Add server-level approval defaults for custom MCP servers (#17843)

## Summary
- Add `default_tools_approval_mode` support for custom MCP server
configs, matching the existing `codex_apps` behavior
- Apply approval precedence as per-tool override, then server default,
then `auto`
- Update config serialization, CLI display, schema generation, docs, and
tests

## Testing
- `cargo check -p codex-config`
- `cargo check -p codex-core`
- `just write-config-schema`
- `just fmt`
- `cargo test -p codex-config`
- Targeted `codex-core` tests for config parsing, config writes, and MCP
approval precedence
- `just fix -p codex-config -p codex-core`

codex-rs/core/tests/suite/code_mode.rs

@@ -239,6 +239,7 @@ async fn run_code_mode_turn_with_rmcp_config(
                 disabled_reason: None,
                 startup_timeout_sec: Some(Duration::from_secs(10)),
                 tool_timeout_sec: None,
+                default_tools_approval_mode: None,
                 enabled_tools: None,
                 disabled_tools: None,
                 scopes: None,

codex-rs/core/tests/suite/js_repl.rs

@@ -629,6 +629,7 @@ async fn js_repl_can_invoke_mcp_tools_by_display_name() -> Result<()> {
                 disabled_reason: None,
                 startup_timeout_sec: Some(Duration::from_secs(10)),
                 tool_timeout_sec: None,
+                default_tools_approval_mode: None,
                 enabled_tools: None,
                 disabled_tools: None,
                 scopes: None,

codex-rs/core/tests/suite/rmcp_client.rs

@@ -151,6 +151,7 @@ fn insert_mcp_server(
             disabled_reason: None,
             startup_timeout_sec: Some(Duration::from_secs(10)),
             tool_timeout_sec: options.tool_timeout_sec,
+            default_tools_approval_mode: None,
             enabled_tools: None,
             disabled_tools: None,
             scopes: None,

codex-rs/core/tests/suite/search_tool.rs

@@ -703,6 +703,7 @@ async fn tool_search_indexes_only_enabled_non_app_mcp_tools() -> Result<()> {
                     disabled_reason: None,
                     startup_timeout_sec: Some(Duration::from_secs(10)),
                     tool_timeout_sec: None,
+                    default_tools_approval_mode: None,
                     enabled_tools: Some(vec!["echo".to_string(), "image".to_string()]),
                     disabled_tools: Some(vec!["image".to_string()]),
                     scopes: None,

codex-rs/core/tests/suite/sqlite_state.rs

@@ -378,6 +378,7 @@ async fn mcp_call_marks_thread_memory_mode_polluted_when_configured() -> Result<
                 disabled_reason: None,
                 startup_timeout_sec: Some(Duration::from_secs(10)),
                 tool_timeout_sec: None,
+                default_tools_approval_mode: None,
                 enabled_tools: None,
                 disabled_tools: None,
                 scopes: None,

codex-rs/core/tests/suite/tools.rs

@@ -162,6 +162,7 @@ async fn historical_unavailable_mcp_call_is_exposed_as_placeholder_tool() -> Res
                     disabled_reason: None,
                     startup_timeout_sec: Some(Duration::from_secs(10)),
                     tool_timeout_sec: None,
+                    default_tools_approval_mode: None,
                     enabled_tools: None,
                     disabled_tools: None,
                     scopes: None,

codex-rs/core/tests/suite/truncation.rs

@@ -382,6 +382,7 @@ async fn mcp_tool_call_output_exceeds_limit_truncated_for_model() -> Result<()>
                 disabled_reason: None,
                 startup_timeout_sec: Some(std::time::Duration::from_secs(10)),
                 tool_timeout_sec: None,
+                default_tools_approval_mode: None,
                 enabled_tools: None,
                 disabled_tools: None,
                 scopes: None,
@@ -480,6 +481,7 @@ async fn mcp_image_output_preserves_image_and_no_text_summary() -> Result<()> {
                 disabled_reason: None,
                 startup_timeout_sec: Some(Duration::from_secs(10)),
                 tool_timeout_sec: None,
+                default_tools_approval_mode: None,
                 enabled_tools: None,
                 disabled_tools: None,
                 scopes: None,
@@ -761,6 +763,7 @@ async fn mcp_tool_call_output_not_truncated_with_custom_limit() -> Result<()> {
                 disabled_reason: None,
                 startup_timeout_sec: Some(std::time::Duration::from_secs(10)),
                 tool_timeout_sec: None,
+                default_tools_approval_mode: None,
                 enabled_tools: None,
                 disabled_tools: None,
                 scopes: None,