[FLO-13.2c.3] Execute deterministic single- and multi-provider composition fixtures #58

Parent: #46
Parent kit: #29
Roadmap-Step: FLO-Q03
Depends on: #57

Outcome

Add minimal deterministic single-provider and multi-provider composition fixtures that use only Flow’s public APIs and the frozen hermetic provider identities, without introducing a production graph scheduler.

Scope

• Add one single-provider composition fixture and one multi-provider composition fixture.
• Preserve explicit stage order, artifact dependencies, provider/package/executable identities, configuration digests, and expected evidence.
• Drive every stage through the public resolve, authorize, execute, observe, and accept boundaries.
• Reuse the hermetic kit’s frozen fake capability IDs rather than inventing real holon capability claims.
• Keep execution offline, bounded, deterministic, and redistribution-safe.

Acceptance criteria

• Single-provider and multi-provider fixtures declare explicit ordered stages and artifact handoffs.
• Every stage preserves its provider, package, executable, invocation, configuration, and accepted-artifact identity.
• Repeated runs produce equivalent normalized evidence and byte-identical accepted outputs.
• The fixtures consume only public Flow APIs and immutable fixture artifacts.
• The fixtures make no claim to production DAG scheduling, retry, resume, durable state, or real provider algorithms.
• No sibling repository source or mutable dependency is introduced.
• Focused tests, Rust 1.85, stable Rust, package checks, and repository validators pass.

Non-goals

• A production scheduler or public Flow CLI.
• Durable checkpoints, retry, resume, or recovery.
• Real Aniflow, Optiflow, or Renderflow algorithms.
• Broad scenario-matrix execution owned by later roadmap work.