convertConstToEnum emits non-string enum values (const: false -> enum: [false]); Gemini rejects with 400 TYPE_STRING

[willowite]

Summary

convertConstToEnum() turns every const into enum: [value], including boolean and number constants. Gemini accepts only string enum values, so any request that carries a tool with const: true / const: false (common in discriminated unions from MCP tools) is rejected with HTTP 400 before the model runs.

Error

Invalid value at 'request.tools[0].function_declarations[194].parameters.properties[0].value.items.any_of[0].properties[12].value.enum[0]' (TYPE_STRING), false
Invalid value at 'request.tools[0].function_declarations[195].parameters.properties[0].value.items.one_of[0].properties[10].value.properties[0].value.enum[0]' (TYPE_STRING), true
... (18 lines like this per request)
Status: 400

Every request with the full tool set fails, so the model is unusable as a subagent until the offending tools are removed.

Where

packages/opencode/src/plugin/request-helpers.ts, convertConstToEnum() on main:

if (key === 'const' && !schema.enum) {
  result.enum = [value]   // value may be boolean or number
}

Repro

Any tool whose JSON schema contains { "const": false } (or true, or a number), for example:

{ "type": "object", "properties": { "flag": { "const": false } } }

sent to google/antigravity-gemini-3.8-flash (effective gemini-3.8-flash-high).

Suggested fix

Convert only string constants, and leave non-string const without an enum (Gemini keeps the declared type):

if (key === 'const' && !schema.enum) {
  if (typeof value === 'string') {
    result.enum = [value]
  }
}

I run this change locally on 2.2.1 and the same tool set is accepted.

Environment

• @cortexkit/opencode-antigravity-auth 2.2.1 (latest on npm)
• OpenCode 1.18.31, Windows 11