Feat: request user input tool (#9472)

### Summary
* Add `requestUserInput` tool that the model can use for gather
feedback/asking question mid turn.


### Tool input schema
```
{
  "$schema": "http://json-schema.org/draft-07/schema#",
  "title": "requestUserInput input",
  "type": "object",
  "additionalProperties": false,
  "required": ["questions"],
  "properties": {
    "questions": {
      "type": "array",
      "description": "Questions to show the user (1-3). Prefer 1 unless multiple independent decisions block progress.",
      "minItems": 1,
      "maxItems": 3,
      "items": {
        "type": "object",
        "additionalProperties": false,
        "required": ["id", "header", "question"],
        "properties": {
          "id": {
            "type": "string",
            "description": "Stable identifier for mapping answers (snake_case)."
          },
          "header": {
            "type": "string",
            "description": "Short header label shown in the UI (12 or fewer chars)."
          },
          "question": {
            "type": "string",
            "description": "Single-sentence prompt shown to the user."
          },
          "options": {
            "type": "array",
            "description": "Optional 2-3 mutually exclusive choices. Put the recommended option first and suffix its label with \"(Recommended)\". Only include \"Other\" option if we want to include a free form option. If the question is free form in nature, do not include any option.",
            "minItems": 2,
            "maxItems": 3,
            "items": {
              "type": "object",
              "additionalProperties": false,
              "required": ["value", "label", "description"],
              "properties": {
                "value": {
                  "type": "string",
                  "description": "Machine-readable value (snake_case)."
                },
                "label": {
                  "type": "string",
                  "description": "User-facing label (1-5 words)."
                },
                "description": {
                  "type": "string",
                  "description": "One short sentence explaining impact/tradeoff if selected."
                }
              }
            }
          }
        }
      }
    }
  }
}
```

### Tool output schema
```
{
  "$schema": "http://json-schema.org/draft-07/schema#",
  "title": "requestUserInput output",
  "type": "object",
  "additionalProperties": false,
  "required": ["answers"],
  "properties": {
    "answers": {
      "type": "object",
      "description": "Map of question id to user answer.",
      "additionalProperties": {
        "type": "object",
        "additionalProperties": false,
        "required": ["selected"],
        "properties": {
          "selected": {
            "type": "array",
            "items": { "type": "string" }
          },
          "other": {
            "type": ["string", "null"]
          }
        }
      }
    }
  }
}
```

codex-rs/app-server-protocol/src/protocol/common.rs

@@ -510,6 +510,12 @@ server_request_definitions! {
         response: v2::FileChangeRequestApprovalResponse,
     },
 
+    /// EXPERIMENTAL - Request input from the user for a tool call.
+    ToolRequestUserInput => "item/tool/requestUserInput" {
+        params: v2::ToolRequestUserInputParams,
+        response: v2::ToolRequestUserInputResponse,
+    },
+
     /// DEPRECATED APIs below
     /// Request to approve a patch.
     /// This request is used for Turns started via the legacy APIs (i.e. SendUserTurn, SendUserMessage).

codex-rs/app-server-protocol/src/protocol/v2.rs

@@ -2277,6 +2277,54 @@ pub struct FileChangeRequestApprovalResponse {
     pub decision: FileChangeApprovalDecision,
 }
 
+#[derive(Serialize, Deserialize, Debug, Clone, PartialEq, JsonSchema, TS)]
+#[serde(rename_all = "camelCase")]
+#[ts(export_to = "v2/")]
+/// EXPERIMENTAL. Defines a single selectable option for request_user_input.
+pub struct ToolRequestUserInputOption {
+    pub label: String,
+    pub description: String,
+}
+
+#[derive(Serialize, Deserialize, Debug, Clone, PartialEq, JsonSchema, TS)]
+#[serde(rename_all = "camelCase")]
+#[ts(export_to = "v2/")]
+/// EXPERIMENTAL. Represents one request_user_input question and its optional options.
+pub struct ToolRequestUserInputQuestion {
+    pub id: String,
+    pub header: String,
+    pub question: String,
+    pub options: Option<Vec<ToolRequestUserInputOption>>,
+}
+
+#[derive(Serialize, Deserialize, Debug, Clone, PartialEq, JsonSchema, TS)]
+#[serde(rename_all = "camelCase")]
+#[ts(export_to = "v2/")]
+/// EXPERIMENTAL. Params sent with a request_user_input event.
+pub struct ToolRequestUserInputParams {
+    pub thread_id: String,
+    pub turn_id: String,
+    pub item_id: String,
+    pub questions: Vec<ToolRequestUserInputQuestion>,
+}
+
+#[derive(Serialize, Deserialize, Debug, Clone, PartialEq, JsonSchema, TS)]
+#[serde(rename_all = "camelCase")]
+#[ts(export_to = "v2/")]
+/// EXPERIMENTAL. Captures a user's answer to a request_user_input question.
+pub struct ToolRequestUserInputAnswer {
+    pub selected: Vec<String>,
+    pub other: Option<String>,
+}
+
+#[derive(Serialize, Deserialize, Debug, Clone, PartialEq, JsonSchema, TS)]
+#[serde(rename_all = "camelCase")]
+#[ts(export_to = "v2/")]
+/// EXPERIMENTAL. Response payload mapping question ids to answers.
+pub struct ToolRequestUserInputResponse {
+    pub answers: HashMap<String, ToolRequestUserInputAnswer>,
+}
+
 #[derive(Serialize, Deserialize, Debug, Clone, PartialEq, JsonSchema, TS)]
 #[serde(rename_all = "camelCase")]
 #[ts(export_to = "v2/")]