diff --git a/codex-rs/app-server/Cargo.toml b/codex-rs/app-server/Cargo.toml
index 6d201bdee3..b6caa2f71d 100644
--- a/codex-rs/app-server/Cargo.toml
+++ b/codex-rs/app-server/Cargo.toml
@@ -37,9 +37,11 @@ codex-core = { workspace = true }
 codex-core-plugins = { workspace = true }
 codex-device-key = { 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-git-attribution = { workspace = true }
 codex-git-utils = { workspace = true }
 codex-hooks = { workspace = true }
 codex-otel = { workspace = true }
diff --git a/codex-rs/app-server/src/extensions.rs b/codex-rs/app-server/src/extensions.rs
new file mode 100644
index 0000000000..3d6f64793e
--- /dev/null
+++ b/codex-rs/app-server/src/extensions.rs
@@ -0,0 +1,13 @@
+use std::sync::Arc;
+
+use codex_core::ExtensionContext;
+use codex_extension_api::ExtensionRegistry;
+use codex_extension_api::ExtensionRegistryBuilder;
+
+pub(crate) fn thread_extensions() -> Arc<ExtensionRegistry<ExtensionContext>> {
+    Arc::new(
+        ExtensionRegistryBuilder::<ExtensionContext>::new()
+            .with_extension(codex_git_attribution::extension())
+            .build(),
+    )
+}
diff --git a/codex-rs/app-server/src/lib.rs b/codex-rs/app-server/src/lib.rs
index 08aab99f65..5a8a357519 100644
--- a/codex-rs/app-server/src/lib.rs
+++ b/codex-rs/app-server/src/lib.rs
@@ -82,6 +82,7 @@ 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;
diff --git a/codex-rs/app-server/src/mcp_refresh.rs b/codex-rs/app-server/src/mcp_refresh.rs
index 8e1ccd3c0a..6a28c31e2b 100644
--- a/codex-rs/app-server/src/mcp_refresh.rs
+++ b/codex-rs/app-server/src/mcp_refresh.rs
@@ -120,6 +120,7 @@ mod tests {
     use std::sync::atomic::AtomicUsize;
     use std::sync::atomic::Ordering;
     use tempfile::TempDir;
+    use crate::extensions::thread_extensions;
 
     #[tokio::test]
     async fn strict_refresh_reports_thread_planning_failures() -> anyhow::Result<()> {
@@ -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()),
diff --git a/codex-rs/app-server/src/message_processor.rs b/codex-rs/app-server/src/message_processor.rs
index 2e7414a178..c098b4680b 100644
--- a/codex-rs/app-server/src/message_processor.rs
+++ b/codex-rs/app-server/src/message_processor.rs
@@ -7,6 +7,7 @@ use std::sync::atomic::AtomicBool;
 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;
@@ -298,6 +299,7 @@ impl MessageProcessor {
             auth_manager.clone(),
             session_source,
             environment_manager,
+            thread_extensions(),
             Some(analytics_events_client.clone()),
             Arc::clone(&thread_store),
             state_db.clone(),
diff --git a/codex-rs/core/src/session/session.rs b/codex-rs/core/src/session/session.rs
index 11fa4109bf..3c23c6a4e3 100644
--- a/codex-rs/core/src/session/session.rs
+++ b/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::ExtensionContext>>,
         skills_watcher: Arc<SkillsWatcher>,
         agent_control: AgentControl,
         environment_manager: Arc<EnvironmentManager>,
@@ -845,6 +846,9 @@ impl Session {
                 skills_manager,
                 plugins_manager: Arc::clone(&plugins_manager),
                 mcp_manager: Arc::clone(&mcp_manager),
+                extensions,
+                session_extension_data: codex_extension_api::ExtensionData::new(),
+                thread_extension_data: codex_extension_api::ExtensionData::new(),
                 skills_watcher,
                 agent_control,
                 network_proxy,
diff --git a/codex-rs/core/src/session/tests.rs b/codex-rs/core/src/session/tests.rs
index b250cadfb0..846489647c 100644
--- a/codex-rs/core/src/session/tests.rs
+++ b/codex-rs/core/src/session/tests.rs
@@ -3596,6 +3596,7 @@ 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()),
         Arc::new(SkillsWatcher::noop()),
         AgentControl::default(),
         Arc::new(codex_exec_server::EnvironmentManager::default_for_tests()),
@@ -3743,6 +3744,9 @@ 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(),
         skills_watcher,
         agent_control,
         network_proxy: None,
@@ -3922,6 +3926,7 @@ async fn make_session_with_config_and_rx(
         skills_manager,
         plugins_manager,
         mcp_manager,
+        Arc::new(codex_extension_api::ExtensionRegistryBuilder::new().build()),
         Arc::new(SkillsWatcher::noop()),
         AgentControl::default(),
         Arc::new(codex_exec_server::EnvironmentManager::default_for_tests()),
@@ -4024,6 +4029,7 @@ 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()),
         Arc::new(SkillsWatcher::noop()),
         agent_control,
         Arc::new(codex_exec_server::EnvironmentManager::default_for_tests()),
@@ -5448,6 +5454,9 @@ 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(),
         skills_watcher,
         agent_control,
         network_proxy: None,
@@ -5994,6 +6003,52 @@ async fn make_multi_agent_v2_usage_hint_test_session(
     (session, turn_context)
 }
 
