extension: wire extension registries into sessions

codex-rs/Cargo.toml

@@ -470,7 +470,6 @@ unwrap_used = "deny"
 [workspace.metadata.cargo-shear]
 ignored = [
     "codex-agent-graph-store",
-    "codex-extension-api",
     "icu_provider",
     "openssl-sys",
     "codex-v8-poc",

codex-rs/app-server/Cargo.toml

@@ -37,6 +37,7 @@ codex-config = { workspace = true }
 codex-core = { workspace = true }
 codex-core-plugins = { workspace = true }
 codex-exec-server = { workspace = true }
+codex-extension-api = { workspace = true }
 codex-external-agent-migration = { workspace = true }
 codex-external-agent-sessions = { workspace = true }
 codex-features = { workspace = true }

codex-rs/app-server/src/extensions.rs

@@ -0,0 +1,9 @@
+use std::sync::Arc;
+
+use codex_core::config::Config;
+use codex_extension_api::ExtensionRegistry;
+use codex_extension_api::ExtensionRegistryBuilder;
+
+pub(crate) fn thread_extensions() -> Arc<ExtensionRegistry<Config>> {
+    Arc::new(ExtensionRegistryBuilder::<Config>::new().build())
+}

codex-rs/app-server/src/lib.rs

@@ -83,6 +83,7 @@ mod config_manager_service;
 mod connection_rpc_gate;
 mod dynamic_tools;
 mod error_code;
+mod extensions;
 mod filters;
 mod fs_watch;
 mod fuzzy_file_search;

codex-rs/app-server/src/mcp_refresh.rs

@@ -99,6 +99,7 @@ async fn queue_refresh(
 #[cfg(test)]
 mod tests {
     use super::*;
+    use crate::extensions::thread_extensions;
     use async_trait::async_trait;
     use codex_arg0::Arg0DispatchPaths;
     use codex_config::CloudRequirementsLoader;
@@ -183,6 +184,7 @@ mod tests {
             auth_manager,
             SessionSource::Exec,
             Arc::new(EnvironmentManager::default_for_tests()),
+            thread_extensions(),
             /*analytics_events_client*/ None,
             thread_store,
             Some(state_db.clone()),

codex-rs/app-server/src/message_processor.rs

@@ -8,6 +8,7 @@ use crate::attestation::app_server_attestation_provider;
 use crate::config_manager::ConfigManager;
 use crate::connection_rpc_gate::ConnectionRpcGate;
 use crate::error_code::invalid_request;
+use crate::extensions::thread_extensions;
 use crate::fs_watch::FsWatchManager;
 use crate::outgoing_message::ConnectionId;
 use crate::outgoing_message::ConnectionRequestId;
@@ -303,6 +304,7 @@ impl MessageProcessor {
             auth_manager.clone(),
             session_source,
             environment_manager,
+            thread_extensions(),
             Some(analytics_events_client.clone()),
             Arc::clone(&thread_store),
             state_db.clone(),

codex-rs/core-api/Cargo.toml

@@ -19,6 +19,7 @@ codex-arg0 = { workspace = true }
 codex-analytics = { workspace = true }
 codex-config = { workspace = true }
 codex-core = { workspace = true }
+codex-extension-api = { workspace = true }
 codex-exec-server = { workspace = true }
 codex-features = { workspace = true }
 codex-login = { workspace = true }

codex-rs/core-api/src/lib.rs

@@ -45,6 +45,7 @@ pub use codex_core::skills::SkillsManager;
 pub use codex_core::thread_store_from_config;
 pub use codex_exec_server::EnvironmentManager;
 pub use codex_exec_server::ExecServerRuntimePaths;
+pub use codex_extension_api::empty_extension_registry;
 pub use codex_features::Feature;
 pub use codex_features::Features;
 pub use codex_login::AuthManager;

