feat: add fast live processing previews

Run previews in the existing worker runtime to avoid a second Pyodide
startup while keeping temporary results isolated from workspace state.

Assisted-by: GPT-5.6 Sol

Author: PierreRaybaut

CHANGELOG.md

@@ -6,12 +6,22 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.1.0/)
 
 ## [Unreleased]
 
+### Added
+
+- **Optional processing previews:** compatible signal and image processings
+  can now render a temporary result while their parameters are edited. The
+  preview is disabled by default, reuses the already-loaded computation worker
+  without changing the workspace, supports bounded numeric sliders and
+  image-profile geometry, and is discarded on Cancel or Escape; OK still
+  performs the normal processing from the original source.
+
 ### Changed
 
 - **Guidata compatibility:** browser runtimes now require guidata 3.15 and use
   its native async DataSet backend and JSON Schema exporter. The former
   backend backport has been removed; a focused compatibility patch preserves
-  the `FloatArrayItem` sizing hints required by the browser array editor.
+  the `FloatArrayItem` sizing and numeric-parity hints required by browser
+  editors.
 
 ## [0.9.0] - 2026-08-11
 

README.md

@@ -21,7 +21,7 @@ The latest release is deployed automatically to GitHub Pages. Open the link in a
 DataLab Web mirrors a large portion of the desktop application surface:
 
 - **Signal & image panels** — 1D curves and 2D arrays with a rich set of synthetic generators, full Plotly visualisation, cross-hair markers, contrast adjustment, cross profiles and stats area tools.
-- **Processing & analysis** — operations, transforms, filters, fitting, FFT/PSD, stability analyses, measurements and profile extraction, exposed automatically through the menu bar by introspecting Sigima's catalog.
+- **Processing & analysis** — operations, transforms, filters, fitting, FFT/PSD, stability analyses, measurements and profile extraction, exposed automatically through the menu bar by introspecting Sigima's catalog. Compatible parameterised processings offer an optional non-publishing live preview before anything is added to the workspace.
 - **ROI & object tree** — segment / rectangular / circular / polygonal regions of interest, plus a multi-group workspace with drag & drop, metadata editor, statistics card and computation history.
 - **Macros & notebooks** — embedded Python editor and multi-tab notebook panel, each running in dedicated Web Workers, with `.ipynb` import/export and bidirectional macro ⇄ notebook conversion. See [doc/notebooks.md](doc/notebooks.md).
 - **Plugins** — Qt-compatible `PluginBase` API: the same plugin source runs in DataLab desktop and DataLab Web. See [doc/plugins.md](doc/plugins.md).

doc/architecture.md

@@ -33,11 +33,14 @@ flowchart TB
             Actions["Action registry<br/>(src/actions)"]
             DBridge["DialogBridge.tsx"]
             RT["DataLabRuntime (TS)<br/>(src/runtime/runtime.ts)"]
+            Preview["ProcessingPreviewController.ts<br/>bounded preview queue"]
             Py0["Pyodide #0 — main<br/>bootstrap.py · processor.py<br/>dlw_*.py · Sigima · numpy · scipy"]
 
