Do C2PA, Open Policy Agent, and study preregistration match the append-only-log-as-truth criterion, or only the broader 'gate at admission, verdict elsewhere' pattern?

Tests three candidate systems against the resolution criterion tracked by question-append-only-ledger-cross-domain-convergence — a system whose mechanism is genuinely "append-only-log-as-truth with judgment held outside the log," as already confirmed for CANONIC (claim-canonic-deliverable-is-an-append-only-evidence-ledger), ActiveGraph (claim-activegraph-rebuilds-babyagi-on-event-log), and R-LAM (claim-rlam-third-noncitng-subfield-append-only-log-with-verdict-separation). The finding: the three systems split. One matches the narrow log criterion; the other two match only the looser "gate at admission, verdict elsewhere" shape without an append-only log underneath it.

Claim: Open Policy Agent's decisions are computed statelessly per query; its optional decision logs are a peripheral audit feature, not the mechanism that produces the decision

Open Policy Agent (OPA) is used as a Kubernetes admission controller: "The Kubernetes API Server is configured to query OPA for admission control decisions when objects (e.g., Pods, Services, etc.) are created, updated, or deleted" (openpolicyagent.org/docs/kubernetes). This is the "gate at admission" half of the pattern. But the decision itself is not produced by consulting or replaying a log — OPA's own architecture page states: "OPA decouples policy decision-making from policy enforcement. When your software needs to make policy decisions it queries OPA and supplies structured data (e.g., JSON) as input" and OPA evaluates that input against currently-loaded policies and data to return a decision. Decision logging is listed as one of several optional add-on management capabilities ("Decision telemetry") alongside bundle distribution, status reporting, and discovery — management-plane features layered on top of the evaluator, not the substrate the evaluator reads from to decide. [Tier 1 — openpolicyagent.org official documentation]

Claim: C2PA's manifest store is a genuine append-only chain — each edit adds a new manifest without deleting prior ones, and the "active" manifest is defined as the last entry in that list

The C2PA technical specification states: "Each time an asset is changed, the existing provenance of the asset is preserved, with each new change being added to the provenance" (§1.1, Overview). The "active manifest" — the one whose content bindings are validated — is defined as "The last manifest in the list of C2PA Manifests inside of a C2PA Manifest Store" (§2.3.7). Redaction of an assertion does not delete a manifest; per §6.8, "an update manifest should be used to document the redaction... to indicate that digital content was not changed" — the redaction itself becomes a new appended entry rather than an erasure. [Tier 1 — spec.c2pa.org, official C2PA technical specification]

Claim: Study preregistration produces a single frozen, time-stamped, read-only snapshot document, not a continuously appended log

The Center for Open Science's own description of the practice: "Preregistration is the practice of posting a time-stamped, read-only version of your study plan to a public repository before beginning data collection or analysis" (OSF Support, "Welcome to Registrations & Preregistrations!"). Once submitted, that document is frozen: "Once you submit a registration, you will not be able to edit or make changes to it or any associated files," and a registration is "a frozen version of your project that can never be edited or deleted, but you can issue a withdrawal of it later, leaving behind basic metadata." [Tier 1 — help.osf.io, Center for Open Science / OSF official support documentation, primary source describing its own registry system]

Claim: Of the three, only C2PA's mechanism matches the narrow append-only-log-as-truth criterion; OPA and preregistration match only the broader "gate at admission, verdict elsewhere" pattern

Putting the three sourced mechanisms side by side: C2PA is structurally an append-only, additive manifest chain functioning as the asset's record of truth, but it lacks an admission gate. OPA is an admission gate (Kubernetes objects, API requests) whose verdict is a stateless live computation, with logging as an optional bolt-on rather than the truth-bearing substrate. Preregistration is an admission gate (must register before the study counts as confirmatory) whose artifact is a single frozen document, not a log. None of the three reproduces the full CANONIC/ActiveGraph/R-LAM shape — "the log is the ground truth AND the log is what gets consulted for judgment is pushed elsewhere." The broader "gate at admission, verdict elsewhere" description covers OPA and preregistration; the narrower append-only-log-as-truth description covers only C2PA's record-keeping half, and even there without the admission-gate component. [Synthesis drawn directly from the three sourced claims above; not itself resting on an independent source.]

Further leads

• C2PA's redaction mechanism (§6.8, "update manifest") looks like it might rhyme with the vault's "correct by surrounding, never by erasing" thread (compare claim-early-modern-printers-corrected-print-with-cancel-slips) — worth a dedicated capture if pursued.
• OPA Gatekeeper "brings awareness of the cluster's state, not just the single object under evaluation at admission time" (per Kubernetes.io blog on OPA Gatekeeper) — suggests some admission-control deployments of OPA do consult broader state; not verified against a Tier 1-2 source in this pass, worth checking whether that state is itself log-structured.
• The Nosek et al. 2018 PNAS "The Preregistration Revolution" is the standard academic primary source for the definitional claims here but was paywalled (403) during this session; a future pass should fetch it via an institutional-access route or the PMC/OSF preprint mirror to upgrade the preregistration claims from OSF-org-documentation to peer-reviewed-primary.
• Registered Reports (a preregistration variant with peer review of the plan itself, before results are known) came up in search results (AJE, RMIT/Surrey library guides) as a related but distinct mechanism from plain preregistration — not explored this pass.