diff --git a/AGENTS.md b/AGENTS.md
index 6939d146b00e..9b1788007d9f 100644
--- a/AGENTS.md
+++ b/AGENTS.md
@@ -108,6 +108,15 @@ See `codex-rs/tui/styles.md`.
 
 ## Tests
 
+When reviewing or adding tests:
+
+- Ask whether the test makes sense.
+- Ask whether it actually asserts something valuable that you care about.
+- Ask how much the test would need to change if the surrounding system were refactored.
+- Ask whether you or someone else would notice the regression if Codex auto-updated the test.
+
+If a unit test mostly covers deep implementation details, static data, removed behavior, or requires heavy monkeypatching, prefer deleting it and writing an integration test that protects meaningful end-to-end behavior instead.
+
 ### Snapshot tests
 
 This repo uses snapshot tests (via `insta`), especially in `codex-rs/tui`, to validate rendered output.
diff --git a/codex-rs/codex-mcp/src/codex_apps.rs b/codex-rs/codex-mcp/src/codex_apps.rs
index 0a7981fb0d5f..ff5098a9ef02 100644
--- a/codex-rs/codex-mcp/src/codex_apps.rs
+++ b/codex-rs/codex-mcp/src/codex_apps.rs
@@ -21,7 +21,7 @@ use serde::Serialize;
 use sha1::Digest;
 use sha1::Sha1;
 
-pub(crate) const CODEX_APPS_TOOLS_CACHE_SCHEMA_VERSION: u8 = 2;
+pub(crate) const CODEX_APPS_TOOLS_CACHE_SCHEMA_VERSION: u8 = 3;
 
 #[derive(Debug, Clone, PartialEq, Eq, Serialize, Deserialize)]
 pub struct CodexAppsToolsCacheKey {
@@ -115,7 +115,7 @@ pub(crate) fn normalize_codex_apps_callable_name(
         && let Some(stripped) = tool_name.strip_prefix(&connector_name)
         && !stripped.is_empty()
     {
-        return stripped.to_string();
+        return stripped.strip_prefix('_').unwrap_or(stripped).to_string();
     }
 
     if let Some(connector_id) = connector_id
@@ -125,7 +125,7 @@ pub(crate) fn normalize_codex_apps_callable_name(
         && let Some(stripped) = tool_name.strip_prefix(&connector_id)
         && !stripped.is_empty()
     {
-        return stripped.to_string();
+        return stripped.strip_prefix('_').unwrap_or(stripped).to_string();
     }
 
     tool_name
@@ -138,9 +138,9 @@ pub(crate) fn normalize_codex_apps_callable_namespace(
     if server_name == CODEX_APPS_MCP_SERVER_NAME
         && let Some(connector_name) = connector_name
     {
-        format!("mcp__{}__{}", server_name, sanitize_name(connector_name))
+        format!("{}__{}", server_name, sanitize_name(connector_name))
     } else {
-        format!("mcp__{server_name}__")
+        server_name.to_string()
     }
 }
 
diff --git a/codex-rs/codex-mcp/src/connection_manager_tests.rs b/codex-rs/codex-mcp/src/connection_manager_tests.rs
index 01b1161b730a..9c3c9fb91013 100644
--- a/codex-rs/codex-mcp/src/connection_manager_tests.rs
+++ b/codex-rs/codex-mcp/src/connection_manager_tests.rs
@@ -35,7 +35,7 @@ use std::sync::Arc;
 use tempfile::tempdir;
 
 fn create_test_tool(server_name: &str, tool_name: &str) -> ToolInfo {
-    let tool_namespace = format!("mcp__{server_name}__");
+    let tool_namespace = server_name.to_string();
     ToolInfo {
         server_name: server_name.to_string(),
         callable_name: tool_name.to_string(),
@@ -71,6 +71,18 @@ fn create_test_tool_with_connector(
     tool
 }
 
+fn create_codex_apps_test_tool(tool_name: &str, callable_name: &str) -> ToolInfo {
+    let mut tool = create_test_tool_with_connector(
+        CODEX_APPS_MCP_SERVER_NAME,
+        tool_name,
+        "calendar",
+        Some("Calendar"),
+    );
+    tool.callable_name = callable_name.to_string();
+    tool.callable_namespace = "codex_apps__calendar".to_string();
+    tool
+}
+
 fn create_codex_apps_tools_cache_context(
     codex_home: PathBuf,
     account_id: Option<&str>,
@@ -276,8 +288,8 @@ fn test_qualify_tools_short_non_duplicated_names() {
     let qualified_tools = qualify_tools(tools);
 
     assert_eq!(qualified_tools.len(), 2);
-    assert!(qualified_tools.contains_key("mcp__server1__tool1"));
-    assert!(qualified_tools.contains_key("mcp__server1__tool2"));
+    assert!(qualified_tools.contains_key("server1__tool1"));
+    assert!(qualified_tools.contains_key("server1__tool2"));
 }
 
 #[test]
@@ -291,7 +303,7 @@ fn test_qualify_tools_duplicated_names_skipped() {
 
     // Only the first tool should remain, the second is skipped
     assert_eq!(qualified_tools.len(), 1);
-    assert!(qualified_tools.contains_key("mcp__server1__duplicate_tool"));
+    assert!(qualified_tools.contains_key("server1__duplicate_tool"));
 }
 
 #[test]
@@ -317,7 +329,7 @@ fn test_qualify_tools_long_names_same_server() {
     keys.sort();
 
     assert!(keys.iter().all(|key| key.len() == 64));
-    assert!(keys.iter().all(|key| key.starts_with("mcp__my_server__")));
+    assert!(keys.iter().all(|key| key.starts_with("my_server__")));
     assert!(
         keys.iter()
             .all(|key| key.chars().all(|c| c.is_ascii_alphanumeric() || c == '_')),
@@ -333,16 +345,16 @@ fn test_qualify_tools_sanitizes_invalid_characters() {
 
     assert_eq!(qualified_tools.len(), 1);
     let (qualified_name, tool) = qualified_tools.into_iter().next().expect("one tool");
-    assert_eq!(qualified_name, "mcp__server_one__tool_two_three");
+    assert_eq!(qualified_name, "server_one__tool_two_three");
     assert_eq!(
-        format!("{}{}", tool.callable_namespace, tool.callable_name),
+        ToolName::namespaced(&tool.callable_namespace, &tool.callable_name).display(),
         qualified_name
     );
 
     // The key and callable parts are sanitized for model-visible tool calls, but
     // the raw MCP name is preserved for the actual MCP call.
     assert_eq!(tool.server_name, "server.one");
-    assert_eq!(tool.callable_namespace, "mcp__server_one__");
+    assert_eq!(tool.callable_namespace, "server_one");
     assert_eq!(tool.callable_name, "tool_two_three");
     assert_eq!(tool.tool.name, "tool.two-three");
 
@@ -362,8 +374,8 @@ fn test_qualify_tools_keeps_hyphenated_mcp_tools_callable() {
 
     assert_eq!(qualified_tools.len(), 1);
     let (qualified_name, tool) = qualified_tools.into_iter().next().expect("one tool");
-    assert_eq!(qualified_name, "mcp__music_studio__get_strudel_guide");
-    assert_eq!(tool.callable_namespace, "mcp__music_studio__");
+    assert_eq!(qualified_name, "music_studio__get_strudel_guide");
+    assert_eq!(tool.callable_namespace, "music_studio");
     assert_eq!(tool.callable_name, "get_strudel_guide");
     assert_eq!(tool.tool.name, "get-strudel-guide");
 }
@@ -624,10 +636,7 @@ fn startup_cached_codex_apps_tools_loads_from_disk_cache() {
         Some("account-one"),
         Some("user-one"),
     );
-    let cached_tools = vec![create_test_tool(
-        CODEX_APPS_MCP_SERVER_NAME,
-        "calendar_search",
-    )];
+    let cached_tools = vec![create_codex_apps_test_tool("calendar_search", "search")];
     write_cached_codex_apps_tools(&cache_context, &cached_tools);
 
     let startup_snapshot = load_startup_cached_codex_apps_tools_snapshot(
@@ -638,14 +647,14 @@ fn startup_cached_codex_apps_tools_loads_from_disk_cache() {
 
     assert_eq!(startup_tools.len(), 1);
     assert_eq!(startup_tools[0].server_name, CODEX_APPS_MCP_SERVER_NAME);
-    assert_eq!(startup_tools[0].callable_name, "calendar_search");
+    assert_eq!(startup_tools[0].callable_name, "search");
 }
 
 #[tokio::test]
 async fn list_all_tools_uses_startup_snapshot_while_client_is_pending() {
-    let startup_tools = vec![create_test_tool(
-        CODEX_APPS_MCP_SERVER_NAME,
+    let startup_tools = vec![create_codex_apps_test_tool(
         "calendar_create_event",
+        "create_event",
     )];
     let pending_client = futures::future::pending::<Result<ManagedClient, StartupOutcomeError>>()
         .boxed()
@@ -667,10 +676,10 @@ async fn list_all_tools_uses_startup_snapshot_while_client_is_pending() {
 
     let tools = manager.list_all_tools().await;
     let tool = tools
-        .get("mcp__codex_apps__calendar_create_event")
+        .get("codex_apps__calendar__create_event")
         .expect("tool from startup cache");
     assert_eq!(tool.server_name, CODEX_APPS_MCP_SERVER_NAME);
-    assert_eq!(tool.callable_name, "calendar_create_event");
+    assert_eq!(tool.callable_name, "create_event");
 }
 
 #[tokio::test]
@@ -695,11 +704,11 @@ async fn resolve_tool_info_accepts_canonical_namespaced_tool_names() {
     );
 
     let tool = manager
-        .resolve_tool_info(&ToolName::namespaced("mcp__rmcp__", "echo"))
+        .resolve_tool_info(&ToolName::namespaced("rmcp", "echo"))
         .await
         .expect("split MCP tool namespace and name should resolve");
 
-    let expected = ("rmcp", "mcp__rmcp__", "echo", "echo");
+    let expected = ("rmcp", "rmcp", "echo", "echo");
     assert_eq!(
         (
             tool.server_name.as_str(),
@@ -764,9 +773,9 @@ async fn list_all_tools_does_not_block_when_startup_snapshot_cache_hit_is_empty(
 
 #[tokio::test]
 async fn list_all_tools_uses_startup_snapshot_when_client_startup_fails() {
-    let startup_tools = vec![create_test_tool(
-        CODEX_APPS_MCP_SERVER_NAME,
+    let startup_tools = vec![create_codex_apps_test_tool(
         "calendar_create_event",
+        "create_event",
     )];
     let failed_client = futures::future::ready::<Result<ManagedClient, StartupOutcomeError>>(Err(
         StartupOutcomeError::Failed {
@@ -793,10 +802,10 @@ async fn list_all_tools_uses_startup_snapshot_when_client_startup_fails() {
 
     let tools = manager.list_all_tools().await;
     let tool = tools
-        .get("mcp__codex_apps__calendar_create_event")
+        .get("codex_apps__calendar__create_event")
         .expect("tool from startup cache");
     assert_eq!(tool.server_name, CODEX_APPS_MCP_SERVER_NAME);
-    assert_eq!(tool.callable_name, "calendar_create_event");
+    assert_eq!(tool.callable_name, "create_event");
 }
 
 #[test]
diff --git a/codex-rs/codex-mcp/src/mcp/mod.rs b/codex-rs/codex-mcp/src/mcp/mod.rs
index 3cfd4d01e194..32f5c92abecf 100644
--- a/codex-rs/codex-mcp/src/mcp/mod.rs
+++ b/codex-rs/codex-mcp/src/mcp/mod.rs
@@ -41,7 +41,6 @@ use crate::connection_manager::McpConnectionManager;
 use crate::runtime::McpRuntimeEnvironment;
 
 pub const CODEX_APPS_MCP_SERVER_NAME: &str = "codex_apps";
-const MCP_TOOL_NAME_PREFIX: &str = "mcp";
 const MCP_TOOL_NAME_DELIMITER: &str = "__";
 const CODEX_CONNECTORS_TOKEN_ENV_VAR: &str = "CODEX_CONNECTORS_TOKEN";
 
@@ -59,9 +58,10 @@ impl McpSnapshotDetail {
 }
 
 pub fn qualified_mcp_tool_name_prefix(server_name: &str) -> String {
-    sanitize_responses_api_tool_name(&format!(
-        "{MCP_TOOL_NAME_PREFIX}{MCP_TOOL_NAME_DELIMITER}{server_name}{MCP_TOOL_NAME_DELIMITER}"
-    ))
+    format!(
+        "{}{MCP_TOOL_NAME_DELIMITER}",
+        sanitize_responses_api_tool_name(server_name)
+    )
 }
 
