FE-1263: Sweep scenario parameters with a navigator that computes the selection

[kube]

Important

Experimental
Behind the Parameter sweeps feature flag.

Summary

Before this PR, experiments take one fixed value per scenario parameter. FE-1263 prototype swept parameters with a bespoke lazy-grid scheduler outside the shared experiment runtime.

Experiments can now sweep scenario parameters. A Sweep toggle per numeric parameter defines evenly spaced values. Ranges form a grid capped at 200 combinations, and the results drawer gains a pinned navigator over it. Only the selected combination computes: runs accumulate in escalating batches that stream into the charts. Moving any control cancels the in-flight batch and restarts on the new combination. Visited combinations keep their results. Prototype's scheduler is replaced by batches through the backend registry.

Links

• Ticket FE-1263
• Docs Parameter sweeps
• Docs Experiments

Changes

UI

• Create drawer gains a Sweep toggle per numeric parameter

  Toggle reveals Min/Max/Values inputs.
  Combination counter warns above 50 and blocks above 200.
  "Runs" is relabelled "Runs per combination" when sweeping.

• Section gains a sticky-band slot in the results drawer

  Band content stays pinned with the title while the body scrolls.
  Sweep's Parameters strip lives there: a segmented control per short axis, a stepper per long one, and a refinement line reading "61 of 100 runs — refining while you stay here".

Sweep session and grid

• New react/experiments/sweep-session.ts runs the refinement loop

  One combination is live at a time.
  Batch b covering runs [from, target) seeds itself with deriveRunSeed(seed, from), so every combination samples the same common-random-numbers sequence and a cancelled rung re-runs identically.

• Finished batches fold into a per-combination cache

  In-flight frames merge with the cache for display and are discarded on cancellation.
  Session is backend-agnostic and consumes an injected instantiateBatch.

• react/experiments/parameter-grid.ts is ported from the prototype

  Range expansion with float-artifact stripping and integer/ratio validation, the cartesian grid with its 200-combination cap, and the run ladder of 8, 25, 100, 500, 1000 up to the per-combination budget.
  Prototype's cell levelling and cross-cell marginalization stay behind, since compute follows the selection.

• Scalar frames merge through the run-aggregate monoid they carry

  Exact rather than a weighted mean.

• Provider runs a sweep's first batch through the plain backend-selection walk

  Same walk as a plain experiment.
  selectExperimentBackend now returns the chosen backend.
  Later batches re-assess that backend per request.

• GPU backend regenerates its shader for each combination's parameter values

  Scenario recompiles per batch because swept values change the compiled initial state.

• New non-terminal status idle means the selected combination is saturated

  Moving a control resumes running.

Test coverage

• parameter-grid.test.ts, 21 tests:

  Range expansion, validation, the grid, the ladder, exact frame merging.

• sweep-session.test.ts, 8 tests:

  Ladder climbing with batch folding, restart on selection change with in-flight discard, mid-ladder resume on revisit, error stop, cell reads for other consumers.

• provider.test.tsx, 4 new tests:

  Fixed/range splitting, per-parameter range errors, the combination cap, undeclared-parameter inputs ignored.

• Parameter sweep story, verified interactively:

  Navigator renders over a streaming distribution chart. Selection click, sticky band under scroll.

How to test

• Open Petrinaut preview on Vercel
• Viewport controls > Settings > Simulation > Parameter sweeps
• Load example, select scenario with numeric parameters
• Simulate > Experiments > Create
• Flip Sweep on one or two parameters, Run
• Move controls in the drawer's Parameters strip
• Expect charts to re-stream

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Project	Deployment	Actions	Updated
hash	Ready	Preview	Sep 2, 2026 7:54pm UTC
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