DEFER_CAPABILITY_MISSING

What failed

Crux found an execution scope or binding, but the host cannot honor the requested operation.

Common cases:

• Inline defer(callback) on a Convex or Lambda named-only host
• Next after() or Vercel waitUntil() is unavailable
• A Workers binding has no request ctx
• A strict wrapper attempts named work without durable finalization

Why

Crux refuses to accept work the host cannot retain or finalize. A retention-port failure propagates after deterministic scope sealing; callback execution failures after successful acceptance remain contained.

Fix

1. Inline unsupported: use await defer(target, input) with Runtime, or choose a host with a real retention port.
2. Next/Vercel port missing: install the supported platform package and configure its binding.
3. Workers context missing: use @use-crux/cloudflare withCrux, or pass workers({ ctx }) to a per-request boundary.
4. Strict named finalization missing: use a binding advertising durableFinalization: true with a configured Runtime.

Config-only named calls use the caller's await as their acceptance barrier; they do not provide strict handler outcome or response commit semantics.

See Host support and Troubleshooting.