The scheduler composes nested BEC sequence components and executes their JSON to the existing run_sequence procedure. It requires the BEC feature/scan_sequencer branch, installed in both this GUI environment and the procedure worker environment. There is no new execution service.

Open Scan Scheduler in bec-app, add a ScanScheduler through the GUI server/Designer, or run:

python -m bec_widgets.examples.scan_scheduler

Opening the example does not move hardware or acquire scans. Its samx and time_scan inputs must be available on your deployment before validation/execution succeeds.

Compose and inspect

Select a sequence or loop, choose a component and click Add step. A selected sequence child inserts a sibling after that child. Wrap surrounds the selected step with a sequence or loop.
Edit the selected component in the inspector. Changes save automatically. Repeat counts must be positive. The card menu provides wrap, reorder and remove actions.
Set targets accept dotted device/signal names. Wait for completion controls native blocking set/move behavior. Visible for_each variables appear in the Variable selector.
Scan definitions use the existing ScanControl widget: its scan selector, argument groups, device bundles, input bounds, units, tooltips and Restore last behavior. The scheduler hides its execution buttons; composing a step does not submit a scan. Inputs accept a visible loop variable directly, for example $exposure. Autocompletion offers the current scope; numeric literals retain their native bounds and units. Existing positional inputs remain positional, and untouched missing arguments remain missing so backend validation can reject them.
Advanced settings → Edit arguments as raw JSON supports metadata, whole argument-mapping references and structured expressions. For example {"ref": "pol"}. Use {"type": "literal", "value": ...} to protect dictionaries resembling reserved expressions.
Description, Python and JSON update automatically after editing. Description is selected first. Validation covers the complete tree, references and definitions. Execution also checks live scan/device inputs before requesting the procedure. Invalid sequences cannot execute.
JSON → Apply JSON imports edits made to the document JSON. Sequence options → Open/Save uses standalone sequence documents. Reusable definitions accepts a JSON list of versioned backend definitions; save/share that list separately alongside a sequence that needs it. This prototype does not provide a reusable-definition authoring form.

Execute

Choose Execute to validate the sequence and request the existing run_sequence procedure. Validation and the request run off the Qt thread. The request contains the current JSON document and the transitive reusable definitions it needs. The worker independently validates these inputs before using native IPython scan/device calls. Scan implementations must be available in that worker.

The widget does not keep submission records, queue views or history. Procedure execution and interruption remain owned by BEC. Closing this editor does not interrupt a running procedure.

Programmatic use

from bec_widgets.widgets.control.scan_scheduler import ScanScheduler

scheduler = ScanScheduler(client=bec)
scheduler.load_json(sequence_json, definitions_json)  # definitions defaults to "[]"
scheduler.show()
scheduler.validate_sequence()  # optional: refresh immediately instead of waiting for automatic updates
# scheduler.execute_sequence()  # explicit execution action