+#[tokio::test]
+async fn build_initial_context_includes_git_attribution_from_extensions() {
+    let (mut session, mut turn_context) = make_session_and_context().await;
+    session.services.extensions = Arc::new(
+        codex_extension_api::ExtensionRegistryBuilder::<crate::ExtensionContext>::new()
+            .with_extension(codex_git_attribution::extension())
+            .build(),
+    );
+    turn_context
+        .features
+        .enable(Feature::CodexGitCommit)
+        .expect("test features should allow git attribution");
+
+    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.contains("Co-authored-by: Codex <noreply@openai.com>")),
+        "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 = Arc::new(
+        codex_extension_api::ExtensionRegistryBuilder::<crate::ExtensionContext>::new()
+            .with_extension(codex_git_attribution::extension())
+            .build(),
+    );
+
+    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.contains("Co-authored-by:")),
+        "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) =
diff --git a/codex-rs/core/src/session/tests/guardian_tests.rs b/codex-rs/core/src/session/tests/guardian_tests.rs
index 857ec950c2..66b85b432f 100644
--- a/codex-rs/core/src/session/tests/guardian_tests.rs
+++ b/codex-rs/core/src/session/tests/guardian_tests.rs
@@ -743,6 +743,7 @@ async fn guardian_subagent_does_not_inherit_parent_exec_policy_rules() {
         skills_manager,
         plugins_manager,
         mcp_manager,
+        extensions: crate::empty_extension_registry(),
         skills_watcher,
         conversation_history: InitialHistory::New,
         session_source: SessionSource::SubAgent(SubAgentSource::Other(
diff --git a/codex-rs/core/src/state/service.rs b/codex-rs/core/src/state/service.rs
index 9cd9e97fbb..d89f74c015 100644
--- a/codex-rs/core/src/state/service.rs
+++ b/codex-rs/core/src/state/service.rs
@@ -6,6 +6,7 @@ use crate::agent::AgentControl;
 use crate::client::ModelClient;
 use crate::config::StartedNetworkProxy;
 use crate::exec_policy::ExecPolicyManager;
+use crate::extensions::ExtensionContext;
 use crate::guardian::GuardianRejection;
 use crate::guardian::GuardianRejectionCircuitBreaker;
 use crate::mcp::McpManager;
@@ -18,6 +19,8 @@ use arc_swap::ArcSwap;
 use codex_analytics::AnalyticsEventsClient;
 use codex_core_plugins::PluginsManager;
 use codex_exec_server::EnvironmentManager;
+use codex_extension_api::ExtensionData;
+use codex_extension_api::ExtensionRegistry;
 use codex_hooks::Hooks;
 use codex_login::AuthManager;
 use codex_mcp::McpConnectionManager;
@@ -59,6 +62,9 @@ pub(crate) struct SessionServices {
     pub(crate) skills_manager: Arc<SkillsManager>,
     pub(crate) plugins_manager: Arc<PluginsManager>,
     pub(crate) mcp_manager: Arc<McpManager>,
+    pub(crate) extensions: Arc<ExtensionRegistry<ExtensionContext>>,
+    pub(crate) session_extension_data: ExtensionData,
+    pub(crate) thread_extension_data: ExtensionData,
     pub(crate) skills_watcher: Arc<SkillsWatcher>,
     pub(crate) agent_control: AgentControl,
     pub(crate) network_proxy: Option<StartedNetworkProxy>,
diff --git a/codex-rs/core/src/tools/handlers/multi_agents_tests.rs b/codex-rs/core/src/tools/handlers/multi_agents_tests.rs
index 6f44673f13..b80064f1ab 100644
--- a/codex-rs/core/src/tools/handlers/multi_agents_tests.rs
+++ b/codex-rs/core/src/tools/handlers/multi_agents_tests.rs
@@ -2,6 +2,7 @@ use super::*;
 use crate::ThreadManager;
 use crate::config::AgentRoleConfig;
 use crate::config::DEFAULT_AGENT_MAX_DEPTH;
+use crate::empty_extension_registry;
 use crate::function_tool::FunctionCallError;
 use crate::init_state_db;
 use crate::session::tests::make_session_and_context;
@@ -3163,6 +3164,7 @@ async fn tool_handlers_cascade_close_and_resume_and_keep_explicitly_closed_subtr
         AuthManager::from_auth_for_testing(CodexAuth::from_api_key("dummy")),
         SessionSource::Exec,
         Arc::new(codex_exec_server::EnvironmentManager::default_for_tests()),
+        empty_extension_registry(),
         /*analytics_events_client*/ None,
         thread_store_from_config(&config, state_db.clone()),
         state_db.clone(),
diff --git a/codex-rs/ext/git-attribution/src/lib.rs b/codex-rs/ext/git-attribution/src/lib.rs
index 3a7e99195c..dcdafd3dc4 100644
--- a/codex-rs/ext/git-attribution/src/lib.rs
+++ b/codex-rs/ext/git-attribution/src/lib.rs
@@ -2,13 +2,14 @@ use std::sync::Arc;
 