 /// Returns true when MCP permission prompts should resolve as approved instead
diff --git a/codex-rs/codex-mcp/src/mcp/mod_tests.rs b/codex-rs/codex-mcp/src/mcp/mod_tests.rs
index fa5cbf1f7adb..10e8b21992b3 100644
--- a/codex-rs/codex-mcp/src/mcp/mod_tests.rs
+++ b/codex-rs/codex-mcp/src/mcp/mod_tests.rs
@@ -36,7 +36,7 @@ fn test_mcp_config(codex_home: PathBuf) -> McpConfig {
 fn qualified_mcp_tool_name_prefix_sanitizes_server_names_without_lowercasing() {
     assert_eq!(
         qualified_mcp_tool_name_prefix("Some-Server"),
-        "mcp__Some_Server__".to_string()
+        "Some_Server__".to_string()
     );
 }
 
diff --git a/codex-rs/codex-mcp/src/tools.rs b/codex-rs/codex-mcp/src/tools.rs
index 9b677e8a07c7..2ee8f937d90c 100644
--- a/codex-rs/codex-mcp/src/tools.rs
+++ b/codex-rs/codex-mcp/src/tools.rs
@@ -134,7 +134,7 @@ pub(crate) fn filter_tools(tools: Vec<ToolInfo>, filter: &ToolFilter) -> Vec<Too
 ///
 /// Raw MCP server/tool names are kept on each [`ToolInfo`] for protocol calls, while
 /// `callable_namespace` / `callable_name` are sanitized and, when necessary, hashed so
-/// every model-visible `mcp__namespace__tool` name is unique and <= 64 bytes.
+/// every flattened model-visible `namespace__tool` name is unique and <= 64 bytes.
 pub(crate) fn qualify_tools<I>(tools: I) -> HashMap<String, ToolInfo>
 where
     I: IntoIterator<Item = ToolInfo>,
@@ -327,17 +327,22 @@ fn fit_callable_parts_with_hash(
     raw_identity: &str,
 ) -> (String, String) {
     let suffix = callable_name_hash_suffix(raw_identity);
-    let max_tool_len = MAX_TOOL_NAME_LENGTH.saturating_sub(namespace.len());
-    if max_tool_len >= suffix.len() {
-        let prefix_len = max_tool_len - suffix.len();
-        return (
-            namespace.to_string(),
-            format!("{}{}", truncate_name(tool_name, prefix_len), suffix),
-        );
+
+    for prefix_len in (0..=tool_name.chars().count()).rev() {
+        let candidate_name = format!("{}{}", truncate_name(tool_name, prefix_len), suffix);
+        if qualified_name(namespace, &candidate_name).len() <= MAX_TOOL_NAME_LENGTH {
+            return (namespace.to_string(), candidate_name);
+        }
     }
 
-    let max_namespace_len = MAX_TOOL_NAME_LENGTH - suffix.len();
-    (truncate_name(namespace, max_namespace_len), suffix)
+    for namespace_len in (0..=namespace.chars().count()).rev() {
+        let candidate_namespace = truncate_name(namespace, namespace_len);
+        if qualified_name(&candidate_namespace, &suffix).len() <= MAX_TOOL_NAME_LENGTH {
+            return (candidate_namespace, suffix);
+        }
+    }
+
+    (String::new(), suffix)
 }
 
 fn unique_callable_parts(
@@ -346,9 +351,15 @@ fn unique_callable_parts(
     raw_identity: &str,
     used_names: &mut HashSet<String>,
 ) -> (String, String, String) {
-    let qualified_name = format!("{namespace}{tool_name}");
-    if qualified_name.len() <= MAX_TOOL_NAME_LENGTH && used_names.insert(qualified_name.clone()) {
-        return (namespace.to_string(), tool_name.to_string(), qualified_name);
+    let qualified_display_name = qualified_name(namespace, tool_name);
+    if qualified_display_name.len() <= MAX_TOOL_NAME_LENGTH
+        && used_names.insert(qualified_display_name.clone())
+    {
+        return (
+            namespace.to_string(),
+            tool_name.to_string(),
+            qualified_display_name,
+        );
     }
 
     let mut attempt = 0_u32;
@@ -360,10 +371,14 @@ fn unique_callable_parts(
         };
         let (namespace, tool_name) =
             fit_callable_parts_with_hash(namespace, tool_name, &hash_input);
-        let qualified_name = format!("{namespace}{tool_name}");
+        let qualified_name = qualified_name(&namespace, &tool_name);
         if used_names.insert(qualified_name.clone()) {
             return (namespace, tool_name, qualified_name);
         }
         attempt = attempt.saturating_add(1);
     }
 }
+
+fn qualified_name(namespace: &str, tool_name: &str) -> String {
+    ToolName::namespaced(namespace, tool_name).display()
+}
diff --git a/codex-rs/core/src/connectors_tests.rs b/codex-rs/core/src/connectors_tests.rs
index b3538d1ff062..c3775193c465 100644
--- a/codex-rs/core/src/connectors_tests.rs
+++ b/codex-rs/core/src/connectors_tests.rs
@@ -112,7 +112,7 @@ fn codex_app_tool(
 ) -> ToolInfo {
     let tool_namespace = connector_name
         .map(sanitize_name)
-        .map(|connector_name| format!("mcp__{CODEX_APPS_MCP_SERVER_NAME}__{connector_name}"))
+        .map(|connector_name| format!("{CODEX_APPS_MCP_SERVER_NAME}__{connector_name}"))
         .unwrap_or_else(|| CODEX_APPS_MCP_SERVER_NAME.to_string());
 
     ToolInfo {
@@ -175,7 +175,7 @@ fn merge_connectors_replaces_plugin_placeholder_name_with_accessible_name() {
 fn accessible_connectors_from_mcp_tools_carries_plugin_display_names() {
     let tools = HashMap::from([
         (
-            "mcp__codex_apps__calendar_list_events".to_string(),
+            "codex_apps__calendar__list_events".to_string(),
             codex_app_tool(
                 "calendar_list_events",
                 "calendar",
@@ -184,7 +184,7 @@ fn accessible_connectors_from_mcp_tools_carries_plugin_display_names() {
             ),
         ),
         (
-            "mcp__codex_apps__calendar_create_event".to_string(),
+            "codex_apps__calendar__create_event".to_string(),
             codex_app_tool(
                 "calendar_create_event",
                 "calendar",
@@ -193,7 +193,7 @@ fn accessible_connectors_from_mcp_tools_carries_plugin_display_names() {
             ),
         ),
         (
-            "mcp__sample__echo".to_string(),
+            "sample__echo".to_string(),
             ToolInfo {
                 server_name: "sample".to_string(),
                 callable_name: "echo".to_string(),
@@ -242,7 +242,7 @@ async fn refresh_accessible_connectors_cache_from_mcp_tools_writes_latest_instal
     let cache_key = accessible_connectors_cache_key(&config, /*auth*/ None);
     let tools = HashMap::from([
         (
-            "mcp__codex_apps__calendar_list_events".to_string(),
+            "codex_apps__calendar__list_events".to_string(),
             codex_app_tool(
                 "calendar_list_events",
                 "calendar",
@@ -251,7 +251,7 @@ async fn refresh_accessible_connectors_cache_from_mcp_tools_writes_latest_instal
             ),
         ),
         (
-            "mcp__codex_apps__openai_hidden".to_string(),
+            "codex_apps__openai_hidden".to_string(),
             codex_app_tool(
                 "openai_hidden",
                 "connector_openai_hidden",
@@ -318,11 +318,11 @@ fn merge_connectors_unions_and_dedupes_plugin_display_names() {
 #[test]
 fn accessible_connectors_from_mcp_tools_preserves_description() {
     let mcp_tools = HashMap::from([(
-        "mcp__codex_apps__calendar_create_event".to_string(),
+        "codex_apps__calendar__create_event".to_string(),
         ToolInfo {
             server_name: CODEX_APPS_MCP_SERVER_NAME.to_string(),
             callable_name: "calendar_create_event".to_string(),
-            callable_namespace: "mcp__codex_apps__calendar".to_string(),
+            callable_namespace: "codex_apps__calendar".to_string(),
             server_instructions: None,
             tool: Tool {
                 name: "calendar_create_event".to_string().into(),
diff --git a/codex-rs/core/src/mcp_tool_call_tests.rs b/codex-rs/core/src/mcp_tool_call_tests.rs
index 524138f017d4..e2a3a85bb85c 100644
--- a/codex-rs/core/src/mcp_tool_call_tests.rs
+++ b/codex-rs/core/src/mcp_tool_call_tests.rs
@@ -1907,7 +1907,7 @@ async fn approve_mode_skips_when_annotations_do_not_require_approval() {
         &turn_context,
         "call-1",
         &invocation,
-        "mcp__test__tool",
+        "test__tool",
         Some(&metadata),
         AppToolApproval::Approve,
     )
@@ -1980,7 +1980,7 @@ async fn guardian_mode_skips_auto_when_annotations_do_not_require_approval() {
         &turn_context,
         "call-guardian",
         &invocation,
-        "mcp__test__tool",
+        "test__tool",
         Some(&metadata),
         AppToolApproval::Auto,
     )
@@ -1995,7 +1995,7 @@ async fn permission_request_hook_allows_mcp_tool_call() {
     let log_path = install_mcp_permission_request_hook(
         &mut session,
         &turn_context,
-        "mcp__memory__.*",
+        "memory__.*",
         &serde_json::json!({
             "hookSpecificOutput": {
                 "hookEventName": "PermissionRequest",
@@ -2036,7 +2036,7 @@ async fn permission_request_hook_allows_mcp_tool_call() {
         &turn_context,
         "call-mcp-hook",
         &invocation,
-        "mcp__memory__create_entities",
+        "memory__create_entities",
         Some(&metadata),
         AppToolApproval::Auto,
     )
@@ -2057,7 +2057,7 @@ async fn permission_request_hook_allows_mcp_tool_call() {
             "transcript_path": null,
             "model": turn_context.model_info.slug,
             "permission_mode": "default",
-            "tool_name": "mcp__memory__create_entities",
+            "tool_name": "memory__create_entities",
             "hook_event_name": "PermissionRequest",
             "tool_input": {
                 "entities": [{
@@ -2075,7 +2075,7 @@ async fn permission_request_hook_uses_hook_tool_name_without_metadata() {
     let log_path = install_mcp_permission_request_hook(
         &mut session,
         &turn_context,
-        "mcp__memory__.*",
+        "memory__.*",
         &serde_json::json!({
             "hookSpecificOutput": {
                 "hookEventName": "PermissionRequest",
@@ -2096,7 +2096,7 @@ async fn permission_request_hook_uses_hook_tool_name_without_metadata() {
         &turn_context,
         "call-mcp-hook-no-metadata",
         &invocation,
-        "mcp__memory__create_entities",
+        "memory__create_entities",
         /*metadata*/ None,
         AppToolApproval::Auto,
     )
@@ -2117,7 +2117,7 @@ async fn permission_request_hook_uses_hook_tool_name_without_metadata() {
             "transcript_path": null,
             "model": turn_context.model_info.slug,
             "permission_mode": "default",
-            "tool_name": "mcp__memory__create_entities",
+            "tool_name": "memory__create_entities",
             "hook_event_name": "PermissionRequest",
             "tool_input": { "entities": [] }
         })]
@@ -2130,7 +2130,7 @@ async fn permission_request_hook_runs_after_remembered_mcp_approval() {
     let log_path = install_mcp_permission_request_hook(
         &mut session,
         &turn_context,
-        "mcp__memory__.*",
+        "memory__.*",
         &serde_json::json!({
             "hookSpecificOutput": {
                 "hookEventName": "PermissionRequest",
@@ -2173,7 +2173,7 @@ async fn permission_request_hook_runs_after_remembered_mcp_approval() {
         &turn_context,
         "call-mcp-remembered",
         &invocation,
-        "mcp__memory__create_entities",
+        "memory__create_entities",
         Some(&metadata),
         AppToolApproval::Auto,
     )
@@ -2253,7 +2253,7 @@ async fn guardian_mode_mcp_denial_returns_rationale_message() {
         &turn_context,
         "call-guardian-deny",
         &invocation,
-        "mcp__test__tool",
+        "test__tool",
         Some(&metadata),
         AppToolApproval::Auto,
     )
@@ -2310,7 +2310,7 @@ async fn prompt_mode_waits_for_approval_when_annotations_do_not_require_approval
                 &turn_context,
                 "call-prompt",
                 &invocation,
-                "mcp__test__tool",
+                "test__tool",
                 Some(&metadata),
                 AppToolApproval::Prompt,
             )
@@ -2385,7 +2385,7 @@ async fn approve_mode_blocks_when_arc_returns_interrupt_for_model() {
         &turn_context,
         "call-2",
         &invocation,
-        "mcp__test__tool",
+        "test__tool",
         Some(&metadata),
         AppToolApproval::Approve,
     )
@@ -2457,7 +2457,7 @@ async fn custom_approve_mode_blocks_when_arc_returns_interrupt_for_model() {
         &turn_context,
         "call-2-custom",
         &invocation,
-        "mcp__test__tool",
+        "test__tool",
         Some(&metadata),
         AppToolApproval::Approve,
     )
@@ -2529,7 +2529,7 @@ async fn approve_mode_blocks_when_arc_returns_interrupt_without_annotations() {
         &turn_context,
         "call-3",
         &invocation,
-        "mcp__test__tool",
+        "test__tool",
         Some(&metadata),
         AppToolApproval::Approve,
     )
@@ -2611,7 +2611,7 @@ async fn full_access_mode_skips_arc_monitor_for_all_approval_modes() {
             &turn_context,
             "call-2",
             &invocation,
-            "mcp__test__tool",
+            "test__tool",
             Some(&metadata),
             approval_mode,
         )
@@ -2701,7 +2701,7 @@ async fn approve_mode_skips_arc_and_guardian_when_guardian_reviewer_is_enabled()
         &turn_context,
         "call-3",
         &invocation,
-        "mcp__test__tool",
+        "test__tool",
         Some(&metadata),
         AppToolApproval::Approve,
     )
diff --git a/codex-rs/core/src/mcp_tool_exposure_test.rs b/codex-rs/core/src/mcp_tool_exposure_test.rs
index cbd4d3b29c76..85df59e297f0 100644
--- a/codex-rs/core/src/mcp_tool_exposure_test.rs
+++ b/codex-rs/core/src/mcp_tool_exposure_test.rs
@@ -48,10 +48,10 @@ fn make_mcp_tool(
     let tool_namespace = if server_name == CODEX_APPS_MCP_SERVER_NAME {
         connector_name
             .map(sanitize_name)
-            .map(|connector_name| format!("mcp__{server_name}__{connector_name}"))
+            .map(|connector_name| format!("{server_name}__{connector_name}"))
             .unwrap_or_else(|| server_name.to_string())
     } else {
-        format!("mcp__{server_name}__")
+        server_name.to_string()
     };
 
