feat: persist and restore codex app's tools after search (#11780)

### What changed
1. Removed per-turn MCP selection reset in `core/src/tasks/mod.rs`.
2. Added `SessionState::set_mcp_tool_selection(Vec<String>)` in
`core/src/state/session.rs` for authoritative restore behavior (deduped,
order-preserving, empty clears).
3. Added rollout parsing in `core/src/codex.rs` to recover
`active_selected_tools` from prior `search_tool_bm25` outputs:
   - tracks matching `call_id`s
   - parses function output text JSON
   - extracts `active_selected_tools`
   - latest valid payload wins
   - malformed/non-matching payloads are ignored
4. Applied restore logic to resumed and forked startup paths in
`core/src/codex.rs`.
5. Updated instruction text to session/thread scope in
`core/templates/search_tool/tool_description.md`.
6. Expanded tests in `core/tests/suite/search_tool.rs`, plus unit
coverage in:
   - `core/src/codex.rs`
   - `core/src/state/session.rs`

### Behavior after change
1. Search activates matched tools.
2. Additional searches union into active selection.
3. Selection survives new turns in the same thread.
4. Resume/fork restores selection from rollout history.
5. Separate threads do not inherit selection unless forked.

codex-rs/core/src/tools/handlers/mod.rs

@@ -33,6 +33,7 @@ pub use read_file::ReadFileHandler;
 pub use request_user_input::RequestUserInputHandler;
 pub(crate) use request_user_input::request_user_input_tool_description;
 pub(crate) use search_tool_bm25::DEFAULT_LIMIT as SEARCH_TOOL_BM25_DEFAULT_LIMIT;
+pub(crate) use search_tool_bm25::SEARCH_TOOL_BM25_TOOL_NAME;
 pub use search_tool_bm25::SearchToolBm25Handler;
 pub use shell::ShellCommandHandler;
 pub use shell::ShellHandler;

codex-rs/core/src/tools/handlers/search_tool_bm25.rs

@@ -10,7 +10,6 @@ use std::collections::HashMap;
 use std::collections::HashSet;
 
 use crate::connectors;
-use crate::features::Feature;
 use crate::function_tool::FunctionCallError;
 use crate::mcp::CODEX_APPS_MCP_SERVER_NAME;
 use crate::mcp_connection_manager::ToolInfo;
@@ -23,6 +22,7 @@ use crate::tools::registry::ToolKind;
 
 pub struct SearchToolBm25Handler;
 
+pub(crate) const SEARCH_TOOL_BM25_TOOL_NAME: &str = "search_tool_bm25";
 pub(crate) const DEFAULT_LIMIT: usize = 8;
 
 fn default_limit() -> usize {
@@ -42,7 +42,6 @@ struct ToolEntry {
     server_name: String,
     title: Option<String>,
     description: Option<String>,
-    connector_id: Option<String>,
     connector_name: Option<String>,
     input_keys: Vec<String>,
     search_text: String,
@@ -66,7 +65,6 @@ impl ToolEntry {
                 .tool
                 .description
                 .map(|description| description.to_string()),
-            connector_id: info.connector_id,
             connector_name: info.connector_name,
             input_keys,
             search_text,
@@ -91,9 +89,9 @@ impl ToolHandler for SearchToolBm25Handler {
         let arguments = match payload {
             ToolPayload::Function { arguments } => arguments,
             _ => {
-                return Err(FunctionCallError::Fatal(
-                    "search_tool_bm25 handler received unsupported payload".to_string(),
-                ));
+                return Err(FunctionCallError::Fatal(format!(
+                    "{SEARCH_TOOL_BM25_TOOL_NAME} handler received unsupported payload"
+                )));
             }
         };
 
@@ -120,15 +118,12 @@ impl ToolHandler for SearchToolBm25Handler {
             .await
             .list_all_tools()
             .await;
-        let mcp_tools = if turn.config.features.enabled(Feature::Apps) {
-            let connectors = connectors::with_app_enabled_state(
-                connectors::accessible_connectors_from_mcp_tools(&mcp_tools),
-                &turn.config,
-            );
-            filter_codex_apps_mcp_tools(mcp_tools, &connectors)
-        } else {
-            mcp_tools
-        };
+
+        let connectors = connectors::with_app_enabled_state(
+            connectors::accessible_connectors_from_mcp_tools(&mcp_tools),
+            &turn.config,
+        );
+        let mcp_tools = filter_codex_apps_mcp_tools(mcp_tools, &connectors);
 
         let mut entries: Vec<ToolEntry> = mcp_tools
             .into_iter()
@@ -172,7 +167,6 @@ impl ToolHandler for SearchToolBm25Handler {
                 "server": entry.server_name.clone(),
                 "title": entry.title.clone(),
                 "description": entry.description.clone(),
-                "connector_id": entry.connector_id.clone(),
                 "connector_name": entry.connector_name.clone(),
                 "input_keys": entry.input_keys.clone(),
                 "score": result.score,
@@ -243,12 +237,6 @@ fn build_search_text(name: &str, info: &ToolInfo, input_keys: &[String]) -> Stri
         parts.push(connector_name.to_string());
     }
 
-    if let Some(connector_id) = info.connector_id.as_deref()
-        && !connector_id.trim().is_empty()
-    {
-        parts.push(connector_id.to_string());
-    }
-
     if !input_keys.is_empty() {
         parts.extend(input_keys.iter().cloned());
     }

codex-rs/core/src/tools/spec.rs

@@ -8,6 +8,7 @@ use crate::features::Features;
 use crate::mcp_connection_manager::ToolInfo;
 use crate::tools::handlers::PLAN_TOOL;
 use crate::tools::handlers::SEARCH_TOOL_BM25_DEFAULT_LIMIT;
+use crate::tools::handlers::SEARCH_TOOL_BM25_TOOL_NAME;
 use crate::tools::handlers::apply_patch::create_apply_patch_freeform_tool;
 use crate::tools::handlers::apply_patch::create_apply_patch_json_tool;
 use crate::tools::handlers::collab::DEFAULT_WAIT_TIMEOUT_MS;
@@ -913,7 +914,7 @@ fn create_search_tool_bm25_tool(app_tools: &HashMap<String, ToolInfo>) -> ToolSp
         SEARCH_TOOL_BM25_DESCRIPTION_TEMPLATE.replace("{{app_names}}", app_names.as_str());
 
     ToolSpec::Function(ResponsesApiTool {
-        name: "search_tool_bm25".to_string(),
+        name: SEARCH_TOOL_BM25_TOOL_NAME.to_string(),
         description,
         strict: false,
         parameters: JsonSchema::Object {
@@ -1507,7 +1508,7 @@ pub(crate) fn build_specs(
         && let Some(app_tools) = app_tools
     {
         builder.push_spec_with_parallel_support(create_search_tool_bm25_tool(&app_tools), true);
-        builder.register_handler("search_tool_bm25", search_tool_handler);
+        builder.register_handler(SEARCH_TOOL_BM25_TOOL_NAME, search_tool_handler);
     }
 
     if let Some(apply_patch_tool_type) = &config.apply_patch_tool_type {
@@ -2579,7 +2580,7 @@ mod tests {
         )
         .build();
 
-        let search_tool = find_tool(&tools, "search_tool_bm25");
+        let search_tool = find_tool(&tools, SEARCH_TOOL_BM25_TOOL_NAME);
         let ToolSpec::Function(ResponsesApiTool { description, .. }) = &search_tool.spec else {
             panic!("expected function tool");
         };