codex-rs/core/Cargo.toml

@@ -35,6 +35,7 @@ codex-config = { workspace = true }
 codex-core-plugins = { workspace = true }
 codex-core-skills = { workspace = true }
 codex-exec-server = { workspace = true }
+codex-extension-api = { workspace = true }
 codex-features = { workspace = true }
 codex-feedback = { workspace = true }
 codex-login = { workspace = true }

codex-rs/core/src/codex_delegate.rs

@@ -83,6 +83,7 @@ pub(crate) async fn run_codex_thread_interactive(
         skills_manager: Arc::clone(&parent_session.services.skills_manager),
         plugins_manager: Arc::clone(&parent_session.services.plugins_manager),
         mcp_manager: Arc::clone(&parent_session.services.mcp_manager),
+        extensions: Arc::clone(&parent_session.services.extensions),
         conversation_history: initial_history.unwrap_or(InitialHistory::New),
         session_source: SessionSource::SubAgent(subagent_source.clone()),
         thread_source: Some(ThreadSource::Subagent),

codex-rs/core/src/lib.rs

@@ -22,6 +22,7 @@ mod config_lock;
 pub use codex_thread::CodexThread;
 pub use codex_thread::CodexThreadTurnContextOverrides;
 pub use codex_thread::ThreadConfigSnapshot;
+pub use session::turn_context::TurnContext;
 mod agent;
 mod attestation;
 mod codex_delegate;

codex-rs/core/src/prompt_debug.rs

@@ -20,6 +20,7 @@ use crate::session::turn::built_tools;
 use crate::state_db_bridge::StateDbHandle;
 use crate::thread_manager::ThreadManager;
 use crate::thread_manager::thread_store_from_config;
+use codex_extension_api::empty_extension_registry;
 
 /// Build the model-visible `input` list for a single debug turn.
 #[doc(hidden)]
@@ -49,6 +50,7 @@ pub async fn build_prompt_input(
                 .await
                 .map_err(|err| CodexErr::Fatal(err.to_string()))?,
         ),
+        empty_extension_registry(),
         /*analytics_events_client*/ None,
         thread_store,
         state_db.clone(),

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

@@ -53,6 +53,7 @@ use codex_config::types::OAuthCredentialsStoreMode;
 use codex_exec_server::Environment;
 use codex_exec_server::EnvironmentManager;
 use codex_exec_server::FileSystemSandboxContext;
+use codex_extension_api::PromptSlot;
 use codex_features::FEATURES;
 use codex_features::Feature;
 use codex_features::unstable_features_warning_event;
@@ -392,6 +393,7 @@ pub(crate) struct CodexSpawnArgs {
     pub(crate) skills_manager: Arc<SkillsManager>,
     pub(crate) plugins_manager: Arc<PluginsManager>,
     pub(crate) mcp_manager: Arc<McpManager>,
+    pub(crate) extensions: Arc<codex_extension_api::ExtensionRegistry<crate::config::Config>>,
     pub(crate) conversation_history: InitialHistory,
     pub(crate) session_source: SessionSource,
     pub(crate) thread_source: Option<ThreadSource>,
@@ -455,6 +457,7 @@ impl Codex {
             skills_manager,
             plugins_manager,
             mcp_manager,
+            extensions,
             conversation_history,
             session_source,
             thread_source,
@@ -650,6 +653,7 @@ impl Codex {
             skills_manager,
             plugins_manager,
             mcp_manager.clone(),
+            extensions,
             agent_control,
             environment_manager,
             analytics_events_client,
@@ -2570,6 +2574,7 @@ impl Session {
     ) -> Vec<ResponseItem> {
         let mut developer_sections = Vec::<String>::with_capacity(8);
         let mut contextual_user_sections = Vec::<String>::with_capacity(2);
+        let mut separate_developer_sections = Vec::<String>::new();
         let (
             reference_context_item,
             previous_turn_settings,
@@ -2714,6 +2719,24 @@ impl Session {
         {
             developer_sections.push(commit_message_instruction);
         }
+        for contributor in self.services.extensions.context_contributors() {
+            for fragment in contributor.contribute(
+                &self.services.session_extension_data,
+                &self.services.thread_extension_data,
+            ) {
+                match fragment.slot() {
+                    PromptSlot::DeveloperPolicy | PromptSlot::DeveloperCapabilities => {
+                        developer_sections.push(fragment.text().to_string());
+                    }
+                    PromptSlot::ContextualUser => {
+                        contextual_user_sections.push(fragment.text().to_string());
+                    }
+                    PromptSlot::SeparateDeveloper => {
+                        separate_developer_sections.push(fragment.text().to_string());
+                    }
+                }
+            }
+        }
         if let Some(user_instructions) = turn_context.user_instructions.as_deref() {
             contextual_user_sections.push(
                 UserInstructions {
@@ -2746,6 +2769,13 @@ impl Session {
         {
             items.push(developer_message);
         }
+        for section in separate_developer_sections {
+            if let Some(developer_message) =
+                crate::context_manager::updates::build_developer_update_item(vec![section])
+            {
+                items.push(developer_message);
+            }
+        }
         if let Some(usage_hint_text) = multi_agent_v2_usage_hint_text
             && let Some(usage_hint_message) =
                 crate::context_manager::updates::build_developer_update_item(vec![