             UI -->|dispatch| Actions
             Actions -->|typed calls| RT
             RT -->|runPython| Py0
+            UI --> Preview
+            Preview -->|previewFeature| RT
             Py0 -->|dialog requests| DBridge
             DBridge --> UI
         end
@@ -68,6 +71,9 @@ Key facts:
 - **Each macro / notebook runs in its own Web Worker** with its own
   Pyodide instance. Workers never touch the main object model directly:
   they call back to the main runtime through `proxyBridge`.
+- **Processing preview reuses the already-loaded computation runtime**. Python
+  deep-copies the source, computes a temporary plotting payload, and never
+  publishes the copy or result to the main object model.
 - **The host page (optional)** controls an embedded DataLab-Web through
   the same RPC vocabulary, but transported by `remoteBridge` over
   `window.postMessage`.
@@ -83,7 +89,7 @@ right.
 flowchart LR
     L1["<b>L1 — UI layer</b><br/>(React components)<br/><br/>src/components/<br/>src/App.tsx<br/>src/main.tsx<br/><br/><i>Purely presentational.<br/>No Pyodide imports.</i>"]
     L2["<b>L2 — Orchestration</b><br/><br/>src/actions/<br/>(registry, menu builder)<br/>src/macros/<br/>src/notebook/<br/>src/plugins/<br/>src/aiassistant/<br/>src/preferences/"]
-    L3["<b>L3 — Runtime / bridge</b><br/>(TypeScript)<br/><br/>RuntimeApi.ts (façade)<br/>runtime.ts<br/>(DataLabRuntime + types)<br/>WorkerRuntimeProxy.ts · kernelWorker.ts<br/>runtimeMode.ts · workerProtocol.ts<br/>RuntimeContext.tsx<br/>WorkspaceContext.tsx<br/>MacroRuntime.ts<br/>proxyBridge.ts · remoteBridge.ts<br/>macroWorker.ts · notebookWorker.ts<br/>src/storage/ (OPFS spill stores)"]
+    L3["<b>L3 — Runtime / bridge</b><br/>(TypeScript)<br/><br/>RuntimeApi.ts (façade)<br/>runtime.ts<br/>(DataLabRuntime + types)<br/>WorkerRuntimeProxy.ts · kernelWorker.ts<br/>runtimeMode.ts · workerProtocol.ts<br/>ProcessingPreviewController.ts<br/>RuntimeContext.tsx<br/>WorkspaceContext.tsx<br/>MacroRuntime.ts<br/>proxyBridge.ts · remoteBridge.ts<br/>macroWorker.ts · notebookWorker.ts<br/>src/storage/ (OPFS spill stores)"]
     L4["<b>L4 — Python kernel</b><br/>(loaded into Pyodide)<br/><br/>bootstrap.py<br/>processor.py<br/>dlw_main.py<br/>dlw_wheels.py<br/>dlw_plugins.py<br/>dlw_applications.py<br/>dlw_h5browser.py<br/>dlw_interactive_fit.py<br/>dlw_title_format.py<br/>notebook_display.py<br/>macro_proxy.py<br/>_guidata_*_shim.py"]
     L5["<b>L5 — Computation engine</b><br/><br/>Sigima<br/>+ numpy · scipy<br/>+ scikit-image<br/>+ h5py · pandas …<br/><br/><i>Installed via micropip<br/>on first load.</i>"]
 
@@ -128,9 +134,12 @@ Presentational React. Notable components:
   metadata / stats / history.
 - `SignalPlot.tsx`, `ImagePlot.tsx`, `MultiImagePlot.tsx`,
   `CentralViewSwitcher.tsx` — Plotly-based central plot area.
-- `DataSetDialog.tsx` + `DataSetForm/` — **auto-generated parameter
+- `DataSetDialog.tsx`, `ProcessingDataSetDialog.tsx` + `DataSetForm/` —
+  **auto-generated parameter
   dialogs** from guidata DataSet JSON schemas (do not hand-write a form
   unless the auto path genuinely cannot express it).
+- `ProcessingPreview.tsx` + `ProcessingPreviewPlot.tsx` — optional,
+  non-publishing signal/image result preview for eligible processing dialogs.
 - `DialogBridge.tsx` — single React entry-point that **receives dialog
   requests from Python** via `bootstrap.set_dialog_bridge()` and routes
   them to the appropriate React dialog component.
@@ -233,7 +242,9 @@ flowchart LR
         MR["MacroRuntime.ts<br/>spawns workers on demand<br/>keeps a warm standby<br/>postMessage glue"]
         PB2["proxyBridge.ts<br/>whitelisted command router"]
         RT3["DataLabRuntime"]
+        PC["ProcessingPreviewController.ts<br/>one active + latest pending"]
         PB2 --> RT3
+        PC -->|previewFeature| RT3
     end
 
     subgraph Workers2["Web Workers"]
@@ -261,6 +272,19 @@ call. Workers cannot invoke arbitrary methods — only the ones explicitly
 listed (add_signal, add_image, list/get/delete object, add/set object
 from pickle, add_group, get/set selection, etc.).
 
