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convertConstToEnum emits non-string enum values (const: false -> enum: [false]); Gemini rejects with 400 TYPE_STRING #17
Description
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-auth2.2.1 (latest on npm)- OpenCode 1.18.31, Windows 11
Activity
willowite commentedon Sep 30, 2026
A source-level follow-up: please cover both schema adapters, not only
constconversion in the OpenCode package.The current
packages/core/src/transform/gemini.tsalso retains non-string enum values:In
packages/opencode/src/plugin/request-helpers.ts,convertConstToEnumstill unconditionally producesresult.enum = [value].Suggested upstream changes
For the Gemini schema boundary, retain an enum only when every value is a string. Do not stringify boolean or numeric values while keeping the original declared type.
} else if (key === 'enum' && Array.isArray(value)) { - // Keep enum values as-is - result[key] = value + if (value.every((entry) => typeof entry === 'string')) { + result[key] = value + }In
convertConstToEnum, guard newly created enums and existing enum arrays:if (key === 'const' && !schema.enum) { - result.enum = [value] + if (typeof value === 'string') result.enum = [value] + } else if (key === 'enum' && Array.isArray(value)) { + if (value.every((entry) => typeof entry === 'string')) result.enum = value } else { result[key] = convertConstToEnum(value)I exercised the public
convertConstToEnumfunction and this change in isolation with synthetic inputs:const: false: currently becomesenum: [false]; proposed change retainstype: "boolean"without an invalid enum.enum: [1, 2]: proposed change omits the unsupported enum.This is not an end-to-end Gemini request test. Omitting an unsupported constraint broadens the provider-side schema, so the original tool's validation must remain authoritative. The same cases should be added to both adapters' tests.
Sources
agauth-alfonso commentedon Oct 13, 2026
Confirmed still present in 3.0.2.
convertConstToEnumemitsenum: [value]for any type (request-helpers.ts), and core'stoGeminiSchemakeepsenumvalues as they are (gemini.ts). We plan one schema fix covering this, #27 and #30.agauth-alfonso commentedon Oct 13, 2026
Fixed in 3.0.3. Boolean and number constants and enums are no longer sent as
enumvalues; the allowed value is described to the model and the parameter keeps its real type, so these schemas no longer fail withTYPE_STRING. Thank you for the detailed report and the exact error path. Please reopen if you still see it on@cortexkit/opencode-antigravity-auth@latest.