codex-rs/core/src/session/session.rs

@@ -364,6 +364,7 @@ impl Session {
         skills_manager: Arc<SkillsManager>,
         plugins_manager: Arc<PluginsManager>,
         mcp_manager: Arc<McpManager>,
+        extensions: Arc<codex_extension_api::ExtensionRegistry<crate::config::Config>>,
         agent_control: AgentControl,
         environment_manager: Arc<EnvironmentManager>,
         analytics_events_client: Option<AnalyticsEventsClient>,
@@ -810,6 +811,16 @@ impl Session {
                 SessionId::from(thread_id)
             };
             let agent_control = agent_control.with_session_id(session_id);
+            let session_extension_data = codex_extension_api::ExtensionData::new();
+            let thread_extension_data = codex_extension_api::ExtensionData::new();
+            for contributor in extensions.thread_start_contributors() {
+                contributor.contribute(
+                    config.as_ref(),
+                    &session_extension_data,
+                    &thread_extension_data,
+                );
+            }
+
             let services = SessionServices {
                 // Initialize the MCP connection manager with an uninitialized
                 // instance. It will be replaced with one created via
@@ -845,6 +856,10 @@ impl Session {
                 skills_manager,
                 plugins_manager: Arc::clone(&plugins_manager),
                 mcp_manager: Arc::clone(&mcp_manager),
+                extensions,
+                // TODO(jif): extract session to share between sub-agents
+                session_extension_data,
+                thread_extension_data,
                 agent_control,
                 network_proxy,
                 network_approval: Arc::clone(&network_approval),