+`ProcessingPreviewController` coordinates requests per `RuntimeApi`: one
+computation may run while a single pending slot retains only the latest
+parameters. `bootstrap.preview_feature` deep-copies the source and delegates
+to the same `BaseProcessor.apply` path as publication, then returns only a
+binary plotting payload. It never inserts the temporary object into `_MODEL`,
+updates processing history, or dirties the workspace.
+
+Disabling preview, Cancel, Escape, or dialog unmount drops pending work and
+invalidates late results. A Python call that has already started is allowed to
+finish; it may delay the next serialised runtime call. Preview controls are
+therefore exposed only for the default worker-hosted runtime and hidden in the
+`runtime=main` fallback, where computation would block the UI thread.
+
 #### Remote control bridge
 
 ```mermaid
@@ -457,12 +481,14 @@ compatibility independently of the application version.
 ```text
 1. User clicks  Processing › <feature>     in MenuBar
 2. action.run(ctx)  (from src/actions/registry.ts)
-3. If params needed → DataSetDialog (auto-generated from JSON schema)
-4. runtime.applyFeature(featureId, selectedOids, paramValues)
-5. pyodide.runPython → processor.apply_*(feature, oids, params)
-6. Sigima computes; new SignalObj/ImageObj added to _MODEL
-7. bootstrap returns new oids; UI refreshes ObjectTree + plots
-8. WorkspaceContext is marked dirty
+3. If params needed → ProcessingDataSetDialog (auto-generated from JSON schema)
+4. Optional Preview → runtime.previewFeature(featureId, sourceOid, paramValues)
+5. bootstrap deep-copies the source and returns a private plotting payload
+6. OK invalidates preview and calls runtime.applyFeature(featureId, selectedOids, paramValues)
+7. pyodide.runPython → processor.apply_*(feature, oids, params)
+8. Sigima computes; new SignalObj/ImageObj added to _MODEL
+9. bootstrap returns new oids; UI refreshes ObjectTree + plots
+10. WorkspaceContext is marked dirty
 ```
 
 ### 5.2 Running a macro

doc/userguide/computation-engine.md

@@ -33,6 +33,27 @@ Each processing's parameters are described by a
 reads that schema and renders the dialog automatically — the same data
 model that the desktop application uses to draw its Qt forms.
 
+Eligible bounded numeric parameters also get a slider beside the exact
+numeric input. The slider never replaces typed entry and is omitted when the
+schema does not provide safe finite bounds.
+
+Compatible one-input/one-output processings expose an optional **Preview**
+checkbox, initially off. Enabling it reuses the already-loaded computation
+runtime to process a private copy of the source; it does not add an object,
+alter history, or mark the workspace as modified. Edits are debounced while
+typing and sampled while dragging a slider, with an immediate refresh when the
+slider is released. If several objects were selected, **Preview source**
+chooses the representative input without changing the selection or the final
+batch operation.
+
+**Cancel** and **Esc** discard the temporary result and any waiting refresh.
+An already-running computation finishes in the background and its late result
+is ignored. **OK** runs the normal processing path from the original source
+and current parameters. Preview is hidden in the `runtime=main` fallback to
+avoid running this interactive work on the UI thread. The Processing tab in
+the object side panel retains its explicit **Apply** and **Reset** controls;
+editing that tab never republishes a result automatically.
+
 ## What the desktop docs do **not** cover
 
 - The **runtime constraints** of the browser (memory limits, OPFS,

src/App.tsx

@@ -90,6 +90,7 @@ import {
 import { MULTI_SIGNAL_LIMIT, useSelectionView } from "./hooks/useSelectionView";
 import { useSignalAxisGroups } from "./hooks/useSignalAxisGroups";
 import { DataSetDialog } from "./components/DataSetDialog";
+import { ProcessingDataSetDialog } from "./components/ProcessingDataSetDialog";
 import type { ProfileFeatureId } from "./components/ProfileDefinitionDialog";
 import { OperandPicker } from "./components/OperandPicker";
 import { HelpDialog, type HelpView } from "./components/HelpDialog";
@@ -389,7 +390,7 @@ function usePersistedSignalLayoutMode(): [
 }
 
 export default function App() {
-  const { runtime, status, message, error } = useRuntime();
+  const { runtime, status, message, error, previewAvailable } = useRuntime();
   const workspace = useWorkspace();
   const confirm = useConfirm();
   const notify = useMessage();
@@ -5129,9 +5130,13 @@ export default function App() {
           />
         )}
         {pending && runtime && (
-          <DataSetDialog
+          <ProcessingDataSetDialog
             title={pending.feature.label.replace(/\u2026$/, "")}
             payload={pending.schema!}
+            runtime={runtime}
+            previewAvailable={previewAvailable}
+            feature={pending.feature}
+            sourceIds={pending.sourceIds}
             resolveChoices={(itemName, currentValues) =>
               runtime.resolveFeatureChoices(
                 pending.feature.id,
@@ -5159,6 +5164,10 @@ export default function App() {
           <Suspense fallback={null}>
             <ProfileDefinitionDialog
               title={pendingProfile.feature.label.replace(/\u2026$/, "")}
+              runtime={runtime}
+              previewAvailable={previewAvailable}
+              feature={pendingProfile.feature}
+              sourceIds={pendingProfile.sourceIds}
               featureId={
                 pendingProfile.feature.id.replace(
                   /^image:/,
@@ -5172,13 +5181,15 @@ export default function App() {
                   pendingProfile.feature.id,
                   itemName,
                   currentValues,
+                  pendingProfile.sourceIds[0],
                 )
               }
               resolveCallbacks={(itemName, currentValues) =>
                 runtime.resolveFeatureCallbacks(
                   pendingProfile.feature.id,
                   itemName,
                   currentValues,
+                  pendingProfile.sourceIds[0],
                 )
               }
               resolveActive={(currentValues) =>