Execute an approved modeling plan for a fresh experiment session.
the approved modeling plan (the approval gate is the agent's job)
the injected dependency bundle (entity factory, trainer, clock, strategist)
optional run tunables (concurrency, prune rules, budget override)
the experiment, session, iterations, final leaderboard, best model, and stop reason
The deterministic experiment orchestrator. Stateless across calls; construct once and reuse. All dependencies are supplied per call via ExperimentDeps.