 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;
-use codex_extension_api::Stores;
 
 const DEFAULT_ATTRIBUTION_VALUE: &str = "Codex <noreply@openai.com>";
 
 pub trait GitAttributionContext {
+    fn git_attribution_enabled(&self) -> bool;
     fn commit_attribution(&self) -> Option<&str>;
 }
 
@@ -24,6 +25,9 @@ impl GitAttributionExtension {
 
     /// Returns the model-visible trailer instruction, if attribution is enabled.
     pub fn instruction<C: GitAttributionContext>(&self, context: &C) -> Option<String> {
+        if !context.git_attribution_enabled() {
+            return None;
+        }
         let trailer = build_commit_message_trailer(context.commit_attribution())?;
         Some(format!(
             "When you write or edit a git commit message, ensure the message ends with this trailer exactly once:\n{trailer}\n\nRules:\n- Keep existing trailers and append this trailer at the end if missing.\n- Do not duplicate this trailer if it already exists.\n- Keep one blank line between the commit body and trailer block."
@@ -32,9 +36,14 @@ impl GitAttributionExtension {
 }
 
 impl<C: GitAttributionContext> ContextContributor<C> for GitAttributionExtension {
-    fn contribute(&self, context: &C, _stores: &Stores<'_>) -> Vec<PromptFragment> {
+    fn contribute(
+        &self,
+        context: &C,
+        _session_store: &ExtensionData,
+        _thread_store: &ExtensionData,
+    ) -> Vec<PromptFragment> {
         self.instruction(context)
-            .map(PromptFragment::developer_capability)
+            .map(PromptFragment::developer_policy)
             .into_iter()
             .collect()
     }
@@ -51,7 +60,6 @@ pub fn extension() -> Arc<GitAttributionExtension> {
     Arc::new(GitAttributionExtension::new())
 }
 
