Bulk mode, partial failures, and error handling

Bulk support is route-specific

Only the routes that explicitly allow bulk mode should be used for comma-separated selector lists. That keeps the rest of the API predictable and avoids hidden branching behavior on endpoints that are meant to stay single-target.

The docs surface bulk as a documented capability of `current` and `convert`, not as a hidden behavior you discover by trial and error.

Per-item failure is not the same as total failure

A bulk array can contain successful items and per-item error wrappers in the same response. That is a normal integration case and should not be treated as equivalent to an HTTP-level failure.

Request-level errors still use the shared error response model with codes, message text, and request metadata.

• Inspect array items individually in bulk mode.
• Log request IDs from gateway or forwarded failures.
• Do not assume a single array shape means every item succeeded.