codex-rs/core/src/session/tests.rs

@@ -3725,6 +3725,7 @@ async fn session_new_fails_when_zsh_fork_enabled_without_zsh_path() {
         skills_manager,
         plugins_manager,
         mcp_manager,
+        Arc::new(codex_extension_api::ExtensionRegistryBuilder::new().build()),
         AgentControl::default(),
         Arc::new(codex_exec_server::EnvironmentManager::default_for_tests()),
         /*analytics_events_client*/ None,
@@ -3871,6 +3872,9 @@ pub(crate) async fn make_session_and_context() -> (Session, TurnContext) {
         skills_manager,
         plugins_manager,
         mcp_manager,
+        extensions: Arc::new(codex_extension_api::ExtensionRegistryBuilder::new().build()),
+        session_extension_data: codex_extension_api::ExtensionData::new(),
+        thread_extension_data: codex_extension_api::ExtensionData::new(),
         agent_control,
         network_proxy: None,
         network_approval: Arc::clone(&network_approval),
@@ -4061,6 +4065,7 @@ async fn make_session_with_config_and_rx(
         skills_manager,
         plugins_manager,
         mcp_manager,
+        Arc::new(codex_extension_api::ExtensionRegistryBuilder::new().build()),
         AgentControl::default(),
         Arc::new(codex_exec_server::EnvironmentManager::default_for_tests()),
         /*analytics_events_client*/ None,
@@ -4163,6 +4168,7 @@ async fn make_session_with_history_source_and_agent_control_and_rx(
         skills_manager,
         plugins_manager,
         mcp_manager,
+        Arc::new(codex_extension_api::ExtensionRegistryBuilder::new().build()),
         agent_control,
         Arc::new(codex_exec_server::EnvironmentManager::default_for_tests()),
         /*analytics_events_client*/ None,
@@ -5586,6 +5592,9 @@ where
         skills_manager,
         plugins_manager,
         mcp_manager,
+        extensions: Arc::new(codex_extension_api::ExtensionRegistryBuilder::new().build()),
+        session_extension_data: codex_extension_api::ExtensionData::new(),
+        thread_extension_data: codex_extension_api::ExtensionData::new(),
         agent_control,
         network_proxy: None,
         network_approval: Arc::clone(&network_approval),
@@ -6133,6 +6142,73 @@ async fn make_multi_agent_v2_usage_hint_test_session(
     (session, turn_context)
 }
 
+struct GitAttributionTestContributor;
+struct GitAttributionTestState;
+
+impl codex_extension_api::ContextContributor for GitAttributionTestContributor {
+    fn contribute(
+        &self,
+        _session_store: &codex_extension_api::ExtensionData,
+        thread_store: &codex_extension_api::ExtensionData,
+    ) -> Vec<codex_extension_api::PromptFragment> {
+        thread_store
+            .get::<GitAttributionTestState>()
+            .is_some()
+            .then(|| {
+                codex_extension_api::PromptFragment::developer_policy(
+                    "git attribution extension enabled",
+                )
+            })
+            .into_iter()
+            .collect()
+    }
+}
+
+fn git_attribution_test_registry()
+-> Arc<codex_extension_api::ExtensionRegistry<crate::config::Config>> {
+    let mut builder = codex_extension_api::ExtensionRegistryBuilder::new();
+    builder.prompt_contributor(Arc::new(GitAttributionTestContributor));
+    Arc::new(builder.build())
+}
+
+#[tokio::test]
+async fn build_initial_context_includes_git_attribution_from_extensions() {
+    let (mut session, turn_context) = make_session_and_context().await;
+    session.services.extensions = git_attribution_test_registry();
+    session
+        .services
+        .thread_extension_data
+        .insert(GitAttributionTestState);
+
+    let initial_context = session.build_initial_context(&turn_context).await;
+    let developer_messages = developer_message_texts(&initial_context);
+
+    assert!(
+        developer_messages
+            .iter()
+            .flatten()
+            .any(|text| *text == "git attribution extension enabled"),
+        "expected git attribution developer text, got {developer_messages:?}"
+    );
+}
+
+#[tokio::test]
+async fn build_initial_context_omits_git_attribution_when_feature_is_disabled() {
+    let (mut session, turn_context) = make_session_and_context().await;
+    session.services.extensions = git_attribution_test_registry();
+
+    let initial_context = session.build_initial_context(&turn_context).await;
+    let developer_messages = developer_message_texts(&initial_context);
+
+    assert!(
+        !developer_messages
+            .iter()
+            .flatten()
+            .any(|text| *text == "git attribution extension enabled"),
+        "did not expect git attribution developer text, got {developer_messages:?}"
+    );
+}
+
 #[tokio::test]
 async fn build_initial_context_adds_multi_agent_v2_root_usage_hint_as_developer_message() {
     let (session, turn_context) =