Enable request_user_input in Default mode (#12735)

## Summary
- allow `request_user_input` in Default collaboration mode as well as
Plan
- update the Default-mode instructions to prefer assumptions first and
use `request_user_input` only when a question is unavoidable
- update request_user_input and app-server tests to match the new
Default-mode behavior
- refactor collaboration-mode availability plumbing into
`CollaborationModesConfig` for future mode-related flags

## Codex author
`codex resume 019c9124-ed28-7c13-96c6-b916b1c97d49`

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

@@ -10,8 +10,9 @@ use codex_protocol::approvals::NetworkApprovalProtocol as CoreNetworkApprovalPro
 use codex_protocol::approvals::NetworkPolicyAmendment as CoreNetworkPolicyAmendment;
 use codex_protocol::approvals::NetworkPolicyRuleAction as CoreNetworkPolicyRuleAction;
 use codex_protocol::config_types::CollaborationMode;
-use codex_protocol::config_types::CollaborationModeMask;
+use codex_protocol::config_types::CollaborationModeMask as CoreCollaborationModeMask;
 use codex_protocol::config_types::ForcedLoginMethod;
+use codex_protocol::config_types::ModeKind;
 use codex_protocol::config_types::Personality;
 use codex_protocol::config_types::ReasoningSummary;
 use codex_protocol::config_types::SandboxMode as CoreSandboxMode;
@@ -1409,6 +1410,30 @@ pub struct ModelListResponse {
 #[ts(export_to = "v2/")]
 pub struct CollaborationModeListParams {}
 
+/// EXPERIMENTAL - collaboration mode preset metadata for clients.
+#[derive(Serialize, Deserialize, Debug, Clone, PartialEq, JsonSchema, TS)]
+#[serde(rename_all = "camelCase")]
+#[ts(export_to = "v2/")]
+pub struct CollaborationModeMask {
+    pub name: String,
+    pub mode: Option<ModeKind>,
+    pub model: Option<String>,
+    #[serde(rename = "reasoning_effort")]
+    #[ts(rename = "reasoning_effort")]
+    pub reasoning_effort: Option<Option<ReasoningEffort>>,
+}
+
+impl From<CoreCollaborationModeMask> for CollaborationModeMask {
+    fn from(value: CoreCollaborationModeMask) -> Self {
+        Self {
+            name: value.name,
+            mode: value.mode,
+            model: value.model,
+            reasoning_effort: value.reasoning_effort,
+        }
+    }
+}
+
 /// EXPERIMENTAL - collaboration mode presets response.
 #[derive(Serialize, Deserialize, Debug, Clone, PartialEq, JsonSchema, TS)]
 #[serde(rename_all = "camelCase")]