feat: drop CodexExtension (#22140)

Drop `CodexExtension` as not needed for now

codex-rs/ext/extension-api/examples/enabled_extensions.rs

@@ -1,29 +1,23 @@
 #[path = "enabled_extensions/shared_state_extension.rs"]
 mod shared_state_extension;
 
-use std::sync::Arc;
-
 use codex_extension_api::ExtensionData;
 use codex_extension_api::ExtensionRegistryBuilder;
-use shared_state_extension::SharedStateExtension;
 use shared_state_extension::recorded_style_contributions;
 use shared_state_extension::recorded_usage_contributions;
 
 fn main() {
-    // 1. Build the extension value owned by the host.
-    let extension = Arc::new(SharedStateExtension);
+    // 1. Install the contributors for the thread-start input type this host exposes.
+    let mut builder = ExtensionRegistryBuilder::<()>::new();
+    shared_state_extension::install(&mut builder);
+    let registry = builder.build();
 
-    // 2. Install it into the registry for the thread-start input type this host exposes.
-    let registry = ExtensionRegistryBuilder::<()>::new()
-        .with_extension(extension)
-        .build();
-
-    // 3. The host decides which stores are shared.
+    // 2. The host decides which stores are shared.
     let session_store = ExtensionData::new();
     let first_thread_store = ExtensionData::new();
     let second_thread_store = ExtensionData::new();
 
-    // 4. Reusing the same session store shares session state across threads.
+    // 3. Reusing the same session store shares session state across threads.
     let first_thread_fragments = contribute_prompt(&registry, &session_store, &first_thread_store);
     contribute_prompt(&registry, &session_store, &first_thread_store);
     contribute_prompt(&registry, &session_store, &second_thread_store);

codex-rs/ext/extension-api/examples/enabled_extensions/shared_state_extension.rs

@@ -2,21 +2,15 @@ use std::sync::Arc;
 use std::sync::atomic::AtomicU64;
 use std::sync::atomic::Ordering;
 
-use codex_extension_api::CodexExtension;
 use codex_extension_api::ContextContributor;
 use codex_extension_api::ExtensionData;
 use codex_extension_api::ExtensionRegistryBuilder;
 use codex_extension_api::PromptFragment;
 
-/// Small tutorial extension that installs two prompt contributors.
-#[derive(Debug, Default)]
-pub struct SharedStateExtension;
-
-impl CodexExtension<()> for SharedStateExtension {
-    fn install(self: Arc<Self>, registry: &mut ExtensionRegistryBuilder<()>) {
-        registry.prompt_contributor(Arc::new(StyleContributor));
-        registry.prompt_contributor(Arc::new(UsageContributor));
-    }
+/// Installs the tutorial contributors used by the example host.
+pub fn install(registry: &mut ExtensionRegistryBuilder<()>) {
+    registry.prompt_contributor(Arc::new(StyleContributor));
+    registry.prompt_contributor(Arc::new(UsageContributor));
 }
 
 #[derive(Debug)]