-// This is just a copy/paste
 fn build_commit_message_trailer(config_attribution: Option<&str>) -> Option<String> {
     let value = resolve_attribution_value(config_attribution)?;
     Some(format!("Co-authored-by: {value}"))
@@ -70,3 +78,6 @@ fn resolve_attribution_value(config_attribution: Option<&str>) -> Option<String>
         None => Some(DEFAULT_ATTRIBUTION_VALUE.to_string()),
     }
 }
+
+#[cfg(test)]
+mod tests;
diff --git a/codex-rs/ext/git-attribution/src/tests.rs b/codex-rs/ext/git-attribution/src/tests.rs
new file mode 100644
index 0000000000..56ec3d717e
--- /dev/null
+++ b/codex-rs/ext/git-attribution/src/tests.rs
@@ -0,0 +1,81 @@
+use super::GitAttributionContext;
+use super::GitAttributionExtension;
+use super::build_commit_message_trailer;
+use super::resolve_attribution_value;
+
+struct TestContext {
+    git_attribution_enabled: bool,
+    commit_attribution: Option<&'static str>,
+}
+
+impl GitAttributionContext for TestContext {
+    fn git_attribution_enabled(&self) -> bool {
+        self.git_attribution_enabled
+    }
+
+    fn commit_attribution(&self) -> Option<&str> {
+        self.commit_attribution
+    }
+}
+
+#[test]
+fn blank_attribution_disables_trailer_prompt() {
+    assert_eq!(build_commit_message_trailer(Some("")), None);
+    assert_eq!(
+        GitAttributionExtension::new().instruction(&TestContext {
+            git_attribution_enabled: true,
+            commit_attribution: Some("   "),
+        }),
+        None
+    );
+}
+
+#[test]
+fn disabled_context_omits_instruction() {
+    assert_eq!(
+        GitAttributionExtension::new().instruction(&TestContext {
+            git_attribution_enabled: false,
+            commit_attribution: None,
+        }),
+        None
+    );
+}
+
+#[test]
+fn default_attribution_uses_codex_trailer() {
+    assert_eq!(
+        build_commit_message_trailer(/*config_attribution*/ None).as_deref(),
+        Some("Co-authored-by: Codex <noreply@openai.com>")
+    );
+}
+
+#[test]
+fn resolve_value_handles_default_custom_and_blank() {
+    assert_eq!(
+        resolve_attribution_value(/*config_attribution*/ None),
+        Some("Codex <noreply@openai.com>".to_string())
+    );
+    assert_eq!(
+        resolve_attribution_value(Some("MyAgent <me@example.com>")),
+        Some("MyAgent <me@example.com>".to_string())
+    );
+    assert_eq!(
+        resolve_attribution_value(Some("MyAgent")),
+        Some("MyAgent".to_string())
+    );
+    assert_eq!(resolve_attribution_value(Some("   ")), None);
+}
+
+#[test]
+fn instruction_mentions_trailer_and_omits_generated_with() {
+    let instruction = GitAttributionExtension::new()
+        .instruction(&TestContext {
+            git_attribution_enabled: true,
+            commit_attribution: Some("AgentX <agent@example.com>"),
+        })
+        .expect("instruction expected");
+
+    assert!(instruction.contains("Co-authored-by: AgentX <agent@example.com>"));
+    assert!(instruction.contains("exactly once"));
+    assert!(!instruction.contains("Generated-with"));
+}