[3P] Tier-2: sandboxed creator code via Dynamic Workers (CRITICAL PATH)

[serge-ivo]

Part of the open-to-third-party program. This is the long pole — the public open is gated on it being solid.

Goal: creators ship custom logic that runs isolated, never touching platform/other-tenant secrets.

• Integrate Worker Loader API (Dynamic Workers): store creator source in D1/R2 → load into an isolated V8 sandbox at runtime. NEVER `eval()` inside the platform worker (would run creator code with platform bindings).
• Scoped per-tenant bindings + server-side secret injection — creator code sees only its instance's scoped resources; platform/other-tenant secrets are injected server-side and never exposed.
• Define the creator-code contract: available tools/bindings, resource limits (CPU/time/subrequests), egress policy (reuse `lib/ssrf.ts`).
• Per-Worker metering hook (CF meters per unique Worker) → feeds usage/cost.
• Consider Workers for Platforms only for the "managed, deployed, custom-domain" creator worker case.
• Threat-model doc + red-team before any third party touches it.

[serge-ivo]

Labelled deferred: no demand — not cancelled, and not started.

Per #250 ("the board contradicts the focus bet — make deferred-by-strategy legible"), and #58's own wording, which gates this work on demand rather than on readiness.

The measurement that decides it, taken 2026-08-06 over 30 days (GET /v1/admin/usage/external):

external users:  0
operator calls:  2,782
spend:           $40.92 — entirely the operator's own

This issue serves third-party creators. There are none, and nothing on the board measures progress toward getting one. Leaving it as live work makes the roadmap read as if it were in flight, which is precisely what #250 objects to.

The un-gate condition is #68's: external users on a first-party runtime agent. When that number is non-zero, this comes back — the endpoint above makes it checkable rather than a matter of opinion.

Nothing here is judged wrong or wasted. The platform work that already landed (capability registry, connector framework, declarative pipelines, per-tool consent) is what makes first-party agents cheap to build, and it stays. What is deferred is the marketplace layer on top: sandboxing untrusted creator code, curated publish review, payout metering, creator onboarding.