#Refactor CLI command dispatch: replace reflection-based partial Program god-class with IFalloutCommand types #392

Problem

Fallout.Cli implements every CLI command as a static int method on one partial class Program, split across ~10 Program.*.cs files and dispatched by reflection (Program.Handle reflects over its own int-returning methods). The partial split looks organized, but the underlying type is a god object — it owns dispatch, secrets, packages, Cake interop, navigation, config, run orchestration, and the Spectre prompts. Reflection dispatch is stringly-typed: a typo'd signature compiles and fails at runtime, and nothing is DI-able or unit-testable in isolation.

Outcome

One command = one type behind a typed IFalloutCommand, discovered by type via DI instead of reflection. The :command CLI surface and shell-function names stay exactly as they are (non-breaking).

public interface IFalloutCommand
{
    string Name { get; }   // e.g. "run", "setup"
    int Execute(string[] args, AbsolutePath rootDirectory, AbsolutePath buildScript);
}

Each Program.X.cs partial becomes a standalone XCommand implementing IFalloutCommand; the dispatcher resolves by Name. The partial keyword disappears. Shared helpers move into injectable services in the final collapse PR.

Acceptance criteria

• IFalloutCommand + a type/DI-based dispatcher replace reflection dispatch
• Every command is its own type; Program collapses to a thin entry point (no partial)
• CLI command names + shell-function spellings unchanged (dash/case-insensitive preserved)
• Dispatch has unit-test coverage
• Shared helpers extracted into injectable services

Approach

Incremental — one command per PR behind a transitional DelegateCommand adapter so nothing regresses. Tracked by the #394 stack.