Split DeveloperInstructions into individual fragments. (#18813)

Split DeveloperInstructions into individual fragments.

codex-rs/core/src/apps/mod.rs

@@ -1,3 +1,2 @@
+#[cfg(test)]
 mod render;
-
-pub(crate) use render::render_apps_section;

codex-rs/core/src/apps/render.rs

@@ -1,22 +1,11 @@
+use crate::context::AppsInstructions;
+use crate::context::ContextualUserFragment;
 use codex_app_server_protocol::AppInfo;
-use codex_mcp::CODEX_APPS_MCP_SERVER_NAME;
 use codex_protocol::protocol::APPS_INSTRUCTIONS_CLOSE_TAG;
 use codex_protocol::protocol::APPS_INSTRUCTIONS_OPEN_TAG;
 
 pub(crate) fn render_apps_section(connectors: &[AppInfo]) -> Option<String> {
-    if !connectors
-        .iter()
-        .any(|connector| connector.is_accessible && connector.is_enabled)
-    {
-        return None;
-    }
-
-    let body = format!(
-        "## Apps (Connectors)\nApps (Connectors) can be explicitly triggered in user messages in the format `[$app-name](app://{{connector_id}})`. Apps can also be implicitly triggered as long as the context suggests usage of available apps.\nAn app is equivalent to a set of MCP tools within the `{CODEX_APPS_MCP_SERVER_NAME}` MCP.\nAn installed app's MCP tools are either provided to you already, or can be lazy-loaded through the `tool_search` tool. If `tool_search` is available, the apps that are searchable by `tools_search` will be listed by it.\nDo not additionally call list_mcp_resources or list_mcp_resource_templates for apps."
-    );
-    Some(format!(
-        "{APPS_INSTRUCTIONS_OPEN_TAG}\n{body}\n{APPS_INSTRUCTIONS_CLOSE_TAG}"
-    ))
+    AppsInstructions::from_connectors(connectors).map(|instructions| instructions.render())
 }
 
 #[cfg(test)]