narrative

OPD kind: System Diagram (the top-level OPD per ISO 19450 §6.5.1). Names the system, its environmental actors, and the system-level data flows.

Architectural commitment: This OPD declares Prism as the single informatical system (Prism is informatical.) with three environmental actors — the Application Author (physical), the Application User (physical), and the Rust Toolchain (informatical-environmental). The system's three input dependencies (Rust Toolchain, Author Source, Host Bytes) and three output products (Grounded Output, Trace, Certified Output) are the system-level surface elaborated in chapters 3 (Context and Scope) and 5 (Building Block View).

Cost-model commitments upheld: All of C1–C4. The SD declares the system whose cost-model the conceptual model establishes:

• C1 (operational cost = declared bandwidth at equality) is realized at this layer as the relationship between one Host Bytes admission (one forward(input) invocation) and one Grounded Output emission. The host-side retry loop (varying Host Bytes to find an admitting κ-label) is the externality C1 names.
• C2 (zero runtime movement) is realized as the single yields relation from Prism to each of its three outputs — no intermediate state object persists across invocations.
• C3 (structural inference) is realized as the directness of the requires / yields relations — Prism's relationship to its inputs is structural admission, not iterative refinement.
• C4 (axis qualification) is realized at this layer through the opacity of the σ-projection inside Prism — the SD does not reveal the canonical hash axis selection because the axis-qualification commitment is per-axis, not per-system; the in-zoom into SD2 surfaces the axis-mediated pipeline.

ISO 19450 vocabulary used:

• essence predicate (§8.3): physical for human actors; informatical for software and data; the Rust Toolchain is both environmental and informatical since it lives outside Prism but is informatical in essence.
• affiliation predicate (§8.4): all three actors are environmental (outside the system boundary); Prism and its data products are systemic (inside the system boundary, implicit since Prism is named as the system).
• handles relation (§7.3.4): connects environmental physical actors to the system they interact with — both Application Author and Application User handle Prism.
• requires / yields (§7.3.2–§7.3.3): the system's input-output procedural surface.

Arc42 cross-reference: Chapter 3 (Context and Scope) — the SD is the OPM realization of §3.1 (Business Context) and §3.2 (Technical Context); chapter 1 (Introduction and Goals) — the SD's actors are the three external stakeholders named in §1.2.