FE-1487: Quick simulation runs an ad-hoc scenario when none is selected

[kube]

🌟 What is the purpose of this PR?

The first consumer of the ad-hoc scenario form (FE-778): with no scenario selected, the Simulation Settings panel edits the run's initial state directly, inline — an "Initial state" column between the parameters and the computation settings, with no separate edition step — and the simulation provider compiles that state through a scenario generated at run time. The generated scenario is never persisted into the net file. Sits above FE-1486 (#9285) in stack #9286.

🔗 Related links

• FE-1487 (internal): this PR
• FE-778 (internal): the umbrella ticket

🔍 What does this change?

react/simulation/context.ts and provider.tsx:

• SimulationContext gains adHocScenario: AdHocScenarioState | null and setAdHocScenario. The setter invalidates the current simulation, the same as every other configuration setter.
• When no named scenario is selected and adHocScenario is set, the provider synthesizes a scenario with synthesizeAdHocScenario and compiles it through the existing compileScenario path. Synthesis errors surface through the existing scenarioCompilationErrors Banner (netParameter errors map to the parameterOverride source, everything else to initialState).
• The panel's parameter inputs stay the single owner of parameter values: the synthesis context's net parameters carry the panel's current values as defaults, and the form receives no parameters section of its own.

simulation-settings.tsx: with "No scenario" selected, the panel's grid grows a third column, Initial state, hosting AdHocScenarioForm inline — bare (the panel's own small-caps heading grammar, no section chrome) and withVariables={false} (this embedding offers no scenario Variables; the panel's parameter inputs stay the single owner of parameter values, so the form gets no Parameters section either). The column scrolls with the same fade treatment as the parameters list, and a Clear button appears next to its title once the state is non-empty. Selecting a saved scenario collapses the panel back to two columns. The form runs its own LSP session, so expressions type-check live against the net. The earlier "Define initial state" pencil-button drawer is gone (ad-hoc-scenario-drawer.tsx deleted) — no edition step, the form is the settings.

Pre-Merge Checklist 🚀

🚢 Has this modified a publishable library?

This PR:

• modifies an npm-publishable library and I have added a changeset file(s) (patch).

📜 Does this require a change to the docs?

The changes in this PR:

• add a user-visible surface. The user-guide page ships with the last PR of the stack, once all three consumers exist, so the guide describes the feature once.

🕸️ Does this require a change to the Turbo Graph?

The changes in this PR:

• do not affect the execution graph.

🛡 What tests cover this?

The FE-1485 tests cover synthesis and compilation of everything the drawer can produce. The four extended mock fixtures keep the existing hook, playback, and story tests passing against the widened context.

❓ How to test this?

1. turbo run dev --filter @apps/petrinaut → open a net → Simulate → simulation settings.
2. Leave the scenario picker on "No scenario": the Initial state column appears — define token rows or counts right there, then run the simulation.
3. Pick a named scenario: the column disappears and the named scenario takes over, unchanged.

🐾 Next steps

FE-1488 wires the experiment drawer's no-scenario branch, FE-1489 the optimization drawer with manifest emission (both hold until the experiment-backend PRs #9178/#9179 merge).

🤖 Generated with Claude Code

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