diff --git a/codex-rs/app-server/src/config_manager_service.rs b/codex-rs/app-server/src/config_manager_service.rs
index aef4393a09..e9f9b8e44f 100644
--- a/codex-rs/app-server/src/config_manager_service.rs
+++ b/codex-rs/app-server/src/config_manager_service.rs
@@ -17,6 +17,7 @@ use codex_config::ConfigLayerStack;
 use codex_config::ConfigLayerStackOrdering;
 use codex_config::ConfigRequirementsToml;
 use codex_config::config_toml::ConfigToml;
+use codex_config::config_toml::ForcedChatgptWorkspaceIds;
 use codex_config::merge_toml_values;
 use codex_core::config::deserialize_config_toml_with_base;
 use codex_core::config::edit::ConfigEdit;
@@ -126,9 +127,16 @@ impl ConfigManager {
 
         let effective = layers.effective_config();
 
-        let effective_config_toml: ConfigToml = effective
+        let mut effective_config_toml: ConfigToml = effective
             .try_into()
             .map_err(|err| ConfigManagerError::toml("invalid configuration", err))?;
+        // The API always returns the normalized list shape, even though config.toml
+        // still accepts the legacy single-string workspace form.
+        if let Some(workspace_ids) = effective_config_toml.forced_chatgpt_workspace_id.take() {
+            effective_config_toml.forced_chatgpt_workspace_id = Some(
+                ForcedChatgptWorkspaceIds::Multiple(workspace_ids.into_vec()),
+            );
+        }
 
         let json_value = serde_json::to_value(&effective_config_toml)
             .map_err(|err| ConfigManagerError::json("failed to serialize configuration", err))?;
diff --git a/codex-rs/app-server/tests/suite/v2/config_rpc.rs b/codex-rs/app-server/tests/suite/v2/config_rpc.rs
index 406dc9ef6c..5c56d215cd 100644
--- a/codex-rs/app-server/tests/suite/v2/config_rpc.rs
+++ b/codex-rs/app-server/tests/suite/v2/config_rpc.rs
@@ -161,6 +161,40 @@ allowed_domains = ["example.com"]
     Ok(())
 }
 
+#[tokio::test(flavor = "multi_thread", worker_threads = 2)]
+async fn config_read_normalizes_legacy_forced_chatgpt_workspace_id() -> Result<()> {
+    let codex_home = TempDir::new()?;
+    write_config(
+        &codex_home,
+        r#"
+forced_chatgpt_workspace_id = "ws_123"
+"#,
+    )?;
+
+    let mut mcp = McpProcess::new(codex_home.path()).await?;
+    timeout(DEFAULT_READ_TIMEOUT, mcp.initialize()).await??;
+
+    let request_id = mcp
+        .send_config_read_request(ConfigReadParams {
+            include_layers: false,
+            cwd: None,
+        })
+        .await?;
+    let resp: JSONRPCResponse = timeout(
+        DEFAULT_READ_TIMEOUT,
+        mcp.read_stream_until_response_message(RequestId::Integer(request_id)),
+    )
+    .await??;
+    let ConfigReadResponse { config, .. } = to_response(resp)?;
+
+    assert_eq!(
+        config.forced_chatgpt_workspace_id,
+        Some(vec!["ws_123".to_string()])
+    );
+
+    Ok(())
+}
+
 #[tokio::test(flavor = "multi_thread", worker_threads = 2)]
 async fn config_read_includes_nested_web_search_tool_config() -> Result<()> {
     let codex_home = TempDir::new()?;