Auto-approve MCP server elicitations in Full Access mode (#17164)

Currently, when a MCP server sends an elicitation to Codex running in
Full Access (`sandbox_policy: DangerFullAccess` + `approval_policy:
Never`), the elicitations are auto-cancelled.

This PR updates the automatic handling of MCP elicitations to be
consistent with other approvals in full-access, where they are
auto-approved. Because MCP elicitations may actually require user input,
this mechanism is limited to empty form elicitations.

## Changeset
- Add policy helper shared with existing MCP tool call approval
auto-approve
- Update `ElicitationRequestManager` to auto-approve elicitations in
full access when `can_auto_accept_elicitation` is true.
- Add tests

Co-authored-by: Codex <noreply@openai.com>

codex-rs/core/src/codex.rs

@@ -1982,6 +1982,7 @@ impl Session {
             // setup is straightforward enough and performs well.
             mcp_connection_manager: Arc::new(RwLock::new(McpConnectionManager::new_uninitialized(
                 &config.permissions.approval_policy,
+                &config.permissions.sandbox_policy,
             ))),
             mcp_startup_cancellation_token: Mutex::new(CancellationToken::new()),
             unified_exec_manager: UnifiedExecProcessManager::new(
@@ -2560,11 +2561,12 @@ impl Session {
         sandbox_policy_changed: bool,
     ) -> Arc<TurnContext> {
         let per_turn_config = Self::build_per_turn_config(&session_configuration);
-        self.services
-            .mcp_connection_manager
-            .read()
-            .await
-            .set_approval_policy(&session_configuration.approval_policy);
+        {
+            let mcp_connection_manager = self.services.mcp_connection_manager.read().await;
+            mcp_connection_manager.set_approval_policy(&session_configuration.approval_policy);
+            mcp_connection_manager
+                .set_sandbox_policy(per_turn_config.permissions.sandbox_policy.get());
+        }
 
         if sandbox_policy_changed {
             self.refresh_managed_network_proxy_for_current_sandbox_policy()