question tool: custom answer option cannot be disabled because "custom" is missing from the Prompt schema #45230

Description

The question tool renders a "Type your own answer" option, and the TUI honours a custom: false flag to hide it — but nothing can ever set that flag, because it is missing from the schema the tool accepts.

packages/schema/src/question.ts:

const base = {
  question: ...,
  header: ...,
  options: ...,
  multiple: ...,
}

export const Info = Schema.Struct({
  ...base,
  custom: Schema.Boolean.pipe(optional).annotate({
    description: "Allow typing a custom answer (default: true)",
  }),
}).annotate({ identifier: "QuestionV2.Info" })

export const Prompt = Schema.Struct(base).annotate({ identifier: "QuestionV2.Prompt" })

custom lives on Info. Both tools take Prompt:

• packages/opencode/src/tool/question.ts:7 — questions: Schema.mutable(Schema.Array(Question.Prompt))
• packages/core/src/tool/question.ts:26 — questions: Schema.Array(QuestionV2.Prompt)

So custom never reaches the JSON schema the model sees, and a custom: false the model emitted anyway would be dropped as an excess property. Grepping the repo, nothing assigns custom anywhere — the only reader is the renderer:

packages/tui/src/routes/session/question.tsx:38

const custom = createMemo(() => question()?.custom !== false)

Since the value is always undefined, custom !== false is always true, and the input is always shown. The Info.custom field, its description, and the !== false guard are all live code for a state that cannot occur.

The tool description compounds it. packages/opencode/src/tool/question.txt:

When custom is enabled (default), a "Type your own answer" option is added automatically; don't include "Other" or catch-all options

"(default)" tells the model this is a setting with a non-default alternative. There is no way to reach it.

Which way to fix it

Two options, and I picked the first:

1. Move custom into base so it reaches Prompt and the capability the renderer already implements becomes usable. One-line change; Info is unchanged in shape since base is spread into it.
2. Drop custom from Info, delete the !== false guard, and remove the sentence from both tool descriptions — i.e. admit the option does not exist.

(1) seemed right because the rendering side is complete and correct; only the input schema is missing the field. Happy to switch to (2) if the intent was for custom to be host-controlled rather than model-controlled.

Steps to reproduce

1. Call the question tool with custom: false on a question.
2. The "Type your own answer" input is still rendered.
3. Inspect the tool's JSON schema — custom is not among the accepted properties.

Operating System

Windows 11 (platform independent)