Port from anomalyco/opencode#24730: Moonshot's JSON Schema validator rejects
two shapes that the rest of the JSON Schema ecosystem accepts:
1. $ref nodes with sibling keywords. Moonshot expands the reference before
validation and then rejects the node if keys like `description`, `type`,
or `default` appear alongside $ref. MCP-sourced tool schemas commonly
put a `description` on $ref-typed properties so the model sees the
field hint — which worked on every provider except Moonshot.
2. Tuple-style `items` arrays (positional element schemas). Moonshot's
engine requires ONE schema applied to every array element. Common in
tool schemas generated from Go/Protobuf that model fixed-length arrays
as `[{type:number}, {type:number}]`.
Repairs applied in `agent/moonshot_schema.py`:
- Rule 3: when a node has `$ref`, return `{"$ref": <value>}` only
(strip every sibling). The referenced definition still carries its own
description on the target node, which Moonshot accepts.
- Rule 4: when `items` is a list, collapse to the first element schema
(falling back to `{}` which is then filled by the generic missing-type
rule). Preserves `minItems` / `maxItems` / other siblings.
Tests: 10 new cases across TestRefSiblingStripping + TestTupleItems,
plus the existing TestMissingTypeFilled::test_ref_node_is_not_given_synthetic_type
still passes (it asserted plain $ref passes through; now it passes through
as exactly `{"$ref": "..."}` which is strictly compatible).
All 35 tests in test_moonshot_schema.py pass.
93e109a1d5