diff --git a/codex-rs/Cargo.lock b/codex-rs/Cargo.lock
index f982373d56..0384f36a25 100644
--- a/codex-rs/Cargo.lock
+++ b/codex-rs/Cargo.lock
@@ -2070,6 +2070,8 @@ dependencies = [
  "base64 0.22.1",
  "chrono",
  "clap",
+ "codex-agent-message-board-client",
+ "codex-agent-message-board-extension",
  "codex-analytics",
  "codex-app-server-daemon",
  "codex-app-server-protocol",
@@ -2951,11 +2953,11 @@ dependencies = [
  "bm25",
  "chrono",
  "codex-agent-graph-store",
- "codex-agent-message-board-client",
  "codex-agent-message-board-extension",
  "codex-agent-roles",
  "codex-analytics",
  "codex-api",
+ "codex-app-server",
  "codex-app-server-protocol",
  "codex-apply-patch",
  "codex-async-utils",
@@ -5944,6 +5946,7 @@ dependencies = [
  "base64 0.22.1",
  "codex-agent-graph-store",
  "codex-analytics",
+ "codex-app-server",
  "codex-arg0",
  "codex-attachment-store",
  "codex-config",
diff --git a/codex-rs/app-server/Cargo.toml b/codex-rs/app-server/Cargo.toml
index cde6f7afc5..21add6dc8c 100644
--- a/codex-rs/app-server/Cargo.toml
+++ b/codex-rs/app-server/Cargo.toml
@@ -25,6 +25,9 @@ doctest = false
 workspace = true
 
 [dependencies]
+codex-agent-message-board-client = { workspace = true }
+codex-agent-message-board-extension = { workspace = true }
+codex-message-board = { workspace = true }
 codex-utils-process = { workspace = true }
 anyhow = { workspace = true }
 base64 = { workspace = true }
@@ -133,7 +136,6 @@ codex-windows-sandbox = { workspace = true }
 
 [dev-dependencies]
 zip = { workspace = true }
-codex-message-board = { workspace = true }
 codex-uds = { workspace = true }
 app_test_support = { workspace = true }
 axum = { workspace = true, default-features = false, features = [
diff --git a/codex-rs/core/src/agent_message_board.rs b/codex-rs/app-server/src/agent_message_board.rs
similarity index 91%
rename from codex-rs/core/src/agent_message_board.rs
rename to codex-rs/app-server/src/agent_message_board.rs
index cb2a6c53cd..6b9054e6fb 100644
--- a/codex-rs/core/src/agent_message_board.rs
+++ b/codex-rs/app-server/src/agent_message_board.rs
@@ -1,19 +1,17 @@
-//! Bridges the board extension to the selected controller, clock and active-turn services.
+//! Supplies board host capabilities through the public Core runtime interfaces.
 //!
 //! The extension owns backend construction, storage and tool registration. This adapter
 //! selects configuration and supplies host capabilities. It never starts or restores
 //! recipients during lookup. Notifications use ordinary agent-message scheduling.
 
-use crate::CodexThread;
-use crate::ThreadManager;
-use crate::config::Config;
-use crate::context::AgentMessageBoardNotification;
-use crate::context::ContextualUserFragment;
-use crate::tools::MULTI_AGENT_V2_NAMESPACE_DESCRIPTION;
 use chrono::DateTime;
 use chrono::Utc;
 use codex_agent_message_board_client::RemoteAgentMessageBoard;
 use codex_agent_message_board_extension::BoardBackend;
+use codex_core::CodexThread;
+use codex_core::MULTI_AGENT_V2_NAMESPACE_DESCRIPTION;
+use codex_core::ThreadManager;
+use codex_core::config::Config;
 use codex_extension_api::ExtensionRegistryBuilder;
 use codex_extension_api::ThreadStartInput;
 use codex_features::Feature;
@@ -206,12 +204,24 @@ impl MessageBoardHost for LocalBoardHost {
                 Err(error) => return Err(error),
             };
             let recipient_path = self.registered_path(&recipient).await?;
-            let notice = AgentMessageBoardNotification(post);
+            let suffix = if post.truncated {
+                "\n[Use read_post for the rest.]"
+            } else {
+                ""
+            };
+            let content = format!(
+                "Message Type: CHANNEL_POST\nSender: {}\nChannel: {}\nMessage ID: {}\nThread ID: {}\nPayload:\n{}{suffix}",
+                post.metadata.author,
+                post.metadata.channel_name,
+                post.metadata.message_id,
+                post.metadata.thread_id,
+                post.text_preview,
+            );
             let communication = InterAgentCommunication::new(
-                notice.0.metadata.author.clone(),
+                post.metadata.author.clone(),
                 recipient_path,
                 Vec::new(),
-                notice.render().into_text().unwrap_or_default(),
+                content,
                 /*trigger_turn*/ false,
             );
             // Remote metadata is untrusted. Skip an oversized notice without closing
diff --git a/codex-rs/app-server/src/extensions.rs b/codex-rs/app-server/src/extensions.rs
index 733df70ed5..ff31e9e395 100644
--- a/codex-rs/app-server/src/extensions.rs
+++ b/codex-rs/app-server/src/extensions.rs
@@ -83,7 +83,7 @@ pub(crate) fn thread_extensions(
         codex_queue_extension::install(&mut builder, queue_service);
     }
     codex_history_notes_extension::install(&mut builder, auth_manager.clone());
-    codex_core::install_agent_message_board(&mut builder, thread_manager.clone());
+    crate::install_agent_message_board(&mut builder, thread_manager.clone());
     if let Some(state_db) = state_db {
         codex_goal_extension::install_with_backend(
             &mut builder,
diff --git a/codex-rs/app-server/src/lib.rs b/codex-rs/app-server/src/lib.rs
index 2ad3aa8cc3..4eee045679 100644
--- a/codex-rs/app-server/src/lib.rs
+++ b/codex-rs/app-server/src/lib.rs
@@ -95,6 +95,9 @@ fn is_unsupported_untrusted_approval_policy_error(err: &std::io::Error) -> bool
     )
 }
 
