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/codex-mcp/src/mcp/mod.rs

@@ -82,6 +82,19 @@ pub fn qualified_mcp_tool_name_prefix(server_name: &str) -> String {
     ))
 }
 
+/// Returns true when MCP permission prompts should resolve as approved instead
+/// of being shown to the user.
+pub fn mcp_permission_prompt_is_auto_approved(
+    approval_policy: AskForApproval,
+    sandbox_policy: &SandboxPolicy,
+) -> bool {
+    approval_policy == AskForApproval::Never
+        && matches!(
+            sandbox_policy,
+            SandboxPolicy::DangerFullAccess | SandboxPolicy::ExternalSandbox { .. }
+        )
+}
+
 /// MCP runtime settings derived from `codex_core::config::Config`.
 ///
 /// This struct should contain only long-lived configuration values that the