    fn submit_mesh_import(&mut self, request: MeshImportRequest) {
        if let Some(tx) = &self.tx {
            let _ = tx.send(Command::MeshImport(request));
        }
    }

    fn poll_mesh_import(&mut self) -> Option<MeshImportReply> {
        self.drain();
        self.mesh_import_buf.pop_front()
    }

    fn poll_mesh_import_phase(&mut self) -> Option<MeshImportPhaseReply> {
        self.drain();
        self.mesh_phase_buf.pop_front()
    }

    fn submit_region_fit(&mut self, job: RegionFitJob) -> bool {
        match &self.tx {
            Some(tx) => tx.send(Command::RegionFit(job)).is_ok(),
            None => false,
        }
    }

    fn poll_region_fit(&mut self) -> Option<RegionFitReply> {
        self.drain();
        self.region_fit_buf.pop_front()
    }

    fn submit_apply_region_choices(&mut self, job: ApplyRegionChoicesJob) -> bool {
        match &self.tx {
            Some(tx) => tx.send(Command::ApplyRegionChoices(job)).is_ok(),
            None => false,
        }
    }

    fn poll_apply_region_choices(&mut self) -> Option<ApplyRegionChoicesReply> {
        self.drain();
        self.apply_choices_buf.pop_front()
    }

    fn submit_step_probe(&mut self, request: StepProbeRequest) {
        if let Some(tx) = &self.tx {
            let _ = tx.send(Command::StepProbe(request));
        }
    }

    fn poll_step_probe(&mut self) -> Option<StepProbeReply> {
        self.drain();
        self.step_probe_buf.pop_front()
    }

    fn submit_topology(&mut self, request: TopologyRequest) {
        if let Some(tx) = &self.tx {
            let _ = tx.send(Command::Topology(request));
        }
    }

    fn poll_topology(&mut self) -> Option<TopologyReply> {
        self.drain();
        self.topology_buf.pop_front()
    }

    fn wait_topology(&mut self, timeout: std::time::Duration) -> bool {
        self.drain();
        let deadline = std::time::Instant::now() + timeout;
        while self.topology_buf.is_empty() {
            let now = std::time::Instant::now();
            if now >= deadline {
                return false;
            }
            match self.rx.recv_timeout(deadline - now) {
                Ok(reply) => {
                    self.file(reply);
                }
                Err(_) => return false,
            }
        }
        true
    }

    fn submit_sheet_lines(&mut self, request: SheetLinesRequest) -> bool {
        match &self.tx {
            Some(tx) => tx.send(Command::SheetLines(request)).is_ok(),
            None => false,
        }
    }

    fn poll_sheet_lines(&mut self) -> Option<SheetLinesReply> {
        self.drain();
        self.sheet_lines_buf.pop_front()
    }

    fn submit_cam(&mut self, job: CamJob) -> bool {
        self.cam_cancel.store(false, std::sync::atomic::Ordering::SeqCst);
        match &self.tx {
            Some(tx) => tx.send(Command::CamGenerate(job)).is_ok(),
            None => false,
        }
    }

    fn poll_cam(&mut self) -> Option<CamReply> {
        self.drain();
        if self.cam_hold {
            return None;
        }
        self.cam_buf.pop_front()
    }

    fn hold_cam_replies(&mut self, hold: bool) {
        self.cam_hold = hold;
    }

    fn poll_cam_progress(&mut self) -> Option<CamProgress> {
        self.drain();
        let latest = self.cam_progress_buf.pop_back();
        self.cam_progress_buf.clear();
        latest
    }

    fn cancel_cam(&mut self) {
        self.cam_cancel.store(true, std::sync::atomic::Ordering::SeqCst);
    }

    fn submit_cam_sim(&mut self, job: CamSimJob) -> bool {
        // A cancel raised for an earlier chunk must not stop this one.
        self.cam_sim_cancel.store(false, std::sync::atomic::Ordering::SeqCst);
        match &self.tx {
            Some(tx) => tx.send(Command::CamSimulate(job)).is_ok(),
            None => false,
        }
    }

    fn poll_cam_sim(&mut self) -> Option<CamSimReply> {
        self.drain();
        self.cam_sim_buf.pop_front()
    }

    fn poll_cam_sim_progress(&mut self) -> Option<CamSimProgress> {
        self.drain();
        let latest = self.cam_sim_progress_buf.pop_back();
        self.cam_sim_progress_buf.clear();
        latest
    }

    fn cancel_cam_sim(&mut self) {
        self.cam_sim_cancel.store(true, std::sync::atomic::Ordering::SeqCst);
    }

    fn poll_progress(&mut self) -> Option<RunProgress> {
        self.drain();
        let latest = self.progress_buf.pop_back();
        self.progress_buf.clear();
        latest
    }

    /// Abandon the thread: raise its stop flag, close its channels, and spawn a
    /// fresh thread with a fresh registry. The old thread cannot be interrupted
    /// inside a feature — it finishes the one it is on (burning CPU until
    /// then), sees the flag, and exits. Always `true`: there is always a
    /// thread to replace.
    fn cancel(&mut self) -> bool {
        self.stop.store(true, std::sync::atomic::Ordering::Relaxed);
        self.tx.take();
        self.handle.take();
        *self = Self::new();
        true
    }

    fn reset(&mut self) {
        self.sent_plugin_revision = None;
        self.plugin_action_buf.clear();
        if let Some(tx) = &self.tx {
            let _ = tx.send(Command::Reset);
        }
        // A reset is a wholesale document switch: any replies still buffered from
        // the old model are stale — drop them (a fresh run/query supersedes).
        self.run_buf.clear();
        self.query_buf.clear();
        self.mesh_import_buf.clear();
        self.mesh_phase_buf.clear();
        self.region_fit_buf.clear();
        self.apply_choices_buf.clear();
        self.step_probe_buf.clear();
        self.topology_buf.clear();
        self.sheet_lines_buf.clear();
        self.progress_buf.clear();
        // `Command::Reset` clears the thread's kernel store, library included,
        // so what we believe it holds is void.
        self.sent_library_revision = None;
        self.library_requested = false;
    }
}

#[cfg(not(target_arch = "wasm32"))]
impl Drop for ThreadRunner {
    fn drop(&mut self) {
        // Closing a document or cancelling an import preview must not block
        // the UI on reconstruction. Closing the channel lets the worker exit
        // and release its registry once already-submitted work finishes.
        self.tx.take();
        self.handle.take();
    }
}