+mod agent_message_board;
+pub use agent_message_board::install_agent_message_board;
+
 mod analytics_utils;
 mod app_info;
 mod app_server_tracing;
diff --git a/codex-rs/core/Cargo.toml b/codex-rs/core/Cargo.toml
index fcbc849a7c..f456872236 100644
--- a/codex-rs/core/Cargo.toml
+++ b/codex-rs/core/Cargo.toml
@@ -72,7 +72,6 @@ codex-skills-extension = { workspace = true }
 codex-state = { workspace = true }
 codex-agent-message-board-extension = { workspace = true }
 codex-message-board = { workspace = true }
-codex-agent-message-board-client = { workspace = true }
 codex-terminal-detection = { workspace = true }
 codex-thread-store = { workspace = true }
 codex-tools = { workspace = true }
@@ -146,6 +145,7 @@ openssl-sys = { workspace = true, features = ["vendored"] }
 openssl-sys = { workspace = true, features = ["vendored"] }
 
 [dev-dependencies]
+codex-app-server = { workspace = true }
 assert_cmd = { workspace = true }
 assert_matches = { workspace = true }
 codex-exec-server-test-support = { workspace = true }
diff --git a/codex-rs/core/src/context/agent_message_board_notification.rs b/codex-rs/core/src/context/agent_message_board_notification.rs
index b56ef296b9..c6136735b3 100644
--- a/codex-rs/core/src/context/agent_message_board_notification.rs
+++ b/codex-rs/core/src/context/agent_message_board_notification.rs
@@ -1,12 +1,11 @@
-//! Attributed discussion notices with bounded previews.
+//! Recognizes legacy board notices in saved user-role messages. New notices use agent mail.
 
 use super::ContextualUserFragment;
-use codex_message_board::PostPreview;
 use codex_protocol::models::ContentItem;
 use codex_protocol::models::ContentItemKind;
 use codex_protocol::models::input_text;
 
-pub(crate) struct AgentMessageBoardNotification(pub(crate) PostPreview);
+pub(crate) struct AgentMessageBoardNotification;
 
 impl ContextualUserFragment for AgentMessageBoardNotification {
     fn role(&self) -> &'static str {
@@ -26,19 +25,6 @@ impl ContextualUserFragment for AgentMessageBoardNotification {
         )
     }
     fn body(&self) -> ContentItem {
-        let post = &self.0;
-        let suffix = if post.truncated {
-            "\n[Use read_post for the rest.]"
-        } else {
-            ""
-        };
-        input_text(format!(
-            "Message Type: CHANNEL_POST\nSender: {}\nChannel: {}\nMessage ID: {}\nThread ID: {}\nPayload:\n{}{suffix}",
-            post.metadata.author,
-            post.metadata.channel_name,
-            post.metadata.message_id,
-            post.metadata.thread_id,
-            post.text_preview,
-        ))
+        input_text(String::new())
     }
 }
diff --git a/codex-rs/core/src/lib.rs b/codex-rs/core/src/lib.rs
index 82276a9299..906e74b345 100644
--- a/codex-rs/core/src/lib.rs
+++ b/codex-rs/core/src/lib.rs
@@ -81,8 +81,6 @@ pub use agent::types::SpawnAgentOptions;
 pub use rollout_budget::RolloutBudgetReminder;
 mod agent_communication;
 pub use agent_communication::PendingAgentMessage;
-mod agent_message_board;
-pub use agent_message_board::install_agent_message_board;
 mod attestation;
 mod code_mode_host;
 mod codex_delegate;
@@ -192,6 +190,7 @@ pub use thread_manager::build_models_manager;
 pub use thread_manager::local_agent_graph_store_from_state_db;
 pub use thread_manager::passthrough_image_store;
 pub use thread_store_builder::ThreadStoreBuilder;
+pub use tools::MULTI_AGENT_V2_NAMESPACE_DESCRIPTION;
 pub use tools::handlers::WaitForEnvironmentToolConfig;
 pub use web_search::web_search_action_detail;
 pub use windows_sandbox_read_grants::grant_read_root_non_elevated;
diff --git a/codex-rs/core/src/tools/mod.rs b/codex-rs/core/src/tools/mod.rs
index 3344ed84b3..eebc88af8b 100644
--- a/codex-rs/core/src/tools/mod.rs
+++ b/codex-rs/core/src/tools/mod.rs
@@ -41,7 +41,7 @@ use codex_utils_output_truncation::TruncationPolicy;
 use codex_utils_output_truncation::formatted_truncate_text;
 use codex_utils_output_truncation::truncate_text;
 pub(crate) use executed_tool_calls::ExecutedToolCalls;
-pub(crate) use multi_agent_tool::MULTI_AGENT_V2_NAMESPACE_DESCRIPTION;
+pub use multi_agent_tool::MULTI_AGENT_V2_NAMESPACE_DESCRIPTION;
 pub use router::ToolRouter;
 