     ToolInfo {
@@ -82,7 +82,7 @@ fn numbered_mcp_tools(count: usize) -> HashMap<String, ToolInfo> {
         .map(|index| {
             let tool_name = format!("tool_{index}");
             (
-                format!("mcp__rmcp__{tool_name}"),
+                format!("rmcp__{tool_name}"),
                 make_mcp_tool(
                     "rmcp", &tool_name, /*connector_id*/ None, /*connector_name*/ None,
                 ),
@@ -165,7 +165,7 @@ async fn directly_exposes_explicit_apps_without_deferred_overlap() {
     let tools_config = tools_config_for_mcp_tool_exposure(/*search_tool*/ true).await;
     let mut mcp_tools = numbered_mcp_tools(DIRECT_MCP_TOOL_EXPOSURE_THRESHOLD - 1);
     mcp_tools.extend([(
-        "mcp__codex_apps__calendar_create_event".to_string(),
+        "codex_apps__calendar__create_event".to_string(),
         make_mcp_tool(
             CODEX_APPS_MCP_SERVER_NAME,
             "calendar_create_event",
@@ -187,7 +187,7 @@ async fn directly_exposes_explicit_apps_without_deferred_overlap() {
     tool_names.sort();
     assert_eq!(
         tool_names,
-        vec!["mcp__codex_apps__calendar_create_event".to_string()]
+        vec!["codex_apps__calendar__create_event".to_string()]
     );
     assert_eq!(
         exposure.deferred_tools.as_ref().map(HashMap::len),
@@ -203,8 +203,8 @@ async fn directly_exposes_explicit_apps_without_deferred_overlap() {
             .all(|direct_tool_name| !deferred_tools.contains_key(direct_tool_name)),
         "direct tools should not also be deferred: {tool_names:?}"
     );
-    assert!(!deferred_tools.contains_key("mcp__codex_apps__calendar_create_event"));
-    assert!(deferred_tools.contains_key("mcp__rmcp__tool_0"));
+    assert!(!deferred_tools.contains_key("codex_apps__calendar__create_event"));
+    assert!(deferred_tools.contains_key("rmcp__tool_0"));
 }
 
 #[tokio::test]
@@ -217,13 +217,13 @@ async fn always_defer_feature_preserves_explicit_apps() {
     let tools_config = tools_config_for_mcp_tool_exposure(/*search_tool*/ true).await;
     let mcp_tools = HashMap::from([
         (
-            "mcp__rmcp__tool".to_string(),
+            "rmcp__tool".to_string(),
             make_mcp_tool(
                 "rmcp", "tool", /*connector_id*/ None, /*connector_name*/ None,
             ),
         ),
         (
-            "mcp__codex_apps__calendar_create_event".to_string(),
+            "codex_apps__calendar__create_event".to_string(),
             make_mcp_tool(
                 CODEX_APPS_MCP_SERVER_NAME,
                 "calendar_create_event",
@@ -246,12 +246,12 @@ async fn always_defer_feature_preserves_explicit_apps() {
     direct_tool_names.sort();
     assert_eq!(
         direct_tool_names,
-        vec!["mcp__codex_apps__calendar_create_event".to_string()]
+        vec!["codex_apps__calendar__create_event".to_string()]
     );
     let deferred_tools = exposure
         .deferred_tools
         .as_ref()
         .expect("MCP tools should be discoverable through tool_search");
-    assert!(deferred_tools.contains_key("mcp__rmcp__tool"));
-    assert!(!deferred_tools.contains_key("mcp__codex_apps__calendar_create_event"));
+    assert!(deferred_tools.contains_key("rmcp__tool"));
+    assert!(!deferred_tools.contains_key("codex_apps__calendar__create_event"));
 }
diff --git a/codex-rs/core/src/tools/handlers/mcp.rs b/codex-rs/core/src/tools/handlers/mcp.rs
index 568e4561583c..cbe6cadbffe2 100644
--- a/codex-rs/core/src/tools/handlers/mcp.rs
+++ b/codex-rs/core/src/tools/handlers/mcp.rs
@@ -142,12 +142,12 @@ mod tests {
                 cancellation_token: tokio_util::sync::CancellationToken::new(),
                 tracker: Arc::new(Mutex::new(TurnDiffTracker::new())),
                 call_id: "call-mcp-pre".to_string(),
-                tool_name: codex_tools::ToolName::namespaced("mcp__memory__", "create_entities"),
+                tool_name: codex_tools::ToolName::namespaced("memory", "create_entities"),
                 source: ToolCallSource::Direct,
                 payload,
             }),
             Some(PreToolUsePayload {
-                tool_name: HookToolName::new("mcp__memory__create_entities"),
+                tool_name: HookToolName::new("memory__create_entities"),
                 tool_input: json!({
                     "entities": [{
                         "name": "Ada",
@@ -191,14 +191,14 @@ mod tests {
             cancellation_token: tokio_util::sync::CancellationToken::new(),
             tracker: Arc::new(Mutex::new(TurnDiffTracker::new())),
             call_id: "call-mcp-post".to_string(),
-            tool_name: codex_tools::ToolName::namespaced("mcp__filesystem__", "read_file"),
+            tool_name: codex_tools::ToolName::namespaced("filesystem", "read_file"),
             source: ToolCallSource::Direct,
             payload,
         };
         assert_eq!(
             McpHandler.post_tool_use_payload(&invocation, &output),
             Some(PostToolUsePayload {
-                tool_name: HookToolName::new("mcp__filesystem__read_file"),
+                tool_name: HookToolName::new("filesystem__read_file"),
                 tool_use_id: "call-mcp-post".to_string(),
                 tool_input: json!({
                     "path": {
diff --git a/codex-rs/core/src/tools/handlers/tool_search.rs b/codex-rs/core/src/tools/handlers/tool_search.rs
index f38b4ee88321..5f20c6e9d470 100644
--- a/codex-rs/core/src/tools/handlers/tool_search.rs
+++ b/codex-rs/core/src/tools/handlers/tool_search.rs
@@ -202,11 +202,11 @@ mod tests {
         let handler = handler_from_tools(
             Some(&std::collections::HashMap::from([
                 (
-                    "mcp__calendar__create_event".to_string(),
+                    "calendar__create_event".to_string(),
                     tool_info("calendar", "create_event", "Create events"),
                 ),
                 (
-                    "mcp__calendar__list_events".to_string(),
+                    "calendar__list_events".to_string(),
                     tool_info("calendar", "list_events", "List events"),
                 ),
             ])),
@@ -226,8 +226,8 @@ mod tests {
             tools,
             vec![
                 LoadableToolSpec::Namespace(ResponsesApiNamespace {
-                    name: "mcp__calendar__".to_string(),
-                    description: "Tools in the mcp__calendar__ namespace.".to_string(),
+                    name: "calendar".to_string(),
+                    description: "Tools in the calendar namespace.".to_string(),
                     tools: vec![
                         ResponsesApiNamespaceTool::Function(ResponsesApiTool {
                             name: "create_event".to_string(),
@@ -380,7 +380,7 @@ mod tests {
             .map(|index| {
                 let tool_name = format!("tool_{index:03}");
                 (
-                    format!("mcp__{server_name}__{tool_name}"),
+                    format!("{server_name}__{tool_name}"),
                     tool_info(server_name, &tool_name, description_prefix),
                 )
             })
@@ -391,7 +391,7 @@ mod tests {
         ToolInfo {
             server_name: server_name.to_string(),
             callable_name: tool_name.to_string(),
-            callable_namespace: format!("mcp__{server_name}__"),
+            callable_namespace: server_name.to_string(),
             server_instructions: None,
             tool: Tool {
                 name: tool_name.to_string().into(),
diff --git a/codex-rs/core/src/tools/registry_tests.rs b/codex-rs/core/src/tools/registry_tests.rs
index d44c3d0f9b8b..c49f113c6a45 100644
--- a/codex-rs/core/src/tools/registry_tests.rs
+++ b/codex-rs/core/src/tools/registry_tests.rs
@@ -23,7 +23,7 @@ impl ToolHandler for TestHandler {
 fn handler_looks_up_namespaced_aliases_explicitly() {
     let plain_handler = Arc::new(TestHandler) as Arc<dyn AnyToolHandler>;
     let namespaced_handler = Arc::new(TestHandler) as Arc<dyn AnyToolHandler>;
-    let namespace = "mcp__codex_apps__gmail";
+    let namespace = "codex_apps__gmail";
     let tool_name = "gmail_get_recent_emails";
     let plain_name = codex_tools::ToolName::plain(tool_name);
     let namespaced_name = codex_tools::ToolName::namespaced(namespace, tool_name);
@@ -35,7 +35,7 @@ fn handler_looks_up_namespaced_aliases_explicitly() {
     let plain = registry.handler(&plain_name);
     let namespaced = registry.handler(&namespaced_name);
     let missing_namespaced = registry.handler(&codex_tools::ToolName::namespaced(
-        "mcp__codex_apps__calendar",
+        "codex_apps__calendar",
         tool_name,
     ));
 
diff --git a/codex-rs/core/src/tools/router_tests.rs b/codex-rs/core/src/tools/router_tests.rs
index ac859d9aa61c..c1dc1283b014 100644
--- a/codex-rs/core/src/tools/router_tests.rs
+++ b/codex-rs/core/src/tools/router_tests.rs
@@ -55,7 +55,7 @@ async fn parallel_support_does_not_match_namespaced_local_tool_names() -> anyhow
         .expect("test session should expose a parallel shell-like tool");
 
     assert!(!router.tool_supports_parallel(&ToolCall {
-        tool_name: ToolName::namespaced("mcp__server__", parallel_tool_name),
+        tool_name: ToolName::namespaced("server", parallel_tool_name),
         call_id: "call-namespaced-tool".to_string(),
         payload: ToolPayload::Function {
             arguments: "{}".to_string(),
@@ -76,7 +76,7 @@ async fn build_tool_call_uses_namespace_for_registry_name() -> anyhow::Result<()
         ResponseItem::FunctionCall {
             id: None,
             name: tool_name.clone(),
-            namespace: Some("mcp__codex_apps__calendar".to_string()),
+            namespace: Some("codex_apps__calendar".to_string()),
             arguments: "{}".to_string(),
             call_id: "call-namespace".to_string(),
         },
@@ -86,7 +86,7 @@ async fn build_tool_call_uses_namespace_for_registry_name() -> anyhow::Result<()
 
     assert_eq!(
         call.tool_name,
-        ToolName::namespaced("mcp__codex_apps__calendar", tool_name)
+        ToolName::namespaced("codex_apps__calendar", tool_name)
     );
     assert_eq!(call.call_id, "call-namespace");
     match call.payload {
@@ -115,7 +115,7 @@ async fn mcp_parallel_support_uses_exact_payload_server() -> anyhow::Result<()>
     );
 
     let deferred_call = ToolCall {
-        tool_name: ToolName::namespaced("mcp__echo__", "query_with_delay"),
+        tool_name: ToolName::namespaced("echo", "query_with_delay"),
         call_id: "call-deferred".to_string(),
         payload: ToolPayload::Mcp {
             server: "echo".to_string(),
@@ -126,7 +126,7 @@ async fn mcp_parallel_support_uses_exact_payload_server() -> anyhow::Result<()>
     assert!(router.tool_supports_parallel(&deferred_call));
 
