Problem

Mesa now has first-class support for Scenarios (#3103, #3168, and updated example #3167), but SolaraViz doesn’t support them. This creates two distinct issues:

Issue 1: Parameter routing during reset
When users create sliders for scenario parameters (density, vision), clicking “Reset” fails because SolaraViz tries to pass these directly to MyModel.__init__(), which doesn’t accept them—they belong to the Scenario.

Issue 2: Leveraging Scenario for auto-generated UI
Scenarios already define typed parameters with defaults. How can we use this to create a clean, minimal-duplication API for generating UI controls? The challenge: Scenarios define defaults but not min/max ranges for sliders.

Current situation:

class MyScenario(Scenario):
    density: float = 0.7
    vision: int = 7

class MyModel(Model):
    def __init__(self, height=40, width=40, scenario: MyScenario | None = None):
        super().__init__(scenario=scenario)

Possible solutions

Option 1: Add scenario_params argument

page = SolaraViz(
    model,
    renderer,
    model_params={"height": 40, "width": 40},
    scenario_params={
        "density": Slider(...),
        "vision": Slider(...),
    }
)

Mesa changes needed:

• Add scenario_params parameter to SolaraViz()
• Update ModelController.do_reset() to reconstruct Scenario from parameters
• Render scenario params in separate UI section

Pros: Clear, explicit, easy to understand
Cons: More verbose, requires manual specification

Option 2: Auto-detect from type hints

# SolaraViz introspects model.scenario and auto-generates UI
page = SolaraViz(model, renderer)

# Optional customization
page = SolaraViz(model, renderer, scenario_params={"density": Slider(...)})

Mesa changes needed:

• Introspect model.scenario to get Scenario class
• Use get_type_hints() and _scenario_defaults to auto-generate controls
• Allow overrides via scenario_params

Pros: Minimal user code, leverages existing type hints
Cons: Less explicit, auto-generated ranges might not fit

Option 3: Something else?

Other nice ideas for a clean API?

Discussion Questions

1. How would the user API look?
2. Should scenario parameters appear in a separate UI section?
3. How do we handle the rng parameter that scenarios own?

Implementation areas

Regardless of option chosen:

• solara_viz.py: Update SolaraViz, ModelCreator, ModelController
• Documentation: Add examples and migration guide