ENGINE_BUSY

The solver was busy with other requests for longer than a call may wait. HTTP 503. Nothing was charged; retry after retry_after_ms.

The service is answering other requests and this one waited as long as a call may wait for the solver. Nothing about the request is wrong, and nothing was charged: a check is charged only once it has the solver.

The envelope

{"ok": false,
 "error": {"code": "ENGINE_BUSY",
           "message": "the solver is busy with other requests; retry this call in 10000 ms",
           "docs": "https://docs.agents.jaxon.ai/errors/engine-busy.md",
           "retry_after_ms": 10000},
 "versions": {"...": "..."}}

The REST door also sends Retry-After, in whole seconds.

What to do

**Wait retry_after_ms, then send the same call again.** Do not change the source or the claims: they were never looked at.
Back off if it happens twice. Double the wait each time rather than retrying in a tight loop, which only lengthens the queue you are waiting in.
If it persists for minutes, report it with the versions block.

See also: [BUDGET_EXCEEDED](budget-exceeded.md), Error codes.