 /// Legacy boundaries such as hook payloads, telemetry tags, and Responses tool
diff --git a/codex-rs/core/src/tools/multi_agent_tool.rs b/codex-rs/core/src/tools/multi_agent_tool.rs
index 2b271af752..6eac80992d 100644
--- a/codex-rs/core/src/tools/multi_agent_tool.rs
+++ b/codex-rs/core/src/tools/multi_agent_tool.rs
@@ -15,7 +15,8 @@ use codex_tools::ToolSpec;
 use futures::future::BoxFuture;
 use std::sync::Arc;
 
-pub(crate) const MULTI_AGENT_V2_NAMESPACE_DESCRIPTION: &str =
+/// Shared namespace description for native tools and host extensions.
+pub const MULTI_AGENT_V2_NAMESPACE_DESCRIPTION: &str =
     "Tools for spawning and managing sub-agents.";
 
 pub(super) fn multi_agent_v2_handler(
diff --git a/codex-rs/core/tests/common/Cargo.toml b/codex-rs/core/tests/common/Cargo.toml
index cb5c222039..6dedb2f13e 100644
--- a/codex-rs/core/tests/common/Cargo.toml
+++ b/codex-rs/core/tests/common/Cargo.toml
@@ -12,6 +12,7 @@ doctest = false
 workspace = true
 
 [dependencies]
+codex-app-server = { workspace = true }
 anyhow = { workspace = true }
 assert_cmd = { workspace = true }
 base64 = { workspace = true }
diff --git a/codex-rs/core/tests/common/test_codex.rs b/codex-rs/core/tests/common/test_codex.rs
index 3cb6b51c1b..722d2cf514 100644
--- a/codex-rs/core/tests/common/test_codex.rs
+++ b/codex-rs/core/tests/common/test_codex.rs
@@ -866,7 +866,7 @@ impl TestCodexBuilder {
             .or_else(|| codex_utils_cargo_bin::cargo_bin("codex-code-mode-host").ok());
         let thread_manager = Arc::new_cyclic(|manager| {
             let mut extensions = self.extensions.to_builder();
-            codex_core::install_agent_message_board(&mut extensions, manager.clone());
+            codex_app_server::install_agent_message_board(&mut extensions, manager.clone());
             if config.features.enabled(Feature::GuardianV2) {
                 codex_guardian_v2::install(&mut extensions, auth_manager.clone(), manager.clone());
             } else {
diff --git a/codex-rs/core/tests/suite/scenarios_agent_message_board.rs b/codex-rs/core/tests/suite/scenarios_agent_message_board.rs
index 88fa3f45d2..4dbd32f443 100644
--- a/codex-rs/core/tests/suite/scenarios_agent_message_board.rs
+++ b/codex-rs/core/tests/suite/scenarios_agent_message_board.rs
@@ -1060,7 +1060,10 @@ async fn codex_instances_share_board_with_fixed_access() -> anyhow::Result<()> {
     let guardian_board =
         LocalBoard::new(SqliteConfig::new_for_testing(alias.try_into()?), board_id);
     let mut extensions = ExtensionRegistryBuilder::new();
-    codex_core::install_agent_message_board(&mut extensions, Arc::downgrade(&test.thread_manager));
+    codex_app_server::install_agent_message_board(
+        &mut extensions,
+        Arc::downgrade(&test.thread_manager),
+    );
     let extensions = Arc::new(extensions.build());
     let mut instances = Vec::new();
     for (index, (connection, source)) in [
diff --git a/codex-rs/ext/agent-message-board/README.md b/codex-rs/ext/agent-message-board/README.md
index 7f0ff61069..ec64c2fffb 100644
--- a/codex-rs/ext/agent-message-board/README.md
+++ b/codex-rs/ext/agent-message-board/README.md
@@ -43,7 +43,7 @@ creating channels and changing another agent's subscriptions return permission
 errors. Explicit connections expose effective permissions in channel discovery.
 Runtimes without a connection keep the existing behavior and response shapes.
 
-Install `codex_core::install_agent_message_board` in the runtime's extension
+Install `codex_app_server::install_agent_message_board` in the runtime's extension
 registry. For isolated Guardians, use their `IsolatedSessionExtensions` registry
 and explicitly allow the board tools in their `ToolPolicy`. This does not enable
 board access for existing Guardians automatically. Connected runtimes use unique