     let different_server_call = ToolCall {
-        tool_name: ToolName::namespaced("mcp__hello_echo__", "query_with_delay"),
+        tool_name: ToolName::namespaced("hello_echo", "query_with_delay"),
         call_id: "call-other-server".to_string(),
         payload: ToolPayload::Mcp {
             server: "hello_echo".to_string(),
diff --git a/codex-rs/core/src/tools/spec_tests.rs b/codex-rs/core/src/tools/spec_tests.rs
index afa586dc62cf..69673ccbe248 100644
--- a/codex-rs/core/src/tools/spec_tests.rs
+++ b/codex-rs/core/src/tools/spec_tests.rs
@@ -61,7 +61,7 @@ fn mcp_tool_info(tool: rmcp::model::Tool) -> ToolInfo {
     ToolInfo {
         server_name: "test_server".to_string(),
         callable_name: tool.name.to_string(),
-        callable_namespace: "mcp__test_server__".to_string(),
+        callable_namespace: "test_server".to_string(),
         server_instructions: None,
         tool,
         connector_id: None,
@@ -133,7 +133,7 @@ fn deferred_responses_api_tool_serializes_with_defer_loading() {
 
     let serialized = serde_json::to_value(ToolSpec::Function(
         mcp_tool_to_deferred_responses_api_tool(
-            &ToolName::namespaced("mcp__codex_apps__", "lookup_order"),
+            &ToolName::namespaced("codex_apps", "lookup_order"),
             &tool,
         )
         .expect("convert deferred tool"),
@@ -893,11 +893,11 @@ async fn search_tool_description_falls_back_to_connector_name_without_descriptio
         &tools_config,
         /*mcp_tools*/ None,
         Some(HashMap::from([(
-            "mcp__codex_apps__calendar_create_event".to_string(),
+            "codex_apps__calendar__create_event".to_string(),
             ToolInfo {
                 server_name: CODEX_APPS_MCP_SERVER_NAME.to_string(),
-                callable_name: "_create_event".to_string(),
-                callable_namespace: "mcp__codex_apps__calendar".to_string(),
+                callable_name: "create_event".to_string(),
+                callable_namespace: "codex_apps__calendar".to_string(),
                 server_instructions: None,
                 tool: mcp_tool(
                     "calendar_create_event",
@@ -945,11 +945,11 @@ async fn search_tool_registers_namespaced_mcp_tool_aliases() {
         /*mcp_tools*/ None,
         Some(HashMap::from([
             (
-                "mcp__codex_apps__calendar_create_event".to_string(),
+                "codex_apps__calendar__create_event".to_string(),
                 ToolInfo {
                     server_name: CODEX_APPS_MCP_SERVER_NAME.to_string(),
-                    callable_name: "_create_event".to_string(),
-                    callable_namespace: "mcp__codex_apps__calendar".to_string(),
+                    callable_name: "create_event".to_string(),
+                    callable_namespace: "codex_apps__calendar".to_string(),
                     server_instructions: None,
                     tool: mcp_tool(
                         "calendar-create-event",
@@ -963,11 +963,11 @@ async fn search_tool_registers_namespaced_mcp_tool_aliases() {
                 },
             ),
             (
-                "mcp__codex_apps__calendar_list_events".to_string(),
+                "codex_apps__calendar__list_events".to_string(),
                 ToolInfo {
                     server_name: CODEX_APPS_MCP_SERVER_NAME.to_string(),
-                    callable_name: "_list_events".to_string(),
-                    callable_namespace: "mcp__codex_apps__calendar".to_string(),
+                    callable_name: "list_events".to_string(),
+                    callable_namespace: "codex_apps__calendar".to_string(),
                     server_instructions: None,
                     tool: mcp_tool(
                         "calendar-list-events",
@@ -981,11 +981,11 @@ async fn search_tool_registers_namespaced_mcp_tool_aliases() {
                 },
             ),
             (
-                "mcp__rmcp__echo".to_string(),
+                "rmcp__echo".to_string(),
                 ToolInfo {
                     server_name: "rmcp".to_string(),
                     callable_name: "echo".to_string(),
-                    callable_namespace: "mcp__rmcp__".to_string(),
+                    callable_namespace: "rmcp".to_string(),
                     server_instructions: None,
                     tool: mcp_tool("echo", "Echo", serde_json::json!({"type": "object"})),
                     connector_id: None,
@@ -999,8 +999,8 @@ async fn search_tool_registers_namespaced_mcp_tool_aliases() {
     )
     .build();
 
-    let app_alias = ToolName::namespaced("mcp__codex_apps__calendar", "_create_event");
-    let mcp_alias = ToolName::namespaced("mcp__rmcp__", "echo");
+    let app_alias = ToolName::namespaced("codex_apps__calendar", "create_event");
+    let mcp_alias = ToolName::namespaced("rmcp", "echo");
 
     assert!(registry.has_handler(&ToolName::plain(TOOL_SEARCH_TOOL_NAME)));
     assert!(registry.has_handler(&app_alias));
@@ -1025,7 +1025,7 @@ async fn tool_search_entries_skip_namespace_outputs_when_namespace_tools_are_dis
     });
     tools_config.namespace_tools = false;
     let mcp_tools = HashMap::from([(
-        "mcp__test_server__echo".to_string(),
+        "test_server__echo".to_string(),
         mcp_tool_info(mcp_tool(
             "echo",
             "Echo",
@@ -1084,7 +1084,7 @@ async fn direct_mcp_tools_register_namespaced_handlers() {
     let (_, registry) = build_specs(
         &tools_config,
         Some(HashMap::from([(
-            "mcp__test_server__echo".to_string(),
+            "test_server__echo".to_string(),
             mcp_tool_info(mcp_tool(
                 "echo",
                 "Echo",
@@ -1096,8 +1096,8 @@ async fn direct_mcp_tools_register_namespaced_handlers() {
     )
     .build();
 
-    assert!(registry.has_handler(&ToolName::namespaced("mcp__test_server__", "echo")));
-    assert!(!registry.has_handler(&ToolName::plain("mcp__test_server__echo")));
+    assert!(registry.has_handler(&ToolName::namespaced("test_server", "echo")));
+    assert!(!registry.has_handler(&ToolName::plain("test_server__echo")));
 }
 
 #[tokio::test]
@@ -1118,7 +1118,7 @@ async fn unavailable_mcp_tools_are_exposed_as_dummy_function_tools() {
         windows_sandbox_level: WindowsSandboxLevel::Disabled,
     });
 
-    let unavailable_tool = ToolName::namespaced("mcp__codex_apps__calendar", "_create_event");
+    let unavailable_tool = ToolName::namespaced("codex_apps__calendar", "create_event");
     let (tools, registry) = build_specs_with_unavailable_tools(
         &tools_config,
         /*mcp_tools*/ None,
@@ -1128,7 +1128,7 @@ async fn unavailable_mcp_tools_are_exposed_as_dummy_function_tools() {
     )
     .build();
 
-    let tool = find_tool(&tools, "mcp__codex_apps__calendar_create_event");
+    let tool = find_tool(&tools, "codex_apps__calendar__create_event");
     let ToolSpec::Function(ResponsesApiTool {
         description,
         parameters,
@@ -1143,10 +1143,10 @@ async fn unavailable_mcp_tools_are_exposed_as_dummy_function_tools() {
         Some(AdditionalProperties::Boolean(false))
     );
     assert!(registry.has_handler(&ToolName::namespaced(
-        "mcp__codex_apps__calendar",
-        "_create_event"
+        "codex_apps__calendar",
+        "create_event"
     )));
-    assert!(!registry.has_handler(&ToolName::plain("mcp__codex_apps__calendar_create_event")));
+    assert!(!registry.has_handler(&ToolName::plain("codex_apps__calendar__create_event")));
 }
 
 #[tokio::test]
diff --git a/codex-rs/core/src/unavailable_tool.rs b/codex-rs/core/src/unavailable_tool.rs
index 39ba21f9b86a..07f57be31900 100644
--- a/codex-rs/core/src/unavailable_tool.rs
+++ b/codex-rs/core/src/unavailable_tool.rs
@@ -39,7 +39,10 @@ pub(crate) fn collect_unavailable_called_tools(
 }
 
 fn should_collect_unavailable_tool(name: &str, namespace: Option<&str>) -> bool {
-    namespace.is_some_and(|namespace| namespace.starts_with("mcp__")) || name.starts_with("mcp__")
+    // New histories preserve the namespace split, so any missing namespaced call
+    // is eligible for a placeholder. Keep the flattened MCP branch for rollouts
+    // written before namespaced MCP calls were preserved in history.
+    namespace.is_some() || name.starts_with("mcp__")
 }
 
 #[cfg(test)]
@@ -58,11 +61,12 @@ mod tests {
     }
 
     #[test]
-    fn collect_unavailable_called_tools_detects_mcp_function_calls() {
+    fn collect_unavailable_called_tools_detects_namespaced_and_legacy_mcp_calls() {
         let input = vec![
             function_call("shell", /*namespace*/ None),
             function_call("mcp__server__lookup", /*namespace*/ None),
             function_call("_create_event", Some("mcp__codex_apps__calendar")),
+            function_call("lookup", Some("calendar")),
         ];
 
         let tools = collect_unavailable_called_tools(&input, &HashSet::new());
@@ -70,6 +74,7 @@ mod tests {
         assert_eq!(
             tools,
             vec![
+                ToolName::namespaced("calendar", "lookup"),
                 ToolName::namespaced("mcp__codex_apps__calendar", "_create_event"),
                 ToolName::plain("mcp__server__lookup"),
             ]
diff --git a/codex-rs/core/tests/suite/code_mode.rs b/codex-rs/core/tests/suite/code_mode.rs
index 3bcb37e7b277..f455b350eac7 100644
--- a/codex-rs/core/tests/suite/code_mode.rs
+++ b/codex-rs/core/tests/suite/code_mode.rs
@@ -367,7 +367,7 @@ async fn code_mode_only_guides_all_tools_search_and_calls_deferred_app_tools() -
                 "exec",
                 r#"
 const tool = ALL_TOOLS.find(
-  ({ name }) => name === "mcp__codex_apps__calendar_timezone_option_99"
+  ({ name }) => name === "codex_apps__calendar_timezone_option_99"
 );
 if (!tool) {
   text(JSON.stringify({ found: false }));
@@ -2075,7 +2075,7 @@ async fn code_mode_can_use_mcp_image_result_with_image_helper() -> Result<()> {
 
     let server = responses::start_mock_server().await;
     let code = r#"
-const out = await tools.mcp__rmcp__image_scenario({
+const out = await tools.rmcp_image_scenario({
   scenario: "image_only_original_detail",
 });
 const imageItem = out.content.find((item) => item.type === "image");
@@ -2176,7 +2176,7 @@ async fn code_mode_can_print_structured_mcp_tool_result_fields() -> Result<()> {
 
     let server = responses::start_mock_server().await;
     let code = r#"
-const { content, structuredContent, isError } = await tools.mcp__rmcp__echo({
+const { content, structuredContent, isError } = await tools.rmcp_echo({
   message: "ping",
 });
 text(
@@ -2214,7 +2214,7 @@ async fn code_mode_only_can_call_mcp_tool() -> Result<()> {
 
     let server = responses::start_mock_server().await;
     let code = r#"
-const result = await tools.mcp__rmcp__echo({ message: "ping" });
+const result = await tools.rmcp_echo({ message: "ping" });
 text(`echo=${result.structuredContent?.echo ?? "missing"}`);
 "#;
 
@@ -2244,12 +2244,12 @@ async fn code_mode_exposes_mcp_tools_on_global_tools_object() -> Result<()> {
 
     let server = responses::start_mock_server().await;
     let code = r#"
-const { content, structuredContent, isError } = await tools.mcp__rmcp__echo({
+const { content, structuredContent, isError } = await tools.rmcp_echo({
   message: "ping",
 });
 text(
-  `hasEcho=${String(Object.keys(tools).includes("mcp__rmcp__echo"))}\n` +
-    `echoType=${typeof tools.mcp__rmcp__echo}\n` +
+  `hasEcho=${String(Object.keys(tools).includes("rmcp_echo"))}\n` +
+    `echoType=${typeof tools.rmcp_echo}\n` +
     `echo=${structuredContent?.echo ?? "missing"}\n` +
     `isError=${String(isError)}\n` +
     `contentLength=${content.length}`
@@ -2287,7 +2287,7 @@ async fn code_mode_exposes_namespaced_mcp_tools_on_global_tools_object() -> Resu
     let code = r#"
 text(JSON.stringify({
   hasExecCommand: typeof tools.exec_command === "function",
-  hasNamespacedEcho: typeof tools.mcp__rmcp__echo === "function",
+  hasNamespacedEcho: typeof tools.rmcp_echo === "function",
 }));
 "#;
 
