[elicitation] Advertise new url elicitation capability when auth_elicitation is enabled. (#22188)

## Why

We've added support for auth elicitation behind the auth_elicitation
flag, but servers need to explicitly check the capability before it
decides to send elicitations in order to be backward compatible. This PR
adds the capability advertising conditioned on the flag.

## What changed

- Build `client_elicitation_capability` from the `AuthElicitation`
feature state.
- Thread that capability through MCP config, session startup, and
`McpConnectionManager` so RMCP initialization advertises the correct
elicitation support.
- Advertise both `form` and `url` elicitation when the feature is
enabled, and preserve the empty default capability when it is disabled.
- Add coverage for the feature-derived config shape and the advertised
initialization payload.

## Testing

- `cargo test -p codex-mcp`
- `cargo test -p codex-core
to_mcp_config_preserves_auth_elicitation_feature_from_config`
- `cargo test -p codex-core` *(currently fails outside this change in
`tools::handlers::multi_agents::tests::tool_handlers_cascade_close_and_resume_and_keep_explicitly_closed_subtrees_closed`
with a stack overflow after unrelated tests have started running)*

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

@@ -31,6 +31,7 @@ use codex_protocol::mcp::Tool;
 use codex_protocol::models::PermissionProfile;
 use codex_protocol::protocol::AskForApproval;
 use codex_protocol::protocol::McpAuthStatus;
+use rmcp::model::ElicitationCapability;
 use rmcp::model::ReadResourceRequestParams;
 use rmcp::model::ReadResourceResult;
 use serde_json::Value;
@@ -129,6 +130,8 @@ pub struct McpConfig {
     /// ChatGPT auth is checked separately at runtime before the host-owned apps
     /// MCP server is added.
     pub apps_enabled: bool,
+    /// Client-side elicitation capabilities advertised during MCP initialization.
+    pub client_elicitation_capability: ElicitationCapability,
     /// Config-backed MCP servers keyed by server name.
     ///
     /// Runtime-only additions are merged later by [`effective_mcp_servers`].
@@ -272,6 +275,7 @@ pub async fn read_mcp_resource(
         config.codex_home.clone(),
         codex_apps_tools_cache_key(auth),
         host_owned_codex_apps_enabled,
+        config.client_elicitation_capability.clone(),
         tool_plugin_provenance(config),
         auth,
         /*elicitation_reviewer*/ None,
@@ -340,6 +344,7 @@ pub async fn collect_mcp_server_status_snapshot_with_detail(
         config.codex_home.clone(),
         codex_apps_tools_cache_key(auth),
         host_owned_codex_apps_enabled,
+        config.client_elicitation_capability.clone(),
         tool_plugin_provenance,
         auth,
         /*elicitation_reviewer*/ None,

codex-rs/codex-mcp/src/mcp/mod_tests.rs

@@ -27,6 +27,7 @@ fn test_mcp_config(codex_home: PathBuf) -> McpConfig {
         codex_linux_sandbox_exe: None,
         use_legacy_landlock: false,
         apps_enabled: false,
+        client_elicitation_capability: ElicitationCapability::default(),
         configured_mcp_servers: HashMap::new(),
         plugin_capability_summaries: Vec::new(),
     }