Errors, explained

An error on this site is an object with three parts, never a code alone. The full taxonomy lives in Reference → Errors; this is what a card looks like.

404 not_found — build is not served by the data plane

Reasonbuild has no plane: field, so it defaults to control. The data plane builds its allow-list from plane !== "control" and 404s everything else — by rule.

Tracecli → POST :3718/capabilities/build → DATA_PLANE_SLUGS.has("build") = false ✕

How to fixReplay and fix it Read GET /capabilities on each plane

What the agent does with retry

change-input: fix the request and go again. needs-human: stop and ask you. retry: try again. no: report the resource id.

Two exceptions worth knowing

MCP errors ride HTTP 200 as JSON-RPC errors. A rejected bearer on /mcp is always 401 invalid_token on the wire; the real reason is on the mcp.auth_reject log line.

The full error taxonomy is in Reference → Errors — six error codes, each with a retry strategy and a sample fix.