@@ -2321,7 +2321,7 @@ async fn code_mode_exposes_normalized_illegal_mcp_tool_names() -> Result<()> {
 
     let server = responses::start_mock_server().await;
     let code = r#"
-const result = await tools.mcp__rmcp__echo_tool({ message: "ping" });
+const result = await tools.rmcp_echo_tool({ message: "ping" });
 text(`echo=${result.structuredContent.echo}`);
 "#;
 
@@ -2502,7 +2502,7 @@ async fn code_mode_exports_all_tools_metadata_for_namespaced_mcp_tools() -> Resu
     let server = responses::start_mock_server().await;
     let code = r#"
 const tool = ALL_TOOLS.find(
-  ({ name }) => name === "mcp__rmcp__echo"
+  ({ name }) => name === "rmcp_echo"
 );
 text(JSON.stringify(tool));
 "#;
@@ -2525,12 +2525,12 @@ text(JSON.stringify(tool));
     assert_eq!(
         parsed,
         serde_json::json!({
-            "name": "mcp__rmcp__echo",
+            "name": "rmcp_echo",
             "description": concat!(
                 "Echo back the provided message and include environment data.\n\n",
                 "exec tool declaration:\n",
                 "```ts\n",
-                "declare const tools: { mcp__rmcp__echo(args: { env_var?: string; message: string; }): ",
+                "declare const tools: { rmcp_echo(args: { env_var?: string; message: string; }): ",
                 "Promise<CallToolResult<{ echo: string; env: string | null; }>>; };\n",
                 "```",
             ),
@@ -2701,7 +2701,7 @@ async fn code_mode_can_print_content_only_mcp_tool_result_fields() -> Result<()>
 
     let server = responses::start_mock_server().await;
     let code = r#"
-const { content, structuredContent, isError } = await tools.mcp__rmcp__image_scenario({
+const { content, structuredContent, isError } = await tools.rmcp_image_scenario({
   scenario: "text_only",
   caption: "caption from mcp",
 });
@@ -2744,7 +2744,7 @@ async fn code_mode_can_print_error_mcp_tool_result_fields() -> Result<()> {
 
     let server = responses::start_mock_server().await;
     let code = r#"
-const { content, structuredContent, isError } = await tools.mcp__rmcp__echo({});
+const { content, structuredContent, isError } = await tools.rmcp_echo({});
 const firstText = content[0]?.text ?? "";
 const mentionsMissingMessage =
   firstText.includes("missing field") && firstText.includes("message");
diff --git a/codex-rs/core/tests/suite/hooks_mcp.rs b/codex-rs/core/tests/suite/hooks_mcp.rs
index 2157630e02b0..bbe8d8ff1f85 100644
--- a/codex-rs/core/tests/suite/hooks_mcp.rs
+++ b/codex-rs/core/tests/suite/hooks_mcp.rs
@@ -26,9 +26,9 @@ use serde_json::Value;
 use serde_json::json;
 
 const RMCP_SERVER: &str = "rmcp";
-const RMCP_NAMESPACE: &str = "mcp__rmcp__";
-const RMCP_ECHO_TOOL_NAME: &str = "mcp__rmcp__echo";
-const RMCP_HOOK_MATCHER: &str = "mcp__rmcp__.*";
+const RMCP_NAMESPACE: &str = "rmcp";
+const RMCP_ECHO_TOOL_NAME: &str = "rmcp__echo";
+const RMCP_HOOK_MATCHER: &str = "rmcp__.*";
 const RMCP_ECHO_MESSAGE: &str = "hook e2e ping";
 
 fn write_pre_tool_use_hook(home: &Path, reason: &str) -> Result<()> {
diff --git a/codex-rs/core/tests/suite/openai_file_mcp.rs b/codex-rs/core/tests/suite/openai_file_mcp.rs
index ac49b5334b3e..13762d6caf9f 100644
--- a/codex-rs/core/tests/suite/openai_file_mcp.rs
+++ b/codex-rs/core/tests/suite/openai_file_mcp.rs
@@ -30,9 +30,9 @@ use wiremock::matchers::header;
 use wiremock::matchers::method;
 use wiremock::matchers::path;
 
-const DOCUMENT_EXTRACT_NAMESPACE: &str = "mcp__codex_apps__calendar";
-const DOCUMENT_EXTRACT_TOOL: &str = "_extract_text";
-const DOCUMENT_EXTRACT_HOOK_MATCHER: &str = "mcp__codex_apps__calendar_extract_text";
+const DOCUMENT_EXTRACT_NAMESPACE: &str = "codex_apps__calendar";
+const DOCUMENT_EXTRACT_TOOL: &str = "extract_text";
+const DOCUMENT_EXTRACT_HOOK_MATCHER: &str = "codex_apps__calendar__extract_text";
 
 fn configure_apps(config: &mut Config, chatgpt_base_url: &str) {
     if let Err(err) = config.features.enable(Feature::Apps) {
diff --git a/codex-rs/core/tests/suite/plugins.rs b/codex-rs/core/tests/suite/plugins.rs
index 5b83d3b13663..00b42c0904f8 100644
--- a/codex-rs/core/tests/suite/plugins.rs
+++ b/codex-rs/core/tests/suite/plugins.rs
@@ -347,11 +347,11 @@ async fn explicit_plugin_mentions_inject_plugin_guidance() -> Result<()> {
     assert!(
         request_tools
             .iter()
-            .any(|name| name == "mcp__codex_apps__google_calendar"),
+            .any(|name| name == "codex_apps__google_calendar"),
         "expected plugin app tools to become visible for this turn: {request_tools:?}"
     );
     let echo_tool = request
-        .tool_by_name("mcp__sample__", "echo")
+        .tool_by_name("sample", "echo")
         .expect("plugin MCP tool should be present");
     let echo_description = echo_tool
         .get("description")
@@ -362,7 +362,7 @@ async fn explicit_plugin_mentions_inject_plugin_guidance() -> Result<()> {
         "expected plugin MCP provenance in tool description: {echo_description:?}"
     );
     let calendar_tool = request
-        .tool_by_name("mcp__codex_apps__google_calendar", "_create_event")
+        .tool_by_name("codex_apps__google_calendar", "create_event")
         .expect("plugin app tool should be present");
     let calendar_description = calendar_tool
         .get("description")
@@ -471,8 +471,8 @@ async fn plugin_mcp_tools_are_listed() -> Result<()> {
     let mut available_tools: Vec<&str> = tool_list.tools.keys().map(String::as_str).collect();
     available_tools.sort_unstable();
     assert!(
-        tool_list.tools.contains_key("mcp__sample__echo")
-            && tool_list.tools.contains_key("mcp__sample__image"),
+        tool_list.tools.contains_key("sample__echo")
+            && tool_list.tools.contains_key("sample__image"),
         "expected plugin MCP tools to be listed; discovered tools: {available_tools:?}"
     );
 
diff --git a/codex-rs/core/tests/suite/rmcp_client.rs b/codex-rs/core/tests/suite/rmcp_client.rs
index 0947f4fba76e..6e4f7d0cbadf 100644
--- a/codex-rs/core/tests/suite/rmcp_client.rs
+++ b/codex-rs/core/tests/suite/rmcp_client.rs
@@ -336,7 +336,7 @@ async fn call_cwd_tool(
     server_name: &str,
     call_id: &str,
 ) -> anyhow::Result<Value> {
-    let namespace = format!("mcp__{server_name}__");
+    let namespace = server_name.to_string();
     mount_sse_once(
         server,
         responses::sse(vec![
@@ -421,7 +421,7 @@ async fn stdio_server_round_trip() -> anyhow::Result<()> {
 
     let call_id = "call-123";
     let server_name = "rmcp";
-    let namespace = format!("mcp__{server_name}__");
+    let namespace = server_name.to_string();
 
     let call_mock = mount_sse_once(
         &server,
@@ -730,7 +730,7 @@ async fn stdio_mcp_tool_call_includes_sandbox_state_meta() -> anyhow::Result<()>
 
     let call_id = "sandbox-meta-call";
     let server_name = "rmcp";
-    let namespace = format!("mcp__{server_name}__");
+    let namespace = server_name.to_string();
     let tool_name = format!("{namespace}sandbox_meta");
 
     let call_mock = mount_sse_once(
@@ -848,7 +848,7 @@ async fn stdio_mcp_parallel_tool_calls_default_false_runs_serially() -> anyhow::
     let first_call_id = "sync-serial-1";
     let second_call_id = "sync-serial-2";
     let server_name = "rmcp";
-    let namespace = format!("mcp__{server_name}__");
+    let namespace = server_name.to_string();
     let args = json!({ "sleep_after_ms": 100 }).to_string();
 
     mount_sse_once(
@@ -957,7 +957,7 @@ async fn stdio_mcp_parallel_tool_calls_opt_in_runs_concurrently() -> anyhow::Res
     let first_call_id = "sync-1";
     let second_call_id = "sync-2";
     let server_name = "rmcp";
-    let namespace = format!("mcp__{server_name}__");
+    let namespace = server_name.to_string();
     let args = json!({
         "sleep_after_ms": 100,
         "barrier": {
@@ -1039,8 +1039,8 @@ async fn stdio_image_responses_round_trip() -> anyhow::Result<()> {
 
     let call_id = "img-1";
     let server_name = "rmcp";
-    let tool_name = format!("mcp__{server_name}__image");
-    let namespace = format!("mcp__{server_name}__");
+    let tool_name = format!("{server_name}__image");
+    let namespace = server_name.to_string();
 
     // First stream: model decides to call the image tool.
     mount_sse_once(
@@ -1176,8 +1176,8 @@ async fn stdio_image_responses_preserve_original_detail_metadata() -> anyhow::Re
 
     let call_id = "img-original-detail-1";
     let server_name = "rmcp";
-    let tool_name = format!("mcp__{server_name}__image_scenario");
-    let namespace = format!("mcp__{server_name}__");
+    let tool_name = format!("{server_name}__image_scenario");
+    let namespace = server_name.to_string();
 
     mount_sse_once(
         &server,
@@ -1263,7 +1263,7 @@ async fn stdio_image_responses_are_sanitized_for_text_only_model() -> anyhow::Re
 
     let call_id = "img-text-only-1";
     let server_name = "rmcp";
-    let namespace = format!("mcp__{server_name}__");
+    let namespace = server_name.to_string();
     let text_only_model_slug = "rmcp-text-only-model";
 
     let models_mock = mount_models_once(
@@ -1408,7 +1408,7 @@ async fn stdio_server_propagates_whitelisted_env_vars() -> anyhow::Result<()> {
 
     let call_id = "call-1234";
     let server_name = "rmcp_whitelist";
-    let namespace = format!("mcp__{server_name}__");
+    let namespace = server_name.to_string();
 
     mount_sse_once(
         &server,
@@ -1522,7 +1522,7 @@ async fn stdio_server_propagates_explicit_local_env_var_source() -> anyhow::Resu
     let server = responses::start_mock_server().await;
     let call_id = "call-local-source";
     let server_name = "rmcp_local_source";
-    let namespace = format!("mcp__{server_name}__");
+    let namespace = server_name.to_string();
     let env_name = "MCP_TEST_LOCAL_SOURCE";
     let expected_env_value = "propagated-explicit-local-source";
 
@@ -1615,7 +1615,7 @@ async fn remote_stdio_env_var_source_does_not_copy_local_env() -> anyhow::Result
     let server = responses::start_mock_server().await;
     let call_id = "call-remote-source";
     let server_name = "rmcp_remote_source";
-    let namespace = format!("mcp__{server_name}__");
+    let namespace = server_name.to_string();
     let env_name = "MCP_TEST_REMOTE_SOURCE_ONLY";
 
     mount_sse_once(
@@ -1787,7 +1787,7 @@ async fn streamable_http_tool_call_round_trip() -> anyhow::Result<()> {
 
     let call_id = "call-456";
     let server_name = "rmcp_http";
-    let namespace = format!("mcp__{server_name}__");
+    let namespace = server_name.to_string();
 
     mount_sse_once(
         &server,
@@ -1954,8 +1954,8 @@ async fn streamable_http_with_oauth_round_trip_impl() -> anyhow::Result<()> {
 
     let call_id = "call-789";
     let server_name = "rmcp_http_oauth";
-    let tool_name = format!("mcp__{server_name}__echo");
-    let namespace = format!("mcp__{server_name}__");
+    let tool_name = format!("{server_name}__echo");
+    let namespace = server_name.to_string();
 
     mount_sse_once(
         &server,
diff --git a/codex-rs/core/tests/suite/search_tool.rs b/codex-rs/core/tests/suite/search_tool.rs
index b4edf24668ef..bf46217866a6 100644
--- a/codex-rs/core/tests/suite/search_tool.rs
+++ b/codex-rs/core/tests/suite/search_tool.rs
@@ -47,11 +47,11 @@ const SEARCH_TOOL_DESCRIPTION_SNIPPETS: [&str; 2] = [
     "- Calendar: Plan events and manage your calendar.",
 ];
 const TOOL_SEARCH_TOOL_NAME: &str = "tool_search";
-const CALENDAR_CREATE_TOOL: &str = "mcp__codex_apps__calendar_create_event";
-const CALENDAR_LIST_TOOL: &str = "mcp__codex_apps__calendar_list_events";
-const SEARCH_CALENDAR_NAMESPACE: &str = "mcp__codex_apps__calendar";
-const SEARCH_CALENDAR_CREATE_TOOL: &str = "_create_event";
-const SEARCH_CALENDAR_LIST_TOOL: &str = "_list_events";
+const CALENDAR_CREATE_TOOL: &str = "codex_apps__calendar__create_event";
+const CALENDAR_LIST_TOOL: &str = "codex_apps__calendar__list_events";
+const SEARCH_CALENDAR_NAMESPACE: &str = "codex_apps__calendar";
+const SEARCH_CALENDAR_CREATE_TOOL: &str = "create_event";
+const SEARCH_CALENDAR_LIST_TOOL: &str = "list_events";
 
 fn tool_names(body: &Value) -> Vec<String> {
     body.get("tools")
@@ -235,7 +235,7 @@ async fn always_defer_feature_hides_small_app_tool_sets() -> Result<()> {
         "small app tool sets should be deferred behind tool_search: {tools:?}"
     );
     assert!(
-        tools.iter().all(|name| !name.starts_with("mcp__")),
+        tools.iter().all(|name| !name.starts_with("codex_apps__")),
         "MCP tools should not be directly exposed: {tools:?}"
     );
 
@@ -996,19 +996,17 @@ async fn tool_search_indexes_only_enabled_non_app_mcp_tools() -> Result<()> {
         "first request should advertise tool_search: {first_request_tools:?}"
     );
     assert!(
-        !first_request_tools
-            .iter()
-            .any(|name| name == "mcp__rmcp__echo"),
+        !first_request_tools.iter().any(|name| name == "rmcp__echo"),
         "non-app MCP tools should be hidden before search in large-search mode: {first_request_tools:?}"
     );
     assert!(
-        !first_request_tools.iter().any(|name| name == "mcp__rmcp__"),
+        !first_request_tools.iter().any(|name| name == "rmcp"),
         "non-app MCP namespace should be hidden before search in large-search mode: {first_request_tools:?}"
     );
 
     let echo_tools = tool_search_output_tools(&requests[1], echo_call_id);
     let echo_output = json!({ "tools": echo_tools });
-    let rmcp_echo_tool = namespace_child_tool(&echo_output, "mcp__rmcp__", "echo")
+    let rmcp_echo_tool = namespace_child_tool(&echo_output, "rmcp", "echo")
         .expect("tool_search should return rmcp echo as a namespace child tool");
     assert_eq!(
         rmcp_echo_tool.get("type").and_then(Value::as_str),
@@ -1018,7 +1016,7 @@ async fn tool_search_indexes_only_enabled_non_app_mcp_tools() -> Result<()> {
     let image_tools = tool_search_output_tools(&requests[1], image_call_id);
     let found_rmcp_image_tool = image_tools
         .iter()
-        .filter(|tool| tool.get("name").and_then(Value::as_str) == Some("mcp__rmcp__"))
+        .filter(|tool| tool.get("name").and_then(Value::as_str) == Some("rmcp"))
         .flat_map(|namespace| namespace.get("tools").and_then(Value::as_array))
         .flatten()
         .any(|tool| tool.get("name").and_then(Value::as_str).is_some());
diff --git a/codex-rs/core/tests/suite/sqlite_state.rs b/codex-rs/core/tests/suite/sqlite_state.rs
index 8250f5493dea..1bc9c42b96fd 100644
--- a/codex-rs/core/tests/suite/sqlite_state.rs
+++ b/codex-rs/core/tests/suite/sqlite_state.rs
@@ -328,7 +328,7 @@ async fn mcp_call_marks_thread_memory_mode_polluted_when_configured() -> Result<
     let server = start_mock_server().await;
     let call_id = "call-123";
     let server_name = "rmcp";
-    let namespace = format!("mcp__{server_name}__");
+    let namespace = server_name.to_string();
     mount_sse_once(
         &server,
         responses::sse(vec![
diff --git a/codex-rs/core/tests/suite/tools.rs b/codex-rs/core/tests/suite/tools.rs
index b85607454061..e781d1a72f2c 100644
--- a/codex-rs/core/tests/suite/tools.rs
+++ b/codex-rs/core/tests/suite/tools.rs
@@ -349,6 +349,184 @@ async fn historical_unavailable_mcp_call_is_exposed_as_placeholder_tool() -> Res
     Ok(())
 }
 
+#[tokio::test(flavor = "multi_thread", worker_threads = 2)]
+async fn historical_unavailable_namespaced_call_is_exposed_as_placeholder_tool() -> Result<()> {
+    skip_if_no_network!(Ok(()));
+
+    let historical_call_id = "historical-namespaced-call";
+    let retry_call_id = "retry-namespaced-call";
+    let unavailable_tool_namespace = "legacy_tools";
+    let unavailable_tool_name = "missing_tool";
+    let unavailable_tool_display_name = "legacy_tools__missing_tool";
+    let server = start_mock_server().await;
+    let codex_home = Arc::new(TempDir::new()?);
+    let mut builder = test_codex()
+        .with_model("gpt-5.4")
+        .with_home(Arc::clone(&codex_home))
+        .with_config(|config| {
+            config
+                .features
+                .enable(Feature::UnavailableDummyTools)
+                .expect("unavailable dummy tools should be enabled for this test");
+        });
+    let test = builder.build(&server).await?;
+
+    let first_turn_mock = mount_sse_sequence(
+        &server,
+        vec![
+            sse(vec![
+                ev_response_created("resp-1"),
+                ev_namespaced_function_call(
+                    historical_call_id,
+                    unavailable_tool_namespace,
+                    unavailable_tool_name,
+                    r#"{}"#,
+                ),
+                ev_completed("resp-1"),
+            ]),
+            sse(vec![
+                ev_response_created("resp-2"),
+                ev_assistant_message("msg-1", "done"),
+                ev_completed("resp-2"),
+            ]),
+        ],
+    )
+    .await;
+
+    test.submit_turn("call a namespaced tool").await?;
+    let rollout_path = test.codex.rollout_path().context("rollout path")?;
+    assert_eq!(first_turn_mock.requests().len(), 2);
+    drop(test);
+
+    let retry_mock = mount_sse_sequence(
+        &server,
+        vec![
+            sse(vec![
+                ev_response_created("resp-3"),
+                ev_namespaced_function_call(
+                    retry_call_id,
+                    unavailable_tool_namespace,
+                    unavailable_tool_name,
+                    r#"{}"#,
+                ),
+                ev_completed("resp-3"),
+            ]),
+            sse(vec![
+                ev_response_created("resp-4"),
+                ev_assistant_message("msg-2", "done"),
+                ev_completed("resp-4"),
+            ]),
+        ],
+    )
+    .await;
+
+    let mut resume_builder = test_codex().with_model("gpt-5.4").with_config(|config| {
+        config
+            .features
+            .enable(Feature::UnavailableDummyTools)
+            .expect("unavailable dummy tools should be enabled for this test");
+    });
+    let test = resume_builder
+        .resume(&server, codex_home, rollout_path)
+        .await?;
+
+    test.submit_turn("retry the namespaced tool").await?;
+
+    let requests = retry_mock.requests();
+    assert_eq!(requests.len(), 2);
+    let first_request_tools = tool_names(&requests[0].body_json());
+    assert!(
+        first_request_tools
+            .iter()
+            .any(|name| name == unavailable_tool_display_name),
+        "historical unavailable namespaced call should add a placeholder tool; got {first_request_tools:?}"
+    );
+    let output_text = requests[1]
+        .function_call_output_text(retry_call_id)
+        .context("placeholder tool output present")?;
+    assert!(output_text.contains("not currently available"));
+    assert!(
+        !output_text.contains("unsupported call"),
+        "placeholder handler should answer instead of falling back to unsupported call: {output_text}"
+    );
+
+    Ok(())
+}
+
+#[tokio::test(flavor = "multi_thread", worker_threads = 2)]
+#[serial(mcp_test_value)]
+async fn reserved_mcp_namespace_is_not_exposed() -> Result<()> {
+    skip_if_no_network!(Ok(()));
+
+    let server = start_mock_server().await;
+    let response_mock = mount_sse_once(
+        &server,
+        sse(vec![
+            ev_response_created("resp-1"),
+            ev_assistant_message("msg-1", "done"),
+            ev_completed("resp-1"),
+        ]),
+    )
+    .await;
+    let rmcp_test_server_bin = match stdio_server_bin() {
+        Ok(bin) => bin,
+        Err(err) => {
+            eprintln!("test_stdio_server binary not available, skipping test: {err}");
+            return Ok(());
+        }
+    };
+
+    let mut builder = test_codex().with_config(move |config| {
+        let mut servers = config.mcp_servers.get().clone();
+        for server_name in ["rmcp", "tools"] {
+            servers.insert(
+                server_name.to_string(),
+                McpServerConfig {
+                    transport: McpServerTransportConfig::Stdio {
+                        command: rmcp_test_server_bin.clone(),
+                        args: Vec::new(),
+                        env: Some(HashMap::new()),
+                        env_vars: Vec::new(),
+                        cwd: None,
+                    },
+                    experimental_environment: None,
+                    enabled: true,
+                    required: false,
+                    supports_parallel_tool_calls: false,
+                    disabled_reason: None,
+                    startup_timeout_sec: Some(Duration::from_secs(10)),
+                    tool_timeout_sec: None,
+                    default_tools_approval_mode: None,
+                    enabled_tools: Some(vec!["echo".to_string()]),
+                    disabled_tools: None,
+                    scopes: None,
+                    oauth_resource: None,
+                    tools: HashMap::new(),
+                },
+            );
+        }
+        config
+            .mcp_servers
+            .set(servers)
+            .expect("test mcp servers should accept any configuration");
+    });
+    let test = builder.build(&server).await?;
+
+    test.submit_turn("which tools are available?").await?;
+
+    let tools = tool_names(&response_mock.single_request().body_json());
+    assert!(
+        tools.iter().any(|name| name == "rmcp"),
+        "non-reserved MCP namespace should remain visible; got {tools:?}"
+    );
+    assert!(
+        !tools.iter().any(|name| name == "tools"),
+        "reserved MCP namespace should be skipped; got {tools:?}"
+    );
+
+    Ok(())
+}
+
 #[tokio::test(flavor = "multi_thread", worker_threads = 2)]
 async fn shell_escalated_permissions_rejected_then_ok() -> Result<()> {
     skip_if_no_network!(Ok(()));
diff --git a/codex-rs/core/tests/suite/truncation.rs b/codex-rs/core/tests/suite/truncation.rs
index 0fd072a70f74..bd8c6e87ce55 100644
--- a/codex-rs/core/tests/suite/truncation.rs
+++ b/codex-rs/core/tests/suite/truncation.rs
@@ -343,7 +343,7 @@ async fn mcp_tool_call_output_exceeds_limit_truncated_for_model() -> Result<()>
 
     let call_id = "rmcp-truncated";
     let server_name = "rmcp";
-    let namespace = format!("mcp__{server_name}__");
+    let namespace = server_name.to_string();
 
     // Build a very large message to exceed 10KiB once serialized.
     let large_msg = "long-message-with-newlines-".repeat(6000);
@@ -445,7 +445,7 @@ async fn mcp_image_output_preserves_image_and_no_text_summary() -> Result<()> {
 
     let call_id = "rmcp-image-no-trunc";
     let server_name = "rmcp";
-    let namespace = format!("mcp__{server_name}__");
+    let namespace = server_name.to_string();
 
     mount_sse_once(
         &server,
@@ -726,7 +726,7 @@ async fn mcp_tool_call_output_not_truncated_with_custom_limit() -> Result<()> {
 
     let call_id = "rmcp-untruncated";
     let server_name = "rmcp";
-    let namespace = format!("mcp__{server_name}__");
+    let namespace = server_name.to_string();
     let large_msg = "a".repeat(80_000);
     let args_json = serde_json::json!({ "message": large_msg });
 
diff --git a/codex-rs/protocol/src/models.rs b/codex-rs/protocol/src/models.rs
index 198a191d4e9c..20723bac86a0 100644
--- a/codex-rs/protocol/src/models.rs
+++ b/codex-rs/protocol/src/models.rs
@@ -2090,8 +2090,8 @@ mod tests {
     fn function_call_deserializes_optional_namespace() {
         let item: ResponseItem = serde_json::from_value(serde_json::json!({
             "type": "function_call",
-            "name": "mcp__codex_apps__gmail_get_recent_emails",
-            "namespace": "mcp__codex_apps__gmail",
+            "name": "get_recent_emails",
+            "namespace": "codex_apps__gmail",
             "arguments": "{\"top_k\":5}",
             "call_id": "call-1",
         }))
@@ -2101,8 +2101,8 @@ mod tests {
             item,
             ResponseItem::FunctionCall {
                 id: None,
-                name: "mcp__codex_apps__gmail_get_recent_emails".to_string(),
-                namespace: Some("mcp__codex_apps__gmail".to_string()),
+                name: "get_recent_emails".to_string(),
+                namespace: Some("codex_apps__gmail".to_string()),
                 arguments: "{\"top_k\":5}".to_string(),
                 call_id: "call-1".to_string(),
             }
@@ -2616,7 +2616,7 @@ mod tests {
             execution: "client".to_string(),
             tools: vec![serde_json::json!({
                 "type": "function",
-                "name": "mcp__codex_apps__calendar_create_event",
+                "name": "codex_apps__calendar__create_event",
                 "description": "Create a calendar event.",
                 "defer_loading": true,
                 "parameters": {
@@ -2637,7 +2637,7 @@ mod tests {
                 execution: "client".to_string(),
                 tools: vec![serde_json::json!({
                     "type": "function",
-                    "name": "mcp__codex_apps__calendar_create_event",
+                    "name": "codex_apps__calendar__create_event",
                     "description": "Create a calendar event.",
                     "defer_loading": true,
                     "parameters": {
@@ -2661,7 +2661,7 @@ mod tests {
                 "execution": "client",
                 "tools": [{
                     "type": "function",
-                    "name": "mcp__codex_apps__calendar_create_event",
+                    "name": "codex_apps__calendar__create_event",
                     "description": "Create a calendar event.",
                     "defer_loading": true,
                     "parameters": {
diff --git a/codex-rs/protocol/src/tool_name.rs b/codex-rs/protocol/src/tool_name.rs
index d09bc1ce72d4..bcd97a063f7a 100644
--- a/codex-rs/protocol/src/tool_name.rs
+++ b/codex-rs/protocol/src/tool_name.rs
@@ -34,7 +34,7 @@ impl ToolName {
 
     pub fn display(&self) -> String {
         match &self.namespace {
-            Some(namespace) => format!("{namespace}{}", self.name),
+            Some(namespace) => flatten_namespaced_tool_name(namespace, &self.name),
             None => self.name.clone(),
         }
     }
@@ -43,12 +43,20 @@ impl ToolName {
 impl fmt::Display for ToolName {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
         match &self.namespace {
-            Some(namespace) => write!(f, "{namespace}{}", self.name),
+            Some(namespace) => f.write_str(&flatten_namespaced_tool_name(namespace, &self.name)),
             None => f.write_str(&self.name),
         }
     }
 }
 
+fn flatten_namespaced_tool_name(namespace: &str, name: &str) -> String {
+    if namespace.ends_with("__") || name.starts_with('_') {
+        format!("{namespace}{name}")
+    } else {
+        format!("{namespace}__{name}")
+    }
+}
+
 impl From<String> for ToolName {
     fn from(name: String) -> Self {
         Self::plain(name)
@@ -60,3 +68,25 @@ impl From<&str> for ToolName {
         Self::plain(name)
     }
 }
+
+#[cfg(test)]
+mod tests {
+    use super::ToolName;
+
+    #[test]
+    fn display_flattens_namespaced_tools_with_double_underscore_separator() {
+        assert_eq!(ToolName::namespaced("foo_", "bar").display(), "foo___bar");
+    }
+
+    #[test]
+    fn display_preserves_legacy_flattened_namespaced_tools() {
+        assert_eq!(
+            ToolName::namespaced("mcp__rmcp__", "echo").display(),
+            "mcp__rmcp__echo"
+        );
+        assert_eq!(
+            ToolName::namespaced("mcp__codex_apps__calendar", "_create_event").display(),
+            "mcp__codex_apps__calendar_create_event"
+        );
+    }
+}
diff --git a/codex-rs/tools/src/responses_api_tests.rs b/codex-rs/tools/src/responses_api_tests.rs
index 3ce13ebfe8c3..62022de2a63e 100644
--- a/codex-rs/tools/src/responses_api_tests.rs
+++ b/codex-rs/tools/src/responses_api_tests.rs
@@ -108,7 +108,7 @@ fn mcp_tool_to_deferred_responses_api_tool_sets_defer_loading() {
 
     assert_eq!(
         mcp_tool_to_deferred_responses_api_tool(
-            &ToolName::namespaced("mcp__codex_apps__", "lookup_order"),
+            &ToolName::namespaced("codex_apps", "lookup_order"),
             &tool,
         )
         .expect("convert deferred tool"),
@@ -133,7 +133,7 @@ fn mcp_tool_to_deferred_responses_api_tool_sets_defer_loading() {
 #[test]
 fn loadable_tool_spec_namespace_serializes_with_deferred_child_tools() {
     let namespace = LoadableToolSpec::Namespace(ResponsesApiNamespace {
-        name: "mcp__codex_apps__calendar".to_string(),
+        name: "codex_apps__calendar".to_string(),
         description: "Plan events".to_string(),
         tools: vec![ResponsesApiNamespaceTool::Function(ResponsesApiTool {
             name: "create_event".to_string(),
@@ -155,7 +155,7 @@ fn loadable_tool_spec_namespace_serializes_with_deferred_child_tools() {
         value,
         json!({
             "type": "namespace",
-            "name": "mcp__codex_apps__calendar",
+            "name": "codex_apps__calendar",
             "description": "Plan events",
             "tools": [
                 {
diff --git a/codex-rs/tools/src/tool_definition_tests.rs b/codex-rs/tools/src/tool_definition_tests.rs
index 0d4d97f5ce9e..da6c2c398386 100644
--- a/codex-rs/tools/src/tool_definition_tests.rs
+++ b/codex-rs/tools/src/tool_definition_tests.rs
@@ -22,9 +22,9 @@ fn tool_definition() -> ToolDefinition {
 #[test]
 fn renamed_overrides_name_only() {
     assert_eq!(
-        tool_definition().renamed("mcp__orders__lookup_order".to_string()),
+        tool_definition().renamed("orders__lookup_order".to_string()),
         ToolDefinition {
-            name: "mcp__orders__lookup_order".to_string(),
+            name: "orders__lookup_order".to_string(),
             ..tool_definition()
         }
     );
diff --git a/codex-rs/tools/src/tool_registry_plan.rs b/codex-rs/tools/src/tool_registry_plan.rs
index 1da71ab04ada..b8b2e00fe7c5 100644
--- a/codex-rs/tools/src/tool_registry_plan.rs
+++ b/codex-rs/tools/src/tool_registry_plan.rs
@@ -68,6 +68,7 @@ use crate::tool_registry_plan_types::agent_type_description;
 use codex_protocol::openai_models::ApplyPatchToolType;
 use codex_protocol::openai_models::ConfigShellToolType;
 use std::collections::BTreeMap;
+use std::collections::HashSet;
 
 pub fn build_tool_registry_plan(
     config: &ToolsConfig,
@@ -260,53 +261,6 @@ pub fn build_tool_registry_plan(
         plan.register_handler("request_permissions", ToolHandlerKind::RequestPermissions);
     }
 
-    let deferred_dynamic_tools = params
-        .dynamic_tools
-        .iter()
-        .filter(|tool| tool.defer_loading && (config.namespace_tools || tool.namespace.is_none()))
-        .collect::<Vec<_>>();
-    let deferred_mcp_tools_for_search = if config.namespace_tools {
-        params.deferred_mcp_tools
-    } else {
-        None
-    };
-
-    if config.search_tool
-        && (deferred_mcp_tools_for_search.is_some() || !deferred_dynamic_tools.is_empty())
-    {
-        let mut search_source_infos = deferred_mcp_tools_for_search
-            .map(|deferred_mcp_tools| {
-                collect_tool_search_source_infos(deferred_mcp_tools.iter().map(|tool| {
-                    ToolSearchSource {
-                        server_name: tool.server_name,
-                        connector_name: tool.connector_name,
-                        connector_description: tool.connector_description,
-                    }
-                }))
-            })
-            .unwrap_or_default();
-
-        if !deferred_dynamic_tools.is_empty() {
-            search_source_infos.push(ToolSearchSourceInfo {
-                name: "Dynamic tools".to_string(),
-                description: Some("Tools provided by the current Codex thread.".to_string()),
-            });
-        }
-
-        plan.push_spec(
-            create_tool_search_tool(&search_source_infos, TOOL_SEARCH_DEFAULT_LIMIT),
-            /*supports_parallel_tool_calls*/ true,
-            config.code_mode_enabled,
-        );
-        plan.register_handler(TOOL_SEARCH_TOOL_NAME, ToolHandlerKind::ToolSearch);
-
-        if let Some(deferred_mcp_tools) = deferred_mcp_tools_for_search {
-            for tool in deferred_mcp_tools {
-                plan.register_handler(tool.name.clone(), ToolHandlerKind::Mcp);
-            }
-        }
-    }
-
     if config.tool_suggest
         && let Some(discoverable_tools) =
             params.discoverable_tools.filter(|tools| !tools.is_empty())
@@ -506,8 +460,96 @@ pub fn build_tool_registry_plan(
         }
     }
 
+    let deferred_dynamic_tools = params
+        .dynamic_tools
+        .iter()
+        .filter(|tool| tool.defer_loading && (config.namespace_tools || tool.namespace.is_none()))
+        .collect::<Vec<_>>();
+    let mut claimed_non_mcp_top_level_names =
+        claimed_non_mcp_top_level_names(&plan, params.dynamic_tools);
+    if config.search_tool
+        && (params.deferred_mcp_tools.is_some() || !deferred_dynamic_tools.is_empty())
+    {
+        claimed_non_mcp_top_level_names.insert(TOOL_SEARCH_TOOL_NAME.to_string());
+    }
+    let mut skipped_mcp_namespaces = HashSet::new();
+    let mut should_expose_mcp_namespace = |namespace: &str| {
+        if reserved_mcp_namespace(namespace) || claimed_non_mcp_top_level_names.contains(namespace)
+        {
+            if skipped_mcp_namespaces.insert(namespace.to_string()) {
+                tracing::warn!(
+                    "skipping MCP namespace `{namespace}` because that top-level tool name is reserved or already claimed"
+                );
+            }
+            return false;
+        }
+        true
+    };
+
+    let deferred_mcp_tools_for_search = if config.namespace_tools {
+        params.deferred_mcp_tools.map(|tools| {
+            tools
+                .iter()
+                .filter(|tool| {
+                    tool.name
+                        .namespace
+                        .as_deref()
+                        .is_some_and(&mut should_expose_mcp_namespace)
+                })
+                .collect::<Vec<_>>()
+        })
+    } else {
+        None
+    };
+
+    if config.search_tool
+        && (deferred_mcp_tools_for_search.is_some() || !deferred_dynamic_tools.is_empty())
+    {
+        let mut search_source_infos = deferred_mcp_tools_for_search
+            .as_ref()
+            .map(|deferred_mcp_tools| {
+                collect_tool_search_source_infos(deferred_mcp_tools.iter().map(|tool| {
+                    ToolSearchSource {
+                        server_name: tool.server_name,
+                        connector_name: tool.connector_name,
+                        connector_description: tool.connector_description,
+                    }
+                }))
+            })
+            .unwrap_or_default();
+
+        if !deferred_dynamic_tools.is_empty() {
+            search_source_infos.push(ToolSearchSourceInfo {
+                name: "Dynamic tools".to_string(),
+                description: Some("Tools provided by the current Codex thread.".to_string()),
+            });
+        }
+
+        plan.push_spec(
+            create_tool_search_tool(&search_source_infos, TOOL_SEARCH_DEFAULT_LIMIT),
+            /*supports_parallel_tool_calls*/ true,
+            config.code_mode_enabled,
+        );
+        plan.register_handler(TOOL_SEARCH_TOOL_NAME, ToolHandlerKind::ToolSearch);
+
+        if let Some(deferred_mcp_tools) = deferred_mcp_tools_for_search.as_ref() {
+            for tool in deferred_mcp_tools {
+                plan.register_handler(tool.name.clone(), ToolHandlerKind::Mcp);
+            }
+        }
+    }
+
     if let Some(mcp_tools) = params.mcp_tools {
-        let mut entries = mcp_tools.to_vec();
+        let mut entries = mcp_tools
+            .iter()
+            .filter(|tool| {
+                tool.name
+                    .namespace
+                    .as_deref()
+                    .is_some_and(&mut should_expose_mcp_namespace)
+            })
+            .cloned()
+            .collect::<Vec<_>>();
         entries.sort_by_key(|tool| tool.name.display());
         let mut namespace_entries = BTreeMap::new();
 
@@ -615,6 +657,25 @@ fn compare_code_mode_tools(
         .then_with(|| left.name.cmp(&right.name))
 }
 
+fn claimed_non_mcp_top_level_names(
+    plan: &ToolRegistryPlan,
+    dynamic_tools: &[codex_protocol::dynamic_tools::DynamicToolSpec],
+) -> HashSet<String> {
+    plan.specs
+        .iter()
+        .map(|tool| tool.name().to_string())
+        .chain(
+            dynamic_tools
+                .iter()
+                .map(|tool| tool.namespace.clone().unwrap_or_else(|| tool.name.clone())),
+        )
+        .collect()
+}
+
+fn reserved_mcp_namespace(namespace: &str) -> bool {
+    matches!(namespace, "functions" | "tools" | "web")
+}
+
 fn code_mode_namespace_name<'a>(
     tool: &codex_code_mode::ToolDefinition,
     namespace_descriptions: &'a BTreeMap<String, codex_code_mode::ToolNamespaceDescription>,
diff --git a/codex-rs/tools/src/tool_registry_plan_tests.rs b/codex-rs/tools/src/tool_registry_plan_tests.rs
index 9564c3eb8664..200aca239506 100644
--- a/codex-rs/tools/src/tool_registry_plan_tests.rs
+++ b/codex-rs/tools/src/tool_registry_plan_tests.rs
@@ -1205,16 +1205,16 @@ fn namespace_specs_are_hidden_when_namespace_tools_are_disabled() {
     let (tools, handlers) = build_specs(
         &tools_config,
         Some(HashMap::from([(
-            ToolName::namespaced("mcp__sample__", "echo"),
+            ToolName::namespaced("sample", "echo"),
             mcp_tool("echo", "Echo", serde_json::json!({"type": "object"})),
         )])),
         /*deferred_mcp_tools*/ None,
         &[],
     );
 
-    assert_lacks_tool_name(&tools, "mcp__sample__");
+    assert_lacks_tool_name(&tools, "sample");
     assert!(handlers.contains(&ToolHandlerSpec {
-        name: ToolName::namespaced("mcp__sample__", "echo"),
+        name: ToolName::namespaced("sample", "echo"),
         kind: ToolHandlerKind::Mcp,
     }));
 }
@@ -1374,7 +1374,7 @@ fn search_tool_description_lists_each_mcp_source_once() {
         &tools_config,
         Some(HashMap::from([
             (
-                ToolName::namespaced("mcp__codex_apps__calendar", "_create_event"),
+                ToolName::namespaced("codex_apps__calendar", "create_event"),
                 mcp_tool(
                     "calendar_create_event",
                     "Create calendar event",
@@ -1382,37 +1382,34 @@ fn search_tool_description_lists_each_mcp_source_once() {
                 ),
             ),
             (
-                ToolName::namespaced("mcp__rmcp__", "echo"),
+                ToolName::namespaced("rmcp", "echo"),
                 mcp_tool("echo", "Echo", serde_json::json!({"type": "object"})),
             ),
         ])),
         Some(vec![
             deferred_mcp_tool(
-                "_create_event",
-                "mcp__codex_apps__calendar",
+                "create_event",
+                "codex_apps__calendar",
                 CODEX_APPS_MCP_SERVER_NAME,
                 Some("Calendar"),
                 Some("Plan events and manage your calendar."),
             ),
             deferred_mcp_tool(
-                "_list_events",
-                "mcp__codex_apps__calendar",
+                "list_events",
+                "codex_apps__calendar",
                 CODEX_APPS_MCP_SERVER_NAME,
                 Some("Calendar"),
                 Some("Plan events and manage your calendar."),
             ),
             deferred_mcp_tool(
-                "_search_threads",
-                "mcp__codex_apps__gmail",
+                "search_threads",
+                "codex_apps__gmail",
                 CODEX_APPS_MCP_SERVER_NAME,
                 Some("Gmail"),
                 Some("Find and summarize email threads."),
             ),
             deferred_mcp_tool(
-                "echo",
-                "mcp__rmcp__",
-                "rmcp",
-                /*connector_name*/ None,
+                "echo", "rmcp", "rmcp", /*connector_name*/ None,
                 /*connector_description*/ None,
             ),
         ]),
@@ -1433,14 +1430,14 @@ fn search_tool_description_lists_each_mcp_source_once() {
         1
     );
     assert!(description.contains("- rmcp"));
-    assert!(!description.contains("mcp__rmcp__echo"));
+    assert!(!description.contains("rmcp__echo"));
 
     assert!(handlers.contains(&ToolHandlerSpec {
-        name: ToolName::namespaced("mcp__codex_apps__calendar", "_create_event"),
+        name: ToolName::namespaced("codex_apps__calendar", "create_event"),
         kind: ToolHandlerKind::Mcp,
     }));
     assert!(handlers.contains(&ToolHandlerSpec {
-        name: ToolName::namespaced("mcp__rmcp__", "echo"),
+        name: ToolName::namespaced("rmcp", "echo"),
         kind: ToolHandlerKind::Mcp,
     }));
 }
@@ -1449,8 +1446,8 @@ fn search_tool_description_lists_each_mcp_source_once() {
 fn search_tool_requires_model_capability_and_enabled_feature() {
     let model_info = search_capable_model_info();
     let deferred_mcp_tools = Some(vec![deferred_mcp_tool(
-        "_create_event",
-        "mcp__codex_apps__calendar",
+        "create_event",
+        "codex_apps__calendar",
         CODEX_APPS_MCP_SERVER_NAME,
         Some("Calendar"),
         /*connector_description*/ None,
@@ -1540,8 +1537,8 @@ fn search_tool_is_hidden_when_only_deferred_namespace_tools_are_available() {
         &tools_config,
         /*mcp_tools*/ None,
         Some(vec![deferred_mcp_tool(
-            "_create_event",
-            "mcp__codex_apps__calendar",
+            "create_event",
+            "codex_apps__calendar",
             CODEX_APPS_MCP_SERVER_NAME,
             Some("Calendar"),
             Some("Plan events and manage your calendar."),
@@ -1691,6 +1688,53 @@ fn search_tool_keeps_plain_deferred_dynamic_tools_when_namespace_tools_are_disab
     }));
 }
 
+#[test]
+fn mcp_namespace_colliding_with_dynamic_namespace_is_skipped() {
+    let model_info = model_info();
+    let features = Features::with_defaults();
+    let available_models = Vec::new();
+    let tools_config = ToolsConfig::new(&ToolsConfigParams {
+        model_info: &model_info,
+        available_models: &available_models,
+        features: &features,
+        image_generation_tool_auth_allowed: true,
+        web_search_mode: Some(WebSearchMode::Cached),
+        session_source: SessionSource::Cli,
+        permission_profile: &PermissionProfile::Disabled,
+        windows_sandbox_level: WindowsSandboxLevel::Disabled,
+    });
+    let dynamic_tools = vec![DynamicToolSpec {
+        namespace: Some("shared".to_string()),
+        name: "automation_update".to_string(),
+        description: "Create or update automations.".to_string(),
+        input_schema: json!({"type": "object", "properties": {}}),
+        defer_loading: false,
+    }];
+
+    let (tools, handlers) = build_specs(
+        &tools_config,
+        Some(HashMap::from([(
+            ToolName::namespaced("shared", "echo"),
+            mcp_tool("echo", "Echo", json!({"type": "object"})),
+        )])),
+        /*deferred_mcp_tools*/ None,
+        &dynamic_tools,
+    );
+
+    assert_eq!(
+        namespace_function_names(&tools, "shared"),
+        vec!["automation_update".to_string()]
+    );
+    assert!(!handlers.contains(&ToolHandlerSpec {
+        name: ToolName::namespaced("shared", "echo"),
+        kind: ToolHandlerKind::Mcp,
+    }));
+    assert!(handlers.contains(&ToolHandlerSpec {
+        name: ToolName::namespaced("shared", "automation_update"),
+        kind: ToolHandlerKind::DynamicTool,
+    }));
+}
+
 #[test]
 fn tool_suggest_is_not_registered_without_feature_flag() {
     let model_info = search_capable_model_info();
@@ -1916,7 +1960,7 @@ fn code_mode_augments_mcp_tool_descriptions_with_namespaced_sample() {
     let (tools, _) = build_specs(
         &tools_config,
         Some(HashMap::from([(
-            ToolName::namespaced("mcp__sample__", "echo"),
+            ToolName::namespaced("sample", "echo"),
             mcp_tool(
                 "echo",
                 "Echo text",
@@ -1935,7 +1979,7 @@ fn code_mode_augments_mcp_tool_descriptions_with_namespaced_sample() {
     );
 
     let ResponsesApiTool { description, .. } =
-        find_namespace_function_tool(&tools, "mcp__sample__", "echo");
+        find_namespace_function_tool(&tools, "sample", "echo");
 
     assert_eq!(
         description,
@@ -1943,7 +1987,7 @@ fn code_mode_augments_mcp_tool_descriptions_with_namespaced_sample() {
 
 exec tool declaration:
 ```ts
-declare const tools: { mcp__sample__echo(args: { message: string; }): Promise<CallToolResult>; };
+declare const tools: { sample_echo(args: { message: string; }): Promise<CallToolResult>; };
 ```"#
     );
 }
@@ -1969,7 +2013,7 @@ fn code_mode_preserves_nullable_and_literal_mcp_input_shapes() {
     let (tools, _) = build_specs(
         &tools_config,
         Some(HashMap::from([(
-            ToolName::namespaced("mcp__sample__", "fn"),
+            ToolName::namespaced("sample", "fn"),
             mcp_tool(
                 "fn",
                 "Sample fn",
@@ -2020,13 +2064,12 @@ fn code_mode_preserves_nullable_and_literal_mcp_input_shapes() {
         &[],
     );
 
-    let ResponsesApiTool { description, .. } =
-        find_namespace_function_tool(&tools, "mcp__sample__", "fn");
+    let ResponsesApiTool { description, .. } = find_namespace_function_tool(&tools, "sample", "fn");
 
     assert!(description.contains(
         r#"exec tool declaration:
 ```ts
-declare const tools: { mcp__sample__fn(args: { open?: Array<{ lineno?: number | null; ref_id: string; }> | null; response_length?: "short" | "medium" | "long"; tagged_list?: Array<{ kind: "tagged"; scope: "one" | "two"; variant: "alpha" | "beta"; }> | null; }): Promise<CallToolResult>; };
+declare const tools: { sample_fn(args: { open?: Array<{ lineno?: number | null; ref_id: string; }> | null; response_length?: "short" | "medium" | "long"; tagged_list?: Array<{ kind: "tagged"; scope: "one" | "two"; variant: "alpha" | "beta"; }> | null; }): Promise<CallToolResult>; };
 ```"#
     ));
 }
@@ -2311,7 +2354,7 @@ fn code_mode_augments_mcp_tool_descriptions_with_structured_output_sample() {
     let (tools, _) = build_specs(
         &tools_config,
         Some(HashMap::from([(
-            ToolName::namespaced("mcp__sample__", "echo"),
+            ToolName::namespaced("sample", "echo"),
             tool,
         )])),
         /*deferred_mcp_tools*/ None,
@@ -2319,7 +2362,7 @@ fn code_mode_augments_mcp_tool_descriptions_with_structured_output_sample() {
     );
 
     let ResponsesApiTool { description, .. } =
-        find_namespace_function_tool(&tools, "mcp__sample__", "echo");
+        find_namespace_function_tool(&tools, "sample", "echo");
 
     assert_eq!(
         description,
@@ -2327,7 +2370,7 @@ fn code_mode_augments_mcp_tool_descriptions_with_structured_output_sample() {
 
 exec tool declaration:
 ```ts
-declare const tools: { mcp__sample__echo(args: { message: string; }): Promise<CallToolResult<{ echo: string; env: string | null; }>>; };
+declare const tools: { sample_echo(args: { message: string; }): Promise<CallToolResult<{ echo: string; env: string | null; }>>; };
 ```"#
     );
 }
diff --git a/codex-rs/tools/src/tool_spec_tests.rs b/codex-rs/tools/src/tool_spec_tests.rs
index 0b986256265e..919d7e813aa3 100644
--- a/codex-rs/tools/src/tool_spec_tests.rs
+++ b/codex-rs/tools/src/tool_spec_tests.rs
@@ -38,12 +38,12 @@ fn tool_spec_name_covers_all_variants() {
     );
     assert_eq!(
         ToolSpec::Namespace(ResponsesApiNamespace {
-            name: "mcp__demo__".to_string(),
+            name: "demo".to_string(),
             description: "Demo tools".to_string(),
             tools: Vec::new(),
         })
         .name(),
-        "mcp__demo__"
+        "demo"
     );
     assert_eq!(
         ToolSpec::ToolSearch {
@@ -178,7 +178,7 @@ fn create_tools_json_for_responses_api_includes_top_level_name() {
 fn namespace_tool_spec_serializes_expected_wire_shape() {
     assert_eq!(
         serde_json::to_value(ToolSpec::Namespace(ResponsesApiNamespace {
-            name: "mcp__demo__".to_string(),
+            name: "demo".to_string(),
             description: "Demo tools".to_string(),
             tools: vec![ResponsesApiNamespaceTool::Function(ResponsesApiTool {
                 name: "lookup_order".to_string(),
@@ -199,7 +199,7 @@ fn namespace_tool_spec_serializes_expected_wire_shape() {
         .expect("serialize namespace tool"),
         json!({
             "type": "namespace",
-            "name": "mcp__demo__",
+            "name": "demo",
             "description": "Demo tools",
             "tools": [
                 {